Locksmith activities aimed at ensuring the smoothness of the surfaces of various materials represent a whole group of operations. These include common grinding, sawing, cutting and polishing techniques. Combining these methods of finishing surfaces is the use of abrasives with varying degrees and configuration of grit. In many ways it is similar to them, but scrubbing also has fundamental differences. This is a technique that allows you to obtain a smooth workpiece surface with high accuracy, which in the future will allow the master to ensure its tight coupling with other materials.

Technology Overview

The operation is most often used in relation to metal, but in some cases plastic and wooden surfaces are treated with similar methods. The essence of the technology is the elimination of pronounced bulges on the product. That is, with the help of a special tool grinding of irregularities is provided. To understand the degree of accuracy, it is worth noting that the height of the removed layer is calculated in microns. From an operational management point of view, scraping is but not an automated process. It is used but machines and easel mechanisms do not yet have widespread use in this area. The peculiarity of the method is that it is also used in working with non-standard rounded surfaces, where radial slope accounting is required. For example, it can be curved and cylindrical products.

Preparing for Scraping

The use of scraping is due to the tasks of obtaining a highly precise surface in terms of smoothness. Therefore, the use of a specialized tool to achieve such a result when working with materials having a rough surface does not justify itself. Accordingly, the workpieces initially go through the stages of initial cleaning, as well as grinding and even polishing. The demand for recent operations is determined by the parameters with which specific locksmithing works are implemented and, in particular, scraping. Experienced craftsmen practice the use of calibration parts. These are blanks that are exemplary for the resulting product. Also at this stage, auxiliary equipment should be ready, with which the operator will carry out individual technological steps. For example, special primer oil or paint may be used.

Scraping technique

After completing the preparatory processing steps, the first thing to do is apply special paint to the work surface. Its task is to identify the lapping pattern, as well as to identify the most prominent areas on the surface. Sometimes large areas are zoned into separate sections, depending on the complexity of their bringing to the desired state. One way or another, according to the formed pattern, scraping is performed. This means that the processing is not carried out over a continuous area, but in a sense pointwise. The efficiency and quality of the resulting slice is determined by the frequency with which stripping is performed. After the planned volume of the cut was completed, the master makes another coating of the surface with paint, which again reveals the bulges and irregularities. Thus, quality control of scraping is performed. By the way, the operation cycle can be repeated several times depending on how much each session brings the surface of the workpiece closer to the sample.

Technical Parameters of Scraping

And in the case of processing flat surfaces, and in fine-tuning curved products, the technology allows to obtain smoothness with an allowance for roughness of the order of 0.002 mm with a length of 1000 mm. For example, a site measuring 25 x 25 mm 2 may have up to 30 exit-treated spots. The number of spots also determines the level of accuracy of scraping. Thin are considered surfaces on which over 22 spots are present. Conversely, a product with no more than 6 spots on its surface will be considered rough. Again, the number of remaining islets treated with paint will be calculated over an area of \u200b\u200b25 x 25 mm 2. Depending on this parameter, types of scraping are also determined - between a thin and rough cut, precise and final refinements are also distinguished. Which result should be obtained in a particular case depends on the technical task. A thin cut with 30 spots is not always required. Rough processing is sometimes sufficient to fulfill the tightness requirements. But coarse scraping cannot be compared with a similar characteristic when grinding - in both cases we are talking about different orders of height of the remaining bulges.

Tool used

In the classic version, the scraper is a metal rod provided with cutting edges. An important feature of the device is a base made of tool carbon steel. Thanks to such alloys, a metalwork scraper works effectively with most metal products. Also, some models can be equipped with special nozzle plates that differ in different properties - accordingly, the equipment is selected for specific tasks.

It has already been noted that mainly scrapping is carried out with a hand tool. This method allows you to get a high-precision quality result, but it has a minus - this operation is time-consuming, requires considerable physical effort. Therefore, if special quality requirements are not provided, use pneumatic and electric gauge machines. Mechanized scraping of parts due to the inability to adjust the pressure exerted on the surface does not always give accurate processing, but it compares favorably with the manual method by the speed of operations.

