RU2451591C2 - Method of ball mill steel lining surface hardening - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to surface hardening and may be used for increasing wear resistance of ball mill lining. Ball mill is loaded with chilled iron shots at loading factor making 30-40% of mill drum inner volume. Ball mill is started at drum rpm V_d to allow shots to fall along normal to lining surface. Note here that V_d=0.75V_{d cr}, where V_{d cr} is drum rpm corresponding to shot parabolic trajectory transition of circular trajectory. Interval of shot bombardment is selected to allow twenty-fold impacts on entire surface of lining.

EFFECT: higher wear resistance.

1 dwg

Description

                                                       The invention relates to the field of hardening of parts and can be used to increase the wear resistance of steel lining plates of ball mills, primarily from steel 110G13L (Hadfield steel).

A known method of processing a fraction of solid-rolled railway wheels (RU 2146996 C1, B24C 1/10, 03/27/2000). This method involves hardening the surface of the wheel disk and the places of its transition into the rim and the hub with shot, carried out by ejecting the shot from six Laval nozzles under a pressure of 4.6-5.5 kgf / cm ² with a duration of 8-10 minutes on both sides of the wheel this Laval nozzle is installed in diametrically opposite directions with the possibility of overlapping zones of the surface treatment of three pairs of nozzles not less than the value of the radius of each treatment zone.

The disadvantage of this method is that for hardening the processing of ball mill linings in this way, additional equipment, namely, Laval nozzles, is necessary. It may also be difficult to install the nozzles inside the ball mill body and with subsequent hardening treatment.

A known method of processing blades of turbomachines (SU 1269391 A1, B24C 1/00, 01/20/2006), in which the processing of the blades of turbomachines, including bead peening in two stages, and at the first stage they protect sharp edges, and at the second stage the processing is carried out with glass balls , characterized in that, in order to improve the quality of processing, after edge protection, steel balls are riveted at a pressure of 2-5.5 kgf / cm ² , then the protection is removed, a layer with a thickness of 0.2-10 microns is removed from the riveted surface, and the final hardening is carried out at a pressure of 2-4 kgf / cm ² , moreover, the ratio of the diameters of the steel balls to glass is chosen in the range of 8 to 53.

The disadvantage of this method is that to carry out the hardening treatment of the ball mill, it is necessary to use additional equipment, also the disadvantage is that the glass balls during the processing of the lining are able to break and, falling in the form of fragments in the cracks between the lining plates, will clog the crushed rock.

A known method of hardening the inner surfaces of the cylinders (RU 2120849 C1, B24C 1/10, 10.27.1998), selected as a prototype. The essence of this method is as follows, the cylinders are treated with steel balls ejected by cutting fluids, together with false cylinders mounted on the ends of the cylinders. Processing is carried out using a ball-torch tool by means of an ejector head with a turbine. The fluid is fed simultaneously to the nozzles and hydraulic bearings.

The disadvantage of this method is that the hardening of the internal surfaces of the structures is carried out using a cutting fluid, which, when used in a ball mill, will fall into the cracks between the lining plates and subsequently contaminate the crushed rock, this method also requires the use of additional equipment, namely a ball torch tool .

The technical result of the invention is to increase the wear resistance of the surface layer of the lining due to its hardening.

The technical result of the invention is achieved by the fact that in the method of surface hardening of steel linings of ball mills, including the processing of the inner surface of the lining with balls, the ball mill is loaded with balls of bleached cast iron, with a load factor in the range of 30-40% of the internal volume of the drum and is launched at a rotational speed of the mill V _b , which is determined from the expression

V _b = 0.75V _{b crit} ,

where V _{b crit} - the speed of rotation of the drum corresponding to the transition of the parabolic trajectory of the balls to the circular,

this ensures that the balls fall on the lining normally to its surface, and the time of bombardment of the lining with balls is selected from the condition of providing a 20-fold impact over the entire surface of the lining.

Steel at high stresses and dynamic loads is able to perceive plastic deformation with an increase in hardness and wear resistance, i.e. to be hardened. To create the conditions under which the steel lining will undergo effective hardening, the present invention proposes to periodically run the ball mill when loading only with balls, with calculated operating conditions and a specific load factor of the mill with balls.

The invention is illustrated by the drawing of figure 1, where D _m is the inner diameter of the mill drum housing, V _n is the speed of the ball at the moment of its contact with the surface when moving along a parabolic path, α is the angle of separation of the balls from the drum mill body.

, The method is as follows (figure 1). A ball mill with a steel lining is loaded with balls of iron-carbon alloy, for example, 0.04 m in diameter, from bleached cast iron. The load factor of the mill with balls is set so that the balls of the outer layer fall on the lining normally to its surface without slipping relative to each other when lifting the balls up, the load factor under these conditions will be 30-40% of the internal volume of the mill drum. Run a ball mill at a speed

,

where V _{b crit} - the speed of rotation of the drum, corresponding to the transition of the parabolic trajectory of the balls to the circular; g is the acceleration of gravity,

at the same time, they ensure that the balls fall on the lining normally to its surface. The time of bombardment of the lining with balls is chosen from the condition of providing a 20-fold impact over the entire surface of the lining. This is due to the fact that an increase in the spherical dent with an increase in the number of strokes takes place only up to 20 strokes, after which it practically stops. This dependence is given in the article by Kudryavtsev I.V. The influence of the curvature of the contacting surfaces on the depth of plastic deformation during hardening of parts by surface hardening / I.V. Kudryavtsev, G.E. Petushkov // Increasing the strength of machine parts by surface deformation: materials of the II scientific and technical conference. Perm: PPI, 1967, on p. 42).

The speed V _{n of the} ball at the moment of impact on the armor is calculated from the equation of free fall of the ball thrown at an angle to the horizon, from the highest point H of the trajectory to the point of contact with the armor plate (Fig. 1).

The method improves the wear resistance of the steel lining, which in turn increases its service life.

Claims (1)

The method of surface hardening of steel linings of ball mills, including the processing of the inner surface of the lining with balls, characterized in that the ball mill is loaded with balls of bleached cast iron with a load factor in the range of 30-40% of the internal volume of its drum, the ball mill is launched with a rotational speed of the drum V _b providing drop balls on the lining normal to its surface, and _b = 0.75 V V _{b crit} where V _{b crit} - a drum rotation speed corresponding to the transition parabolic trajectory Motion Nia balls circular, the lining treatment time of bombardment balls define conditions provide 20-fold impact of balls on the entire surface of the liner.