TO category:

Measurements

Tools for checking flatness and straightness

Measurement refers to the comparison of a quantity of the same name (length with length, angle with angle, area with area, etc.) with a quantity taken as a unit.

All measuring and control equipment used in plumbing can be divided into control instruments and measuring instruments.

The first group includes:
– tools for checking flatness and straightness;
– plane-parallel gauge blocks (tiles);
– line instruments that reproduce any multiple or fractional value of a unit of measurement within the scale (vernier instruments, vernier protractors);
– micrometric instruments based on the action of a screw pair (micrometers, micrometric bore gauges and depth gauges).

The group of measuring instruments (second group) includes:
– lever-mechanical (indicators, indicator bore gauges, lever brackets, minimeters);
– optical-mechanical (optimeters, instrumental microscopes, projectors, interferometers);
– electrical (profilometers, etc.). The measuring instruments indicated above are precise, expensive instruments, therefore, when using and storing them, you must follow the rules set out in the relevant instructions.

Pattern rulers are made in three types: with a double-sided bevel (DS) with a length of 80, 125, 200, 320 and (500) mm; triangular (LT) - 200 and 320 mm and tetrahedral (LC) - 200, 320 and (500) mm (Fig. 365, a-c). Checking straightness with curved rulers is carried out using the light slit method (through the light) or using the trace method. When checking straightness using the light slit method, a straight edge is applied with a sharp edge to the surface being checked, and a light source is placed behind the ruler and the part. The ruler is held strictly vertically at eye level, observing the gap between the ruler and the surface in different places along the length of the ruler. The presence of a gap between the ruler and the part indicates a deviation from straightness. With sufficient skill, this method of control allows you to capture a gap from 0.003 to 0.005 mm (3 - 5 µm).

When checking using the mark method, the working edge of the ruler is carried out along the clean surface being tested. If the surface is straight, there will be a continuous mark on it; if not, the trail will be intermittent (spots).

Straight edges with a wide working surface are made of four types (sections): rectangular ShP, I-beam ShD, bridges ShM, angular triangular UT.

Depending on the permissible deviations from straightness, straight edges of the ШП, ШД and ШМ types are divided into three classes: 0.1 and 2nd, and straight edges of the UT type are divided into 2 classes: 1st and 2nd. Rulers of the 0th and 1st classes are used for high-precision tests, and rulers of the 2nd class are used for installation work medium thickness.

Rice. 1. Straight edges: a - LD with double-sided bevel, b - J1T triangular, c - LC tetrahedral

Rice. 2. Checking with a pattern ruler according to the light slit method for transmission: a - position of the eye, b - installation of the ruler, 1 - ruler, 2 - plate

Rice. 3. Rulers with a wide working surface: a - rectangular ShP, b - I-beam ShD, c - bridge ShM, d - angular triangular (wedges) UT

Rice. 4. Checking straightness with rulers: a - ShD, b - with a ShM bridge using strips of tissue paper

Checking straightness and flatness with these rulers is carried out by linear deviations and by paint (spot method). When measuring linear deviations from straightness, the ruler is placed on the surface being tested or on two measuring tiles of the same size. The gaps between the ruler and the controlled surface are measured with a feeler gauge.

Accurate results are obtained by using strips of tissue paper, which are placed under the ruler at certain intervals. By pulling the strip out from under the ruler, the magnitude of the deviation from straightness is judged by the pressing force of each of them.

When testing for paint, the working surface of the ruler is covered with a thin layer of paint (soot, red lead), then the ruler is placed on the surface being tested and moved smoothly without pressure along the surface being tested. After this, the ruler is carefully removed and the straightness of the surface is judged by the location, number, and size of spots on the surface. With good flatness, paint spots are distributed evenly over the entire surface. The greater the number of spots on the tested surface of a 25x25 mm square, the higher the flatness. Triangular straight edges are made with angles of 45, 55 and 60°.

