The cutting is called the locksmith operation, in which with the help of a cutting tool (chisel, crossbody), the excess metal layers are removed from the workpiece or they are cut into pieces. Cutting is performed in cases when it is difficult or irrational to machine workpieces on metal-cutting machines or when high precision machining is not required.
Instruments. Chisel(Fig. 17, a) is made of carbon tool steel U7A. The cutting part of the chisel has the shape of a wedge (Fig. 17, c), which is ground at a certain angle. The angle of tapering (sharpening) of the chisel is chosen depending on the hardness of the material being processed: the harder the material, the greater the angle.
Apply the following sharpening angles (in degrees):
for cutting iron and bronze 70
for cutting steel 60
for chopping brass and copper 45
for cutting aluminum and zinc 35
Chisels are the length of 100, 125, 150, 175, 200 mm. The cutting part of the chisel is hardened to Rockwell hardness HRC 53-56, and the tail - to hardness HRC 30-35.
Fig. 17 Metal Cutting Tools:
a - chisel, b - kretsmeysel, in - the angles of the cutting tool
Kreuzmeisel(fig. 17, b) is intended for cutting out narrow grooves and keyways. It differs from a chisel in a narrower cutting part. The angles of sharpening are exactly the same as those of a chisel.
Sharpen chisels and crossbuttons with an ordinary grinding wheel on sharpening machines. For sharpening, a chisel or crossbutton is mounted on handpiece 1, as shown in fig. 18, and with slight pressure, slowly move across the entire width of the circle.
Fig. 18. :
1 - handkerchief, 2 - protective screen, 3 - sharpener casing
In this case, it is necessary to avoid strong pressure on the chisel, as this will lead to heating and tempering, as a result of which the cutting part of the chisel will lose its hardness. Sharpen best with cooling.
Hammers designed for strikes when performing most plumbing operations (logging, riveting, straightening, bending, chasing, assembling, etc.).
In the middle part of the hammer there is an oval-shaped hole with a double conical extension for fastening the handle. The length of the handle should be 200-260 mm for small hammers, 270-350 mm for medium, and 380-400 mm for heavy hammers. The mass of hammers, depending on the nature of the work performed, is different: 50, 100, 150, 200, 300 g (light hammers for tool and marking works); from 300 to 500 g (medium hammers) and from 500 to 800 g (heavy hammers for repair and other works). Wooden hammers with fiber, copper and rubber tips are used for installation and assembly work.
A chisel, a skull-meissel and a groove (Fig. 35) serve as a cutting tool for cutting metals. Chisels for cutting hot metal called blacksmiths, and for cutting cold metal - metalwork.
The chisel plumbing consists of three parts: working, middle and impact.
During the machining process, the required shape of the part is achieved due to the cutting edge of the tool breaking the connection between the metal grains and removing excess metal in the form of chips. At the same time the cutting part is shaped into a wedge. The chisel is the simplest cutting tool in which the wedge is particularly pronounced (Fig. 36).
The action of the wedge-shaped tool on the treated metal varies depending on the position of the wedge and on the direction of the force applied to its base.
There are two main types of wedge work:
1) the axis of the wedge and the direction of the force applied to its base,
Fig. 36. Diagram of the cutting process when working chisel: a - the distribution of forces on the wedge; b - the effect of the sharpening angle on the cutting process; in - the process of formation of chips when chopping and the geometry of the chisel
Perpendicular to the surface of the workpiece (Fig. 36, a). In this case, the workpiece is cut (cracked) (Fig. 36, b)
2) the axis of the wedge and the direction of the force applied to its base form an angle less than 90 ° with the surface of the workpiece. In this case, chips are removed from the workpiece (Fig. 36, c).
The shape of the cutting part (fig. 36, c) and the angles of its sharpening determine the geometry of the cutting tool (chisel).
On the workpiece, the following surfaces are distinguished: machined, machined, and also the cutting surface.
The surface to be treated is the surface from which the material layer (chips) will be removed.
The treated surface is the surface from which the metal layer (chips) has been removed.
The face on which the chips come off during cutting is called the front, and the opposite face, facing the workpiece surface, is called the rear. The intersection of the front and rear edges form a cutting edge, the width of which at the chisel is usually 15-25 mm.
