Field of the invention

The present invention relates to a wear liner element for a grinding mill , to a grinding mill comprising such wear liner elements , to a method of dismounting at least one wear liner element from a grinding mill , and to the use of an expandable ej ector unit such as a li fting bag to dismount a wear liner element from a grinding mill .

Prior Art

Grinding mills are used to grind mine ore or primary crusher product .

One type of grinding mills comprises a drum, in which the material to be ground, i . e . the charge , is ground by rotating the drum . The drum is either hori zontally or vertically orientated . The charge is ground by the action of impacts of portions of the charge with each other, as well as impacts o f particles that orbit and hit the charge .

In some types of hori zontal drum mills , called a ball mill or pebble mill , balls of hard material , are introduced in the drum, with the charge . When the drum is rotated, the charge is ground also by the action of impacts from the balls .

Another type of grinding mill comprises a container in which an agitator is arranged . Grinding media, such as steel balls or ceramic or natural pebbles , is provided in the container . Water and the material to be ground are fed into the container By rotating the agitator, the charge is agitated, such that the grinding media grinds the material to be ground by abrasion and attrition . Also this type of grinding mill may be orientated both vertically and hori zontally . The inside parts of these types of grinding mills are heavily exposed to wear during the grinding process . Therefore , the inside parts of a grinding mill can be covered with some kind of wear protection, such as wear-resistant liner elements . In vertical mills , the inner circumferential surface of the ( essentially cylindrical ) shell can be provided with wear liner elements . In hori zontal mil ls , the material to be ground ( e . g . lumps of ore ) is fed into one end of the mill and the ground product removed from the other end, and all of the ( essentially circular ) entrance end wall , the inner circumferential surface of the ( essentially cylindrical ) shell and the ( essentially circular ) discharge end wall can be provided with wear liner elements .

Apart from protecting the mill shell from wear caused by the impact and abrasion of the mill charge , such wear liner elements are also operative to elevate and tumble the mill contents in the necessary manner to create a grinding action . To achieve this , the mill liner profile must be constructed from high wear resistant materials and incorporate correct geometry to help determine the elevation of the mill charge and how the material is ground .

In the past , grinding mills were typically lined with cast metal linings of varying steel or iron alloys , such as manganese steel or chilled cast iron, depending on the character of the material to be crushed and the particular class of service for which the machine is intended . Manganese steel combines extreme toughness with high wear resistance .

As materials technology and des ign technique has advanced, today some alternatives exist to metal linings . Rubber compounds and composites have been developed to protect mill shells from wear, while new cast alloys and wear resistant plates can be bonded into rubber to withstand high impact abrasiveness . In primary mills , rubber steel composites ( Polymet ) and metallic liners are common . Typically, the wear liner elements wear and distort due to the significant pressures and impact loading forces they transmit. It is common to use a backing - commonly a rubber backing, with polyurethane (PU) being common for vertical mills - behind the wear liner elements for further protection as well as corrosion protection and to prevent unevenness, assisting with contact between the outward facing surfaces of the wear liner elements and the inward facing surfaces of the housing of the mill, i.e. the shell and end wall. In fact, the loading forces must be transferred to the wear liner elements from the structural mill parts which they protect, and for that, intimate contact is needed between the back of the wear liner elements and the inner surface of the shell or end wall. The rubber backing is typically bonded by adhesives, e.g. vulcanizing adhesives, to the inward facing surfaces of the housing of the mill.

The aforementioned wear liner elements are changed regularly, e.g. in intervals of 4, 12, 18 or 24 months. The replacement of the wear liner elements cumbersome. Generally speaking, a shell liner is comprised of a plurality of metal segments (made, for example, of manganese steel) mounted in end-to-end relationship, with their flat ends almost touching, a small gap being generally provided between the ends. After a certain operational period, the segments may be difficult to remove: on the one hand, parts of the charge combined with the slurry within the mill creates a cement like substance which will get in between the liners and make then more difficult to remove. Small grinding media or small pieces of the grinding balls which have come loose could also get in between the liners. On the other hand, because the liners are subject to great impact, metal flow occurs along the length of the liner (linear strain) , wherein the linear expansion of the liner segments creates great pressure at abutting flat end faces which tends to lock the liner segments in place and makes it difficult to remove them for maintenance purposes. Therefore, the wear liner elements are removed one by one using a rock breaker, i.e. a hydraulic or pneumatic hammer which is driven behind the wear liner elements.

