RU2779978C1 - Method for manufacturing the tooth of the excavator bucket - Google Patents

Abstract

FIELD: excavator structural elements.

SUBSTANCE: invention relates to structural elements of excavators and other earth-moving machines. As a result of intense high-temperature plastic deformation in combination with rapid cooling, the metal of the lower half of the tooth, which is subject to the greatest wear, receives an increased intensity of plastic deformation, which remains during cooling and hardening, which ensures that this half of the tooth is given wear resistance that exceeds the wear resistance of the upper half, as a result of which both halves of the tooth during operation, they will wear out at the same speeds with the tooth retaining its original shape, i.e. the effect of self-sharpening of the tooth will be provided.

EFFECT: increasing the wear resistance of the tooth and reducing energy consumption for rock excavation.

1 cl, 9 dwg, 1 tbl

Description

The invention relates to structural elements of excavators and other earth-moving machines.

There is a known method for casting excavator teeth (patent RU No. 2048255, publ. 11/20/1995), which consists in pouring steel into a mold and controlled cooling of one or two side surfaces of the tooth, in which the cooling rate increases by 2.5-10 times compared to normal cooling rate of the end surfaces, to increase wear resistance and ensure the effect of self-sharpening of the tooth during operation.

The disadvantage of this method is the low hardness and wear resistance of the cast tooth compared to the teeth made by stamping.

A known excavator bucket tooth and a method for its manufacture (patent RU No. 2269628, publ. 06/10/2004), which consists in increasing the service life and the effect of self-sharpening due to the location in the steel casting of the tooth on one of its surfaces of small parts made of wear-resistant cast iron, protecting the steel base from intense abrasive wear.

The disadvantage of this method is the low resistance of wear-resistant cast iron to impacts that occur during operation of the excavator bucket tooth, which can lead to the destruction of parts made from it.

A method of manufacturing a tooth of an earth-moving machine is known (RU No. 2228409, publ. 05/10/2004), which consists in connecting individual elements of the tooth, made of various wear-resistant materials, sequentially one into the other by welding.

The disadvantage of this method is the occurrence of post-welding stresses in the tooth, which can lead to premature destruction of the tooth during operation.

There is a known method for manufacturing bucket teeth of a mining excavator (CN patent No. 105483344 A, publ. 04/13/2016), which consists in a certain process of heat treatment of tooth castings, consisting of: heating the teeth to 940 ° C at a speed of 200 ° C / h and holding at this temperature 3-4 hours, cooling to 630-650°C at a rate of 150°C/h and holding at this temperature for 30-50 minutes, cooling to 300-320°C and holding in an oven with a salt bath for 150 minutes, followed by cooling on air.

The disadvantage of this method is the need to use complex thermal equipment that provides heating and cooling of the tooth at a given rate in three stages of its heat treatment.

A known method for manufacturing an excavator bucket tooth (CN patent No. 107663614 A, publ. 02/06/2018), which consists in sequential casting of a tooth holder and tooth head from alloys of a certain composition, subsequent heat treatment and welding of two components using an electrode made of cast iron with a high chromium content .

The disadvantage of this manufacturing method is the occurrence of post-weld stresses in the tooth, which can lead to premature tooth failure during operation.

A known method for manufacturing an excavator bucket tooth (CN patent No. 106311945 A, publ. 01/11/2017), which consists in heating a cylindrical billet with certain geometric parameters to a forging temperature, a preliminary forging stage, to give the billet approximate geometric shapes and final, where using special dies form the final shape of the tooth, and subsequent heat treatment, which ends with stepwise cooling, increasing the strength index on the cutting edge by 12-14% relative to the rest of the tooth.

The disadvantage of this method is the need to use stamps of complex geometric shapes, the manufacture of which requires specialized equipment.

A known method for manufacturing an excavator bucket tooth (CN patent No. 104002099 A, publ. 08/27/2014), taken as a prototype, consisting in heating an iron ingot, forging, consisting of a preliminary stage, to give the workpiece approximate geometric shapes and a final one, where the final shape is formed teeth, marking, normalization and heat treatment.