The angle formed by the sides of the wedge is called the tapering angle; it is denoted by the Greek letter 3 (beta). The angle between the front face and the surface to be machined is called the cutting angle and is denoted by the letter 8 (delta). The angle between the front face and the plane drawn through the cutting edge perpendicular to the surface to be machined is called the leading angle and is denoted by the letter y (gamma). The angle between the back face and the machined surface is called the back angle and is denoted by the letter a (alpha).
The smaller the sharpening angle, the less effort must be made to carry out the cutting. Therefore, the angle of tapering is chosen depending on the hardness of the metal being processed and the tool itself. The greater the hardness and brittleness of the metal, the stronger its resistance to the penetration of the wedge into it and the greater the angle of the taper of the chisel. For felling of cast iron and bronze take p = 70 °, for steel of average hardness P 60 °, for copper and brass p 45 °, for aluminum and zinc p = 35 °
The larger the rake angle, the easier the chips to separate. However, as the rake angle increases, the taper angle of the tool, and consequently, its strength, also decreases. Therefore, the value of the rake angle is also chosen depending on the operating conditions of the tool.
The rear angle has a smaller value in the cutting process, its purpose is to reduce the friction between the tool and the surface to be machined. The back angle is usually 3-8 °
The middle part of the chisel has a shape that is convenient for keeping it in the process of cutting. Usually this part of the chisel has a rectangular cross-section with oval faces or the shape of a polyhedron.
The chisel head is always made in the form of a truncated cone with a semicircular upper base. In this form of the head, the force of the blow on the chisel with a hammer is used with the greatest effect, since the striking blow always falls on the center of the shock of the chisel. The conical head, moreover, less rivets during operation.
Chisels are manufactured with a length of 100, 125, 160, 200 mm, the width of the cutting edge, respectively, is 5, 10, 16, 20 mm.
Chisels 100-125 mm long are used for minor work, and 150-200 mm long - for rough work.
The quality of the chisel is determined by compliance with the established mode of heat treatment (quenching and tempering) and the correctness of sharpening. Hardening of the working part of the chisel is carried out by heating it to a length of 40–70 mm to a temperature of 800–830 ° (light cherry red hardening) and cooling in water over a length of 15–30 mm, followed by tempering until a violet color appears.
Hardening of the chisel head is performed in the same way over a length of 15–20 mm with tempering to gray tinge.
The degree of hardening of the chisel can be determined by an old file, which is carried out on the hardened part of the chisel. If the file does not remove the chips from the hardened part of the chisel (there are only subtle risks on it), the hardening is done well.
The kreytsmeysel (fig. 35, b) differs from a chisel in a narrower cutting edge. It is used for cutting out narrow grooves, key grooves, etc. In order for the kreuzmeisel to go deeper into the groove and not to become wedged, its cutting edge is made somewhat wider than the working part following it. However, quite often it is used to chop up the surface layer from a wide cast-iron plate: first, grooves are cut through the crutzmeisel, and the remaining protrusions are cut down with a chisel. Materials for the manufacture of kreysmeysle and angles of tapering, the hardness of the working and impact parts are the same as for the chisel.
For cutting out the profile grooves - semicircular, dihedral, etc., special crackers are used, called groove (Fig. 35, c), differing from the cross-cutter only in the shape of the cutting edge. Grooves are made with pointed and semicircular cutting edges. Their sizes depend on the diameter of the bearing bushings and bushings, in which it is necessary to cut out the lubricating grooves.
The grooves are made of U8A steel with a length of 80, 100, 120, 150, 200, 300 and 350 mm.
It should be noted that the operation of cutting grooves is laborious and responsible; grooves after cutting are often uneven, with unequal depth, etc.
When sharpening chisels and crossbones usually use simple grinding machines. The sharpened tool is installed on the handpiece 1 of the grinding machine (Fig. 37, a) and with light pressure slowly moves it across the entire width of the grinding wheel. Sharpening should be carried out with cooling in water. In this case, it is necessary to ensure that
The tool did not exceed 120 “; heating above the specified temperature leads to tempering and reduces the hardness of the cutting edge of the tool. In the process of sharpening a chisel (crosspiece) should be rotated one way or the other side, this ensures uniform sharpening. The cutting edge of the chisel after grinding should have the same width and inclination to the axis of the chisel. The angle of sharpening the chisel or kreuzmeysel is checked against a template representing a plate with angular cuts at 70, 60, 45 and 35 °. When sharpening a chisel or kreysmeysel it is necessary to close the protective screen 2 and the protective cover 3.
