KR20220058803A - Accelerated lifetime test methods for evaluating abrasion performance of rock cutting tool by using hollow specimen - Google Patents

Abstract

The present invention relates to a method for testing durability or cutting performance of a rock cutting tool by using a hollow rock specimen. In addition, according to the present invention, the test is done by an acceleration life test, at least one of a cutting load and a cutting speed is increased, a reliability life is defined as a reliable excavation amount instead of a concept of a reliable time, and a failure-free acceleration test method is designed and provided.

Description

Accelerated lifetime test methods for evaluating abrasion performance of rock cutting tool by using hollow specimen}

The present invention relates to a method for performing an accelerated life test for durability or cutting performance of a rock cutting tool with a hollow rock specimen.

Specifically, the present invention relates to (i) a rock cutting tool test method for forming an Archimedes spiral trajectory on a hollow specimen at a constant speed by the cutting tool to perform the pin-on-disk test specified in ASTM, (ii) ) This test is an accelerated life test by increasing the cutting load and/or cutting speed, but instead of the reliable time concept, the reliable life is defined as a reliable excavation concept, and a failure-free accelerated test is designed and provided.

In general, for rock/resource cutting tools installed in rod headers, continuous miners, and TBMs, their durability performance is directly related to work efficiency.

However, no standard test method or an official test method for quantitatively evaluating the durability performance of a rock cutting tool has been proposed so far. ASTM (American Society for Testing and Materials) discloses a pin-on-disk test and a pin-on-drum test. These two tests test metal-to-metal abrasion, so It is not suitable for direct application.

As shown in FIG. 1 , in the pin-on-disk test, in a state in which a disk-shaped specimen is rotating about a vertical axis, the pin moves in a straight line in the radial direction to generate wear. For the pin-on-disk test, the cutting tool must form an Archimedean spiral trajectory at a constant speed (constant velocity) on the upper surface of the specimen.

However, ASTM does not specifically describe the motion equations and control methods of pins and specimens, only the basic principles and drawings for the wear test method of metal specimens. The control method, the equation of motion, and the data extraction method are not specifically described.

The present invention has been proposed to solve this problem, and in order to perform the pin-on-disk test stipulated in ASTM on a hollow specimen, the control equation for the cutting tool to form the Archimedes' helical trajectory at a constant speed is newly developed. It aims to propose and provide a test method for rock cutting tools using this control equation.

Another object of the present invention is to make this test an accelerated life test by increasing the cutting load and/or cutting speed, but use the reliable excavation concept instead of the reliable time concept in reliability engineering to define the reliable life, and accelerate without failure To design and provide test methods.

In order to solve the problems described in [Technical Background of the Invention], as shown in FIG. 2, the present applicant has an Archimedean spiral while a cutting tool moves at a constant speed on a solid-type rock specimen (a solid rock specimen). A control equation for forming a trajectory was proposed and a test method using it was developed.

In the test method, the cutting tool 10 moves linearly from the center of the upper surface 3 of the rock specimen 1 to the outside or from the outside to the center while the rock specimen 1 is being rotated with respect to the rotation shaft 112 . The rock specimen (1) is cut while moving linearly, and accordingly, a spiral-shaped trajectory is formed on the upper surface (3).

Specifically, the rotational force of the driving motor 110 is transmitted to the specimen fixing unit 130 through the rotation shaft 112 , and accordingly, the rock specimen 1 is rotated. The cutting tool 10 is pressed by a load unit (not shown in the drawing) or moved linearly from the center of the rock specimen 1 to the outside (arrow direction) in a state in which the displacement is adjusted, or from the outside of the rock specimen 1 It moves linearly to the center, or repeatedly moves back and forth between the center and the periphery. The linear movement of the cutting tool 10 may be performed by a linear movement unit (not shown in the drawing).

In the test method, the radius (R) of the outermost part of the helix, the time it takes for the cutting tool 10 to complete one movement along the helix trajectory (T), and the number of helixes (N) are input from the user. The trajectory of the helix, the distance from the center to the cutting tool (r), the rotation angle (θ) of the rock specimen 1, the distance L the cutting tool 10 moves along the helix trajectory, and the cutting tool 10 ) is calculated using the following equation to calculate the speed (V _L ) at which it moves along the helical trajectory. 3 shows the definition of the radius (r) and rotation angle (θ) of the spiral.