Verification plates are used mainly for checking wide surfaces using the paint method, and are also used as auxiliary devices for various tests in workshop conditions. The plates are made of gray fine-grained cast iron. According to the accuracy of the working surface, the slabs come in four classes: 0.1, 2 and 3; the first three classes are surface slabs, the fourth are marking slabs. Checking for paint using surface plates is carried out as described above.

The plates are protected from impacts, scratches, and contamination; after work, they are thoroughly wiped, lubricated with mineral oil, turpentine or petroleum jelly and covered. wooden shield(lid).

Rulers ШД, ШМ and УТ cannot be stored leaning against each other, against the wall at a certain angle: they bend and become unusable.

The performance of the surfaces of machine parts in contact with each other is largely determined not only by the given dimensions, but also by the deviation from straightness and flatness.

When measuring flatness, it is determined how much the surface of a machined part deviates from an ideal plane.

The most common means of measuring straightness are test rulers (GOST 8026-64), which are divided into the following types:

1. Pattern rulers: with double-sided bevel (LD), triangular (LT), tetrahedral (TC).
2. Rulers with a wide working surface: rectangular section (RH), I-section (I-section), bridges (BH).
3. Angular rulers: triangular wedges (UT).

(Fig. 64, a) with a double-sided bevel (LD) are made of tool alloy steel with high precision and have thin working surfaces called ribs or blades with a radius of curvature of no more than 0.1-0.2 mm, thanks to which it is possible to very accurately determine deviations from straightness.

Rice. 64. Pattern rulers:
a - with a double-sided bevel, b - with a wide working surface - bridge (SM), c - triangular angular - wedge (UT)

GOST 8026-64 provides for two accuracy classes for rulers: 0 and 1st, with class 0 being more accurate.

Checking with a ruler is carried out using the light slit method. Place a ruler on the surface being tested with a sharp edge and hold it vertically strictly at eye level, observing the clearance between the ruler and the surface in different places along the length of the ruler. The presence of a gap between the ruler and the part indicates a deviation from straightness. With sufficient skill, this method of control allows you to capture a gap from 0.003 to 0.005 mm.

Rulers with a wide working surface - ShM bridges (Fig. 64, b) according to GOST 8026-64 are manufactured in length 400; 630; 1000; 1600; 2500; 4000 mm, 0, 1 and 2 accuracy classes. They are used to check flatness using the linear relationship method and “paint test”. The first method is to determine the gap between the working edge of the ruler and the plane being tested. Using thin plates of a probe or tissue paper, strips of which no more than 0.02 mm thick are placed under the ruler evenly in several places, the gap size is measured.

Paint testing gives greater accuracy. The working surface of the ruler is evenly coated with a thin layer of paint (soot, red lead) and then it is smoothly moved without pressure in two or three circular movements along the surface being tested, after which the ruler is carefully removed and the straightness of the product is judged by the location and number of spots on the surface. With ideal flatness, the surface of the part is covered with paint evenly. However, any surface has alternating protrusions and depressions, and therefore the paint falls on the protruding parts.

Triangular angular rulers - wedges (UT) are used to check for paint on planes that are at an angle to each other, and are often used when repairing cars.

Triangular corner rulers (Fig. 64. c) according to GOST 8026-64 are made with working angles of 45; 55 and 60° and length 250; 500; 750; 1000 mm, tetrahedral - 630 and 1000 mm long. These rulers are used to check the paint.

The verticality and horizontality of a surface is usually measured by a plumb line or level. When measuring with a plumb line or level, it is necessary that the parts being measured and the measuring instruments be at rest.

Levels are designed to check the horizontal and vertical position of the surfaces of machine elements during installation.

Bar levels(Fig. 65) are used to control deviations from the horizontal position of surfaces. The metal body of the level has a length of 100; 150; 200 (250) and 500 mm, inside it there is a glass longitudinal tube - ampoule 2 and installation (transverse) ampoule 3. Ethyl ether or ethyl alcohol is poured into the ampoules so that a bubble is formed. Ampoule 2 has a scale.

