Technical Field of the Invention
This invention relates to a combi roll comprising a roll
shaft and a roll ring mounted on the same against which at least one other ring
is axially pressed, end contact surfaces of the rings pressed against each other
serving as torque-transferring friction joints.
Background of the Invention
Generally, combi rolls include two or more roll rings,
which are kept separated by intermediate spacer rings, the entire set of rings being
kept fixed on the roll shaft by way of, on one hand, a fixed stop ring, e.g., a
shoulder of the roll shaft and, on the other hand, a lock nut, which via an internal
thread may be tightened on a male thread of the shaft. Furthermore, between the
lock nut and the set of roll rings and spacer rings, respectively, springs as well
as additional rings may be present.
In many cases, the roll rings are manufactured from a hard
material, such as cemented carbide, while intermediate spacer rings are manufactured
of a softer or more ductile material, preferably steel or cast iron. Considerable
torque should be transmitted from the roll shaft to the roll rings. When the roll
rings exclusively are made of cemented carbide, the transmission of torque usually
takes place by an axial (cylindrical) train of forces from the lock nut to the fixed
stop ring via the end contact surfaces between the individual rings. More precisely,
the torque is transmitted from the individual ring to an adjacent ring by friction
action in those interfaces where an end surface of a ring is pressed against a co-operating
end surface of the adjacent ring. In order to manage this purpose throughout the
train of forces, the individual interfaces or friction joints between the rings
have to be powerful, i.e., be able to transmit torque without the rings slipping
in relation to each other.
In previously known combi rolls (see, for instance,
), the end surfaces of the individual interfaces are metallic in so far
as the surfaces have been generated by machining, such as turning and/or grinding,
of a metal blank that should form the individual ring. In other words, the end surfaces
of a spacer ring of steel are steel surfaces, while the end surfaces of cemented
carbide roll ring are a cemented carbide surfaces. Dependent on the surface finish
and the nature of the different materials, the friction between such surfaces may
become inferior, something that may lead to the rings slipping in relation to each
other. Another shortcoming of previously known combi rolls is that the roll rings
as well as the spacer rings are formed with end surfaces that extend radially all
the way from the inside of the ring to the outside thereof, i.e., from the envelope
surface of the roll shaft to the external cylinder surface of the individual ring.
This design of the end surfaces results in transmission of torque in a zone situated
approximately halfway between the inside and the outside of the spacer ring, i.e.,
relatively near the envelope surface of the roll shaft. Furthermore, the surface
pressure in the interfaces between the end contact surfaces will be fairly low because
the contact surfaces are comparatively large.
Objects and Features of the Invention
The present invention aims at obviating the above-mentioned
disadvantages of previously known combi rolls and at providing an improved roll.
Therefore, a primary object of the invention is to provide a combi roll in which
large torque may be transmitted between adjacent rings via friction joints that
in a reliable way counteract slipping between the rings. In other words, the invention
aims at providing powerful and efficient friction joints between the rings of the
roll. It is also an object to provide the improved friction joints by simple elements.
According to the invention, at least the primary object
is attained by way of the features defined in the characterizing clause of the independent
claim 1. Preferred embodiments of the roll according to the invention are further
defined in the dependent claims.
Brief Description of the Appended Drawing
In the drawing:
Detailed Description of a Preferred Embodiment of the Invention
- Fig. 1
- is a partly cut longitudinal view through a combi roll according to the invention,
- Fig. 2
- is a perspective view of a spacer ring included in the roll,
- Fig. 3
- is an enlarged detailed section showing a spacer ring separated from two roll
rings before being urged against these, and
- Fig. 4
- is an extremely enlarged section showing a part of the interface between the
contact surfaces of the rings.
In Fig. 1, a roll is shown that includes a drivable roll
shaft 1, a number of roll rings 2, and a number of spacer rings 3. The roll shaft
1 has a rotationally symmetrical basic shape defined by a centre axis C.
The set of rings 2, 3 is kept in place between a fixed
stop ring 4, which in the example is in the form of a ring-shaped shoulder, and
a lock nut 5 at the opposite end of the shaft. The lock nut 5 has an internal thread
(not shown), which may be tightened on an external thread of the roll shaft. Between
the lock nut 5 and the first roll ring 2, there is in this case also a dynamic spring
6, which is separated from the lock nut by a ring 7. Furthermore, in the lock nut,
there are a number of peripherically spaced-apart adjusting devices 8, by way of
which the spring force of the spring 6 may be adjusted.
In the example, the roll rings 2 are assumed to be composed
of solid cemented carbide, while the spacer rings 3 consist of a softer metal, e.g.,
steel. Each individual roll ring 2 is delimited by, on one hand, external and internal
cylinder surfaces 9, 10 and, on the other hand, opposite end surfaces 11, each one
of which is planar and extends perpendicularly to the centre axis C. Each end surface
11 is limited outwardly by an outer, circular edge line 12, and inwardly by an inner,
circular edge line 13.
In an analogous way, the individual spacer ring 3 (see
Fig. 2) is delimited by an external cylinder surface 15 that determines the outer
diameter of the ring, an internal cylinder surface or hole edge surface 10 that
determines the inner diameter of the ring, as well as two opposite planar end surfaces
11 that are ring-shaped and extend perpendicularly to the centre axis C.
As far as the shown roll has been described hitherto, the
same is in all essentials previously known (however with the exception of the design
of the spacer rings 3).
According to an aspect of the present invention the individual
interface between each pair of end contact surfaces 11, being pressed against each
other, there is distributed a large number of small grains of a material that is
harder than the hardest material of anyone of the rings. The grains are advantageously
dispersed in a viscous fluid, e.g., a paste. In Fig. 3, three rings are shown spaced-apart
from each other, on the end contact surfaces 11 of the spacer ring 3, a thin layer
14 of a paste being shown, which contains hard grains, and which has been applied
to the surface in a suitable way, e.g., by painting. Alternatively, the hard grains
may be applied using plating technique.
When the rings 2, 3, by way of the lock nut 5 and the adjusting
devices 8, are pressed against each other by full force, the grains included in
the paste will partially penetrate into each one of the end contact surfaces 11,
such as is shown in Fig. 4. The individual grains will then serve as diminutive,
mechanical bridges between the contact surfaces and in such a manner radically improve
the torque-transmitting ability of the friction joint.
The grains in the interface shall have an average grain
size of 10-125 µm, preferably 25-100 µm. Suitably, coarser grains are
used when the contact surfaces are rough.
In the present case, when the roll rings consist of cemented
carbide, the grains may advantageously be diamond, cubic boron nitride, ceramics
or the like.
In accordance with a preferred embodiment of the invention,
the individual spacer ring 3 (see Fig. 2) has been formed in such a way that the
inner limiting edge line 13 of the individual end surface 11 is greater than the
outer diameter of the roll shaft, i.e., greater than the diameter of the hole edge
surface 10. In such a way, the total area of the end surface 11 for a given outer
diameter is reduced, whereby the surface pressure against the end surface of an
adjacent roll ring is increased. Furthermore, the force transmission zone, i.e.,
an imaginary circular line about halfway between the edge lines 12, 13, is moved
outwardly in comparison with the corresponding force transmission zones in previously
known spacer rings. In other words, the efficient torque arm increases, such as
this is determined by the radial distance between the centre axis C and the force