Note: Descriptions are shown in the official language in which they were submitted.
CA 02526653 2005-11-22
BU/mo 030441CA
21. November 2005
Method for the Manufacture of Slide Bearing Bushings
The invention relates to a method for the manufacture of
slide bearing bushings which have on the outside a metal
jacket provided with a corrosion protection layer as a
support and a slide layer made of plastic. The invention
further relates to slide bearing bushings manufactured in
accordance with the method.
Slide bearing bushings of the type referred to in the
preamble are generally known and are widely used in
hinges and bearings of the most widely differing type, in
particular in the automotive sector. The operation of
slide bearing bushings is maintenance-free, i.e. there is
no requirement for the bearings to be lubricated. The
installation of the slide bearing bushings into the
corresponding hinges and bearings is effected as a rule
by pressing them in with suitable tools. The slide
bearing bushings are therefore also designated as press-
in maintenance-free slide bearing bushings.
Examples of known press-in slide bearing bushings are
described, among others, in the printed specifications DE
35 34 242, EP 0 217 462, and WO 90/12965 A1. Such
bushings usually have a metal casing (jacket) which is
provided on its inside face with a plastic slide layer
("running layer") based on fluoropolymer compounds (such
as PTFE with glass fibre-graphite filler material).
Depending on the running properties required, the plastic
slide layer additionally contains a tin/bronze wire woven
fabric or an expanded metal rib mesh as reinforcement
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material, which is embedded in the fluoropolymer
compound. In addition, the principle is also known, for
example from WO 99/05425 A1, of providing a surface-
structured metal sheet with honeycomb cut-outs as the
plastic slide layer, wherein the fluoropolymer compound
is attached by adhesive to the surface of the metal
sheet, and fills the honeycomb cut-outs. Metal jacket
and plastic slide layer in the slide bearing bushings
described are usually connected to one another by a hot-
melt adhesive film (e. g. FFA, ETFE).
To provide protection against corrosion, it is also usual
for the metal jacket of the slide bearing bushing to be
provided on its outside and on the face surfaces with a
corrosion protection layer made of zinc or zinc/nickel,
tin, zinc-aluminium, and possibly chromium. During the
manufacture of the known slide bearing bushings, the
application of the zinc or zinc/nickel layer is effected
by galvanizing; i.e. the finished slide bearing bushing
is introduced into a zinc or zinc/nickel galvanizing
bath, in which the zinc or zinc/nickel corrosion
protection layer is deposited by electrolytic means.
Research by the applicants in the field of the invention
has now shown that, during the galvanizing of the slide
bearing bushings, zinc deposits occur on the running
layer in the flange area, which deposits have a
disadvantageous effect on the sliding properties of the
bushings. It is assumed that the zinc deposits occur as
a result of the fact that micro-cracks occur in the
plastic running layer during the moulding of the flange,
through which the electrolyte can penetrate as far as the
metal reinforcement (e. g. bronze fabric) and so allows
for the electrolytic depositing of zinc. It has beer
found that the zinc deposits, despite their small
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volumes, in the microgram range, have a disadvantageous
effect on the initial slide properties of the slide
bearings. In particular, it has been found that the zinc
deposits lead, in the running-in phase of the slide
bearing bushing, to an increase in the friction
coefficient as well as to a reduction in the load-bearing
capacity and the wear resistance. The increased wear has
a disadvantageous effect on the service life of the slide
bearings.
A further disadvantage with the galvanizing of the slide
bearing bushings is that damage is frequently caused to
individual bushings due to arcing, accordingly resulting
in a relatively high wastage rate with defective
bushings. This arcing is to be attributed to deficient
electrical contact of the polymer-coated bushings, and
the local field concentrations associated with this
during electrolysis.
From DIN ISO Standard 12683 the principle is further
known of mechanically plating metallic components, i.e.
providing them with a zinc coating, which is applied with
the aid of a suitable drum device. The method is also
designated as ball-plating since it is substantially
based on the principle that, in the drum, small glass
balls of different dimensions press zinc powder particles
into the surface of the components which are to be
plated. With this method, neither electrical current nor
heat application are required.
