Field of the Invention

The present invention relates to grinding mills and, in particular to the liner bolts used to secure the sacrificial liners of such mills.

Background Art

Grinding mills are used in a wide range of mining activities such as the milling of hard rock ores, including copper ore, the production of cement, and other such activities. Typically the mill consists of a hollow steel cylinder which is rotated about its longitudinal axis. The interior of the cylinder is lined with the sacrificial liner. Inside the liner are the lumps of ore and the grinding bodies, such as steel balls. As the mill is rotated, so the grinding bodies grind the lumps of ore up into a fine powder which is then utilised in the next stage of the process.

During routine maintenance, it is necessary to replace the sacrificial lining with a new lining. Since the sacrificial lining is bolted to the mill body, this replacement task normally requires the bolts holding the lining in place to be knocked out by means of hydraulic hammers, pneumatic hammers, manually operated hammers, or suspended hammering devices similar to a battering ram. Approximately 30% of the time spent in doing a re-line of a grinding mill is spent in removing the liner bolts holding the worn liner in place. Typically 4-6 personnel are employed in this job.

Genesis of the Invention

The genesis of the present invention is a desire to reduce the amount of effort required to change the sacrificial lining.

Summary of the Invention

In accordance with a first aspect of the present invention there is disclosed a liner nut having an exterior surface and a blind threaded hole, said exterior surface being shaped to mate with a recess in a grinding mill liner plate to thereby prevent rotation of said nut relative to said recess. In accordance with a second aspect of the present invention there is disclosed a liner bolt having a substantially conventional head, a shank extending from said head, and a threaded portion of said shank adapted to threadably engage with the threaded blind hole of the abovementioned liner nut.

In accordance with a third aspect of the present invention there is disclosed the combination of the above-mentioned liner nut and liner bolt.

According to another aspect of the present invention there is provided a method of assembling a liner plate having a shaped recess therein to a mill wall having a through aperture, said method comprising the steps of:

aligning said recess and aperture,

inserting a liner nut as defined above into said recess,

inserting the shank of a liner bolt as defined above into said aperture, and threadably engaging the thread of said shank with the thread of said blind hole in said liner nut.

According to a still further aspect of the present invention there is provided a method of disassembling a liner plate from a mill wall having a through aperture, said liner plate being held against said wall by means of a liner nut as defined above, being retained in a recess of said liner plate, and a liner bolt as defined above extending through said aperture and into said liner nut, said method comprising the steps of : rotating the head of said liner bolt to disengage the threaded shank thereof from the thread of the blind hole of said liner nut,

discarding said liner plate and liner nut, and

retaining said liner bolt for use in the subsequent assembly of a new liner plate to said mill wall.

Brief Description of the Drawings

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is an exploded cross-sectional view taken through the cylindrical wall of a prior art grinding mill and showing a prior art nut and bolt which retains the liner in place, Fig. 2 is an end elevation of the head of the bolt of Fig. 1 ;

Fig. 3 is a cross-sectional view equivalent to Fig. 1 but in accordance with a preferred embodiment of the present invention;

Fig.4 is an end elevation of the nut of Fig. 3; and

Fig. 5 is a combined side elevation and end view of a bolt of a second embodiment.

Detailed Description

As seen in Figs. 1 and 2, a mill wall 1 has an aperture 2 therethrough. A liner plate 3 and rubber backing sheet 6 are positioned adjacent the mill wall 1. The liner plate 3 and has a shaped recess 5 which opens towards the interior of the mill. The recess 5 extends through the liner plate 3 and is aligned with the aperture 2. A liner bolt 7 has a shank 8 and a head 9. The tip of the shank 8 is threaded in conventional fashion. The head 9 has a generally oval shape and mates with the recess 5 so as to stop the liner bolt 7 rotating within the recess 5.

In order to secure the liner plate 3, the liner bolt 7 is passed into the recess 5 and through the aperture 2, a rubber washer 1 1 and a steel washer 12 are then passed over the shank 8, and a conventional nut 13 secured to the thread. Tightening the nut 13 clamps the liner plate 3 against the mill wall 1.

After several months, when the liner plate 3 comes to be replaced, the nut 13 and washers 1 1, 12 are removed from the liner bolt 7. Then the bolt 7 is knocked out of the aperture 2 and liner plate 3. This is a very time-consuming task which requires manually guided hammers and numerous people. Since the threaded portion of the shank 8 protrudes from the nut 13, the threads on the shank 8 become corroded due to their exposure to the elements, and thus the nut 13 quite often requires cutting off with an oxyacetylene torch, rather than being removed with a pneumatic wrench, or similar. In addition, due to wear and peening the bolt can become deformed from the hammer impacts, thus making the bolts 7 difficult to remove and also causing damage to the apertures 2 in the mill wall 1.

Turning now to Figs. 3 and 4, the mill wall 1 , liner plate 3, rubber backing sheet 6, and washers 1 1, 12 are as before. However, the liner bolt 17 has its orientation reversed. The liner bolt 17 has a shank 18 and a head 19 and a threaded portion 20 which is of reduced diameter relative to the shank 18. A liner nut 23 has an exterior shape (for example oval when viewed end on) designed to exactly match the recess 5 and thus corresponds in shape to the head 9 of the conventional liner bolt 7. As a consequence, the liner nut 23 cannot rotate within the recess 5. The liner nut 23 is also provided with a blind hole 25 which is threaded with a thread which matches that of the threaded portion 20.

During installation, the liner plate 3 has the recess 5 aligned with the corresponding aperture 2, the liner nut 23 is positioned into the recess 5, the shank 18 of the liner bolt 17 is inserted into the aperture 2 and the liner bolt 17 is rotated, preferably using an impact gun or similar, to engage the threaded portion 20 with the blind hole 25 in the liner nut 23. This engagement brings the liner plate 3 into contact with the mill wall 1 and holds the liner plate 3 in a stable position.

The liner bolt 17 and liner nut 23 are designed so that there is no need to knock out the liner bolt 17 prior to removal of the liner plate 3 during routine maintenance. As the male thread of the threaded portion 20 and the female thread of the blind hole 25 are both protected, this eliminates the possibility of them becoming seized, for example because of fines or ore dust entering the thread. Thus there is no need for any cutting equipment. Instead, the liner bolt 17 can be undone using a conventional pneumatic wrench, for example.

There is no need to remove the liner nut 23 from the liner plate 3 since the liner plate 3 is to be discarded. The liner nut 23 will normally be "cemented" into the recess 5 by the penetration of fine ore dust around the liner nut 23. It is this "cementing action" which requires the conventional liner bolt 7 to be hammered out of the recess 5. However, the reversal of the direction of the liner bolt 17 overcomes the problems caused by this "cementing action".

Furthermore, the liner bolt 17 is reusable. Although the liner bolt 17 and the liner nut 23 can both be manufactured of the same grade steel, if the liner bolt 17 is manufactured with a higher grade steel, it is reusable on more occasions. As seen in Fig. 5, an alternative form of liner bolt 27 has a head 29 an internal square drive recess 30.

The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the mining arts, can be made thereto without departing from the scope of the present invention. For example, the axial length of the liner bolt 17 and liner nut 23 can be varied to suit the thicknesses of the mill wall 1 and the liner plate 3. Preferably, the shank 18 and blind hole 25 are provided with 6 threads per inch, however, this can be modified depending upon the mill structure thickness and clamping force required the different sized wear liners. In addition, the nut 23 can be of any shape with the recess 5 of the mill liner plate 3 having a corresponding complementary shape.

The term "comprising" (and its grammatical variations) as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of

"consisting only of.