Plumbing operation scrapping. Scraping the surface - metalwork and instrumental work. Scraping accuracy and quality control

  The geometric 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 with respect 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 = 90 ... 100 0 (Fig. 12.2, a); steel - 75 ... 90 0 (Fig. 12.2, b); soft metals - 35 ... 40 0 ​​(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 material being processed 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.

To process 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 = 60 ... 70 0.

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 to the working end as possible. Leaning on the handrail with the flat face of the scraper, 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 must 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 serves to remove burrs and irregularities on the edges, the presence of which reduces the quality of the 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, onto 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 on the block vertically. 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, with both hands, hold the scraper in a horizontal position on the bar, and, moving it along the bar, bring both cutting edges in turn. 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 lays 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 downwards (Fig. 12.6, a). Take the working position relative to the vice or the workpiece being processed as during filing and install the scraper at an angle of 30 ... 40 0 ​​to the surface to be scrapped. The working stroke when scrapping is forward movement, i.e. push. When moving backward (idle), the scraper is raised. Shabri should not bend when the casing is in a free position.

Scraping is done in several transitions: draft (preliminary), semi-finished (spot) and fine (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 scrubbing cycle, the surface to be treated must be wiped dry, checked again for paint and scrubbing continued 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 angled 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.

TO  category:

Scraping, lapping, etc.

The essence of the scraping process and scrapers

Scraper is the operation of removing (scraping) from the surfaces of parts of very thin metal particles with a special cutting tool - a scraper. The purpose of scraping is to ensure a snug fit on the mating surfaces and the tightness (impermeability) of the joint. Straight and curved surfaces are handled by scraper manually or on machines.

In one pass, a metal layer with a thickness of 0.005-0.07 mm is removed with a scraper, high precision is achieved by scraper - up to 30 load-bearing spots in a square of 25 x 25 mm, surface roughness no more than Ra 0.32.

Fig. 1. Sawing the surface with a "paint" test

Scraping is widely used in tool production as the final process for processing non-hardened surfaces.

The widespread use of scraping is explained by the special qualities of the resulting surface, which are as follows:
   - in contrast to polished or obtained by grinding with abrasives, the scraper is more wear-resistant, because it does not have abrasive grains in its pores sharpened to accelerate the wear process;
   - the scraped surface is better wetted and retains lubricants longer due to the presence of the so-called breakdown (scraping) of this surface, which also increases its wear resistance and reduces the coefficient of friction;
   - the scraped surface allows you to use the simplest and most affordable method for assessing its quality by the number of spots per unit area.

Manual scraping is a laborious process, so it is replaced with more productive machining methods on machines.

Finishing is preceded by cutting.

The surface to be scraped is cleaned and precisely treated, filed with a personal file, planed or milled. An allowance of 0.1-0.4 mm is left for scraping, depending on the width and length of the surface. With large allowances and significant irregularities, first they are sawed with a personal file with a “paint” check, while the file is pre-rubbed with chalk to eliminate slipping on the paint and greasing the notches.

The file is moved around, removing the metal from the painted places. In order to prevent the formation of deep scratches, the file is cleaned with a steel brush.

Sawing is carried out carefully, since with excessive passes the file can leave deep depressions.

After filing the painted spots, the workpiece (part) is freed from the vise and the planes on the painted calibration plate are checked a second time, then the metal layer is continued to file through the new paint spots.

Fig. 2. Flat unilateral (a) and bilateral (b) scrapers and their sharpening angles

Fig. 3. Scrapers with a curved end and their sharpening angles

The alternation of filing and testing is repeated until a smooth surface is obtained, with a large number of evenly spaced spots on the entire plane of the part (especially along the edges).

Scrapers - metal rods of various shapes with cutting edges. They make scrapers from tool carbon steel U10 and U12A. The cutting end of the scraper is quenched without tempering to a hardness of HRC e 64 - 66.

