ROLLER MILLWITH CONTINUOUS GRINDING-OFFOFTHOSE GRINDING SURFACES _j ^ ARESUBJECTEDTOLEASTWEAR

The present invention relates to a roller mill for grinding of particulate material, which roller mill comprises at least one grinding roller which operates interactively with at least one further grinding body, such as a grinding table, a grinding ring or a grinding roller.

Roller mills of the abovementioned kind are well-known. Thus, a vertical mill is known e.g. from DK patent No. 150818, a ring roller mill is known e.g. from DK patent application No. 748/93 and a roller press is known e.g. from international patent application No. PCT/EP92/00141.

A problem which is common to these types of roller mills is that the surfaces of the grinding bodies are not uniformly subjected to wear across their entire width. During operation of a roller press it has thus been ascertained that the centre areas of the rollers are subjected to wear much faster than is the case at the edges of the rollers, thereby imparting a trough-like cross profile to the roller surfaces. This is undesirable for operational reasons, and, in actual practice, it will necessitate grinding-off, turning, milling, or replacement of the high areas of the roller surfaces at appropriate intervals. Similar undesirable wear profiles are also known for the two other types of roller mills referred to above.

In EP patent specification No. 0 383 004 is described a roller press where an attempt has been made to resolve the aforementioned problem of uneven wear by that the areas of the roller surfaces which are subjected to least wear are manufactured from a less wear-resistant material than is the case for the remaining areas of the roller surfaces. In this way a more uniform wear profile should be achieved.

The actual wear to which the grinding surfaces are subjected during operation depends on various operating

parameters, the characteristics of the material to be ground, and other factors. In practice, it will therefore be difficult for the equipment manufacturer to select materials for the different areas of the surfaces of the grinding bodies which will ensure total elimination of the mentioned problem. At best, this known solution will only lead to an extension of the operating cycle of the roller press between two maintenance shutdowns.

It is the objective of the present invention to provide a roller mill whereby the aforementioned problem is eliminated.

This objective is achieved according to the invention by a roller mill of the kind mentioned in the introduction, and being characterized in that it comprises means which provide for continuous grinding-off of at least the areas on the surfaces of the grinding bodies which are subjected to least wear during the grinding process.

As a result hereof, the surfaces of the grinding bodies are worn more uniformly across their entire width, thereby avoiding undesirable wear profiles and extending the effective lifetime of the grinding bodies.

Further features of the invention are indicated in the claims 2-8.

In the following, the invention will be described in further details with reference being made to the drawing, which is diagrammatical, and in which

Fig. 1 shows a horizontal sectional view of a first embodiment of a roller press viewed from above, which comprises grinding-off means according to the invention, Fig. 2 shows a section through the roller press illustrated in Fig. 1 viewed from the side,

Fig. 3 shows a part of a second embodiment of a roller press viewed from the side, which comprises grinding-off means according to the invention,

Fig. 4 shows a horizontal sectional view of a vertical mill viewed from above, which comprises grinding-off means according to the invention, and

Fig. 5 shows a section through a ring-roller mill viewed from the side, which comprises grinding-off means according to the invention.

Illustrated in Fig. 1 and 2 is a roller press which comprises two oppositely rotating rollers 1 and 3, each being mounted in bearings which are not shown. At least one of the rollers 1, 3 may be fitted so that it can be displaced radially and horizontally, making it possible to adjust the gap width between the rollers. The rollers 1, 3 rotate about separate axes in the direction indicated by means of the arrows. During operation, the material to be ground is fed via a shaft 5 to the gap between the rollers 1, 3, which involves that the material is drawn through the gap and subjected to grinding, possibly with simultaneous formation of a grinding bed.

After some lenght of time of operation of such a roller press it has been ascertained that the centre area of the roller surfaces, which are indicated in Fig. 1 at A, incurs wear more quickly than is the case at the areas around the edges which are indicated at B.

In order to overcome the problems which any such wear pattern may involve, it is suggested according to the invention to fit wear blocks 7 which drag against the surfaces of the two rollers in such a way that they provide for a continuous grinding-off of the areas of the roller surfaces which are subjected to least wear during the

grinding process. The roller press shown in Fig. 1 and 2 comprises in connection with each roller two wear blocks 7 which are fitted in a support structure 9 which is movably hinged to the machine frame 11 of the mill. In Fig. 2 the roller press is further seen equipped with spring means 13 so as to thrust the wear blocks against the roller surfaces. The shown wear blocks 7 are mounted at the edge zones B of the rollers and have a width which corresponds to the width hereof. Alternatively, the roller press may in connection with each roller comprise a wear block 7 which extends across the entire width of the roller.

Fig. 3 shows a roller press in which each wear block 7 via a spring means 15 is directly mounted in the machine frame 11.

In Fig. 4 is shown a horizontal section through a vertical mill which comprises a rotating grinding table 21 and three grinding rollers 23 rolling thereon. For equalization of the uneven wear profile which will occur during the operation of this mill on the grinding surface of the grinding table 21 as well as on the grinding surfaces of the rollers 23, the mill is equipped, in similar manner as practised for the roller press mentioned above, with wear blocks 7. In Fig. 4 the shown wear blocks 7 extend across the entire width of the grinding surfaces, but may, alternatively, be designed to cover only the areas of the grinding surfaces which are subjected to least wear. The wear blocks 7 are envisaged for mounting in a support structure, not shown, which, rotatably and with possible application of spring loading, is hinged to the housing of the mill or the machine frame 25.

In Fig. 5 is seen a sectional side view through a ring roller mill which comprises a grinding ring 31 and a grinding roller 33. For equalization of the uneven wear profile which will occur during the operation of this mill

on the grinding surface of the grinding table 31 as well as on the grinding surfaces of the roller 33, the mill is equipped, in similar manner as practised for the previously mentioned mills, with wear blocks 7. The wear blocks 7 may extend across the entire width of the grinding surfaces, but may, alternatively, be designed to cover only the areas of the grinding surfaces which are subjected to least wear. The wear blocks 7 are envisaged for mounting in a support structure, not shown, which, rotatably or displaceably and with possible application of spring loading, is hinged to the housing of the mill or machine frame, not shown.

For all the embodiments illustrated in Figs. 1 - 5, the wear blocks are envisaged for installation in such a way that they can be inverted and/or turned gradually as they are subjected to wear.

The wear blocks may be manufactured from many different materials, but they are primarily envisaged for being manufactured from granite rock, Densit, fusion-cast basalt, or a similar high-abrasive material.