“Smart” bowed roll

Details “Smart” bowed roll “Smart” bowed roll

2001-06-27

2003-04-29

Cuda-Rosenbaum, I (Department: 3726)

Roll or roller

With measuring, testing, or indicating means

Including signal or control means

C492S009000, C492S039000, C492S040000, C026S099000, C026S101000, C226S190000

Reexamination Certificate

active

06554754

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to bowed roll assemblies, and more particularly to an apparatus and system for adjusting a bowed roll assembly to alter critical speeds and inhibit harmonic vibration during operation of the assembly.
BACKGROUND OF THE INVENTION
A bowed roll is a banana shaped, rubber covered or segmented metal roller used to remove wrinkles in a continuously moving web of media such as paper, foil, plastic film or the like. The bowed roll is comprised of a series of rotating segments (or spools), fitted with bearings, along a curved stationary axle.
The bowed roll is normally installed with the bow oriented more or less in the downstream direction. Under this condition, the incoming web contacts the roll surface on the backside of the bow. The web then remains in contact with the roll surface for 25-to-35 degrees of rotation before separating from the roll surface on the front-side of the bow. Since the roll is bowed, it stands to reason that the face width of the roll (measured along the roll's surface) increases gradually from the back-side to the front-side. It is this “widening” of the roll face that induces lateral tension (or stretch) in the web while it is in contact with the roll surface to reduce or remove wrinkles.
An example of a prior art bowed roll assembly
10
is depicted in FIG.
1
. The bowed roll is comprised of a series of rotating segments or spools along a curved stationary axle (FIG.
3
). The individual spools, each supported by a bearing centered within the spool, are placed along the axle and spaced so they turn freely yet in unison with each other. Referring to
FIG. 1
, the bowed roll includes a central axle
12
and a centerline
14
, and is typically supported on each end with self-aligning mounting brackets
16
. The position of the bow is adjusted by rotating the axle
12
in the self-aligning brackets
16
. By changing the bow position, the amount of lateral stretch or tension in either the center or edges of the web can be controlled. In addition, the lateral tension induced by the bowed roll can also be used to aid in separating a single web which has been slit in two or more webs to prevent interweaving during winding operations or the like. Bowed rolls find numerous applications above and beyond the examples cited here.
At predictable rotational speeds, bowed rolls (as is the case with all rotating machinery) are subject to a multitude of harmonic vibration modes, which can occur during normal operation depending upon the construction of the roll, the materials used in its construction, and the process speed. The speeds at which the phenomenon of harmonic vibration occurs is often referred to as the “whirling” or “critical” speeds. The critical speed of a roll is essentially the rotational speed equivalent to the roll's natural frequency of vibration. If a roll is operating at these speeds, oscillations may occur that can damage a forming sheet, among other things. This phenomenon is well known to those engaged in the design of shafts, rollers and other rotating machinery.
The first three critical speeds (“criticals”) are of great significance in that their related amplitudes of oscillation are great enough to either disturb the web handling process and/or result in damage to the spool bearing raceways and rolling elements.
FIGS. 2A-2C
illustrate the harmonic vibration mode shapes for a bowed roll centerline when operating at the first three critical speeds, and show the dynamic shape of the bowed roll centerline
14
a,
14
b,
14
c
at the first, second and third critical speeds, respectively. Bowed rolls have been proven to experience premature spool bearing failures when the roll is operated at these criticals for significant periods of time.
Referring to
FIG. 3
, an embodiment of a prior art bowed roll construction is shown. In the current state of the art/science of bowed roll construction, a series of spool assemblies
20
comprising a rotating segment (or spool)
22
fitted with bearings
24
, are positioned along a curved stationary axle
12
. These spool assemblies
20
are positioned so as to be in near proximity to each other and are coupled together individually by means of elastomer couplings
28
. In the case of rubber-cover rolls, an elastomer covering or sleeve
28
(as shown) is fitted over the entire series of spool assemblies.
As depicted, the spool assemblies
20
are held in near proximity by means of annular spacers
30
, which are fitted over the curved axle
12
(with the axle having an annular cross section) with their ends abutting the inner races
32
of the spool bearings
24
. The entire series of spool assemblies
20
and spacers
30
are held in position along the bowed roll axle
12
by means of set collars
34
affixed to the axle
12
at either end
40
a,b
of the assembly
10
.
In another embodiment of a bowed roll assembly, designated generally with the numeral
38
′ and shown in
FIGS. 4 and 5
, the ends
40
a′,
40
b′
of the axle
12
′ comprise threads
46
′ to which large reinforcing nuts
48
a′,
48
b′
are affixed to the axle ends. Each end
40
a′,
40
b′
of the axle
12
′ is mounted in a roll supporting bracket
42
′ that includes a ball clamp
44
′. In this instance, a predetermined torque is applied to the nuts, which in turn loads the spool bearing inner races
32
′ and annular spacers
30
′ in compression, which induces an amount of tension in the axle and increases the stiffness of the roll. In the manufacture of bowed rolls, this technique is referred to as “reinforcing,” and the assembly
38
′ can be referred to as a reinforced bowed roll assembly. A reinforced roll is similar to a standard bowed roll (
FIG. 3
) except with a reinforced axle. As shown in
FIG. 5
, the ends
36
a′,
36
b′
of the assembly
38
′ include an end cap
50
′ and an end shield
52
′.
It is well known to those versed in the art/science of rotating machinery that the critical speeds for rollers, shafts, and the like, occur as a function of the roller's mass and stiffness. The step of reinforcing a bowed roll increases the roll's stiffness, which in turn alters the rotational speeds at which the roll's “criticals” occur. By changing the torque applied to the axle nuts
48
′, one can tune (i.e., increase, decrease, shift) the criticals to speeds out of the range of the operating speed of the bowed roll assembly so the criticals will not be encountered during normal operation for a known process machine speed. However, the adjustment of the applied torque requires that the roll be taken out of service and partially disassembled. Hence, it is not practical to perform this procedure in the field. While the ability to tune the criticals for a roll is helpful in preventing harmonic vibration, it requires that the machine process speed be limited. This is often unacceptable in that it may limit the machine's productivity.
SUMMARY OF THE INVENTION
The present invention provides an improved bowed roll assembly for use in machines for processing paper and other continuous web of flexible media, among other applications.
In one aspect, the invention provides a bowed roll assembly that can be adjusted during operation of the assembly to alter critical speeds to outside the range of the operational speed of the assembly. The bowed roll assembly generally comprises a non-rotating central axle having a first end and a second end, at least two tubular segments, each supported on a rolling bearing and rotatably mounted on the central axle, and a plurality of annular spaces mounted on the axle between the roller bearings to maintain the tubular segments in near proximity.
In one embodiment of a bowed roll assembly, the first end of the axle comprises a member mounted thereon for applying or loading pressure against the bearings and the spacers which can be varied to compress and uncompress the tubular segments along the axle and alte

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