Friction saws are used for cutting steel

Friction cutting

Friction cutting The tamping of sheet metal is based on the friction forces generated by the moving of a fast running belt over the material (Fig. 2.10 и 2.11). Belt speed varies from 1000 to 4000 m/min. To cut thick metals and organic materials, bands with teeth are used. The teeth in this case serve to remove particles of material from the cut (Fig. 2.10).

The advantage of friction cutting is that this method enables cutting of metals of any strength, including hardened steels. Plastics, silicate materials cut well.

Flame cutting. During flame cutting, the metal to be cut is heated to its melting point and burned in an oxidizer gas environment. Cutting with acetylene and oxygen, for example. Acetylene burns and heats the metal, which burns with oxygen.

Cutting causes a significant temperature difference between the heat affected zone and the bulk of the material. Often the physical and mechanical properties of the material are changed during flame cutting. The chemical composition of the metal may change in the cutting zone. The advantage of flame cutting is mobility and the ability to cut in the field.

Flame cutting can be either manual or stationary.

When cutting by hand, allowance for further processing must be 3 to 5 mm per side.

Better mechanization and automation of the cutting is achieved by using stationary gas cutting units. Up to 6 to 8 torches can be mounted on a carriage at the same time. When edges are to be cut at the same time with cutting, torch units with different angles are used.

Productivity of gas cutting machines when cutting steel with thickness from 4 to 40 mm is from 20-40 m/h. Cutting width for automatic cutting from 2 to 6 mm with deviations from the nominal size of 0.3 to 0.5 mm. Cutting width of 3 to 10 mm for manual cutting.

Oxygen-flux cutting. Cutting of chromium-nickel stainless steel and cast iron is performed with fluxes in the flow of cutting oxygen. This type of cutting is called oxygen-flux cutting. Flux, when burned in oxyacetylene flame, produces large amount of heat and slags chrome oxides. The liquid slag runs off and frees the base metal of the surface film.

For cutting metal with thicknesses over 100 mm special torches are used, and as a combustible gas they use hydrogen.

Cutting of double-layered steel must be performed from the base layer side.

Electric arc cutting. During electric arc cutting the material to be cut is heated to the melting point by the heat of the arc, which occurs between the material and the electrode, and is removed from the cut with a jet of gas.

Electric arc cutting is performed with carbon-graphite or tungsten electrodes. The gas jet can be oxidizing or inert. Oxygen and air are used as oxidizing agents, while argon and hydrogen are used as inert gases.

Surface after electric arc cutting in most cases does not require additional cleaning or mechanical treatment. Carbonization of the surface in the base metal is negligible (0.01-0.03%).

Depending on the thickness of the material to be cut and electrode diameter, a current of 200 to 600 A is used. Arc voltage 40-50 V. Maximum cutting depth 5 to 6 mm. Thick plates are cut in several passes.

Metal electrodes with double cladding are used for oxyfuel-arc cutting. Carbon-graphite electrodes are coated with a thin layer of copper. These electrodes are more stable and last longer. For cutting of magnesium, aluminum, titanium, copper and some other metals it is recommended to use argon-arc cutting with gas jet that consists of 65% argon and 35% hydrogen. Cutting with this method produces a narrow cut. Cutting zone temperature reaches 3700°C.

Plasma arc cutting. Plasma technology is widely used for cutting and welding materials. High plasma temperature, simplicity and reliability of plasma torches combined with their high efficiency, wide range of variation of the process parameters, possibility of using various plasma-forming gases, high intensity and productivity of plasma units make this method not only economical but sometimes even irreplaceable.

Plasma cutting involves deep penetration of the workpiece with plasma and simultaneous removal of the molten material with a high velocity gas jet. It is one of the most efficient blanketing processes. For plasma cutting (welding), plasma. a significantly ionized gas. is the main energy source for heating the material. The plasma is a mixture of electrically neutral gas molecules and electrically charged ions, sometimes also heavy negative ions. The presence of electrically charged particles makes plasma sensitive to electric fields. an electric field transmits energy to charged particles and through them to the plasma. This increases the temperature of the plasma to 20000-30000°C.

