RU2333971C2 - Method of saw strengthening - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention is related to the field of thermal treatment of metals and may be used in production of tape, disc saws for materials cutting. In order to increase resistance, service life and efficiency of saws, method includes formation of tempered sections in the form of strips in the place of teeth location by means of heating and cooling at the account of heated sections heat removal to non-heated sections of saw with provision of re-sharpening of teeth, at that width of strip heated for tempering is selected on the basis of the following proportion: b=K x A, where: b - tooth width, mm; K coefficient = 0.05-0.3; A - distance between teeth tops, mm, and length is selected on the basis of the following proportion: L=R x H, where: L - length of heated strip, mm; R - coefficient =0.5-30.0; H - tooth height, mm, and strip location is selected with provision of installation of its teeth tops in tempered strip during saw re-sharpening in the process of its operation. Heating is carried out with high frequency current or laser radiation, or with effect of gas jet, or simultaneous pulse heating of strip is carried out.

EFFECT: development of efficient method of saw blade strengthening.

6 cl, 2 dwg

Description

The invention relates to the heat treatment of metals and can be used in the manufacture of tape, circular saws for cutting materials from wood, plastic, composite, metal and other materials.

The method includes forming sections of hardened metal in the form of strips of limited width arranged in such a way that, when re-sharpening the saw during operation, the tips of its teeth would be located in the zone of the hardened strip on the metal of the manufactured band or circular saw.

Band and circular saws work in difficult conditions. In the process, due to friction, the temperature of these saws increases significantly, they experience enormous dynamic loads (tensile, impact, and periodic bending, after which the saws must return to normal) and continuous abrasive wear. Due to the difficult operating conditions, these saws are dull quite quickly. They have to be sharpened and throttled periodically, while each time reducing the width (diameter) of the saw (for example, the usual width of the band saw is from 35 to 55 mm; the width of the saw, at which its strength is still ensured, is 25 mm, up to this size the width of the saw decreases in 20-30 hours of its correct operation). Those. saws are consumables that have to be changed often enough, and therefore, they should be cheap enough.

Given the specifics of the operation of band saws, special, largely contradictory requirements are presented to them:

1) resilience to ensure that the saw returns to normal after bending;

2) hardness, the high value of which increases the time intervals between the need for sharpening the saw;

3) sufficient softness, which allows the saw material to work on bending and stretching without tearing the blade;

4) cheapness.

Most manufacturers of band saws follow the traditional path - the creation of materials that to one degree or another satisfy these requirements, and the production of saws from these materials. Therefore, a large number of saws from various steels are sold on the market, each of which has its own advantages (that is, it satisfies to some extent one of the above requirements).

It should be noted that the softness requirement is imposed on the saw body working on bending and stretching, and the hardness requirement is imposed on the actually working part of the saw, on its tooth. Therefore, some manufacturers supply band saws with a hardened tooth to the market (it is impossible to harden the entire saw, because the material becomes much more brittle, which increases the likelihood of the saw body breaking during bending and tensile work).

Various manufacturers harden the saw teeth in various ways, and hardening modes are a strictly guarded secret. For example, Hakansson, which was founded in 1944, is the progenitor of band hardening technology for band saws and the oldest manufacturer of band saws with hardened teeth in the world. In 1946, they were the first in the world to develop a technology for hardening teeth of a band saw by induction current, known as high-frequency hardening. For over 40 years, this technological discovery has been a well-kept secret and until now a patent for this technology gives the company products an advantage over other manufacturers (detailed information on these saws can be found on the website of Avangard LLC [avanguard.ru]).

Another method of hardening the teeth of the saws involves hardening the teeth using a twin oxygen-acetylene burner, the nozzles of which are located on both sides of the saw, and the torches are directed at a certain angle to the saw blade. Thus, the well-known American company SIMONDS hardens the teeth of its saws (detailed information on these saws can be found on the GLOBAL EDGE ™ website [lentochnye_pily.ru]).