In a large grinding mill, there can easily be over 1.000 wear liner elements to replace (several hundreds for the shell and further several hundreds for the end wall) . The existing methodology for the removal and replacement of wear liner elements - a process also known as a "re-lining" - is very time consuming, often taking multiple days to complete. This equals downtime and lost production for the operator of the mill .

Also, these wear liner elements are large, heavy and difficult to handle in a safe and reliable way. Different types of tools and lifting devices have been provided in order to be able to handle the liner elements in a way that is safe for the maintenance personnel. The removal of wear liner elements is also a hazardous task requiring the use of hot works.

Exemplary grinding mill shell liner elements are disclosed in US 4,231,528. US 2005/0116077 Al describes shell liner profiles. Exemplary grinding mill end liners are known from US 2,893, 650, and AU 2014/201893 Al discloses a device and method for handling an end wall liner element of a grinding mill.

Summary of the invention

In view of the above, an object underlying the invention is to facilitate the removal of worn liner elements from a grinding mill .

To achieve this object, the present invention provides a wear liner element for a cylindrical shell of a horizontal or vertical grinding mill as recited in claim 1, and a wear liner element for an end wall of a horizontal grinding mill as recited in claim 3.

According to the invention, the wear liner element is provided with an expandable ejector unit to be arranged between the outer surface of the wear liner element and the opposite inner surface of the shell ( claim 1 ) or the endwall ( claim 3 ) of the grinding mill . The ej ector unit has a first part for abutting or engaging with the outer surface of the wear liner element and a second part for abutting or engaging with the inner surface of the shell or endwall , and is operable to increase a spacing between the first and second parts to thereby increase the spacing between the outer surface of the wear liner element and the inner surface of the shell or endwall .

The ej ector unit is mounted in its undeployed state between the outer surface of the wear liner element and the opposite , inner surface of the shell or endwall . In other words , the ej ector unit is pre-installed between the wear liner element and the opposite surface of the shell or endwall . I f time has come for the wear liner element to be removed, the ej ector unit is operated to be expanded, prising the wear liner element away from its support .

The invention therefore removes the need for use of a hydraulic / pneumatic hammer to assist with the removal of the worn wear liner elements from the grinding mill and dispenses with the necessity to have workers operate immediately in the area of the wear liner elements . The invention will also result in signi ficant reduction in downtime during maintenance .

The invention will thereby result in an overall improvement in shutdown ef ficiency and ef fectiveness for all re-lining works .

Optional further features of the wear liner element for a grinding mill of the present invention are recited in the dependent claims .

The wear liner element for the shell may have a substantially elongated shape with a profiled cross section . The wear liner element for the endwall may have essentially the shape of a segment of a circle , or of a part thereof . The ejector unit may be expandable pneumatically or hydraulically. Also conceivable in principle are mechanically operable ejector units though, such as a high-powered spring released by remote control, or a servo-actuated lever arm.

The ejector unit may be operable to increase a volume of the ejector unit.

Specifically, the expandable ejector unit may include a lifting bag.

A lifting bag is capable of lifting loads of several tons, wherein a lifting bag with a capacity of e.g. eight tons could be used for the purposes of the invention (currently used wear liner segments for grinding mills have a weight of up to 8 tons) . The lifting bag is usually inflated with compressed air and in some cases with water or grout.

In comparison with other types of jacking equipment, lifting bags have major advantages such as the very small insertion height and fast operation. They are also light-weight and practically maintenance-free.

The lifting bag to be used according to the invention may be made from one or several layers per side. Suitable materials for the layer (s) include woven steel and Kevlar with neoprene. The surfaces of the lifting bags may be structured to provide an anti-slip effect.

The lifting bag functions according to the following principle: Force (F) = Pressure (P) x Area (A) . It is therefore advantageous to provide the lifting bag with a sufficiently large surface area to apply the desired force to the wear liner element to be removed. Suitable high-pressure inflatable li fting bags are available on the market , e . g . from MatJack Inc . , for li fting, moving, spreading and fixing applications .

