Technological features of equipment and tools for metal cutting. Metal felling purpose and purpose of the felling
The tools used in the cutting are related to cutting, they are made of carbon tool steels of grades U7, U8, U8A. The hardness of the working part of the cutting tools after heat treatment should be at least HRC 53 ... 56 over a length of 30 mm, and the impact part - HRC 30 ... 35 over a length of 15 mm. The dimensions of cutting tools for cutting depend on the nature of the work performed and are selected from the standard range. As a percussion instrument when cutting, hammers of various sizes and designs are used. Most often, when felling, they use hand hammers with a round striker of various weights.
Cold chisel(Figure 33) consists of three parts: working, medium, shock. As with any cutting treatment, the cutting part of the tool is a wedge (Figure 33, but).
The action of the wedge-shaped tool on the metal being processed varies depending on the position of the wedge and the direction of action of the force applied to its base. Distinguish two osnew types of wedge operation during cutting:
The axis of the wedge and the direction of action of the force applied to it are perpendicular to the surface of the workpiece. In this case, the workpiece is cut into pieces (Figure 33, b)
The axis of the wedge and the direction of action of the force applied to its base form an angle less than 90 ° with the surface of the workpiece. In this case, the chips are removed from the workpiece (Figure 33, c).
a - general view of the chisel and its working part; b - the angle of sharpening and the action of forces; c - cutting elements during cutting; P is the cutting force; w, w 1, w 2 - components of the cutting force; β, β 1, β 2 - taper angles; γ is the rake angle; α is the rear angle; β - cutting angle
Figure 33 - Bench chisel
The planes bounding the cutting part of the tool (Figure 1, c) , called surfaces. The surface on which the chips come off during the cutting process is called the front, and the surface opposite to it, facing the workpiece’s surface, is called the back. Their intersection forms the cutting edge of the tool. The angle between the surfaces forming the working part of the tool is called the point angle and is indicated by the Greek letter β (beta). The angle between the front and the machined surfaces is called the cutting angle and is denoted by the letter δ (delta). The angle between the front surface and the plane drawn through the cutting edge perpendicular to the cutting surface is called the front angle and is denoted by the letter γ (gamma).
The angle formed by the back and machined surfaces is called the back angle and is denoted by the letter α (alpha).
The smaller the angle of sharpening of the cutting wedge, the less force must be applied when cutting. However, with a decrease in the cutting angle, the cross section of the cutting part of the tool, and therefore its strength, also decreases. In this regard, the value of the angle of sharpening must be selected taking into account the hardness of the material being processed, which determines the cutting force necessary to separate the metal layer from the surface of the workpiece, and the impact force on the tool, necessary to create a cutting force.
With increasing hardness of the material, it is necessary to increase the angle of sharpening of the cutting wedge, since the force of impact on the tool is large enough and its cross section should provide the necessary cross-sectional area for the perception of this force. The values \u200b\u200bof this angle for various materials are approximately: cast iron and bronze - 70 °; steel of medium hardness - 60 °; brass, copper - 45 °; aluminum alloys - 35 °.
The rear angle α determines the amount of friction between the rear surface of the tool and the workpiece surface being machined; its value ranges from 3 to 8 °. The size of the rear angle is adjusted by changing the inclination of the chisel relative to the surface being machined.
Crosshead(Figure 34) differs from the chisel by a narrower cutting edge. Crossheads are used for cutting grooves, cutting keyways and the like. In order to prevent jamming of the crosshead during operation, its working part has a gradual narrowing from the cutting edge to the handle. The heat treatment of the working and impact parts, as well as the geometric parameters of the cutting part and the procedure for determining the sharpening angles of the cutting part for crossheads are exactly the same as for the chisel.
Figure 34 - Crosshead
Groove(Figure 35) is used for cutting lubrication grooves in the bushings and bushings of sliding bearings and profile grooves for special purposes. The cutting edges of the pocket can have a rectilinear or semicircular shape, which is selected depending on the profile of the cut groove. The groove differs from the chisel and crosshead only in the shape of the working part. The requirements for heat treatment and the choice of sharpening angles for grooves are the same as for a chisel and crosshead.
