AU710348B2

AU710348B2 - Grinding roll and method for operation and repair thereof

Info

Publication number: AU710348B2
Application number: AU17849/97A
Authority: AU
Inventors: Johann Dipl.-Ing. Knecht; Norbert Dipl.-Ing. Patzelt
Original assignee: Krupp Polysius AG
Current assignee: ThyssenKrupp Industrial Solutions AG
Priority date: 1996-05-06
Filing date: 1997-04-14
Publication date: 1999-09-16
Anticipated expiration: 2017-04-14
Also published as: DE19618143A1; AU1784997A; ZA973379B; CA2202213A1; BR9703075A

Description

2 Grinding roll and method for operation and repair thereof The invention relates to a grinding roll according to the preamble to Claim 1, and also to a method for operation and repair thereof according to the preamble to Claim 8.

Grinding rolls of the type referred to, in the preamble to Claim 1 are known for example from EU-BI 0 516 952. In the operation of such grinding rolls the spaces between the pinshaped profiled bodies projecting with a part of their length over the roll surface are filled with material for comminution which is fed into the material bed roll mill, and thus this constitutes a certain autogenic protection against wear for the surface of the roll. However, in the course of the operating time the pin-shaped profiled body are worn increasingly and as a consequence of this the material of the roll body, i.e. the base material, which forms the surface of the roll is then subjected to unavoidable wear which is generally greater than the already considerable wear on the profiled bodies. The material hitherto used for the surface of the rol 1 body has a hardness of 40 to 45 HRc (Rockwell I hardness).

If the wear on the pin-shaped profiled bodies and the roll surface has reached a certain amount, then a repair of the wear usually takes place in such a way that first of all the profiled bodies are removed, which in the case of fixing by glueing generally involves burning off of the entire surface.

Then the roll surface is provided with a thick, often multilayer build-up welding which must then, however, be face turned in order to produce the required cylindrical roll surface. Finally, in a last operation new pin-shaped profiled bodies must be inserted into the roll surface. Such repair of wear is extraordinarily costly.

The object of the invention, therefore, is to develop a 3 grinding roll and method for operation and repair thereof which permit a substantially more economical repair of wear.

This object is achieved according to the invention by the characterising features of Claims I and 8. Advantageous embodiments of the invention are the subject matter of the subordinate claims.

According to the invention a material with a substantially greater hardness than those which were usual hitherto is used as the material of the roll body forming the roll surface, i.e. as the base material of the grinding roll. According to the invention this hardness is greater than 56 HRc (Rockwell hardness); it is preferably between 60 and 68 HRc, particularly between 62 and 64 HRc.

In this case the grinding roll is kept in comminuting operation until a substantial proportion of all profiled bodies, preferably at least 80%, is completely worn and/or has fallen out of the roll body. For repair of the wear the roll surface is then brought back to a cylindrical shape by partial removal of material, and new recesses are produced in the roll surface and new profiled bodies are inserted into these recesses.

Due to the use of an extraordinarily hard base material the material of the roll body forming the roll surface is worn approximately only to the same extent as the pin-shaped profiled bodies. Thus even in the case of increasing wear of the profiled bodies not only is an autogenic protection against wear of the roll surface maintained (in which moreover material for grinding is deposited between the profiled bodies and thus protects the roll surface), but due to the reduced wear of the base material because of the greater hardness the pin-shaped profiled bodies embedded in the roll surface retain a sufficient anchorage during a substantially longer 4 operating time, so that they are a match for the radially and tangentially acting forces which occur during the grinding operation. Not until the pin-shaped profiled bodies and the roll surface are so far worn that only a small part of the length of the profiled bodies is anchored in the roll body do the profiled bodies finally break away.

Due to the use of a base material with great hardness and thus with relatively high resistance to wear there is still, after individual pin-shaped profiled bodies have fallen out, a sufficiently long operating time remaining in which a further large number of profiled bodies can also reach this critical amount of wear for breaking away, without the base material, i.e. the material of the roll body forming the roll surface, undergoing unacceptably severe wear beforehand. As tests have shown, with suitable dimensioning it is possible without further effort to ensure that a large proportion of the pinshaped profiled bodies break away from the roll surface approximately simultaneously. In this way the very costintensive removal of a large number of profiled bodies during the repair of wear is minimised.

