Note: Descriptions are shown in the official language in which they were submitted.
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~OLLER WITH AN ELASTIC COVER
. . _
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a roller with an elastic
cover layer in which the cover layer includes a jacket of
an elastomeric material and a rigid, inner reinforcing tube
that is impermeable to liquid~
Prior Art
.
In industry/ for example, the paper, steel and te~tile
industries, as well as in commercial graphics and the other
arts, a great number of rollers are required, the steel
cores of which are covered with a softer, usually elastic
rubber or plastic cover layer. The cover layers are
applied to the roller cores by being cast, rolled or
sprayed thereon. In order to achieve a good adhesion with
the roller core, the core must be cleaned (degreased),
sandblasted and coated with a bonding agent which provides
a good bond with the cover layer through the action of
heat. With certain materials, such as polyurethane, the
2C roller core and tools mus~ be heated to temperatures as
high as 80 to 100 C before the cover layer is applied.
After application, some cover layers, such as elastomers,
must remain in the furnace at temperatures of up ~o 170 C
for perhaps several hours for the cross-linkage process.
Thereafter; curing at a constant temperature of 25 C is
often necessary which, depending on quality and cover layer
thickness, may take as much a~ three weeXs.
These expensive, apparatus-intensive methods r in wh ich
the roller core is directly covered, make it necessary for
the industry to deliver worn rollers to resurfacing plants.
This results in production losses, and significant
transport costs, due to ~he generally very heavy weight of
the cores, which may weigh as much as several tons and may
be up to 6 m in length.
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For many years it has been attempted to manufacture
covers, also known as sleeves, which can be kept in
storage, thus permitting defective cover layers to be
replaced quickly. In ~arious tests it was examined whether
5 i~ is possible to glue elastomer or plastic sleeves to the
roller cores. The differences between ~he materials,
plastic/steel, and the heavy loads p~aced on the rollers
during use (fulling stress and/or high rpms~ resulted in
unsatisfactory bonds. The mounting under pressure of the
soft and some~hat elastic sleeve on ~o the cores soon led
to a weakening of the contact pressure, so that the bond to
the steel core was entirely lost. Completely aside from
these factors, however, it is only possible to force
relatively short sleeves onto the steel cores.
For this reason it was attempted to manufacture
reinforced sleeves by embedding fabric or a metal screen
cylinder in the cover material. In this case the co~Jer
material permeates the reinforcement, 50 that the inner
layer of the ~leeve is made of the same material as the
cover~ The weakening of the prestress experienced in
forcing on the cover was thus avoided in part/ but problems
were experienced in maintaining proper tolerances.
Difficulty was also experienced in forcing the sleeve onto
long cylinders.
Prior art development has been primarily directed
toward the textile industr~, where short and small diameter
spindles and rollers must be covered. However, as soon as
rollers longer than 100 mm were provided with the known
sleeves, severe difficulties developed. It turned out, for
example, that under the heavy loads involved (linear
compression of up to 100 N/mm) due to the resulting fulling
stress, the sleeves became greatly heated (up to 80~ C) and
the different thermal expansion coefficients caused a
separa~ion of the sleeve from the roller core. In direct
vulcaniza~ion of the cover to the roller core this problem
does not occur, because subsequent to the vulcanization a
tnermal contraction takes place which leads to a
prestressing that compensates Eor even the greatest thermal
expansion during operation.
SUMMARY OF THE INVENTION
An object of this invention is ~o create an elastic
cover for a roller, which cover is reinforced for added
strength and has an inner layer ~hat makes possible a
proper bonding to the roller while simultaneously being
able to accommodate close~ tolerances than known covers.
The cover should be able to be stored at the site of the
user industry and te able to be quickly mounted on the
rollers, without these rollers having to be sent in to the
resurfacing factory. The importan~ fac~or is proper
adhesion of the cover layer to the roller, even under
extreme loads.
Thi~ is achieved by having the thermal coefficient of
expansion of the tube approximately correspond to that of
the core with an adhesive-filled annular gap between the
tube and the core.
BRIEF DESCRIPTION OF T~E DRAWINGS
.