Pros and Cons of Technology

The main drawback of scraping is the cost and complexity of the process. This is one of the most troublesome locksmith operations, which is resorted to only in special cases. Moreover, even manual equipment, involving the use of a simple tool for the device, will be expensive because of the need to use consumables in the form of scraper paint. The advantages, which are still many in this processing method, include obtaining a high-precision cut. Other metalwork cannot provide a similar effect (with the exception of technological equipment for grinding and polishing). But in this case, the same drawbacks will occur - grinding machines with increased productivity operate on a different principle and are not always able to achieve a similar quality level of cut. And this is not to mention the cost of the equipment itself, which at a price can exceed pneumatic and electric scrapers.

Where is the metalwork scraper used?

Practice shows that scraping in the professional sphere of performing locksmithing occupies about 20% of all operations. However, the niche in which products manufactured in this way are used is rather limited. Basically, scrapers are used in the manufacturing processes of parts for machine tools, machines, industrial equipment, etc. It is important not to forget that scraping is a way to obtain surfaces that are highly accurate in terms of smoothness. Moreover, the surfaces themselves can be curved. For example, high-quality bearings with optimal radial planes can only be obtained in this way.

Conclusion

The difficulty of bringing metal surfaces to a state in which there will be no irregularities even visible to the eye has also determined the high responsibility of the performer himself. The fact is that the highest-quality operation (scraping) involves manual revision, which directly depends on the skills of the master. An experienced locksmith must take into account a lot of nuances in the process. These include the selection of scraper paint, and the use of one or another tool stroke frequency, and other subtleties that will determine the merits of the final result.

231. What is scraping?

Scraping - - / This is the process of obtaining the required accuracy under the working conditions of the shapes, sizes and relative position of the surfaces to ensure a snug fit or tight connection.

When scraping, thin chips are cut from uneven surfaces that have already been previously processed by cutting with a file or other cutting tool.

232. What tools are used for scrapping?

Scraping is done by tools called

Scrapers. For the manufacture of scrapers, tool carbon steels UІ0, UYUA, U12, U12A, alloy steel X05, as well as carbide alloys are used.

Ggini inserted into steel holders. Used and failed trihedral or flat files after appropriate grinding can also serve as scrapers.

233. Name the types of scrapers.

There are manual and mechanical scrapers, and they can be flat single-sided and double-sided, solid and with inserted plates, trihedral solid and trihedral single-sided, semicircular one-sided

They are both double-sided, spoon-shaped and universal (Fig. 36).

234. What tools, except scrapers, are used in scraping?

When scraping, cast-iron plates are used to check the surfaces of flat parts for paint, flat and trihedral rulers to check the flatness of the surface, prisms, rectangular parallelepiped plates, control rollers, probes and other tools for controlling the quality of scraping and grinding. In addition to the tools mentioned, brushes and cleaning materials should be used.

235. What parts does a universal scraper consist of?

The universal scraper consists of a replaceable plate (the working part of the scraper), a body, a stick, a screw and a handle.

236. In what cases is scraping used?

Scraping is applied when you need to remove

Traces of processing with a file or other tool, as well as when you want to get a high degree of accuracy and a small surface roughness of machine parts connected to each other. Scrapering is especially often used in the processing of degales of friction pairs.

237. What needs to be done before proceeding with scraping?

Before proceeding to shabrennya, it is necessary to check the degree of surface roughness and the place of unevenness to be scraped. Plates, rulers, prisms, rollers, probes are used to detect surface irregularities. When scraping onto paint, scab paint is used. In some cases, scraping is carried out to shine.

238. Name the tool and material used for scraping on the paint.

To scrape parts onto paint, use a plate or ruler, and also paint.

As a paint for scraping, a mixture of machine oil with Parisian blue or ultramarine is used, which has a light paste consistency. Sometimes a mixture of engine oil with soot is used,

239. Explain the process of shabrettz on the paint.

Paint is applied with a thin layer of slab or a ruler.

With a brush or frequent rags, after which the plate or ruler is superimposed on the surface of the part intended for scraping.

After several circular motions of the plate or reciprocating movements of the ruler over the part or part on the plate, the part is carefully removed from the plate.

Appeared colored spots on the part indicate irregularities protruding on the surface of the part. These irregularities are removed by scraping.

240. What spots appear on the surface of the product when it is lapped to the plate on the paint?

During lapping of the part to the plate on the paint, painted spots appear on the surface of the part, larger or smaller, between which there are light gaps.