Figure 35 - Groove
Hand hammers(Figure 36) are used when cutting as a percussion instrument to create cutting forces and are of two types - with a round one (Figure 36, but)and square (Figure 36, b)briskly. The end of the hammer, opposite the striker, is called the toe; it has a wedge-shaped shape and is rounded at the end. The hammer is fixed on the handle, which during operation is held in the hand, striking the tool (chisel, crosshead, groove). To reliably hold the hammer on the handle and prevent it from slipping during operation, use wooden or metal wedges (usually one or two wedges), which are hammered into the handle (Figure 36, at)where it enters the hammer hole.
a - with a round striker; b - with a square brisk; c - ways to fix the handle
Figure 36 - Bench hammers
The cutting of small workpieces (up to 150 mm) from sheet material, wide surfaces of steel and cast iron workpieces of small sizes, as well as grooving in bearing shells, is performed in a vice.
On a plate or anvil, chopping the blanks into parts or cutting along the contour of blanks from sheet material is performed. Cutting on the stove is used in cases where the workpiece being processed is impossible or difficult to fix in a vice.
In order to give the working part of the chisel, crosshead or groove the necessary angle of sharpening, it is necessary to sharpen it.
Sharpening cutting toolcarried out on grinding machines (Figure 37, but).Tool to be sharpened 3 and with light pressure they slowly move it along the entire width of the grinding wheel. During sharpening, the tool is periodically cooled in water. Sharpening of the surfaces of the cutting wedge is carried out alternately - then one side, then the other, which ensures uniformity of sharpening and obtaining the correct sharpening angle of the working part of the tool. The grinding wheel during operation must be closed by a casing 2. Eye protection against ingress of abrasive dust is carried out using a special protective screen 1 or goggles. The sharpening angle of the cutting tool during sharpening is controlled using a special template (Figure 37, b)
a - grinding unit of the machine; b - a template for controlling sharpening angles; 1 - a protective screen; 2 - a casing; 3 - handyman
Figure 37 - Sharpening machine
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Metal cutting
Cuttingdivide the workpiece into parts, remove excess metal ( allowance), make lubricating grooves in the details, etc. This operation is carried out using chisels (fig. on the right) and a hammer.
Cutting part the chisel, like any other cutting tool, has the form wedge .
Point angle (sharpening) depends on the hardness of the metal being processed: the harder the metal, the greater should be the angle of sharpening. For steel processing, an angle of 60 ° is recommended, for non-ferrous metals - 35 ° ... 40 °.
A special chisel is used for grooving crosshead (fig. on the right).
When cutting, hammers weighing 400 or 500 g are used.
Before cutting, the workpiece is fixed in a vice slightly to the left of the right edge of the jaws so that there is room for the installation of a chisel (Fig. Left). The hammer is briskly put to the left on the workbench to the right of the vise, and the chisel - on the left, the cutting part on itself. A safety net (or screen) must be installed at the cutting site to protect others from metal fragments.
During felling, it is very important to take the correct working position (Fig. To the right). You should stand straight, the body must be turned in relation to the vise, the right shoulder should be opposite the chisel head. The left leg must be pushed forward for stability, the body rests on the right leg.
The chisel and hammer are held so that the impact part and the edge of the handle protrude by 15 ... 30 mm (Fig. Left).
Felling in a vise can be done according to the marking risks and the level of the jaws of the vise. In the first case, the workpiece is set so that the marking risk is 1.5 ... 2 mm above the jaws of a vice. The chisel is placed at an angle of 30 ... 40 ° (Fig. To the right) to the work surface. After each stroke, the chisel is returned to its original position.
In the second case, the marking risks are lowered below the level of the jaws in such a way that after processing, an allowance of 1 ... 1.5 mm remains on the surface of the workpiece.
Depending on the hardness of the processed material and its thickness, a hammer strikes a chisel of various strengths.
Distinguish carpal
, ulnar
and shoulder bumps (
see pic below).
Brush
(fig. but) blow remove small irregularities and thin chips, elbow
(fig. b) - cut off excess metal and cut into pieces a workpiece of small thickness. At carpal
hit hammer moves due to movement of the hand.
At elbow
the bend of the arm bends at the elbow and the bump becomes stronger (Fig. b). Loktev
they cut off the excess metal with a blow and divide the workpieces into parts.
Plechevym
blow (Fig. at) - cut down thick shavings, cut rods, strips of large thickness.
In cases where the workpiece cannot be fixed in a vice, it is processed on stove (fig. on the left). The chisel is placed vertically on the marking risk and strikes.
After each stroke, the chisel is moved to half the cutting edge. This makes it easier to set the chisel in the correct position and a continuous cut is formed. In a large-thickness blank, the marking risk is applied from opposite sides. First, they cut about half the thickness of the sheet on one side, then on the other.
