Mill liner bolt for a mill liner of an ore grinding mill

Abstract

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Description

Mill liner bolt for a mill liner of an ore grinding mill TECHNICAL FIELD The present disclosure relates to a mill liner bolt arranged to attach a mill liner in an ore grinding mill. BACKGROUND One of the steps in mineral ore processing is grinding, wherein the ore is ground in rotating steel drums or grinding mills to assist in the liberation of precious metal contained in the ore. The grinding mills are lined internally with either steel liners, rubber liners or a combination of steel and rubber composite liners. The liners protect the mill drum from damage during tumbling of the ore and also assist in the grinding process by lifting the ore and any attrition balls located within the milling drum during the grinding process. Typically, the steel and some composite liners are joined to the mill drum by mill liner bolts that are passed through countersunk through-holes and secured to nuts located externally of the mill drum. The mill liner bolts generally include a non-round head defining a load-bearing tapered neck that leads into a threaded shank. Commonly, the non-round heads are obround in shape when seen end-on being designed with a central rectangular section having opposed semicircular ends. Example of such common prior art mill liner bolts are shown in US 4,018,393 (see Figure 7) and US 6,220,802 (see Figures 1-3). When each mill liner bolt is tightened, the bolt is tensioned to create a clamping force between the tapered neck and the mill liner to hold the mill liner against the mill drum housing. The bolt holes or cores in the mill liners are designed with a desired clearance tolerance for the non-round headed bolts. Unfortunately, the casting of the mill liners is not an exact process and there is often variation in the sizes of the bolt holes from mill liner to mill liner and even from hole to hole in the same mill liner. All of this variation affects the amount of contact between the mill liner bolts and the mill liner, which often results in the bolt and mill liner forming minimal contact at discrete locations —causing point loading at those locations. Such point loading often results in the mill liner bolt and / or mill liner undergoing plastic deformation, thereby causing the bolt to lose tension, becoming poorly seated within the liner, and this eventually causes the mill liner bolt to loosen. Subsequent rotational motion of the rotating mill drum causes vibration or shaking of the mill liner with respect to the mill drum and results in fatigue in the mill liner bolt. If suitable maintenance on the mill drum is not conducted in time to tighten the bolts they will eventually fail and can even result in the mill liners detaching from the mill drum. The need to conduct maintenance has a great cost implication due to down-time of the grinding mill, which must be stopped, isolated and made safe for entry so that the bolts can be tightened or changed. On bigger grinding mills this can take up to 4 - 5 hours; that is 4 — 5 hours of lost production. The above problem with the loosening of liner bolts is well appreciated. As one example, US 10,232,378 discloses a mill liner bolt which has plastically deformable projections extending from its tapered load-bearing surfaces. The projections are configured to deform under load during tightening so that the mill liner bolt head tends to conform to any potentially inconsistently cast shape of the tapered bolt hole. In large grinding mills, having an internal diameter exceeding three metres, it is typically necessary for a worker to enter the mill drum to locate the mill liner in place and then feed the mill liner bolts through the mill liner for tightening by another worker situated outside the mill drum. Having a worker inside the mill drum is potentially dangerous as it is an unsafe working environment. Itis to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. SUMMARY OF THE DISCLOSURE According to a first aspect of the disclosure, there is provided a mill liner bolt arranged to attach a mill liner in an ore grinding mill, wherein the mill liner bolt is to be inserted into a through-hole in the mill liner, the through hole having an entry opening and an exit opening, wherein the entry opening has a pair of opposed curved sides and a pair of opposed straight sides and wherein the exit opening is circular, which through-hole further has a conically tapered side wall located between the entry opening and the exit opening, the mill liner bolt comprising a bolt head having opposed arcuate faces and opposed substantially flat faces; an elongated cylindrical threaded shank