An object of the present invention is to provide a method
for the manufacture of slide bearing bushings of the type
described in the preamble, which have excellent slidinc
properties and outstandingly good corrosion resistance.
In particular, the application of the corrosion
CA 02526653 2005-11-22
protection layer should not impair the function and
service life of the bushings.
This object is achieved according to the invention by a
method for the manufacture of a slide bearing bushing
comprising a metal jacket as a support, said metal jacket
being provided with a corrosion protection layer, and a
slide layer made of plastic, on which, to form the
corrosion protection layer, a corrosion protection agent
in powder form is applied by mechanical means.
By contrast with known manufacturing processes, which
make provision for an electrolytic application of the
corrosion protection layer (e.g. by galvanizing), the
application of the corrosion protection agent is effected
with the method according to the invention by mechanical
means, e.g. by pressing into the surface of the metal
jacket.
Surprisingly, it was found that the mechanical
application of the corrosion protection layer by
mechanical means leads, in comparison with the
conventional galvanizing process, to an increase in the
service life and improved sliding properties of the slide
bearing bushings. In particular, it was found that with
the mechanical application of the corrosion protection
agent, by contrast with the galvanizing method, there was
no formation of zinc deposits in the flange area of the
running layer. The fact that, with the method according
to the invention, the occurrence of zinc deposits in the
flange area can be avoided was particularly surprising,
because even with the method according to the invention
the flange areas of the bushings come into direct contact
with zinc powder (or other metal powdersj. This contact,
however, surprisingly does not lead to a long-term
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depositing of zinc in the areas referred to. The
undesirable increase in the friction coefficient and
reduction in Load-bearing capacity and wear resistance
which occurs when slide bearing bushings galvanized in
the conventional manner are being run-in, does not arise
with the method according to the invention. The slide
bearing bushings manufactured with the method according
to the invention have an increased service life in
comparison with conventional galvanized slide bearing
bushings.
In addition to this, the slide bearing bushings
manufactured with the method according to the invention
have a better adherence between the metal jacket and the
plastic slide layer than galvanized bushings. There is
no flaking of the plastic slide layer, in particular in
the flange area which is prone to this. It has also been
shown that the method according to the invention is
gentler in comparison with the conventional galvanizing
process, and leads to less damage to the bushings, and
therefcre to lower wastage rates during manufacture.
The features of the dependent claims relate to
advantageous further embodiments of the method according
to the invention.
The method according to the invention is well-suited to
the manufacture of slide bearing bushings of all kinds,
and is not restricted to specific slide bearing bushings.
The only essential factor is that the slide bearing
bushings exhibit a bond between the metal jacket and the
plastic slide layer. Usually the slide bearing bushinc
has on its front faces an open hollow cylindrical body,
which has on its outside the metal jacket and on its
inside the plastic slide layer. The slide bearing
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bushing can have a flange on at least one of its face
surfaces, which allows for the simple pressing of the
bushing into a hinge or bearing. In particular, the
method according to the invention is well-suited to the
manufacture of maintenance-free slide bearings.
The metal jacket of the slide bearing bushing may consist
of any desired metals and metal alloys. Particularly
suitable metals are steel, stainless steel, aluminium,
bronze, brass, titanium, and/or copper, as well as alloys
of these metals.
The plastic slide layer of the slide bearing bushing
contains a slide bearing material made of plastic.
Plastics which are well-suited to such purposes generally
have, in addition to good sliding properties, a high
mechanical loading capacity and/or high temperature
resistance. Suitable plastics are, for example, plastics
based on fluorinated polymers, in particular
polytetrafluoroethylene (PTFE, polyfluoralkoxyalkenes
(PFA, MFA), and/or tetrafluoroethylene-hexafluoropylene
(FEP), as well as non-fluorinated polymers, such as, in
particular, polyether-etherketone (PEEK) or polyethylene
(PE), and in particular high-molecular weight
polyethylene (HMW-PE) and/or ultra- high-molecular weight
polyethylene (UHMW-PE).
