Scraping and grinding in plumbing. Metal scraper - ultra-fine workpiece alignment. Used tools and machines

Scraping is a metalwork finishing operation used to level and fit flat and curved (usually cylindrical) surfaces to get a snug fit. Cutting is preceded by cutting, for example filing, grinding, planing, milling, etc.

When scraping, the metal is cut off from the areas in contact with the sample on the scraping paint with the surface to which this part fits. Gradually, these areas become smaller (“broken up”) until a “net” is obtained, that is, a sufficient number of contact spots. Details are attached to each other, on standard or calibration plates.

Gauge paint is applied to the plate with a swab in an even thin layer. The workpiece is gently lowered onto the plate and slowly moved over the entire surface of the plate in a circular motion in different directions. Then the workpiece is carefully removed. Heavy workpieces

ki are treated on site by applying a test plate with paint on their surface. On pre-prepared surfaces, the paint lays evenly, on poorly prepared surfaces - unevenly. So, on a surface prepared for scrapping, white spots indicate the most deepened places (no paint), dark spots - less deepened (paint accumulation), gray spots - the most prominent (thin layer of paint).

The scraping process consists in the gradual removal of metal from the painted areas (gray spots). During operation, the scraper is held with the right hand, and the palm of the left hand covers the tool in the middle, holding four fingers down. Set it at an angle of 30 ° to the surface to be clad. The working move during scrapping is moving forward, that is, away from you. When moving backward (idle), the scraper is raised. Shabri should be in the free position of the body, not bending. Scraping includes several transitions: draft (preliminary), semi-finished (spot) and finishing (finishing). In special cases, precise and delicate scraping is performed.

At the beginning of scraping, the length of the tool stroke should be 15 .., 20 mm, and then, as the surface levels, it is reduced to 2 ... 5 mm. Each time, the direction of the stroke must be changed so that the resulting strokes intersect at an angle of 45 ... 60 °. The scattering of a flat surface starts from the farthest edge, gradually approaching the proximal edge. After each cycle of scraping, the surface to be cleaned is wiped dry, checked again for paint and scrubbing is continued until the entire surface to be finished is covered with uniformly alternating spots of paint.

The final scrapping consists in rasprabivanii round spots in half or several parts of equal size and shape, and oblong - into smaller in the transverse direction. The more precisely the surface needs to be finished, the thinner the paint layer to be applied to the test plate.

In this case, use a narrow scraper (8 ... 10 mm), the length of its working stroke is not more than 4 ... 5 mm.

The quality of scraping is determined by the number of spots per unit of the treated surface, for which the control frame with a square window measuring 25X25 mm is used. It is applied to the gouged surface and the number of spots is counted. Counting the number of spots is carried out in 2 ... 4 places of the tested surface.

By scrapering it is possible to obtain flatness and straightness of the surface with an accuracy of 0.002 mm over a length of 1000 mm (30 spots on an area of \u200b\u200b25X25 mm2). Scraping is considered thin when the number of spots on an area of \u200b\u200b25X25 mm is more than 22 (/? A \u003d 0.08 μm), accurate - at 10 ... 14 (^ a \u003d 0.63 μm), fine - at 6 ... 10 ( Ra- \u003d 1.25 μm) and coarse - at 5 ... 6

Up to 5 IX ... X Fixed work surfaces (abutment, butt, base) machines of low accuracy and machines operating under light loads

Scrap allowances Set depending on the size of the machined surfaces. For a plane measuring 500X500 mm, the average allowance is 0.2 mm; for the plane 500X600 mm - 0.5 mm. For holes with a diameter of up to 80 mm with a length of 200 ... 300 mm, the allowance for scraping is 0.1 mm.

Scraping 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 resulting surface. Unlike "polished or obtained abrasive lapping, the scraper surface is more wear-resistant, since it does not have inclusions of abrasive grain residues that accelerate the wear process; it is better lubricated and retains lubricants longer due to the presence of so-called breakdown into spots (alternation of protruding and deepened places); allows you to use the simplest and most affordable way to assess its quality - by the number of spots per unit area. By scrubbing you can get a surface with a low roughness (0.003 ... 0.01 mm), so As in one pass, a metal layer with a thickness of 0.005 ... 0.07 mm is removed with a scraper for finishing and more than 0.01, .. 0.03 mm for preliminary processing.