According to the shape of the cutting part, the scrapers are divided into flat, trihedral, shaped; by the number of cutting ends (faces) - on one-sided and bilateral; by design - on solid and with insert plates.

Flat scrapers are used for scraping flat surfaces - open, grooves, grooves, etc.

According to the number of cutting ends, flat scrapers can be one-sided and two-sided. Rational is the convex shape of the blade, outlined by an arc with a radius of 30 - 40 mm for semi-scraping and 40 - 55 mm for finishing.

Flat scrapers are made with straight (Fig. 307) and curved (Fig. 308) ends. Open planes are scraped with straight end scrapers; walls of grooves, grooves and adjacent planes, as well as soft metals (aluminum

niy, zinc, babbit, etc.) - scrapers with a bent end.

The length of flat double-sided scrapers is 350 - 400 mm. The width of the scraper for coarse scraping is taken from 20 to 25 mm, for the exact - 5 - 10 mm. The thickness of the end of the cutting part ranges from 2 to 4 mm. The sharpening angle of the scrapers is taken for rough scraping 70 - 75 °, for finishing - 90 °.

The double-sided flat scraper due to the presence of two cutting ends has a long service life.

Trihedral scrapers are used for scraping concave and cylindrical surfaces. Trihedral scrapers are sometimes made from old trihedral files. ,

As a rule, they are made only one-sided. Trihedral scrapers are 190, 280, 380 and 510 mm long.

To facilitate sharpening of the planes, the scraper has grooves forming cutting edges with an angle of sharpening of 60 - 75 ° for steel.

Compound scrapers are much lighter than whole scrapers of the same size. According to the shape of the cutting part, they are divided into flat, trihedral straight and trihedral curved. Such scrapers spring up during operation, and this increases the sensitivity of the hands of the scraper and helps to increase the accuracy of scraping.

Due to the smoothness and ease of penetration into the metal, the scraper with radius sharpening greatly facilitates scrapping, since it requires less effort than when scrapping with a flat scraper. For preliminary scraping, the grinding radius is 30 - 40 mm, and for the final 40 - 55 mm.

If the scraper is designed to work on white cast iron or other hard metal, then hard alloy plates, for example VK6 or T15K6, are used. The blunt plate is replaced by turning the handle (rod), since the jaw of the clamping part

Fig. 4. Three- and four-sided scrapers and their sharpening angles

Fig. 5. Compound scrapers: a - flat, b - trihedral straight line, c - trihedral curved

Fig. 6. Compound scraper with radius sharpening V. A. Alekseev

Fig. 7. Scraper with interchangeable inserts

Fig. 8. Advanced scraper

Fig. 9. Scraper with a chuck: a - scraper, b - a set of plates

Fig. 10. Disk (a), universal (b) scrapers: 1 - cutting disc, 2 - nut, 3 - holder, 4 - plate, 5 - screw, 6 - head, 7 - lock nut, 8 - shaft, 9 - textolite handle , 10 - fastening ring, 11- wooden handle

The disk scraper is used for scraping wide planes. The cutting part is a steel hardened disc, fixed to the holder with a nut. A disk with a diameter of 50-60 mm and a thickness of 3-4 mm is ground on a circular grinding machine. As it becomes dull, it is turned at a certain angle and is operated with a dull area. Thus, the entire scraper disk is used, which significantly saves time for sharpening, increases labor productivity.

Universal hex scraper has 12 cutting edges. They can work for 7 hours without regrinding, which saves working time. The scraper is easy to manufacture, versatile in operation, since all six faces can be sharpened at different angles to scrape the surfaces of hard and soft metals, cast iron, steel, aluminum, etc. In addition, it allows you to have a set of plates of different hardness made of U13A steel , P6M5, BK10. Their replacement takes a little time.

For the operation of the scraper, the plate is inserted into the groove of the head and fixed with a screw. The plate in the working position is pressed by the rod 8, which is fixed with a lock nut.