Colored spots appear due to irregularities on this surface. 95

The highest irregularities on the surface have a lighter color than the paint due to some erasure of the paint during grinding movements. The main bulges are characterized by a good paint coating and therefore they have a dense color.

Light and shiny spots on the surface of the part indicate recesses on the surface that are not coated with paint.

241. What is the order of spot removal?

The sequence for removing stains from the surface determines their color.

Scraping begins with the most protruding places indicated by the light color of the paint. Then there are spots with a dense color. Light spots do not scrape.

The degree of accuracy and surface roughness is determined by the number of spots of paint squared with a side of 25 mm (about 16 - good scraping, 25 - very accurate scraping).

242. What are the disadvantages and advantages of scraping?

The disadvantages of scraping are too slow

The processing process and considerable laboriousness, which requires a lot of precision, patience and time from the locksmith. The advantage of this type of processing is the ability to obtain high precision with simple tools (up to 2 microns). The advantages also include the possibility of obtaining precise and smooth curved surfaces, processing closed surfaces and surfaces all the way. Cast iron and steel surfaces of low hardness are well scrapped.

Hardened steel surfaces should be ground.

243. What safety rules should be followed when scraping?

First of all, around the workplace you need to keep clean and tidy, otherwise the employee may slip and fall, and ultimately get injured. The tool must be used carefully and skillfully, in between work and after its completion, you need to put the tool in a drawer. The scraper should always be held so that the cutting part is facing away from the worker.

Scraper should be well sharpened. When scraping, be sure to remove sharp edges from the parts.

Very precise alignment of hard surfaces - this is scrapping (scrapping, scrapping) of metal; plumbing today calls this operation one of the most difficult and critical.

1 What is metal scraping, what tool does it perform?

By this procedure, it is customary to understand the final operation of metalwork processing of metal (very rarely plastic or wooden) surfaces, the essence of which is scraping thin layers (0.005-0.07 mm) from the top of the parts using a scraper. An operation is recommended for situations when extremely small surface roughness levels are processed.
  The pattern is ideal for mating surfaces (friction) that move relative to each other.

It holds grease between them, provides the mating products with a snug fit, which guarantees high accuracy of the geometric parameters of the workpieces, which include:

• elements of devices;
• curved and flat surfaces;
• surfaces of calibration plates, rulers, squares and other measuring devices;
• plain bearings;
• some building materials (tiles are often scrapped).

A tool for performing a scrapping operation called a scraper can be:

• trihedral, flat or shaped (classification by type of cutting part);
• composite or integral (separation by design);
• two- or one-sided (the number of cutting parts is taken into account).

Raw materials for the production of scrapers are tool steels. Composite construction tools are often supplied with plates of high hardness alloys or of tool high-speed steel.

Dimensions (geometric) of scrapers depend on:

• the angle of their installation in relation to the surface to be treated;
• material of parts;
• specific type of workpiece processing.

Flat surfaces are easily amenable to two- and one-sided scrapers, characterized by a curved or rectilinear cutting part. The end section of the tool with respect to its axis is sharpened at an angle:

• from 90 to 100 degrees when finishing metal processing;
• 90 degrees when finishing;
• 75 to 90 for roughing.

Soft metals are processed by a scraper with an angle from 35 to 40 degrees, steel - from 75 to 90, bronze and cast iron products - from 90 to 100.

The required roughness of the part and an indicator of its hardness determine the radius of curvature and the length of the edge of the tool that performs the cutting operation. The edge will have a smaller radius and a narrower edge, the greater the hardness of the workpiece. Finishing scraping of surfaces is carried out with a tool with an edge width for cutting from 5 to 12 mm, fine - from 15 to 20 mm, rough - from 20 to 30 mm.

When processing sliding bearings, scraper rings are used that reduce the number of regrindings during scrapping. Concave surfaces are machined with a tool with three faces, equipped with special grooves in the longitudinal direction and an angle of sharpening of 60 °. Such devices are easy to refill and sharpen.

2 Scrapping planar surfaces - process diagram

There are two options for performing the operation: on-the-go (working) and on-the-go. Experts say that the first method is more productive and modern (scrapping and lapping are now more often performed precisely on oneself).  Its scheme will be presented below, and before that we will briefly talk about how to prepare a metal surface for the procedure.