Rice. 65. Bar level:

At the value of the scale division of the main ampoule 2, the movement of the bubble by one division indicates a difference in the levels of these points equal to 0.02 mm. The value of a level division is understood as its slope, corresponding to the movement of the bubble of the main ampoule by one scale division, expressed in mm per 1 m.

When using, the level is placed on the surface to be tested and, moving it in the longitudinal and transverse directions, the amount of deviation from the horizontal position is determined on the scale of ampoule 2.

Frame levels(Fig. 66) are designed to control the horizontal and vertical position of surfaces.

Rice. 66. Frame level:
1 - body, 2 - longitudinal ampoule, 3 - transverse ampoule

The length of the working surface of the frame levels is 100; 150; 200 and 300 mm.

The frame level consists of a body 1, a main (longitudinal) 2 and an installation 3 (transverse) ampoules. The main scale determines the magnitude and direction of the deviation.

The accuracy of the level is determined on a test plate. The vial of the main ampoule should show the same position when

STATE STANDARD OF THE USSR UNION

METAL PRODUCTS

Methods for measuring shape deviations

GOST 26877-91

COMMITTEE OF STANDARDIZATION AND METROLOGY OF THE USSR

STATE STANDARD OF THE USSR UNION

Date of introduction 01.07.92

This standard establishes methods for measuring deviations, shapes of blooms, slabs, sheets, tape, strip, coil, rods, pipes, hot-rolled and bent profiles, wire rods and wires made of ferrous and non-ferrous metals and alloys. Terms and explanations of deviations in the shape of metal products are given in Appendix 1.

1. MEASURING INSTRUMENTS

2. PREPARATION FOR MEASUREMENT

3. TAKE MEASUREMENTS

2) using a rigid steel ruler adjacent to the upper surface and a measuring ruler located vertically (Fig. 3);

3) using a stretched steel string adjacent to the upper surface and a measuring ruler located vertically (Fig. 4);

4) an indicator mounted on a bracket and moving parallel to the plane of location of the metal products. Waviness, warping and deflection are expressed in millimeters or percentages of the standardized length. Wavelength is expressed in millimeters. If necessary, determine the wavelength (L) by measuring the distance between the points of contact of the surface to the metal product using a measuring steel ruler (Fig. 1). 3.3. Torsion is measured in any plane at a standardized distance L from the base cross section. Metal products are laid so that one of its sides in the base cross section is in contact with a flat surface. 1) measure the value of the lag D of the cross section from a flat surface using a measuring ruler or probe (Fig. 5 and 6);

Crap. 5 Damn. 6 2) measure the value of the lag D of the cross section of the metal product from the adjacent plane using a square lying on one side on a flat surface and a measuring ruler or feeler gauge (Fig. 7). The twist angle a of the cross section of the metal product relative to the base cross section can also be measured with a protractor.

Twisting is expressed in millimeters or degrees per standardized length. 3.4. The thickness difference is defined as the difference between the largest S 1 and the smallest S 2 thickness values ​​of metal products or their elements at a given distance from the edges (Figures 8 and 9).

Convexity and concavity are measured using a square and a measuring ruler or a feeler gauge and are expressed in millimeters. 3.6. Curvature (crescent) is determined by the greatest distance between the surface of the metal product and the applied ruler or stretched string (Fig. 11).

Curvature and crescent shape are measured with a ruler or feeler gauge and expressed in millimeters per standardized length. 3.7. Ovality is defined as half the difference between the largest d 1 and smallest d 2 diameters in one cross section (Fig. 12). Measurements are taken with a micrometer or caliper and expressed in millimeters.

(Amendment. IUS 5-2005) 3.8. The deviation from the angle is determined by the difference between the real angle a 1 and the given angle a 2 (Fig. 13 and 14). Deviation from the angle is measured with a protractor or measuring ruler and expressed in millimeters or degrees.