having a longitudinal axis; a conically tapered neck integral with and extending from the bolt head to the shank, wherein a taper angle of the tapered neck is preselected to be congruent to a taper angle of the tapered side wall of the through hole; and wherein the arcuate faces of the bolt head and the tapered neck have a common central axis that extends co-linear with the longitudinal axis and defines a common rotational axis so that, during use, the tapered neck remains in contact with the tapered side wall through a constant contact area during rotation of the bolt head relative to the mill liner. The taper angle may be selected to be about 20° — 70°, or about 20° — 60°, or about 45° — 55°. In one embodiment the taper angle is 50°. The flat faces may extend tangentially with the shank. The bolt head may comprise one or more elastically deformable projections that project outwardly from the bolt head transversally to the longitudinal axis, wherein during use the or each projection is able to elastically deform when the bolt head is inserted into a through-hole in a mill liner, thereby to frictionally retain the bolt head within the through- hole. The bolt head may comprise an annular groove configured to receive the one or more projections. In one embodiment the one or more projections comprises a substantially C-shaped retaining circlip made of spring steel. According to a second aspect of the disclosure, there is provided a mill liner bolt and mill liner assembly for an ore grinding mill, the assembly comprising a mill liner bolt having a bolt head having opposed arcuate faces and opposed substantially flat faces, an elongated cylindrical threaded shank having a longitudinal axis, and a conically tapered neck integral with and extending from the bolt head to the shank; and a mill liner having one or more countersunk through-holes for receiving the mill liner bolt, each through-hole having an entry opening and an exit opening, wherein the entry opening has a pair of opposed curved sides and a pair of opposed straight sides and wherein the exit opening is circular, which through-hole further has a conically tapered side wall located between the entry opening and the exit opening; wherein the tapered neck and the tapered side wall have taper angles being congruent to each other; and wherein the arcuate faces of the bolt head and the tapered neck have a common central axis that extends co-linear with the longitudinal axis and defines a common rotational axis so that, during use, the tapered neck remains in contact with the side wall through a constant contact area during rotation of the bolt head relative to the mill liner. The taper angle may be selected to be about 20° — 70°, or about 20° — 60°, or about 45° — 55°. In one embodiment the taper angle is 50°. The mill liner bolt may comprise one or more elastically deformable projections that project outwardly from the bolt head transversally to the longitudinal axis, wherein during use the or each projection is able to elastically deform when the bolt head is inserted into the through-hole in the mill liner, thereby to frictionally retain the bolt head within the through-hole while a nut is attached to the shank. The bolt head may comprise an annular groove configured to receive the one or more projections. In one embodiment the one or more projections comprises a substantially C-shaped retaining circlip made of spring steel. BRIEF DESCRIPTION OF DRAWINGS The above and other features will become more apparent from the following description and with reference to the accompanying schematic drawings. In the drawings, which are given for purpose of illustration only and are not intended to be in any way limiting: Figure 1 is a perspective view of a first embodiment of a bolt for a mill liner; Figure 2 is a head-side end view of the bolt of Figure 1; Figure 3 is a side view of the bolt of Figure 1; Figure 4 is a shank-side end view of the bolt of Figure 1; Figure 5 is an end view of the bolt of Figures 1-4 shown in a partially inserted position within a through-hole of a liner; Figure 6 is a sectional side view of the bolt and liner of Figure 5 with the bolt shown in a partially inserted position within the through-hole of the liner, and wherein the fully inserted position of the bolt is shown in hashed outline; and Figure 7 is a perspective view of a second embodiment of a bolt for a mill liner. DETAILED DESCRIPTION The present disclosure relates to a mill liner bolt 10 for a mill liner of an ore grinding mill drum. A first embodiment of the mill liner bolt 10 is shown in Figures 1 to 6, wherein the mill liner bolt 10 includes a bolt head 12, a conically tapered neck 14 and a threaded cylindrical shank 16 (the threads have been omitted for ease of drawing and clarity). The mill liner bolt 10 has a longitudinal axis 18 aligned longitudinally along the length of the shank 16. The bolt head 12 comprises opposed arcuate faces 20 that have a common central axis, and wherein the central axis is co-linear with the longitudinal axis 18 so that the arcuate faces 20 are arranged concentric around the longitudinal axis 18, i.e. also being concentric around the shank 16 as can be more clearly seen in Figure 4. The neck 14 is frusto-conically shaped having a right circular cone base (major radius) integral with the bolt head 12 and that leads from the arcuate faces 20 to a circular cone top (minor radius) integral with the shank 16. The neck 14 defines an enclosed taper angle a of about 20° — 70° with the longitudinal axis 18. In some embodiments the taper angle a is about 20° — 60° and in one embodiment the taper angle a is about 45° — 55°, preferably being about 50°. It will be appreciated that reducing the taper angle a causes an increase in the length of the neck 14 and consequently increases a contact area between the neck 14 and a mill liner 100 (see Figures 5 and 6) when the mill liner bolt 10 is located in a through- hole 102 in the mill liner 100. The taper angle a is selected to be congruent to a taper angle B of the through-hole 102. The bolt head 12 further has opposed substantially flat faces 22 between the arcuate faces 20. In one embodiment, as is shown in the exemplary embodiment of the mill liner bolt 10, the flat faces 22 are arranged substantially parallel to each other and tangentially with the shank 16. In such case the flat faces 22 extend along the axial length of both the bolt head 12 and the neck 14, whereas the arcuate faces 20 only extend along the axial length of the bolt head 12. In other embodiments the flat faces 22 may be spaced further apart from each other so that the bolt head 12 is wider than the diameter of the shank 16. In such case the flat faces 22 will extend only partway along the axial length of the neck 14. Alternatively, the flat faces 20 can be angled with respect to each other or otherwise faceted. The various intersecting edges between the bolt head 12, neck 14 and shank 16 may be filleted or chamfered. Referring now to Figures 5 and 6, the mill liner bolt 10 is shown located within and extending partially through the countersunk through-hole 102 of the mill liner 100. When the mill liner bolt 10 is inserted to its full extent within the through-hole 102 the mill liner bolt 10 will be in the position indicated by the hashed lines indicating mill liner bolt 10’ (shown in Figure 6). The through-hole 102 has an entry opening 104 and an exit opening 106 with a conically tapered side wall 108 between the entry opening 104 and the exit opening 106. As can be seen in Figure 5, the entry opening 104 is shaped geometrically similar to the bolt head 12, with the entry opening being dimensioned slightly larger than the bolt head 12. The entry opening 104 has a pair of opposed curved sides 110 and a pair of opposed straight sides 112. The entry opening 104 is shaped to retain the bolt head 12 and restrict rotation thereof around the longitudinal axis 18. The exit opening 106 is substantially cylindrical / circular and is dimensioned slightly larger than the shank 186. The tapered side wall 108 is dimensioned to have its taper angle B be congruent to the taper angle a of the mill liner bolt 10 so that when the mill liner bolt 10 is fully inserted (see Figure 6), the neck 14 will lie flush against the tapered side wall 108. Such flush lying arrangement improves and maximises the contact area between the neck 14 and the tapered side wall 108 and reduces or substantially eliminates any point loading contact between the neck 14 and the mill liner 100. It should further be appreciated that the provision of the circular conical shape of the neck 14 around the longitudinal axis 18 permits slight rotation of the mill liner bolt 10 around the longitudinal axis 18 without altering the contact area between the mill liner bolt 10 and the tapered side wall 108 of the mill liner 100. For example, such slight rotation of the mill liner bolt 10 within the through-hole 102 may occur when operatively tightening a nut onto the shank 16 of the mill liner bolt 10, but such slight rotation may also occur during use due to vibrations passing through the mill liner 100. This differs markedly from prior art bolts (such as that disclosed in US 10,232,378) in that rotational movement of the mill liner bolt 10 in either a clockwise or anti-clockwise direction around the longitudinal axis 18 will not alter the contact area between the mill liner bolt 10 and the