Lectures tolerances and landings for spo. Tolerances and fits.Measuring tool

at the rate:

"Interchangeability,

standardization

technical measurements"

Donetsk 2008

Lecture No. 1 “The concept of interchangeability and standardization. Fundamentals of the principle of interchangeability. 3

Lecture No. 2 "Tolerance and fit systems for elements of cylindrical and flat joints" 10

Lecture No. 3 "Calculation and selection of landings for the GCC" 17

Lecture No. 4 "Calculation and design of gauges for the control of parts of smooth joints" 28

Lecture No. 5 "Tolerances and fits of rolling bearings" 36

Lecture No. 6 "Normalization and designation of surface roughness" 42

Lecture No. 7 "Tolerances for the shape and location of surfaces" 47

Lecture No. 8 "Dimensional chains" 56

Lecture No. 9 "Interchangeability, methods and means of measuring and controlling gears" 68

Lecture No. 10 "Interchangeability of threaded connections" 77

Lecture No. 11 "Interchangeability of keyed and splined connections" 82

Lecture No. 12 “Angle tolerances. Interchangeability of conical connections» 86

Lecture No. 13 "The concept of metrology and technical measurements" 91

Lecture No. 1 “The concept of interchangeability and standardization. Fundamentals of the principle of interchangeability.

Modern mechanical engineering is characterized by:

continuous increase in the capacity and productivity of machines;

continuous improvement of machine designs and other products;

increasing requirements for the accuracy of manufacturing machines;

the growth of mechanization and automation of production.

For the successful development of mechanical engineering in these areas great importance has the organization of production of machines and other products on the basis of interchangeability and standardization.

The purpose of the discipline: familiarity with the methods of ensuring interchangeability,

standardization, as well as measurement and control methods

applied to modern products engineering.

From the history of the development of interchangeability and standardization.

Elements of interchangeability and standardization appeared a very long time ago.

So, for example, the water supply system built by the slaves of Rome was made of pipes of a strictly defined diameter. To build the pyramids Ancient Egypt unified stone blocks were used.

In the 18th century, by decree of Peter the Great, a series of warships with the same size, armament, and anchors was built. In the metalworking industry, interchangeability and standardization were first applied in 1761 at the Tula and then Izhevsk arms factories.

The concept of interchangeability and its types.

Interchangeability is the ability to assemble independently manufactured parts into a unit, and units into a machine without additional processing and fitting operations. In this case, the normal operation of the mechanism must be ensured.

To ensure the interchangeability of parts and assembly units, they must be manufactured with a given accuracy, i.e. so that their dimensions, surface shape and other parameters are within the limits specified in the design of the product.

The complex of scientific and technical initial provisions, the implementation of which during the design, production and operation ensures the interchangeability of parts, assembly units and products, is called the principle of interchangeability.

Distinguish between complete and incomplete interchangeability of parts assembled into assembly units.

Full interchangeability provides the possibility of free assembly (or replacement during repair) of any independently manufactured parts of the same type with a given accuracy into an assembly unit. (For example, bolts, nuts, washers, bushings, gears).

Partially interchangeable are such parts, during assembly or change of which a group selection of parts (selective assembly), the use of compensators, adjustment of the position of parts, fitting may be required. (For example, assembling a gearbox, rolling bearings).

The level of interchangeability in the production of a product is characterized by an interchangeability coefficient equal to the ratio of the labor intensity of manufacturing interchangeable parts to the total labor intensity of manufacturing a product.

There are also external and internal interchangeability.

External - this is the interchangeability of purchased or cooperative products (mounted in other more complex products) and assembly units in terms of performance, size and shape of the connecting surfaces. (For example, in electric motors, external interchangeability is provided by the shaft speed, power, and also by the shaft diameter; in rolling bearings - by the outer diameter of the outer ring and the inner diameter of the inner ring, as well as by rotation accuracy).

Internal interchangeability applies to parts, assembly units and mechanisms included in the product. (For example, in a rolling bearing, rolling elements and rings have internal group interchangeability).

The basis for the implementation of interchangeability in modern industrial production is standardization.