After sharpening a chisel or crossbuttle, the burrs are removed from the cutting edges. The magnitude of the tapering angle is checked by a template, which is a plate with an angle cut 70, 60, 45 and 35 ° (Fig. 37, b).
Percussion instrument. The types of percussion instruments include hammers for various purposes and designs.
Fitters produce two types of hammers: square and round dies (Fig. 38, a, b). The process of making hammers with a square striker is simpler, they are cheaper and, therefore, in the practice of locksmithing are widespread. At the same time, hammers with a round head are advantageous in that they have a large weight predominance of the striking part over the rear part, which provides greater force and accuracy of impact.
The choice of the hammer by weight is essential. The weight of the hammer must match the width of the cutting edge of the chisel. Practice shows that for normal impact when cutting metal, each millimeter of the width of the cutting edge of the chisel should correspond to 40 g of the hammer weight, and each millimeter of the width of the cutting edge of the crosshead should be 80 g of the weight of the hammer. The weight of the hammer is determined by its size. When choosing a hammer weight, of course, you must also take into account the age and physical strength of the worker.
Bench hammers are round-sized in six sizes. Hammers weighing 200 g are recommended for instrumental work, as well as for marking and straightening; hammers weighing 400 g, 500 g and 600 g - for plumbing; hammers weighing 800 g 1000 g are rarely used, mainly for repair work.
Bench hammers with square brisk manufacture eight sizes: weighing 50 g, 100 g and 200 g - for metalwork and tool works; weighing 400 g, 500 g, 600 g - for plumbing work: cutting, bending, riveting, etc. 800 g and 1000 g are rarely used (when performing repair work).
For heavy work, they use hammers weighing from 4 to 16 kg, called sledge hammers.
The opposite end of the hammer is called a toe. The sock is wedge-shaped, rounded at the end. Toes are used for dressing, ripping and
T. D. Boiko a - with square striker; b - with a round put ud - brisk; in - with inserts of soft software ON chisel tal; g - wooden (mallet); d - spread
OR KREITZ - handle cleaning
They produce hammers from steel 50 and 40X and tool carbon steel U7 and U8. In the middle part of the hammer there is an oval-shaped hole that serves for fixing the handle.
The working parts of the hammer — a square or round shaped peen and a wedge-shaped toe — are thermally treated to a hardness of SNN 49-56. Hammer handles are made of hard wood
(dogwood, mountain ash, oak, maple, hornbeam, ash, birch or synthetic materials).
The handle has an oval cross section, the ratio of small section to large 1 1.5, i.e. free
The end is 1.5 times thicker than the end on which the hammer is placed.
The end on which the hammer is placed is wedged by a wooden wedge lubricated with wood glue, or a metal wedge on which notches (ruffs) are made. The thickness of the wedges in the narrow part is 0.8-1.5 mm, and in the wide part 2.5-6 mm. If the hammer hole has only lateral expansion, clog one longitudinal wedge; if the expansion goes along the hole, then two wedges are hammered (Fig. 38e), and finally, if the hole's expansion is directed in all directions, three steel or three wooden wedges are hammered, having two parallel, and the third is perpendicular to them. A correctly fitted hammer is one in which the handle forms a right angle with the axis of the hammer.
In addition to conventional steel hammers, in some cases, for example when assembling machines, they use so-called soft hammers with inserts made of copper, fiber, lead and aluminum alloys (Fig. 38, c). When struck by a soft hammer, the surface of the workpiece material is not damaged. Due to the scarcity of copper, lead, and rapid wear, these hammers are expensive to operate. In order to save metals, copper or lead inserts replace
rubber, cheaper and more comfortable to work with. Such a hammer (fig. 39) consists of a steel body 7, on the cylindrical ends of which are put on heads 2 of hard rubber. Rubber brakes are sufficiently resistant to impact and are easily replaced with new ones when worn. Hammers of this design are used for accurate assembly work, especially when you have to have with details of low hardness.
