Wear element for a rotating mill-drum

The invention relates to a lifter bar intended to be mounted internally in a rotating mill drum for grinding ore and minerals. According to the invention, the upper portion of the lifter bar has a carcass of metal, comprising an elongated forward wall element facing in the direction of movement of the wear element, an elongated rear wall element and between these two wall elements transverse wall elements, the wall elements of the carcass defining between them a plurality of spaces, which are at least partially filled with a filler of another material than any of the components of the mill charge, and of greater abrasive specific volume loss than the metal of the carcass.

The present invention relates to a wear element in the form of a so-called 
lifter bar to be mounted on the inside of a rotating drum, in particular a 
mill for grinding ore and minerals, in order to protect, as a portion of 
the lining, the drum against wear during its rotation, said wear element 
consisting of a foot portion, for fixing the wear element in the drum, and 
an upper portion joined to the foot portion and arranged to extend into 
the drum. 
A mill for grinding ore and minerals is always provided on the inside of 
the drum with a lining to protect the drum against wear during the milling 
work which is carried out by pebbles, the ore itselves or milling bodies 
of metal, such as balls, rods and cylpebs. Such a lining can be made in 
many ways, but often consists of plates and lifter bars of a 
wear-resistent material, for example steel or rubber. The lifter bars 
extend normally in the longitudinal direction of the mill and essentially 
radially on the heads of the drum and are most often fixed in the drum 
between the wear plates which are thus clamped in place. A lining 
consisting of lifter bars and plates has the advantage over smoother 
designs, that the lifter bars lift the mill charge which thus exerts less 
slippage and abrasion against the drum walls during the rotation of the 
drum. By virtue of the fact that the lifter bars are Substantially higher 
than the plates, these are protected by the lifter bars, which are 
subjected, primarily from above, to most of the wear. This means that if 
the wear on the top of the lifter bars can be reduced, the wear on the 
plates will also be reduced automatically. Lifter bars of wear-resistent 
rubber are often reinforced or capped with a steel top or steel profile on 
the side facing the direction of rotation to extend the life of the lifter 
bar and the lining as a whole. 
The purpose of the present invention is to suggest a new type of lifter bar 
design, which makes it possible in mills such as pebble mills and ball 
mills, to extend the life of the lifter bars and thus possibly extend the 
intervals between liner replacements. 
In order to solve this task, the wear element of the type described by way 
of introduction, is broadly characterized in that the upper portion has a 
carcass of metal, preferably of wear-resistent steel or white cast iron, 
comprising an elongated forward wall element facing in the direction of 
rotation of the wear element, an elongated rear wall element and between 
these wall elements transverse wall elements, the wall elements of the 
carcass defining between them a plurality of spaces which are at least 
partially filled with a filler of another material than one of the 
components of the mill charge, and of greater abrasive specific volume 
loss than the metal of the carcass. 
The cell-like structure of the metal carcass is used primarily to achieve a 
partly continuous self-protecting effect of the lifter bar. The filler in 
the spaces of the metal carcass is selected so that it is worn by volume 
more rapidly than the metal carcass. Cavities are thus gradually dug out 
at the tops of the lifter bars limited in size by the wall elements of the 
metal carcass. Components from the mill charge which are wedged between 
the wall elements in the dug-out cavities or lie loosely therein protect, 
during the milling process, the upper edges of the metal carcass of the 
lifter bar which are most subjected to wear by periodically extending 
thereabove. This increases the life of the lifter bar. Continuity in the 
self-protecting process is assured by the fact that the depths of the 
dug-out holes are limited by the relatively short distances between the 
wall elements. 
Since it is advantageous to retain the original height of the lifter bar as 
long as possible, one can use the metal carcass of the lifter bar and the 
filler lying in its spaces to support and hold one or more wear bodies of 
harder material than the metal carcass, the filler next to the wear body 
essentially serving as a binding agent. In this case, it is assumed that 
the carcass is made in the hardest possible material in view of the 
application, at the same time as one should keep in mind that a wear body 
can be made harder and is stressed more uniformly the smaller it is. Such 
a body can also be embedded in an elastomeric filler in the spaces of the 
carcass, which has a dampening effect on the wear body, thus reducing its 
tendency to crack. The wear body is also surrounded by the wall elements 
of the metal carcass, which greatly reduces the risk of the end edges of 
the wear body being chipped-off by the impact of the mill charge. Such 
wear bodies can consist of a metal harder than that of the metal carcass 
or of a special material, such as carbides, nitrides or ceramics. The 
extreme hardnesses of the last mentioned material group has up to now not 
been utilized either technically or economically for mill linings in the 
mining industry. 