To improve the load-bearing capacity and reduce the wear,
cold flow, and static friction, the plastic slide layer
may contain organic and/or inorganic filler materials
("compounds"). Preferred filler compounds contain glass
fibres, carbon, graphite, and/or an aromatic polyester.
Particularly well-suited are fluoropolymers/glas~
fibres/graphite compounds, fluoropolymer/carbon/graphite
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compounds, and fluoropolymer/aromatic polyester
compounds.
The plastic slide layer of the slide bearing bushings may
further contain a metallic component for reinforcement,
wherein the metallic component may be a reinforcement
material with open structure, a fabric, in particular a
wire fabric, an expanded metal rib mesh, a non-woven
fleece material, in particular a metal fleece, a metal
foam, a porous metal layer, and/or a perforated disk. In
the case of a porous metal layer (in particular a porous
bronze layer), this is preferably sintered onto the metal
jacket. The metallic component may consist of any
desired metals or metal alloys. Preferably it consists
of a material selected from bronze, copper, chrome,
nickel, zinc, zinc-iron alloy, zinc-nickel alloy,
aluminium, tin bronze, steel, stainless steel, and alloys
thereof .
The plastic slide layer of the slide bearing bushing is
connected internally to the metal jacket and forms a
composite material. Preferably, the plastic slide layer
is connected to the metal jacket by means of a hot-melt
adhesive film, in particular of ethylene
tetrafluoroethylene copolymer (ETFE), and/or
perfluoroalkoxy-copolymer (PFA). It is also possible,
however, for the metal case and the metallic component of
the plastic slide layer (e. g. wire fabric or expanded
metal rib mesh) to be connected to one another
metallically, for example by sintering or welding, and
for the slide material then to be introduced into the
metallic component. With a metallic connection of this
kind, the use of a melt adhesive to connect the metal
jacket and the plastic slide layer is not necessary.
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The mechanical plating procedure for applying the
corrosion protection layer used in the method according
to the invention is described in greater detail
hereinafter.
The method according to the invention is characterised in
that, in order to form the corrosion protection layer, a
corrosion protection agent in powder form is applied
mechanically onto the metal jacket of the slide bearing
bushing. The process of mechanical application is also
designated as plating.
Any desired materials may be considered as corrosion
protection agent which are suitable, as surface coating,
for reducing the propensity of the material to corrode.
The corrosion protection material is preferably a ductile
material, in particular a ductile metal, which during
plating can be pressed into the surface of the metal
jacket. Particularly well-suited as corrosion protection
agents are metal powders, in particular zinc, tin,
aluminium, cadmium, and/or alloys thereof. Non-metallic
corrosion protection agents are also conceivable,
however, such as certain ductile polymers. According to
a particularly preferred embodiment of the invention,
zinc is used as the corrosion protection agent, in
particular in the form of zinc powder.
The corrosion protection agent is present in powder form.
The term "powders" in the meaning of the invention is
understood to mean particles with a mean particle
diameter from 20 mm to 1 um. The smaller the mean
particle diameter of the powder used, the easier the
application. Advantageously, this diameter ranges from
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~m to 1 mm, and more preferably 1 to 10 um and, in
particular, 3 to 8 um.
The mechanical application of the corrosion protection
agent is effected preferably by pressing into the surface
of the metal jacket. This can be done, for example, by
rolling the slide bearing bushing in a mixture containing
corrosion protection agent in powder form and hard
material bodies. In this situation, during the rolling
of the mixture the hard material bodies press the
particles of the corrosion protection agent into the
surface of the metal jacket of the slide bearing
bushings.
As hard material bodies, use is preferably made of
spherical hard material bodies, such as glass balls. The
hard material bodies have preferably a mean particle
diameter of 0.1 to 10 mm, in particular from 0.4 to 1.c
mm. The size of the hard material bodies used has an
influence on the speed and grain size of the coatinc
cbtained. Large bodies with a particle diameter from I
to 10 mm have a high impact effect, which leads to a more
rapid plating process. The advantage in using small
bodies with a mean particle diameter from 0.1 to 0.5 mm,
by contrast, lies in the fact that they break down
agglomerates which are formed from the coating materials
under the conditions of the process, and lead to
undesirable coarse-grained coating surfaces. The use of
smaller bodies therefore does indeed lead to a slower
coating process, but in the final result leads to a
finer-grained coating.