Then, when the cutting tool 10 is linearly moved in the radial direction using the calculation result and the rock specimen is rotated, the cutting tool 10 forms an Archimedes spiral trajectory on the upper surface 3 at a constant speed. In this case, the interval between the spiral trajectories is constant. 4 shows the Archimedean spiral trajectory formed by the cutting tool in the case of an outward spiral.

[Equation 1]

[Equation 2]

In the above formula,

t: time, R: radius of the outermost part of the helix, N: number of helices,

θ(t): rotation angle of the rock specimen,

T: Time it takes for the cutting tool to move from center to edge or from edge to center along the helical trajectory.

However, since a lot of trigonometric functions for time (t) are included in Equations 1 and 2, it is impossible to calculate the radial speed and rotation speed that satisfy the constant speed through simple inverse calculation (equation solving) (that is, It is impossible to calculate an exact solution of a differential equation).

On the other hand, in order to increase the scanning quality in the fields of atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM), a method for moving the Archimedean spiral at a constant speed (Constant Linear Velocity, CLV) has been developed. It has been studied as follows.

According to the research results, in the outward path from the inside of the circle, the spiral radius (r) and the rotation angle (θ) can be expressed as Equations 3 and 4 below.

[Equation 3]

r(t) = R f(t _* )

[Equation 4]

θ(t) = 2πN·f(t _* )

In the above formula, t _* : t/T

f(t _* ): When the cutting tool moves linearly from the center to the outer edge of the rock specimen, f(t _* ) is an arbitrary function satisfying f(0)=0 and f(1)=1. When the cutting tool moves linearly from the outer to the center of the rock specimen, f(t _* ) is an arbitrary function satisfying f(0)=1 and f(1)=0.

를 제안하고 내향 나선(inward spiral)인 경우

를 제안한 바 있다. In the above study (thesis), in the case of an outward spiral

is proposed and in the case of an inward spiral

has been proposed

를 식 3, 4에 대입하고 t에 대해 미분하면 아래 식 5, 6을 얻을 수 있다.

By substituting in Equations 3 and 4 and differentiating with respect to t, Equations 5 and 6 below can be obtained.

Equation 5 shows the linear movement speed of the cutting tool in the case of an outward spiral. However, when t=0, for example, when 0≤t≤1, the linear movement speed becomes excessively large, so a constant linear movement speed may be input to the test apparatus during an actual test.

And, Equation 6 shows the rotational speed of the rock specimen in the case of an outward spiral. However, at the start stage of the test near t=0 (for example, when 0≤t≤0.1 seconds), the rotational speed temporarily increases excessively and then converges to a constant speed. . This part is an error of the approximation solution, but it occurs locally within 0.1 second, so it is a negligible error.

를 식 3, 4에 대입하고 t에 대해 미분하면 아래 식 7, 8을 얻을 수 있다. 도 5는 inward spiral인 경우에 절삭 공구가 형성하는 아르키메데스 나선 궤적을 보여준다. On the other hand, in the case of an inward spiral,

By substituting in Equations 3 and 4 and differentiating it with respect to t, Equations 7 and 8 below can be obtained. 5 shows the Archimedean spiral trajectory formed by the cutting tool in the case of an inward spiral.

[Equation 7]

[Equation 8]

Equation 7 shows the linear movement speed of the cutting tool in the case of an inward spiral. However, when t = T, for example, when T = 100 sec, when 99.9 sec ≤ t ≤ 100 sec, the linear movement speed becomes excessively large and converges at a constant speed, so the user must consider this when processing data. However, this is also an error that occurs for a very short time and is negligible by the user.

As described above, the present applicant proposed a control equation for a cutting tool to move at a constant speed while forming an Archimedean spiral trajectory on a solid-type rock specimen, and developed a test method using the same. This test method has the advantage that the test is simple and the test time can be saved compared to the conventional linear cutting test (for example, disclosed in Korean KR 701979 B1, etc.).