Plasma can be produced in various ways. The simplest and most common of these is gas heating in an arc discharge. As gas they use the following mixtures: argon 20% and helium 80%; argon 50% and hydrogen 50%; argon and nitrogen etc.п.

Two plasma-forming schemes are used for cutting in industry: 1) direct arc, which is excited at the work surface of metal, which is anode; 2) indirect (independent) arc is excited between the electrodes in the plasma torch (shown in Fig. 2.12).

It is reasonable to use the first scheme when cutting, as it provides more complete use of the arc energy. Plasma arc (second diagram) is used in the cutting process as an auxiliary process and for processing non-conductive materials and sometimes thin metals. The plasma torch works as follows. An arc is created by applying voltage to the electrodes. Gas is fed into the chamber through tangential inlets, swirled and heated and ionized by the arc. The plasma flux picks up the arc and pulls it in the direction of the exit. The induction coil serves to stabilize the plasma flow and the arc.

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Friction saws have high productivity, their cutting tools are easy to make and cheap. However, they have a great disadvantage, which lies in the molten ends of the cut billets, which inhibits the widespread introduction of them in forging shops. In addition, the cutting process on them is accompanied by a sharp noise, which is detrimental to human health. [1]

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An electric friction saw cuts material by the joint operation of a friction ( toothless) saw with a voltaic arc. The rotating blade is connected to one pole of the power supply and the material to be cut. With another; a voltaic arc is formed. The metal in the kerf melts and the rotating blade only removes the molten metal. The surface of the metal in the kerf is fairly flat and clean. [3]

In an electric friction saw, the rotating disk is connected to one pole of the power source and the workpiece to be cut is. with another; a voltaic arc is formed. The rotating disc removes molten metal. [5]

Cutting with friction saws is based on the fact that the pipe metal is quickly heated to a near-melting temperature due to the intense friction between the rapidly rotating disc and the stationary pipe. Fine red-hot metal particles are gradually torn off by the disc. The circumferential speed of the disc is up to 100 m/sec. At this rotational speed, the disc does not have time to heat up because every point on its circumference, after contact with the metal to be cut, is cooled by water. The discs are made of mild steel with a thickness of 2 mm. 3 mm with fine knurling on the circumference. The notch increases the friction between the disk and the pipe being cut. [6]

High-performance friction saws. Or, as they are called, friction saws. The blade of such a saw is made of low-carbon steel of special rolling. [7]

A general view of a friction saw is shown in Fig. [8]

friction, saws, used, cutting, steel

How a friction saw can cut metal. which is a steel disc without teeth. [9]

How a friction saw can cut metal. which is a steel disk without teeth. [10]

A rolled tube is cut to the required length with a friction saw. In some HPT mills, pipe cutting is done on the move. [12]

The process is somewhat analogous to cutting with a friction saw. The difference is that the melting ( destruction) of metal takes place by means of electric arc discharges. The toothless saw, which is a steel disc with a thickness of 0.5 to 2 mm, is connected to the negative pole of the current source and is the cathode. The metal to be cut is connected to the positive pole and is the anode. As the saw approaches the metal, an arc discharge occurs, melting the metal, which is removed by the rotating saw. [13]

Guillotine and angle shears and friction saws driven by asynchronous motors are used for cutting metal. [14]

Guillotine and angle shears and friction saws driven by asynchronous motors are used to cut metals. Oxyfuel and plasma cutting is also used. [15]

Cutting metal with friction saws

Friction disk Friction disk sawing tool is kinematically similar to a circular sawing tool. in this case, the cut is also performed by means of a rotating saw blade.

However, the mechanism of metal separation here is completely different: if in the first case purely mechanical cutting of the metal is performed, then in the friction machines the separation occurs due to melting of the metal in the treated area.

friction, saws, used, cutting, steel

Friction saw equipment far exceeds other types of cutting machines in terms of the rotation speed of the saw blade.

The friction saw blade itself has no segments or teeth: its working edge is smooth, which, when pressed, dramatically increases friction. The metal is heated, becomes brittle and its shearing resistance drops sharply. Friction saws are made of high quality tool steel of R12, R18 type and have the hardness no lower than 66.70 NRC.