When cutting a workpiece of complex shape, the cutting edge is placed at a distance of 1 ... 1.5 mm from the marking risks and the workpiece is cut with light strokes along the entire contour. After that, they chop along the entire contour with stronger blows. Then the workpiece is turned over and cutting is completed along the designated contour.
You can only work with a working tool. The impact part of the chisel and hammer should be free of cracks and burrs.
The handle of the hammer must be firmly set and free of cracks.
Do not touch the quality of the cutting by hand.
At the end of the wheelhouse, loosen the force of impact.
To avoid personal injury, wear a rubber washer on the upper end of the chisel.
Cutting can only be carried out with a protective shield and goggles.
You can not stand behind the worker.
Manual cutting is a laborious operation. In industrial production, it is replaced by other processing methods. Where it is impossible to do without cutting, it is performed locksmiths via pneumatic or electric chipping hammers. Most often, blanking of sheet metal is performed on presses using special dies. Among the high-performance methods that have been used recently, it should be noted oxygen, laser, etc. These installations serve metal cutters.
A variety of chisels and crossheads are shown in the figure below.
Cutting is a locksmith operation in which, using a cutting tool (a chisel, crosshead), excess metal layers are removed from the workpiece or cut into pieces. Cutting is carried out in cases where it is difficult or irrational to process workpieces on metal-cutting machines or when high precision processing is not required.
Instruments. Chisel(Fig. 17, a) are made of tool carbon steel U7A. The cutting part of the chisel has the shape of a wedge (Fig. 17, c), which is sharpened at a certain angle. The angle of sharpening (sharpening) of the chisel is selected depending on the hardness of the processed material: the harder the material, the greater the angle.
Apply the following sharpening angles (in degrees):
for cutting cast iron and bronze 70
for steel cutting 60
for cutting brass and copper 45
for cutting aluminum and zinc 35
Chisels are 100, 125, 150, 175, 200 mm long. The cutting part of the chisel is hardened to a Rockwell hardness of HRC 53-56, and the tail part to a hardness of HRC 30-35.
Fig. 17. Metal chopping tools:
a - chisel, b - crosshead, c - corners of the cutting tool
Crosshead(Fig. 17, b) is intended for cutting narrow grooves and keyways. It differs from a chisel by a narrower cutting part. The sharpening angles are exactly the same as those of a chisel.
Sharpen the chisel and crossheads with the usual grinding wheel on grinding machines. For sharpening, a chisel or crosshead is mounted on the handrail 1, as shown in Fig. 18, and with light pressure slowly move across the entire width of the circle.
Fig. 18. :
1 - handicraft, 2 - protective shield, 3 - grinder cover
In this case, strong pressure on the chisel should be avoided, as this will lead to heating and tempering, as a result of which the cutting part of the chisel will lose hardness. Sharpen best with cooling.
Hammers Designed for striking during most locksmith operations (chopping, riveting, straightening, bending, chasing, assembling, etc.).
In the middle part of the hammer there is an oval-shaped hole with a double conical extension to secure the handle. The length of the handle should be 200-260 mm for small hammers, for medium 270-350 mm, for heavy hammers 380-400 mm. The mass of hammers, depending on the nature of the work performed, varies: 50, 100, 150, 200, 300 g (light hammers for tool and marking work); 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.
This tool is a metal rod, one end of which (striker) has the shape of a truncated cone with a semicircular base, and the other (blade) is a wedge. Both ends are hardened and tempered.
A chisel is used for metal processing. Its length is approximately 100-200 mm, the width of the blade is 5-52 mm. The blade of the tool should be well sharpened, since the impact force depends on this (the sharper the blade, the less effort is applied upon impact).
The angle of sharpening the chisel blade is different. Blade with blunt sharpening angle work with hard metals. It should be borne in mind that steel of medium hardness is treated with a blade with a sharpening angle of at least 60 °; cast iron, bronze, solid steel - 70 °.
A smaller angle of sharpening the blade of a chisel requires working with soft metals such as copper and brass. The blade sharpening angle should be approximately 45 °. Zinc and aluminum are machined with a chisel, the blade sharpening angle of which is 35 °. The tool blade is sharpened on a grinder. Granularity of electrocorundum circles in this case should be 40, 50 or 63.
To control the angle of sharpening of the chisel, a special template is used, which is a bar of metal, on which 4 grooves with angles of different sizes are cut.