To turn the plate with the new cutting edges to the working position, you need to unscrew the lock nut one turn and turn the shaft two turns, turn the plate to the desired position, then screw the bar all the way into the plate and tighten the lock nut.

Fig. 11. Scraper rings and their sharpening

Shaped scraper is a set of replaceable hardened steel plates mounted on a rod with a handle. These scrapers are designed for scraping in hard-to-reach places - hollows, closed loops, grooves, grooves and other shaped surfaces. The end faces of the plates are sharpened in accordance with the shape of the machined surfaces.

Scraper rings are made of worn tapered roller bearings or large piston rings; these scrappers replace the trihedral and curved scraper and reduce the number of regrindings. They are sharpened on a grinding wheel and brought to an end face on a fine-grained wheel. These scrapers provide significantly greater performance than trihedral.

Ticket number 17

1. Organization of the workplace of a toolmaker

2. Scraping (definition, types of scrapers, control of scraping)

Workplace of the toolmaker

The organization of the workplace directly affects the quality and productivity of the tool-maker. This is due to the complex, responsible and diverse nature of the work he performs. He uses a large number of different in design tools, fixtures and devices. Their rational use is possible only with strict and proper organization of the workplace. At present, standard designs for the workplace of a tool-maker based on the principles of the scientific organization of labor have been developed.

The base of the workplace of the toolmaker (Fig. 1) is made up of the main and auxiliary workbenches. On the main workbench they perform dimensional processing, and on the auxiliary - assembly. To work with bulky workpieces, the workplace is equipped with a stationary control and cutting plate.

Fig. 1. The workplace of the tool-maker 1.3 - workbenches, 2 - control and marking plate

On the main workbench, a parallel vise of a rotary type, a local lighting lamp, a device for using drawings and a chair, as well as (if necessary) a table vise of various designs, used to perform precision locksmithing and processing small workpieces, are installed.

In the drawers of the workbench they store all the tools necessary for work, and the storage conditions must correspond to those required for each type of tool. Each instrument must have a fixed location. Tools should be grouped by purpose (i.e. files should be stored in one place, measuring tools in another, etc.). If there is not enough space in the drawer of the workbench for all the necessary tools, then additional devices are also used for its storage - turning tables, tabletop portable tool boxes, etc.

The work surface of the workbench should be flat and covered with sheet steel, textolite or linoleum. The height of the workbench is considered correct if the hand of a standing locksmith bent at the elbow at an angle of 90 °, with the vertical position of its shoulder part, is at the level of the jaws of a vice.

In the worktop of the workbench and on the scribing plate, only those tools and devices that are necessary to carry out this work should be placed. Tools, fixtures and workpieces should be arranged according to the principle: what is taken with the left hand should be located to the left of the worker, and what is taken with the right hand is on the right. Closer have tools and appliances that are used more often.

The workplace of a tool-maker performing accurate and responsible work must meet the highest requirements of a production culture.

SCABRING

Scraper  The operation of removing (scraping) from the surfaces of parts of very thin metal particles is called a special cutting tool - a scraper.

The purpose of scraping is to ensure a snug fit on the mating surfaces and the tightness (impermeability) of the joint. Straight and curved surfaces are handled by scraper manually or on machines.

Figure 17.1 Schematic, on the left is a surface with an oil-retaining pattern (Glenn McKechnie, September 2005)

In one working stroke, a metal layer with a thickness of 0.005 ... 0.07 mm is removed with a scraper.

As a result of scraping, processing accuracy can be ensured, characterized by such indicators: flatness and straightness reaches values ​​up to 0.002 mm / m, or up to 30 spots on an area of ​​25 X 25 mm when checking for paint and surface roughness no more than Ra0.16. It is widely used in tool manufacturing as the final process for processing non-hardened surfaces.