In order to combine the advantages of large and smal-~
hard material bodies, it is also possible to use mixture
of these. It has been shown that with a mixing ratio of
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10:90 to 50:50 % by volume, in particular 20:80 to 30:7C
by volume, of bodies with a particle diameter from 3 to
mm to bodies with a mean particle diameter from 0.1 to
0.5 mm, a coating can be obtained which has surface and
corrosion protection properties which are particularly
advantageous for use with slide bearing bushings.
Preferably glass balls of different sizes are used in the
mixing proportions indicated.
As material for the hard material bodies, any materials
are suitable of which the hardness is greater than the
hardness of the particles of the corrosion protection
material. According to a preferred embodiment of the
invention, glass balls are used as the hard material
bodies, since glass balls are simple and economical,
available in many sizes, non-toxic, chemically inert,
non-absorbent, wear-resistant, and reusable, as well as
having a low friction coefficient and high impact
resistance.
According to a preferred embodiment of the invention,
hard material bodies and slide bearing bushings are
present in the mixture in approximately equal volume
parts. It is also possible, however, for a higher or
lower proportion of hard material bodies to be selected.
A higher proportion of hard material bodies is expedient,
in particular for the coating of heavy slide bearing
bushings, or also if a high layer thickness is desired.
Usually, the volume ratio of hard material bodies to
slide bearing bushings in the method according to the
invention is approximately 0.3 to approximately 3.
The method according to the invention is preferably
carried out in a rotating drum filled with the mixture,
and in which the mixture is rolled. In order to improvE
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the rolling of the mixture in the drum, the drum
preferably has corner arrangements on the inside. A
further improvement to the rolling process can be
achieved by the drum being provided with a floor, and the
cross-section of the drum decreasing towards the floor.
In addition, the drum should be resistant to the
substances being used. Accordingly, a drum made of
stainless steel is therefore preferably used, which drum
can additionally be coated with acid-resistant and wear-
resistant plastic or rubber.
According to a further preferred embodiment of the
invention, in addition to corrosion protection agent and
slide bearing bushings, the mixture also includes a
fluid, in particular water. In particular if a metal
powder is being used as the corrosion protection agent,
such as zinc powder, it has proved to be advantageous for
water to be added to the mixture and for the aqueous
phase of the mixture to be adjusted to a pH value of 0 tc
7, in particular from 1 to 3.
The pH value can be adjusted by the addition of an acid.
In an acidic medium, the surface of the metal jacket of
the slide bearing bushing is etched and therefore
activates. The higher the pH value is, in general the
slower the coating process takes place. The pH value
should therefore amount to 0 to 7, preferably 1 to 3, and
more preferably 1.7 to 2.~. The adjustment of the pH
value is effected by the addition of an acid. The acid
concerned is preferably a non-oxidising acid.
The volume ratio of hard material bodies and slide
bearing bushings to fluid amounts preferably to some 2:1.
In this context it is advantageous for the fluid level tc
be adjusted in such a way that, during the rotation of
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the drum, it remains just above the solid constituent
parts of the mixture.
In addition to the components referred to, conventional
additives can also be added to the mixture, such as
activators, promoters, defoaming means, and metal salts.
The addition of additives of this type is generally usual
and generally known to the person skilled in the art from
the literature relating to mechanical galvanizing.
Good results can also be achieved if the temperature of
the mixture is at 5 to 40 °C, and in particular 21 to 26
°C. If work is being carried out at higher temperatures,
a rapid coating process can be attained, but this does
tend to lead to a somewhat coarse-grained surface. At
low temperatures, by contrast, the coating takes place
more slowly, whereby, however, a more even surface is
formed.