The main types and causes of defects during bending.
When studying various bending techniques, the reasons for the possible appearance of defects in forgings were considered. The main defects that occur during the bending process include: tension in the place of bending, cracks, creases, inaccuracies in size and shape.
The formation of tension, discussed in detail earlier, leads not only to a distortion in the shape of the forging, but also to a decrease in the strength of the part. The weight is eliminated as a preliminary set of metal at the bend, and the landing of the workpiece during bending.
The appearance of cracks on the outer surface of the workpiece in the bending section is most often possible if the metal is bent with low ductility, i.e., in a cold or cold state. For example, bending of duralumin blanks in the cold state is flexible, accompanied not only by cracking, but also by complete destruction of the metal. High requirements for the bending mode are imposed when machining high-carbon and alloy steels and other alloys. The choice of a rational mode of bending consists in the correct choice of the processing temperature, the bending scheme, the optimal minimum bending radius, the sequence of transitions, etc.
When bending billets at large angles, it is necessary that wrinkles do not form on the inside of the forging angle, since they are stress concentrators and reduce the strength of the part.
A defect in the form of inaccurate sizes appears most often with inaccurate determination of the length (volume) of the original workpiece. If a mistake is made in the calculation, the forging is either longer than required or shorter.
The inaccuracy of the form is the result of improperly selected bending transitions, poor-quality preparation of the initial billet, improper selection of the necessary tool or method of bending, as well as insufficient experience of the blacksmith.
Cutting. Appointment and types of cutting. The device of manual and lever scissors for cutting sheet metal, a manual hacksaw. Methods of cutting metal with a hacksaw, scissors. Drive scissors; lever, eccentric, roller, vibration, their scope, device and principle of operation.
Cutting called the operation of separating the material (object) into two separate parts using hand scissors, a chisel or special mechanical scissors. Sawing is the operation of separating a material (object) using a manual or mechanical hacksaw or circular saw.
Appointment and types of cutting.
The quality of metal products in various sectors of the economy (industrial production, construction, light industry, etc.) directly affects the degree of safety of the end use of the product (building hardware, ceiling in the hangar, metal door, pipeline). Thus, the task of ensuring high quality metal structures is key, one solution of which is reliable production equipment. Guillotines and others metal cutting machines Designed for cutting or chopping sheet metal, as well as metal blanks. Currently, such equipment is used in various fields of industrial activity of enterprises. Machine tools are widely used due to their high efficiency, which helps to optimize the production process, improves the quality of products and minimizes costs.
In accordance with the various needs of the processes and production goals, the following types of equipment are distinguished that are presented in the catalog of our company: machines for laser and plasma cutting, guillotines, shears, coordinate-slotting presses. Modern production facilities allow metal cutting with high accuracyrequired by the customer.
The main characteristic of any equipment for metal cutting is the accuracy of operations.
There are several classes of equipment for metal cutting:
A - equipment of particularly high accuracy;
B - high-precision equipment;
C - conventional metal cutting machines;
P - precision cutting machines;
N - machines of normal accuracy.
The most basic cutting equipment finds its application in the transportation of metal, while laser cutting machines are used in the production of non-standard parts. The guillotine equipment and various presses are used for chopping pipes of various diameters, rolled metal, thereby ensuring their high-quality cutting (no burrs, sagging, creasing of the edges). Thus, depending on the needs and tasks of the production cycle, there are various types of metal cutting machines depending on the purpose.
Category: Locksmithing
Metal cutting
With modern methods of processing material or workpieces, chopping metal is an auxiliary operation. It is used in cases where it is necessary, with low precision machining with a hand tool, to divide the metal into parts for billets, remove a thick layer of metal, eliminate bumps and tides on forgings and castings, remove the hard crust, cut through the groove.
Metal felling is carried out in a vice, on a stove and on an anvil using a bench hammer, a chisel, a crosshead, a blacksmith's chisel and a sledgehammer.
Metal felling is horizontal and vertical, depending on the location of the chisel during the operation. Horizontal cutting is carried out in a vice. In this case, the rear face of the chisel is set to the plane of the jaws of a vice at an angle of no more than 5 °.
Vertical felling is carried out on a stove or anvil.
The chisel is installed vertically, and the chopped material is laid horizontally on the plate.
