EP1960110B1

EP1960110B1 - Equipment lifting arrangements

Info

Publication number: EP1960110B1
Application number: EP06817589A
Authority: EP
Inventors: James Sulzberger
Original assignee: Bradken Resources Pty Ltd
Current assignee: Bradken Resources Pty Ltd
Priority date: 2005-12-07
Filing date: 2006-12-06
Publication date: 2011-01-26
Anticipated expiration: 2026-12-06
Also published as: EP1960110A1; ZA200803449B; ATE496699T1; WO2007065214A1; EP1960110A4; PL1960110T3; DE602006019908D1

Abstract

An annular grinding mill ring has a radially inner wall, a radially outer wall and an annular recess between the walls for receiving grinding balls; the radially inner wall has a multiplicity of recesses spaced around the ring and extending into the wall of the ring for cooperation with lifting hooks and accessible at a location intermediate the axial ends of the grinding mill ring.

Description

FIELD OF THE INVENTION

The present invention relates to lifting arrangements and is especially applicable to systems for providing for safe lifting of large objects such as ring shaped objects requiring installation and removal from working positions.

BACKGROUND OF THE INVENTION

As disclosed in document US-A-3 044 717 one known type of grinding mill comprises upper and lower rings which confront each other and each has an annular recess of part spherical shape in cross-section with grinding balls located between the confronting recesses with an inverted upper ring resting via the grinding balls on top of the lower ring. The lower ring when in use is supported on a table which rotates so that particulate feedstock is supplied generally vertically downwardly between the rings and migrates radially outwardly through the rings and grinding balls as it is pulverised. Periodically, the mill needs to be disassembled and in particular the lower ring removed and replaced. Such rings are typically of white iron to provide resistance to wear. It is known that such materials do not lend themselves to machining for the purpose of attachment to securing devices to facilitate lifting or for being provided with recesses to accommodate lifting components such as hooks. Therefore, one approach is to cast into the structure recesses spaced around the exterior and lower periphery of the lower ring, whereby lifting hooks may be engaged in the recesses. The hooks are attached to chains which extend downwardly from a lifting suspension point.
Usually four lifting recesses are cast into the bottom of the rings for connection to hooks, a typical ring being 3.5 metres diameter and 7,500 kgs in weight.
The present invention is directed to new and useful alternatives for such applications.

SUMMARY OF THE INVENTION

The invention manifests itself in both methods of operation as well as specific new equipment designs to facilitate the lifting process.
In a first aspect, the invention consists in An annular grinding mill ring having a radially inner wall, a radially outer wall and an annular recess between the walls for receiving grinding balls, the radially inner wall having a multiplicity of recesses spaced around the ring and extending into the wall of the ring for cooperation with lifting hooks and accessible at a location intermediate the axial ends of the grinding mill ring.
Usually the hooks are generally j-shaped hooks having a main leg with an upper end portion when in normal orientation adapted for connection to a swivel and chain system and the opposite end of the j-shaped hook having a tip portion adapted to fit with a clearance into a recess.
The grinding mill ring may have its radially inner wall portion defined by surfaces which in use lie adjacent or contact portions of the j-shaped hook for each recess. The arrangement may provide for a pure vertical lift from the hook ie. in a direction parallel to the axis of the ring despite lifting chains angling inwardly to an axially located central lifting point for each hook.
In one embodiment the interior wall portion of the grinding mill ring into which the recesses are located comprises an axially upper end portion which extends at a shallow angle to the axis of the ring to an intermediate location at a greater radial distance from the axis than the upper end.
Each recess may be arranged to extend extends into the ring from the intermediate location, and is defined between substantially parallel spaced walls substantially parallel to the angled upper end portion, the recess being directed upwardly.
The spaced wall spaced wall which is radially in wards leads to a tip having a substantially semi-circular profile which is adapted to be a loose fit with a complementary portion (between major and minor legs) of a j-shaped hook. The recess may have an interior terminating wall also of substantially semicircular profile against which the free tip of the minor leg of the j-shaped hook in use engages for transmitting lifting load and is also a loose fit.
The grinding mill ring may be otherwise conventional in having a cylindrical wall in its lower portion extending around the axis of the ring and substantially fitting over a yoke table. A yoke cover of disc shape may be supported on the yoke table with a spacing of around 50mm between the outer cylindrical edge of the yoke cover and the confronting wall of the inner surface of the grinding mill ring. The yoke cover can have an upper surface lying substantially in the same plane as the.top of the grinding mill ring.
The invention does also manifest itself in a grinding mill having the structure described above in combination with a bottom ring as also described in any one of the forms above.
The invention also manifests itself in a methodology of operating a grinding mill in which a generally j-shape hook is used in each of a multiplicity of circumferentially spaced recesses in a bottom ring as described in any one of the forms above, each such hook being dimensioned to have a height less than the distance between the top of the yoke cover and the yoke table so that when lifting forces are released each hook drops down to be supported on the yoke table, the hook is a loose fit in the recess and the hook having a screw-threadably attached swivel for lifting chains, the methodology being characterised by, after installing the bottom ring, unscrewing the swivels and removing them thereby leaving a screw threaded blind bore in each hook adapted to receive and secure a cover arrangement to prevent the ingress of material to be ground into a zone occupied by the hook. Removal of the ring can then be achieved by re-attaching the swivel and chain to each hook and lifting.
In yet another aspect the invention manifests itself in a hook for use with a lower ring of grinding mill and in any one of the forms as described herein and the grinding mill having structure for supporting the lower ring and including a yoke table supporting a yoke cover with an annular gap between the radially outer edge of the yoke cover and the radially inner wall portion of the grinding mill ring, the hook having height less than the axial distance between the top of the yoke table and the yoke cover, the hook being generally j-shaped with a top wall having a blind, screw-threaded bore for receiving a swivel to which a lifting chain is attached and the hook having major and minor legs joined by a base portion having a base wall for supporting the hook on a yoke table.
The major leg may have a surface extending at a shallow angle to the axial direction when in use and for contacting or lying adjacent the complementary surface of the bottom ring and the minor leg has a corresponding surface facing away from the major leg and also at a similar shallow angle to the axial direction when in use whereby the hook is adapted for provide a vertical lift of the ring with lifting chains angled radially inwardly eg at around 20° to the axial direction.
The j-shaped hook may have a substantially semicircular tip surface for engaging for lifting the end wall of the recess of the ring but in a loose fit and also the base portion of the j-shaped hook may have a curved surface defining a space between the legs of the hook and defining a recess for accommodating in a loose fit a corresponding curved dip portion of the bottom ring.
In a further aspect the present invention provides a lifting hook for use with or when used in conjunction with a grinding mill ring according to the first aspect of the invention.
The invention will be further explained and exemplified but by way of example only with reference to the accompanying drawings of which:-