3.9. The miter of the cut is determined by the greatest distance from the plane of the end of the metal product to the plane perpendicular to the longitudinal planes of the metal product and passing through the extreme point of the edge of the end or the angle a between them (Fig. 15).

It is allowed to determine the cutting angle of flat metal products (sheets, strips and slabs) as the difference in diagonals, provided that the metal product has a right angle at one end (Fig. 16). The cutting angle is measured with a measuring ruler and a square or a protractor and is expressed in millimeters or degrees.

3.10. Deviation from symmetry is determined by the difference in the distances of the opposite extreme points lying on the surface of the metal product from the axis of symmetry (Fig. 17). Deviation from symmetry is measured with a measuring ruler using a square.

3.11. The bluntness of the corners is measured as the distance from the apex of the angle formed by the lines of intersection of adjacent faces to the boundaries of the bluntness. The technique for monitoring the blunting of square and hexagon corners is given in Appendix 4. 3.12. Telescopicity is controlled using a measuring ruler according to the diagram shown in Fig. 18.

B - strip width; T - telescopicity

APPENDIX 1
Mandatory

TERMS AND EXPLANATIONS OF SHAPE DEVIATIONS OF METAL PRODUCTS

Table 1

APPENDIX 2
Mandatory

LIST OF STANDARDIZED MEASUREMENT INSTRUMENTS

Table 2

Non-standardized automatic measuring instruments (NSI) of shape deviations

Table 3

METHOD FOR CONTROL OF BLUTTING CORNERS OF ROLLED CORNERS

Table 4

Control of bluntness D is carried out using the vernier of a caliper, the measured value of which should not exceed the permissible value of bluntness, calculated by the formula D = 0.15a ´ cos 45° = 0.15 a ´ 0.7 = 0.105 a . In this case, the boundaries of the dullness determined by the scale of the square should not exceed the dullness values ​​​​established by the standard.

The permissible value of blunting the corners of a square with a side of more than 58 mm is given in table. 5.

Table 5

Table 6

INFORMATION DATA

Pattern rulers are made in three types: with double-sided bevel (DS)

length 80, 125, 200, 320 and 500 mm; triangular (LT) - 200 and 320 mm and tetrahedral (LC) - 200, 320 and 500 mm (Fig. 365, a - c). Checking straightness with curved rulers is carried out using the light slit method (through the light) or using the trace method. When checking straightness using the light slit method, a straight edge is applied with a sharp edge (Fig. 366, b) to the surface being checked, and the light source is placed behind the ruler and the part. The ruler is held strictly vertically at eye level (Fig. 366, a), observing the gap between the ruler and the surface in different places along the length of the ruler. The presence of a gap between the ruler and the part indicates a deviation from straightness. With sufficient skill, this method of control allows you to capture a gap from 0.003 to 0.005 mm (3 - 5 µm).

When checking using the mark method, the working edge of the ruler is carried out along the clean surface being tested. If the surface is straight, there will be a continuous mark on it; if not, the trail will be intermittent (spots).

Straight edges with a wide working surface are made of four types (sections): rectangular ShP (Fig. 367, a), I-beam ShD (Fig. 367, b), ShM bridges (Fig. 367, c), angular triangular UT (Fig. 367 , G).

Depending on the permissible deviations from straightness, straight edges of the ШП, ШД and ШМ types are divided into three classes: 0, 1 and 2, and straight edges of the UT type are divided into two classes: 1 and 2. Rulers of the 0th and 1st classes are used for high-precision control work, and rulers of the 2nd class are used for installation work of medium accuracy.

Checking straightness and flatness with these rulers is carried out by linear deviations and by paint (spot method). When measuring linear deviations from straightness, the ruler is placed on the surface being tested or on two measuring tiles of the same size. The gaps between the ruler and the controlled surface are measured with a probe (Fig. 368, a).

Accurate results are obtained by using strips of tissue paper, which are placed under the ruler at certain intervals. By pulling the strip out from under the ruler, the magnitude of the deviation from straightness is judged by the pressing force of each of them (Fig. 368, 6).