The use of a particularly hard roll body material (in place of the segment material usually used) also provides the advantage of a higher compression strength, which makes the replacement of the pin-shaped profiled bodies easier. In fact, due to the increased compression strength both in the grinding operation and also during any removal of the remaining profiled bodies within the framework of the repair of wear the danger of plastic deformation of the base material in the base of the bore and thus in the supporting region of the profiled bodies is substantially reduced. An undeformed bore ensures a substantially better removal of the remaining profiled bodies- Also as a result considerable savings of costs can be achieved in the repair of wear of the grinding roll.

5 According to the invention the hardness of the pin-shaped profiled bodies is advantageously between 1000 and 1700 HV (Vickers hardness).

The material of the roll body forming the roll surface can advantageously consist of an alloy which is known under the trade name Nihard IV or the alloy designation G-X 300 CrNiSi 952. It contains 2.5 to 3.5% C, 1.5 to 2.2% Si, 0.3 to 0.7% Mn, 8 to 10% Cr, 4.5 to 6.5% Ni and up to 0.5% Mo. A further suitable material with great hardness for the material of the roll body forming the roll surface is chrome chill casting (alloy designations G-X 300 CrMo 153 or G-X 300 CrMoNi 1521) with 2.3 to 3.6% C, 0.2 to 0.8% Si, 0.5 to 1.0% Mn, 14 to 17% Cr, 0.8 to 1.2% Ni and 1.0 to 3.0% or, respectively, 1.8 to 2.2% Mo.

o In the initial state the pin-shaped profiled bodies advantageously have a length of 15 to 50 mm, preferably from to 25 mm, and they project with a length between 3 and mm, preferably between 4 and 8 mm, over the roll surface.

a The invention is illustrated schematically in the drawings, in which: a Figure 1 shows a partial section through a roll body with embedded pin-shaped profiled bodies, Figures 2 and 3 shows schematic representations of a new and a worn grinding roll, Figures 4 and 5 show schematic representations (corresponding to Figures 2 and 3) of a variant.

In the roll body I of the grinding roll of a material bed roll mill there are provided a plurality of recesses (in the form of blind bores) into which pin-shaped profiled bodies 2 are 6 embedded so that they only project with a part of their length over the roll surface. The profiled bodies can for example have a length of 20 to 25 mm and can project approximately mm over the roll surface 3.

In this case the pin-shaped profiled bodies 2 have a cylindrical main part 2a and ends 2b and 2c which are constructed approximately in the shape of truncated cones.

The end 2b can for example have a height of approximately 1 mm and the end 2c can have a height of approximately 2.5 mm.

The hardness of the material of the roll body 1 forming the roll surface 3 is greater than 56 HRc; it preferably lies between 60 and 68 HRc, in particular between 62 and 64 HRc.

The pin-shaped profiled bodies consist of a material which is even harder than the material of the roll body 1 forming the roll surface. The hardness of the profiled bodies 2 is advantageously between 1000 and 1700 HV.

In the embodiment i l lustrated in Figures 2 and 3 the roll surface 3' is occupied approximately over its entire axial length L by pin-shaped profiled bodies 2 in uniform spacing.

After a certain operating time of this roll according to figure 2 the wear pattern according to Figure 3 is produced: Whilst in the two axial edge regions of the roll body there are still pin-shaped profiled bodies 2 present, the central main part of the roll surface is worn by an amount a (of for example 20 to 45 mm, depending upon the original height of the profiled bodies 2).

The repair of the wear takes place in such a way that first of all the pin-shaped profiled bodies remaining in the edge regions are removed. This advantageously takes place by mechanical pulling (after carbonisation of the glue used for fixing) or by burning out of the profiled bodies. A further possibility is to remove the remaining remnants of the profiled bodies by abrasion.

Then the base material, i.e. the material of the roll body forming the roll surface, is brought to a cylindrical shape by machining by turning and/or grinding. In so far as it is necessary, individual points on the roll surface can be further improved at a later stage by build-up welding.

However, in many cases this will not be necessary. Then the recesses to receive new profiled bodies are bored and new pinshaped profiled bodies are inserted and fixed by means of a glue.

In the variant illustrated schematically in Figures 4 and the roll surface 3" in the new state (Figure 4) is only occupied in the central main part Lm of its length by pinshaped profiled bodies 2, whilst the two axial edge regions of the roll surface have no such profiled bodies. The part Lm of the roll length which is occupied by profiled bodies 2 can preferably amount to 70 to 90% of the total length of the rol I.

