RU2490112C1 - Method of cleaning cubic boron nitride abrasive wheel - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machine building and may be used for grinding of work pieces from various materials by cubic boron nitride wheels. Abrasive stick is pressed to working surface of glazed grinding wheel for cleaning. Stick abrasive grains remove pickups of machined billet metal from wheel grains located at different distance from conventional outer surface of the wheel. Force of pressing the stick to wheel is defined by mathematical formula with allowance for sizes of axes of ellipse circumscribed nearby facets of grinding wheel abrasive grains.

EFFECT: higher efficiency and quality of grinding, longer life of grinding wheel.

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Description

The invention relates to mechanical engineering, namely to processing by grinding, and can be used for elbor grinding of workpieces from materials with high plasticity, viscosity and adhesive activity with respect to the grinding wheel.

A known method of cleaning grinding wheels, which consists in acting on the working surface of a rotating grinding wheel with an elastic tool, which is used as an elastomer (AS 1775282 USSR, MKI ³ V24V 53/007. Method for cleaning abrasive tools II Kuznetsov, No. 4847739 / 08; claimed 03.05.90; publ. 15.11.92, BI No. 42).

The reasons that impede the achievement of the technical result indicated below when using the known method include the low efficiency of removing metal deposits from the grains of the grinding wheel and the large dimensional wear of the cleaning tool.

A known method of cleaning grinding wheels, which consists in pressing against the working surface of a rotating grinding wheel of an abrasive bar on an elastic bond (Patent 2185273 RU, MKI V24V 53/007. Method for cleaning grinding wheels / L.V. Khudobin, A.N. Unyanin, D. V. Tartas No. 2000114938/02; declared 09.06.00, published on 07.20.02, BI No. 20).

The reasons that impede the achievement of the technical result indicated below when using the known cleaning method include the low efficiency of removing metal deposits from the grains of the circle.

Closest to the claimed invention in terms of features is a method for cleaning the grinding wheel selected as a prototype (Patent 2266189 RU, MKI V24V 53/007. Method for cleaning the grinding wheel / LV Khudobin, AN Unyanin. No. 2004116060/02; Dec. 25.05.04, publ. 20.12.05, BI No. 35), which consists in clamping to the working surface of a rotating grinding wheel of an abrasive bar on an elastic bond, and the pressing force is determined by mathematical dependence.

The reasons that impede the achievement of the technical result indicated below when using the known cleaning method adopted as a prototype include limiting the scope of the method for cleaning grinding wheels from traditional abrasives (electrocorundum, silicon carbide), therefore, the impossibility of using the method for elbor grinding.

The invention consists in the following. Between dressings of a wheel when grinding workpieces from plastic, viscous and adhesive-active materials, its cutting ability is unstable and gradually decreases, which leads to the need for a corresponding decrease in the performance of defect-free grinding or (and) to a deterioration in the quality of polished parts. One way to increase the efficiency of grinding workpieces is to clean the working surface of the grinding wheel. The cleaning carried out several times between the edits of the wheel leads to stabilization of the cutting ability of the wheel between the edits, which makes it possible to increase the processing productivity and the durability of the wheel. The latter leads to a reduction in the number of edits and saving circles, as well as to an improvement in the quality of polished parts.

The technical result is an increase in the performance of defect-free grinding by forcing the machining mode and (or) increasing the durability period of the elbor grinding wheel and thereby reducing the number of edits while ensuring the specified quality of the polished parts.

