Tolerances and technical measurements. Lecture notes
GBOU SPO "NATK"
I APPROVE Deputy Director for NGOs __________ G.B. Korotysh
METHODOLOGICAL INSTRUCTIONS
for laboratory and practical classes
by discipline: Technical measurements.
Developed Reviewed and approved at the meeting
Subject (cycle) commission
Teacher Protocol No. ___ dated ____________
M.S. Lobanova Chairman ______L.N.Veselova
2014
Preview:
State budget educational institution
secondary vocational education
"NIZHNY NOVGOROD AVIATION TECHNICAL COLLEGE"
(GBOU SPO "NATK")
I approve
Deputy Director for SPO
T.V. Afanasyeva
"___" _______ 2013
Set
control and measuring materials
for conducting intermediate certification in the academic discipline
OP.01 Technical measurements
code and name
basic professional educational program
by profession / specialty
01/15/25 Machine operator (metalworking)
code and name
Nizhny Novgorod
2013
Developers: Teacher Lobanova M.S.
Considered by the PCC "Machine-building
Minutes No. ____ dated "___" _______ 2013
Chairman of the PCC Veselova.L.N ______
1. General Provisions
Control and measuring materials are intended for control and evaluation educational achievements students who have mastered the program of the academic disciplineTechnical measurements
CMMs include control materials for intermediate certification in the form oral on tickets.
2. The results of mastering the discipline, subject to verification
(the results of mastering the discipline are indicated in accordance with the work program of the discipline)
Mastered Skills | Assimilated knowledge |
|
|
3. Measuring materials for evaluating the results of mastering the academic discipline Technical measurements
3.1 Form of differentiated credit - oral by ticket
3.2 Tasks for a differentiated test:
Ticket number 1
1. Give a definition of tolerance, limit sizes, deviations
2. Surface roughness and its parameters
Ticket number 2
1. Interchangeability, measurement error
2.Total tolerances, their definition
Ticket number 3
1. Draw a diagram of the location of the tolerance fields in the hole and shaft system
2. Roughness parameters
Ticket number 4
Ticket number 5
1. Order of selection and appointment of qualifications of accuracy and selection of landings
2. Designation of roughness in the drawings
Ticket number 6
1. Classification of landings
Ticket number 7
2.Smooth micrometer device
Ticket number 8
1. Table of symbols for tolerances of shape and location
2. Control gauges, their devices
Ticket number 9
1. Influence of roughness on the operational properties of units and mechanisms
2.Automatic controls
Ticket number 10
1. Name the basic principles for building tolerances and landings
2. Checking rulers and plates
Ticket number 11
1. The concept of error and size accuracy
2. Means of measurement and control of linear quantities
Ticket number 12
1.Measuring rulers
2. Limit dimensions and deviations
Ticket number 13
1. Tolerances and fits of conical joints
2. Surface roughness. Basic terms and definitions
Ticket number 14
1. Designation of landings in the drawings
2.ShTs-2 caliper device
Ticket number 15
1. Gauge control
2.Characteristics of fastening threads
Ticket number 16
1.Sign of roughness. Designation of roughness in the drawings
2.Tolerances and fits of threads with clearance
Ticket number 17
1.Tolerances and fit of threads with interference
2.ShTs-1 caliper device
Ticket number 18
1.Tolerances and fits of keyed connections
2.Micrometer tool
Ticket number 19
1.Methods and means of thread control
2. Deviations of the shape of cylindrical surfaces
Ticket number 20
1.Classification of calibers
2. Determination of limit deviations
Criteria for assessing assignments
"five" 2 ticket questions + additional task
"4" 2 ticket questions
"3" 1 ticket question
"2" No response to ticket
Conditions for completing the task
1. Place, conditions for completing the task - class
2. Maximum task execution time: 2 hours
3. Sources of information permitted for use in the exam, equipment -Zaitsev.S.A. textbook, posters, stands, reference book
The item (s) corresponding to the results (objects) and types of certification specified in section 1 is filled in. The rest are deleted.
Preview:
Lab #1
Measurement and control of the average diameter of external threads with thread gauges
Objective:
Learn how to measure and control the average diameter of an external thread with working and control gauges
1. Working and control gauges for bolts
2. Threaded through and non-through rings
3. Threaded brackets
4. Detail - bolt for thread measurement
5. Threaded micrometers
6.Procrastination
Work order:
1.Repeat general information about threads: thread elements, working surfaces
2. Familiarize yourself with the provided control gauges in the form of KPR-NE, U-PR, U-NE, K-I, KI-NE KHE-PR, KHE-HE
3. Measure the average diameter using the three-wire thread method and gauge
4.Create a report
Report generation algorithm:
1. The measured size H is recorded (according to the outer diameter of the wires)
2. According to the formula d 2 \u003d M - 3d + 0.866Р the average thread diameter is calculated d - the diameter of the wires
3. According to a special table, knowing the size M, the thread pitch and the diameter of the wires, we find the values of the average diameter of the external thread d 2
Test questions:
1. List the main parameters of a cylindrical thread and draw a sketch of them
2. What is meant by the reduced average thread diameter?
3. What working gauges are used to control the thread of the bolt?
Preview:
Lab #2
Measurement of size and shape deviation with a smooth micrometer
Objective:
To study micrometric measuring instruments, their main characteristics, to learn how to measure dimensions with an allowable error
Material and technical equipment:
1.Micrometer
2. Depth gauge
3. Bore gauge of a cylindrical part
Work order:
1. Repeat the purpose of the main means of measuring and controlling linear dimensions, measurement techniques, basic tools, measurement accuracy, basic characteristics of tools
2. Familiarize yourself with the device of the micrometer, with its measurement limits
3. Take measurements of the proposed parts
4.Create a report
Report generation algorithms:
1. Independently measure parts with a smooth micrometer
2. Determine the value of the reference using the formula l \u003d S x n
3.Svit data into a table
Test questions:
1. What is the usual thread angle when measuring with a micrometer
2.What are the characteristics of micrometer instruments
3. What is the measurement limit of the micrometer?
Laboratory work is designed for 2 hours
Preview:
Lab #3
Tolerance as the difference between the maximum deviations from the nominal size
Objective:
To teach the student to determine the limit deviations, arithmetically calculate the upper deviation, lower deviation, the largest limit size, the smallest limit size, shaft and hole tolerance
Material and technical equipment:
1.Calculators
2.Posters of tolerance fields in the hole system and in the shaft system
3.Tables
4. References
5. Stand "Scheme of tolerance fields and allowances for processing holes and shafts"
Order of execution:
1. Repeat the basic definitions (nominal size, tolerance, actual size)
2. Familiarize yourself with the poster of tolerances
3. Study the definition of IN, BUT
4. Familiarize yourself with the scheme of tolerances for parts: shaft, hole
5.Create a report
Report generation algorithm:
1. Draw a schematic sketch of the hole shaft according to the assignment received
2. Independently choose the tolerances for the dimensions of the shaft, holes according to the table
4. Independently draw a diagram of tolerance fields
5.Svit data into a table
Given | Solution | Result |
Dmax Dmin D action dmax dmin | ES=D max – D es = d max – d EI = D min - D ei = dmin – d TD= D max - D min = l ES-EI l Td = d max - d min = l es – ei l | ES, es-? EI, ei - ? D action , d action - ? TD-? Td-? |
Test questions:
1. What are the largest and smallest size limits?
2.What is measurement error?