However, the test method has a problem in that it is difficult to control the cutting depth of the cutting tool in the center of the specimen. That is, as shown in FIG. 6 , in the case of an inward spiral, the cutting depth of the cutting tool is adjusted from the outside of the specimen (d ₁ , d ₂ , etc.) and then the cutting depth can be adjusted because it enters the outside of the specimen, but at the center of the specimen, the cutting tool It is difficult to control the depth of cut of

In addition, as shown in FIG. 7 , when the cutting proceeds to a certain depth or more, there is also a problem in that the tool frame and the central portion of the specimen interfere (collide).

In order to solve this problem, the present applicant newly proposed a control equation for the cutting tool to form an Archimedes spiral trajectory at a constant speed on a hollow specimen (a specimen with an empty space in the center), and developed a test method using it. . In addition, this test was performed as an accelerated life test by increasing the cutting load and/or cutting speed, but a test method was also developed to calculate the failure-free accelerated excavation volume using the reliable excavation amount instead of the reliable life span.

The present invention has the following effects.

First, it is possible to solve the problem that occurs when a wear test of a rock cutting tool is performed on a solid type rock specimen. That is, a new control equation is proposed for a rock cutting tool to form an Archimedes spiral trajectory at a constant speed on a hollow specimen, and a test method using this is provided.

Second, this test is an accelerated life test by increasing the cutting load and/or cutting speed, but instead of the reliable time concept, the reliable life is defined as a reliable excavation amount, and a failure-free accelerated test method is designed and provided.

1 is a perspective view showing a pin-on-disk test specified in ASTM.
Figure 2 is a perspective view showing a rock wear test using a solid-type rock specimen.
3 is a view showing the definition of a helix radius (r) and a rotation angle (θ) in an Archimedean spiral.
4 is a graph showing a trajectory when the cutting tool moves from the center of the solid-type rock specimen to the outside (hereinafter referred to as an outward spiral) along the Archimedean spiral.
5 is a graph showing the trajectory of the cutting tool moving from the outer to the center of the solid-type rock specimen (hereinafter referred to as an inward spiral) along the Archimedean spiral.
Fig. 6 is a cross-sectional view showing the adjustment of the cutting depth in the case of forming an inward spiral trajectory in a solid-type rock specimen.
7 is a view showing interference (collision) between the center part of the rock specimen and the tool frame as cutting proceeds when a cutting test is performed on a solid-type rock specimen.
8 is a perspective view showing an example of a hollow specimen used for a cutting test according to the present invention.
9 is a view showing an inward spiral path (left) and an outward spiral path (right), respectively, when there is a separation distance (R _offset ).
10 is a view showing an inward spiral formed in a hollow specimen (left), an outward spiral formed in a hollow specimen (middle), and a slope discontinuity (right) at a point connecting from the inward spiral to the outward spiral, respectively.
11 is a graph showing regions of s and R such that the difference in inclination between the two helices is less than 1° at the connection point of the inward helix and the outward helix.
12 is a view showing a pick cutter installed on a cutting head and a cutting track;
13(a) and 13(b) are views showing the length (Lc) of the outline of the cutting head and the distance (s) between the pick cutters, respectively;
14 is a view showing a press-fitting depth during a thumbing operation.
15 is a view showing a working speed and an indentation depth during a shearing operation.
16 is a graph showing a ratio (Rt) of a contact time according to a cutting depth (y) during a shearing operation.
17 is a graph showing the relationship between the cutting depth (d) and the cutting force (Fc).
18 is a graph showing changes in cutting load (Fc) and vertical load (Fn) according to uniaxial compressive strength (UCS).

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention. Accordingly, the embodiments described in the present specification and the configurations shown in the drawings are merely embodiments of the present invention and do not represent all the technical spirit of the present invention, so various equivalents that can be substituted for them at the time of the present application It should be understood that there may be variations and variations.

1. Pin-on-disk test of hollow rock specimens

(1) Why is a hollow rock specimen necessary?

The problems with solid-type rock specimens and the reason for the need for hollow-type rock specimens have been described in [Means of Solving the Problem], so their description will be omitted here.

