U.S. patent application number 14/363990 was filed with the patent office on 2014-12-04 for method of manufacture a sliding bearing.
The applicant listed for this patent is Mahle Engine Systems UK Limited, Mahle International GmbH. Invention is credited to John Carey, Selma Hansal, Wolfgang Hansal, Roohollah Kachoosangi, Gentiana Qorri.
Application Number | 20140353161 14/363990 |
Document ID | / |
Family ID | 45541461 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140353161 |
Kind Code |
A1 |
Kachoosangi; Roohollah ; et
al. |
December 4, 2014 |
METHOD OF MANUFACTURE A SLIDING BEARING
Abstract
A method of manufacturing a sliding bearing comprising providing
a substrate as a cathode in an electrolyte within which a hard
particulate is suspended, and depositing a composite layer of hard
particulate embedded in a metallic matrix by applying a repeating
cycle of bias pulses to the substrate wherein each cycle comprises
a high cathodic bias portion and a further bias portion selected
from the group consisting of a low cathodic bias portion, a zero
cathodic bias portion and an anodic bias portion, and a sliding
bearing manufactured by such a method.
Inventors: |
Kachoosangi; Roohollah;
(Oxfordshire, GB) ; Carey; John;
(Northamptonshire, GB) ; Hansal; Wolfgang;
(Leobersdorf, AT) ; Hansal; Selma; (Leobersdorf,
AT) ; Qorri; Gentiana; (Leobersdorf, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mahle International GmbH
Mahle Engine Systems UK Limited |
Stuttgart
Warwickshire |
|
DE
GB |
|
|
Family ID: |
45541461 |
Appl. No.: |
14/363990 |
Filed: |
December 6, 2012 |
PCT Filed: |
December 6, 2012 |
PCT NO: |
PCT/GB2012/053037 |
371 Date: |
June 9, 2014 |
Current U.S.
Class: |
205/109 |
Current CPC
Class: |
C25D 15/00 20130101;
C25D 5/18 20130101; C25D 7/10 20130101 |
Class at
Publication: |
205/109 |
International
Class: |
C25D 15/00 20060101
C25D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 2011 |
GB |
1121175.2 |
Claims
1. A method of manufacturing a sliding bearing comprising providing
a substrate as a cathode in an electrolyte within which a hard
particulate is suspended, and depositing a composite layer of hard
particulate embedded in a metallic matrix by applying a repeating
cycle of bias pulses to the substrate wherein each cycle comprises
a high cathodic bias portion and a further bias portion selected
from the group consisting of a low cathodic bias portion, a zero
cathodic bias portion and an anodic bias portion.
2.-27. (canceled)
Description
[0001] The present invention relates to a method of electroplating
a sliding bearing with a composite layer of hard particulate
incorporated in a metallic matrix, and more particularly, but not
exclusively, to bearing shells and thrust washers.
BACKGROUND
[0002] Bearing shells for journaled engine bearings typically
comprises a strong steel backing layer, a lining layer and an
overlay layer that provides the running surface for the journaled
shaft, e.g. a hollow generally semi-cylindrical steel backing
layer, a copper-based alloy lining layer, and a tin, tin-based
alloy or composite overlay layer on the inner surface.
[0003] It is desirable to provide increased wear resistance and to
improve the fatigue strength of layers in bearing linings,
particularly overlay layers. A particular challenge to bearing
overlay layer performance is provided by the configuration of
vehicle engines to save fuel by using a stop-start operation, in
which the engine is stopped each time the vehicle stops, in
contrast to conventional engine operation, in which the engine is
kept running throughout a vehicle's journey. Engines configured for
stop-start operation may restart their engines more than one
hundred times more frequently than conventionally configured
engines running continuously throughout each vehicle journey. The
particular problem that an engine configured for stop-start
operation presents arises because engine bearings are
conventionally hydrodynamically lubricated, with little or no
lubrication initially being provided to the bearings when the
engine starts, leading to particularly significant wear during the
start-up phase.
[0004] It has been proposed to increase the wear resistance of
engine bearings by the incorporation of hard inorganic particles,
which are substantially insoluble in the electroplating
electrolyte, into bearing overlay layers. Exemplary materials are
the incorporation of aluminium oxide, silicon nitride, silicon
carbide or boron carbide hard particulate into a tin-based alloy
matrix. However, the production of such composite layers, with a
high concentration of hard particulate, is difficult by
conventional electroplating techniques, particularly in a tin-based
alloy matrix (e.g. at least 50% wt tin), and most particularly in
the case of a pure tin matrix.
SUMMARY OF THE DISCLOSURE
[0005] According to a first aspect, there is provided a method of
manufacturing a sliding bearing comprising providing a substrate as
a cathode in an electrolyte within which a hard particulate is
suspended, and depositing a composite layer of hard particulate
embedded in a metallic matrix by applying a repeating cycle of bias
pulses to the substrate wherein each cycle comprises a high
cathodic bias portion and a further bias portion selected from the
group consisting of a low cathodic bias portion, a zero cathodic
bias portion and an anodic bias portion.