There is a special paint for scrapping, consisting, as a rule, of a combination of minium, azure or blue with ordinary machine oil. It is applied with a tampon to the calibration plate, then from there it is transferred to the workpiece in a circular motion. Subsequently, the master first aligns the most prominent colored areas, and then little colored.

The scheme of performing scraping "on oneself":

• detail set in a vice;
• using an elongated tool with insert-type plates, the scraping operation is started (the device should be held in its middle part with both hands, bringing the cutting part of the scraper at an angle of about 80 degrees to the surface);
• the edge of the tool is brought to the border of the "destroyed" spot;
• scrapping is performed (towards the remote edge of the part from the closest to the worker) "on itself" - rough (it is called preliminary) and fine (final).

As soon as at least 12–16 spots of scraping paint will be visually fixed on the treated surface with an area of \u200b\u200b25 by 25 millimeters, which will uniformly cover the workpiece, the leveling procedure can be considered complete. After that, quality control is carried out using a special frame placed on the surface:

• in the resulting window consider the number of spots;
• repeat this operation several times in different places of the part;
• calculate the arithmetic mean;
• compare with the desired (12-16 spots) value.

Curved surfaces are checked with a celluloid pattern (mesh with 25 to 25 mm sections). It can reproduce the workpiece configuration, which is aligned. If there are as many spots on 75 sections of the template as were stipulated by the technical processing conditions, scoring is considered satisfactory.

3 Lapping and scraping of metal - similar processes

Lapping is necessary to ensure the tightness and high density of the mating sections of the workpieces in contact with each other. The surface during such a procedure is characterized by a leveling accuracy of up to 0.0001 mm. Perform it after scraping with the following abrasives:

• Soft: diamond pastes and GOI pastes. Such compositions are recommended for copper and aluminum sheets, cast iron products, annealed steel surfaces.
• Solid: flint, emery, monocorund, diamond, quartz, natural corundum, synthetic albor, electrocorundum (white, plain, chromium), silicon carbides. The latter are used for cast iron processing.

Lapping is accompanied by cooling and lubrication of surfaces that are performed with soda water, gasoline, kerosene or mineral oils. And the main tool for performing the procedure is lapping. It is made of natural wood, glass, bronze, cast iron, copper, has a cylindrical, flat or other configuration, which is similar to the leveling surface.

The lapping pattern is as follows:

• Abrasive compounds are placed on a lapping tool (cartooning step). The grinding of a round lapping is carried out between the plates, flat - using a metal bar or roller, which went through the hardening procedure. In some cases, a lubricating compound is applied to the tool, which attracts and holds abrasive grains.
• Lapping is carried out directly. Conical parts are processed by rotating them on one or the other side with a scoop or a wrench, flat parts are processed in a circular motion on lapping flat plates. A workpiece of small thickness is recommended to be collected in a bag, and then processed at the same time.

Scraper  - this is a plumbing operation, in which the smallest shavings are removed (scraped off) from the surface of the product with a cutting tool - scraper. Scratch, as a rule, after processing with a cutter, file or other cutting tool.

Scrabble is most often when it is necessary to fit the surfaces of two parts so that they fit together most tightly. So, they will scrape the guides of the bed of lathes, calipers, as well as the surfaces of sliding bearings.

Scraping is a labor-intensive operation that requires a lot of time, since it is necessary to gradually remove very thin layers of metal from the treated surface; with thin scraping, chips with a thickness of up to 0.01 mm are removed in one stroke of the scraper.

To identify which places need to be scraped, the product is placed on the surface of the test plate covered with a thin layer of paint with the processed surface. Gently pushing the product, move it in different directions. As a result, protruding spots on the surface of the product are stained with paint. These places are treated with a scraper.

  Questions

1. What is called scraping?
2. What is scrapery used for?
3. What parts and parts of machines will scrape?

Types of scrapers

Surfaces scrape one-sided and two-sided scraper.

According to the shape of the working surface, the scrapers are divided into flat, trihedral, shaped. Scrapers are made of carbon tool steel and hardened their cutting part.

According to the shape of the cutting ends, the scrapers distinguish between straight and curved. Flat scraper process straight surfaces.

Curved-end scrapers process surfaces in sharp corners or soft metals (e.g. aluminum).