The disadvantage of this method is that the hardness obtained by quenching is unstable. The hardness of the cutting edges of the saw teeth varies from 55 to 64 HRC. In addition, an additional operation is required - vacation. The disadvantages of this method are related to the difficulty of accurately dosing the energy invested in the tooth and the long time for heating the tooth (heating is carried out due to the heat conduction from the heated tooth surface in contrast to the high-frequency hardening, in which the entire volume of the hardened part of the tooth is heated).

There is also known a method of deep hardening of band saws, which is used by the well-known German company "Banholzer GmbH" (saws "BANSO FLEX-BACK"). By this method, not only the tooth itself is tempered, but also the part of the saw body located next to it [information of Center for Cutting Tool LLC]. Such hardening allows you to increase the number of regrind of the teeth of the saw. The material of the cavities between the teeth also turns out to be hardened, which significantly increases the likelihood of brittle fracture of the saw in these places and does not significantly increase the strength of the hardened layer.

Currently, various companies are conducting intensive research on alternative methods of hardening teeth, which would provide an increase in the operational qualities of saws. This search led, in particular, to the development of a new method of hardening saws [RF No. 2033437, C21B 9/24, publ. 04/20/1995.]. In this method, the processing is carried out by continuous emission of a CO ₂ laser, the laser beam being directed from above onto the back surface of the teeth and the saw blade is moved.

This method allows to obtain a hardened layer in the form of relatively thin strips (0.5-0.7 mm) located on the rear surfaces of the saw teeth. The main advantage of this hardening method is that the main part of the tooth material remains plastic (it is not hardened), as a result of which the likelihood of brittle tooth decay is significantly reduced, especially when a tooth gets on solid inclusions in wood (for example, knots).

The disadvantages of this method are:

- a change in the angle of inclination of the front surface of the teeth due to the difference in the strength characteristics of the material of this surface, which requires more frequent sharpening of the saw;

- insufficient depth of the obtained hardened layer on the cutting edges of the saw (0.6-0.7 mm), which limits the use of this method when hardening saws that are sharpened during operation.

The disadvantages noted above lead to the fact that the method described above is practically not used when hardening the saw teeth.

- 15 ч. Обычный незакаленный зуб служит

4 часа. Однако при суммарном возможном уменьшении ширины пилы в 20 мм отличия в сроке службы оказываются не так значительны для пилы с первоначально закаленным зубом

часов, для пилы с незакаленным зубом

часов, таким образом общее время работы увеличивается примерно на 40%.In all of the above methods, hardening provides a significant increase in tooth strength and, consequently, a decrease in its wear. Such a saw at the beginning of its operation (until the periodic sharpening of the tooth falls below the hardening zone) dulls much more slowly, which reduces the cost of its periodic sharpening and increases the service life of the saw (during operation, the width of the saw with an unhardened tooth is ~ 0.8 mm / h , with a hardened tooth ~ 0.2 mm / h. With a typical size of a hardened tooth of 3 mm, its service time until the quenching limit

- 15 hours. An ordinary non-hardened tooth serves

4 hours. However, with a total possible reduction in saw width of 20 mm, differences in service life are not so significant for a saw with an initially hardened tooth

hours, for a saw with an unhardened tooth

hours, so the total operating time is increased by about 40%.

The closest analogue is the following source of information.

A known method of hardening saws, including the formation of hardened sections in the form of a strip at the location of the teeth by heating and cooling due to the heat transfer of the heated sections to the body of the blade to ensure the re-sharpening of the teeth (SU 94812A, C21D 9/24, 01.01.1953).

The objective of the invention is to increase the durability, service life and efficiency of the saws while ensuring the durability and wear resistance of the product as a whole and increase the depth of the hardened layer on the cutting edges of the saw teeth and the bearing surface at optimal costs for routine maintenance.

The solution to this problem is provided by using the proposed set of essential features.