Concepts about standardization. Categories of standards

The largest international organization in the field of standardization is ISO (until 1941 it was called ISA, organized in 1926) supreme body ISO is the General Assembly, which meets every 3 years, decides on the most important issues and elect the President of the organization. The organization consists of a large number clients. The Constitution states the main purpose of ISO - “to promote the favorable development of standardization throughout the world in order to facilitate the international exchange of goods and to develop mutual cooperation in various fields of activity.

Basic terms and definitions in the field of standardization are established by the ISO Committee for the Study of the Scientific Principles of Standardization (STACO).

Standardization is a planned activity to establish mandatory rules, norms and requirements, the implementation of which improves product quality and labor productivity.

A standard is a regulatory and technical document that establishes requirements for groups of homogeneous products and rules that ensure its development, production and use.

Specifications(TU) - normative - white paper, which establishes requirements for specific products, material, their manufacture and control.

To strengthen the role of standardization, a state (state) standardization system DSS has been developed and put into action. It defines the goals and objectives of standardization, the structure of standardization bodies and services, the procedure for developing, formalizing, approving, publishing and implementing standards.

The main goals of standardization are:

improving product quality;

export development;

development of specialization;

development of cooperation.

Depending on the scope of the DSS, the following categories of standards are provided:

GOST (DST) - state;

OST - industry;

STP - enterprises.

Basic terms and definitions of the principle of interchangeability

Basic terms and definitions are established in GOST 25346 - 82.

A connection is two or more parts that are movably or fixedly mated to each other.

Figure 1 - Connection examples

The nominal size is the common size for the connection parts, obtained as a result of the calculation and rounded in accordance with the series of normal linear dimensions established by GOST 6636 - 69 and distributed on the basis of the series of preferred numbers GOST 8032 - 56.

Rows of preferred numbers (Renard series) are geometric progressions.

R5:
=1,6 – 10; 16; 25; 40; 63; 100…

R10:
= 1,25 – 10; 12,5; 16; 20; 25…

The actual size is the size obtained as a result of the processing of the part and measured with an allowable error.

When making drawings, it is most convenient to put down the size in the form of a nominal size with deviations.

55

Limit dimensions are two maximum allowable dimensions, between which the actual size of a suitable part must be. (
)

Figure 2 - Limiting dimensions of the hole, shaft

Size tolerance is the difference between the largest and smallest limit sizes (T - Tolerance)

Tolerance is a measure of dimensional accuracy and determines the complexity of manufacturing a part. The larger the tolerance, the easier and cheaper it is to manufacture the part.

The concept of nominal size and deviations simplifies the graphical representation of tolerances in the form of tolerance field layouts.

Picture 3 - Scheme of a smooth cylindrical connection

The zone enclosed between the two lines corresponding to the upper and lower deviations is called the tolerance field.

The tolerance field is a broader concept than tolerance. The tolerance field is characterized by its size (tolerance) and location relative to the nominal size. Thus, the tolerance field can be set in two ways:

a) in the form of upper (es, ES) and lower (ei, EI) deviations;

b) in the form of the main deviation and tolerance (T).

Consider the connection of the hole and the shaft.

The difference between the dimensions of the hole and the shaft before assembly determines the nature of the connection of the parts, or fit.

If a
(gap)

If a
(preload)

In connections where a gap is required, the actual gap must be between the two limit values - the largest and smallest gaps (S
).Accordingly, in connections with an interference fit - between
.

Limit gaps and tightness in the drawings are not indicated. The designer assigns a fit in the form of a certain combination of hole and shaft tolerance fields. In this case, the nominal size of the hole and the shaft is common and is called the nominal size of the connection d
.

Landing types.

Depending on the relative position of the tolerance fields of the hole and the shaft, there are three types of landings: with clearance, interference and transitional.

Figure 4 - Types of landings

Basic terms and definitions

State standards(GOST 25346-89, GOST 25347-82, GOST 25348-89) replaced the OST system of tolerances and landings, which was in effect until January 1980.

Terms are given according to GOST 25346-89"Basic norms of interchangeability. one system permits and landings.