Fig. 1. The vice is parallel: 1 - worm screw, g-movable sponge, 5-fixed sponge, 4 - turntable, 5 - turntable screw, 6 - bottom plate, 7 - nut
The vice is parallel (fig. 1) - cast iron with steel hardened false jaws and chair (fig. 2) - steel. The material is cut predominantly in a chair vise, since they are stronger than parallel ones. On a parallel vise, only thin steel may be cut.
Thinning of thin metal, cutting of planes, tides, burrs, cutting of grooves is carried out in a vice, and cutting of thick metal or long strips and rods is done on a stove or anvil.
The bench hammers used in the cabin are with round or square strikers (Fig. 3, a, b).
Fig. 2. Chair vice: 1-lever, 2-washer, 3-screw, 4-casing
The working parts of the hammer are quenched and released. The hammer must be in good condition, without cracks, captivity, shells or other defects.
Hammers weighing 500, 600 and 800 g are used for locksmithing. Hammers are planted on handles made of hard and viscous wood (birch, maple, oak, mountain ash). Handles should have an oval shape, smooth and clean surface, without knots and cracks. The length of the handle of a hammer weighing 500-600 g is 350 mm, and a weight of 800 g is 380-450 mm.
Fig. 3. The tool for the wheelhouse: a - a bench hammer with a round striker, b - a bench hammer with a square striker, c - a bench chisel, d - crosshead
To prevent the hammer from slipping during operation, the end of the handle on which the hammer is mounted is wedged with 1-3 mm thick wooden or metal wedges. Wedges are placed along the major axis of the handle section. Wooden wedges are placed on the glue, and metal wedges are sealed so that they do not fall out.
The working part of the chisel and crosshead is hardened to a length of at least 30 mm, and the head is hardened weaker than the blade (to a length of about 15-25 mm) so that it does not crumble and crack when hit with a hammer. The rest of the chisel and crosshead must remain soft.
Chisels and crossheads 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 grooves in steel and cast iron, crossheads 150-175 mm long with a blade 5-10 mm wide are used.
The chisel and crosshead heads are forged onto 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.
Chisels with a blade 20 mm wide have a head 12X12 mm in size, 18 mm long; with a blade of 25-16 × 28 mm, a length of 20 mm. Crossheads with a 5 mm wide blade have a head measuring 8X14 mm, 12 mm long and with a 10 mm blade - 12X28 mm, 15 mm long.
The angle of sharpening of chisels and crossheads depends on the hardness of the metal being processed. For chopping cast iron, hard steel and solid bronze, the tool sharpening angle is 70 °, for chopping medium and mild steel - 60 °, for chopping brass, copper and zinc - 45 °, for cutting very soft metals (aluminum, lead) -35- 45 °.
Fig. 4. Sharpening a chisel on a grinding machine: a - techniques for holding the chisel during sharpening, b - a template for checking the correctness of the angle of sharpening
Grinding tools are sharpened on grinding machines with abrasive wheels. During sharpening, the working part of the tool (blade) is very hot and may release. When tempering, the hardness of hardening is lost and the tool becomes unsuitable for further work. To avoid this, the working part of the tool is cooled with water during sharpening.
In fig. Figure 6 shows how to hold the chisel when sharpening and check the correctness of sharpening the angle. Productivity and cleanliness of metal cutting depend on the correct working methods.
When cutting, stand steadily and straight, half-turn to the vise. The hammer is supposed to be held by the handle at a distance of 15-20 mm from the end and inflict strong blows in 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.
The chisel is supposed to be kept at a distance of 20-25 mm from the head.
In fig. 5 shows the correct position of the body and legs of the worker, as well as how to hold the hammer and chisel.
Cutting metal in a vice is as follows. Billets made of sheet steel or steel can be cut in a vise by the level of the sponges or by risks above the level of the jaws of the vise.
Fig. 5. The position of the body and legs of the worker in a vise during cutting and tricks of the grip of the tool: a - elbow swing, b - shoulder swing
When cutting according to the level of the jaw jaws, the workpiece is clamped firmly into the vise so that the upper edge protrudes 3-4 mm above the jaws and cut the first chip for the entire length of the workpiece. Then the workpiece is rearranged in a vice so that the upper rib protrudes 3-4 mm above the level of the jaws of the vice, and cut the second chip. So sequentially chop off the product to the desired size.
When cutting above the vise jaw level, the workpiece is clamped in a vise so that the marked risk is above and parallel to the level of the vise jaws. Cutting is carried out according to marked risks sequentially, as in the case of cutting according to the level of vice jaws. When cutting, the chisel blade should be located at an angle of 45 ° to the metal being cut, and the head is raised upward at an angle of -25-40 °, as shown in Fig. 6. With this arrangement of the chisel, the cutting line will be flat and cutting will be faster.