The set of essential features

The method of hardening saws involves forming sections of hardened metal in the form of a band or circular saw made in metal in the form of strips of limited width, arranged so that during re-sharpening of the saw during operation, the tips of its teeth would be located in the zone of the hardened band, and the width of the strip heated for hardening metal (b) is selected from the ratio

b = K × A,

where A is the distance between the tops of the teeth; K - coefficient = 0.05-0.3,

and the length of the metal strip (L) heated for quenching is selected from the ratio

L = R × H,

where H is the height of the tooth; R - coefficient = 0.5-30.0,

wherein

- heating during quenching is carried out either by high-frequency currents, or by laser radiation, or by the action of a gas stream;

- pulse heating of the entire hardened strip of metal is carried out simultaneously;

- the metal strip is heated by induction currents, the frequency of which is selected from the relation f∈ {0.5 · f ₀ , 9 · f ₀ }, where f ₀ = ρ · 2 / (μ ₀ · h ² ), where ρ is the resistivity of the heated material saws at hardening temperature; μ ₀ is the magnetic permeability of steel at a quenching temperature; h is the thickness of the body of the saw;

- the hardening zone is selected so that the zone with the maximum hardness of the material is located on the axis of the tooth with a decrease in its hardness to the edges of the tooth;

- the depth of the hardened layer (g) is selected from the relation g = K1 · h, where K1 is the coefficient = 0.01-1.0; h is the thickness of the body of the saw.

The method is as follows.

For each saw tooth using high-intensity heating (for such heating high-frequency currents or laser radiation can be used) for a short period of time (0.1-1.0 s), a region (width b and length L of figure 1) is created in the metal, the temperature of which exceeds the temperature hardening. At the same time, the location of this area is selected so that when the saw is re-grind during operation, the tip of the tooth falls into the hardened area all the time (the dotted line shows the position of the teeth of the saw after several re-sharpening in Fig. 1). A short heating time is necessary to ensure conditions in which cooling could be ensured by removing heat into unheated areas of the saw. In order to obtain a regime with a minimum heating time, it is necessary to exclude heating stages that require a significant time. These stages primarily include the process of energy transfer by thermal conductivity. This stage can be excluded if all the material that needs to be hardened is simultaneously heated. In the case of through hardening of the strip, this can be achieved by using volumetric heat sources. Energy in this case is released in the volume of the metal, which can significantly reduce the duration of the heating process. The volumetric energy contribution can be obtained using induction RF heating of the metal. The correct choice of frequency in this case makes it possible to ensure an almost uniform volumetric energy contribution to the local region of the metal strip. To obtain such an effect, it is necessary that the penetration depth (Δ) of the electromagnetic field into the metal strip in the hot mode (heating is carried out to a temperature exceeding the Curie temperature, therefore, Δ must be calculated for the relative magnetic permeability μ = 1) is approximately equal to the thickness of the metal strip . To fulfill this condition, it is necessary to select the frequency of the supplying RF source in the range f∈ {0.5 · f ₀ , 9 · f ₀ }, where f ₀ = ρ · 2 · / (μ ₀ · h ² ), where ρ is the resistivity of the heated saw material at hardening temperature; μ ₀ is the magnetic permeability of steel at a quenching temperature; h is the thickness of the body of the saw. [Installations for induction heating. Training manual for universities / A.E.Slukhotsky, BC Nemkov, N.A. Pavlov, A.V. Bamuner: Under. ed. A.E.Slukhotsky. - L .: Energoizdat, 1981. - 328 p.].