The wear liner element may further comprise means for operating the ej ector unit , e . g . including a hydraulic or pneumatic line or hose extending to each ej ector unit in the grinding mill .

The ej ector unit may be disposed in the area of an edge of the wear liner element . Compared to the case in which the ej ector unit would be arranged in a central area of the wear liner element , the removal of the wear liner element is facilitated thereby : When activated, the ej ector unit acts upon the edge portion of the wear liner element to "peel" the wear liner element away from the underlying surface of the shell or endwall .

A cavity or recess may be included in the outer surface of the wear liner element to accommodate the expandable ej ector unit . The recess acts as an ej ector unit engagement portion . In other embodiments , the ej ector unit could be installed between the rear or outer surface of the wear liner element and the opposite surface of the shell without such a recess being formed in the back of the segment .

The invention also provides a grinding mill as recited in claim 13 , wherein at least one wear liner element is provided with an expandable ej ector unit arranged between the outer surface of the wear liner element and the opposite inner surface of the shell or endwall . The ej ector unit has a first part for abutting or engaging with the outer surface of the wear liner element and a second part for abutting or engaging with the inner surface of the shell or endwall and is operable to increase a spacing between the first and second parts to thereby increase the spacing between the outer surface of the wear liner element and the inner surface of the shell or endwall . The wear liner element of the grinding mill may include one or several of the features described above for the wear liner element and ejector unit.

The grinding mill may further comprise means for operating the ejector unit, e.g. including a hydraulic or pneumatic line or hose extending to each ejector unit in the grinding mill.

The wear liner elements may be supported end-to-end along a longitudinal direction of the shell and/or in a circular array on the inner surface of the at least one end wall, and a series of several wear liner elements may be arranged so that one, several or all wear liner elements in the series are provided with an ejector unit.

One lifting bag could in principle be installed to act upon several (adjacent) wear liner elements. A load distributor plate could then be provided so that the lifting bag is unaffected by any potential gap between the wear liner elements or if one wear liner element comes off before the other .

In the grinding mill, a backing such as arubber backing may be disposed on the inner surface of the shell or endwall facing the outer surface of the wear liner element to provide a base protection and prevent unevenness. The rubber backing may be bonded to the inner surface of the shell or endwall in a manner known per se, using suitable adhesives.

The grinding mill may further be associated with a control unit to control the activation of the ejector unit(s) , e.g. from a remote location, e.g. by way of a wireless connection.

The present invention further provides a method of dismounting at least one wear liner element from a grinding mill as recited in claim 18. The method includes the steps of arranging an expandable ejector unit between the outer surface of the wear liner element and the opposite inner surface of the shell or endwall , the ej ector unit having a first part abutting or engaging with the outer surface of the wear liner element and a second part abutting or engaging with the inner surface of the shell or endwall , and operating the ej ector unit to increase a spacing between the first and second part to thereby increase the spacing between the outer surface of the wear liner element and the inner surface of the shell or endwall .

I f the wear liner elements are arranged in a circular array on the inner surface of the at least one end wall , one keystone wear liner element in the array may be removed, e . g . with the aid of an associated ej ector unit , to release any stresses prior to removing the remaining segments in said array, be it by activating corresponding ej ector unit ( s ) or by other means . In embodiments , only the keystone wear liner element is removed with an ej ector unit whereas the remaining elements in the array on the end wall are removed by alternative means .

The ej ector units for the individual segments in a row or array could be activated one after the other so as to dismount the segments one after the other along the shell or end wall ; or several ej ector units could be activated simultaneously to dismount several , possibly several adj acent , wear liner elements simultaneously .

I f several rows of liners are provided, as it is usually the case in grinding mills , the removal of the rows of segments often starts with a row of liner elements in a lower part of the mill .

Upon completion of the dismounting of one row of elements , the dismounted wear liner elements can then be removed from the grinding mill in any known manner . The invention covers the use of an expandable ejector unit such as a lifting bag to dismount a wear liner element from a grinding mill, as recited in claim 20.