The disadvantage of this method is that when it is used, products are obtained in which the upper and lower halves of the tooth have the same wear resistance, which leads to faster wear of the lower half of the tooth and its blunting during operation, accompanied by an increase in energy consumption for rock excavation.

The technical result is to increase the wear resistance of the tooth and reduce energy consumption for rock excavation.

The technical result is achieved by the fact that at the preliminary stage of forging the workpiece is shaped into a pentagonal straight prism, the height of which coincides with the width of the tooth, and the base is made of two parts, one of which is in the form of a right triangle with an angle at the apex equal to half the angle of sharpening of the tooth α repeats the shape of the upper half of the tooth and with the opposite leg H, which is equal to half the height of the tooth; axis of the tooth at an angle β, which determines the ratio of deformations of the upper and lower parts of the forging, and its value is determined by the formula:

β = (1.0-2.7) ⋅ α,

the values of the angle β and the length l are interrelated, and provide conditions for the equality of the volumes of the upper and lower parts of the future forging, while the length l is determined by the formula:

where k _region is the coefficient that compensates for the loss of metal during stamping, depending on the value of the angle β, is calculated by the formula:

The method is illustrated by the following figures:

fig. 1 - general view of the excavator bucket tooth;

fig. 2 - general view of the proposed casting blank;

fig. 3 - General view of the forging of the tooth after the preliminary stage of forging;

fig. 4 - distribution of the intensity of plastic deformation of the metal over the cross section of the forging of the tooth, established using computer simulation at β = 25°;

fig. 5 - values of deformation of the upper part of the forging depending on the angle of inclination β;

fig. 6 - values of deformation of the lower part of the forging depending on the angle of inclination β;

fig. 7 - average ratios of deformations of the upper and lower parts of the forging depending on the angle of inclination β;

fig. 8 - the volume of metal flowing into the flash groove of the stamp;

fig. 9 is a graph of the dependence of the loss of relative mass of samples with different degrees of hardness on the test time, where:

1 - angle of sharpening of the tooth;

2 - tooth length;

3 - axis of symmetry of the tooth;

4 - tooth width;

5 - tooth height;

6 - landing cavity;

7 - prism height;

8 - the length of the smaller base of a rectangular trapezoid;

9 - the angle between the inclined side of the trapezoid and the axis of the tooth;

10 - half of the angle of sharpening of the tooth;

11 - the larger base of a rectangular trapezoid;

12 - height of a rectangular trapezoid;

13 - half the height of the tooth.

The method is carried out as follows. For the manufacture of an excavator bucket tooth, with a tooth sharpening angle 1 (Fig. 1), a tooth length 2, a tooth width 4, a tooth height 5, a tooth symmetry axis 3 and a seating cavity 6, a workpiece in the form of a pentagonal prism is made by casting, where the height of the prism is 7 (Fig. 2), coincides with the width of the tooth 4. The base of the prism is a combination of two geometric shapes. The first is a rectangular triangle that repeats the shape of the section of the upper half of the tooth with an angle at the apex equal to half the angle of sharpening of the tooth 10 and with the opposite leg equal to half the height of the tooth 13. The second is a rectangular trapezoid with a smaller base 8 and a larger base 11 equal to the length of the tooth 2 , in contact with the large leg of a right triangle along the axis of symmetry of tooth 3. The inclined side of the trapezoid is located to the axis of symmetry of tooth 3 at an angle between the inclined side of the trapezoid and the axis of tooth 9, the value of which is determined from the equality:

where β is the angle between the inclined side of the trapezoid and the axis of the tooth

Since the value of the angle between the inclined side of the trapezoid and the axis of the tooth 9 and the length of the smaller base of the rectangular trapezoid 8 are interrelated and are determined from the condition of ensuring equality of the volumes of the upper and lower parts of the future forging, the length of the smaller base of the rectangular trapezoid 8 is calculated by the following formula:

where l is the length of the smaller base of the rectangular trapezoid;

L is the length of the tooth;

H - half the height of the tooth.