Определить глубину проникновения можно по известной формуле [Установки для индукционного нагрева: Учебн. пособие для вузов / А.Е.Слухоцкий, B.C.Немков, Н.А.Павлов, А.В.Бамунэр: Под. ред. А.Е.Слухоцкого. - Л.: Энергоиздат, 1981. - 328 с.]:To obtain a hardened strip in the saw body during the heating time, it is necessary to provide conditions under which the heating rate of this strip will be significantly higher than its cooling rate due to thermal conductivity and radiation from the surface. Estimates obtained by solving the heat equation for the geometry and properties of the saw material studied indicate that such conditions can only be achieved at heating rates exceeding 2000 ° C / s. In this case, if it is necessary to harden the strip to its entire depth, the entire hardened volume should be heated at such speeds. To ensure uniform current (in depth) heating by high frequency currents (HDTV), it is necessary to select a frequency so that it allows for an approximate equality of the penetration depth of the electromagnetic wave into the saw material and the thickness of the body of this saw

You can determine the penetration depth by the well-known formula [Installations for induction heating: Training. manual for universities / A.E.Slukhotsky, BCNemkov, N.A. Pavlov, A.V. Bamuner: Under. ed. A.E.Slukhotsky. - L .: Energoizdat, 1981. - 328 p.]:

where ρ is the resistivity of the heated saw material at the quenching temperature; μ = 12.56 · 10 ^-7 GN / m is the magnetic permeability of steel at a quenching temperature.

From this formula and the relation Δ ~ h, we can express the frequency required for effective through hardening: f ₀ = 2 · ρ / (h ² · μ). In the case of steel quenching, ρ = 0.5 · 10 ^-6 Ohm / m, thickness h = 10 ^-3 m, f ₀ = 2 · 0.5 · 10 ^-6 /(12.56·10 ^-7 · 10 ^-6 ) = 0.78 · 10 ⁶ Hz The closest permissible frequency for use is f = 440 kHz. It was at this frequency that the experimental studies described in the application were conducted.

The lower frequency limit of 0.5 · f ₀ is determined by the fact that at lower frequencies the saw in the hot mode is practically “transparent” to the electromagnetic wave. The upper frequency limit f = 9 · f ₀ is determined by the need for surface hardening of only the most loaded lateral surface of the tooth.

The region into which the energy contribution is made has the form of a strip of limited width, located so that the midline of this strip coincides with the line that the tops of the saw teeth form when re-grinding it during operation (Fig. 1).

After the heating is turned off, rapid cooling of the heated areas is carried out by thermal conductivity (due to heat removal to unheated areas of the metal) and radiation from the surface. These mechanisms provide high cooling rates and, as a result, effective hardening modes [A.S. Vasiliev. High intensity induction heating. Electricity. 2001. No. 12].

For efficient operation, the saw teeth are “bred” (deviated from the vertical axis of the saw). Depending on the manufacturer and the sawing conditions, the teeth of the band saws are bred to values up to 0.4 mm, either each tooth in turn in different directions, or through one tooth. As a result, the main load falls on a part of the tooth lateral surface (region 1 in FIG. 2). These parts should have the greatest hardness. Moreover, the fact that the rest of the tooth is not hardened significantly reduces the likelihood of brittle tooth decay when it enters solid inclusions during sawing. Considering that only part of the tooth surface should have the highest hardness, only this part can be hardened, and the depth of the hardened layer (g) should be selected from the relation g = K1 · A, where K1 is the coefficient = 0.01-1.0; h is the thickness of the band saw. The depth of the hardened layer will be from 0.01 mm (purely surface hardening of the most loaded part of the tooth) to 1 mm (through hardening of the tooth and strip).

Under the most severe conditions, the cutting edge of the tip of the saw tooth “works”. Due to the fact that this edge is dull, the saw must be sharpened periodically. Those. in order to increase the service life of the saw between the grindings, it is necessary to harden a narrow strip of the tooth and the body of the saw, on which the tip of the tooth falls when it is re-grind. During hardening, it is possible to obtain a smooth transition from harder to less hard layers. For example, in the case of the use of HDTV, to obtain such an effect, it is enough that in the zone where it is necessary to obtain a higher hardness, the inductor - part distance would be less than for areas with lower hardness [A.S. Vasiliev. High intensity induction heating. Electricity. 2001. No. 12]. During the sawing process, such hardening will ensure uniform wear of the entire tooth (harder areas “work” under more severe conditions, relatively less hard areas in less severe conditions). With uniform wear during operation, the shape of the tooth remains unchanged, which significantly increases the time between periodic sharpening of the saw.