A disadvantage of friction cutting machines is their high noise level and the need for an efficient suction system to ensure that the metal particles are removed from the cutting zone in a timely manner.

Friction (toothless) saws

A friction or toothless saw is a thin steel disc driven by an electric motor; the disc feeds in the direction of the material to be cut and due to the resulting friction heats the metal particles in the kerf to a temperature at which the melting begins.

The disc itself removes the molten metal from the kerf, which is not heated because it is cooled by air and water.

To increase friction, the surface of the wheel is provided with a frequent notch, which slightly increases the kerf, but at the same time the wheel rotates more freely.

Cutting speed of friction saws is 100. 140 m/sec. The disk feed is manual and mechanical, 200-500 mm/min.

dimensions of friction saws: diameter from 300 to 1300 mm with thickness from 1,5 to 8 mm.

These saws work very fast. e. g. a 450 mm I-beam cut in 50 seconds., angle iron 160 X 100 mm. 25 sec.

The main disadvantage of friction saws is that they require a high power of the electric drive motor, which must be about 5-6 times higher than for conventional circular saws.

For example for a saw with a diameter of 600 mm an electric motor of 40 litres is needed. с. Hardened steel parts that cannot be cut with common saws can be cut with friction cutting saws.

Electric friction saw

The working process on this saw is carried out by the joint operation of the frictionless friction saw with a voltaic arc (Fig. 47).

The saw, rotating at 120. 150 m/s, is connected to one pole of the power supply and the material to be cut is connected to the other pole; a Voltaic arc is created.

The metal in the kerf melts and the rotating saw only removes the molten metal.

The structure of the metal in the kerf changes very little, and the surface is fairly flat and clean.

Schematic diagram of an electric friction saw. Fig. 47.

Metal circular saws for cold cutting

This name is derived from the principle of the cut-off saw. While cutting metal, the body and teeth of the blade absorb all the heat that is generated. The workpiece is therefore kept cold. This has many advantages, especially no risk of distorting the workpiece in any way. Saws, on the other hand, are quite demanding. They require a cooling system on the machine. Otherwise, the blade itself can be destroyed by excessive heat.

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Disc type tools are installed on: manual automatic, semi-automatic cutting and mitre saws, pendulum saws.

It is possible to distinguish two types of circular saws for cold cutting:

HSS saws are made of high-speed steel. Monolithic tools. Both teeth and body are made of the same material. Low cost and ease of use are its main advantages. circular saws with HSS steel are easy to resharpen and can be used repeatedly. The disadvantage of metal cutting tools is relatively high level of brittleness. In the case of considerable frontal or side loads, the saw is liable to break. That is why the tool operates at low RPM.

Used for cutting solid and profiled materials of ferrous metals and alloys. The assortment of sizes of circular saws with HSS steel is limited to 600 mm. That is why circular saw blades cannot be used to cut workpieces with large cross-sections.

Saws with carbide tips are made of two types of materials. Body is cast in regular steel, and special hard (HW) alloy inserts are mounted on the teeth. Circular saw blades are considerably superior to HSS steel in hardness and wear resistance. Hard alloy has a disadvantage. difficult to service. Only saw blades with the simplest point shape are suitable for resharpening. Specialized teeth do not require re-sharpening.

HW discs predominantly cut tubular material and shapes in ferrous and non-ferrous metals. The assortment includes both small-diameter and industrial, large-diameter discs.

Advantages and disadvantages of circular saws for metal.

The main area where the advantages of HSS circular saws can be seen is in automated line production. The use of discs pays for itself very quickly with a complete machine cycle with minimal need for operator intervention. This feature makes the tool indispensable in the production of pipes and profiles.

Disc type tools have a much longer service life than band type tools and if used properly, are more profitable in the long run. Virtually all such saws can be resharpened to almost their original specifications. So, for example, when using simple shape tip saws, even if the latter break down, the carbide inserts can be replaced. In HSS and friction saws the teeth can be re-cut.