In some cases, especially in the manufacture of products from thin sheet metal, wooden hammers (mallets) are used (see Fig. 38, d).
Chopping called an operation in which using a chisel and a small hammer to remove the metal layers from the workpiece or cut the workpiece.
The physical basis of the cutting is the action of the wedge, the shape of which has the working (cutting) part of the chisel. Cabin is used in cases where the machining of workpieces is difficult to implement or irrational.
With the help of cutting, removal (chopping) of the billets of metal irregularities, removal of hard peel, scale, sharp edges of the part, cutting of grooves and grooves, cutting the sheet metal into parts is made.
The cutting is made, as a rule, in a vice. Cutting sheet material into pieces can be done on a plate.
The main working (cutting) tool for chopping is a chisel, and the hammer is a hammer.
Cold chisel (Figure 8) is made of tool carbon steel U7A or U8A. It consists of three parts: shock, medium and working. Shock part 1 running tapering upward, and its top (firing pin) - rounded; for the middle part 2 chisel held during logging; working (cutting) part 3 has a wedge shape.
Figure 8 Chisel
The tapering angle is selected depending on the hardness of the material being processed. The following angles are recommended for the most common materials:
For solid materials (solid steel, cast iron) - 70 °;
For materials of medium hardness (steel) - 60 °;
For soft materials (copper, brass) - 45 °;
For aluminum alloys - 35 °.
Kreuzmeisel - a chisel with a narrow cutting edge (Figure 10), designed for cutting out narrow grooves, keyways of low accuracy and chopping off the heads of rivets. Such a chisel can also be used to remove wide metal layers: first, grooves are cut through with a narrow chisel, and the remaining protrusions are cut down with a wide chisel.
Hammers , used in the cutting of metals, there are two types: round and with square briskly. The main characteristic of the hammer is its mass.
Hammers with a round brisk have a number : from 1st to 6th . Nominal weight of the hammer number 1 - 200 g; No. 2 - 400 g; No. 3 - 500 g; No. 4 - 600 g; No. 5 - 800 g; No. 6 - 1000 g. Hammers with a square brisk have numbers from the 1st to the 8th and weight from 50 to 1000
The material of the hammers is steel 50 (not lower) or steel U7.
The working ends of the hammers are heat treated to a hardness of HRC 49-56 at a length equal to 1/5 of the total length of the hammer at both ends.
At locksmith's work, they use hammers with a round striker No. 2 and 3, with a square striker No. 4 and 5. The length of the hammer handle is approximately 300-350 mm.
3.4 Metal cutting
Cutting - plumbing operation to divide the whole a piece(blanks, parts) on the part. It is carried out without removing the chips: with pliers, scissors and pipe cutters and with the removal of chips: with hacksaws, saws, mills and special methods (gas cutting, anodic mechanical and electric-spark cutting, plasma cutting).
The wire is cut with needle nose pliers (nippers), the sheet material is cut with scissors; round, square, hexagonal and strip material of small sections - hand saws, and large sections on cutting machines with hacksaw blades, circular saws, in special ways.
The essence of the operation of cutting metal with pliers (nippers) and scissors consists in the separation of wire, sheet or strip metal into parts under the pressure of two wedges (cutting knives) moving towards each other.
Pliers cut (bite off) steel parts of circular cross section and wire. Make them 125 and 150 mm long (for a wire biting up to 2 mm in diameter) and 175 and 200 mm long (for diameters to 3 mm).
The cutting edges of the jaws are straight and sharply sharpened at an angle of 55-60 °. The wire cutters are made of tool carbon steel U7, U8 or steel 60-70. Sponges are thermally treated to hardness HRC 52-60.
Hand shears designed for cutting soft mild steel sheet, brass, aluminum and other metals. Make 200 and 250 mm long for cutting metal up to 0.5 mm thick, 320 mm (for thickness up to 0.75 mm), 400 mm (for thickness up to 1 mm).
The material of the scissors is 65, 70 steel. The blades of the scissors are thermally treated to hardness HRC 52-58. The cutting edges of the blades are sharply sharpened at an angle of 70 °. The scissors blades in the closed state overlap each other, and the overlap at the ends does not exceed 2 mm.