In order to confirm the possibility of obtaining a hardened area with the parameters proposed in the application, and the effectiveness of the proposed method, a set of experimental studies was carried out.

In these studies, the simultaneous hardening of the strip was carried out using pulsed heating by high-frequency currents (HDTV). For heating, we used a VChG1-25 / 0.44 tube generator operating at a frequency of 440 kHz and a specially manufactured inductor with magnetic field concentrators. The heating time and operating modes of the generator were determined experimentally in such a way as to obtain a hardened strip with a length of 15 mm and a width of 2.5 mm.

During the pause between pulses, which was 2 s (a pause is necessary in order to move the saw by one tooth), the hardened area managed to cool to a temperature of 150 ± 20 ° C (the temperature was measured using a Fluke 65 infrared thermometer, the sensor of which was located at an angle 90 ° to the plane of the saw). No additional tempering tempering was carried out in the experiments.

Under the experimental conditions described above (measurements were carried out at 6 arbitrary points on the side surface of the saw, on a section of length L and width b (Fig. 1) in five randomly selected quenching bands), it was possible to provide

1) the deviation of the linear dimensions of the hardening region, not exceeding 5% of their average parameters;

2) almost uniform hardness in the hardening zone (63-64 HRC). In the area adjacent to the quenching zone (1-1.5 mm around the strip), a decrease in hardness was observed compared to non-quenched material (54-55 HRC). In the rest of the saw body, hardness remained unchanged (58-59 HRC).

Experimental studies of the obtained samples of band saws in the technological cycle of a woodworking enterprise showed that hardened samples compared with samples hardened by traditional technology have the following advantages.

- Significantly longer saw life (~ 2 times). The increase in the service life of a periodically sharpened saw is achieved due to the fact that the working part of the tooth is hardened all the time the saw is working up to the limit of its strength.

- A significant decrease in the likelihood of brittle fracture of a hardened tooth when it enters solid inclusions in wood. This advantage is due to the fact that the hardened working area of the tooth is surrounded by not hardened, and therefore, more ductile metal.

- Greater elasticity of the saw blade, which allows the saw to return to its normal state after bending in the machine pulley and reducing beating during sawing (manifests itself in better cut quality).

Claims (6)

1. The method of hardening saws, including the formation of hardened sections in the form of strips at the location of the teeth by heating and cooling due to the heat of the heated sections in the unheated area of the saw with the provision of the re-sharpening of the teeth, characterized in that the width of the strip to be tempered is selected from the ratio: b = K · A, where K is the coefficient = 0.05-0.3; A is the distance between the tips of the teeth, mm, and the length of the metal strip heated for quenching (b) is selected from the ratio: L = R · H, where R is the coefficient = 0.5-30.0; H - tooth height, mm, and the location of the strip is chosen to ensure the location of the top of its teeth in the hardened strip during re-grinding of the saw during its operation. 2. The method according to claim 1, characterized in that the heating is carried out by high-frequency currents or by laser radiation, or by the action of a gas stream. 3. The method according to claim 1, characterized in that the simultaneous pulse heating of the strip. 4. The method according to claim 1, characterized in that the heating is conducted by high-frequency currents, which is selected from the ratio: f∈ {0,5 · f ₀ , 9 · f ₀ }, where f ₀ = ρ · 2 / (μ ₀ · h ² ), where ρ is the resistivity of the heated saw material at the quenching temperature; μ ₀ is the magnetic permeability of steel at a quenching temperature; h is the thickness of the body of the saw. 5. The method according to claim 1, characterized in that the hardening at the location of the teeth in the form of a strip is carried out with maximum hardness on the axis of the tooth and a decrease in hardness to the edges of the tooth. 6. The method according to claim 1, characterized in that the depth of the hardened layer (g) is selected from the ratio: g = K1 · h, where K1 is the coefficient = 0.01-1.0, h is the thickness of the saw body.

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