tapered side wall 108 of the mill liner 100 — in contrast, the prior art bolts have non-circular / non-conically tapered necks (or tapered necks having two discrete centres offset from each other) and thus will automatically experience a change in the contact area between the bolt neck 14 and the tapered side wall 108 when any axial rotation or reverse rotation occurs and after any deforming protrusions have been deformed. Referring now to Figure 7, there is shown a second embodiment of a mill liner bolt 210 for a mill liner of an ore grinding mill. The mill liner bolt 210 is substantially the same as the mill liner bolt 10 and therefore equivalent parts will be indicated using the same reference numerals. The mill liner bolt 210 includes a bolt head 12, a conically tapered neck 14 and a threaded cylindrical shank 16. In the mill liner bolt 210, the bolt head 12 is provided with an annular groove that traverses and encircles the arcuate faces 20 and the flat faces 22. A retaining clip 214 is located and retained within the groove 212, whereby both the groove 212 and the retaining clip 214 have an equivalent axial thickness allowing the retaining clip to be securely held within the groove 212. The retaining clip 214 is a generally C-shaped circlip having an opening 216 aligned with one of the arcuate faces 20. The retaining clip 214 is arranged to project laterally from the bolt head 12. The retaining clip 214 is typically made of a suitable elastic material, with the exemplary embodiment being made of steel, such as spring steel. The retaining clip 214 is sized so that it has at least one transverse outer dimension (being transverse to the longitudinal axis 18) that is larger than the equivalent transverse internal dimension of the entry opening 104 of the through-hole 102. For example, the arcuate parts of the retaining clip 214 that lie adjacent to the arcuate faces 20 may be sized to have an outer dimension larger than the diameter of the curved walls 110 of the through-hole 102. Alternatively, the straight parts of the retaining clip 214 that lie adjacent to the flat faces 22 may be sized larger than the flat walls 112 of the through-hole 102. In yet a further alternative, both the arcuate parts and the straight parts of the retaining clip 214 may be transversally larger than the internal dimensions of the entry opening 104. During use, the mill liner bolt 210 provides the advantage in that it can be attached to the mill liner 100 before the mill liner 100 is located within a mill drum. When the mill liner bolt 210 is inserted through the through-hole 102, the retaining clip 214 will contact the mill liner 100 and, with further pressing of the mill liner bolt 210 through the through-hole 102, the retaining clip 214 will deform so that its outer edge bends away from the neck 14, thereby allowing the retaining clip 214 to enter into the entry opening 104. Due to its elastic nature, the retaining clip 214 presses against the mill liner 100, creating resistance that holds the bolt 210 in position within the through- hole 102. Thereafter the mill liner 100 can be properly installed within the mill drum, with the respective shanks 16 being passed through bolt openings in the mill drum wall, without the need for a worker to climb into the mill drum to insert the bolts. It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the mill liner bolt as shown in the specific embodiments without departing from the spirit or scope of the disclosure as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. For example, instead of the mill liner bolt 210 having the annular groove 212 arranged to locate the retaining clip 214, the mill liner bolt 210 could simply be provided with one or more discrete recesses provided annularly around its bolt head 12, into which recesses suitable rods can be inserted so that the rods project outwardly from the bolt head 12. When the rods are similarly made from an elastic material, such as spring steel, the rods can deform in an equivalent manner to the retaining clip 214 to hold the mill liner bolt 210 within the through-hole 102. In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in a non-limiting and an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in the various embodiments. A reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. Reference numerals 10, 10° mill liner bolt (1% embodiment} 12 bolt head 14 neck 16 shank 18 longitudinal axis 20 arcuate faces 22 flat faces 100 mill liner 102 through-hole 104 entry opening 106 exit opening 108 tapered side wall 110 curved walls 142 flat walls 210 mill liner bolt (2 embodiment) 212 groove 214 retaining clip 216 opening a taper angle (neck) B taper angle (tapered side wall)