Chair scissors cut sheet metal up to 3-5 mm thick. One of the scissors' handles is bent at an angle of 90 ° and rigidly attached to a table or other base. The length of the working handle scissors - 400-800 mm, the cutting part - 100-300 mm.
Lever shears used for cutting sheet metal with a thickness of 5 mm. Scissors are made of tool steel U8A and heat treated to hardness HRC 52-58. The sharpening angle of the cutting edges of knives is 75-85 °.
Pipe cutters designed for manual cutting of thin-walled (gas) pipes of mild steel, cutting is performed without removing chips. Available in two sizes: for cutting pipes from 1/2 to 2 "and for pipes - from 1 to 3".
The main parts of the pipe cutter are the rollers: one cutting (working) and two guides. The pipe is cut by a working roller; while it is fixed on the guide rollers and tightened the screw.
Hand saw (Figure 9, a) is used for cutting relatively thick sheets of metal and round or profile rolled products. The hacksaw can also be used for cutting slots, grooves, cutting and cutting blanks along the contour and other work. They are made of steel U8-U12 or 9HS with a hardness of the cutting part of HRC 58-61, cores - HRC 40-45. It consists of a frame 1 , tension nut with a wing nut 2, handles 6, hacksaw blade 4, which is inserted into the slotted heads 3 and fastens with pins 5.
|
Figure 9 Manual hacksaw a - the device, b - the angles of sharpening, c - the arrangement of the teeth “along the tooth”, g — the arrangement of the teeth “along the web”. |
Each tooth of the blade has a wedge (cutter) shape. On it, as well as on the cutter, there is a back corner. α, taper angle β , cutting angle γ and cutting angle δ = α + β (Figure 9, b). When notching the teeth take into account the fact that the formed chips should be placed between the teeth before they exit the cut. Depending on the hardness of the materials being cut, the angles of the tooth can be γ = 0-12 °, β = 43-60 ° and α = 35 -40 °. In order for the width of the cut made by the hacksaw to be slightly larger than the thickness of the blade, the teeth are “wired” (Figure 9, at)or “on the canvas” (Figure 9, g). This prevents the blade from jamming and facilitates the work. |
§ 3. Tools and devices for metal cutting
The cutting is called the locksmith operation, in which with the help of a cutting tool (chisel) extra layers of metal are removed from the workpiece or part or the workpiece is cut into pieces.
With modern methods of processing material or blanks, metal cutting is an auxiliary operation.
The cutting of the metal is carried out in a vice, on the plate and on the anvil with the help of a hammer, chisel, cross-cutter, blacksmith and sledgehammer.
Felling of the metal is horizontal and vertical, depending on the location of the chisel during the operation. Horizontal cutting is performed in a vice. At the same time, the rear face of the chisel is mounted almost horizontally to the plane of the jaws of the jaws, at an angle of no more than 5 °. Vertical cutting is performed on a slab or anvil. The chisel is mounted vertically, and the material being chopped is laid horizontally on the plate.
Hammers weighing 400, 500, 600 and 800 are used for the metal logging. Hammers are placed on handles made of hard and viscous wood (birch, maple, oak, rowan). Handles should be oval-shaped, with a smooth and clean surface, without knots and cracks. The length of the handle of the hammer weighing 400-600 g is equal to 350 mm, and the weight of 800 g is 380-450 mm. So that the hammer does not jump off during operation, the end of the handle, on which the hammer is mounted, is wedged with wooden or metal wedges 1-3 mm thick. Wedges put along the major axis of the cross section of the handle. Wooden wedges are put on the glue, and metal wedges, so that they do not fall out.
The working part of the chisel and kreytsmeysel- (5, c, d) hardened to a length of at least 30 mm, and the head hardened weaker than the blade (about 15-25 mm long), so that when struck with a hammer it does not crumble and crack.
The rest of the chisel and crosshead must remain soft. Chisels and crossbuttons should not have cracks, captivity and other defects.