4. What is called the actual size?
Laboratory work is designed for 4 hours
Preview:
Lab #4
Determination of the maximum dimensions of holes and shafts, tolerances of gaps and tightness
Objective:
1. Learn to draw a layout of tolerance fields for landings and tightness
2. Learn to determine the maximum dimensions of the tolerance for gaps and interference
The task:
1. Draw according to the initial data the layout of the tolerance fields
Choice of measuring instruments
Objective:
1.Teach the student to choose measuring instruments to control parts
2.Teach the student to control the dimensions with measuring instruments with an allowable error
Material and technical equipment:
1.Measuring rulers
2.Smooth micrometer
3. Caliper
4.Details
5.Drawings
6.Tutorial
7.Posters
The task:
1. Study the detail drawing
2. Select a measuring tool according to the dimensions of the drawing with an allowable error
3. Measure the proposed part with a measuring tool
4.Create a report
Performance:
1. Study the device and metrological characteristics of measuring instruments
2. Draw a sketch of the part, putting down all the dimensions
3. Draw sketches of the selected measuring instruments
4.Measure the dimensions of the part
5.Svit data into a table
Output:
Laboratory work is designed for 2 hours
The concept of interchangeability, tolerances and fits In modern factories, machine tools, cars, tractors and other machines are manufactured not in units, and not even in tens and hundreds, but in thousands. With such production scale, it is important that each part or assembly unit fits exactly into place during assembly, without any additional fitting. In addition, it is necessary that any part or assembly unit entering the assembly allows the replacement of one part (assembly unit) by another, identical in purpose, without prejudice to the operation of the entire finished machine. Parts or assembly units that meet these conditions are called interchangeable.
Spare parts for machines and instruments, various fasteners (bolts, nuts, washers), ball and roller bearings for shafts and axles, spark plugs for internal combustion engines, lenses for cameras, etc. should be interchangeable. Thus, interchangeability is understood as such a principle of design and production of products, parts, assembly units, in which their installation during the assembly process or replacement is carried out without fitting, selection or additional processing. The principle of interchangeability and the rational organization of mass production of products require the establishment of certain norms and rules that must be satisfied by the types, sizes and quality characteristics of products.
To implement the principle of interchangeability, the accuracy of manufacturing products is necessary. However, it is almost impossible to accurately measure the dimensions of the parts. And sometimes achieving high dimensional accuracy is not even economically feasible. In the process of designing parts, the largest and smallest limit sizes are set to ensure the normal functioning of the product, its reliability and durability. The main calculated size (the size that is affixed to the drawing of the part) is called the nominal size.
The difference between the largest limit and nominal dimensions is called the upper deviation, and the difference between the smallest limit and nominal dimensions is called the lower deviation. When setting the dimensions in the drawing, the allowable deviations are indicated to the nominal size. For example, 30 ±": here 30 mm nominal size, +0.2 upper deviation, 0.1 lower deviation. Therefore, the part size can be in the range from 29.9 mm (smallest limit size) to 30.2 mm (largest size limit.) In this example, the upper deviation is positive and the lower deviation is negative." But deviations can be both positive (4O±0.1), both negative (50-0.1), identical in absolute value (30±0.1), or one of them is equal to zero (20+0.1).
The difference between the largest and smallest limit sizes is called the size tolerance. With a graphical representation of tolerances, the concepts of a zero line and a tolerance field are introduced. The zero line is the line corresponding to the nominal size, from which dimensional deviations are plotted. The tolerance field is the field limited by the upper and lower deviations. The tolerance field is determined by the tolerance value and its position relative to the zero line ( nominal diameter). Constructions technical devices and other products require different contacts of mating parts. Some parts must be movable relative to others, while others must form fixed joints. The nature of the connection of parts, determined by the difference between the diameters of the hole and the shaft, creating a greater or lesser freedom of their relative movement or a degree of resistance to mutual displacement, is called fit.
There are three groups of landings: mobile (with a gap), fixed (with an interference fit) and transitional (a gap or interference is possible). The gap is formed as a result of the positive difference between the diameter of the hole and the shaft. If this difference is negative, then the fit will be with an interference fit. Distinguish between the largest and smallest gaps and tightness. The largest gap is the positive difference between the largest hole size limit and the smallest shaft size limit. The smallest gap is the positive difference between the smallest hole size limit and the largest shaft size limit. The largest interference is the positive difference between the largest limit size of the shaft and the smallest limit size of the hole. Least interference is the positive difference between the smallest shaft size limit and the largest hole size limit. The combination of two tolerance fields (hole and shaft) determines the nature of the fit, i.e. the presence of a gap or tension in it.
The system of tolerances and fits established that in each pairing of one of the parts (the main one), any deviation is equal to zero. Depending on which of the mating parts is taken as the main one, there are landings in the hole system and landings in the shaft system. Landings in the hole system are landings in which various gaps and interferences are obtained by connecting various shafts to the main hole. Landings in the landing shaft system, in which various gaps and interferences are obtained by connecting various holes with main shaft. When designating the fit (on the assembly drawings), the maximum dimensions of the holes and the shaft can also be indicated conditionally. For example, 40H7 / g6 (or 40), where 40 is the nominal size (in mm) common to the hole and shaft; H tolerance field and hole quality; g6 tolerance field and quality of the shaft. Using these designations, using tables, you can determine the maximum dimensions of the hole and shaft, the values of gaps or interferences, and establish the nature of the fit.
Designation of landings in the drawings Tolerance fields of linear dimensions are indicated on the drawings either by conventional (letter) designations, for example Ø50H6, Ø32f7, Ø10g6, or by numerical values of limit deviations, for example Ø, or by letter designations of tolerance fields with simultaneous indication of the numerical values \u200b\u200bof limit deviations in brackets ( Fig. 1, a, b) The fits of the mating parts and the maximum deviations of the dimensions of the parts shown on the assembly drawings are indicated by a fraction, in the numerator of which is the letter designation or the numerical value of the maximum deviation of the hole, or the letter designation indicating its numerical value in brackets to the right, and in the denominator there is a similar designation of the shaft tolerance field (Fig. 1, c, d). In the legend of the tolerance fields, it is necessary to indicate the numerical values \u200b\u200bof the limit deviations in the following cases: for sizes not included in the series of normal linear dimensions, for example Ø41.5 H7 (+0.021); when assigning limit deviations, conventions which are not provided for by GOST, for example, for a plastic part (Fig. 1, e) with maximum deviations in accordance with GOST
The mechanisms of machines and devices consist of parts that perform certain relative movements in the process of work or are connected motionlessly. Details that interact to some extent in a mechanism are called conjugated.
Manufacturing experience showed that the problem of choosing the optimal accuracy can be solved by setting for each size of a part (especially for its mating sizes) the limits within which its actual size can fluctuate; at the same time, it is assumed that the assembly, which includes the part, must correspond to its purpose and not lose its operability under the required operating conditions with the necessary resource.
Recommendations for the choice of maximum deviations in the dimensions of parts are developed on the basis of many years of experience in the manufacture and operation of various mechanisms and devices and scientific research, and are set out in a unified system of tolerances and landings (ESDP CMEA). Tolerances and landings established by the CMEA ESDP can be carried out according to the hole or shaft systems.
Basic terms and definitions are established by GOST 25346-89 “Basic norms of interchangeability. ESDP. General provisions, series of tolerances and basic deviations.
Dimensions - the numerical value of linear quantities (diameters, lengths, etc.) in mechanical engineering and instrument making, dimensions are indicated in millimeters (mm). All dimensions are divided into nominal, actual and limit.