Fig~ 1 is a schematic part-sectional view of a first
exemplary embodiment for the manufacture of the elastic
cover,
Fig. 2 is a view similar to Fig. 1 showing the
mounting of the cover according to Fig. 1 on a roller
core~
Fig. 3 is a perspective view of a roller with the
cover in place thereon,
Fig. 4 is a schematic part-sectional view of a further
exemplary embodimen~ for the manufacture of the cover,
Fig. 5 is a view similar to Fig. 4 showing the cover
according to Fig. 4 being mounted onto a roller core,
Fig. 6 is a cross section through the band like
original material for a third exemplary embodiment of an
elastic cover,
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Figs. 7 and 8 schematically show the manufacture of a
cover made from the band according to Fig. 6, and
Fig. 9 is a cover rnanufactured from the band
material.
DETAILED DE~CRIPTION OF THE PREFERRED EMBODIMENTS
_ .
According to Fig. 1, the first step in the manufacture
of the cover, also called a sleeve, is the casting of a
polyurethane ring base 1. The outer circumference of the
ring base 1 has offset steps, whereby three ring steps 2,
3, 4 of different diameters are provided.
A tube 5 of fiberglass-reinforced polyester serves as
inner reinforcement for the sleeve. The inner diameter
d1 f this tube is about 1 to 5 mm larger than the
outside diameter d2 f the steel ro1ler 6 to be covered.
The polyester tube is thermally stable and absolutely rigid
up to temperatures of 120 C. It is impermeable to liquids
and bonds completely with the material of jacket 7 of the
sleeve. Its thermal coefficient of expansion is comparable
to that of steel ~thermal coefficient of steel: approx.
12.0 x 10-6/C)o The thermal coefficient of expansion
of the polyester tube should be ~ 15.0 x 10-6/C. The
thickness of the tube is 1.5 to 4 mm.
Other rigid materials could also be used in place of
the fiberglass-reinforced polyester tube~ or example a
sheet metal sleeve. The manufacture and preparation of a
metal sleevet however, is relatively expensive and the bond
with the polyurethane material and the adhesive can only be
achieved through expensive pretreatments, which is not
necessary with the polyester tube 5. The end of the
polyester tube 5 is then fitted onto the second ring step 3
of the ring base 1, whereby the polyester tube serves as a
break mold or hidden casing. It can be tightly bonded to
the ring base 1 for example with an epoxy adhesive 9.
~Uql~
The end of a steel tube 8 is fitted onto the outside
ring step 2 as an outer casing for the polyurethane jacket
material~ which is hot cast at a temperature of ao to
120~ C and bonds with the ring base 1. After the casting
and cross-linkage, ~hich takes about 8 to 10 hours, the
finished sleeve, consis~ing of the jacket 7, the
reinforcement 5 and the ring base 1, can be pulled frorn the
outer casing 8. As a result of the hot casting~ a thermal
contraction takes place due to cooling, which leads to a
prestressing of the jacket onto the reinforcement.
The sleeve is then delivered to a user operation and
stored there until used~ If necessary, the sleeve can be
mounted immediately onto the roller core, as shown
schematically in Fig. 2.
The sleeve is pushed onto the roller core 6 until the
ring base 1 meets the face surface 10 of the roller~ The
clearance S between ~he roller surface and the inner
surface of the sleeve is 0.5 to 2.5 mm. For purposes of
the invention ~he sIeeve is also centered on the roller
core, so that the clearance, i.e. the gap 13, is equalized
all around. The sleeve can then be placed in a vertical
position.
A hole 12 is then drilled through the sleeve in the
vicinity of the annular space 11, which is bounded by the
third step 4 of the ring base 1 and the face surface 10 of
the roller. A solvent-free adhesive with a polyester,
epoxy or polyurethane base is then forced through this
bore 12 into the annular space 11 under a pressure o up to
10 atm. The adhesive should not be overly viscous. A
viscosity of under 2500 cp has been shown to be most
satisfactoryO The adhesive then flows into the gap 13,
completely filling sameO
Extensive tests have shown that the sleeve does not
separate frGm the roller ccre even under heavy loads and
heating. Because the polyurethane ~acket 7 is arranged on
'7~
the rigid reinforcing tube 5 prestressed, an increase in
temperature leads at ~ost ~o a reduction of the prestress,
not to a separation from the reinorcing tube 5~ This
tube, which possesses a thermal coefficient of expansion
comparable to the steel core, expands a~ an eg~al rate with
this core and can therefore also not separate fro~ the
core~ The pressure injected adhesive produces a secure
bond between the reinforcemer1t and the roller core.