Hand scraping is a time-consuming operation. Mechanized devices for scrapping, for example, an electric scraper machine, greatly facilitate labor and reduce processing time by 4 ... 6 times. There are also special gauge machines. However, the use of mechanizing devices when scrapping is not always possible (for example, scrapping in semi-closed cavities of small sizes), in addition, when using such devices in some cases it is difficult to obtain high precision processing due to insufficient accuracy in determining the pressure on the scraper.

Scrapers - metal rods of various shapes with cutting edges. They are made of carbon tool steel of grades U10 ... U13, hardened to a hardness of HRCq 56 ... 64. Sometimes scrapers are equipped with high speed steel or carbide inserts. 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; by design - on solid and with insert plates. Shape and Geometry

the scraper cutting edge parameters are selected depending on the shape and size of the surface and the properties of the material being processed. So, for scraping flat surfaces, flat scrapers with a straight or radius cutting edge are used; for curved and internal (concave) surfaces - trihedral and shaped scrapers. Scraper with a straight cutting edge is convenient to use when processing the edges of the workpiece,

since it does not slip off its surface. When scraping the rest of the workpiece, a straight cutter scraper

the edge is less suitable, yy // 7 /////////// as the lateral edges of the blade can leave deep scratches on the surface. In this case, scrapers with radius (arcuate) cutting edges should be used.

The geometric parameters of the scrapers depend on the type of processing, the material of the workpiece 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 sharpening

90 ... 100 ° in relation to the axis of the tool. In rough processing, the angle of sharpening is equal to 75, .. 90 °, when finishing - 90 °, and when especially clean - 90 ... 100 °. Depending on the material being processed, "the angle of sharpening of a flat scraper should be as follows; when machining cast iron and bronze - 90 ... 100 ° (2.30, a), steel - 75 ... 90 ° (2.30, 6), soft metals -35 ... 40 °

The choice of the length of the cutting edge and the radius of its rounding 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 preliminary (rough) scraping, a scraper with a blade 20 ... 30 mm long is required, for the exact - 15 ... 20 mm, for the most accurate - 5 ... 12 mm. For the final (finishing) scraping, the radius of the cutting blade is chosen larger than for the rough, since in this case the deviation from the flatness of the surface will be the smallest. For processing curved concave surfaces using trihedral scraper, on the sides of which are cut longitudinal grooves to facilitate sharpening. The point angle of the trihedral scraper is 60 ... 70 °.

Sharpening of scrapers is carried out on a grinding machine using cooling. For scrapers made of tool steels, fine-grained electrocorundum grinding wheels (ГШ 25А 16 П СМ2 7 К5 А) are used, and for scrapers with carbide inserts, grinding wheels made of green silicon carbide (PP 63С 16П СМ2 7 К5 А) are used. Sharpening order: 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 on the handrail with the flat face of the scraper, the end end is smoothly brought to the grinding wheel. The scraper is installed horizontally or with a slope that provides the desired angle of sharpening. In this case, its axis must coincide with the center of the circle. When sharpening, the scraper is slightly swayed by the shank in a horizontal plane, maintaining the required radius of curvature of the cutting edge

Sharpening 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 parallel faces to each other.

Finishing (dressing) of the cutting edges of the scraper after sharpening is necessary to remove burrs and irregularities on the edges. It is produced on grinding (abrasive) whetstones (donkeys) with grain size M14 and finer, having previously lubricated its surface with a thin layer of machine oil. Instead of a grinding bar for refueling the scraper, you can use a flat cast-iron tile, the surface of which is coated with paste made of abrasive micropowder M28 ... M20 in machine oil. When refining, the block is placed on a wooden fixed lining, and the scraper with the end part is installed vertically on it. With two fingers of the left hand, the scraper is held by the handle, gently pressing it to the bar, and with the right hand hesitate

with precise movements, the end face of the scraper is moved along the bar along the cutting edge. Then the lateral wide surfaces are brought up, for which the scraper is held with both hands in a horizontal position on the bar, simultaneously processing both cutting edges. 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.