Figure 1 is a schematic section view of the grinding arrangement of a known grinding mill;
Figure 2 is a cross sectional view of a grinding arrangement including a grinding mill ring and a lifting hook according to an embodiment of the present invention and at the time of installing the grinding mill ring:
Figure 3 is a cross section view of the grinding arrangement of figure 2 with swivel removed;
Figure 4 is a top view of the lifting hook of figure 2;
Figure 5 is a front view of the lifting hook of figure 2;
Figure 6 is a cross sectional view along the line A-A in figure 5; and
Figure 7 is an enlarged view of detail C of figure 6.

Referring first to figure 1, a known type of grinding arrangement used in a grinding mill for grinding coal is illustrated. The main components are a rotatable yoke table 2 supporting a lower grinding ring 10 with grinding balls 3 located in an annular trough 12 in the ring and supporting an upper complementary grinding ring 4. A yoke cover 5 of disc shape is mounted on the yoke table and provides a horizontal surface at the same height as the upper rim of lower ring 10 and onto which particulate material to be ground is dropped in use. In operation of the mill the coal migrates radially outwardly between the rings and is ground by the grinding balls into a pulverised form for discharge.
The lower grinding mill ring 10 is usually made of white iron and is highly resistant to abrasion. However, periodically it will need replacement and the machine must then to be disassembled and the lower ring removed using lifting tackle. The ring is typically 3.5m in diameter and over 7,000kg in weight and must be handled safely and reliably. Thus, readily engagable fixing arrangements are needed and recesses 14 are provided about the periphery of the ring 100 for the purpose of engaging lifting hooks to lift the ring.
Referring to figure 2, a modified grinding arrangement is shown at the time of installing a modified lower grinding ring 100 and identical reference numerals to figure 1 will be used to indicate identical components. In this embodiment, three recesses 20, only one of which is visible in figure 2, are provided spaced about the inner portion of grinding ring 100. One of hooks 22 (only one of which is visible) engage with each recess 20. Each hook 22 includes a blind threaded bore 23 which receives a threaded swivel 24. Swivel 24 affixes to lifting chain 26 in a known fashion.
To install ring 100, it is lowered into position on yoke table 2. Thereafter, each of swivels 24 is disconnected from each hook 22 (see figure 3). In this embodiment a small clearance is provided underneath hook when installed to allow it to drop down a small distance to rest upon yoke table 2. This ensures the hook 22 is not under load after installation and does not interfere with correct alignment of mill parts, or obstruct material being ground in the mill.
Recess 20 and hook 22 are shaped to maintain hook 22 in a generally vertical orientation during lifting. By way of explanation, and referring to figure 2, a lifting force F applied to lifting chain 26 is made up of a horizontal component H and a vertical component V. The tendency for the hook to rotate in a clockwise direction as a result of the horizontal component of the force is resisted by abutment of hook 22 with recess 20 at contact points A and B. This interaction of hook 22 and recess 20 resists rotation of the hook and avoids the upper part of hook fouling against yoke plate 5 during installation or removal.
Hooks 22 remain in place in recesses 20 for the useful life of the grinding ring 100. Plugs to prevent ingress or particles may be installed in the threaded bores 23 of the locks 22, and/or a cover ring may be installed over the zone between the yoke cover 5 and the lower ring 100.
Removal of grinding plate 100 such as for the purpose of replacing a worn grinding plate 100 is a reversal of installation. Swivels are re-attached to each of hooks 22 and the swivels are attached to lifting chains. Upon lifting, each of hooks 22 engage with recesses 20 and the ring 100 is lifted out of position.
The shape of hook 22 is apparent from figures 4 to 7. Each hook 22 has a main limb 30 having an upper end into which a threaded lined bore 23 is provided and around an axis 31. The main limb is of substantially rectangular of sectional shape with its outer and inner side faces 31 and 32 parallel to the axis 31. The main limb 30 has a lower portion 33 with inner and outer side faces which are inclined at about 15° to the axis 31 and towards a curved tip portion 34. The hook has a base portion 35 providing a flat base surface 36 at right angles to the axis 31 with curved corners joining the flat base 36 to the inclined lower outer surface 37 and an inner surface 38.
An aperture 39 is defined between the lower portion of the inner surface 32 and a confronting surface 40 of the tip 34. The tip terminates in a pan cylindrical upper surface 41 which leads to an outer face 42 of the tip and which is inclined at about 11° to the axis 31.
The recess 39 is shown in more detail in figure 7. It is designed to provide a convenient clearance fit with a complementary curved projection 50 at the periphery of the lower ring 100, the curved projection being of part cylindrical form. As illustrated in figure 7 the curved recess 39 is formed with a smooth joining of two different radius portions as indicated with lateral and vertical spacing to obtain the desired fit.
Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.