Before the plating process it is advantageous for the
slide bearing bushings first to be thoroughly cleaned and
degreased. Degreasing can be carried out in any way
desired, and, in particular, hot, alkaline soap solution
is well-suited as a grease solvent. The degreased
bushings can then be immersed in an acid bath and then
rinsed with water.
According to a preferred embodiment of the invention, the
coating process is followed by further surface treatment
steps. Thus, for example, after the mechanical plating
the slide bearing bushings can be chromated and/or sealed
in the usual manner. For chromating, a yellow chromating
process (Cr-VI) or blue chromatina (Cr-III) may be
considered. For sealing, sealing with a silicate sealer
may in particular be considerec.
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A possible sequence of the method according to the
invention is described hereinafter by way of example.
The slide bearing bushings to be coated, if appropriate
after preliminary cleaning, are filled into a drum in
mixture with hard material bodies (e.g. glass balls) and
water.
An activator can be additionally added to the mixture,
such as glycol ether, in particular nonylphenol glycol
ether. Preferably the activators can be added to the
mixture in acid solution, in particular in diluted
sulphuric acid.
All the components are mixed with one another by brief
rotation of the drum (about 2 minutes).
In order to create a priming for the coating, as the next
step in the process a metal salt can be added to the
mixture, in particular a copper salt such as copper
sulphate. In addition to this, promoters can also be
added to the mixture, such as tin salts, in particular
tin sulphate, as a reaction accelerator. Preferably the
promoters are added to the mixture in an acid solution,
in particular in a mixture of dilute sulphuric acid and
hydrochloric acid. The promoter solution may
additionally contain tensides and/or organic salts as
additives. In addition, conventional defoaming means can
also be added to the reaction mixture. These components
are likewise mixed with the other constituents by brief
rotation of the drum (4 to 8 minutes).
In order to create a basis for the coating, it is now
possible for a small volume of corrosion protection agent
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to be added as flash, wherein rotation is continued for
as long as required until the slide bearing bushings
acquire a silver sheen.
In order to obtain uniform layer thicknesses, the
corrosion protection agent is preferably added in
portions in several stages, in particular in 2 to 5
steps, and more preferably in 3 steps. The addition is
effected in each case preferably with a time interval of
to 60 minutes, in particular 10 to 20 minutes. After
the complete addition of the corrosion protection agent,
the pH value is adjusted with the aid of the activator
and/or by the addition of acid to a value of between 1.6
and 2.C. This value is preferably kept constant until
the end of the coating process.
When the slide bearing bushings have reached the desired
thickness, they are washed and separated from the other
components of the mixture. The separation can take
place, for example, by separation by screening or by
means of magnets.
The subject matter of the application is also a slide
bearing bushing manufactured by the method according to
the invention.
The invention is described in greater detail hereinafter
on the basis of embodiment examples.
Comparison Example 1:
From a 1.0 mm metal/plastic laminate of the type
Norglide~ PRO XL from Saint-Gobain Performance Plastics
Pampus GmbH, Willich (Germany , with the following layer
structure:
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1. Metal jacket: DC4 cold strip, plated on both sides
with Cu/Bz, Bz side structured,
Hot melt adhesive film (PFA film),
3. Plastic slide Layer: Fluoropolymer compound film
(PTFE and organic fillers)
From strip sections of 10 mm in width, using an automatic
stamping-bending device in a series mould, some 12,000
units of rolled and flanged composite bushings were
manufactured in the following dimensions:
a) Flange diameter . 13 mm
b;- Inside diameter . 7 mm
c) Wall thickness . 0.98 mm
d) Length . 7 mm
To obtain corrosion protection for use as a bearing for
the door hinge of private cars, 6,000 units of the
bushings described above are galvanized in the
conventional manner and then yellow chromated to providE
protection against white rust (Cr-VI).