The widespread use of scraping is explained by the fact that the resulting surface has special qualities:

• more wear-resistant than grinding or obtained by grinding with abrasives, because it does not have remnants of abrasive grains sharpened into the pores, accelerating the wear process;
• it is better wetted and retains lubricants longer due to the presence of the so-called breakdown (scraping) of this surface, which also increases its wear resistance and reduces the coefficient of friction;
• allows you to use the simplest and most affordable method for assessing its quality by the number of spots per unit area.

Manual scraping is a time-consuming process, so it is replaced by more productive processing on machines.

Finishing is preceded by cutting. The surface to be scraped is cleaned and precisely treated, filed with a personal file, planed or milled. An allowance of 0.1 ... 0.4 mm is left for scrapping, depending on the width and length of the surface.

With large allowances and significant irregularities, the surface is first sawed with a personal file with a check for paint (Figure 17.2), the file is pre-rubbed with chalk to eliminate slipping over the paint and grease the notches.

Figure 17.2 Sawing the surface with a check for paint (Makienko NI General course of plumbing M .: Higher. Shk., 1989.)

The file is moved in a circular motion, removing metal from painted places. In order to prevent the formation of deep files, they are cleaned with a steel brush. Sawing is carried out carefully, since with excessive filing, deep depressions can remain.

After filing the painted spots, the workpiece (part) is freed from the vise and the planes on the painted calibration plate are checked a second time, then the metal layer is continued to file through the new paint spots. Sawing and checking alternate until a smooth surface is obtained with a large number of evenly spaced spots (especially along the edges).

Figure 17.3 Detail prepared for scraping (http://www.bs-wiki.de/mediawiki/index.php?title=Schaben)

Scrapers - metal rods of various shapes with cutting edges. They are made of tool carbon steels. The cutting end of the scraper is quenched without tempering to a hardness of HRC 64 ... 66.

According to the shape of the cutting part, the scrapers are divided into flat, trihedral, shaped; by the number of cutting ends (faces) - on one-sided and bilateral; by design - on solid and with insert plates.

Figure 17.4 Manual scrapers (http://www.bs-wiki.de/mediawiki/index.php?title=Schaben)

Types of scrapers

Surfaces scrape with 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.

Flat scraper

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

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

Surface painting. Paint is applied to the surface of the plate with a swab of clean linen rags folded in several layers. It is convenient to stain a bag made of a clean canvas (canvas), in which the paint is applied (in no case should you put dry paint in the bag and dip it in oil).

Figure 17.5 Surface painting (http://www.bs-wiki.de/mediawiki/index.php?title=Schaben)

To obtain a high-quality surface, draft, semi-finishing and finishing scraping are performed sequentially.

Rough scraping  (preliminary) consists in rough surface treatment - wide traces remove traces and risks of previous processing. At first, due to insufficiently thorough preparation of the surface, individual, most prominent places will be densely colored and large spots will form on them. In this case, a “breakdown” of large spots is made: they remove the metal from the strong colored spots. After each coloring, the direction of movement of the scraper is changed. The scraper captures the entire spot, otherwise burrs will form on the surface. When the spots are evenly spaced, the breakdown is completed and begin to increase the number of spots, scrubbing all the painted spots, including slightly colored ones. Having received four to six spots in a square of 25X25 mm, the preliminary scrapping is completed.

Figure 17.6 First Scraper Pass

Figure 17.7 Rough scraping. stroke length over 20 mm.

Figure 17.8 Rough scraping began to "baptize" the first pass

The work is performed with a scraper 20 ... 30 mm wide with a stroke length of 10 ... 15 mm. The direction of the scraper is continuously changed so that the subsequent stroke is located at an angle of 90 ° to the previous one.

In one stroke of the scraper, a layer with a thickness of 0.02 ... 0.05 mm is removed. Scrabber until visible risks disappear. The quality of the scraping is checked for paint, which is applied to the calibration plate. After applying and moving the slab (or part), the protruding protruding spots will again scrape.

