Note: Descriptions are shown in the official language in which they were submitted.
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Grindin~ 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-B1 O 516 952. In the
operation of such grinding rolls the spaces between the pin-
shaped 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 roll body has a hardness of 40 to 45 HRc (Rockwell
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 multi-
layer 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
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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 1 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
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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 pin-
shaped profiled bodies break away from the roll surface
approximately simultaneously. In this way the very cost-
intensive 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.
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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
ad~antageously 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.
In the initial state the pin-shaped profiled bodies
advantageously have 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 roll surface.
The invention is illustrated schematically in the drawings, in
which:
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 1 of the grinding roll of a material bed roll
mill there are pro~ided a plurality of recesses (in the form
of blind bores) into which pin-shaped profiled bodies 2 are
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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 4 5
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 l forming the
roll surface. The hardness of the profiled bodies 2 is
advantageously between lO00 and 1700 HV.
In the embodiment illustrated 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
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- 6 -
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 pin-
shaped profiled bodies are inserted and fixed by means of a
glue
In the variant illustrated schematically in Figures 4 and 5
the roll surface 3" in the new state (Figure 4) is only
occupied in the central main part Lm of its length by pin-
shaped profiled bodies Z, 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
roll.
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