The specified technical result during the implementation of the invention is achieved by the fact that, as in the known method of cleaning, an abrasive block is periodically pressed to the working surface of a rotating elbor grinding wheel, the feature being that the force of the block against the wheel is determined by the mathematical dependence

, $$Q={\tau }_s\cdot K_s\cdot K_y\cdot a_n\cdot a\cdot \sqrt{\mathrm{one}-\mathrm{four}\cdot b^{-2}\cdot {\left(\frac{b}{2}-h_{\mathrm{and}}\right)}^2}\cdot \sqrt{z_R}\cdot H$$

,

where τ _s is the shear stress during dispersion by a grain of a bar of nalip on the grain of a circle, Pa;

and _n - the height of the tack, m;

K _s - salinity coefficient, equal to the ratio of the size of the tack to the size of the blunt pad on the grain of the elbor circle;

z _p - the number of working grains in a single area of the working layer of the elbor circle, 1 / m ² ;

a, b are the dimensions of the axes of the ellipse described near the faces of the abrasive grain of the circle, m;

H - the height of the working surface of the grinding wheel, m;

h _and - linear wear of abrasive grain, m;

K _y - coefficient determined by the formula

, $$K_y=\frac{\cos \left(\beta +{\varphi }_s\right)}{\sin \beta \cdot \sin {\varphi }_s}$$

,

where β is the shear angle when dispersing the material of the tack, deg .;

φ _s is the angle of internal friction, deg.

If the force with which the bar is pressed against the circle is lower than the value determined by the above dependence, then the dispersion of the material of the sticks will not be effective enough. A large force will lead to intensive wear and blunting of the grains of the circle and bar, which will reduce the efficiency of the grinding process.

Schematizing the objects interacting during cleaning, it was assumed that the contours of the grains from the elbor are described by rotation ellipsoids, and the abrasive grains of a bar made of traditional abrasive material (electrocorundum) were presented in the form of truncated pyramids with blunting areas. A similar representation is widely used in modeling abrasive tools and the grinding process. The grains of the bar are dispersed by the nalipa formed at the blunt grains of the circle grains located at some distance from the top of the most prominent grain. The assumption was made that the physicomechanical properties of the nalipa material do not differ from the corresponding properties of the material of the grinded workpiece.

To calculate the clamping force Q of the bar against the wheel during the cleaning process, we determined the area of metal sticks removed by all the cutting grains of the bar in a plane parallel to the axis of the circle, assuming that the sticks formed on the sites of blunting the grain of the circle.

Area of adherents in the considered plane

F _n = a _n · L _n ,

where a _n - the height of the tack, m;

L _n - the total size of the sticks in the plane parallel to the axis of the circle, m:

, $$L_n=y\cdot \sqrt{z_R}\cdot H$$

,

where z _p is the number of working grains in a single area of the working layer of the elbor circle, 1 / m ² ;

H is the height of the circle, m;

y is the size of the blunt pad on the grain of the elbor circle, m.

The cross-sectional area f of the ellipse described near the faces of the abrasive grain of the circle:

, $$f=\frac{\pi a^2}{\mathrm{four}}\left(\mathrm{one}-\mathrm{four}{b}^{-2}{\left(\frac{b}{2}-h_{\mathrm{and}}\right)}^2\right)$$

,

where a, b are the dimensions of the axes of the ellipse described near the faces of the A3 circle, m;

h _and - linear wear AZ, m

Since the cross section of the biaxial ellipse is a circle, the following expression is true:

, $$f=\frac{\pi y^2}{\mathrm{four}}$$

,

4 Hence the size of the blunt pad y:

. $$y=a\sqrt{\mathrm{one}-\mathrm{four}{b}^{-2}{\left(\frac{b}{2}-h_{\mathrm{and}}\right)}^2}$$

.

The force of the bar to the circle is determined by the dependence:

Q = τ _s · K _s · K _y · F _n ,

where τ _s is the shear stress during dispersion by a grain of a bar of nalip on the grain of a circle, Pa;

F _n - the area of the sticks in a plane parallel to the axis of the circle, m ² ;

K _s - salinity coefficient, equal to the ratio of the size of the tack to the size of the pad dull grain circle;

K _y is the coefficient.

Substituting in the last dependence the expression for calculating F _n , we obtain the expression:

. $$Q={\tau }_s\cdot K_s\cdot K_y\cdot a_n\cdot a\cdot \sqrt{\mathrm{one}-\mathrm{four}\cdot b^{-2}\cdot {\left(\frac{b}{2}-h_{\mathrm{and}}\right)}^2}\cdot \sqrt{z_R}\cdot H$$

.