Shaft- a term conventionally used to refer to the external elements of parts, including non-cylindrical elements;
Hole- a term commonly used to refer to internal elements parts, including non-cylindrical elements;
main shaft- shaft, the upper deviation of which is equal to zero;
Main hole- hole, the lower deviation of which is equal to zero;
The size- numerical value of a linear quantity (diameter, length, etc.) in the selected units of measurement;
actual size- the size of the element, established by the measurement with the allowable accuracy;
Nominal size- the size relative to which deviations are determined;
Deviation- algebraic difference between the size (actual or limit size) and the corresponding nominal size;
quality- a set of tolerances considered as corresponding to the same level of accuracy for all nominal sizes;
Landing- the nature of the connection of two parts, determined by the difference in their sizes before assembly.
Gap is the difference between the dimensions of the hole and the shaft before assembly, if the hole over size shaft;
Preload- the difference between the dimensions of the shaft and the hole before assembly, if the size of the shaft is larger than the size of the hole;
fit tolerance- the sum of the tolerances of the hole and the shaft that make up the connection;
Tolerance T- the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations;
Standard IT approval- any of the tolerances established by this system of tolerances and landings;
Tolerance field- a field limited by the largest and smallest limit sizes and determined by the tolerance value and its position relative to the nominal size;
Landing with clearance- landing, in which a gap is always formed in the connection, i.e. the smallest limit size of the hole is greater than or equal to the largest limit size of the shaft;
Interference landing- landing, in which an interference is always formed in the connection, i.e. the largest hole size limit is less than or equal to the smallest shaft size limit;
transition fit- landing, in which it is possible to obtain both a gap and an interference fit in the connection, depending on the actual dimensions of the hole and shaft;
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;
Fits in the shaft system- landings in which the required clearances and interferences are obtained by combining different hole tolerance fields with the tolerance field of the main shaft.

Tolerance fields and their corresponding limit deviations installed in different ranges of nominal sizes:
up to 1 mm- GOST 25347-82;
from 1 to 500 mm- GOST 25347-82;
over 500 to 3150 mm- GOST 25347-82;
over 3150 up to 10.000 mm- GOST 25348-82.

GOST 25346-89 establishes 20 qualifications (01, 0, 1, 2, ... 18). Qualities from 01 to 5 are intended primarily for calibers.
The tolerances and limit deviations set in the standard refer to the dimensions of the parts at a temperature of +20 o C.
Installed 27 basic shaft deviations and 27 main hole deviations. The main deviation is one of two limit deviations (upper or lower), which determines the position of the tolerance field relative to the zero line. The main deviation is the closest to the zero line. The main deviations of the holes are indicated capital letters Latin alphabet, shafts - lowercase. The layout of the main deviations, indicating the qualifications in which it is recommended to use them, for sizes up to 500 mm is shown below. The shaded area refers to holes. The scheme is shown in abbreviation.

Appointment of landings. Landings are chosen depending on the purpose and operating conditions of the equipment and mechanisms, their accuracy, assembly conditions. At the same time, it is necessary to take into account the possibility of achieving accuracy when various methods product processing. First of all, preferred landings should be applied. Basically, landings are used in the hole system. Shaft system fits are useful when using some standard parts (for example, rolling bearings) and in cases where a shaft of constant diameter is used along its entire length to install several parts on it with various landings.

The tolerances of the hole and the shaft in the fit should not differ by more than 1-2 quality. A larger tolerance is usually assigned to the hole. Clearances and interferences should be calculated for most types of connections, especially for interference fits, fluid friction bearings and other fits. In many cases, fits can be assigned by analogy with previously designed products that are similar in terms of working conditions.

Application examples of fits, mainly related to the preferred fits in the hole system in sizes 1-500 mm.

Landings with clearance. hole combination H with shaft h(sliding fits) are used mainly in fixed joints when frequent disassembly is necessary (replacement parts), if you need to easily move or rotate parts relative to one another when setting up or adjusting, to center fixed parts.