Semi-finished(point) scraping  consists in removing only gray ones, i.e. most prominent spots identified by a paint test. The work is performed with a flat narrow (12 ... 15 mm) scraper with a stroke length of 5 ... 10 mm; in one stroke of the scraper, a layer with a thickness of 0.01, .. 0.02 mm is removed.

Clean(finishing) scraping  used to obtain very high surface accuracy. With light pressure on the scraper, a thin (8 ... 10 μm) layer is removed. Apply scrapers with a width of 5 ... 10 mm with a stroke length of 4 ... 5 mm (small strokes).

Decorative scraping  carried out as follows. On the treated surface with a scraper, strokes are applied that form one or another pattern on the surface. The most commonly used chess pattern is when rhombuses with different strokes are formed on the surface. It is performed in two steps: first, strokes are applied in a checkerboard pattern in one direction, then, in between, strokes in the opposite direction. "Frost" is induced on working and non-working surfaces. By creating strokes on the surface in a certain direction, decorative scrapping at the same time improves the conditions for its lubrication, since lubrication is better retained in the resulting strokes due to surface tension.

By the disappearance of strokes, wear is judged (with wear greater than 3 μm, the pattern disappears).

PRECISION ACCURACY AND QUALITY CONTROL

Preparing for scraping.Before scrapping, the surfaces are cleaned, and if necessary, they are washed, wiped and then a special paint is applied to them. This paint is a mixture of machine oil and azure powder, less commonly ultramarine (blue) or samecarbon black mixed in a mixture of autol with kerosene.