Nominal size - the size that is indicated on the drawing on the basis of engineering calculations, design experience, ensuring structural perfection or ease of manufacture of the part (product). Relative to the nominal size, the limiting dimensions are determined; it also serves as the starting point for deviations. In order to reduce the variety of sizes assigned by designers with all the ensuing advantages (narrowing the range of materials, the range of measuring cutting and measuring tools, reducing the standard sizes of products and spare parts for them, etc.), as well as in order to use scientifically based, most rationally constructed series of numbers , when designing, one should be guided by GOST 6636 - 69 for normal linear dimensions. In standardization, series of numbers are used, the members of which are members of a geometric progression.
Product quality is one of the most important indicators of production and economic activity of enterprises. The economic characteristics of the enterprise, its competitiveness, and its position in the market of goods and services largely depend on the level of quality of manufactured products.Underproduct quality is understood as a set of features and properties of products that determine its ability to satisfy certain needs.
There are two groups of indicators that reflect the quality of products.
Performance indicators , which reflect the properties of product quality associated with the satisfaction of needs in accordance with the purpose of the products. Among such indicators, in relation to engineering products, include specifications machines and devices, their reliability and durability, design, resistance to environment and others, as well as the price of the product and the cost of its operation.
Production and technological indicators that characterize a machine or device as an object of production in the conditions of the manufacturer.These indicators indicate the compliance of the quality of manufactured products with the requirements of standards or technical specifications, the degree of their manufacturability, the labor intensity and cost of products in production, etc.
Each enterprise is called upon to produce products of proper quality that can meet all consumer requirements. . Release high quality products determines the need to provide the enterprise with a set of technical, organizational and managerial measures aimed at producing products of appropriate quality. The international standard ISO 8402 series interprets the concept of quality assurance as follows:
"Quality assurance 'are all planned and systematically carried out activities within the quality system, as well as confirmed (if required), necessary to create sufficient confidence that the object will fulfill the quality requirements.'
Ensuring the quality of products - one of the important functions of the organization of production in the enterprise. To implement this function, the enterprise forms a product quality assurance system, which is a set of organizational measures aimed at creating necessary conditions to produce high quality products.
GOST - state standard - is developed for products of intersectoral importance.Unlike TU, GOST requirements are developed not by the manufacturer, but by state industry structures, approved at the highest level by the Interstate Council for Standardization, Metrology and Certification.
Each GOST undergoes serious testing and verification in certified laboratories, is evaluated by industry researchers, passes interdepartmental approvals, and only after that is it allowed for publication.
Many institutes, enterprises, and experts are involved in the creation and approval of GOST. GOSTs are approved by the Federal Agency for Technical Regulation and Metrology (abbreviated name in 2004-2010 - Rostekhregulirovanie; since June 2010 - Rosstandart) - the federal executive body that performs the functions of providing public services, management state property in the field technical regulation and metrology. It is under the jurisdiction of the Ministry of Industry and Trade of the Russian Federation. In other countries (CIS) - similarly.
Specifications
THAT - technical conditions - are developed by the manufacturer and approved by the sectoral ministry with minimal formalities. Therefore, specifications can be softer compared to GOST, or they can be more stringent when the standard is outdated and does not meet the requirements of a particular production, for example, in terms of manufacturing accuracy, the amount of impurities, etc. Enterprises, in order to avoid unnecessary costs, often develop their specifications in order to certify their products.
GOST establishes technical requirements for products, safety requirements, analysis methods, scope and methods of application. GOST requirements are mandatory for all government bodies management and business entities. If GOST is at the very top of the pyramid of standards, then TU is at its very bottom: specifications are mostly developed by manufacturers on their own, based on their own ideas about how a particular product should be made and what properties it should have.
Industry Standard
OST - industry standard - is developed for products of industry importance.
Industry standard (OST) - is established for those types of products, norms, rules, requirements, concepts and designations, the regulation of which is necessary to ensure the quality of products in this industry.
Objects of industry standardization in particular may be certain types products of limited use, technological equipment and tools intended for use in this area, raw materials, semi-finished products for intra-industry use, certain types of consumer goods. Also, objects can be technical standards and typical technological processes specific to the industry, norms, requirements and methods in the field of design organization; production and operation of industrial products and consumer goods.
Industry standards are approved by the ministry (department), which is the head (leading) in the production of this type of product. The degree of obligation to comply with the requirements of the industry standard is determined by the enterprise that applies it, or by agreement between the manufacturer and the consumer. Execution control mandatory requirements organized by the agency that adopted this standard.
Size
Nominal size
actual size
Limit dimensions
The larger one is Dmax and dmax, and the smaller one is Dmin and dmin.
Limit dimensions allow you to determine the accuracy of processing, using them, reject parts.
In modern mechanical engineering, machine parts are manufacturedinterchangeable . This means that during assembly, any part from the entire mass of identical parts can be connected to the parts mating with it without additional processing (fitting), while obtaining the required type of connection (fitting). Only under this condition is it possible to assemble machines by the in-line method.
It is impossible to process parts perfectly precisely, there will always be small deviations from the required dimensions due to the inaccuracies of the machines on which the parts were processed, the inaccuracies of the measuring tools used to measure, etc. Therefore, in order for the parts to meet the requirements of interchangeability, it is necessary to indicate on the drawings tolerances from the nominal dimensions for a given type of connection of parts
The largest allowable size for the required connection (fitting) of parts is calledlargest size limit ;
The smallest allowable size for the required connection (landing) is calledsmallest size limit (Fig. 626).
The difference between the largest and smallest limits is calledadmission .
The difference between the largest size limit and the nominal size is calledupper limit deviation .
The difference between the smallest size limit and the nominal size is calledlower limit deviation.
In FIG. 1 shows the upper positive deviation (with the + sign) and the negative lower one (with the - sign).
However, the largest limit size is not always greater, and the smallest limit size is less than the nominal size. Usually, in the case of a fixed fit, the largest and smallest limit dimensions of the shaft must be greater than the nominal size (Fig. 1).
With a rolling fit, the largest and smallest shaft dimensions must be less than the nominal size (Fig. 627). In this case, a gap is formed between the parts to be joined, the value of which is determined by the positive difference between the diameter of the hole and the diameter of the shaft. In this case, a gap is formed between the parts to be joined, the value of which is determined by the positive difference between the diameter of the hole and the diameter of the shaft.
Size tolerance called the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations.
Nominal size , relative to which the limiting dimensions and deviations are determined. The nominal size is common for connections.actual size set by measurement with an allowable error.
Limit dimensions - these are two maximum allowable sizes between which it must be, or which the actual size can be equal to.
Validity condition of valid parts: The valid actual size must be no more than the maximum and not less than the minimum or be equal to them.
Hole Condition:
Dmin< Dd < Dmax
Shaft conditions:
dmin< dd < dmax
The expiration condition must be supplemented with the characteristics of the marriage: the marriage is correctable, the marriage is irreparable.
Example : The designer, based on the strength conditions, determined the nominal size of the shaft 54 mm. But, depending on the purpose, size 54 may deviate from the nominal within the following limits: largest size dmax = 54.2 mm, smallest dimension dmin = 53.7 mm. These dimensions are limiting, and the actual size of a suitable part may have dimensions between them, that is, from 54.2 to 53.7 mm.
However, it is inconvenient to set two sizes on the drawing, therefore, in addition to the nominal size, the top and bottom deviations are put down on the drawing.
The upper limit deviation is the algebraic difference between the largest limit and nominal sizes.
The lower limit deviation is the algebraic difference between the smallest limit and nominal sizes.
In the drawing, the maximum deviations of dimensions are indicated on the right immediately after the nominal size: the upper deviation is above the lower one, and the numerical values of the deviations are written in a smaller font, (the exception is a symmetrical two-sided tolerance field, in which case the numerical deviation value is written in the same font as the nominal size) . The nominal size and deviations are marked on the drawing in mm.Before the value of the maximum deviation, a + or - sign is indicated, but if one of the deviations is not affixed, this means that it is equal to zero.