The above-mentioned self-protecting effect and protecting effect with the 
aid of extra wear bodies can be combined in the same lifter bar. 
U.S. Pat. Nos. 939,637, 864,357 and 1,055,395 describe mill linings which 
can provide a certain amount of self-protecting effect but which relate to 
designs with initially open oblong channels between ribs for capturing 
protective grinding pebbles. These known designs have, however, never 
functioned well in practice, primarily due to the fact that the open 
channels immediately capture stones which stuck in the bottom of the 
channels, thus making impossible a continuous repetition of the 
self-protecting effect. 
In the present invention, it is the top surface of the lifter bar (the rib) 
which is to capture the components from the mill charge, not the open 
spaces which are formed between the lifter bars (ribs). Furthermore, no 
initial completely open spaces on the top of the lifter bar are used, 
rather a metal carcass with wall elements limiting spaces filled with a 
filler of another material than any of the components of the mill charge, 
and which is worn down more rapidly than the surrounding metal wall 
elements, thus successively creating dug-out cavities, which assures 
repetition of the self-protecting effect, since components from the mill 
charge fixed to the top of the lifter bar and projecting therefrom can be 
gradually replaced by new charge material. 
Additional characteristics of the wear element according to the invention 
are disclosed in the subsequent dependent claims.

FIG. 1 shows a section of a portion of a mill liner in a cylindrical mill 
drum for grinding ore and minerals. The drum has a shell 10 with a lining 
consisting of wear plates 12 of an elastomeric material, for example 
rubber, and lifter bars 14, located between the plates 12 and extending in 
the longitudinal direction of the drum. Each lifter bar 14 consists of a 
foot portion 16 by which the lifter bar is anchored to the shell 10 of the 
drum by means of suitable fixing means, whereby the plates 12 are clamped 
in place, and an upper portion 17 which extends into the interior of the 
drum. The upper portion 17 of each lifter bar 14 has a carcass 18 of 
metal, preferably of wear-resistent steel or white cast iron. The carcass 
18 comprises a forward elongated wall element 20 facing the rotational 
direction B of the drum, a rear elongated wall element 22 and transverse 
wall elements 24. These wall elements delimit between themselves open 
spaces 26 (see FIG. 2) designed to be at least partially filled with an 
elastomeric filler 28 of greater abrasive specific volume loss than the 
metal in the carcass 18. 
In this in detail described embodiment of the invention, the foot portion 
16 and the filler 28 in the spaces 26 are formed in one piece of 
elastomeric material, the metal carcass 18 being joined to the foot 
portion 16 and the filler 28 by e.g. vulcanization. The filler 28 can 
suitably extend up to a surface which essentially levels with the upper 
edges of the walls 20, 22, 24, i.e. so that they fill out the entire or 
almost the entire spaces 26. Since the inner walls of the metal carcass 
have a very large total area, the elastomeric filler in this entirely open 
elastomeric version does not need to extend, for the sake of adhesion, up 
to the level of the upper edges of the carcass, but can terminate at a 
lower level with another filler material in the upper end of the spaces. 
From a practical point of view, it is, however, better to have a filler 
consisting of only one filler material. In addition to connecting the foot 
portion 16 and the metal carcass 18, the filler in the spaces is intended 
to be gradually worn to capture components from the mill charge and thus 
assure continuity in the self-protecting effect. It is not required that 
the filler have high wear resistance. Rather, it is advantageous as 
regards capture and life, if the filling has a markedly poorer resistance 
to wear than the metal in the carcass. The captured components from the 
mill charge thus periodically extend up above the upper edges of the walls 
of the carcass and thus form a protection therefore, so that the metal 
carcass 18 is worn less rapidly. When the projecting captured components 
have been worn down to essentially the level of the upper end edges of the 
wall elements of the carcass 18, they have a greater tendency to crack and 
break and loosen from the cavities, so that they can be replaced by new 
larger protective bodies from the mill charge, thus repeating the 
self-protecting function, possibly after an additional digging-out of the 
filling in the cavities. 