Finally, the present invention also relates to a wear liner element for a grinding mill as recited in claim 21 or 22. The wear liner element of claim 21 or 22 comprises an ejector unit engagement portion configured to receive or accommodate an expandable ejector unit.

The wear liner element of claim 21 or 22, and the expandable ejector unit which it is configured to receive or accommodate, may comprise any of the aforementioned features or combinations thereof.

Also, the ejector unit engagement portion could for example be a recess or cavity in the outer surface of the wear liner element to accommodate the expandable ejector unit. The recess or cavity could have a temporary, easy to remove, material inserted therein during installation. When it is time to install the ejector unit, this insert could be removed or destroyed in place to make room for the ejector unit.

The shape of the recess in the wear liner element can be designed to match the shape of the ejector unit, e.g. the lifting bag. The matching shapes may provide for a form-fit between the ejector unit and the wear liner element.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein: Figure 1 schematically illustrates a shell of a hori zontal grinding mill equipped with wear liner elements ;

Figure 2a illustrates an exemplary shell liner element and Figure 2b an exemplary end wall liner element for a grinding mill ;

Figure 3a is a schematic illustration of a shell liner element according to one embodiment of the present invention;

Figure 3b shows a li fting bag in a deflated state ;

Figures 4a and 4b illustrate the wear liner element with the li fting bag in a perspective view and from the side ;

Figures 5a and 5b illustrate the wear liner element , again in a perspective view and from the side , with the li fting bag after inflation; and

Figure 5c shows the li fting bag in the inflated state .

Detailed description of a preferred embodiment

Fig . 1 schematically illustrates a grinding mill . The sole purpose of this illustration is to explain the basic operating principle of a grinding mill , and it is not to be understood to imply any limitation of the present invention . The mill illustrated here is a hori zontal mill which is designed for grinding e . g . crude ore and generally comprises a cylindrical shell made of steel and supported for rotation about a hori zontal axis , and vertical end walls which confine the charge . The invention is equally applicable to vertical mills though .

The inner peripheral surface of the shell as well as the inner surfaces of the end walls , speci f ically the discharge end wall , are subj ected to signi ficant wear and tear . To control the movement of the ore in the mill and to protect the steel shel l and end walls against abrasion and erosion, wear resistant liner elements are mounted thereon .

Figure 1 shows that the entrance end wall , the cylindrical portion of the shell , and the discharge end wall of the grinding mill are all provided with wear liner elements . The cylindrical shell is lined by a plurality of substantially flat liner members (made , for example , of manganese steel ) mounted in end-to-end relationship, with their flat ends almost touching, a small gap being generally provided between the ends , and supported in cylindrical array by being individually bolted to the inner surface of the grinding mill shell . After a certain operational period, the wear liner elements may be di f ficult to remove : on the one hand, parts of the charge combined with the slurry within the mill creates a cement like substance which will get in between the liners and make then more di f ficult to remove . Small grinding media or small pieces of the grinding balls which have come loose could also get in between the liners . On the other hand, because the liners are subj ect to great impact , metal flow occurs along the length of the liner ( linear strain) , wherein the linear expansion of the liner elements creates great pressure at abutting flat end faces which tends to lock the liner elements in place and makes it di f ficult to remove them for maintenance purposes .

Figure 2a illustrates one of the substantially flat liner elements 30 for the inner circumference of the shell ( also designated " shell liners" ) . The wear liner element illustrated here has a speci fic profile to assist in moving the material to be ground inside the grinding mill , but the profile is not essential to the invention and other profiles could be used .

The shell liners may be alternately spaced by li fter-bars for li fting the ore to the top of the rotating shell or drum from which the ore tumbles by gravity to the bottom where it is crushed or reduced in si ze . On the other hand, the liners themselves may be configurated with raised rib portions to act as li fters in raising the ore .

The entrance and discharge end walls are provided with wear liner elements 30 ' . Since the end walls are essentially cylindrical , the wear liner elements 30 ' for the end walls ("end wall liners" ) commonly have the shape of a segment of a circle . While the end wall liner in Figure 2b is made from two parts , other configurations are possible in this regard, too .