However, the range of applications for circular saws is narrow and limited not only by the material cross section, but also by the shape of the material. This disadvantage is offset by the diversity of the range of circular saws for metal. For example, segmented circular saws and other industrial analogues capable of cutting workpieces with larger cross sections than band, friction and carbide saws operate at higher speeds. But given the cost of industrial tools, buying multiple types of saws is not always economically feasible.

Pros and cons of carbide metal discs

it should be noted at once that advantages over abrasive drives have plenty of carbide discs, but the price of equipment and drives themselves restrains the popularity of their use. Let’s talk about it one at a time!

  • Cutting precision. In order to maintain precision when cutting metal workpieces, a carbide blade on a pendulum saw is one of the best options for the job.
  • Speed of operation. You will be surprised at how fast a carbide saw blade.
  • Great blade life. On average the life of a disc is 5,000 cuts. Compared with an abrasive blade, it is immortal.
  • No harmful emissions. When working with abrasive, the work area produces a cloud of fine particles, which negatively affects human health.
  • Metal is not heated. After you cut the workpiece, you can safely pick it up, it will be cool. The main advantage is that the properties of the metal do not change without exposure to temperature.
  • Price. Carbide disc costs ten times as much as an abrasive disc. At home, with infrequent use, such a disk will not pay for itself.
  • Metal loss. Since the disk is thicker than the abrasive disk, it is worth considering that the cutting line for the trimmer will be thick.
  • They are rust-resistant. If you are thinking of sawing metal with rust, remember that it will wear out the blade faster.

Concluding all of the above, we can say that carbide discs belong to the more professional consumables. They have fewer drawbacks than competitors, but the price makes them unaffordable for home use.

Classification of saws by type of holder

Metal hacksaws use several types of holder:

Blade tensioning makes the saw blade more rigid, which in turn gives the saw high reliability and durability. Of course, there are some locksmith operations that do not require the saw to be tensioned.

  • Hacksaws with a tensioned blade are the vast majority of metal saws. In such hacksaws, the blade is attached between the ends of a staple holder. Saws of this type are equipped with mechanism for fine tension adjustment of saw blade.
  • Hacksaws with non-tensioned blade surfaces have a considerably limited field of application. In such saws, the blade is simply inserted into the handle, and a thrust roller or support bracket is provided roughly in the center of the blade.

In saws without blade tension, the cutting part from the center to the opposite end of the handle simply dangles freely. This is done so that the thin cog can pass freely into places that are difficult to reach. Yes, the reliability of such saws is low, but in return, the non-tensioned blade hacksaws provide the ability to cut through gaps and crevices.

What else you need to know about types of metal hacksaws.

The friction circular toothed saw

The invention belongs to mechanical engineering and can be used in pipe production for cold sawing. Purpose of the utility model. Improvement of serviceability of the saw and quality of cutting off the rolled product. To achieve a technical result, the main rear surfaces of the saw have chamfers with positive rear angles, and on the front surface of the teeth there are grooves adjacent to the main cutting edges with a width not exceeding half the tooth height. 2 з.п. f., 4 ill.

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The useful model relates to mechanical engineering and can be used in pipe production for cold cuts of rolled products.

Technology of friction sawing consists in cutting with local melting of workpiece material in the place of contact with the saw blade, arising due to friction and deformation of cut layer at high circumferential speeds of 100-130 m/sec.

Friction circular saw for cold cutting of pipes with a triangular tooth shape is known [Catalogue of friction saws of the company B Lecher (Germany), 2013 (http://vmw.blecher.com/pdfs/trennkreissaegeblatt.pdf)]. A disadvantage of the saw is high intensity of tooth tips wear in the initial period of cutting.

We know a friction circular saw with a curvilinear back surface and small negative front angles [Catalogue of friction saws of Blecher company (Germany), 2013 (http://wvvrw.blecher.conVpdfs/treraikTeissaegeblatt.pdf)]. Saw is used for a limited range of workable materials. One of the disadvantages of the design is the low rigidity of the saw tooth. When such saws are operated, the cyclic loading results in cracks in the saw blade, which leads to accidents in the mill.