(2) Definition of new eigen constant (R _offset )

8 is a perspective view showing an example of a hollow specimen used for a cutting test according to the present invention. As shown in the figure, a hollow (empty space) is formed in the vertical direction in the center of the hollow specimen.

In the cutting test, after the nth wear is finished, the n+1th wear should be performed after adjusting the depth of cut. At this time, the deviated radial length is defined as R _offset .

On the other hand, in the present invention, a motor (not shown in the drawing) is used to rotate the rock specimen, but it takes time to accelerate the motor, so the set constant velocity cannot be satisfied from the start of the test. For this reason, it is necessary to secure the acceleration section by setting R _offset as the acceleration section. In FIG. 8 , acceleration times corresponding to R _offset are t ₁ -t ₀ and T - t ₂ . The wear test can be performed after reaching the constant speed only when the acceleration time is sufficiently set by comparing this acceleration time with the specifications of the motor.

(3) Arrangement of variables according to specimen shape

The test parameters for the Archimedean spiral test (pin-on-disk test) on hollow rock specimens are summarized below.

R: Outer diameter of hollow specimen [mm]

R ₀ : inner diameter of hollow specimen [mm]

R _offset : The length of the cutting tool (pick cutter, etc.) out of the hollow specimen [mm] or the length of the cutting tool moving into the hollow.

t ₀ : Time taken for the cutting tool to move from the center of rotation of the hollow specimen to (R ₀ - R _offset ) [s]

t ₁ : Time taken by the cutting tool to move from the center of rotation of the hollow specimen to R ₀ [s]

t ₂ : time taken by the cutting tool to move from the center of rotation of the hollow specimen to R [s]

T = T _total : Time taken by the cutting tool to move from the center of rotation of the hollow specimen to (R+R _offset ) [s]

T _move : The time taken for the cutting tool to actually move during the cutting test. That is, the time it takes to move from (R ₀ - R _offset ) to (R + R _offset ) [s]

T _test : Actual wear test time of hollow rock specimen (time in contact with specimen, t ₂ - t ₁ ) [s]

N (= N _total ): Mathematically, the total number of spirals generated from the center of the specimen to (R + R _offset ).

N _move : Number of spirals actually realized during the cutting test

N _test : the number of spirals formed in the area where the cutting tool comes into contact with the hollow rock specimen

s: spacing between spirals [mm]

v : the resultant velocity of the helix movement of the cutting tool [mm/s]. That is, the speed at which the cutting tool moves along the helix.

In this test, there are five eigen constants defining the Archimedes spiral test, and the rest of the test variables are dependent constants calculated by the eigen constants.

(4) Eigen constant relational expression theorem

The relationship between the dependent constant and the eigen constant is calculated by the following equation. The total number of spirals (N=N _total ), the number of actual moving spirals (N _move ), and the number of spirals actually formed in contact with the specimen (N _test ) can be calculated as follows.

The relation to the travel time variable can be calculated as follows.

The travel distance variables can be calculated as follows.

Here, L _inwtotal , L _inwtest , L _outwtotal , and L _{outwtest mean} the total travel distance in the inward direction, the inward cutting test distance, the outward total travel distance, and the outward cutting test distance, respectively.

In addition, the calculation formulas of the trajectory of the inward spiral (P _xinw , P _yinw ) and the trajectory of the outward spiral (P _xoutw , P _youtw ) are as follows.

In the above formula,

P _xinw , P _yinw : Position coordinates of the cutting tool at a specific time (t) during inward testing

r _inw : radius of the cutting tool position at a specific time (t) for inward testing

θ _inw : phase angle of the cutting tool position at a specific time (t) in the inward test

P _xoutw , P _youtw : Position coordinates of the cutting tool at a specific time (t) during outward testing

r _outw : radius of the cutting tool position at a specific time (t) during outward testing

θ _outw : phase angle of the cutting tool position at a specific time (t) during outward testing

The rotary motor that rotates the rock specimen and the linear motor drive that moves the cutting tool in a straight line are both controlled by speed. Therefore, since the path calculation formula (Equations 12 to 15) expresses the current point of the cutting tool, it is necessary to convert it into linear speed and RPM by differentiating it.

Considering R _offset , the radial speed (vr _outw , vr _inw ) and RPM(RPM _outw , RPM _inw ) are as follows.

