Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
2001-05-15
2004-02-10
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C384S279000, C384S291000, C384S297000
Reexamination Certificate
active
06688768
ABSTRACT:
This invention relates to bearing arrangements in the form of cylindrically tubular bushes or cylindrically part tubular shells mounted against radial expansion and in particular relates to such arrangements in which the bush or shell comprises a plastically deformable and ductile lining material comprising or including a low friction polymer-based material and fillers, referred to hereinafter as a filled polymer, that is compressible in the sense of being less than fully dense before compression. Such a filled polymer based bearing material is, in the following description and claims, referred to as “filled polymer compressible lining”.
The invention is particularly, but not exclusively, concerned with such bearing arrangements in which the filled polymer compressible lining is defined by a filled polymer infiltrated into a sponge-like sintered metal matrix to form the lining material, which matrix may itself be carried on a backing strip of solid metal, such as steel or bronze or like material commonly used as a backing material in bearing applications. It is known to form bearing arrangements in which the sintered metal matrix is bronze and such lining material is herein referred to as ‘filled polymer infiltrated sintered bronze’ or ‘FPISB’ for short, and as ‘backed filled polymer infiltrated sintered bronze’ or ‘BFPISB’ for short, respectively.
Such BFPISB is manufactured and sold by the Applicant with various low friction polymer materials and filled with different combinations of fillers. For example, the material known as DU has a polymer base of PTFE with lead filler and is described in patent specification no GB-A-2172296, the material known as DP which has a polymer base of PTFE and zinc and fine bronze instead of lead and is described in patent specifications no GB-A-2248238, the material known as DP4 which has PTFE with fillers of calcium fluoride and fibrillated Kevlar (RTM) and is described in patent specification no GB-A-2279998, and the material known as DU (B) which has the same lining material and bronze sinter as DU but a bronze backing instead of steel. The above is not an exhaustive list, and bearing bushes and shells of such bearing material are employed, for example, in vehicle door hinges to support a rotatable hinge pin and in suspension components to support reciprocating rods, both in rotational and rectilinear motion.
A typical steel backed, filled polymer infiltrated bronze bearing material is formed as a laminar strip manufactured by depositing bronze powder onto a steel backing, heating the combination to sinter point to develop a sponge-like bronze matrix layer, depositing a solvent-borne paste or mush of the low friction polymer and fillers, rolling to infiltrate it within the interstices of the bronze layer and again heating the combination to dry and sinter the filled polymer so that it completely impregnates the bronze sinter matrix. It is a feature of such manufacture that the filled polymer not only infiltrates the interstitial spaces between the partially fused bronze particles (leaving only about 1% porosity) but also forms a relatively thin skin overlying them. Depending upon the eventual use of the bearing arrangement an amount of filled polymer may be used that causes such skin to exist in a thickness of 0.010 mm to 0.04 mm. Such structure is sometimes described in terms of the polymer skin being an overlay that is intimately bonded to a substrate provided by the fused metal particles, the substrate being itself intimately bonded to a backing strip where appropriate.
In a typical manufacture, tubular bush bearings are formed by deforming or bending a laminar plate-like blank, cut from such strip, around a cylindrical mandrel into a longitudinally slit tubular form having the ISB lining innermost. The tubular form, which is of course circumferentially discontinuous and unstable against radial forces, is thereafter mounted within a radially stronger housing for reception of hinge pin or like cylindrical object to be borne thereby.
It will be appreciated that in the manufacture of the tubular bush form there will be variations in dimensions, particularly the inside and outside diameters thereof as defined by the mandrel diameter and strip thickness, and that furthermore the variations will be exacerbated when the tubular form is finally mounted within a separately manufactured housing that is itself subject to manufacturing tolerances.
Whereas a bush having a conventional bearing metal lining or homogeneous (incompressible) polymer can be manufactured to have an undersized inside diameter and have lining surface material removed by a reaming tool or the like to achieve a desired nominal inside diameter, it is not readily possible to provide inside diameter accuracy for, in particular, an ISB bearing by removing lining material.
To more clearly illustrate the steps involved in production of such a known bush bearing arrangement having an ISB lining and understand constraints placed upon achieving dimensional accuracy, reference is made to FIGS.
1
(
a
) to
1
(
f
), the bush and its manufacture being known in the art and briefly described here as an aid to understanding the invention.
Referring to FIG.
1
(
d
), a bearing arrangement
10
is defined by a tubular bush form
12
that has a circumferential discontinuity
14
and is mounted within a radially constraining housing
16
. Referring also to FIG.
1
(
a
) a laminar strip
18
of steel backed ISB bearing stock, having steel backing
19
and ISB lining
20
, manufactured as outlined above and with a width corresponding substantially to the desired bush length, is pulled from a coil
22
and at a trimming station
24
its edges are trimmed by chamfering to prepare the eventual bush ends
12
1
and
12
2
. The strip is fed to a blanking station
26
at which a predetermined length is a cropped to form a plate or blank
30
. The cropped blank is positioned with the ISB surface
20
adjacent a cylindrical mandrel
32
that has a circular cross section of predefined diameter. Referring also to FIG.
1
(
b
), a first ram
34
clamps the blank to the mandrel and bends the blank about the mandrel into a U-shape; thereafter a pair of second rams
36
1
and
36
2
close it around the mandrel into substantially tubular form before a third ram
38
applies pressure to the ends of the strip, the rams in unison pressing the blank against the mandrel to effect tubular uniformity with the mandrel so that the erstwhile opposite ends of the blank meet as a circumferential discontinuity of the tubular form. Referring also to FIG.
1
(
c
), the tubular form, indicated generally art
40
, therefore has its tubular wall, conveniently identified as
42
, corresponding substantially to the thickness of the BISB
18
. The tubular form
40
, still held closed on the mandrel is displaced with the mandrel through a die
44
which defines or gauges the outside diameter of the tubular form and, relative to the mandrel, the thickness of the tubular wall
42
. Any changes in wall thickness necessary to permit it to pass through the die are the result of elongation or drawing of the radially confined components of the wall which retain their relative thicknesses, although there may be a certain amount of recovery of wall thickness as the materials leave the die. The mandrel is thereafter withdrawn from the tubular form to leave the bush.
The structure of the wall on an enlarged scale is illustrated in FIG.
1
(
e
), illustrating not only backing strip
18
and ISB
20
but also within the ISB the sintered bronze matrix
20
1
, filled polymer
20
2
and the polymer surface layer
20
3
.
As a consequence of the circumferential discontinuity
14
, the bush
40
is relatively weak against radial forces and it is mounted for use within an encircling housing
16
to comprise the aforementioned bearing arrangement
10
.
As discussed above, manufacturing tolerances in respect of BISB strip thickness and the operations associated with forming of the bush on the mandrel and gauging or defining wall thickness prior to removin
Footland Lenard A.
Glacier Garlock Bearings Inc.
Harrington John M.
Kilpatrick & Stockton LLP
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