The most commonly used chisels are 175 and 200 mm long with blades 20 and 25 mm wide. For cutting through the grooves in steel and cast iron used kreytsmeyseli 150-175 mm long with a blade width of 5-10 mm. The heads of the chisel and crossheads are forged on a cone, which ensures the correct direction of impact with a hammer and reduces the possibility of the formation of a mushroom cap on the head.
The angle of sharpening chisels and crossbuttons depends on the hardness of the metal being processed. For cutting iron, hard steel and hard bronze the tool sharpening angle is 70 °, for cutting medium and mild steel - 60 °, for cutting brass, copper and zinc - 45 °, for cutting very soft metals (aluminum, lead) - 35- 45 °.
Bench tool sharpen on grinding machines with abrasive wheels. During sharpening, the working part of the tool (blade) becomes very hot and it can be temporarily released. During tempering, the hardness of quenching is lost and the tool becomes unsuitable for further work. In order to avoid this, the working part of the tool is cooled with water during sharpening. 6 shows how to hold the chisel when sharpening and how to check the correctness of sharpening the angle.
§ 4. Rules and techniques for cutting metal
The performance and cleanliness of metal cutting depends on the correct methods of work. When chopping, you need to stand steadily and straight, half-turned to a vice. The hammer is supposed to hold the handle at a distance of 15-20 mm from the end and apply strong blows to the center of the chisel head. You should look at the chisel blade, and not at its head, otherwise the chisel blade will go wrong. Chisel relies hold at a distance of 20-25 mm from the head.
Billets of sheet steel or steel can be chopped in a vise at the level of sponges or risks above the level of vise sponges.
When cutting at the level of the jaws of the vise (8, a, b), the workpiece is clamped firmly in a vise so that the upper edge protrudes above the jaws by 3-4 mm and cuts the first chip to the entire length of the workpiece. Then the workpiece is rearranged in a vice so that the upper edge protrudes 3-4 mm above the level of the jaws of the vice, and the second chip is cut down. So consistently chop off the product to the desired size.
When felling above the level of the vise jaws (8, c) for risks, the workpiece is clamped in a vise so that the marked risk is above the level of the vise jaws and parallel to them. Cutting is done according to the marked risks sequentially, as when cutting according to the level of the jaws. When cutting, the chisel blade should be located at an angle of 45 ° to the metal to be chopped off, and the head should be raised upwards at an angle of 25-40 °. With this arrangement, the chisel line will be cut and the cutting will be faster.
A large layer of metal on the wide plane of the workpiece is cut down as follows: the workpiece is clamped in a vice, the chisel is cut off with a chisel, the transverse grooves are cut through with a chop, and then the protruding edges are cut down with a chisel. When cutting the grooves with a crossbutton, the chip thickness should be no more than 1 mm, and when cutting out the protruding faces with a chisel, it should be from 1 to 2 mm.
Strip steel is cut on a slab or anvil (9). Previously on both sides of the strip chalk overlay lines. Then, laying the strip on the anvil, set the chisel vertically on the marked risk and with strong blows of the hammer, they cut the strip to half its thickness. Then the strip is turned over, cut on the other side and break off the cut off part.
The round metal is cut in the same way, with the bar turning after each stroke. Having hacked the bar around the entire circumference to a sufficient depth, break off the part to be cut off.
Carbon and alloyed structural steel with a thickness of up to 20-25 mm can be chopped cold on a slab or anvil using forge chisels (10, a, b) and sledgehammers (10, c, d). To do this, on -t * "ipi, over the side of the workpiece, put a line of overlap with chalk. Then the metal is laid on the anvil, the forging chisel is placed vertically on the marking line and by heavy blows from the sledgehammer the metal is cut to the required depth along this line, gradually rearranging the chisel. They also cut the metal from the other side or from all four sides, after which the part to be chopped off. To speed up and simplify logging, an auxiliary tool is used — niziiik (cutting). Cutting the shank is inserted into the square hole of the anvil, then the workpiece is placed on the hooking, and a blacksmith chisel is placed on top, as shown at 10, D, and the hammer is struck on the chisel with a sledge hammer. Thus, the simultaneous cutting of metal from both sides by a chisel and a hooking occurs.
