DK152834B - INTERNAL CLOTHING FOR BALL MILLS - Google Patents

Description

DK 152834B

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an inner casing for ball mills, the casing being composed of grinding plates, each grinding plate having grooves having a circular segmental cross-section, the radius of which circle segment substantially corresponds to the radius of the largest of the grinding balls used in the mill.

Paint plates of this kind are known and are described e.g. in Austrian Patent Specification No. 283092. There are a number of advantages associated with said paint plates over paint plates of conventional embodiments. These advantages consist of the relatively lower weight of the garment, a lower energy consumption at the same capacity, the ability to run the paint drum at a relatively lower speed, resulting in additional energy savings, and a reduced repair need with consequent greater reliability and the like.

The use of grooved plates, of course, results in the fact that, in comparison with the grinding process of grinding plates without grooves, the comminution process undergoes a fundamental change, in which the impact of the bullets on the plates is considerably dampened and the available energy is used to a considerable extent for the comminution work. .

It is known to manufacture the grinding plates and grinding balls 25 of iron-chromium-carbon alloys, whereby particular attention must be paid to the fact that the residual austenite content of these tools in the installation state is as low as possible, e.g. lower than 5¾. As a result of the impact loads, residual austenite is converted to martensite, resulting in a 30 risk of brittleness and tension and thus fracture damage. This is why the residual austenite content should be as low as possible.

DK 152834 B

2

In the grooved plates according to the invention, this risk in principle also exists, but clearly to a greatly reduced degree, which is why, for the life of the painting plates, wear due to rubbing wear must be taken into account to a greater extent.

Although it has now been recognized in principle that large restau-stenite contents are harmful, experiments have found that at comparable loads, the life of the grooved plates can be increased by at least 20% if they are made of an iron-chromium carbon. casting alloy with 0.5-3% carbon, 5-30% chromium, 0.5-2% silicon, 0.5-5% manganese, preferably 0.7-1.2% manganese, 0.05-0, 5% nitrogen, preferably 0.1-0.3% nitrogen, residual iron and inevitable impurities.

The usual size of the nitrogen additive is, in the usual melting of the alloy, dependent on the size of nitride formers, especially the size of chromium, manganese and. the molybdenum content and, if applicable, the size of the aluminum, zircon and titanium content and may be between 0.05 and 0.5%. Preferably, nitrogen content between 0.1 and 0.3% is used.

Whether the improvements in the wear-to-wear ratio attained by the nitrogen content are due to higher residual oustenite content or nitride formation, or whether both of these phenomena work together, must still be considered unclear. It is interesting, however, that the nitrogen addition according to the invention, especially at the places in the mill where the loads are greatest, ie where the coarse grinding takes place, has a particularly advantageous effect.

The invention thus consists of an inner casing for ball mills, which casing is composed of paint plates, each painting plate having grooves having a circular segment-shaped cross-section, the radius of which circle segment1 corresponds substantially to the radius of the largest of the mills. used paint balls, characterized in that 5 each paint plate is made of iron-chromium-carbon cast coating with 0.5-3¾ carbon, 5-30% chromium, 0.5-2% silicon, 0.5- 5% manganese, preferably 0.7-1.2% manganese, 0.05-0.5% nitrogen, preferably 0.1-0.3% nitrogen, residual iron and inevitable impurities.

The iron-chromium-carbon casting alloy used according to the invention may further contain 0-5% molybdenum, preferably 0.3-1.5% molybdenum, 0-5% tungsten, 0-1% vanadium, 0-5 % nickel and optionally up to 0.5% of one or more of the metals aluminum, zircon and titanium.

15 In the ball mills equipped with such grooved plates it is appropriate to use paint balls whose chromium content is greater than the chrome content of the paint plates, but where the chrome content of the balls must not be less than 12%.

The grooved plates can be used in natural hardened, hardened and annealed or in refined condition, as is also the case with plates without grooves. The paint balls are mostly brought up to hardness over 60 hardness Rockwell C. when they contain 12% chrome or more.

25 Addition of nitrogen to the alloys from which the paint balls are made has, so far, not resulted in any noticeable improvements. However, if one is to choose an alloy containing aluminum, zirconium or ti- 3 ° tan in small quantities up to a maximum of approx. 0.5% of each, by adding nitrogen in an amount of up to approx. 0.5% get a slight improvement in the wear ratio.

Claims (2)

An inner casing for ball mills, which casing is composed of painting plates, each painting plate having grooves having a circular segmental cross-section, the radius of the circle segment substantially corresponding to the radius of the largest of the milling balls used in the mill, characterized by: that each grinding plate is made of an iron-chrome-carbon casting alloy with 0.5-3¾ carbon, 5-30¾ chromium, 0.5-2¾ silicon, 0.5-5¾ manganese, preferably 0.7-1.2¾ manganese , 0.05-0.5¾ nitrogen, preferably 0.1-0.3-0 nitrogen, residual iron and inevitable impurities. Interior lining according to claim 1, characterized in that the iron-chromium-carbon casting alloy further contains 0-5¾ molybdenum, preferably 0.3-1.5¾ molybdenum, 0-5¾ tungsten, 0-1¾ vanadium, 0. -5¾ nickel and optionally up to 0.5¾ of one or more of the metals aluminum, zircon and titanium.