Among 360 of the bushings manufactured in this way,
galvanized and yellow-chromated against white rust,
slight zinc separations were observed on the running
layer of the flange. These separations are caused by the
fact that, during the moulding of the flange, micro-
cracks occur in the polymer running layer, through which
the electrolyte can penetrate as far as the bronze fabric
reinforcement, and accordingly makes t~ossible the
electrolytic separation of zinc. The zinc particle
deposited on the PTFE running layer cause a negative
influence on the running-in properties and service lifE
of the slide bearing bushings.
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In addition to this, in 230 of the bushings there were
clear film separations in the flange area. Moreover, on
all the flanges subsurface corrosion of the film to a
depth of up to 3 mm was observed, extending outwards from
the intersection edges. In the flange area and the
intersection edges with the subsurface corrosion, the
polymer film could be detached relatively easily with the
aid of a deburring knife. Beneath the detached film
there was clear corrosion of the metal surface due to the
attack of the electrolytes which had diffused into the
interior via the thin polymer layer.
In the salt spray test according to DIN 50021, instead of
the required 120 hours, only 72 hours standing time was
attained before red rust began to occur. The subsurface
corrosion and film detachment were perceptibly
intensified in the salt spray test.
Example 1:
To obtain a corrosion protection for use as a bearing for
the door hinge of private cars, 6,000 units of the
bushings of the same type as in Comparison Example 1
(approx. 50 1 apparent volume) were mechanically
galvanized.
To do this, the bushings were first cleaned and degreased
with a mildly alkaline cleaner, and then filled into a
conical octagonal coating drum. After filling with an
approximately equal quantity of glass balls, related tc
the volume (diameter range 0.4 - 1.2 mm) and an equal
quantity of mains water, related to the volume, the
coating drum was set in rotation at 30 r.p.rr~.. To
initiate the coating process, ~ 1 of a to solution of
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nonylphenol polyglycol ether in dilute sulphuric acid
(Activator B from Tolkmit Industries, Balve, Germany), 50
g of a 5% tin sulphate solution in a mixture of dilute
sulphuric acid and hydrochloric acid (Promoter 2001 from
Tolkmit Industries, Balve, Germany), and 50 g of zinc
powder as zinc flash with a mean particle size of <30 um
are then added and rotated for 10 minutes. At a time
interval of 10 minutes, 150 g of zinc powder in each case
were added four times, and rotated for a further 30
minutes. The pH value of the aqueous phase in this case
amounted to 1 to 2, which was checked at regular
intervals. After the coating process, the bearings were
removed from the drum, rinsed with water, and dried.
The bushings manufactured in this way have a uniform zinc
layer with a thickness in the range from 12 to 18 um.
The bushings do not present either zinc deposits on the
slide layer, nor film detachments, nor subsurface
corrosion of the polymer layer. In the salt spray test
according to DIN 50021, all the test bushings achieved a
resistance to red rust of greater than 130 hours. The
bushings were characterised by improved running-in
properties in comparison with the comparison example 1.
Comparison example 2:
From a 0.5 mm metal/plastic laminate of the type
Norglide° T 0.5 from Saint-Gobain Performance Plastics
Pampus GmbH, Willich (Germany), with the following layer
structure:
1. Metal jacket: DC4 cold strip, galvanized on botr
sides and yellow-chromated,
Hot melt adhesive film (EFTE filmi,
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3. Plastic slide layer: Fluoropolymer compound film
(PTFE + carbon/graphite)
From strip sections of 11 mm in width, using an automatic
stamping-bending device in a series mould, 36,000 units
of rolled and flanged composite bushings were
manufactured in the following dimensions:
a) Flange diameter . 17 mm
b) Inside diameter . 11 mm
c) Wall thickness . 0.48 mm
d) Length . 7 mm
To obtain corrosion protection for use as engine bonnet
hinge bearings on private cars, 30,000 units of the
bearings described above were galvanized in the usual
manner and then yellow-chromated to provide protection
against white rust [Cr (VI)].
On about 3% of the bushings manufactured in this way,
severe deformation was determined in both the area of the
flange as well as in the cylindrical part of the
bushings. The cause of this deformation was identified
as mechanical deforming due to the relatively heavy
electrodes in the galvanizing drum. A further 11
bushings with damage due to over-arcing were screened
out. Due to the defects described, a 1000 quality
control of the bushings was required. In the salt spray
test resistance to the start of red rust of 132 hours was
determined.