As a result after a certain operating time the pattern of wear according to Figure 5 is produced: the roll has lost almost all profiled bodies. Consequently no or hardly any profiled bodies have to be removed here before the roll surface is brought back to the cylindrical shape by partial material removal.

8 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. Grinding roll for a material bed roll mill, with a plurality of pin-shaped profiled bodies which are embedded with a part of their length in recesses in the roll body and with the remaining part of their length project over the roll surface and which consist of a material which is harder than the material of the roll body forming the roll surface, characterised in that the hardness of the material of the roll body forming the roll surface is greater than 56 HRc (Rockwell hardness),preferably between 60 and 68 HRc, particularly between 62 and 64 HRc.

2. Grinding roll as claimed in Claim I, characterised in that the hardness of the pin-shaped profiled bodies is advantageously between 1000 and 1700 HV (Vickers hardness).

3. Grinding roll as claimed in Claim 1, characterised in that the material of the roll body forming the roll surface consists of an alloy which contains 2.5 to 3.5% C, 1.5 to 2.2% Si, 0.3 to 0.7% Mn, 8 to 10% Cr, 4.5 to 6.5% Ni and up to Mo.

2. Grinding roll as claimed in Claim 1, characterised in that the material of the roll body forming the roll surface consists of an alloy which contains 2.3 to 3.6% C, 0.2 to 0.8% Si, 0.5 to 1 Mn, 14 to 17% Cr, 0.8 to 1 Ni and 1.0 to or, respectively, 1.8 to 2.2% Mo.

Grinding roll as claimed in Claim 1, characterised in that the materinitial state the pin-shaped profiled bodies havesurface consists of an alloy which contains 2.5 to 3.5% C, 1.5 to 2.2% Si, 0.

3 to 0.7% Mn, 8 to 10% Cr, 4.5 to 6.5% Ni and up to Mo.

a length of 15 to 50 mm, preferably from 20 to 25 mm, and they project with a length between 3 and 10 mm, preferably between 4 and 8 mm, over the rol I surface.

6. Grinding roll as claimed in Claim 1, characterised in 6. Grinding roll1 as claimed in Claim 1, characterised in

Claims

7. Grinding roll as claimed in Claim 1, characterised in that the roll surface is occupied by pin-shaped profiled bodies in uniform spacing only in the central main part of its length which is exposed to high wear, whilst the two axial edge regions of the roll surface which are exposed to less wear have no pin-shaped profiled bodies. 0:.0 8. Method for operation during which wear is likely and for subsequent repair of wear of a grinding roll for a .9 material bed roll mill, with a plurality of pin-shaped profiled bodies which are embedded with a part of their length in recesses in the roll body and with the remaining part of their length project over the roll surface and which consist of a material which is harder than the material of the roll body forming the roll surface, wherein the hardness of the material of the roll body forming the roll surface is greater than 56 HRc (Rockwell hardness), preferably between 60 and 68 HRc, particularly between 62 and 64 HRc, characterised in that a) the grinding roll is kept in comminuting operation until a substantial proportion of all profiled bodies, preferably at least 80%, is completely worn and/or has fallen out of the roll body b) and that for repair of the wear the roll surface is then brought back to a cylindrical shape by partial removal of material, new recesses are produced in the roll surface and new profiled bodies are inserted into these recesses.
9. Method as claimed in Claim 8, characterised in that before the removal of material the remaining profiled bodies still present in the roll body are mechanically removed, preferably by pulling after carbonisation of a glue used for fixing the profiled bodies. Method as claimed in Claim 8, characterised in that the removal of material takes place by machining by turning and/or grinding and any subsequent build-up welding is undertaken only in order to improve individual points on the roll surface.
11. A grinding roll as herein described with reference to the accompanying drawings. DATED this 14th day of April 1997 KRUPP POLYSIUS AG By their Patent Attorneys CULLEN CO. 11- Abstract The invention relates to a grinding roll with pin-shaped profiled bodies embedded in the roll body, the roll body having a hardness of more than 56 HRc. This grinding roll is used in comminuting operation until a substantial proportion of all profiled bodies is completely worn and/or has fallen out of the roll body. For the repair of wear the roll surface is brought back to a cylindrical shape by partial removal of material, after which new recesses are produced and new profiled bodies are inserted. U. C C C