When testing for paint, the working surface of the ruler is covered with a thin layer of paint (soot, red lead), then the ruler is placed on the surface being tested and moved smoothly without pressure along the surface being tested. After this, the ruler is carefully removed and the straightness of the surface is judged by the location, number, and size of spots on the surface. With good flatness, paint spots are distributed evenly over the entire surface. The greater the number of spots on the tested surface of a 25 × 25 mm square, the higher the flatness. Triangular straight edges are made with angles of 45, 55 and 60° (see Fig. 367, d).

Test plates (see Fig. 367, a, 6) are used mainly for checking wide surfaces using the paint method, and are also used as auxiliary devices for various control work in workshop conditions. The plates are made of gray fine-grained cast iron. According to the accuracy of the working surface, the slabs come in four classes: 0, 1, 2 and 3; the first three classes are surface slabs, the fourth are marking slabs. Checking for paint using surface plates is carried out as described above.

The plates are protected from impacts, scratches, and contamination; after work, they are thoroughly wiped, lubricated with mineral oil, turpentine or petroleum jelly and covered with a wooden shield (lid).

Rulers ШД, ШМ and УТ cannot be stored leaning against each other, against the wall at a certain angle: they bend and become unusable.

TO category:

Helping a tool worker

Tools for checking straightness and flatness

To check flatness and straightness, straight edges, plates, flat glass plates and various devices special purpose.

Rulers of the LD, LT and LC types are the most common tools for checking straightness. They are called pattern rulers. They come with a double-sided bevel, triangular and tetrahedral. They are made of 0th and 1st accuracy classes from steel grade X or ShKh15 and heat treated to a hardness of HRC 58.

When checking measuring instruments, rulers of the 0th accuracy class are used.

The straightness of surfaces is controlled using rulers in two ways: against light and against paint. When testing for transmission, a ruler is placed with a sharp edge on the surface being tested, and the light source is placed behind it. In the absence of deviations from straightness and flatness, light should not break through anywhere. Linear deviation is determined by eye or by comparison with a lumen sample. The minimum width of the slit that can be detected by the eye is 3-5 µm.

Examples of control of treated surfaces using pattern rulers are shown in Fig. 1, a - d.

When testing by the paint method, a thin layer of glaze or soot diluted in oil is applied to the surface on a surface plate or ruler, and then the surface being tested is applied to the painted surface and lightly rubbed against it. The quality of the surface is assessed by the uniformity of stains and their number on an area measuring 25X25 mm in several places. The difference in the number of spots on neighboring areas should be no more than two or three.

Rice. 1. Examples of control with rulers.

Rulers of types ShP, ShD, ShM and UT with a wide working plane are used to control the straightness and flatness of large parts (400 mm or more). They are called straight edges.

The ShP and ShD rulers of the 0th, 1st and 2nd accuracy classes are made of steel grade U7 with a working surface hardness of HRC50. They wander to control straightness using the transmission method or using a feeler gauge.

Lines of ShM and UT types of the same accuracy classes are made of gray cast iron SCh18-36 or high-strength cast iron VCh45-5 with hardness HB 170...229. They are intended for control using the paint method.

Surface plates are used to check flatness using the paint method and for use as an auxiliary device during various control operations.

Verification plates are manufactured in five accuracy classes: 01st, 0th, 1st, 2nd and 3rd. The working surfaces of the plates for inspection using the paint method must be scraped and have precise flatness, which is achieved by scraping using the three-plate method. Surface plates intended for other purposes can be ground or lapped. Marking boards can be produced by finishing planing. Their working surface can be divided into rectangles by shallow longitudinal and transverse grooves.

Rice. 2. Test plates.

When checking the flatness and quality of the working surfaces of scraped slabs using the paint method, the number of spots in a square with a side of 25 mm should be: for slabs of classes 01 and 0 - no less than 30, class 1 - no less than 25 and class 2 - no less than 20.