Claims

Annular grinding mill ring (100) having a radially inner wall, a radially outer wall and an annular recess (20) between the walls for receiving grinding balls (3), the radially inner wall having a multiplicity of recesses (20) spaced around the ring and extending into the wall of the ring (100) for cooperation with lifting hooks (22) and accessible at a location intermediate the axial ends of the grinding mill ring (100).
Mill ring as claimed in claim 1, where the radially inner wall of the grinding mill ring (100) in which the recesses (20) are located comprises an axially upper end portion which extends at a shallow angle to the axis of the ring to an intermediate location at a greater radial distance from the axis than the upper end.
Mill pain ring as claimed in claim 2, wherein each recess (20) extends into the ring (100) from the intermediate location, and is defined between substantially parallel spaced walls substantially parallel to the angled upper end portion, the recess (20) being directed upwardly.
Mill ring as claimed in claim 3. wherein the spaced wall which is radially in wards leads to a tip (50) having a substantially semi-circular profile which is adapted to be a loose fit with a complementary portion (between major and minor legs) of a j-shaped hook.
Lifting hook (22) when used in conjunction with a grinding ring (100) according to claim 1.
Lifting hook (22) for use with a grinding ring according to claim 1, and being of generally J shape with a main limb (30), base and curved tip (34), the hook having a threaded bore extending into an upper surface of the main limb (30) for attachment to a lifting swivel (24) and extending around an axis of the main limb (30) of the J shaped hook (22), the hook having a side surface of the curved tip of the hook for engaging with corresponding faces of a recess of grinding mill ring (100) and the hook (22) being a clearance fit in the recess, the curved tip (34) and the recess (20) each being of substantially circular shape in cross section.
Lifting hook as defined in claim 6 and having an axial dimension less than the thickness of the ring (100) whereby on disengagement of lifting means (24, 26), the hook (22) can drop down to be supported on a yoke table (2) and left in position during a service period for the grinding mill.
Lifting hook as defined in claim 7, wherein the base (36) is flat for supporting the hook (22) on the yoke table (2).
Lifting hook as defined in any one of claims 6-8 wherein the side of the main limb (30) to lie adjacent an axially middle portion of a radially inwardly facing wall of the mill ring (100) is at a shallow angle to the axial direction for complementing a corresponding angle on the radially inner wall.
Lifting hook as defined in any one of claims 6-8, wherein the curved tip (34) has lateral faces substantially parallel to one another and inclined towards the main limb (30) and at a shallow angle to the axis (31).
Method of handling an annular grinding mill ring having the form of a mill ring (100) of any one of claims 1-4 comprising using a lifting hook (22) as claimed in any one of claims 6-10 in each recess (20), installing a swivel (24) and lifting chain (26) in each hook (22), lifting the ring (100) and after installation on a yoke table (2), removing the swivel (24) and chain (26) for a period of service.