In an alternative embodiment of the invention, a wear body 30 of harder 
material than that in the metal carcass can be used, as is shown in the 
right hand lifter bar in FIG. 1 and in the right hand portion of the metal 
carcass in FIG. 2. The wear body 30, which can be several times harder 
than the metal in the metal carcass or the components in the mill charge, 
is embedded in the filler of the cavity leaving a binding layer of filler 
between the wear body and the walls of the carcass. The wear body 30 
normally only takes up a portion of the depth of the space, as can be seen 
to the right in FIG. 1. In this way, when the wear body 30 has been worn 
down completely, components from the mill charge can serve as an extra 
protector for the metal carcass, as described previously. One or several 
of the transverse walls can be completely or partially eliminated below 
the hard wear body 30 in order to be able to capture components from the 
mill charge which are larger than the wear body. 
Within the scope of the invention, the metal carcass 18 and its wall 
elements 20, 22, 24 can be made and oriented in various manners. In the 
Figures, all of the opposite surfaces of the wall elements are essentially 
plane parallel. This is, however, not always preferable. The wall elements 
of the metal carcass can have upper edge surfaces which lie at different 
levels. According to FIG. 2, the transverse wall elements 24 extend 
essentially perpendicular to the front and back walls 20, 22. However, the 
term "transverse" used here and in the patent claims is to be understood 
as not only referring to such perpendicular wall elements, but also 
obliquely extending elements, such as are indicated by the dashed lines at 
24a in FIG. 2 and also wall elements which are inclined in other manners, 
are rounded-off or sloped. The spacing between the transverse wall 
elements can also vary. 
A row of lifter bars which extends from end wall to end wall in the mill 
drum, normally consists of a plurality of lifter bars 14 which are placed 
end to end. FIG. 2 shows an elastic lifter bar 14 with a longitudinally 
divided metal carcass 18 which has been made so that a hole 26a is formed 
between the surfaces of two adjacent parts of the carcass, said hole being 
approximately as big as the rest of the holes 26 in the metal carcass 18. 
The hole 26a is thus formed in the joint between lifter bars in the same 
row. 
Depending on the method of manufacture, the wall elements in the metal 
carcass can consist of different alloys, and the wall elements can also 
form a metal carcass via at least one of the wall elements not being 
securely joined to the other wall elements. 
When the foot portion of the lifter bar and the filling is made in one 
piece of elastomeric material, the metal carcass can be fixed to the 
elastomeric piece in other ways than by vulcanization, for example 
mechanically or chemically. According to a suitable embodiment, which is 
shown in FIG. 1, the forward and back walls 20, 22 are inclined forwards 
in the direction of rotation. This provides inter alia an advantageous 
angle of attack for the components of the mill charge against the top side 
of the lifter bar filling for a rapid digging out and less wear of the 
lining as a whole during the milling process. The inclination of each of 
these walls can be the same or differing, as shown in FIG. 1 and FIGS. 
3a-e. 
FIGS. 3a-e show additional variants of the construction of the metal 
carcass when the lifter foot and a substantial portion of the filler is 
elastomeric, these being made in one piece. 
FIG. 3a shows with solid lines a variant where the forward wall element is 
inclined backwards and the back wall stands approximately radially in the 
drum. The dashed lines show that the upper surface of the rear wall is at 
a higher level than the front edge, so that a forwardly inclined or raised 
top side is formed similar to that in FIG. 1. PG,10 
FIG. 3b shows variants where both the longitudinal wall elements stand 
straight up, with or without an inclined top surface. 
FIG. 3c shows a "symmetrical" metal carcass of a lifter bar which can be 
used when the drum is driven in either rotational direction, if the drum 
rotation can be reversed. This can be used to, in general, extend the life 
of the lining and to get a certain portion of the almost worn-out captured 
protective bodies from the mill charge to loosen from the wall element of 
the carcass, and this can additionally extend the life of the lifter bar. 
FIG. 4 shows an embodiment of the lifter according to the invention where 
the upper portion and the foot portion are formed in one piece of metal. 
The spaces in the upper portion preferably have closed bottoms and are 
filled with a suitable filler with the purpose of being gradually dug-out 
and/or serving as a binder material for extra wear bodies as discussed 
above. A lifter bar with a foot portion of metal can essentially have 
metal carcasses according to the embodiments in FIGS. 1-3.