In the above formula,

Vr _outw : Radial linear movement speed of the cutting tool when moving outward

RPM _outw : Rotational speed of rock specimen when moving outward

Vr _inw : Radial linear movement speed of the cutting tool when moving inward

RPM _inw : Rotational speed of the rock specimen when moving inward

(5) Example of spiral test design

Five natural constant values of the spiral wear test were arbitrarily set as shown in the table below, and the movement path was simulated. The calculation output table of the spiral function according to 5 constants is composed as shown in Table 3.

On the other hand, when the trajectory (path) of the inward spiral is expressed as a graph, it is the same as the left graph of FIG. 9 , and when the trajectory (path) of the outward spiral is expressed as a graph, it is the same as the right graph of FIG. 9 . In FIG. 9 , a gray path indicates an entire path, and a red and blue path indicates a path actually cut.

(6) Solving the problem of discontinuous points in the spiral

10 shows a path of an inward spiral (left), a path of an outward spiral (middle), and a path in the case where an outward movement is performed after inward movement (right), respectively. In FIG. 10 , the direction of rotation of the rock specimen during inward movement and outward movement is the same. When the continuous test is performed in this way, a discontinuous point in the inclination of the helix occurs at the time when the inward-extroverted type is changed. Here, if the discontinuity angle becomes too large, problems such as applying a large load to the equipment may occur, so this should be considered when designing the test.

Empirically, the applicant has found that if the difference between the inclination of the inward movement endpoint and the inclination of the outward movement start point and the inclination difference between the outward movement endpoint and the inward movement start point are less than a specific angle (δ°), the direction change during the wear test can be smooth. found that When the specific angle is 1°, it is expressed as Equation 20 below. If the inclination difference is more than a specific angle, the connection between the spirals is not smooth, so that the motor motion changes rapidly, which is not preferable because problems such as straining the equipment may occur.

Therefore, the area maintained at less than 1° was irradiated, and the range of the specimen radius (R) value and the spiral interval (s) at that time was simulated as shown in FIG. 11(a)(b). It was investigated that the region less than 1° and the region above 1° were almost linearly separated. The inequality in this case is the same as Equation 21. Therefore, when the specific angle is set to 1°, it is safe to set the test parameters within the scope of this formula. The range of the inequality below is an example.

2. Accelerated life wear test design method

(1) Method of calculating cutting conditions

12-13 , each pick of the cutting head (an example of a cutting tool) has a different rotating track. Therefore, the designed cutting interval (s) can be estimated by dividing the total length of the track by the number of picks arranged on the cutting head. That is, the value obtained by dividing the length (Lc) of the outline of the end of the drum of the cutting head by the number of picks (n) is calculated as the cutting interval (s). For reference, '+' and 'x' in FIG. 13 indicate picks, respectively.

The indentation depth means the depth of cutting the rock per one revolution of the cutting head. The cutting operation of the cutting head can be divided into a thumbing operation and a shearing operation.

The indentation depth (d _sump ) during the thumbing operation is generally described in the operation manual of the equipment. In FIG. 14 , the x value (X1, X2, etc.) is the indentation depth per rotation (d _sump ).

As shown in FIG. 15 , the indentation depth per rotation (d _shear ) during shearing operation is calculated from the slewing or shearing speed: v _shear of the cutting head and the rotation speed (rpm). The formula for d _shear is as follows.

(2) Conversion of cutting speed

The cutting speed is determined by converting it from the designed rotational speed (rpm) or linear speed (v _l ) of the cutting head. Equation 24 is applied to this as a conversion formula between the linear speed and the rotational speed of the pick end point from the cutting head. In most cases, you can set the radius of the drum to the r value. Since the picks in the nose area, which are both ends of the cutting drum, have different positions in the radius of the drum, the r value must be set in consideration of the pick's location.

(3) Conversion of cutting distance

While the machine is running, the cutting head continues to contact the rock, but the pick only makes contact with the rock a fraction of the time. Therefore, the cutting time of the pick varies according to the contact surface and contact angle during operation. The work is divided into thumbing and shearing.

