Note: Descriptions are shown in the official language in which they were submitted.
CA 02670200 2009-05-21
PCTCN2008.%071081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
Specification
A Lead-free Self-Lubricating Bearing and its Producing Method
Field of the Invention
The invention relates to a sliding bearing, particularly a lead-free self-
lubricating bearing made of
a three-layer compounded material.
Background Art
The DU bearing, which came into existence as early as 1970s, is a three-layer
compounded
bearing, but the inner lining of its frictional layer is sintered with a
mixture of
polytetrafluoroethylene (PTEE) and lead (Pb). In some application fields such
lining may replace a
copper alloy shaft sleeve and achieve a lower manufacturing cost and a longer
service duration
but since the friction-reduction layer of the bearing comprises lead
components where lead and its
compounds are toxic substances, when the bearing is in operation lead powder
will he generated
as a result of wear caused by abrasive grain and gaseous lead will be emitted
under a high
temperature condition. Besides, the recycling of used and waste bearings is an
issue. Such
problems bring harm to the human body and the environment. With an increased
environmental
consciousness among people, the use of such product has been prohibited or
restricted in
automobile, food, pharmacy, home electric appliance, fitness, office, beverage
and other machine
manufacturing industries. We have noticed that relevant environmental
protection standards have
been issued in Europe and America: for example the European ROHS Directive
regarding heavy
metals and hazardous substances has laid down specific requirements in this
regard.
It will be an ideal upgrade for conventional products like the DU bearing if
the critical problem
related to the existence of lead, other heavy metals and hazardous substances
in the plastics lining
layer, or the friction-reduction, wear-resistant layer, of the bearing can be
overcome effectively
while the bearing operates satisfactorily.
The main object of the invention is to investigate and provide a material
composition of the inner
-1-
CA 02670200 2009-05-21
PCT'CN2008071081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
lining (the friction-reduction plastics laver) of the bearing, so as to not
only exclude the hazardous
substance -- lead used in the DU bearing but also replace the lead, which has
a low friction
coefficient, with a polymer comprising the materials described below.
Meanwhile, the mechanical.
physical and frictional properties of the upgraded bearing will be made
superior to those of the
DU bearing.
Polvtetrafluoroethvlene, PTFE for short, exhibits excellent frictional
behaviour and has the lowest
friction coefficient among all plastics. It is often used as lubrication agent
for the inner lining of a
sliding bearing, and it may serve as a filling with a low-friction coefficient
therefor. However,
polytetrafluoroethylene is rarely used alone as its mechanical strength and
modulus of elasticity is
extreme low when used alone. It is well known that, in practice, a wear-
resistance filling and/or
other materials for strengthening the lining must he added to make the lining
suitable for
heaN s-load, low-speed or light-load, high-speed movement.
Among all engineering plastics, aromatic polyester, EKONOI for short, is
characterized by its
metal-like properties and the highest thermal conductivity, farther it
exhibits excellent dimensional
stability outstanding creep behaviour under compression, good anti-abrasion
property; excellent
self-lubrication and hardness. The above attributes effectively overcome the
problems arising from
using polytetrafluoroethylene alone. Pol\imide, PI for short, has similar
characteristics and is
therefore a substitute material for aromatic polyester.
Polyphenylene sulphide, PPS for short, is a kind of thermoplastic polymer with
high temperature
resistance. It features outstanding high-temperature resistance, corrosion
resistance, chemical
stability and it can enhance the adhesive strength with respect to metal,
various powders or fibres.
It is proved to be the best high-temperature adhesive. Tests show that adding
polyphenylene
sulphide to a friction-reduction plastic layer improves fatigue strength and
reduces cavitation.
However, pohphenylene sulphide should firstly go through chemical cross-
linking, a matured
technology. and usually, accelerant such as magnesium-fluoride need to be
added. The
cross-linking lasts 20 minutes.
-2-
CA 02670200 2009-05-21
PCT=CN2008=071081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
Aramid fibre, with a trade name Kevlar (produced by DuPont Company based in
US), is an
organic fibre with excellent performances and features super high strength,
super high modulus,
high temperature resistance and low density. Its strength is 3 times higher
than that of ordinary
organic fibres and its modulus of elasticity is 10 times that of nylon and 9
times that of polyester.