There is no negative tolerance, it is always a positive value.
A dimension without a drawing does not exist, it must be correlated with the surface, the processing of which is determined by it.
For convenience and simplification of operating with drawing data, it is customary to reduce the whole variety of specific elements of parts to two elements:
external (covered) elements - shaft,
internal (covering) elements - a hole.
In this case, the accepted term “shaft” should not be identified with the name of a typical part. The variety of elements such as "shaft" and "hole" is in no way connected with a certain geometric shape, which is usually associated with the word "cylinder". Specific structural elements of the part can be either in the form of smooth cylinders or be limited by smooth parallel planes. Only the generalized type of the detail element is important: if the element is external (male) - this is a “shaft”, if internal (female) - this is a “hole”.
A part is considered good if:
Dmin ≤ DD ≤ Dmax(for hole)
dmin ≤ dD ≤ dmax (for shaft)
We fix the marriage if:
DD< Dmin (для отверстия)
dD > dmax (for shaft)
The specified image is built as follows. First, a zero line is drawn, which corresponds to the nominal size and serves as the starting point for dimensional deviations.
At horizontal arrangement zero line, positive deviations are laid up from it, and negative deviations are laid down. Next, the values of the upper and lower deviations of the hole and the shaft are noted, and from them horizontal lines of arbitrary length, which are connected by vertical lines. The tolerance field obtained in the form of a rectangle is shaded (the tolerance field of the hole and the tolerance field of the shaft, as well as adjacent parts, are shaded in different directions). Such a scheme makes it possible to directly determine the size of the gaps, limit dimensions, tolerances; tightness.
Schematic graphic representation of tolerance fields
Landing - the nature of the connection of two parts, determined by the difference in their sizes before assembly. Landing characterizes the freedom of relative movement of the connected parts or the degree of resistance to their mutual displacement.There are three types of landings: with a gap, with an interference fit and transitional landings.
Landings with clearance
Gap S
Interference landings
Preload N - positive difference between the dimensions of the shaft and the hole before assembly. Preload ensures the mutual immobility of the parts after their assembly.
transitional landings . A transitional fit is a fit in which both clearance and interference can be obtained, depending on the actual dimensions of the hole and shaft.
Transition fits are used for fixed joints in cases where during operation it is necessary to carry out disassembly and assembly, as well as when increased requirements are imposed on the centering of parts.
Transition fits usually require additional fastening of the mating parts to ensure the immobility of the connections (keys, pins, cotter pins and other fasteners).
fit tolerance - the sum of the tolerances of the hole and the shaft that make up the connection.
Rice. 2. Scheme of conjugation of the hole and the shaft with a gap
There are also landings in the hole system and landings in the shaft system.
Landings in the hole system - landings in which the required clearances and interferences are obtained by combining different shaft tolerance fields with the tolerance field of the main hole, denoted by the letter H. The main hole is a hole whose lower deviation is zero.
Fits in the shaft system - landings in which the required clearances and interferences are obtained by combining different tolerance fields of holes with the tolerance field of the main shaft, denoted by the letter h. The main shaft is a shaft whose upper deviation is zero.
In the system of tolerances and landings, landings are provided in the hole system and in the shaft system.Landings in the hole system - landings in which various gaps and interferences are obtained by connecting various shafts with the main hole, which is denoted by the letter H.
Fits in the shaft system - landings in which various gaps and interferences are obtained by connecting various holes to the main shaft, which is denoted by the letter h.
Landings with clearance . A clearance fit is a fit that always provides clearance in the joint, i.e. the smallest hole size limit is greater than or equal to the largest shaft size limit (the hole tolerance field is located above the shaft tolerance field).
Gap S - positive difference between the hole and shaft dimensions. The gap allows the relative movement of the mating parts.
Interference landings . An interference fit is a fit in which an interference fit is always provided in the connection, i.e. the largest limit hole size is less than or equal to the smallest limit size of the shaft (the hole tolerance field is located under the shaft tolerance field).
How to determine the type of landing?
Example.
Nominal shaft size 122 mm
lower shaft deflectionei = -40 microns (-0.04 mm)
upper shaft deflectiones = 0 micron (0 mm). Ø122H7/h7
Nominal hole size 122 mm,
hole bottom deviationEI = 0 micron (0 mm),
upper deviation of the holeES = +40 microns (+0.040 mm).
Solution.
1. The largest shaft size limitd max
d max =d + es = 122 + 0 = 122 mm.
2. Smallest shaft size limitd min
d min = d+ei= 122 + (-0.04) = 121.96 mm.
3. Shaft tolerance field
ITd = d max - d min = 122 - 121.96 = 0.04 mm
orITd = es - ei \u003d 0- (-0.04) \u003d 0.04 mm.
4. Largest hole size limit
D max = D+ES = 122 + 0.04 = 122.04 mm.
5. Smallest hole size limit
D min = D + E1 = 122 + 0 = 122 mm.
6. Hole tolerance
ITD=D max - D min = 122.04 - 122 = 0.04 mm
orITD = ES - E1 = 0.04 - 0 = 0.04 mm.
7. Maximum joint clearance
S max = D max - d mia = 122.04 - 122.96 = 0.08 mm
orS max=ES-ei= 0.04 - (-0.04) = 0.08 mm.
8. Minimum joint clearance
S mia = D mia - d max= 122 - 122 = 0 mm
orS min =EI-es= 0 - 0 = 0 mm.
9. Fit tolerance (clearance)
ITS = S max - S min = 0.08 - 0 = 0.08 mm
orITS = ITd+ITD = 0,04 + 0,04 = 0,08 mm.
It should be understood that S=-N and N=-S.
Conclusion: landing with a gap.
Lesson #17SURFACE TOLERANCES AND DEVIATIONS
Deviation of the location of the EP called the deviation of the real location of the element under consideration from its nominal location. Undernominal refers to the location determined by the nominal linear and angular dimensions.
To assess the accuracy of the location of surfaces, bases are assigned (an element of the part, in relation to which the location tolerance is set and the corresponding deviation is determined).
admission location called the limit that limits the permissible value of the deviation of the location of the surfaces.
TP location tolerance field - an area in space or given plane, inside which there must be an adjacent element or axis, center, symmetry plane within the normalized area, the width or diameter of which is determined by the tolerance value, and the location relative to the bases - by the nominal location of the element in question.
Table 2 - Examples of applying shape tolerances in the drawing
The standard establishes 7 types of deviations in the location of surfaces:
from parallelism;
from perpendicularity;
inclination;
from alignment;
from symmetry;
positional;
from the intersection of the axes.
Deviation from parallelism - the difference ∆ of the largest and smallest distances between the planes (axis and plane, straight lines in the plane, axes in space, etc.) within the normalized area.
Deviation from squareness - deviation of the angle between the planes (plane and axis, axes, etc.) from right angle, expressed in linear units ∆, over the length of the normalized section.
tilt deviation - deviation of the angle between the planes (axes, straight lines, plane and axis, etc.), expressed in linear units ∆, over the length of the normalized section.
Deviation from symmetry - the largest distance ∆ between the plane (axis) of the considered element (or elements) and the plane of symmetry of the base element (or the common plane of symmetry of two or more elements) within the normalized area.
Misalignment is the largest distance ∆ between the axis of the considered surface of revolution and the axis base surface(or the axis of two or more surfaces) along the length of the normalized section.
Deviation from the intersection of the axes – the smallest distance ∆ between the nominally intersecting axes.
Positional deviation - the largest distance ∆ between the actual location of the element (center, axis or plane of symmetry) and its nominal location within the normalized area.