Landing H7/h6 apply:

For interchangeable gear wheels in machines;
- in connections with short strokes, e.g. for spring valve shanks in guide bushings (fit H7/g6 is also applicable);
- for connecting parts that should move easily when tightened;
- for precise guidance in reciprocating movements (piston rod in pump guide bushings high pressure);
- for centering housings for rolling bearings in equipment and various machines.

Landing H8/h7 used for centering surfaces with reduced alignment requirements.

Landings H8 / h8, H9 / h8, H9 / h9 are used for fixed parts with low requirements for the accuracy of mechanisms, light loads and the need to ensure easy assembly (gear wheels, couplings, pulleys and other parts connected to the shaft with a key; rolling bearing housings , centering of flange connections), as well as in movable joints with slow or rare translational and rotational movements.

Landing H11/h11 used for relatively roughly centered fixed joints (centering of flange covers, fixing overhead conductors), for non-critical hinges.

Landing H7/g6 it is characterized by a minimum guaranteed gap compared to the rest. Used in movable joints to ensure tightness (for example, a spool in the sleeve of a pneumatic drilling machine), accurate guidance or when short moves(valves in the valve box), etc. In particularly precise mechanisms, landings are used H6/g5 and even H5/g4.

Landing H7/f7 used in plain bearings at moderate and constant speeds and loads, including in gearboxes; centrifugal pumps; for gear wheels rotating freely on shafts, as well as wheels switched on by couplings; for guiding pushers in internal combustion engines. A more precise fit of this type - H6/f6- used for precise bearings, distributors of hydraulic transmissions of passenger cars.

Landings H7/e7, H7/e8, H8/e8 and H8/e9 used in bearings at high speeds (in electric motors, in the gear mechanism of an internal combustion engine), with spaced supports or a long mating length, for example, for a gear block in machine tools.

Landings H8/d9, H9/d9 used, for example, for pistons in cylinders steam engines and compressors, in the joints of the valve boxes with the compressor housing (for their dismantling, a large gap is required due to the formation of soot and significant temperature). More accurate fits of this type -H7 / d8, H8 / d8 - are used for large bearings at high speeds.

Landing H11/d11 used for mobile joints operating in dust and dirt conditions (assemblies of agricultural machines, railway wagons), in swivel joints of rods, levers, etc., for centering the covers of steam cylinders with sealing the joint with ring gaskets.

Transition landings. Designed for fixed connections of parts subjected to assembly and disassembly during repairs or operating conditions. The mutual immobility of the parts is ensured by keys, pins, pressure screws, etc. Less tight fits are prescribed if necessary for frequent disassembly of the connection, in case of inconvenience, high centering accuracy is required, with impact loads and vibrations.

Landing H7/n6(like deaf) gives the most strong connections. Application examples:

For gears, couplings, cranks and other parts under heavy loads, shocks or vibrations in joints that are usually disassembled only when overhaul;
- landing adjusting rings on the shafts of small and medium-sized electric machines; c) landing of conductor bushings, locating pins, pins.

Landing H7/k6(tension type) on average gives a slight gap (1-5 microns) and provides good centering, without requiring significant effort for assembly and disassembly. It is used more often than other transitional landings: for landing pulleys, gears, couplings, flywheels (on keys), bearing bushings.

Landing h7/js6(dense type) has larger average gaps than the previous one, and is used instead of it, if necessary, to facilitate assembly.

Landings with interference. The choice of landing is made from the condition that, at the least interference, the strength of the connection and transmission, loads are ensured, and at the greatest interference, the strength of the parts.

Landing H7/r6 used for relatively small loads (for example, landing on a shaft sealing ring, fixing the position of the inner ring of the bearing for crane and traction motors).

Landings H7/r6, H7/s6, H8/s7 used in connections without fasteners at low loads (for example, a bushing in the head of a connecting rod of a pneumatic motor) and with fasteners at high loads (fitting gears and couplings on a key in rolling mills, oil drilling equipment, etc.).