A large layer of metal on a wide plane of the workpiece is cut as follows: the workpiece is clamped in a vice, a chamfer is cut off with a chisel, transverse grooves are cut with a cross-cutel, and then the protruding faces are cut with a chisel.
When cutting through the grooves with the crosshead, the chip thickness should be no more than 1 mm, and when cutting the protruding faces with a chisel, from 1 to 2 mm.
Strip steel is cut on a stove or anvil (Fig. 7). Pre-cut lines on both sides of the strip with chalk. Then, laying the strip on the anvil, set a bench chisel vertically on the marked risk and, with strong blows of a bench hammer, cut the strip into half its thickness.
Then they turn the strip over, cut it on the other side and break off the chopped part.
Round metal is cut in the same way, with the rotation of the bar after each stroke. Chopping the bar around the entire circumference to a sufficient depth, break off the chopped part.
Metal made of carbon and alloy structural steel up to 20–25 mm thick can be cut in the cold state on a plate or anvil using forging chisels and a sledge hammer (Fig. 6, a, b, c, d).
Fig. 6. The location of the chisel when cutting in a vice: a - at the level of the jaws of the vice (front view), b - the same (top view), c - above the level of the vice
Fig. 7. Techniques for cutting flat steel on the anvil (vertical felling)
To do this, chalk lines are applied to two or four sides of the workpiece with chalk. Then the metal is laid on the anvil, the forging chisel is mounted vertically on the marking line and, with strong blows, the sledgehammers cut the metal along this entire line to the required depth, gradually rearranging the chisel. Metal is also cut from the other side or from all four sides, after which the chopped part is broken off.
To speed up and simplify the felling, an auxiliary tool is used - a lower (hook). An auger is inserted with a shank into the square hole of the anvil, then the workpiece is put on the anvil, and a blacksmith chisel is installed on top, as shown in Fig. 8, d, and they strike a chisel with a sledgehammer. Thus, simultaneous cutting of metal occurs on both sides with a chisel and a hook.
More productive is the mechanized cutting of metal with a pneumatic hammer (Fig. 9), working under the action of compressed air with a pressure of 5-6 kgf / cm2.
Fig. 8. A tool for cutting thick steel in a cold state: o, b - forging chisels, c-sharp-nosed sledge, d-dull sledge, 3- ”position of the chisel and cutting during cutting
Compressed air is supplied to the hammer through hoses from the compressor. The pneumatic hammer consists of a cylinder, at the end of which a chisel, a piston moving in the cylinder, and an air distribution device are inserted. Thanks to the air distribution device, the piston receives translational and reverse motion and quickly moves forward and backward along the cylinder. With translational motion, the piston hits the chisel, which cuts the metal.
Fig. 9. Pneumatic hammer: a - diagram, 6 - chisel for a pneumatic hammer; 1 - piston, 2 - spool, 3, 4, 5. 9, 10 - channels of the air distribution device, 6 - trigger, 7 - nipple, 8 - ring undercut, 11 - cylinder
During the stroke of the piston, compressed air enters the channel on the right side of the cylinder; at this time, air is displaced from the left side of the cylinder along the channel, the annular undercut and the channel. At the end of the stroke, compressed air, passing through the channel, moves the spool to the right and goes along the channel, moving the piston back. From the right side of the cylinder, air escapes through the channel. By the end of the return stroke, the channel is blocked by the piston, the air on the right side of the cylinder begins to compress, moves the spool to the left, and the working stroke begins again.
Fig. 10. Cutting of a cast-iron tube a - the position of the pipe and tool, b - the perpendicular position of the chisel
The hammer is turned on by pressing the trigger 6. The worker holds the hammer with both hands and guides the chisel to the place of cutting.
Cast-iron pipes are cut with a chisel on wooden lining. First, the line of the cut is marked with chalk with a chalk around the pipe, and then, laying linings under the pipe, for two or three passes cut the pipe with a chisel along the marking line (Fig. 10, a), gradually turning it. After checking the depth of the cut groove, which should be at least 1/3 of the thickness of the pipe wall, part of the pipe is separated with light hammer blows.
During operation, the chisel must be held perpendicular to the axis of the pipe (Fig. 10, 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 end face is checked by eye, and for control by a square. More productive is the process of cutting pig-iron pipes on a Hramkov hand screw press.