Cast iron pipes are cut with a chisel on wooden linings. First, around the circumference of the pipe, chalk out a line for cutting with a chalk, and then, placing linings under the pipe, in two or three passes, cut the pipe with a chisel along the marking line (And, a), gradually turning it. Having checked the depth of the cut-out grooves, which should be at least 7 times the thickness of the pipe wall, part of the pipe is separated with a light hammer blow. When working, the chisel must be held perpendicular to the pipe axis (11, b). The end of the pipe in the place of the cut should be flat, perpendicular to the axis of the pipe and coincide with the intended line of the cut. The correctness of the Butt is checked by eye, and controlled by a square.
§ 3. Mechanisms and devices for cutting metal
More productive is the mechanized cutting of a metal with a pneumatic hammer (12), operating under the action of compressed air with a pressure of 5-6 kgf / cm2. Compressed air is supplied to the hammer through the hoses from the compressor. A pneumatic hammer consists of a cylinder /) into which a chisel is inserted, a piston / moving in a cylinder, and an air-distributing device. Thanks to the air distribution device, the piston receives forward and backward movement and quickly moves back and forth through the cylinder. With the forward movement of the piston hits the chisel, which cuts the metal. The hammer is put into operation by pressing the trigger 6. The worker holds the hammer with two hands and guides the chisel to the cutting site.
Manual screw press (13) is used for cutting iron sewer pipes with a diameter of 50 and 100 mm. It consists of a welded bed 2, two side racks 5, having in the upper part of the neck with thread, which are put on the traverse 6. Traverse is attached to the racks by nuts. On the traverse, a nut and a screw. In the lower part of the uprights, there is a lower fixed holder with an inserted lower knife, and in the upper part of the uprights - an upper movable holder 3 with an insertable upper knife. The upper movable holder is fastened with a lead screw lining 12 and bolts 4 and together with them it rises and falls. Side racks 5 are guides for the upper yoke. A channel bar with racks at the ends is welded to the base plate of the bed. This channel is a guiding element when laying the pipe for cutting.
Knives are attached to the cage with bolts. The inner diameters of the blades of the knives should be 2 mm smaller than the outer diameters of the pipes being cut. For each pipe diameter there is a pair of knives and a pair of rollers mounted on a channel bar to feed the pipes to the knives.
On the press work as follows. First install the knives and rollers in accordance with the diameter of the pipes being cut. Having lifted the flywheel with the knife, put the pipe on the rollers so that the overlap line coincided with the tip of the lower knife. Then, with a sharp jerk, turn the flywheel in the opposite direction, while lowering the spindle with the upper knife. From the sharp pressure of the lower and upper knives on the sides of the pipe, an incision first appears, the pipe is wedged, and then two pieces are cracked. The press serves one worker.
The mechanism VMS-36A (14) for cutting cast iron sewer pipes with a diameter of 50 and 100 mm works on the principle of a drive press. The gearbox with two heads 2 is mounted on the welded bed / mechanism. One head is intended for re-cutting pipes with a diameter of 50 mm, the second one for pipes with a diameter of 100 mm. The pipes are cut by four movable knives mounted into the chucks of the mechanism heads. The mechanism is activated by a 1.5 kW electric motor with a rotational speed of 1420 rpm. The engine is started by a foot pedal.
For re-cutting the pipes, an electric motor is first switched on. Then
they take a previously marked pipe and put it on supports so that the marking line on the pipe coincides with the blade of the knife. After that, the foot is pressed on the pedal. The knives are lowered onto the pipe, which is cut by the marking line by the pressure of the knives. After the cutting, the knives return to their original position and the operation of the head automatically stops. The time for cutting a pipe of one cycle is 3 seconds. Each of the four knives covers a chop pipe at a length equal to a quarter of its circumference. 15 shows the planes of the cutting knives, the geometry of which takes into account the characteristics of the material being cut, that is, the brittleness of cast iron. To prevent destruction and to ensure a smooth and even surface of the cut of the pipe being cut, the cutting edges of the knives are made intermittent due to the cut transverse grooves. The radius of the circle formed by the cutting edges of the knives should be less than the outer radius of the pipe being cut. Knife taper angle 60 °. The process of cutting is as follows.