Landings H7/u7 and H8/u8 used in connections without fasteners under significant loads, including alternating ones (for example, connecting a pin with an eccentric in the cutting apparatus of agricultural harvesting machines); with fasteners at very high loads (fitting large couplings in rolling mill drives), at light loads, but a short mating length (valve seat in the cylinder head truck, bushing in the combine harvester cleaning lever).

High Precision Interference Fits H6/r5, H6/r5, H6/s5 they are used relatively rarely and in joints that are especially sensitive to interference fluctuations, for example, the landing of a two-stage bushing on the armature shaft of a traction motor.

Tolerances for incompatible dimensions. For non-matching dimensions, tolerances are assigned depending on functional requirements. Tolerance fields usually have:
- in the "plus" for holes (denoted by the letter H and the quality number, for example, HZ, H9, H14);
- in "minus" for shafts (denoted by the letter h and the quality number, for example h3, h9, h14);
- symmetrical about the zero line ("plus - minus half of the tolerance" denote, for example, ±IT3/2, ±IT9/2, ±IT14/2). Symmetrical tolerances for holes can be marked with the letters JS (eg JS3, JS9, JS14) and for shafts with the letters js (eg js3, js9, js14).

Tolerances for 12-18 The th qualification is characterized by non-conjugated or conjugated dimensions of relatively low accuracy. Repeatedly repeating limit deviations in these qualifications are allowed not to be indicated in the dimensions, but to be stipulated by a general entry in the technical requirements.

For sizes from 1 to 500 mm

Preferred fits are framed.

Electronic table of hole and shaft tolerances with indication of the fields according to the old OST system and according to the ESDP.

A complete table of tolerances and fits of smooth joints in the hole and shaft systems, indicating the tolerance fields according to the old OST system and according to the ESDP:

Related Documents:

Angle Tolerance Tables
GOST 25346-89 "Basic standards of interchangeability. Unified system of tolerances and fits. General provisions, series of tolerances and basic deviations "
GOST 8908-81 "Basic standards of interchangeability. Normal angles and angle tolerances"
GOST 24642-81 "Basic norms of interchangeability. Tolerances of the shape and location of surfaces. Basic terms and definitions"
GOST 24643-81 "Basic norms of interchangeability. Tolerances of the shape and location of surfaces. Numerical values"
GOST 2.308-79 "Unified system for design documentation. Indication on the drawings of tolerances of the shape and location of surfaces"
GOST 14140-81 "Basic standards of interchangeability. Tolerances for the location of the axes of holes for fasteners"

Third lecture

2. Basic concepts of landings (conjugations)

Lecture plan

Concepts of clearance and tension.

Landing types.

The formation of landings in the hole system and in the shaft system.

Previously, the concepts shaft and holes as, respectively, the outer male and inner female elements. When pairing these elements belonging to two different parts, one or another fit is obtained.

Landing - the nature of the connection of two parts, determined by the values \u200b\u200bof the gaps and interferences resulting in this connection.

Clearance - the difference between the dimensions of the hole and the shaft before assembly:

The gap characterizes the freedom of relative movement of the parts to be joined. The larger the gap, the greater the freedom of relative movement of the interface elements. You can also remember the term backlash(German - Luft), indicating the gap between the mating surfaces of the assembly parts.

If the shaft size is larger than the hole size, a positive interference is obtained in the connection. Preload - the difference between the dimensions of the shaft and the hole before assembly:

Both the gap and the tightness can, generally speaking, be considered as algebraic quantities, assuming that S \u003d - N.

The concept of "landing" refers to a set of pairs of mating elements, the size of each of which is a random variable. The scattering field of a given random variable is limited by the specified limit deviations. Therefore, the resulting gaps (preloads) during assembly are also random variables.

The nature of the mating (that is, the fit) is conveniently represented on the diagram of the tolerance fields of the hole and shaft. In the geometric interpretation, the tolerance field is a part of the plane bounded above and below by lines of limiting dimensions (deviations). Deviations ES and EI (es and ei) on the tolerance field diagrams (Fig. 2.1) are plotted from the nominal size line - the zero line - in microns.

The specific content of the given tolerance field scheme can be better understood from Fig. 2.2, which shows the same nature of the connection.