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 of 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 \u200b\u200bup to 0.002 mm / m, or up to 30 spots on an area of \u200b\u200b25 X 25 mm when checking for paint and surface roughness of not more than Rbut0.16. 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\u003dSchaben)

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\u003dSchaben)

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\u003dSchaben)

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 of thickness 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 of thickness 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).

  Scraping techniques

TO  category:

Scraping, lapping, etc.

Scraping techniques

Before scrapping, the surfaces are cleaned, washed, wiped, and then paint is applied to them.

Paints for scraping. After cleaning the workpiece before scrapping, unevenness is revealed by painting the surfaces with paint. Pattern paint is a mixture of machine oil with azure and less often with minium and ultramarine (blue), which, unlike azure, do not mix well with oil and are not clearly visible on the details. Azure can be replaced with soot mixed in a mixture of autol with kerosene. The paint is crushed so that no grains are felt between the fingers. Then paint 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 applied to the plate.

Fig. 1. Sharpening angles of scrapers for processing: a - cast iron and bronze, b - steel, c - soft metals

Fig. 2. Sharpening of flat scrapers: a - end face, b - side surface; s - clearance not more than 3 mm

Fig. 3. Finishing (dressing) of the scraper on the bar: a - end surface, b - lateral

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 apply the paint also with a bag made of a clean canvas (canvas) into which the paint is applied.

The bag and tampons in the pauses between staining are placed in a clean glass dish or a tin jar. In no case should you put dry paint in a bag and dip it in oil.

Before painting, the chips and dirt are removed from the surface of the part with a hair brush or a clean rag, the part is carefully placed on the surface of the plate with the machined surface and slowly moved. To achieve uniform wear of the plate, it is necessary to use its entire surface.

After two or three circular motions along the plate (Fig. 4, b), the part is carefully removed.

Fig. 4. Painting of flat surfaces during scraping: a - painting the plate with a swab, b - moving the part along the plate, c - part after painting, d - moving the plate over the part

Fig. 5. Techniques for scraping flat parts :. a - “from myself”, b - “from myself”

On well-treated surfaces, the paint lays evenly over the entire surface, on poorly prepared surfaces - unevenly. In small depressions, the paint will accumulate, and in places deeper it will not be at all. So there are white spots - the most deep places that are not covered with paint; dark spots - less deepened, paint has accumulated in them; gray spots are the most prominent, on them the paint lies in a thin layer.

When determining irregularities on the surfaces of heavy parts that cannot be removed from the spot, the painted calibration tool - a plate or a ruler - is moved along controlled surfaces.

Light parts (products) when scrapping are installed on a bench, and large and heavy ones are set on goats.

The process of scraping consists in the gradual removal of metal from the painted areas (gray spots). The scraper is held with a straight hand by the handle, and the left click on the end of the scraper. In relation to the treated surface, the scraper is set at an angle of 25 - 30 °, and the cutting edge should be on the painted surface. Metal is removed by scraping. The working move when scrapping is moving forward, that is, “away from you”, and when working with a flat scraper with the end bent down, moving backward, that is, “towards yourself”. When moving backward (idle), the scraper is raised.

The part prepared for scrapping in most cases is fixed in a vice; medium-weight parts are often scraped directly on workbenches without additional fastening or installed in fixtures, and the surfaces of heavy and bulky parts are scraped in place.

As a rule, scraping is performed in three transitions.

The first transition - rough scraping - begins with the removal of traces of the tool after machining on the protruding parts of the surface, detected during control. The work is performed by a scraper with a wide cutting blade (the width of the scraper should not exceed 20-25 mm), as otherwise the locksmith quickly gets tired and its productivity decreases. The length of the working stroke of the scraper is 15-20 mm; the thickness of the chips removed in one pass, 0.01-0.03 mm Draft scraping is considered complete when the entire surface to be priprivodimy when applied to it is covered with large spots - up to four spots of paint on an area of \u200b\u200b25X25 mm2.

For the second transition - semi-finished - more precise scraping is performed. The surface is treated with a scraper with a width of not more than 12-15 mm with a working stroke of 7-12 mm. The thickness of the removed chips does not exceed 0.005-0.01 mm. After this transition, the number of spots on the surface to be primed should be from 8 to 16 on an area of \u200b\u200b25 × 25 mm2.