Aramid fibre has such characteristics as high impact toughness and fatigue
strength, good
dielectric property and chemical stability, low expansion rate, low thermal
conductiyit',
non-ignitability, infusibility, etc. Filling PTFT with aramid fibre may
greatly improve the
mechanical performance. load capability, anti-friction and wear resistance of
the bearing.
Molybdenum disulphide. MoS2 for short, belongs to the family of hexagonal
system laminate
structures. Its layers can slide over each other very easily and it thus has
good self lubricating
property, it can firmly adhere to a metal surface and is not easily damaged
under friction, thus it
can bear heavy load. Statistics shows that an MoS2 film with a thickness of
2.51.m can bear a
pressure of over 2800MPa while at a friction speed of 40m/s. When MOS2 is
added the friction and
wear properties of the bearing will be obviously improved and the initial
abrasion of the bearing
will be reduced. Sometimes MoS2 may be replaced by graphite.
The above description of the conventional sliding bearings and DU bearings
fully proves the
progress made by the mankind in scientific and technical development. The main
object of the
present invention is to investigate and provide compositions of lead-free
materials for a
friction-reduction lining of a self-lubricating bearing. At the same time, the
bearing exhibits
superior mechanical, physical and frictional properties to those of a DU
bearing. The ultimate
object is to provide a three-layer compounded lead-free self-lubricating
bearing and methods of
manufacturing thereof.
Summary of the Invention
The object of the invention is to provide a lead-free self-lubricating bearing
and methods of
manufacturing thereof The lead-free self-lubricating bearing can not only
operate under oil
-3-
CA 02670200 2009-05-21
PCT CN2008 07109 1 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
lubricating conditions and is corrosion resistant, but it can also operate
under rigorous lubricating
conditions, such as marginally oil lubricating or even dry- friction
conditions. Particularly, the
bearing does not comprise lead or lead compounds and it can meet the
requirements of the
European ROHS regulations on heavy metals and hazardous substances. The self-
lubricating
bearing can be widely used in automobile, food, pharmacy, home electrical
appliance, beverage,
office. medicine and other machine manufacturing industries.
The object of the invention is achieved through the following technical
solution: The lead-free
self-lubricating bearing mainly comprises a metal base-plate, a porous layer
of spherical bronze
powder sintered on the base-plate, and a friction-reduction and wear-resistant
plastic layer which
penetrates into and covers the bronze powder layer. Further, a roll-
manufacturing technique is used
to make the sliding hearing. A characteristic of the invention is that said
spherical bronze powder is
lead-free and the friction-reduction plastic layer is lead-free. The polymer
composition of said
friction-reduction, wear-resistance plastic layer, i.e. the bearing lining,
comprises, by weight,
10--20% polyphenyl thioether superfine powder, 1 0 -20% aromatic polyester
superfine powder,
10--20% aramid fibre with a fibre length of 40--120 m, and 6-10% molybdenum
disulphide
superfine powder, the rest being polytetrafluoroethylene superfine powder.
Said metal base-plate is made of a rolled belt of high quality mild steel. The
width of the rolled steel
belt 150-300mm and the thickness thereof is 0.25-2.70mm. A surface of the
rolled steel belt is
plated with copper: the plated copper layer having a thickness of 4-61tm.
Either CuSn8P or
CuSn10 is selected as the spherical bronze powder sintered on the metal base-
plate.
A method of manufacturing a lead-free self-lubricating sliding bearing
comprises the following
procedures:
A. Select SAE1010 or SAE1008 brand or SPCC rolled steel belt as the metal base-
plate.
B. Sinter on the metal base-plate a layer of lead-free spherical bronze
powder. the diameter of
the spherical powder being 60.140 m and the sintered thickness being 025-
0.40mm.
C. Make an extendable soft paste for a friction-reduction and wear-resistant
laver:
-4-
CA 02670200 2009-05-21
PCT CN2008d) i 1081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
(1) Perform pohphenylene sulphide chemical Cross-linking. As this is a
publicly
known matured technology, no details thereof will be described herein.
(2) Prepare powder and fibre according to the above mentioned weight
composition.
(3) Stir: mix the prepared powder and fibre and stir them at least three
times, 5-10
minutes each time, to form a mixture. The rotation speed of the stirring
machine is
2000-4000r/min. Sieve the mixture at least three times, with sieve mesh of 100
or more.