Depending on the relative position of the tolerance fields of the mating landing elements, there are three types:

With guaranteed clearance, P(S > 0) = 1;

With guaranteed tightness, P(S< 0) = 1 или P(N > 0) = 1;

Transitional, i.e. 0< P(s) < 1.

Of course, P(S > 0) + P(N > 0) = 1.

A measure of the accuracy of the connection is the fit tolerance. Just as the size tolerance is the difference between its maximum and minimum limit values, the landing tolerance is found as the difference between the largest and smallest gaps:

TS \u003d S max - S min \u003d D max - d min - (D min - d max) \u003d T D + T d.

The relation obtained illustrates a simple idea: high connection accuracy can only be ensured with a correspondingly high dimensional accuracy of the mating elements.

Landings are appointed, as a rule, either in hole system either in shaft system.

The word "system" means order, regularity. The regularity, first of all, is expressed in the fact that the tolerance field of one of the mating parts has a well-defined constant location relative to the nominal size line. Such a detail is called the main one. The constant certainty of the location of the tolerance field of the main part is that it is in contact with the zero line and is overturned “into the material of the part” (the so-called principle of “saving metal”).

Landings in the hole system are obtained by a combination of different tolerance fields of the outer male connection elements (shafts) with the tolerance field of the main hole (Fig. 2.3):

Here, the upper deviation of the hole for all mates is constant and equal to the hole size tolerance (ES = T D = const), and the lower deviation of the hole is zero (EI = 0). The maximum deviations of the shaft mating with this hole are selected according to the nature of the assigned interface.

Fits in the shaft system are obtained by combining different tolerance fields of internal female elements (holes) with the tolerance field of the main shaft (Fig. 2.4):

Here es = 0, ei = - T d ; depending on the required nature of the connection, the limit deviations of the hole (ES, EI) are selected.

It is preferable to use a hole system: the manufacture of an internal element (hole) is often more difficult and expensive; for processing holes, a measured cutting tool is usually used (for example, reamers, broaches), the range of which should be reduced.

In some cases more profitable system shaft:

The use of standardized components, the outer elements of which must be matched in different ways (that is, with the formation of different landings) with the holes of other parts;

Using the same shaft to obtain several different matings with female internals of other parts;

The use of standard calibrated bars for the manufacture of parts without their mechanical processing.

Literature

Belkin V.M. Tolerances and landings (Basic standards of interchangeability). - M .: Mashinostroenie, 1992. - 528 p.

Dunin-Barkovsky I.V. Interchangeability, standardization and technical measurements. - M.: Publishing house of standards, 1987. - 352 p.

Anukhin V.I. Tolerances and landings: Tutorial. - St. Petersburg: Peter, 2008. - 207 p.

test questions

Plan

Standardization

Lecture notes

at the rate:

"Interchangeability,

technical measurements"

Donetsk 2008

Lecture No. 1 “The concept of interchangeability and standardization. Fundamentals of the principle of interchangeability. 3

Lecture No. 2 "Tolerance and fit systems for elements of cylindrical and flat joints." ten

Lecture No. 3 "Calculation and selection of landings for the GCC." 17

Lecture No. 4 "Calculation and design of gauges for the control of parts of smooth joints." 28

Lecture No. 5 "Tolerances and fittings of rolling bearings." 36

Lecture No. 6 "Normalization and designation of surface roughness." 42

Lecture No. 7 "Tolerances for the shape and location of surfaces." 47

Lecture No. 8 "Dimensional chains." 56

Lecture No. 9 "Interchangeability, methods and means of measurement and control gears". 68

Lecture No. 10 "Interchangeability threaded connections". 77

Lecture No. 11 "Interchangeability of keyed and splined connections." 82

Lecture No. 12 “Angle tolerances. Interchangeability of conical connections. 86

Lecture No. 13 "The concept of metrology and technical measurements". 91

Lecture No. 1 “The concept of interchangeability and standardization. Fundamentals of the principle of interchangeability.

Modern mechanical engineering is characterized by:

Continuous increase in capacity and productivity of machines;

Continuous improvement of machine designs and other products;

Increasing requirements for the accuracy of manufacturing machines;

The growth of mechanization and automation of production.