① Cutting distance during thumbing operation

You can think of a section where half of the cutting head is press-fitted from the beginning of the thumbing. The drum-type rod header has an initial contact time of 0 and the maximum depth of thumb is press-fitted to the radius of the drum (D/2=R). Therefore, since the ratio of contact time to operation time (Rt=ratio of contact time) is 50%, it can be assumed that the contact time is 1/4 times of the cutting time on average. Therefore, the cutting distance (Lc) of one individual pick can be calculated using the load header operation time (t) as shown below.

② Cutting distance during shearing operation

Most of the shearing operates the rod header while maintaining the vertical excavation depth (y) value at 1/2~1/4 or less of the drum diameter (D), except for the first shearing operation section. This is because the excavation speed is faster. The result of investigating the contact time ratio (R _t ) to the working depth ratio (y/D) of the cutting drum during shearing operation is shown in FIG. 16 . If this is linearly regressed, the following Equation 26 is obtained, and accordingly, the total shearing cutting distance according to the working time (t) is calculated as Equation 27. (Here, the maximum value of R _t is 0.5.)

(4) Cutting load accelerated life test method

① How to adjust the depth of cut (d)

It is known that the cutting force (Fc) increases linearly as the depth of cut increases in the same rock. Therefore, the accelerated life test can be designed by adjusting the cutting depth (d) to increase the cutting load. Since the cutting force is also 0 when d = 0, it is reasonable to assume that the y-intercept of the linear regression equation is 0. Therefore, the cutting load according to the indentation depth can be predicted with the following linear function. Here, a is the slope of the linear function and is a coefficient calculated through experiments.

The road header can excavate up to the initial area of hard rock. Therefore, the data were analyzed by setting the weakest soft rock as 10 MPa as the compressive strength and the initial area of hard rock at 100 MPa. The minimum-maximum range of the slope was 3 to 11, as shown in FIG. 17 .

② Method of integrating rock properties and cutting depth

There is a method to increase the accelerated life by increasing the physical properties of the rock to be cut. In general, since the uniaxial compressive strength (UCS) of a rock is a representative physical property, the accelerated life wear test can be performed by raising the UCS. Here, if UCS and d are selected as input variables and cutting force (Fc) is selected as output, their relationship can be regressed to a specific function. A typical example of the regression equation is as follows. Here, Fc = cutting load, UCS = uniaxial compressive strength, d = depth of cut, and a, b, m, and n are coefficients of the regression equation, respectively.

The power function of Equation 30 is more accurate, but for convenience, a linear function such as Equation 29 is often used. In this equation, the coefficient values of a and b can be determined to complete a model that increases the cutting load. Through this, the accelerated life test can be designed. According to the experimental results of an existing study (Bilgin, 2006), it has been reported that a=0.83, b=21.8, m=2.3, n=0.8 in the range from soft rock to hard rock (N. Bilgin et al.). ., Dominant rock properties affecting the performance of conical picks and the comparison of some experimental and theoretical results International Journal of Rock Mechanics & Mining Sciences 43 (2006) 139.156)

The vertical load during cutting can also be estimated using Equation 31 below. In the case of vertical load, it has been reported that n=1 can be estimated. Therefore, it can be expressed by estimating one coefficient by the following linear equation (see FIG. 18 ). In other words, as the strength of the rock increases, the vertical load becomes larger than the cutting load, so it can be seen that care must be taken when performing a cutting test for hard rock or more.

③ Cutting speed acceleration test

The accelerated life test can also be performed by increasing the cutting speed. The cutting speed can be increased by increasing the tool's combined movement speed (v _Re , resultant velocity). The formula is as follows.

In the above equation, v _r is the radial linear speed of the cutting tool, and v _t is the tangential rotational speed of the tool. After all, since the combined movement speed is the final speed, the acceleration test can be designed only by converting the speed.

(5) Acceleration coefficient setting of accelerated life test

① Load of accelerated life test

(i) Equivalent load

샘플링 빈도(sampling frequency, Hz)이라고 할 때 그 등가하중 계산식은 아래와 같다.The average value of the cutting force (Fc) described above can be defined as an equivalent load. Since it is impossible to extract the average value of the cutting load with the actual vehicle test, the average value should be derived based on the data obtained through the linear or rotary cutting test. The real-time test load extracted from the cutting test is Fc(t), the number of samples: n, t ₁ : start time (sec), t ₂ : end time (sec),

When it comes to sampling frequency (Hz), the equivalent load calculation formula is as follows.