Table 3 - Types of location tolerances
On the working drawings of the parts, precise indications are given of the surface roughness that is permissible for the normal operation of these parts.
Undersurface roughness refers to a set of microroughnesses of the surface, measured at a certain length, which is called the base.
The amount of roughness on the surface of a part is measured in micrometers (µm). 1 µm = 0.001 mm.
Surface roughness parameters.
altitude settings.
Rz, µm is the average height of microroughness over 10 points (1 μKm = 0.001 mm).
We draw any line. In relation to it, the distances up to 5 protrusions and up to 5 depressions - the average distance between five within the base length l highest points protrusions and five lowest points of depressions, numbered from a line parallel to the midline.
Ra, µm - arithmetic mean deviation of the profile - the average conclusion, within the base length l, the distance of the points of the protrusions and points of the depressions from the center line:
Roughness classes.
GOST established 14 classes of surface cleanliness.
Surface roughness is classified according to the numerical values of the Ra and Rz parameters with normalized basic data in accordance with the table.
The higher the class (lower numerical value of the parameter), the smoother (cleaner) the surface. Roughness classes from 1 to 5, from 13 to 14 are determined by the Rz parameter, all others from 6 to 12 are determined by the Ra parameter.
The surface roughness of the part is specified during design, based on the functional purpose of the part, i.e. from the conditions of its work, or from aesthetic considerations.
The required purity class is provided by the manufacturing technology of the part.
Roughness designation
Designation
Surfaces to be machined
R z 20
Non-working surfaces of gears
The inner surface of the piston skirt
Internal non-working surface of the sleeve
R but 2,5
End surfaces that serve as a support for the hubs of the gears.
Side surface teeth of large modules of slotted and planed wheels
outer surface of the ring gear
The inner surface of the housing for rolling bearings
R but 1,25
Non-working surfaces of bronze wheels
Block cover reference plane
Reference scraped plane of the control toolbar
Ground rod for studs
R but 0,63
Mating surfaces of bronze wheels
Non-working crankshaft and camshaft journals
Nests under liners of a cranked shaft
Cylindrical surface of power studs
Working surfaces of lead screws
Shaft surfaces for rolling bearings
R but 0,32
The outer surface of the piston crown
Piston boss holes finger-to-finger
The surface of the connecting rods. Working surfaces of centers
Shaft surfaces for rolling bearings of classes B, A and c
R but 0,16
Working necks of the crankshaft of a high-speed engine. Working camshaft journals. The working plane of the valve. The outer surface of the piston skirt. The surface of the impeller blades
R but 0,08
Valve guide. The outer surface of the piston pin. Mirror of a cylindrical sleeve. Balls and rollers of rolling bearings. Working necks of precision high-speed machines.
R but 0,04
Measuring surfaces of limit gauges for 4th and 5th accuracy classes.
Working surfaces of parts of measuring instruments in movable joints of medium precision Balls and rollers of high-speed critical gears.
R a 0,1
Measuring surfaces of devices and calibers of high accuracy (1, 2 and 3 classes). Working surfaces of parts in movable joints of medium precision.
R z 0,05
Measuring surfaces of tiles. Measuring surfaces of measuring instruments of very high accuracy. Measuring surfaces of tiles of high classes. Surfaces of exceptionally critical precision instruments
Measuring instrument (SI) - this technical means or a set of tools used to carry out measurements and has normalized metrological characteristics. With the help of measuring instruments physical quantity can not only be detected, but also measured.In the scientific literature, technical measuring instruments are divided into three large groups. This:measures , calibers Anduniversal facilities measurements , which include measuring instruments, instrumentation (CIP), and systems.
Caliber called scaleless control instruments designed to limit deviations in size, shape and relative position product surfaces. With the help of gauges, it is impossible to determine the actual deviations in the dimensions of the product, but their use allows you to establish whether or not the deviations in the dimensions of the product are within the specified limits.
Caliberserve not to determine the actual size of the parts, but tosorting them into suitable and two groups of marriage (from which not the entire allowance was removed and from which the extra allowance was removed).
Sometimes, with the help of calibers, parts are sorted into several groups suitable for subsequent selective assembly.
Depending on the type of controlled products, calibers are distinguished for:
checking smooth cylindrical products (shafts and holes),
smooth cones,
cylindrical external and internal threads,
conical threads,
linear dimensions,
gear (spline) connections,
arrangement of holes, profiles, etc.
Limit calibers are divided into passing and non-passing.
When inspecting a good part, the through gauge (PR) should be included in the good product, and the non-going gauge (NOT) should not be included in the good product. The product is considered fit if the pass gauge is included, but the non-pass gauge is not. A pass gauge separates good parts from a repairable defect (these are parts from which not all allowance has been removed), and a non-pass gauge separates from an incorrigible defect (these are parts from which an extra allowance has been removed).
According to the technological purpose, the gauges are divided into working gauges used to control products in the manufacturing and acceptance process. finished products QCD employees and control gauges (counter gauges) for checking working gauges.
Basic requirements for calibers
1. Manufacturing precision. The working dimensions of the gauge must be made in accordance with the tolerances for its manufacture.
2. High rigidity with low weight . Rigidity is necessary to reduce errors from gauge deformations (especially large staples) during measurement. Light weight is required to increase the sensitivity of the control and to facilitate the work of the inspector when checking medium and large sizes.
3. wear resistance . To reduce the cost of manufacturing and periodic verification of calibers, it is necessary to take measures to increase their wear resistance. The measuring surfaces of the gauges are made of alloyed steel, hardened to high hardness and covered with a wear-resistant coating (for example, chrome plated). They also produce calibers small size made of hard alloy.
4. Control Performance ensured by a rational design of calibers; where possible, one-sided limit gauges should be used.
5. Stability of working dimensions achieved by appropriate heat treatment (artificial aging).
6. Corrosion resistance , necessary to ensure the safety of calibers, is achieved by the use of anti-corrosion coatings and the choice of materials that are little susceptible to corrosion.
caliper tools are common types of measuring instruments in mechanical engineering. They are used to measure outer and inner diameters, lengths, thicknesses, depths, etc.Three types of calipers are used: ShTs-I, ShTs-I and ShTs-Sh.
Caliper ШЦ - I: 1- rod, 2, 7 - jaws, 3- movable frame, 4- clamp, 5- vernier scale, 6- depth gauge ruler
Caliper ShTs - I is used to measure external, internal dimensions and depths with a vernier reading of 0.1 mm. The caliper (figure 1.8) has a rod 1, on which a scale with millimeter divisions is applied. At one end of this rod there are fixed measuring jaws 2 and 7a; at the other end there is a ruler 6 for measuring depths. A movable frame 3 with jaws 2 and 7 moves along the bar.
The frame is fixed on the rod with clamp 4 during the measurement process.
The lower jaws 7 are used to measure the outer dimensions, and the upper 2 - for the inner dimensions. On the beveled edge of the frame 3, a scale 5, called the vernier, is applied. Nonius is designed to determine the fractional value of the bar division price, i.e., to determine a fraction of a millimeter. The vernier scale, 10 mm long, is divided into 10 equal parts; therefore, each division of the vernier is 19:10 \u003d 1.9 mm, i.e. it is shorter than the distance between each two divisions printed on the rod scale by 0.1 mm (2.0-1.9 \u003d 0.1) . With closed jaws, the initial division of the vernier coincides with the zero stroke of the caliper scale, and the last 10th stroke of the vernier coincides with the 19th stroke of the scale.
Before measuring with closed jaws, the zero strokes of the vernier and the rod must match. In the absence of a gap between the jaws for external measurements or with a small gap (up to 0.012 mm), the zero strokes of the vernier and the rod must match.