For the successful development of mechanical engineering in these areas, the organization of the production of machines and other products on the basis of interchangeability and standardization is of great importance.

The purpose of the discipline: familiarity with the methods of ensuring interchangeability,

standardization, as well as measurement and control methods

in relation to modern engineering products.

From the history of the development of interchangeability and standardization.

Elements of interchangeability and standardization appeared a very long time ago.

So, for example, the water supply system built by the slaves of Rome was made of pipes of a strictly defined diameter. Unified stone blocks were used to build pyramids in ancient Egypt.

The concept of interchangeability and its types.

Distinguish between complete and incomplete interchangeability of parts assembled into assembly units.

There are also external and internal interchangeability.

External - this is the interchangeability of purchased or cooperative products (mounted in other more complex products) and assembly units in terms of performance, size and shape of connecting surfaces. (For example, in electric motors, external interchangeability is provided by the shaft speed, power, and also by the shaft diameter; in rolling bearings - by the outer diameter of the outer ring and the inner diameter of the inner ring, as well as by rotation accuracy).

The basis for the implementation of interchangeability in modern industrial production is standardization.

Concepts about standardization. Categories of standards

The largest international organization in the field of standardization is ISO (until 1941 it was called ISA, organized in 1926). The supreme body of ISO is the General Assembly, which meets every 3 years, makes decisions on the most important issues and elects the President of the organization. The organization consists of a large number of clients. The Constitution states the main purpose of ISO - “to promote the favorable development of standardization throughout the world in order to facilitate the international exchange of goods and to develop mutual cooperation in various fields of activity.

Basic terms and definitions in the field of standardization are established by the ISO Committee for the Study of the Scientific Principles of Standardization (STACO).

Standardization is a planned activity to establish mandatory rules, norms and requirements, the implementation of which improves product quality and labor productivity.

A standard is a regulatory and technical document that establishes requirements for groups of homogeneous products and rules that ensure its development, production and use.

Specifications (TS) - a regulatory and technical document that establishes requirements for specific products, materials, their manufacture and control.

To strengthen the role of standardization, a state (sovereign) DSS standardization system has been developed and put into action. It defines the goals and objectives of standardization, the structure of standardization bodies and services, the procedure for developing, formalizing, approving, publishing and implementing standards.

The main goals of standardization are:

Improving the quality of products;

Export development;

Development of specialization;

Development of cooperation.

Depending on the scope of the DSS, the following categories of standards are provided:

GOST (DST) - state;

OST - industry;

STP - enterprises.

Basic terms and definitions of the principle of interchangeability

Basic terms and definitions are established in GOST 25346 - 82.

A connection is two or more parts that are movably or fixedly mated to each other.

Figure 1 - Connection examples

Rows of preferred numbers (Renard series) are geometric progressions.

R5: \u003d 1.6 - 10; sixteen; 25; 40; 63; 100…

R10: = 1.25 - 10; 12.5; sixteen; 20; 25…

The actual size is the size obtained as a result of the processing of the part and measured with an allowable error.

When making drawings, it is most convenient to put down the size in the form of a nominal size with deviations.

Limit dimensions are two maximum allowable dimensions, between which the actual size of a suitable part must be. ()

Figure 2 - Limiting dimensions of the hole, shaft

Size tolerance is the difference between the largest and smallest limit sizes (T - Tolerance)

Tolerance is a measure of dimensional accuracy and determines the complexity of manufacturing a part. The larger the tolerance, the easier and cheaper it is to manufacture the part.

The concept of nominal size and deviations simplifies the graphical representation of tolerances in the form of tolerance field layouts.

Dimensions on drawings

Introduction

In a mass production environment, it is important to ensure interchangeability the same details. Interchangeability allows you to replace a spare part that has broken during the operation of the mechanism. The new part must exactly match the replaced part in size and shape.

The main condition for interchangeability is the manufacture of a part with a certain accuracy. What should be the accuracy of the manufacture of the part, indicate on the drawings the permissible limit deviations.