The double-sided flat scraper serves for the same purposes as the single-sided, but has a longer service life.

The length of flat unilateral scrapers is 200 - 300 mm, and bilateral - 200 - 400 mm. The width of the scraper for roughing and semi-finishing scraping is 20 - 30 mm, for finishing - 15 - 20 mm. The sharpening angle for rough and semi-final scrapers is 60 - 75 °, for fine - 90 °.

Trihedral scrapers, which, as a rule, are released only one-sided, process concave and cylindrical surfaces. Often trihedral scrapers are made from worked trihedral. The length of trihedral scrapers is 100 - 150 mm.

Questions

1. What are the types of scrapers?
2. Why use flat scrapers?
3. Why use trihedral scraper?

  "Plumbing", I.G. Spiridonov,
  G.P. Bufetov, V.G. Kopelevich

In the process, the scrapers are dull; therefore, they are ground on electric sharpeners with a corundum circle. Sharpening lead the end or side surface of the circle. First sharpen the end, and then the edges of the scraper. Sharpening a flat scraper a - end; b - facets; in - sharpened cutting edges. After that, the scraper is adjusted. When sharpening, press the scraper firmly. Sharpening should be carried out with ...

Theme 12 Patterning

The student must:

know:

Purpose and purpose of scraping;

Varieties of scrapers;

Differences in draft and finishing scraping;

Safety precautions for scraping.

be able to:

Perform scraping with various methods of rectilinear and curved surfaces.

Workplace and site equipment:  Workbench; vice is metalwork; overhead jaws; flat blunt files 200 ... 300 mm long with notch No. 3; different flat scrapers; rulers calibration (pattern); calibration plates; sharpening machine with grinding wheels PP 25A 16 V SM1 6 K3 A (for sharpening steel scrapers) and software 63C 16 V SM1 K3 A (for sharpening carbide scrapers); abrasive bars for finishing scrapers; 25x25 mm frame for checking the number of spots; paint - azure, soot, ultramarine (blue), etc .; machine oil; rags; tampons; cast iron blanks with flat surfaces requiring scraping.

Scraper It is called a fitting finishing operation, used to level and fit flat and curved (usually cylindrical) surfaces to get a snug fit. Scrapering is used for processing and repairing the friction surfaces of mating parts - beds, calipers, sliding bearings and surfaces of checking tools - plates, squares, rulers, etc. As well as filing, scrapping is one of the most common locksmith operations. In the practice of locksmith, locksmith, assembly and repair operations, the volume of scraper work reaches 20 ... 25%. The widespread use of scraping is explained by the special properties of the obtained surface, which are as follows: the scraped surface, in contrast to the polished or obtained abrasive grinding, is more wear-resistant, since it does not have abrasive grains sharpened in its pores (risks, scratches), accelerating the process of wear of rubbing surfaces; the scraped surface is better lubricated and retains lubricants longer due to the presence of the so-called breakdown of this surface into spots (alternation of protruding and deepened places), which also increases its wear resistance and reduces the coefficient of friction; the scraped surface allows you to use the simplest and most affordable way to assess its quality - by the number of spots per unit area. Cutting is preceded by cutting, for example filing, grinding, planing, milling, etc. Scrapering makes it possible to obtain a surface with low roughness (0.003 ... 0.01 mm), since in one pass the metal layer with a thickness of 0.005 ... 0.07 mm is removed with a scraper during finishing and not more than 0.01 ... 0 , 03 mm during pretreatment. The essence of scraping lies in the fact that very thin metal particles are scraped off from the convex (towering) places of the pre-worked surface of the workpiece by a cutting tool - a scraper.

Scrapers  - these are metal rods of various shapes with cutting edges made of carbon tool steel of grades U10 to U13 and hardened to a hardness of 56 ... 64 HRC e. Sometimes made equipped with plates of high speed steel or carbide. According to the shape of the cutting part, the scrapers are divided into flat, trihedral, shaped and special; by the number of cutting ends (faces) - on one-sided and bilateral (Fig. 12.1, a ... g); by design - on solid and with insert plates. Shape and geometrical parameters of cutting edges

choose depending on the shape and size of the work surface and the properties of the workpiece material. So, for scraping flat surfaces, flat scrapers with a rectilinear or radius cutting edge are used, for curved and internal (concave) surfaces - trihedral and shaped scrapers. Scraper with a straight cutting edge is more convenient to use when processing the edges of the workpiece, since during operation it will not come off the workpiece and will not damage its surface. When processing the rest of the workpiece, a scraper with a straight cutting edge is less convenient, since the lateral edges of the blade can leave deep scratches on the surface. In this case, it is more convenient to use scrapers with radius (arcuate) cutting edges, which provide a lower roughness of the scuffed surface than when working with a straight edge scraper.