When measuring, the part is taken in the left hand, which should be behind the jaws and grab the part not far from the jaws, the right hand must support the rod, while the thumb of this hand moves the frame until it comes into contact with the surface to be checked, avoiding distortion of the jaws and achieving normal measuring force.
The frame is fixed with a clamp large and index fingers right hand, supporting the bar with the rest of the fingers of this hand; the left hand should support the lower jaw of the bar. When reading the testimony, the caliper is held directly in front of the eyes. An integer number of millimeters is measured from left to right on the bar scale with a zero stroke of the vernier. The fractional value (the number of tenths of a millimeter) is determined by multiplying the reading value (0.1 mm) by the serial number of the vernier stroke, not counting the zero coinciding with the bar stroke. Sample counts are shown in the figure below.
39+0,1*7= 39,7; 61+0,1*4=61,4
Height gauges designed to measure heights from flat surfaces and precise markings, manufactured in accordance with GOST 164-90.
Height gauges are designed as follows: they have a base with a rod with a scale rigidly fixed on it, a movable frame with a vernier and a locking screw, a micrometric feed device, which consists of a slider, a screw, a nut and a locking screw, which allows you to install interchangeable legs with a sharp point for marking (drawing risks).
List of recommended literature:
Zaitsev S. A. Tolerances and technical measurements. / S.A. Zaitsev, A. D. Kuranov, A. N. Tolstvo. – M.: Academy, 2017. – 304 p.
Taratina E.P. Tolerances, landings and technical measurements. Tutorial–M.: Akademkniga \ Textbook, 2014
Zaitsev, S.A. Tolerances, landings and technical measurements in mechanical engineering / S.A. Zaitsev, A.D. Kuranov, A.K. Tolstov. – M.: Academy, 2016. – 238 p.
Internet resources:
https://studfiles.net/
Compiled by: D. A. Mogilnaya
Basic concepts and definitions. When sending finished parts to the assembly shop or repair shops, you need to be absolutely sure that in the processing shops all the parameters of the parts are performed with the required accuracy, i.e. it is necessary to measure the actual dimensions of the parts. And this requires reliable means of measurement and control.
Metrology is the science of the means and methods of measurement and control. It covers all areas of technical measurement and control of various production processes. Like any science, metrology has its own terminology. The main terms and definitions of metrology are regulated by GOST 16263-70.
In engineering, there are two main terms - measurement and control. There is no clear boundary between them: both characterize the quality of the part being checked. However, it is customary to understand the measurement as the process of comparing any value (length, angle, etc.) with the same value, conditionally taken as a unit. The result of the measurement is a number expressing the ratio of the measured value to the value taken as a unit. Control is understood as the process of comparing a quantity with prescribed limits. During the control, the actual size of the part is not set, but only its position in relation to the limiting dimensions. The result of the control is a conclusion about the suitability or unsuitability of the part.
Measuring tools and measurement technique. To determine the size of parts and the correctness of their processing, measuring and testing tools are used. Depending on the degree of accuracy measuring tools divided into simple and exact. Simple measuring tools provide measurement accuracy up to 0.5 mm. These include measuring rulers, meters, tape measures, calipers, calipers. Precise measuring instruments allow measurements with an accuracy of 0.1 to 0.001 mm. These include calipers, micrometers, goniometers, limit gauges, indicators, levels, probes, as well as various optical-mechanical, electromechanical, pneumatic and other devices.
For accurate measurements, it is necessary to first compare the readings of the instrument in circulation with the readings of the control instrument (standard) and eliminate inaccuracies; if the design of the instrument does not allow this, then the deviations allowed by it during the measurement should be taken into account. Control instruments are periodically checked in the laboratory. Accurate measurements are performed at an ambient temperature of 20 C. Measurements cannot be taken immediately after processing the part, since the part is heated and the measurement results will be inaccurate. More accurate results can be obtained by taking the average of the initial and repeated measurements at the end of each operation, as well as after the completion of the manufacture of the part as a whole.
Measurement accuracy depends on experience and ability to use the tool. If there are no special instructions on the rules for using the tool, then when measuring, it is necessary to ensure that the measuring tool is in a plane perpendicular to one of the axes of the part, without any distortion or inclination.
According to the purpose and design, all measuring and testing instruments are divided into seven groups: dash fixed, portable, sliding, goniometric, one-dimensional, indicator and planar testing.
Linear non-sliding tools are used to measure linear dimensions. This group includes measuring rulers, folding rules, tape measures. The distance between individual strokes (divisions) for rulers and meters is 1 or 0.5 mm, for tape measures - 1 or 10 mm.
Portable tools are used to transfer dimensions from a scale (measuring) ruler to a product or vice versa. They are used when measuring with a ruler is not possible due to complex shape details or the presence of chamfers and roundings on its edges. These tools include: calipers, marking compasses and inside gauges. A caliper is used to measure external curved surfaces (for example, the outer diameter of a pipe), a marking compass is used to measure and mark flat surfaces or mark parts, a bore gauge is used to measure internal surfaces(for example, inner diameter of a pipe, hole, groove, etc.). When using these tools, the size is determined by the ruler.
Stroke sliding instruments are used to measure external and internal surfaces, depths and heights. These include: vernier calipers, micrometers, pin masses and other measuring instruments that allow measurements to be made with high accuracy due to the mobility of the measuring parts.
The caliper (Fig. 50) consists of a rod 6 with jaws 1 and 2, along which a frame 5 moves with jaws 3 and 9 and a depth gauge 7. The frame on the rod is fixed with a screw 4. The rod is a scale ruler with a division value of 1 mm. On the frame there is an auxiliary scale 8, which serves to count fractions of a millimeter and is called the vernier. Dimensions are measured on the main scale in whole millimeters and on the vernier - in fractions of a millimeter. The vernier counting accuracy can be 0.1; 0.05 and 0.02 mm depending on the scale.
Rice. 50. Caliper.
The vernier scale is obtained by dividing 9 mm into 10 parts. Therefore, the size of each division of the vernier is 0.9 mm, i.e. 0.1 mm less than the division of the main scale. If you move the vernier to the right from its original position, then when its stroke 1 coincides with stroke 1 of the main scale, the zero division of the vernier will move from the zero division of the main scale by 0.1 mm; between jaws 1 and 9 a gap of the same size is formed. With further movement of the vernier to the right, its strokes 2, 3, 4 and all further up to the 10th consecutively coincide with strokes 2, 3, 4, etc. the main scale and the distance between the zero strokes will be 0.2, respectively; 0.3; 0.4 mm and further up to 1 mm. The distance between the jaws of the rod and the frame will increase by the same amount.
To read the size using a vernier caliper, you need to take the number of whole millimeters on the main scale to zero division of the vernier, and the number of tenths of a millimeter - on the vernier, determining which stroke of the vernier coincides with the stroke of the main scale.
For a vernier caliper with a vernier reading accuracy of 0.05 mm, the vernier scale 19 mm long is divided into 20 equal parts. Therefore, each division of the vernier is 0.05 mm less than the division on the bar. Calipers with a readout accuracy of 0.02 mm have a division value of 0.5 mm on the bar, and the vernier scale 12 mm long is divided into 25 parts, i.e. has a division value equal to 12 25 \u003d 0.48 mm, or 0.5 - 0.48 \u003d 0.02 mm less than the division price on the bar.
A micrometer (Fig. 51) is used to measure external surfaces with an accuracy of 0.01 mm. It consists of a bracket 1 with a heel 2 and a stem 7, a micrometric pint 6, on which the drum 4 is fixed, a ratchet 5 and a locking device 3.