(4) Make the extendable soft paste: mix 1000g of the powder mixture with 800g
polvtetrafluoroethylene emulsion with 60% solid content; stir for 5-I0min in a
stirring
machine at a rotation speed of 20-60r/min; a preferable environment
temperature is
1525 C.
(5) In order that the soft paste exhibits good fluidity when spread on the
sintered
layer of spherical bronze powder, 4-6% ethanol should be added when the
mixture and
the polytetrafluoroethylene emulsion are stirred, so as to make the soft paste
even softer.
D. Automatically spread and roll the soft paste on the bronze powder layer of
the two-layer
compounded belt on a production line in a way that part of the soft paste
penetrates into the pores of
the porous layer of spherical bronze powder and a lining layer is formed to
cover the spherical powder
layer. Preferably no bronze powder is exposed. Usually, the covering layer is
0.01-0.03nun thick, but
it can be thickened to up to 0.2mm if needed. E. Dry the belt at the
temperature of 220-28(>"C for
15-25 minutes, until the moisture in the pohietrafluoroethylene emulsion
completely volatilizes.
F. Intermediate rolling: Roll the dried belt once, with a rolling reduction of
0.0150.03mm. to
increase the density of the polytetrafluoroethylene in the pores of the
spherical bronze powder layer
and the cohesion there-between.
G Sinter the friction-reduction plastic layer in a channel-type nitrogen
shield sintering furnace,
including three phases, namely, preheating, heating and heat preserving. The
sintering heating
temperature is 380-390 C. The total sintering period is 15--25 minutes of
which 8- 10 minutes are for
the pre-heating. In order that the belt is not oxidized during the sintering,
nitrogen is used in the
furnace channel as a protective gas with a purity of 99.9% or above. The
minimum flow rate of
nitrogen for different sintering furnaces is determined based on that
oxidization does not occur.
H. Final rolling: roll the sintered belt into a finished belt in compliance
with the requirement of a
-5-
CA 02670200 2009-05-21
PCT. CN2008 0 7 1081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
finished belt. The minimum rolling reduction is 0.02mm or more.
1. Wind up the finished three-layer compounded lead-free self-lubricating belt
with a winding
machine. Unload it after fixing it by binding.
J. Cut the belt into strips according to bearing specifications. For mass
production, unwind the
wound three-layer compounded lead-free self-lubricating rolled belt and cut it
into strips of a same
width or different widths and wind up each strip.
K. Bearing manufacturing: the whole process of manufacturing the three-layer
compounded
lead-free self-lubricating bearing is completed by forming, on an automatic
moulding machine, the
stripes into the three-layer compounded lead-free self-lubricating bearing
according to bearing
requirements. For small scale production where manufacturing on an automatic
moulding machine
is not suitable, a conventional rolling technique for manufacturing bearings
may be adopted:.
conventional equipment and working procedure are used to complete the
manufacturing of the
three-layer compounded lead-free self-lubricating bearing.
The invention sinters a laver of lead-free spherical bronze powder on the
metal base-plate made of a
rolled steel belt. The sintering furnace is a channel-type sintering furnace
using mixed
hydrogen-nitrogen as a protective gas, with 50% hydrogen and 50% nitrogen. The
sintering lasts
8-10 minutes at 880-900 C. If needed, pigment that can withstand a sintering
temperature of up to
400 C may be added during the procedure of preparing the powder and fibre in
order to color the
lining of the finished bearing.
As described above, the invention further optimizes the material composition
of the
friction-reduction and wear-resistant plastic layer. Particularly. high
performance organic fibre
Kevlar is added. greatly enhancing the wear resistance. the fatigue strength
and the load capacity
of the bearing.
The metal base-plate according to the invention is made of a rolled steel
belt. The whole
manufacturing process of the three-layer compounded material can be
accomplished on a
production line. A whole roll of steel belt purchased from a steel mill is
plated with copper and
-6-
CA 02670200 2009-05-21
PCT CN2008 07 1081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
then loaded on a unwinding machine. Through unwinding and flattening, being
automatically
spread with bronze powder, and sintering and rolling, it is made into a two-
layer compounded
porous belt. Further through automatic spreading and rolling of a soft paste
of friction-reduction,
wear-resistant plastics, followed by drying, intermediate rolling. sintering,
final rolling and winding
up, the whole process of manufacturing the three-layer compounded material for
a self-lubricating
bearing is completed.