Calculation of the force Q was performed to clean the 125/100 grit circle with a blunt pad of size n = 0.053 mm using an alumina bar of M10 grit (12X18H10T steel nalip material). The number of working grains, depending on the grinding mode, was: z _p = 1.3 ... 5.1 1 / mm ² . The height of the circle and the bar for cleaning N = 10 · 10 ^-3 m. Shear stress during micro-cutting of sticks, τ _s = 133 MPa. and _n = 2 μm = 2 · 10 ^-6 m.

The average calculated value of the clamping force for these conditions is Q = 0.48 N.

Information confirming the possibility of carrying out the invention with obtaining the above technical result.

Upon reaching a certain degree of salting and blunting of the working surface of the elbor grinding wheel, rotating at a working speed, a cleaning tool made in the form of an abrasive bar is brought down and pressed to it. The abrasive grains of the bar remove the adhered metal from the workpiece from the abrasive grains of the grinding wheel. Due to the elastic properties of the tool bundle, the grains of the circle located at a distance from the conditional outer surface of the latter are cleaned. Using the optimal force of pressing the bar to the working surface of the circle allows the dispersion of the sticks on the grains of the circle without the formation of areas of blunting. Cleaning the working surface of the grinding wheel provides increased grinding performance while ensuring the specified quality of the polished parts. Improving grinding performance is achieved by forcing the processing mode and (or) increasing the durability of the grinding wheel and thereby reducing the number of edits.

Experimental studies were carried out with flat pendulum grinding of 12Kh18N10T steel billets using an LO125 / 100ST1B1 elbor circle. The working circle speed was 35 m / s, the longitudinal feed rate was 10 m / min, the mortise feed rate was 0.005 mm / dv. move. A 1% solution of soda ash with a flow rate of 10 dm ³ / min was fed into the grinding zone. The working surface of the circle was cleaned with white alumina 25AM10 BM1K20 bars. The bars were pressed against the grinding wheel 3 times during the resistance period.

As a criterion for evaluating the efficiency of the grinding process, the components P _y and P _{z of} the grinding force during processing of the workpieces were used.

The research results are presented in the table.

The force of the clamp bar to the circle Q, N Components of grinding force, N P _y P _z 0 28 22 0.3 19 15,5 0.5 17 12 1,5 19 13 3.0 24.5 17

From the results it follows that if, when cleaning the circle, the bar is pressed to its working surface with a force of Q = 0.5 N, which is close to the calculated one, equal to Q = 0.48 N, then the grinding process is characterized by a minimum value of grinding forces and, therefore, less heat stress and burn formation. If the clamping force is different from the value determined by the dependence, then the efficiency of the grinding process is lower.

Claims (1)

The method of cleaning elborovogo grinding wheel, including the clamp to the working surface of the rotating circle of the abrasive bar, characterized in that the force of the clamp bar to the wheel is determined by the dependence:
$$Q={\tau }_s\cdot K_s\cdot K_y\cdot a_n\cdot a\cdot \sqrt{\mathrm{one}-\mathrm{four}\cdot b^{-2}\cdot {\left(\frac{b}{2}-h_{\mathrm{and}}\right)}^2}\cdot \sqrt{z_R}\cdot H$$

where τ _s is the shear stress during disnergation by a grain of a nalip bar on the grain of a circle, Pa;
and _n - the height of the tack, m;
K _s - salinity coefficient equal to the ratio of the size of the tack to the size of the blunt pad on the grain of the circle;
z _p - the number of working grains in a single area of the working layer of the elbor circle, 1 / m ² ;
a, b are the dimensions of the axes of the ellipse described near the faces of the abrasive grain of the circle, m;
H - the height of the working surface of the grinding wheel, m;
h _and - linear wear of abrasive grain, m;
K _y - coefficient determined by the formula
$$K_y=\frac{\cos \left(\beta +{\varphi }_s\right)}{\sin \beta \cdot \sin {\varphi }_s}$$

where β is the shear angle when dispersing the material of the tack, deg;
φ _s is the angle of internal friction, deg.