Claims

CLAIMS 1. A mill liner bolt arranged to attach a mill liner in an ore grinding mill, wherein the mill liner bolt is to be inserted into a through-hole in the mill liner, the through hole having an entry opening and an exit opening, wherein the entry opening has a pair of opposed curved sides and a pair of opposed straight sides and wherein the exit opening is circular, which through-hole further has a conically tapered side wall located between the entry opening and the exit opening, the mill liner bolt comprising a bolt head having opposed arcuate faces and opposed substantially flat faces; an elongated cylindrical threaded shank having a longitudinal axis; a conically tapered neck integral with and extending from the bolt head to the shank, wherein a taper angle of the tapered neck is preselected to be congruent to a taper angle of the tapered side wall of the through hole; and wherein the arcuate faces of the bolt head and the tapered neck have a common central axis that extends co-linear with the longitudinal axis and defines a common rotational axis so that, during use, the tapered neck remains in contact with the tapered side wall through a constant contact area during rotation of the bolt head relative to the mill liner.

2. A mill liner bolt as claimed in claim 1, wherein the taper angle is selected to be about 20° — 70°, or about 20° - 60°, or about 45° — 55°.

3. A mill liner bolt as claimed in claim 2, wherein the taper angle is 50°.

4. A mill liner bolt as claimed in any one of claims 1 to 3, wherein the flat faces extend tangentially with the shank.

5. A mill liner bolt as claimed in any one of claims 1 to 4, wherein the bolt head comprises one or more elastically deformable projections that project outwardly from the bolt head transversally to the longitudinal axis, wherein during use the or each projection is able to elastically deform when the bolt head is inserted into a through-hole in a mill liner, thereby to frictionally retain the bolt head within the through-hole.

6. A bolt as claimed in claim 5, wherein the bolt head comprises an annular groove configured to receive the one or more projections.

7. Abolt as claimed in claim 6, wherein the one or more projections comprise a substantially C-shaped retaining circlip made of spring steel.

8. A mill liner bolt and mill liner assembly for an ore grinding mill, the assembly comprising a mill liner bolt having a bolt head having opposed arcuate faces and opposed substantially flat faces, an elongated cylindrical threaded shank having a longitudinal axis, and a conically tapered neck integral with and extending from the bolt head to the shank: and a mill liner having one or more countersunk through-holes for receiving the mill liner bolt, each through-hole having an entry opening and an exit opening, wherein the entry opening has a pair of opposed curved sides and a pair of opposed straight sides and wherein the exit opening is circular, which through- hole further has a conically tapered side wall located between the entry opening and the exit opening; wherein the tapered neck and the tapered side wall have taper angles being congruent to each other; and wherein the arcuate faces of the bolt head and the tapered neck have a common central axis extend co-linear with the longitudinal axis and define a common rotational axis so that, during use, the tapered neck remains in contact with the side wall through a constant contact area during rotation of the bolt head relative to the mill liner.

9. An assembly as claimed in claim 8, wherein the taper angle is selected to be about 20° — 70°, or about 20° — 60°, or about 45° — 55°, 10. An assembly as claimed in claim 9, wherein the taper angle is 50°.

11. An assembly as claimed in any one of claims 8 to 10, wherein the mill liner bolt comprises one or more elastically deformable projections that project outwardly from the bolt head transversally to the longitudinal axis, wherein during use the or each projection is able to elastically deform when the bolt head is inserted into the through-hole in the mill liner, thereby to frictionally retain the bolt head within the through-hole while a nut is attached to the shank.

12. An assembly as claimed in claim 11, wherein the bolt head comprises an annular groove configured to receive the one or more projections.

13. An assembly as claimed in claim 12, wherein the one or more projections comprise a substantially C-shaped retaining circlip made of spring steel.

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