Scraper  - this is a locksmith operation in which the smallest shavings are removed (scraped off) from the surface of the product with a cutting tool - a 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 What is called scraping? What is scrapery used for? What parts and parts of machines will scrape? Types of scrapers Surfaces scrape with 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 What are the types of scrapers? Why use flat scrapers? Why use trihedral scraper?   "Plumbing", I.G. Spiridonov,   G.P. Bufetov, V.G. Kopelevich In the process, the scrapers are dull; therefore they are sharpened 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 this, the scraper is adjusted. When sharpening, press the scraper firmly. Sharpening should be carried out with ... Scraperthe operation of removing (scraping) from the surfaces of parts of very thin metal particles is called a special cutting tool - a scraper. The purpose of scraping is to ensure a snug fit on the mating surfaces and the tightness (impermeability) of the joint. Straight and curved surfaces are processed by scraper, manually or on machines. In one pass, a metal layer with a thickness of 0.005-0.07 mm is removed with a scraper, high precision is achieved by scraper - up to 30 load-bearing spots in a square of 25 × 25 mm, surface roughness is not more than Ra 0.32. Scraping is widely used in tool production as the final process for processing non-hardened surfaces. The widespread use of scraping is explained by the special qualities of the resulting surface, which are as follows: unlike polished or obtained by grinding with abrasives, scraper is more wear-resistant, because it does not have abrasive grains that are sharpened in its pores and accelerate the wear process; the scraper surface is better wetted and retains lubricants longer due to the presence of the so-called breakdown (scraping) of this surface, which also increases its wear resistance and reduces the coefficient of friction; the scraped surface allows you to use the simplest and most affordable method for assessing its quality by the number of spots per unit area. Manual scraping is a laborious process, so it is replaced with more productive machining methods on machines. Finishing is preceded by cutting. The surface to be scraped is cleaned and precisely treated, filed with a personal file, planed or milled. An allowance of 0.1-0.4 mm is left for scraping, depending on the width and length of the surface. With large allowances and significant irregularities, first they are sawed with a personal file with a check for "paint" (Fig. 306). In this case, the file is pre-rubbed with chalk to eliminate slipping on the paint and greasing the notches. The file is moved around, removing the metal from the painted places. In order to prevent the formation of deep scratches, the file is cleaned with a steel brush. Sawing is carried out carefully, since with excessive passes the file can leave deep depressions. After filing colored spots, the workpiece (part) is freed from the vise and the planes are checked for the second time on the painted calibration plate, then the metal layer is continued to file through the new spots of paint. The alternation of filing and testing is repeated until a smooth surface with a large number of evenly spaced spots on the entire plane of the part (especially along the edges) is obtained. Scrapers- metal rods of various shapes with cutting edges. They make scrapers from tool carbon steel U10 and U12A. The cutting end of the scraper is quenched without tempering to a hardness of HRC 56 - 64. According to the shape of the cutting part, the scrapers are divided into flat, trihedral, shaped; by the number of cutting ends (faces) on one-sided and bilateral; by design - on solid and with insert plates. Fig. 306. Sawing the surface with a check "on the paint" Flat scrapers are used for scraping flat surfaces - open, grooves, grooves, etc. By the number of cutting ends, flat scrapers can be one-sided (Fig. 307, a) and bilateral (Fig. 307, 6). Rational is the convex shape of the blade, outlined by an arc with a radius of 30 - 40 mm for receiving true scraping and 40 - 55 mm for finishing. Flat scrapers are made with straight (Fig. 307) and curved (Fig. 308) ends. Open planes are scraped with straight end scrapers; walls of grooves, grooves and adjacent planes, as well as soft metals (aluminum, zinc, babbit, etc.) - with scrapers with a bent end. The length of flat double-sided scrapers is 350 - 400 mm. The width of the scraper for coarse scraping is taken from 20 to 25 mm, for the exact - 5 - 10 mm. The thickness of the end of the cutting part ranges from 2 to 4 mm. The sharpening angle of the scrapers (Fig. 307, 308, 309) is taken for rough scraping 70 - 75 °, for finishing - 90 °. A two-sided flat scraper (Fig. 307, b) due to the presence of two cutting ends has a long service life. Trihedral scrapers (Fig. 309) are used for scraping concave and cylindrical surfaces. Trihedral scrapers are sometimes made from old trihedral files. As a rule, they are made only one-sided. Trihedral scrapers are 190, 280, 380 and 510 mm long. To facilitate sharpening of the planes, the scraper has grooves forming cutting edges with an angle of sharpening of 60 - 75 ° for steel. Compound scrapers are much lighter than whole scrapers of the same size. According to the shape of the cutting part, they are divided into flat, trihedral straight and trihedral curved (Fig. 310, a, b, c). Such scrapers spring up during operation, and this increases the sensitivity of the hands of the scraper and helps to increase the accuracy of scraping. Due to the smoothness and ease of penetration into the metal, a scraper with radius sharpening (Fig. 311) greatly facilitates scrapping, since it requires less effort than when scrapping with a flat scraper. For preliminary scraping, the grinding radius is 30 - 40 mm, and for the final 40 - 55 mm. In fig. 312 shows a universal scraper with interchangeable cutting inserts. It consists of a housing 3, a holder 2, a handle 5, a clamping screw 4, a replaceable cutting insert 7 made of high speed steel or hard alloy. The plate inserted into the holder is clamped by a screw while rotating the handle (handle) of the scraper clockwise (to remove the plate, the handle is rotated counterclockwise). An advanced scraper consists of three parts: a holder, a wooden handle and a removable plate (Fig. 313). A replaceable plate with a dovetail shank is inserted into the groove of the holder, this ensures its reliable fastening. In fig. 314 shows the most advanced scraper, consisting of a removable plate 7, a chuck 2 and a rod 3. The plates 4 of such scraper are made 3 × 16 × 50 mm in size from U12A steel, and the rod is made from steel 45. If the scraper is designed to work on white cast iron or other hard metal, then hard alloy plates, for example VK6 or T15K6, are used. The blunt plate is replaced by the handle (rod), since the jaw of the clamping part of the cartridge is pivotally connected to the housing. This design of the scraper allows the use of a set of plates sharpened at different angles. Disk scraper (Fig. 315) is used for scrapping wide planes. The cutting part 7 is a steel hardened disk, fixed on the holder 3 with a nut 2. The disk with a diameter of 50-60 mm, a thickness of 3-4 mm is sharpened on a circular grinding machine. As it becomes dull, it is rotated by a certain angle and is operated by a non-dull area. Thus, the entire scraper disk is used, which significantly saves time for sharpening, increases labor productivity. a shaped scraper (Fig. 316) is a set of replaceable hardened steel plates 7 mounted on a rod 2 with a handle 3. These scraper are designed for scraping in hard-to-reach places - hollows, closed loops, grooves, grooves and other shaped surfaces. The end faces of the plates are sharpened in accordance with the shape of the machined surfaces. Scraper rings are made of worn tapered roller bearings or large piston rings; these scrappers replace the trihedral and curved scraper and reduce the number of regrindings. They are sharpened on grinding wheel 7 (Fig. 317) and brought to an end face on a fine-grained wheel 2. These scrapers provide significantly greater productivity than trihedral ones.	Theme 12 Patterning The student must: know: Purpose and purpose of scraping; Varieties of scrapers; Differences in roughing and finishing scraping; Safety regulations for scraping. be able to: Perform scraping with various methods of rectilinear and curved surfaces. Workplace and site equipment:  crafting table; 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 ПП 25А 16 В СМ1 6 К3 А (for sharpening steel scrapers) and software 63С 16 В СМ1 К3 А (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 called fitting finishing operation, used to align and fit flat and curved (usually cylindrical) surfaces to obtain 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 ground or obtained by abrasive grinding, is more wear-resistant, since it does not have abrasive grains sharpened in its pores (risks, scratches), accelerating the wear process 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. Scraping makes it possible to obtain a surface with a 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 straight-edge scraper 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 cutting scraper.
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