The advantages of the above-described sleeve are again
summarized below:
- The sleeve can be mounted on the roller core on
site by the user, can be bonded at room
temperature and subsequently externally turned
and/or ground. The hardening of the adhesive
takés place within a few hours. The troublesome
shipment of rollers back to a resurfacing plant
can be avoided.
- The sleeve is suitable for rapid re~covering of
both small and even the largest roller cores.
- It has a superior bond with the steel core and
withstands the hiqhest linear pressures and
fulling stresses.
- It can be manufactured in advance and stored at
the user's site, whereby the lost production time
due to the re-covering process is decreased and
the cost of transportation is reduced.
- Expensive preparation processes such as
sandblasting, bonding agent application, etc.~
are eliminated. The surface of the roller core
requires no special structure; it is sufficient
if the surface is ~urned and subsequently
degreased. Small variations in diameter are
compensated for by the adhesive layer.
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- The sleeve can be manufactured extremely
economi~ally, both with regard to quality and
price.
- Because of a large clearance of between 0.5 to
2.5 mm beiween the rol1er core and the sleeve,
the requirements with respect to manufacturing
tolerances are relatively small.
The s~eel cores do not need to he heated to
temperatures of from 80 to 170 C during the
cross-linking of the cover layer.
- The sleeves do not need to be forced onto the
rollers, but can simply be pushed thereon without
the exertion of force.
- If a colorless p3lyester material is used for the
reinforcing tube, the adhesion of the
polyurethane jacket to the reinforcing tube can
be checked. This type of simple visual checking
is not possible with direct casting of the cover
layer onto the roller core.
- In rollers used in intaglio printing, the
reinforcing tube and the adhesive form an
electrically insulating layer between the
polyurethane jacket and the roller core. As is
well known, in intaglio printing electrostatic
2S printing assists are employed to improve the
printing quality. Until now~ the outer,
conductive layer of the polyurethane cover (the
conductivity is achieved, for example, by adding
carbon black) had to be cast on an inner,
insulating polyure~hane layer. This expensive,
double casting process can now be avoided.
In a further exemplary embodiment according to Figs. 4
and 5, the reinforcing tube 5 and the steel tu~e 8 are
inserted vertically into the annular groQve 14 of a steel
plate 15~ whereby an additional sealing ring 16 is arranged
:~2~ 7~
between the end of the steel tube 8 and the base of the
annular groove 14. The annular groove 14 and the inner
surface of the steel tube 8 are coa~ed w-th silicone, in
order to facilitate the later removal of the sleeve.
The casting of jacket 7 in ~he space between ~he two
tubes 5,8 takes place from the bottom toward the top
through the opening 17 in the lower portion of the steel
tube 8. This has the advantage that the casting process
can be precisely guided and performed in a controlled
manner, which is particularly important with exacting
qualities of polyurethaneO The cross-linking then also
takes place from the bottom ~oward the top.
This demQnstates one of the ad~antages of the new
method. In the known process of casting the jacket
directly onto the roller core, the danger existed that
cracks would form and the bond would be lost beca~se of
thermal and contraction tensions due to nonuniform cooling.
A different thermal potential of the roller core also had
to be taken into consideration, depending on the size and
volume of the roller core, which strongly influenced the
cross-linking process. These influences could only be
determined to some extent after several casting attempts,
on a trial and error basis, with corresponding losses.
With a thin reinforcing tube, however, the thermal
potential is small and can be well controlled during the
casting process.