The third transition - fine - is used in the final surface treatment. Scraper width from 5 to 12 mm; scrapping is carried out with a small stroke (the length of the working stroke of the scraper is 3-5 mm). After the third transition, the surface to be attached should have a square of 25 × 25 mm2 from 20 to 25 spots. To obtain greater surface cleanliness follows the opposite. During the course, raise the scraper slightly.

During scrapping (each time after removal of paint-covered spots by the scraper), the surface of the part is cleaned with a brush and thoroughly wiped with a dry cloth. The part with the added surface is again applied to the painted calibration plate, the formed spots are removed and scrapped again. This is continued until the number of spots on the surface to be primed reaches the established norm.

Scraping planes. When scraping the plane, the scraper, held by the handle with the right hand, is set at an angle of 20-30 ° to the surface to be attached; with your left hand, press the end of the scraper near the cutting edge and move it forward (working stroke) and back (idle).

At the beginning of the scraping process, they begin the so-called breakdown of large spots. Reception is carried out by strong movements of the scraper, scraping the chips from the painted places. The surface is cleaned of chips and again checked for paint, after which the process of scraping is repeated. When the spots are evenly spaced on the surface, the breakdown is completed and the number of spots is increased, scraping all the painted spots that appear after checking on a plate or ruler. Obviously, each subsequent removal of the chips will reduce the height of the bumps, which will be divided into slightly lower protrusions; their total number will increase. At the same time, the direction of the working stroke of the scraper changes each time, so that the traces of the scraper from the previous passage intersect with the traces of the subsequent scraping at an angle of about 45-90 °, and the areas formed by the strokes look like rhombuses or squares.

Fig. 1. Methods of scraping: a - position of the hands when scraping the plane; b - type of strokes on the surface to be attached; c - the position of the hands when scraping by the method of "on yourself"

To give the surface to be trimmed a decorative look, sometimes the so-called "frost" of various shapes is applied to it - symmetrically arranged cells or strips.

The fitter-innovator of the Leningrad plant of automatic machines A. A. Baryshnikov has developed a fundamentally new method of manual scrapping, in which the working movement of the scraper is made "on yourself". The scraper is taken by the middle part (rod) with both hands in the girth and set with a blade to the surface to be machined at an angle of 65-75 °, and not 20-30 °, as when scraping "on your own"; the upper part of the scraper, ending with a wooden handle, abuts against the shoulder of the worker. The scraper in this case is like a lever of the second kind with the center of rotation at the point of contact of the scraper with the shoulder of the worker. With this method of scraping, the quality of the processed surface is significantly improved, since the possibility of "crushing", which is often observed when scraping "from oneself", is completely excluded. This is due to the fact that due to the increased length (up to 450-550 mm), the scraper springs “onto itself” during springing, due to which its blade smoothly cuts into metal and also smoothly leaves the cutting zone. When scrapping "on your own", the scraper usually cuts into the metal during the working stroke and there are burrs at the end of each stroke, which then have to be removed with additional attachment.

As the experience of the innovator A. A. Baryshnikov and his followers has shown, labor productivity when finishing scraping “for oneself” as compared to scraping “for oneself” doubles.

Scraping planes using the three-plate method. The essence of this method lies in the fact that one of the plates (plane) of this set (for example, I) is taken as the main one and two others are attached on it - II and III. These two plates are attached to one another. Next, the plates are alternately again added to the main plate I and then alternately between themselves. Test plates, full-length and side brackets, etc. are usually scraped with a set of three pieces, moreover, each plate (square) is checked against two other plates (squares). After each similar fit, the plates are more accurate. The scrapping of each plate ends when 20-25 spots on an area of \u200b\u200b25 × 25 mm2 are obtained on the planed surfaces.

If, for example, you need to attach three test plates, then first the prepared plates will be scraped up to an accuracy of 0.03 mm with a check of their straightness on the calibration plate, ruler and probe, and then the plates will be numbered and they will be scraped according to the three-plate method.

The work is carried out in the following sequence:
  1) they alternate plates II and III on plate I;
  2) add plates II and III one after another;
  3) add plates I and III on plate II;
  4) they add plates I and III one by one;
  5) add plates I and II on plate III;
  6) they add plates I and II one by one. Scraping planes located at sharp angles. An example of such processing is the swallowing of dovetail guides. In this case, scrapers are used, the cutting part of which has some curvature and a special sharpening.