(ii) Accelerated load

The acceleration load (Fc _a ) is a value determined during test design, and the ratio of the acceleration load (a _F ) is calculated by Equation 34 below. Here, λ is the fatigue damage index, which is a value that defines the degree of damage versus load of each part, and is calculated by regressing the SN curve obtained through a fatigue test or fatigue analysis. For general bearings and gear parts, a value of 2.0 is used.

② Speed of accelerated life test

(i) equivalent speed

Equivalent speed means the average resultant speed of the tool in operation, and is calculated through the rotation radius and rpm of the equipment as described above.

(ii) acceleration rate

는 속도에 의한 피로손상지수이다. 속도의 차이에 따른 마모의 영향이 아직 알려지지 않은 암석절삭공구에 대해서는 1.0으로 가정한다. The ratio (a _v ) of the acceleration speed during the test is expressed as the ratio of the acceleration speed (v _a ) and the equivalent speed (v _eq ), and the formula is as follows. here

is the fatigue damage index due to speed. It is assumed to be 1.0 for rock-cutting tools for which the effect of wear due to the difference in speed is not yet known.

가 1.0이라면, 가속속도 비는 2.0이 된다. 이 때 가속속도는 반경방향속도와 접선방향 속도가 상기 제안된 수식에 따라 정확히 제어되어야 한다. The acceleration velocity (v _a ) is a value belonging to one of five eigen constants and is set by the experimenter. For example, when the constant acceleration (v _eq ) of the load header is measured to be 1.5 m/s, the user sets the acceleration speed (v _a ) to 3.0 m/s, and the fatigue damage index

If is 1.0, the acceleration speed ratio becomes 2.0. At this time, the acceleration speed must be precisely controlled according to the above-mentioned equations for the radial speed and the tangential direction speed.

③ Acceleration factor

The acceleration factor (AF) is calculated as the product of a _F and a _v . By setting the corresponding acceleration factor, the test time or excavation amount of the accelerated life test can be significantly reduced.

④ Failure-free excavation amount calculation formula

As is known, the failure-free test time is defined as the minimum time that a product must operate without failure in an actual use environment in order to satisfy the reliability goal. In other words, in order to trust C(%) that Rx (%) of the product will operate without failure until Lx time, no failure should occur during the non-failure test time in the actual use environment. And, a method for calculating this failure-free test time is already known.

However, for rock cutting tools, it is reasonable to set the target of the test to the amount of excavation rather than the test time. Because the operating rate of the equipment is usually less than 50%, and the contact time of each rock cutting tool (eg, pick) is very different depending on the operation scenario, it is often impossible to accurately estimate the operating time of a rock cutting tool. Because.

Therefore, it is desirable to replace the reliable life (Lx) of the product with the reliable drilling amount (Lv). In this case, the formula for calculating the amount of excavation without failure and the volume of accelerated excavation without failure (Vc _a ) is as follows.

In the above formula,

L _v : Reliable drilling volume (=reliable life, m ³ ), Vc : No-failure drilling volume (m ³ ),

AF : acceleration factor, C : confidence level, n : number of samples, R _x : reliability

Since C, n, and Rx are dimensionless constants, the unit of the entire formula is unified as the unit of volume.

Here, assuming that no failure occurs when the product is tested with an accelerated load cycle while excavating the fault-free accelerated excavation volume (Vc _a ), Rx (%) of a specific tool product is determined until the cutting volume of Lv is excavated. It means that C(%) can be trusted that there will be no failure.