  The geometrical parameters of the scrapers depend on the type of processing, the material being processed and the angle of installation of the tool with respect to the surface being machined. The end surface of the scraper is sharpened at an angle of 60 ... 100 0 relative to the axis of the tool, forming an angle of sharpening β, which is equal to: for rough processing - 60 ... 75 0, for finishing - 90 0, and for especially clean work - 90 ... 100 0.

The processed material influences the choice of the angle of sharpening β of a flat scraper as follows: when cast iron and bronze are processed, β \u003d 90 ... 100 0 (Fig. 12.2, a); steel - 75 ... 90 0 (Fig. 12.2, b); soft metals - 35 ... 40 0 \u200b\u200b(Fig. 12.2, c).

The choice of the length of the cutting edge and the radius of its rounding also depends on the hardness of the processed material and the required surface roughness. The harder the material, the narrower the cutting edge and the smaller the radius of curvature. The length of the cutting edge also depends on a given number and size of spots per unit area. So, for a preliminary (rough) layout, choose a scraper with a wide blade - 20 ... 30 mm, for an exact one - 15 ... 20 mm; for the most accurate layout - 5 ... 12 mm. For the final (final) scraping, the radius of the cutting blade is taken larger than for the roughing, since in this case the smallest deviation from the surface plane is obtained.

For processing curved concave surfaces, trihedral scrapers are used, on the sides of which longitudinal grooves are cut to facilitate sharpening. The point angle of the trihedral scraper β \u003d 60 ... 70 0.

  a - flat one-sided; b - flat bilateral; in - with a curved end; d - trihedral and tetrahedral Figure 12.1 Scrapers
Figure 12.2 Sharpening angles of scrapers for various metals

Sharpening of scrapers is carried out on a grinding machine using cooling. For scrapers made of tool steels, fine-grained electrocorundum grinding wheels (PP 25A 16V CM1 6 K3 A) are used, and for scrapers equipped with carbide inserts, grinding wheels made of green silicon carbide (PP 63C 16 V CM1 6 K3 A). The sharpening procedure is as follows: take the scraper with the right hand by the handle, and with the left cover it as close as possible to the working end. Leaning with the flat face of the scraper on the handrail, the end end is smoothly brought to the grinding wheel. The position of the scraper should be horizontal or inclined to provide the desired angle of sharpening. The scraper axis should coincide with the center of the circle. Gently shaking the scraper by the shank in a horizontal plane, sharpen the scraper, maintaining the required radius of curvature of the cutting edge (Fig. 12.3, a).

Sharpening of the wide edges of the scraper at a length of 25 ... 30 mm from the cutting edges is carried out in the same order, keeping the edges parallel to each other (Fig. 12.3, b).

Finishing (dressing) of the cutting edges of the scraper after sharpening is used to remove burrs and irregularities on the edges, the presence of which reduces the quality of scraping. Finishing is done on abrasive bars with grain size M14 ... M40 and smaller. The surface of the bar is lubricated with a thin layer of engine oil. Instead of an abrasive bar, a smooth cast iron tile can be used to refuel the scraper, on the surface of which a paste of abrasive micropowder M28 ... M20 in machine oil is applied.

The block during fine-tuning (Fig. 12.4, a) is placed on a wooden fixed lining, and the scraper with the end part is installed vertically on the block. With two fingers of the left hand, the scraper is held by the handle, gently pressing it to the bar, and the right hand oscillates the end of the scraper along the bar along the cutting edge in order to obtain a curved cutting edge. Then the lateral wide surfaces are brought (Fig. 12.4, b), for which two hands hold the scraper in horizontal position on the bar, and, moving it along the bar, both cutting edges are brought in alternately. Re-scraper finish immediately, as soon as they feel a slight dullness and deterioration of metal cutting. On average, the scraper is adjusted after every hour of work, depending on the mechanical properties of the processed material, the quality and accuracy of the scraper.