Strokes are applied on the stem on both sides of the longitudinal line. The distance between the lower and adjacent upper strokes is 0.5 mm. The micrometric screw is made with a pitch of 0.5 mm, and the lower conical surface of the drum is divided into 50 equal parts. Therefore, the rotation of the drum by one division corresponds to the axial movement of the screw by 0.5: 50 = 0.01 mm.
When measuring with a micrometer, the part to be checked is placed between the heel 2 and the end of the screw 6. By rotating the ratchet, the part is clamped so that there is no distortion. Readings are counted first on the scale of the stem from the zero stroke to the edge of the drum. These readings will be multiples of 0.5. Tenths and hundredths of a millimeter are counted according to the divisions on the scale of the drum, coinciding with the longitudinal risk on the stem. The measured size is determined by the sum of the obtained values.
Rice. 51. Micrometer.
In the figure, the outer edge of the drum is 7 mm open on the stem, and the longitudinal risk of the stem coincides with the 35th division of the drum scale, which corresponds to 0.35 mm. Therefore, the part size is 7 + 0.35 = 7.35 mm.
Before using a micrometer, check the correctness of its readings. To do this, the ends of the heel and the micrometric screw are combined with a ratchet. In this position, the edge of the drum should be on the zero stroke of the stem, and the zero division of the drum should coincide with the longitudinal risk on the stem. If this is not the case, the micrometer is adjusted by zeroing with a locking device and a clamping nut located on the drum.
Micrometers are produced for different measurement limits with intervals: 0-25, 25-50, 50-75 mm, etc. up to 1600 mm.
A micrometric pin (Fig. 52) is used to measure the internal dimensions of a part with an accuracy of 0.01 mm. It is used to determine the ovality of pipes, shells, holes with a size of 35 mm or more. The method of counting with a shtihmas is the same as with a micrometer. For measurements of large diameters, a set of interchangeable calibrated extensions is attached to the micrometer head of the pin, with which you can make any size.
Rice. 52. Micrometric pin.
1
- butt of a replaceable extension
2
- replaceable extension cord
3
- micrometer head
4
- head drum
5
- head end
When measuring, the pin is inserted into the hole and one end of it rests against some point, then, shaking the pin about this point and simultaneously turning the head drum, find the largest diameter of the hole.
Goniometric tools are used to check and measure angles. These include: squares, corner templates and tiles, goniometers. Right angles are checked with squares, and all other angles are checked with corner templates and tiles.
On fig. 53 shows a universal goniometer, which measures angles from 0 to 180 ° with an accuracy of 2 °. The protractor consists of a ruler 3, with a half-disk 4 fixed on it. The second ruler 1 rotates on the axis together with the vernier 6. On the ruler 1, with the help of a clamp, a square 2 is fixed, which serves to measure angles up to 90 °, when measuring large corners, the square is removed and 90 C is added to the reading obtained.
Rice. 53. Universal goniometer.
To measure the angle of the part, the movable ruler 1 is set to the desired angle along the zero stroke of the vernier 6. Then, by rotating the head of the micrometer screw 5, the vernier is finally set. When reading the readings, they first notice which stroke of the half-disk scale has passed the zero stroke of the vernier; this stroke will show the angle in whole degrees. Next, they look at which stroke of the vernier coincides with the stroke of the half-disk; the numeric value and the vernier stroke will show the number of minutes in the measured angle.
One-dimensional tools are used to control or measure any one quantity. These include: calibers, templates, probes, thread gauges.
Calibers are made in the form of plugs - to control the size of the hole (Fig. 54, a) and in the form of brackets - to control the outer dimensions (Fig. 54, b). The dimensions of the sides of the calibers: through passage (Pr) and non-through passage (He) correspond to the largest and smallest limit sizes, i.e. show whether the actual size of the part being checked is within the specified tolerance.
Rice. 54. One-dimensional tools
but- caliber-cork
in- caliber-bracket
in- a set of templates for checking chamfers and welds
G- lamellar probe
Templates are used to check the contours or dimensions of parts, mainly irregular shape. The discrepancy between the contours of the part being checked and the contours of the template is determined “through the light”. On fig. 54c shows a set of templates for checking chamfers and welds when connecting pipes by welding. Each template plate is designed to determine the diameter and wall thickness of the pipe. The end of the plate checks the chamfers and the gap between the ends of the joined pipes, and the recesses on its sides serve to control the dimensions of the reinforcement of the weld.
Feelers (Fig. 54, d) are used to measure small gaps between the surfaces of assembled parts. The probe consists of a set of steel plates, each of which is calibrated to a certain thickness in the range of 0.03-1 mm. The gaps can be checked with one or several plates stacked together.
Thread gauges are used to check the pitch, the number of threads and the correctness of the thread. The thread gauge, like the probe, consists of a set of plates on which thread profiles are applied and dimensions are indicated.
Indicator tools are used to measure small deviations in the size and shape of parts, to check the correctness and relative position in structures and mechanisms, as well as to check the elongation of the studs when tightening flange connections.
The most widespread are dial indicators with a dial (Fig. 55). The indicator mechanism, enclosed in a housing, consists of a set of gears. The gears are selected so that as a result of moving the measuring rod 4 by 0.01 mm, the arrow 1 moves along the dial 3 by 0.01 mm, and when the rod is moved by 1 mm, the arrow 1 makes a full turn, and the arrow 2 moves one division .
When using the indicator, its tip is brought to the measured surface and arrow 1 is set to zero division. Then loosen the screw for one or two full turns of arrow 1. This is done so that during the measurement the indicator can show as negative. and positive deviations from the size by which it is set to zero.
The indicator on the stand is moved along the surface of the product or the product - along the end of the measuring rod. To determine the elongation of the studs when tightening the flange connections, the indicator is fixed in a special clamping sleeve with a flat end surface that is in contact with the measured end of the tightened stud. Deviation in shape or dimensions will cause the rod to move, and arrow 1 will show the magnitude of this deviation.
Planar inspection tools are used to check the surface cleanliness, as well as the straightness of the position of the product in relation to a given mark. These tools include: test squares, rulers, scraper plates, levels.
Checking squares, rulers and scraper plates are used to check the flatness of parts using the light gap method, or spots on the paint. When checking this method, the plate is covered with a layer of paint (azure, Dutch soot, ink, etc.). The paint is rubbed in such a way that no lumps are felt, and placed in a bag of canvas. When rubbing the plate, the paint will come out through the pores of the bag and paint over the surface of the plate thin layer. Then the part is placed on the plate (or the plate on the part) and freely moved along it in different directions. In this case, all areas protruding on the surface of the part are painted. The number of evenly spaced spots of paint on the surface characterizes the purity of its processing. The more evenly spaced ink prints, the higher the surface finish. This method checks the cleanliness of the surface treatment of the part after fine filing, scraping, lapping. The number of paint spots per 1 cm2 of the surface being checked and their area are specified by the technical conditions.
Levels (water levels) are used to check the horizontal and vertical position of surfaces. Levels are used when marking the pipeline route, reconciling its position, checking slopes, etc.
To control small deviations of the surface from a horizontal or vertical position, a locksmith (gross) level is used (Fig. 56). Its main part is a longitudinal ampoule 2 - a glass tube filled with liquid (water, alcohol, ether in such a way that an air bubble remains inside.
The air bubble always tends to take the highest position. Its deviation from the central zero position is determined by the divisions of the scale, which is printed on the glass tube. The price of one division of the scale can be from 0.6 to 0.1 mm per 1 m. So, for example, the deviation of a bubble by one division, the price of which is 0.6 mm, will show that the difference in height of two points located at a distance 1 m apart is 0.6 mm.