	Fig. 90. Techniques for examining and checking the surface before scraping.

The paint is crushed so that no grains are felt between the fingers. Then it is poured into a jar (metal or glass) and oil is poured there. The amount of engine oil in the mixture should be such that the paint has a paste consistency, but not liquid, since the excess oil will spread over the control plate and the surface to be tested will be covered with paint when it is placed on the plate.

Paint is used in the scraping process to control surface quality. A thin uniform layer of paint is applied to the calibration plate with a tampon (Fig. 90, a) made from a clean rag.

Accuracy of scraping. After checking with a calibration plate or a ruler of a surface to be attached, separate colored spots and dots remain on its protruding places. The quantity, size and distribution of such spots judge the quality of scraping. The check is carried out with two to three circular motions of the part to be finished on the plate (Fig. 90, b)

On well-treated surfaces, the paint lays evenly over the entire surface. With poor-quality processing on the surface, only a few large spots appear (Fig. 90, at)

The accuracy of the scraping is determined by the number of colored spots (dots) per

per unit surface. As a unit of surface take a square measuring 25X25 mm. The more such points and the more evenly spaced, the higher the quality of scraping andmore precisely the surface.

Quality control of scraping.For aboutverification of the quality of scraping is used

special inspection frame (Fig. 91). It is laid on the surface and the number of paint points in the frame window is counted. Finally, their number is determined as the arithmetic average of measurements in several places of the surface being checked (Table 114).
	Fig. 91. Quality control of scraping with a check frame.
	When calculating the number of spots on the pinholes or bearing shells, you can use a celluloid pattern bent along the radius of the liner. A grid with 25X25 mm squares is applied to the template using
	Table114

TEST RULES AND PLATES

Verification plates, rulers * angular rulers and prisms are used to check the straightness, flatness and relative position of the scuffed surfaces, and rulers of the appropriate size and shape are used to check cylindrical and conical holes (Table 115).

Often, to check the quality of surface scraping, the surfaces of the parts to which they are attached are used.

 

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