Friction circular toothed saw for cold cuts of pipes with trapezoidal tooth form is known [Catalogue of friction saws of Blecher company (Germany), 2013 (http://wvvw.blecher.com/pdfs/trennkreissaegeblatt.pdi)]. The teeth of the circular saw have a symmetrical shape with large negative front angles and chamfers on the main rear surfaces. This saw design as the closest to the utility model is accepted as a prototype.

Disadvantages of the saw are low tool serviceability and quality of pipe cutting. In the process of cutting pipe, the periphery of the saw’s teeth begin to participate in chip formation, acting as front surfaces with large negative angles. Material layer to be cut is completely crushed under the chamfer. Intensive deformation of the metal layer squeezed between the tooth of the saw and the cutting surface occurs, pressure and temperature on the working surfaces of the tool increases sharply. The result is increased adhesion of metal particles to the saw’s teeth and a worsening of the cutting process. Due to the large contact surface of the saw with the workpiece, intensive heat sinks into the teeth and the tool heats up more quickly to the critical heat resistance temperature.

Objective of the utility model. Increase of saw’s operability and quality of cutting of rolled material.

The technical result is achieved due to the fact that on the main rear surfaces of the saw there are chamfers with positive rear angles, and on the front surface of the teeth the grooves adjacent to the main cutting edges with a width not exceeding half the height of the tooth are made.

Increase of saw efficiency is due to reduction of plastic deformation zone as source of heat generation and reduction of heat sinking into the tooth from the back surface. Durability of saw blade is provided by high rigidity of tooth, reduction of cutting forces and stresses on the bottom of chip groove.

Reduced plastic deformation zone, cutting forces and heat generation result from optimized saw tooth geometry. The presence of a groove on the front surface increases the front angle, which has a positive effect on the mechanics of cutting and causes a reduction of the friction component of machining. Groove width does not exceed half the height of the saw tooth, which does not reduce the stiffness of the tooth, and with the reduced cutting force the fatigue strength of the blade increases.

Grinding of positive chamfer on the rear edge of the saw leads to a more favorable redistribution of thermal flows, sharply reducing the thermal load and the rate of saw teeth heating to the critical values. Reduced friction cutting component leads to better quality of pipe ends after cutting.

In Fig. 1 shows tooth profile of friction circular saw with flat back surface; Fig. 2. isometric view of the saw teeth; Fig. 3. tooth profile of friction circular saw with curvilinear back surface; in Fig. 4. Cutting process of friction saw with modified tooth shape.

Saw teeth 1 have front surfaces 2, main rear surfaces 3, auxiliary rear surfaces 4. Chamfers on the back surface 5 are made with positive back angles. a on the front surface of the teeth there are grooves 6 adjacent to the main cutting edges 7, and the width of the grooves H does not exceed half the height of the teeth. Friction circular saws can be made with straight lines (Fig. 1) or curved back tooth surfaces (Fig. 3).

friction, saws, used, cutting, steel

Depending on the cutting conditions, the chamfer on the back surface can be made from 0.5 mm to 1.5 mm. Rear angle of the bevel is recommended to take =2030 °. Saw is sharpened with CBN wheel, which ensures higher sharpness of cutting edge. Cutting edge rounding radius should not exceed 15 μm. The groove on the front tooth surface is made at an angle = 10° with a width not exceeding half the tooth height. This tooth shape reduces cutting forces while maintaining the rigidity of the tooth base. These design changes significantly reduce the likelihood of fatigue cracks on the saw blade. Hollows between the teeth of the friction saw are made with a radius of r=12 mm.

When cutting with saw with modified teeth shape the volume of intensive plastic deformation zone decreases, cutting forces and cutting power decrease. A more favorable distribution of heat fluxes results in less heat stress on the saw tooth and improved wear resistance. Tests show that the durability of a newly sharpened saw blade increases by an average of 1.52 times. The stability and quality of the rolled product cut off is significantly improved. Cutting forces increase gradually as the saw wears out. The monotonous changes of the controlled cutting characteristics make it possible to predict with a high accuracy the onset of the critical saw’s wear, without leading to accidents. It is reasonable to include the proposed geometry of friction saw teeth into the number of standard shapes for CNC sharpening machines.

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