Fig. 2. The sequence of scraping planes according to the method of three plates

For the correct processing of the guides, you need to have a trihedral ruler, as well as a carriage (slider) with a well-pinned bottom base. Using the carriage, the extreme horizontal guiding planes are scrapped. They are brightened up on the lower base of the carriage, on which the paint is applied. Then the inclined guides will be scraped along the trihedral ruler.

The scribing of planes conjugated at sharp or obtuse angles can be done using calibration prisms. In this case, the check of the surface to be painted on for the paint is carried out by the bevel of a prism mounted on the plate.

Dovetail guides are checked for so-called wedging. Reception is carried out using rollers and vernier calipers. The parallelism of the rollers is checked with a caliper. ‘The lack of parallelism gives reason to believe that the guides are not processed correctly. The first check for wedging should be done during the preparation of the guides for scraping. If there are significant deviations from parallelism, they are sawn under the ruler with a check on the rollers.

Fig. 3. Scraping of the planes forming the angles: o-using the carriage: b-along a trihedral ruler; prism

Scraping curved surfaces. The group of parts with curved surfaces that the locksmith often has to scrape include bearing shells, bushings, sleeves, etc. They will be scrapped with a trihedral scraper, and checked on the shaft. Initially, the test shaft is coated with a thin and uniform layer of paint and laid on the lower bearing shell. Then, the upper liner is applied to this shaft and the bearing cover is tightened uniformly from angle to angle with the help of nuts so that the shaft can be rotated to the right and left by 2-3 turns with some effort. After that, the bearing is disassembled and scrapped painted places at the beginning of the lower and then the upper liner, moving the scraper around the circumference of the liner.

In the process of scraping, the trihedral scraper should be tilted to the surface at such an angle that the middle part of its cutting edge removes the chips. The resulting strokes from the scraper on the surface of the part should be in the form of a quadrangle or rhombus. Depending on the configuration and position of the insert, the working movement of the scraper can be directed to the right and left sides. The cutting angle 6 \u003d a + p for coarse scraping with a trihedral scraper is usually 70-75 °, and for finishing - about 120 °. An increase in the cutting angle during finishing allows you to remove very thin chips.

Fig. 4. Techniques for scraping bearing shells (a, b); special scraper rings for scraping bearing shells (h, d, e, e)

When processing bearing shells, scrapping with periodic painting of the surface of the shell along the turning shaft is carried out until the surface to be primed is uniformly covered with spots of paint on an area of \u200b\u200bat least 3/4 of the surface of the shell.

To accelerate the scrapping of bearings by reducing the number of regrindings and finishing of scrapers in

in some cases, instead of the usual trihedral or curved scrapers, special ring scrapers are used.

The scraper ring is made of a worn conical roller bearing housing by sharpening it on a conventional grinder. After sharpening, the end face of the scraper is brought on a fine-grained circle.

The layout of the scraper ring in the bearing bore during scrapping is shown in Fig. 4, e. The skillful use of such scrapers significantly increases labor productivity when machining cylindrical holes.

Precise scraping techniques. Some parts of measuring machines, instruments and tools need to be scraped with very high accuracy. Finishing the surfaces of such parts with conventional scraping techniques in some cases does not satisfy the technical conditions, often the process of precise scraping is associated with a significant investment of time. To achieve high performance with accurate scrapping and to improve the quality of this work, they use pastes developed by the State Optical Institute (GOI pastes).

Scraping using GOI pastes should be performed in this order. After one or two passes with a scraper for the part, the diluted rough paste is applied to the calibration plate. On this plate, the surface to be primed is rubbed until the paste loses its green color and becomes the color of the black waste mass. Having wiped the grinding surfaces of the plate and the parts with a clean rag, paste again on the plate; grinding is repeated 3-4 times. After that, they wipe the surface of the part clean, break wide brilliant spots with a scraper and grind it again with a paste until a surface that meets the technical specifications is obtained.

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.

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?

Under 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 upper part of the parts using a scraper. Recommended operation 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 the smaller radius and 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 when 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 Flattening of 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 (scraping 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 circular motions. Subsequently, the master first aligns the most prominent colored areas, and then little colored.

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 evenly 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, monocorundum, 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 lubricant 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 package, and then processed at the same time.