In the operational state of the mill , a rubber backing (not speci fically illustrated) would be disposed between the outer surfaces of the wear liner elements 30 , 30 ' and the facing inner circumferential surface of the shell or endwall . The rubber backing is , in a manner known per se , provided to form a base protection and prevent unevenness , assisting with contact between the outward facing surfaces of the wear liner elements 30 , 30 ' and the inward facing surfaces of the shell and endwalls .

The wear liner elements are usually bolted to the shell and end walls . For this purpose , the wear liner elements may be equipped with through holes , threaded inserts or threaded bushings .

As will be clearly apparent , shell and end wall liners are subj ected to aggravated wear and tear due to continuous high impact loads and abrasion during the grinding operation, thus requiring periodic replacement of the liners .

To facilitate the removal of the wear liner elements from the shell or endwalls and exchange against new wear liner elements , at least some of the wear liner elements 30 , 30 ' are each provided with an expandable ej ector unit (not shown in Figures 1 , 2a and 2b ) arranged between the outer surface of the wear liner element 30 , 30 ' and the opposite inner surface of the shell or endwall . The ej ector unit is expandable so as to increase the spacing between the outer surface of the wear liner element 30 and the inner surface of the shell or endwall. The ejector unit is mounted in its undeployed state between the outer surface of the wear liner element and the opposite surface of the shell or endwall. In other words, the ejector unit is pre-installed between the wear liner element 30 and the opposite surface of the shell or endwall.

If time has come for the wear liner element 30, 30' to be removed, the ejector unit is operated to be expanded, prising the wear liner element 30, 30' away from its support.

The invention therefore removes the need for use of a hydraulic / pneumatic hammer to assist with the removal of the worn wear liner elements from a grinding mill and avoids the need for workers being present in the area of the wear liner elements proper. This will result in significant reduction in downtime during maintenance on the other hand.

The invention encompasses ejector units which are expandable in different ways, e.g. pneumatically or hydraulically. One practical implementation of the expandable ejector unit, which is also used in the embodiment shown in Figures 1 through 5, is an inflatable lifting bag 50. The lifting bag 50 is arranged between the outer surface of the wear liner element 30, 30' and the opposite inner surface of the shell or endwall of the grinding mill. The lifting bag 50 has opposite main surfaces, a first one abutting or engaging with the outer surface of the wear liner element 30, 30' and a second one abutting or engaging with the inner surface of the shell 40. The lifting bag 50 is installed in its deflated state. When the lifting bag 50 is operated to be inflated, the volume of the lifting bag 50 increases, and the spacing between the first and second surfaces is enlarged to thereby push the wear liner element 30, 30' away from the inner surface of the shell or endwall, dismounting the wear liner element 30, 30' from the shell or endwall. The force applied by the lifting bag 50 thereby helps breaking up any material that has deposited in the gaps between the liner elements over time, e.g. the cement-like material or pieces of grinding balls described further above, and held the liner elements stuck.

Figure 3a shows a wear liner element 30, 30' for a grinding mill, for the time being without a lifting bag 50. The wear liner element 30, 30' of this embodiment is distinguished from similar wear liner elements of the prior art in that a cavity or recess 60 is included in the back of the wear liner element 30, 30' which is large enough to accommodate the deflated lifting bag 30, 30' when the wear liner element 30, 30' is mounted to the grinding mill.

Illustrated in Figure 3b is one exemplary implementation of a lifting bag which is available under the trade name "MatJack" for lifting, moving, spreading and fixing applications. The lifting bag is capable of lifting a predetermined weight such as e.g. 6 tons if inflated with air under a corresponding pressure. In the present embodiment, the lifting bag has an approximately square shape, but a lifting bag for use in the invention could as well have other shapes such as rectangular or round.

The lifting bag 50 and the recess 60 in the wear liner element 30, 30' have matching shapes, e.g. to provide for a form-fit between the lifting bag 50 and the wear liner element 30, 30' . In the present embodiment, the lifting bag 50 has four tabs 51 integrally molded to the edges thereof for lifting or attaching to fixtures. In the present embodiment, the recess 60 in the back of the wear liner element 30, 30' includes corresponding cut-outs 61.