A manual screw press (Fig. 11) consists of a welded bed, two side racks with a threaded neck in the upper part, on which a traverse is mounted, attached to the racks by nuts. A special nut with a worm thread is mounted on the traverse with a nut and a screw, along which the lead screw moves.
A flywheel is attached to the top of the lead screw. At the bottom of the uprights there is a lower fixed cage with an inserted lower knife, and at the top of the uprights - an upper movable cage with an inserted upper knife. The upper movable cage is fastened to the lead screw by means of a cover and bolts, and with it rises and falls. Side racks are guides for the upper clip. A channel with welded ends is welded to the bottom of the bed plate. This channel is a guiding element when laying a pipe for cutting.
Fig. 11. Manual screw press for cutting cast-iron sewer pipes and the position of the knives when cutting pipes: 1 - lower fixed cage, 2 - bed, 3 - upper movable cage, 4 - bolt, 5 - stand, 6-traverse, 7 - lead screw, 8 - flywheel, 9 - nut, 10 - screw, 11 - special nut, 12 - overlay, 13 - upper knife, 14 - pipe, 15 - lower knife; position / - when the upper clip is raised, position // - when the upper clip is lowered, position /// - at the time of chopping
Knives are bolted to the clips. The inner diameters of the blades of the knives should be 2 mm less than the outer diameters of the cut pipes.
On a manual screw press, cast-iron sewer pipes with a diameter of 2 and 4 ”are cut. For each pipe diameter there is a pair of knives and a pair of rollers mounted on the channel for supplying pipes to the knives.
Work on the press as follows.
First, knives and rollers are installed in accordance with the diameter of the pipes being cut. Using the flywheel, lifting the upper holder with the knife, lay the pipe on the rollers so that the cut line coincides 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, an incision appears on the sides of the pipe, the pipe wedges and then splits into two parts.
The press is served by one worker. It takes 1 min to cut the pipe.
The VMS-36 mechanism (Fig. 12) for cutting pig-iron sewer pipes with a diameter of 50 and 100 mm works on the principle of a drive press.
The mechanism has a welded bed on which a gearbox with two heads is mounted. Pipe cutting is carried out using four movable knives mounted in the cartridge of each head of the mechanism. One head is designed for cutting pipes with a diameter of 50 mm, the second - for pipes with a diameter of 100 mm.
Fig. 12. The mechanism for chopping cast iron pipes VMS-36: 1 - bed, 2-heads, 3-knives
The mechanism is switched on by a 1-kW electric motor with a speed of 930 revolutions per minute. The engine is started by push-button starters.
To chop the pipes, first turn on the electric motor. Then they take a pre-marked pipe and lay it on the supports so that the marking line on the pipe coincides with the knife blade. After that, they press the pedal with the foot. The knives are lowered onto the pipe, which is cut off along the marking line from the pressure of the knives. After. making the chopping cycle, the knives return to their original position and the operation of the head automatically stops. The cutting time of pipes of one cycle is 3 seconds.
Each of the four knives covers the chopped pipe at a length equal to a quarter of its circumference.
In fig. 13 shows the planes of cutting knives, the geometry of which takes into account the features of the material being cut, i.e., the fragility of cast iron.
To prevent destruction and ensure a smooth and pink 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 chopped pipe. Knife sharpening angle 60 °. The cutting process is as follows.
When rapprochement knives at the first moment touch the pipe at eight points. With further approach, they crash into the pipe; holes formed around the circumference are formed. Microcracks occur near the holes, directed from hole to hole and deep into the metal. During the process, microcracks merge and running cracks of the same direction form, which are ahead of the blade feed. This leads to the separation of one end of the pipe from the other.
Knives of the described design can be cut from cast-iron sewer pipes of a ring 20 mm long.
Fig. 13. The planes of the cutting knives: 1 - pipe, 3 - knives
When cutting, in order to avoid bruises and injuries, the following precautions must be observed: - firmly push the hammer or sledgehammer on the handle; - reliably strengthen the metal in a vice and, when cutting on the anvil, support the cut-off part of the workpiece; - use enclosing nets when chopping hard or brittle metal so that flying fragments do not damage a person who is working or who is near; - work with a working tool and working machines; - when cutting pipes on the press, work in gauntlets.
Before cutting pipes, it is necessary to check the serviceability of the mechanism, electrical equipment and protective fences.