When approaching, the knives at the first moment touch the pipe at eight points. With further approach, they crash into the pipe; wells are formed around the circumference. Microcracks occur near the wells and are directed from the well to the well and deep into the metal. During the process, the microcracks merge and form running cracks of the same direction, which are ahead of the knife supply. This leads to the fact that one end of the pipe is separated from the other.
Knives of the design described can be cut from a cast-iron sewer pipe ring length of 20 mm.
The following precautions should be observed when cutting to avoid bruises and injuries:
firmly stick a hammer or sledge hammer on the handle;
reliably strengthen the metal in a vise and when cutting on the anvil to support the part of the workpiece being cut off;
to use fencing nets when cutting hard or brittle metal so that flying off fragments do not damage a working or nearby person;
work as a serviceable tool and on serviceable machines;
when cutting pipes on a press, work in mittens.
Before cutting the pipes, it is necessary to check the serviceability of the mechanism, electrical equipment and protective barriers.
The cutting is called the locksmith operation, in which with the help of a cutting tool, excess layers of metal are removed from the workpiece or part, or the workpiece is cut into pieces. With modern methods of processing a material or blanks, felling of metal is an auxiliary operation.
The cutting of the metal is carried out in a vice, on the plate and on the anvil with the help of a hammer, chisel, cross-cutter, blacksmith and sledgehammer.
Felling of the metal is horizontal and vertical, depending on the location of the chisel during the operation. When horizontal cutting is performed in a vice, the rear edge of the chisel is installed almost horizontally to the plane of the jaws of the jaws, at an angle of not more than 5 ° C. Vertical cutting is performed on a slab or anvil. The chisel is mounted vertically, and the material being chopped is laid horizontally on the plate.
Fig. 3. Vice parallel:
1 - worm screw, 2, 3 - moving and fixed jaws, 4 - turntable,
5 - turntable screw, 6 - bottom plate
Fig. 4. Vice chairs:
1 - lever, 2,3-movable and fixed jaws, 4 - sleeve, 5-spring, 6-foot, 7 - spacer sleeve
Hammers with round strikers are used when greater force and accuracy of impact are required, and with square hammers for easier work. Hammers are made of tool steel U7. The working parts of the hammer harden and release. The hammer must be in good condition, without cracks, captivity, shells and other defects.
Hammers weighing 400, 500, 600 and 800 are used for the metal logging. Hammers are placed on handles made of hard and viscous wood (birch, maple, oak, rowan). Handles should be oval-shaped, with a smooth and clean surface, without knots and cracks. The length of the handle of the hammer weighing 400-600 g is equal to 350 mm, weight 800 g -380-450 mm.
The working part of the chisel and the crossbutton (, e, g) is hardened to a length of at least 30 mm, and the head is weaker than the blade (about 15-25 mm long) so that it will not crumble or crack when struck with a hammer. The rest of the chisel and crosshead must remain soft. Chisels and crossbuttons should not have cracks, captivity and other defects.
Fig. 5. Cutting tool: a - Hammer with a round head, b - a hammer hammer with a square head, C - chisel, g - creamer
Fig. 6. Sharpening the chisel on a sharpening machine: a - Methods of holding the chisel when sharpening, b - a template for checking the correctness of the sharpening angle
The most commonly used chisels are 175 and 200 mm long with blades 20 and 25 mm wide. For cutting through grooves in steel and cast iron, creame chips are used with a length of 150-175 mm with a blade 5-10 mm wide. The heads of the chisel and creitzmeisele are forged on a cone, which ensures the correct direction of impact with a hammer and reduces the possibility of the formation of a mushroom cap on the head.
The angle of sharpening chisels and crossbuttons depends on the hardness of the metal being processed. For cutting iron, hard steel and hard bronze the tool sharpening angle is 70 °, for cutting medium and mild steel -60 °, for cutting brass, copper and zinc -45 °, for cutting very soft metals (aluminum, lead) - 35- 45 °.
Bench tool sharpen on grinding machines with abrasive wheels. During sharpening, the working part of the tool (blade) becomes very hot and it can be temporarily released. During tempering, the hardness of quenching is lost and the tool becomes unsuitable for further work. In order to avoid this, the working part of the tool is cooled with water during sharpening. In fig. 6 shows how to hold a chisel when sharpening and how to check the correctness of sharpening the angle,