In other embodiments, the lifting bag 50 could be installed between the rear surface of the wear liner element 30, 30' and the opposite surface of the shell 40 without such a recess 60 being formed in the back of the wear liner element 30, 30' .

The lifting bag 50 functions according to the following principle: Force (F) Pressure (P) x Area (A) . The surface area of the lifting bag 50 should therefore be sufficiently large to create the desired force. The surface area of the lifting bag 50 should suitably amount to a sufficient percentage of the surface area of the wear liner element 30, 30' , i.e. the surface area of the rear or outer surface of the wear liner element as shown in Figure 3a. In the illustrated embodiment, the surface area of the lifting bag 50 could amount to about one quarter of the surface area of the rear or outer surface of the wear liner element 30, 30' , to give an example .

Figures 4a and 4b illustrate the wear liner element 30, 30' , in a perspective view and from the side, with the lifting bag 50 installed in the aforementioned recess 60. Figures 5a and 5b illustrate the wear liner element 30, 30' , again in a perspective view and from the side, with the lifting bag 50 after inflation. Also shown is the exemplary lifting bag 50 in the inflated state (Figure 5c) . Figures 5a and 5b are partial views from the side and in perspective of the wear liner element 30, 30' and the shell or endwall in a state in which the lifting bag 50 between the outer surface of the wear liner element 30, 30' and the inner surface of the shell or endwall has been inflated and has separated the wear liner element 30, 30' from the shell or endwall.

For operating the ejector units, i.e. lifting bags 50, a pneumatic line or hose (not shown) extends from each lifting bag in the grinding mill towards a source of compressed air (not shown) . The lifting bags 50 in Figures 3b and 5c include a corresponding connector 52 for a pneumatic line. The pneumatic lines from several lifting bags 50 could be combined via corresponding manifolds. A control unit (not shown) such as push button, deadman or joy stick controller is provided to control the supply of compressed air to independently or simultaneously inflate one or more of the lifting bags 50.

Considering the grinding mill as a whole, one or several wear liner elements in each row (for the shell) or array (for the endwall) are provided with an ejector unit. In one implementation, only one wear liner element in each row or array is provided with an ejector unit, or even only one wear liner element of the shell or an end wall is provided with an ejector unit. Once this wear liner element is removed, the remaining wear liner elements fall out or at least are removed more easily.

The lifting bags 50 for the individual segments 30, 30' in a row can in principle be activated one after the other so as to dismount the segments 30, 30' one after the other along the length of the shell and along the perimeter of the endwall. One could also consider activating several lifting bags 50 simultaneously to dismount several, possibly several adjacent, wear liner elements 30, 30' simultaneously. Anyhow, the process is continued until all elements 30, 30' in a row are dismounted and ready to be removed from the grinding mill.

The dismounted wear liner elements 30, 30' are then removed from the grinding mill in any known manner.

Each of the wear liner elements 30, 30' illustrated in Figure 1 may be provided with a lifting bag 50. In one practical embodiment, one wear liner element 30, 30' in a row of wear liner elements 30, 30' would be provided with an expandable ejector unit for reasons set forth further below.

In the illustrated embodiment, the lifting bag 50 is disposed in the area of a top edge of the respective wear liner element 30, 30' . Compared to the case in which the lifting bag 50 would be arranged in a central area of the wear liner element 30, 30' , the removal of the wear liner element 30, 30' is facilitated thereby: When inflated, the lifting bag 50 then acts upon the upper portion of the wear liner element 30, 30' to "peel" the wear liner element 30, 30' away from the underlying surface of the shell or endwall. The invention will result in an overall improvement in shutdown efficiency and effectiveness for all re-lining works.

While one embodiment of the invention has been described with reference to Figures 1 to 5c, the scope of the invention is not restricted to this embodiment but defined by the appended claims. Various modifications are included within the scope.

For example, in the present embodiment, each lifting bag 50 is associated with one wear liner element 30, 30' . In principle it is conceivable to associate a lifting bag 50 with several, i.e. two, three or even more, adjacent wear liner elements 30, 30' which would then be acted upon simultaneously.