Preparation of the workpiece for scrapping consists in sawing (or in another form of processing) the desired surface, leaving as little as possible an allowance, which, depending on the length and width of the surface, is 0.1 ... 0.4 mm. Before scrapping, the surface is cleaned, washed, wiped, and then paint is applied to it.

The test plate is stained with a scraper paint, which is a mixture of engine oil (or autol on kerosene) with soot, azure or ultramarine, which is applied with a swab to the test plate with an even thin layer (Fig. 12.5, a). Then the workpiece to be processed is gently lowered onto the test plate and slowly moved in a circular motion in different directions using the entire surface of the plate, then the workpiece is carefully removed from the plate (Fig. 12.5, b). When scrapping heavy workpieces, they are left in place, and a test tool is applied to the treated surfaces to determine the protruding places (Fig. 12.5, d). On pre-treated surfaces, the paint lies evenly, but poorly prepared - unevenly. In small depressions, paint accumulates, and in places deeper it will not exist at all. So, on a surface prepared for scrapping, white spots appear - the most deepened places that are not covered with paint, dark spots - less deepened, paint has accumulated in them, gray spots are the most prominent, a thin layer of paint falls on them (Fig. 12.5, c).

The scraping process consists in the gradual removal of metal from the painted areas (gray spots). When working, the scraper should be held with the right hand, and with the palm of your left hand grab the tool in the middle, holding four fingers downward (Fig. 12.6, a). Take the working position relative to the vice or workpiece as when filing and set the scraper at an angle of 30 ... 40 0 \u200b\u200bto the surface to be scored. When scrapping, the forward stroke, i.e. push. When moving back (idle), the scraper is lifted. Shabri should not bend with the free position of the case.

Scraping is performed in several transitions: draft (preliminary), semi-finished (spot) and finishing (finishing). In special cases, precise and delicate scraping is performed. At the beginning of scrapping, the movement of the tool (stroke length) is 15 ... 20 mm, and then, as the surface becomes level, it decreases to 2 ... 5 mm. Each time, the direction of the working stroke must be changed so that the resulting strokes intersect at an angle of 45 ... 60 0 (Fig. 12.6, b). It is necessary to begin scrapping a flat surface from the most distant edge, gradually approaching the proximal edge. After each scraping cycle, the surface to be treated must be wiped dry, checked again for paint and scrubbing continues until the entire surface to be finished is covered with uniformly alternating spots of paint. Preliminary scrapping is considered successful if the spots of paint are evenly spaced on the entire surface.

The final scrapping is to undo large spots in half or into several parts of equal size and shape, and oblong ones into smaller ones in the transverse direction. The more precisely the surface needs to be prikrabilat, the thinner a layer of paint should be applied to the test plate, a narrower scraper (8 ... 10 mm), and the stroke length should not be more than 4 ... 5 mm.

The quality of scraping is determined by the number of spots per unit of the treated surface, for which there is a control frame with a square window of 25 x 25 mm, which is applied to the bonded surface and the number of spots is considered (Fig. 12.6, c). Counting the number of spots is carried out in 2 ... 4 places of the tested surface. With rough scraping, the number of spots should be at least 10, with semi-finished - 12, with fine - 15, with accurate - 20, with thin - 25.

Since scraping is the final operation of metalwork, the quality of its implementation must be monitored throughout the process. For these purposes, verification tools are intended.

Testing tools (Fig. 12.7) include: test plates for monitoring wide flat surfaces; flat test rulers (Fig. 12.7, a, b) used to control the scraping of long and relatively narrow flat surfaces; trihedral angular rulers (Fig. 12.7, c) used to control the scraping of surfaces located at an internal angle; corner plates - for quality control of scraping surfaces at right angles; as well as test rollers - to control the scraping of cylindrical surfaces and recesses. The quality control of scraping with all of these tools is based on identifying irregularities on the surface treated with scraping. Irregularities on the surface to be treated become visible after applying it to the painted test tool or, conversely, after applying the painted tool to the treated surface and moving them relative to each other.

It is very important that the test tools are kept in proper condition, therefore, after work, the test tool should be cleaned, lubricated and only then put into a case or covered with a lid.