Metal cutting is used to remove an extra layer of metal, cut a hole or cut the workpiece into pieces. Cutting is carried out on an anvil or a massive metal plate. Smaller chopping parts are clamped in a vice.
It should be noted that when cutting is not possible high precision machining, it is used either for rough processing of the workpiece or in cases where precision is not required.
Metal chopping tool
In the process of metal cutting, the following bench tools are used: chisel, crosshead and grooves.
The cutting blade of a chisel has a wedge shape. The blade and hammer of the chisel must be hardened and tempered. The chisel head is a truncated cone with a semicircular base. This is done so that the blow of the hammer always falls in the center of the striker. The length of the chisel is usually 10-20 cm, the width of the blade is from 5 to 52 mm. The sharper the chisel is sharpened, the less impact force is required for cutting the metal. However, it must be borne in mind that hard and brittle metals require a larger sharpening angle. In other words, hard metals are cut with a blade with a blunter sharpening angle. So, for chopping bronze, cast iron, solid steel and other solid materials, a sharpening angle of the chisel blade of 70 ° is required. Steel of medium hardness needs to be cut with a chisel with a blade sharpening angle of 60 °. Soft materials - copper, brass - can be chopped at a grinding angle of 45 °. Very soft materials, such as aluminum alloys and zinc, require a sharpening angle of 35 °.
To cut narrow grooves and grooves, a variety of chisels with a narrower cutting edge are used. This instrument is called the crossmaster. The working surface of the crosshead is sharpened in the same way as with a chisel.
It is most convenient to cut the lubrication grooves in the bearing shells and bushings into grooves. Their main difference from the chisel and crosshead is the curved edge of the cutting part.
When working with a chisel, depending on the purpose of the work, three types of strokes are used.
A brush stroke is used to remove a thin layer of metal, minor irregularities, and also when it is required to cut a sheet of thin steel. Hand strokes should be performed at a pace of 40-60 beats per minute, while only the wrist moves. When swinging, it is recommended to unclench the fingers of the brush, holding the handle of the hammer only with the index and thumb, and to compress the brush when hit.
The elbow strike is more powerful than the wrist. The rate of beats is slow, about 40-50 per minute. When swinging the arm, it is recommended to bend at the elbow to failure, the ring and middle fingers slightly open. Elbow bumps are used to cut through grooves and grooves, as well as to remove a layer of metal of medium thickness.
The shoulder blow is the most powerful. The force of the impact is achieved by a large swing, in which the hand moves in the shoulder joint. Fingers, a brush and an elbow work as with a wrist and an elbow strike, but when swinging, the arm bent at the elbow joint should be raised so that the brush is at ear level. The beat rate should be even slower - 30-40 per minute. Such strokes are used for processing large surfaces, cutting thick metal, as well as in cases where it is necessary to remove a large allowance in one pass of the chisel.
The quality of the cutting and the safety of the person who produces it also depends on how he holds the tool. The fingers on the handle of the hammer are located at a distance of 15-30 mm from its end, and the thumb is superimposed on the index. The chisel should be kept at a distance of 20-30 mm from its head, fingers should not be tightly squeezed. The likelihood of the hammer coming off the chisel head is significantly reduced by putting a rubber washer with a diameter of 50 mm and a thickness of about 10 mm on the top of the chisel.
When performing this type of work with metal, it is important to observe the correct setting of the chisel relative to the workpiece. In the case of cutting along the plane of the jaws of the vice, the angle between the axis of the chisel and the plane of the jaws should be approximately 45 °. When the cutting direction is perpendicular to the plane of the jaws of the vice when removing the metal layer, the angle between the plane of the workpiece and the axis of the chisel should be 30-35 °. If the angle turns out to be too large, the chisel will go deep into the metal upon impact, creating a significant unevenness on the surface being machined. If the angle of inclination is not large enough, the chisel will slip over the surface of the metal, and not cut it.
A significant observation - newcomers to working with metal when they hit a chisel with a hammer look, as a rule, at the chisel head, on which the hammer strikes. This is a gross error, leading to a decrease in the quality of work. You need to look at the cutting edge of the chisel to control the angle of inclination and see the result of each stroke. In this case, it is possible to control the quality of work and adjust the tilt of the chisel and the impact force without interrupting the work.
With the workpiece in a vise, you need to ensure that the marking risks are located exactly at the level of the sponges and do not skew. The felled part of the metal (shavings) should be located above the level of the jaws of the vice.
- Metal cutting