Example 2:
To obtain corrosion protection for use as engine bonnet
hinge bearings on private cars, some 6,000 bearings of
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the same type as in Comparison Example 2 were initially
mechanically galvanized as described in Example 1,
wherein a total of 300 g of zinc was used and a zinc
layer of 15 um in thickness was formed. Next, for
passivation a blue-chromated [Cr (III)] coating was
applied, as well as a sealer of the Finigard 105 type
from Coventya in Giitersloh, Germany.
After a visual assessment of the bushings manufactured in
this way, and mechanically galvanized, blue-passivated
and sealed, no defects could be ascertained. In the salt
spray test an excellent degree of resistance against red
rust of over 300 hours was achieved. The bushings are
characterised by improved running-in properties in
comparison with the bushings manufactured in accordance
with Comparison Example 2.
Comparison example 3:
From a 0.75 mm metal/plastic laminate of the type
Norglide~' T 0.75 from Saint-Gobain Performance Plastic
Pampus GmbH, Willich (Germany), with the following layer
structure:
1. Metal jacket: DC4 cold strip, galvanized on both
sides and yellow-chromated,
Hot melt adhesive film (EFTE film),
3. Plastic slide layer: Slide Layer reinforced with
bronze fabric (E-PTFE + glass fibre/graphite)
From strip sections of 8.5 mm in width, using an
automatic stamping-bending device in a series mould,
38,OOC~ units of rolled and flanged composite bushing
were manufactured in the following dimensions:
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a) Flange diameter . 20 mm
b) Inside diameter . 13 mm
c) Wall thickness . 0.78 mm
d) Length . 5 mm
To obtain corrosion protection for use as multi-joint
hinge bearings for private cars, 32,000 of the bushings
described above were galvanized in the usual manner.
They were then yellow-chromated (Cr-VI) to provide
protection against white rust.
In 350 of the bushings manufactured in this way, slight
zinc separation was observed on the running layer of the
flange. These separations are caused by the fact that
micro-cracks occur in the polymer running layer during
the moulding of the flange, through which the electrolyte
can penetrate as far as the bronze fabric reinforcement,
and so allow for the electrolytic separation of zinc.
The zinc particles deposited on the PTFE running layer
lead, during the operation of the slide bearing bushings,
to increased wear during the running-in phase and to
shortening of the service life. In the salt spray test
the bushings have a resistance to red rust of greater
than 120 hours.
Example 3
To obtain corrosion protection for use as multi-joint
hinge bearings on private cars, about 6,000 bushings of
the same type as in Comparison Ex«mple 3 were initially
mechanically galvanized as described in Example 1,
wherein a total of 300 g of zinc was used and a zinc
layer of 15 um thickness was formed. The bushings were
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then coated with a silicate sealer by immersion,
centrifuging, and drying.
After a visual assessment of the bushings manufactured in
this way, neither zinc deposits nor any other
irregularities could be determined. In the salt spray
test, a good resistance to red rust of over 140 hours was
achieved. It was determined by tribological examinations
that the corrosion layer treatment described above does
not exert a negative influence on the friction and wear
behaviour of the slide bearings.
The examples described above show that the mechanically
galvanized bearing bushings manufactured in accordance
with the method according to the invention have the
following advantages in comparison with bearing bushings
which are galvanized in the conventional manner:
The adherence of the plastic slide layer to the metal
jacket is not impaired by the mechanical galvanizing.
For this reason, there is neither any detachment nor
subsurface corrosion of the slide layer, with the result
that no areas with increased susceptibility to corrosion
arisE. Moreover, mechanical deformation and damage tc
the bushings incurred by field concentrations due tc
aver-arcing are avoided. In addition, the sliding
capacity of the slide layer is not impaired by deposits
of corrosion protection agent, which leads to an
improvement in the running-in properties and to an
increase in service life.