To mount the finished sleeve 5,7 on the roller core 6,
the roller core 6 is placed in the vertical on a plate 18,
whereby a polyurethane support ring 19 is arranged between
the plate and the end 10 of the roller core 6. The outside
diameter of this polyurethane support ring 19 is smaller
than the core diameter of the sleeve. A seal 20 made of
felt is located on the plate 18.
To center the sleeve, plastic spacers 21 are bonded to
the surface of the roller core 6 with an epoxy-based
adhesive. Three to six such spacers are placed at the top
and at the bottom~ With longer rollers it may be necessary
to place an additional three to six such spacers near the
center.
The sleeve is then slipped over the roller core 6 and
is again rigidly connected therewith by the injectlon of
adhesive. In order to prevent the sleeve from separating
from the base plate during the bonding process, the sleeve
is best strapped down on the plate 18. After the ~lue has
set, the roller with the sleeve is externally turned and/or
groundO The overflow is removed at both bottom and top, so
that the sleeve is flush with ~he end 10 Gf the roller. By
means of the spacers 21, a proper centering of the sleeve
on the roller core is assured.
In renewing the cover layer, the old layer is first
removed from the roller by being turned down to the roller
core, whereby a shaving is usually al50 removed from the
roller core. For this reason the roller cores of older
rollers have increasingly smaller diameters which, however,
does not matter in renewing the cover layers with the
present method. The somewhat enlarged annular gap 13
simply requires somewbat more adhesive and correspondingly
higher spacers to be glued in place in centering the
sleeve.
With smaller rollers, under certain conditions the
injection of ~he adhesive can be dispensed with. The
sleeve can be covered on the inside with a layer of an
absorbent, compressible material, for example a felt
material or a fabric. To cover the roller, the absorbent
layer of the sleeve is saturated with adhesive and the
sleeve is forced onto the roller, so that the adhesive
serves as a lubricant during forcing of the sleeve on the
roller.
The manufacture of a sleeve will be described below,
in accordance with Figs. 6 and 9, said sleeve having an
absorbent layer. In the manufacture of the sleeve, one
starts with a band-like reinforcing material 22, which
consists of a polyester felt 23, a screen fabric 24 and a
1 0
cover layer 25 of polyurethane coated on the sc~een
fabric ~4. The reinforcing band 22, which is about 2 to
3 mm thick depending on the roller diameter, is wound onto
a mandrel, such as a steel tube 26, whereby the felt is on
the inside and the coating is on the outside.
The abutting edges 27 are covered with a narrow band
of polyurethane foil 28 and welded together. In this
manner the felt is protected from absorbing the sleeve
material during the casting, mounting and duri~g the
cross-linking process of the sleeve material. Penetration
in such a case would jeopardize the sub~equent bonding.
In another process according to Fig. 8, a wider
band 22 is placed about the mandrel 29 and the abutting
edges 27 are also covered, glued or welded.
The covered mandrel 26 is then placed in a tube 29 of
larger dia~eter, and the intermediate space 30 is filled
with polyurethane by casting. For purposes of this
invention, the larger tube 29 stands in a furnace, so that
the casting can take ~lace directly in the furnace. After
the casting and cross-linking, which lasts for about 8 to
10 hours, the finished sleeve 31, consisting of the
jacket 32 and the reinforcing layer 22, can be re~oved.
The jacket material can also be sprayed on. In place
of polyurethane, the jacket can also consist of rubber,
which is rolled on and then vulcanized~
The finished sleeve achieves a perfect bond with the
roller and accepts wider tolerance differences. Prior to
mounting the sleeve, the absorbent, compressible inner
layer is completely saturated with adhesive. The liquid
adhesive acts as a lubricant, so that the sleeve can be
mounted on the roller core without great exertion of force.
The compressible polyester layer makes possible a certain
amount of play, which is necess~ry during mounting. The
setting of the glue takes place at room temperature within
a few hours.
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1 1
As with the first exemplary embodiments according to
Figs~ 1 through 5, also this cover layer is made from the
elastic jacket material 32, the adhesive-saturated felt as
reinforcement, and a thin adhesive layer between the
reinforcement and the roller core r The reinforcement,
which is rigid after the hardeniny of the glue, has a
thermal coefficient of expansion which at least
approximates that of the roller core~