Since the geometric dimensions of the upper part of the workpiece form an insufficient volume to fill the stream with a punch due to the fact that part of the workpiece metal flows into the flash groove of the stamp, depending on the angle of inclination, length 8 is multiplied by the metal loss compensation coefficient per flash k _reg , determined by the formula:

Then the billet is placed in a furnace, where it is heated to the optimal initial forging temperature T ₁ , characteristic for each steel grade. Heating time t ₁ in hours from 0°C to temperature T ₁ is calculated by the formula:

where D is the height of the workpiece, m;

k is a factor equal to 10 for iron and mild steel and 20 for high alloy steel.

This is followed by a preliminary forging stage, at which the workpiece is removed from the furnace and, in a heated state, is forged on a stamping machine or a forging press with the acquisition of the external outline of the finished excavator bucket tooth, with the tooth sharpening angle 1 (Fig. 3), tooth length 2, axis of symmetry tooth 3, tooth width 4 and tooth height 5. Using a specially designed geometric shape of the workpiece, the flow of its material at this stage of forging leads to the formation in the volume of the upper half of the forging of a zone of increased intensity of plastic deformation of the metal, which is established using computer simulation in Fig. four.

At the final stage of forging, a cavity is formed in the workpiece, which is a seat for connection with the excavator bucket, and the volume of metal squeezed out of the cavity is cut off with the tooth acquiring its final shape.

After that, the forging is removed from the die cavity and subjected to hardening by immersion in a coolant.

Then low-temperature tempering is performed at a temperature of 150-200°C for a time t ₂ calculated by the formula:

where t ₂ - the duration of low-temperature annealing, min;

δ - time in minutes, taken equal to the height of the workpiece, expressed in mm.

After the heat treatment is completed, the tooth goes through the stages of sandblasting, in order to remove oxidation products from the surface, and flaw detection, which searches for defects on the tooth surface.

As a result of intense high-temperature plastic deformation in combination with rapid cooling, the metal of the lower half of the tooth, which is subject to the greatest wear, receives an increased intensity of plastic deformation, which persists during cooling and hardening, which ensures that this half of the tooth is given wear resistance that is 1.5–1.7 times higher than wear resistance of the upper half, as a result of which both halves of the tooth during operation will wear out at the same speed while maintaining the tooth of its original shape, i.e. the effect of self-sharpening of the tooth will be provided.

The method is illustrated by the following example.

It is required to make an excavator bucket tooth, with a tooth width 4 = 150 mm, a tooth length 2 = 525 mm, a tooth height 5 = 292 mm, a tooth sharpening angle 1 = 30°C and a mounting hole 6.

For the manufacture of an excavator bucket tooth, a workpiece is made by casting, from steel 110G13L, as a material widely used for the manufacture of excavator bucket teeth, in the form of a pentagonal prism with a prism height of 7 = 150 mm. The base of a prism is a combination of two geometric shapes. The first one is a rectangular triangle repeating the shape of the upper half of the tooth with an angle at the apex equal to half the angle of sharpening of the tooth 10 = 15°C and with an opposite leg equal to half the height of the tooth 13 = 146 mm. The second is a rectangular trapezoid with a smaller base 8 and a larger base 11, equal to the length of the tooth 2 = 525 mm, in contact with the large leg of the right triangle along the axis of symmetry of the tooth 3. Since, based on the experiments carried out, the results of which are presented in Fig. 5 - fig. 7, the value of the angle 9 between the inclined side of the trapezoid and the axis of the tooth 9 determines the ratio of deformation of the upper and lower parts of the forging, then to ensure the greatest difference between the degree of deformation of both parts of the forging and, as a result, a uniform wear rate of the tooth, the angle is assumed to be 25°.

In connection with the analysis of metal losses during the stamping process, the result of which is shown in Fig. 8, the geometric dimensions of the upper part of the blank form an insufficient volume to fill the punch groove due to the loss of the volume of the blank metal, which flows into the flash groove of the die. The metal loss compensation coefficient for flash is calculated by formula 3 and is assumed to be 0.875. Thus, the value of the length of the smaller base of the rectangular trapezoid 8 is 291.85 mm.

Then the billet is placed in a furnace, where it is heated to the optimum initial forging temperature T ₁ , which for steel 110G13L is 1150°C. Heating time t ₁ in hours from 0°C to temperature T ₁ is calculated by the Dobrokhotov formula and is:

This is followed by a preliminary forging stage, at which the workpiece is removed from the furnace and, in a heated state, is forged on a stamping machine or a forging press with the acquisition of the external outline of the finished excavator bucket tooth, with the tooth sharpening angle 1 (Fig. 3), tooth length 2, axis of symmetry tooth 3, tooth width 4 and tooth height 5.