Rice. 56. Locksmith level
1
- transverse ampoule
2
- longitudinal ampoule
3
- frame
The correctness of the level in the vertical position is determined by the air bubble in the transverse ampoule 1, which should occupy the middle position.
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There are three main types of production: single (single production of various products), serial (production of batches of products of the same design at certain intervals) and mass (release a large number products of the same type and design for a long time).
Serial production, in turn, is divided into small-scale, serial and large-scale.
Production is referred to one type or another rather conditionally. The type of production is characterized by the coefficient of fixing operations for one workplace or piece of equipment, which is the ratio of the number of different operations O necessary for the production of products to the number of workplaces at which these operations are performed P:
Production types are characterized the following values transaction consolidation ratio (Table 28):
Table 28Interchangeability is called such a property of completed individual parts, which makes it possible, without additional processing or adjustment, to connect them during assembly or when replacing parts that are damaged or failed during operation while maintaining the specified quality of the product.
The production of interchangeable parts makes it possible to specialize enterprises, which reduces the cost of manufacturing these parts, increases labor productivity, and also eliminates manual refinement of parts during assembly and repair.
For the manufacture of any part, the workpiece (casting, forging, stamping) is subjected to mechanical or other types of processing in accordance with the requirements of the drawing and specifications. The workpieces must have certain processing allowances to ensure that parts are obtained within the configuration (shape) specified by the drawing, dimensions and tolerances for their implementation, as well as certain physical and mechanical properties of the machined surfaces.
The amount of the machining allowance depends on the type of material, the size and weight of the part, the volume of its output (production volume), the method of manufacturing the workpiece, as well as the requirements for accuracy and roughness of the machined surfaces on the part.
7.2. Surface roughness and tolerances
The surfaces of all parts after machining are not perfectly smooth, since cutting edges tools leave traces on the surface in the form of certain irregularities and scallops.
The totality of all irregularities with relatively small steps on the base length is called roughness.
The main characteristics of the roughness of the treated surfaces are the height and step parameters. The high-altitude ones include the arithmetic mean deviation of the profile, the height of the profile irregularities at ten points and highest altitude profile irregularities. The roughness step parameters are the average roughness step and the reference length of the profile.
Surface roughness is also characterized by a number of additional options: radii of curvature of the protrusions and cavities of microroughnesses, the angle of inclination of the sides of microroughnesses and the direction of processing strokes on the surface of the part.
The surface roughness is indicated by special signs and the values \u200b\u200bof the allowable roughness in micrometers inscribed above them.
The dimensions of the part that are indicated on the technical drawing are called nominal, and the dimensions actually obtained as a result of processing the part are called actual. The actual size is always slightly different from the nominal size, since in practice it is almost impossible to obtain a nominal size.
In order to achieve a certain accuracy in the execution of the part, the tolerance on the nominal size is indicated on the drawing, which determines the boundaries of the permissible error in manufacturing. The nominal size tolerance corresponds to the maximum dimensions within which the part is considered suitable.
The upper and lower limit dimensions are determined by the nominal size tolerance. The larger of the two sizes, usually denoted by the letter IN, - this is the upper limit; smaller, denoted by letter BUT, - lower limit size.
Dimension T tolerance is the arithmetic difference between the upper and lower limit sizes:
T \u003d B - A.
Deviation from the nominal size called arithmetic difference between the upper or lower limit sizes and the nominal size D. In this case, the upper deviation is defined as
and the bottom one
If the upper limit size is greater than the nominal, then the deviation is set with a plus sign; the lower deviation has a minus sign. When one of the limiting dimensions is equal to the nominal, then the deviation is zero and is not set in the drawings.
The tolerance value can be determined by the difference between the upper and lower limit sizes.
There are the following types of tolerances: symmetrical - both deviations have the same value and differ only in sign; asymmetric - one deviation is zero; asymmetric double-sided - the magnitudes and signs of deviations are different; asymmetric unilateral - both deviations have the same signs.
7.3. Landings
landing called the interconnection of two machine parts with the same nominal dimensions and their certain deviations.
The purpose of landings is to achieve the correct (according to technical documentation) connection of elements and parts of machines for their joint operation, as well as ensuring interchangeability during assembly and repair in operation. Landing determines the nature of the connection of two parts, depending on the gap or interference obtained as a result of their processing, when assembling the machine.
The landing tolerance system is divided into hole system And shaft system.
gap The positive difference between the dimensions of the hole and the shaft is called. The gap is greater, the greater the difference between the actual size of the hole and the actual size of the shaft.
interference is the positive difference between the size of the shaft and the size of the hole. An interference occurs when the shaft size over size holes. In this case, there is no gap.
The tolerance system provides for three types of deviations from the nominal size: upper, lower and main. The main deviation is the deviation closest to the zero line. It defines the position of the tolerance field relative to the nominal size.
Tolerance fields are indicated by letters of the Latin alphabet, for holes in capital letters ( A, B, C, D etc.), for shafts - lowercase ( a, b, c, d and etc.).
All possible sizes up to 3150 mm are divided into intervals that form three groups of sizes: up to 1 mm, from 1 mm to 500 mm and from 500 mm to 3150 mm. Each group has different rows of tolerance fields and recommended fits, of which fits in the hole system are preferred.
Hole tolerance H is the main one in the hole system, its lower deviation is zero. The main shaft is the tolerance field h, its upper deviation is zero.
Landings are divided into three groups: with a guaranteed tightness (press), with a guaranteed gap (moving) and transitional.
fit tolerance called the difference between the largest and smallest gaps in clearance fits and the difference between the largest and smallest interference in interference fit. In transitional landings, the landing tolerance is equal to the difference between the largest and smallest interference or the sum of the largest interference and the largest gap.
The fit tolerance is also equal to the sum of the bore and shaft tolerances.
In the shaft system, the main one is the shaft, the upper diameter deviation of which is zero. In landings on the shaft system, various gaps and interferences are obtained by connecting holes of various diameters to the main shaft.
In the hole system, the main one is the diameter of the hole, the lower deviation of which is zero. In landings according to the hole system, various gaps and interferences are obtained by connecting shafts of different diameters with the main hole.
The fit in the hole system is indicated by putting down the nominal size, the hole fit symbol (capital letter), and then a number indicating the degree of accuracy.
The fit in the shaft system is indicated by putting down the nominal size, then the shaft fit symbol (small letter), as well as a number indicating the degree of accuracy.
In mechanical engineering, the hole system is mainly used, since it makes it possible to reduce the number of required sizes of cutting and measuring tools for making holes. Making a shaft with a size within the desired fit is significantly easier to manufacture holes.
7.4. measurements
The purpose of the measurements is the systematic control of manufactured products, as well as verification of the conformity of the dimensions obtained during processing with the required ones (according to the drawings and specifications) allowance.
According to the method of obtaining the values of the measured quantities, the measurement methods are divided into absolute and relative, direct and indirect, contact and non-contact.
Absolute measurement method characterized by the determination of the entire measured value directly from the readings of the measuring instrument (for example, measurement with a caliper).
Relative (comparative) measurement - this is a method in which the deviation of the measured value from a known size, setting standard or sample is determined (for example, control using an indicator device).
At direct method measurements using a measuring instrument (eg micrometer) the set value (eg shaft diameter) is measured directly.
At indirect measurement method the desired value is determined by direct measurements of other quantities associated with the desired specific relationship.
Contact measurement method lies in the fact that during the measurement, the surface of the measured product and the measuring tool come into contact.
At contactless method the surfaces of the workpiece to be measured and the measuring device do not come into contact (for example, when using optical means or pneumatic jet measuring devices).
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