[0006] According to a second aspect, there is provided a sliding
bearing manufactured according to the method of the first
aspect.
[0007] According to a third aspect, there is provided an engine
comprising a sliding bearing manufactured according to the first
aspect.
[0008] The method may further comprise agitating the electrolyte to
maintain the hard particulate in suspension.
[0009] The further bias portion may be a low cathodic bias
portion.
[0010] The high cathodic bias portion may have a bias of at least
125% of the low cathodic bias portion.
[0011] The further bias portion may be a zero cathodic bias
portion.
[0012] The further bias portion may be an anodic bias portion.
[0013] The absolute value of the anodic bias portion may be between
0.25 and 3.0 times the absolute value of the high cathodic bias
portion (i.e. between 0.25 and 3.0 times the magnitude, but of
opposite polarity).
[0014] The repeating cycle may have a sawtooth profile in which
each cycle comprises a monotonically increasing cathodic bias.
[0015] The pulse cycle may have a length of 5 to 200 ms, and
preferably of 10 to 100 ms.
[0016] The high cathodic bias portion may consist of 10 to 95% of
the pulse cycle.
[0017] The high cathodic bias portion may have a peak current
density of 0.5 to 10 A/dm.sup.2.
[0018] The mean average cathodic current density of the cycle is
lower than 5 A/dm.sup.2.
[0019] The hard particulate may be selected from the group
consisting of TiCN, SiC, NbC, Si.sub.3N.sub.4, Al.sub.2O.sub.3,
TiN, and B.sub.4C.
[0020] The suspension may comprise 20 to 200 g hard particulate per
litre of electrolyte, and preferably 40 to 100 g per litre.
[0021] The metallic matrix may be a pure metal, apart from
incidental impurities.
[0022] The metallic matrix may be pure Sn, apart from incidental
impurities.
[0023] The metallic matrix may be a metal alloy, apart from
incidental impurities.
[0024] The metallic matrix may be a Sn-based alloy, apart from
incidental impurities.
[0025] The electrolyte may be a tin methanesulfonic acid
electrolyte.
[0026] The electrolyte may comprise 15 to 80 g/l Sn.
[0027] The electrolyte may comprise brightener.
[0028] The sliding bearing may be a bearing shell or a thrust
washer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Embodiments of the invention are further described
hereinafter with reference to the accompanying drawings, in
which:
[0030] FIG. 1 shows a schematic illustration of a bearing
shell;
[0031] FIG. 2 shows a first bias pulse profile;
[0032] FIG. 3 shows an SEM micrograph of a section of a sliding
bearing having an overlay with a B.sub.4C hard particulate
incorporated into a Sn metallic matrix; and
[0033] FIG. 4 shows a second bias pulse profile; and
[0034] FIG. 5 shows a third bias pulse profile.
DETAILED DESCRIPTION
[0035] FIG. 1 illustrates a hollow generally semi-cylindrical
bearing shell 1 having a steel backing layer 2, a copper-based
alloy lining layer 3, a nickel or cobalt diffusion barrier 4, and a
composite overlay layer 5 of hard particulate incorporated into a
Sn matrix.
[0036] The bearing shell onto which the composite layer is
deposited is provided as a cathode in a bath containing a
suspension of hard particulate in an electroplating electrolyte,
with an anode formed of a material corresponding to the metallic
matrix, e.g. a high purity tin anode.
[0037] The electrolyte is a lead-free, tin methanesulfonic acid
(MSA) electrolyte (tin ions in methanesulfonic acid), which may
comprise performance enhancing additives, such as brightener and
anti-foaming agent. For example the electrolyte may be the Bright
Tin GBF 30 acidic electrolyte system from Schlotter.RTM.
Galvanotechnik, which uses a recipe of Schlotter's ingredients
consisting of 13.0 litres Tin Concentrate FS 20 (which contains 310
g/l tin(II)), 6.0 litres GBF 31 Starter (20 to 25% wt
2-naptholpolyglycolether, 1 to 2.5% wt 1,2-dihydroxybenzene, and 1
to 2.5% wt methacrylic acid), 0.4 litres GBR 32 Brightener (35 to
50% wt 2-isopropoxyethanol, and 5 to 10% wt
4-phenylbut-3-en-2-one), 11.0 litres GBF 33 Make Up Concentrate
(which is 45% wt MSA), and the balance to 100 litres of deionised
water. This forms a solution of 30 to 60 g/l tin, although
concentrations of 15 to 80 g/l may be used. The suspension is
maintained at a temperature of 20 to 30.degree. C. The chemical
composition and pH is maintained during deposition by replenishment
of the consumed chemicals.
[0038] Hard particulate, such as boron carbide, alumina, silicon
nitride, boron nitride, silicon carbide, niobium carbide, titanium
nitride, or titanium carbo-nitride, with a particle size of less
than 7 .mu.m, is suspended in the solution with a concentration of
approximately 60 g/l (operation has been demonstrated with 20 to
200 g/l hard particulate, and preferably 40 to 70 g/l). Ultrasonic
and/or mechanical stirring agitation is used to maintain the hard
particulate in suspension.