With the help of a specially designed billet shape, the flow of its metal at this stage of forging leads to the formation of a zone of increased intensity of metal plastic deformation in the upper half of the tooth.

At the final stage of forging, a cavity is formed in the workpiece, which is a seat for connection with the excavator bucket, after which the volume of metal squeezed out of the cavity is cut off with the tooth acquiring its final shape.

After that, the forging is removed from the die cavity and subjected to hardening by immersion in a coolant (water).

After that, low-temperature tempering is carried out at a temperature of 200 ° C for a period of time

After completion of the heat treatment, the hardened tooth goes through the stages of sandblasting, in order to remove oxidation products from the surface, and flaw detection, which searches for defects on the tooth surface.

From a comparison of the results presented in table. 1 and FIG. 9, testing samples of steel 110G13L for abrasive wear resistance during wear on a highly abrasive artificial rock - electrocorundum, it can be seen that high-temperature deformation of steel before hardening contributes to an increase in its wear resistance, which increases with an increase in the intensity of deformation, the degree of hardening, α: for a sample deformed with maximum intensity, sample No. 2 α = 2.25 compared with No. 5 α = 0, this parameter increases by 66%, 0.48 mm ² min/mg compared to 0.29 mm ² min/mg.

Table 1 - Results of testing for abrasive wear resistance of steel samples 110G13L after various heat treatment methods Sample No. Processing method UKov degree, α ΣΔm/S, mg/mm ² for time t, min 0.5 one 1.5 2 2.5 3 3.5 one Hardening from forging temperature 2.25 2.20 3.86 5.62 6.97 8.32 9.60 10.74 2 Hardening from forging temperature 2.25 2.12 3.74 5.08 6.09 7.13 8.12 8.88 3 Hardening from forging temperature 1.56 2.18 3.80 5.36 6.72 8.65 9.97 11.23 four Hardening from forging temperature 1.56 2.01 3.37 5.05 6.68 7.96 9.12 10.34 5 Heating and holding at 1150°C followed by quenching - 2.17 4.06 5.91 7.87 9.66 10.99 12.77 6 Heating and exposure at 1150°C followed by hardening - 2.09 3.84 5.73 7.28 8.94 10.62 12.10

Thus, as a result of intense high-temperature plastic deformation in combination with rapid cooling, the metal of the lower half of the tooth, which is subject to the greatest wear, receives an increased intensity of plastic deformation, which persists during cooling and hardening, which ensures that this half of the tooth is given wear resistance exceeding the wear resistance of the upper half, as a result, both halves of the tooth during operation will wear out at the same speeds with the tooth retaining its original shape, i.e. the effect of self-sharpening of the tooth will be provided.

Claims (6)

A method for manufacturing an excavator bucket tooth, which includes heating the workpiece, forging, consisting of a preliminary stage to give the workpiece the necessary geometric shape and a final stage, where the final shape of the tooth is formed, and heat treatment, characterized in that at the preliminary stage of forging the workpiece is shaped into a pentagonal straight prism, the height of which coincides with the width of the tooth, and the base is made of two parts, one of which is in the form of a right triangle with an angle at the apex equal to half the angle of sharpening of the tooth α, repeats the shape of the upper half of the tooth, and with the opposite leg H, which is equal to half the height of the tooth , the second - in the form of a rectangular trapezoid with a smaller base l and a large base L, which is equal to the length of the tooth in contact with the first part along the axis of symmetry of the tooth, and the inclined side of the trapezoid is located to the tooth axis at an angle β, which determines the ratio of deformations of the upper and lower parts forgings, and its value is determined by the formula β = (1.0-2.7) ⋅α, the values of the angle β and the length l are interrelated and provide conditions for the equality of the volumes of the upper and lower parts of the future forging, while the length l is determined by the formula

where k _reg is the coefficient that compensates for the loss of metal during stamping, depending on the value of the angle β, is calculated by the formula K _region = 0.005⋅β+0.75.

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