A commodity name of the three-layer compounded, lead-free, self-lubricating
bearing
manufactured according to the above method is CSB-50.
The invention overcomes the disadvantage that a lead comprising friction-
reduction plastics layer
makes a compounded bearing unsuitable for use in automobile, food, pharmacy,
home appliance,
office., beverage and other machine manufacturing industries. The product is
characterized by a
simple structure, high operation efficiency, a long service duration, and an
easy and convenient
manufacturing technique, etc. The results of three tests for comparing the
invented CSB-50
three-layer compounded lead-free self-lubricating bearing and the DU bearing
on the market
under the same working conditions -are given below:
(1) Comparison made on M2000 friction/wwear testing machine (F=196N V=0.4m/s,
Time: 120
minutes)
Dry friction Oil lubrication
Bearing Model Friction Grinding crack Friction Grinding crack
Coefficient ( ) width (b) Coefficient ( ) wwidth (b)
DU on the
0.13 3.9 0.03 2.7
market
CSB-50 0.12 2.8 0.03 2.2
(2) Comparison made on MMU-12 end-face friction/wear testing machine (Dry
friction
P=8N/mm2, V=0.2mis. Time: 180 minutes)
-7-
CA 02670200 2009-05-21
PCT CN2008%071081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
Loss caused by wear
Bearing Model Friction Coefficient (.t) Temperature (F I)
(E)
DU on the market 0.13 93 16
CSB-50 0.12 87 11
(3) Test of gravity loss of PTFE friction-reduction laver in ultrasonic
Oscillation frequency: 20KHz. Oscillation amplitude: 501un. Medium: water.
Clearance: 1.3mm.
Time: 10 minutes
Bearing Model Gravity loss in 10 minutes (mg)
DU on the market 22
CSB-50 14
The results of the above three different tests show that, regardless of the
type of test, the CSB-50
lead-free self-lubricating bearing is obviously superior to the DU bearing
available on the market
in terms of friction and wear properties.
Description of the Figure
Figure 1 is a flow chart showing a manufacturing process according to the
invention.
Detailed Description of the Embodiments
Below is a detailed description of the invention with reference to the figure
and particular
embodiments: The invention mainly comprises a metal base-plate, a porous laver
of spherical
bronze powder sintered on the base-plate, and a friction-reduction and wear-
resistant plastics layer
that penetrates into and covers the bronze powder layer. Further, a rolling
technique is used to make
a sliding bearing. Said spherical bronze powder is lead-free and the friction-
reduction plastic layer
is also lead-free. The polymer composition of said friction-reduction plastic
layer, i.e. the inner
lining of the bearing, comprises, by weight, 10-20% polyphenyl thioether
superfine powder,
10-20% aromatic polyester superfine powder, 10-20% aramid fibre with a fibre
length of
40-120 m, and 6-10% molybdenum disulphide superfine powder, the rest being
-8-
CA 02670200 2009-05-21
PCT CN2008 071081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
polytetrafluoroethylene superfine powder.
Said metal base-plate is made of a rolled belt of high quality mild steel. The
width of the rolled steel
plate is 150-300mm and the thickness thereof is 0.25-2.70mm. A surface of the
rolled steel belt is
plated with copper, the plated copper layer having a thickness of 46 m. Either
CuSn8P or
CuSn10 is selected as the spherical bronze powder to be sintered on the metal
base-plate.
Referring to Fig. 1, a method of manufacturing the lead-free self-lubricating
sliding bearing according
to the invention comprises the following procedures:
A. Select SAEIOIO or SAE1008 brand or SPCC rolled steel belt as the metal base-
plate.
B. Sinter on the metal base-plate a laver of lead-free spherical bronze
powder, the diameter of
the spherical diameter being 60-1401tm, the sintered thickness being 0.25-
0.40mm. The sintering
furnace is a channel-type sintering furnace using mixed hydrogen-nitrogen as a
protective gas, with
50% hydrogen and 50% nitrogen. The sintering lasts 8-10 minutes at 880900 C.
C. Make an extendable soft paste for a friction-reduction and wear-resistant
laver:
(1) Perform pohphenylene sulphide chemical cross-linking.
(2) Prepare powder and fibre according to the above-mentioned weight
composition. If
needed, pigment that can withstand a sintering temperature of up to 400 C may
be added to
color the lining of the finished bearing.