Claims (9)

In a state in which the rock specimen is rotated with respect to the center of the rock specimen, the cutting tool moves linearly from the outer to the center of the upper surface of the rock specimen to cut the rock specimen in inward motion, and outwardly moves the rock specimen while linearly moving from the center to the outside. It is a test method that alternately repeats movement,
The cutting tool forms a spiral trajectory at a constant speed during the inward movement and the outward movement, but the interval between the spirals is constant,
The rock specimen is a specimen in which a hollow is formed vertically in the center, and the cutting tool moves to the hollow by at least a predetermined distance when moving inward to adjust the indentation depth and then starts moving outward. A continuous wear test method for a rock cutting tool, characterized in that the inward movement starts after the depth is adjusted. The method of claim 1,
When moving inward, the cutting tool enters the rock specimen while spirally moving from a place spaced apart by R _offset to the outside of the rock specimen.
When moving outward, the cutting tool enters the rock specimen while moving spirally from a place spaced apart by R _o -R _offset from the center of the rock specimen.
R _o is a continuous wear test method of a rock cutting tool, characterized in that the radius of the hollow. The method of claim 1,
A continuous wear test method for rock cutting tools, characterized in that the radial movement speed of the cutting tool and the rotation speed of the rock specimen are calculated by the following equation.
[ceremony]

In the above formula,
Vr _outw : Radial linear movement speed of the cutting tool when moving outward
R: radius of the specimen
R _offset : The distance that the cutting tool leaves the rock specimen when moving outward, or the distance it moves toward the center of the rock specimen when moving inward.
t: time
T : Time taken to move from the center of the rock specimen to 'R+R _offset ' when the cutting tool moves inward or outward
RPM _outw : Rotational speed of rock specimen when moving outward
N : Number of spirals formed from the center of the rock specimen to 'R+R _offset '
Vr _inw : Radial linear movement speed of the cutting tool when moving inward
RPM _inw : Rotational speed of the rock specimen when moving inward 4. The method of claim 3,
In the inward movement and outward movement, the rotation direction of the rock specimen is the same, and the difference between the spiral slope at the end point of the inward movement and the spiral slope at the start point of the outward movement is less than a specific angle (δ = 1°), and the following equation is satisfied. A continuous wear test method for rock cutting tools.
[ceremony]

In the above formula,
s: spacing between spirals 5. The method according to any one of claims 1 to 4,
The test method is a continuous wear test method of a rock cutting tool, characterized in that it is made by an accelerated life test and is made by increasing at least one of a cutting load (Fc) and a cutting speed (v _Re ). 6. The method of claim 5,
The increase in the cutting force (Fc) is made by increasing at least one of the cutting depth (d) and the uniaxial compressive strength (UCS) of the rock specimen, characterized in that it is calculated by any one of the following equations, a rock cutting tool of continuous wear test method.
[ceremony]

a ₁ : Slope of a straight line representing the relationship between depth of cut (d) and cutting load (Fc)
a ₂ , b ₂ , m, n : coefficients of the regression equation with UCS and d as input variables and Fc as output 6. The method of claim 5,
The cutting speed (v _Re ) is a continuous wear test method of a rock cutting tool, characterized in that it is calculated by the following formula.
[ceremony]

v _r : radial movement speed of the cutting tool
v _t : tangential speed of the cutting tool 6. The method of claim 5,
In the accelerated life test, the reliable life is defined as the reliable excavation amount (Lv) instead of the reliable time concept,
The continuous wear test method of a rock cutting tool, characterized in that the failure-free accelerated excavation volume (Vc _a ) is calculated by the following formula.
[ceremony]

In the above formula,
Vc: no-failure drilling volume (m ³ ), L _v : reliable drilling volume (=reliability life, m ³ ), C: confidence level,
n: number of samples, Rx : reliability, β: failure characteristic index (shape parameter), AF: acceleration factor 9. The method of claim 8,
The AF is a continuous wear test method of a rock cutting tool, characterized in that calculated by the following formula.
[ceremony]

In the above formula,
a _F : the ratio of the accelerating load,

Fc _a (accelerated load): A value determined during test design.
Fc _eq (equivalent load): The average value of the cutting force (Fc) for a certain time (t ₁ ~t ₂ ).

Fc(t) : Real-time cutting force
λ (fatigue damage index): A value that defines the degree of damage compared to the load of each part.
a _V : ratio of acceleration speed,

v _a : acceleration speed
v _eq : equivalent velocity,

r : Radius where the cutting tool is located. rpm : the rotational speed of the rock specimen

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