Slabs with dimensions from 250X250 mm to 4000X1600 mm are made from gray pearlitic cast iron SCh28-52 without solid inclusions and porosity. The hardness of the working surface should be HB 200…220.

When testing using the paint method, a plate (or part) with the controlled surface is placed on the working surface of the slab and lightly rubbed. Flatness and straightness are assessed by the uniformity of the spots and their number on an area of ​​25x25 mm in several places.

Flat glass plates. To measure gauge blocks and to control the grindability and flatness of their measuring surfaces, as well as the surfaces of gauges and other tools, flat glass plates are used.

Depending on the purpose, two types of plates are distinguished: – lower (support) plates, to which plane-parallel gauge blocks are ground when measuring them using the interference method. These plates are also used to check the grindability and flatness of the measuring surfaces of gauge blocks, gauges and other tools. They are available in diameters of 60, 80, 100, 120 mm and thicknesses of 20, 25 and 30 mm; – upper ones for measuring plane-parallel gauge blocks using the interference method.

Rice. 3. Flat glass plates.

Deviations from the flatness of the working surfaces should not exceed 0.03-0.05 microns for plates of the 1st and 0.1 microns for plates of the 2nd accuracy class.

In accordance with the standard, the industry produces plane-parallel glass plates and sets of them for checking the flatness and mutual parallelism of the measuring surfaces of micrometers and lever brackets using the interference method. The sets consist of four plates with a diameter of 30, 40 and 50 mm. The thickness of the plates differs from each other by 0.125 mm. So, in set No. 1 of category 1, the plates have the following dimensions: 15.00; 15.12; 15.25 and 15.37 mm.

The essence of the interference control method is as follows. A flat glass plate is tightly placed on the controlled surface and then one of its edges is slightly raised until an angle of less than G is formed. A thin wedge-shaped air layer is created between the controlled surface and the plate. If a beam of light rays is directed at a glass plate, then each ray, passing through the plate, will be reflected from its lower plane FH at point A, and part of them will be refracted and fall on the controlled surface, reflected from it and, having refracted at point b, will come out of the wedge . A beam, for example, will interfere with a beam incident on point C. A number of interference fringes will be observed on the surface. In daylight, they are painted in different colors, and if you use uniform light, passing it through a green or yellow filter, you will see an alternation of black stripes with stripes brightly colored in any specific color.

The interference fringes are located in such a way that along each of them the distance from the surface of the plate to the controlled surface will be the same. The distance between the two stripes corresponds to a change in the thickness of the air wedge by 0.25 μm. Therefore, a change in the thickness of the air wedge between the plate and the controlled surface by 1 μm corresponds to the appearance of four stripes.

In cases where the tested surface is an exact plane (deviation from plane-parallelism is about 0.25 μm), at the point of contact of the two surfaces, the observed stripes will be straight and parallel. In the same cases, when the controlled surface is brought to the precision of a glass plate, the interference fringes will disappear and a uniform color of the same color will be observed. When inspecting surfaces manufactured with deviations, distortion of interference fringes is observed. By the nature of their curvature, one can judge the convexity or concavity of the surface and easily determine the magnitude of this deviation from flatness.

Rice. 4. The essence of the interference control method.

Two test surfaces, convex and concave, are shown in Fig. 4, b. To determine whether there is a convex or concave surface on the surface, you need to determine the position of the wedge, and its expansion is directed in the direction where the strips move when lightly pressing on the glass plate. If the convexity of the interference fringes is directed towards the expansion of the wedge, then the surface is convex, but if it is concave, then the surface is concave.

The amount of curvature can be determined as follows. If you mentally draw a straight line touching the strip in the middle, you can see that the edges of the strip are shifted relative to the middle by one strip, i.e., the distance between the surfaces of the part and the plate changes by 0.25 microns. Therefore, the convexity value is 0.25 µm. From Fig. 4, c it is clear that the controlled surface has a concavity of half a strip, i.e. 0.125 μm.

The interference method is used to control surfaces with dimensions up to 100X100 mm.