[0039] A cathodic bias (i.e. a negative bias is applied to the
cathode relative to the anode) creates a cathodic current (i.e. a
negative current, with respect to the anode) that drives the
positively charged tin ions towards the sliding bearing cathode,
and deposits the tin ions onto the cathode surface. To provide an
enhanced incorporation of the B.sub.4C hard particulate the cathode
bias is cyclically pulsed at with a pulse cycle period of 10 to 20
ms (although operation has been demonstrated with a pulse cycle
period of 10 to 40 ms). The peak cathodic current density is
between 0.5 and 5.0 A/dm.sup.2, and the mean average current
density across the pulse cycle is up to 3.6 A/dm.sup.2.
[0040] As illustrated in FIG. 2, in one embodiment a bias pulse
cycle is used having a high cathodic bias V.sub.H pulse portion
t.sub.1 and a zero cathodic bias V.sub.0 portion t.sub.2. The high
cathodic bias portion is applied for up to 95% of the pulse cycle
(preferably between 10 and 95%), and produces a high cathodic
current density.
[0041] By using pulsed electroplating, it is possible to uniformly
incorporate up to 20% wt B.sub.4C hard particulate into a Sn
metallic matrix of a sliding bearing overlay layer. FIG. 3
illustrates a sectional view of such a layer, in which the hard
particulate 6 appear as dark specks in the metallic matrix of the
overlay layer 5.
[0042] The rate of metallic matrix deposition under a constant
cathodic current is limited by the ionic mobility of the metal ions
(e.g. tin ions), due to the presence of a depletion region in the
electrolyte, against the cathode surface. Although hard particulate
from the suspension adheres onto the surface, slow deposition of
the metal ions that occurs under constant cathodic current is
inefficient at incorporating the surface particles into the
deposited layer, with the particles instead remaining on the
surface as the metallic matrix layer grows. In contrast, during the
zero cathodic bias portions (and similarly during lower cathodic
bias portions or during anodic bias portions), the concentration of
metal ions close to the cathode surface is able to increase,
leading to a rapid burst of deposition occurring during the high
cathodic bias portions, which increases the efficiency of
incorporation of the hard particulate into the deposited layer.
[0043] Alternatively, as illustrated in FIG. 4, the pulse cycle may
have an alternating high cathodic bias V.sub.H portions t.sub.1'
and low cathodic bias V.sub.L portions t.sub.2'. The high cathodic
bias V.sub.H is at least 1.25 times greater than the low cathodic
bias V.sub.L. Additionally there may also be a zero cathodic bias
portion (also known as off-time), for example following the high
cathodic bias portion.
[0044] In a yet further embodiment, a double polarity pulse cycle
may be used, in which an anodic bias pulse portion (i.e. a reverse
bias, relative to the cathodic bias) may be provided. For example,
as illustrated in FIG. 5, the pulse cycle may have high cathodic
bias V.sub.H pulse portion t.sub.1'', an anodic bias V.sub.R pulse
portion t.sub.2'', a zero cathodic bias V.sub.0 portion t.sub.3'',
and a low cathodic bias V.sub.L portion t.sub.4''. The anodic bias
portion has a bias that is between -0.25 and -3.0 times the bias of
the high cathodic bias portion (i.e. its magnitude is between 0.25
and 3.0 times the magnitude, but of opposite polarity).
[0045] Such anodic bias pulses may de-plate metal ions from the
deposited layer, providing a high concentration of ions close to
the cathode surface, further increasing the subsequent rate of
deposition during the high cathodic bias pulse portion, further
enhancing the incorporation of hard particulate into the deposited
layer of metallic matrix.
[0046] The sliding bearing may be a bearing lining or a thrust
washer, which is inserted into the bearing assembly of an
engine.
[0047] Throughout the description and claims of this specification,
the words "comprise" and "contain" and variations of them mean
"including but not limited to", and they are not intended to (and
do not) exclude other moieties, additives, components, integers or
steps. Throughout the description and claims of this specification,
the singular encompasses the plural unless the context otherwise
requires. In particular, where the indefinite article is used, the
specification is to be understood as contemplating plurality as
well as singularity, unless the context requires otherwise.
[0048] Features, integers, characteristics, compounds, chemical
moieties or groups described in conjunction with a particular
aspect, embodiment or example of the invention are to be understood
to be applicable to any other aspect, embodiment or example
described herein unless incompatible therewith. All of the features
disclosed in this specification (including any accompanying claims,
abstract and drawings), and/or all of the steps of any method or
process so disclosed, may be combined in any combination, except
combinations where at least some of such features and/or steps are
mutually exclusive. The invention is not restricted to the details
of any foregoing embodiments. The invention extends to any novel
one, or any novel combination, of the features disclosed in this
specification (including any accompanying claims, abstract and
drawings), or to any novel one, or any novel combination, of the
steps of any method or process so disclosed.
[0049] The reader's attention is directed to all papers and
documents which are filed concurrently with or previous to this
specification in connection with this application and which are
open to public inspection with this specification, and the contents
of all such papers and documents are incorporated herein by
reference.
* * * * *