(3) Stir: mix the prepared powder and fibre and stir them three times, 5-10
minutes each
time., to form a mixture. The rotation speed of the stirring machine is 2000-
4000r/min. Sieve
the mixture three times, with sieve mesh of 100 or more.
(4) Make the extendable soft paste: mix 1000g of the powder mixture with 800g
polvtetrafluoroethylene emulsion with 60% solid content: stir for 5-10min in
the stirring
machine at a rotation speed of 20-60r/min: a preferable environment
temperature is
15--25 C.
(5) In order that the soft paste exhibits good fluidity when spread on the
sintered
layer of spherical bronze powder, 4-6% ethanol should be added when the
mixture and
the polytetrafluoroethylene emulsion are stirred, so as to make the soft paste
even softer.
-9-
CA 02670200 2009-05-21
PCT CN2008 071081 Version: 15 Mav 2009
English translation of the amended application for the Canadian national phase
- clean copy
D. Automatically spread and roll the soft paste on the bronze powder layer of
the two-layer
compounded belt on a production line in a way that part of the soft paste
penetrates into the pores of
the porous layer of spherical bronze powder and a lining layer is formed to
cover the spherical powder
layer. Preferably the bronze powder is not exposed. Usually. the covering
layer is 0.01-0.03mm thick.
but it can be thickened up to 0.21n in if needed.
E. Dry the belt at the temperature of 220-280 C for 15-25 minutes, until the
moisture in the
pohvtetrafluoroethylene emulsion completely volatilizes.
F. Intermediate rolling: Roll the dried belt once, with a rolling reduction of
0.015--0.03mm, to
increase the density of the polytetrafluoroethylene in the pores of the
spherical bronze powder layer
and the cohesion there-between.
G Sinter the friction-reduction plastic layer in a channel-type nitrogen
shield sintering furnace,
including three phases, namely, preheating. heating and heat preserving. The
sintering heating
temperature is 380-390 C. The total sintering time is 15-25 minutes of which 8-
10 minutes are for
the pre-heating. In order that the belt is not oxidized during the sintering,
nitrogen is used in the
furnace channel as a protective gas: the purity of the nitrogen is 99.9 /o or
above. The minimum flow
rate of nitrogen for different sintering furnaces is determined based on that
oxidization does not occur.
H. Final rolling: roll the sintered belt into a finished belt in compliance
with the requirement of
the finished belt. The minimum rolling reduction is 0.02mm or more.
1. Wind up the finished three-layer compounded lead-free self-lubricating belt
with a winding
machine. Unload it after fixing it by binding.
J. Cut the belt into strips according to bearing specifications. For mass
production. unwind the
wound three-layer compounded lead-free self-lubricating rolled belt and cut it
into strips of a same
width or different widths and wind up each strip.
K. Bearing manufacturing: the whole process of manufacturing the three-layer
compounded
lead-free self-lubricating bearing is completed by forming, on an automatic
moulding machine, the
stripes into the three-layer compounded lead-free self-lubricating bearing
according to bearing
requirements. For small scale production where manufacturing on an automatic
moulding machine is
not suitable. a conventional rolling technique for manufacturing bearings may
be adopted:
conventional equipment and working procedure are used to complete the
manufacturing process of
-10-
CA 02670200 2009-05-21
PCTCN2008 071081 Version: 15 May 2009
English translation of the amended application for the Canadian national phase
- clean copy
the three-layer compounded lead-free self-lubricating bearing.
According to a practical embodiment of the invention, the following parameters
are preferred:
The material composition by weight is 10-20% pol}phenyl thioether superfine
powder, 10-20%
aromatic polyester superfine powder, 10-20% aramid fibre with a fibre length
of 40 1201un, and
6-10% molybdenum disulphide superfine powder, the rest being
polytetrafluoroethelene powder.
For drying, the temperature is 250-280 C and the duration is 15-25 minutes.
Most preferably, the
moisture in the PTFE emulsion completely volatilizes.
The sintering is carried out in a nitrogen shield sintering furnace. The
sintering temperature is at
380-390 C. The sintering period is 10-20 minutes. The purity of the nitrogen
is 99.9% or above.
The flow rate and the pressure of the nitrogen nary in view of different
sintering furnaces. Most
preferably, oxidation of the steel base-plate does not occur.
-11-