The surfaces along which parts are connected are called conjugated . In the connection of two parts that are included one into the other, a female surface and a covered one are distinguished. The most common in mechanical engineering are connections with cylindrical and flat parallel surfaces. In a cylindrical connection, the surface of the hole covers the surface of the shaft (Fig. 1, a). The enclosing surface is called hole covering - shaft . These same terms hole and shaft conventionally used to refer to any other non-cylindrical enclosing and covered surfaces (Fig. 1, b).

Rice. 1. Explanation of terms hole and shaft

Landing

Any assembly operation of parts consists in the need to connect or, as they say, plant one detail to another. Hence, in technology, the expression landing to indicate the nature of the connection of parts.

Under the term landing understand the degree of mobility of the assembled parts relative to each other.

There are three groups of landings: with a gap, with an interference fit and transitional.

Landings with clearance

gap call the difference between the sizes of the hole D and the shaft d, if the size of the hole is larger than the size of the shaft (Fig. 2, a). The gap ensures free movement (rotation) of the shaft in the hole. Therefore, landings with a gap are called mobile landings. The larger the gap, the greater the freedom of movement. However, in reality, when designing machines with moving landings, such a gap is chosen that will minimize the friction coefficient of the shaft and hole.

Rice. 2. Landings

Interference landings

For these fits, the hole diameter D is less than the shaft diameter d (Fig. 2, b). .In reality, this connection can be made under pressure, when the female part (hole) is heated and (or) the male part (shaft) is cooled.

Interference landings are called fixed landings , since the mutual movement of the connected parts is excluded.

transitional landings

These landings are called transitional because before assembling the shaft and the hole, it is impossible to say what will be in the connection - a gap or an interference fit. This means that in transitional fits, the hole diameter D can be less than, greater than or equal to the shaft diameter d (Fig. 2, c).

Size tolerance. Tolerance field. Quality of accuracy Basic concepts

Dimensions in part drawings quantify the magnitude of the part's geometric shapes. Dimensions are divided into nominal, actual and limit (Fig. 3).

Nominal size - this is the main calculated size of the part, taking into account its purpose and the required accuracy.

Nominal connection size – this is the common (same) size for the hole and shaft that make up the joint. The nominal dimensions of parts and connections are not chosen arbitrarily, but according to GOST 6636-69 "Normal linear dimensions". In real production, in the manufacture of parts, nominal dimensions cannot be maintained and therefore the concept of actual dimensions is introduced.

actual size - this is the size obtained during the manufacture of the part. It always differs from the nominal up or down. The permissible limits of these deviations are established by means of limiting dimensions.

Limit dimensions two boundary values are called, between which the actual size must be. The larger of these values is called largest size limit, smaller - smallest size limit. In everyday practice, on the drawings of parts, it is customary to indicate the limiting dimensions by means of deviations from the nominal.

Limit deviation - this is the algebraic difference between the limiting and nominal sizes. Distinguish between upper and lower deviations. Upper deviation is the algebraic difference between the largest size limit and the nominal size. lower deviation is the algebraic difference between the smallest size limit and the nominal size.

The nominal size serves as the starting point for deviations. Deviations can be positive, negative and zero. In standards tables, deviations are given in micrometers (µm). In the drawings, deviations are usually indicated in millimeters (mm).

Actual deviation - this is the algebraic difference between the actual and nominal sizes. The part is considered fit if the valid deviation of the checked size is between the upper and lower deviations.

Size tolerance - this is the difference between the largest and smallest limit sizes or the absolute value of the algebraic difference between the upper and lower deviations.

Under quality understand a set of tolerances that vary depending on the size of the nominal size. 19 qualifications have been established, corresponding to different levels of accuracy in the manufacture of a part. For each qualification, rows of tolerance fields are built

Tolerance field is a field bounded by upper and lower deviations. All tolerance fields for holes and shafts are indicated by letters of the Latin alphabet: for holes - in capital letters (H, K, F, G, etc.); for shafts - lowercase (h, k, f, g, etc.).

Rice. 3. Explanation of terms

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