DE4227909A1 - Metal-plastic composite bearing material - has metal backing, middle layer of porous sintered metal and sliding layer of PTFE contg. finely-dispersed co-polyimide particles - Google Patents

Abstract

A metal-plastic composite bearing material (I) has a metal backing (A), esp. of steel or copper-plated steel, coated with a porous layer of sintered metal (B) and a sliding layer (C) consisting of a PTFE matrix contg. a polymeric additive. The additive contains finely-dispersed copolyimide(s) (II) in amts. of 10-40 wt.% w.r.t. the PTFE. USE/ADVANTAGE - (I) is a dry bearing material with a low coefft. of friction and with wear resistance and cavitation resistance at least no worse than those of prior-art materials (esp. e.g. those with sliding layers contg. PTFE with other additives); addn. of (II) makes the material less brittle without increasing the coefft. of friction or lowering the thermal stability, so that the prodn. reject rate is lower. The material is not difficult to process and is suitable for use under complex operating conditions, esp. high running speeds and high specific loads, as required in motor vehicles, etc.

Description

The invention relates to a metal-plastic Composite bearing material with a metal back, in particular made of steel or copper-plated steel, one on the Porous metal backing Metal sintered layer and one on the Metal sintered layer applied sliding layer, the sliding layer being PTFE as the matrix material and a polymer additive contained in the matrix material having. The invention also relates to a method to produce such Metal-plastic composite bearing materials, where a metal sintered layer on a metal back is applied and then the Sliding layer material as a paste on the sintered layer is applied and sintered.

Dry bearings made of metal-plastic composites are known and essentially consist of a porous sintered layer made of, for example, CuSn8, CuSn10 or CuPb10Sn10 alloys, which are applied to a steel support. Mixtures of fluoropolymers with a wide variety of active fillers, such as e.g. B. Pb, PbO, metallic sulfides, MoS _{2 can} be incorporated so that a sliding layer covering the sintered structure is obtained from 10 to 30 microns.

The most widely used fluoropolymer is Polytetrafluoroethylene (PTFE), which because of its extraordinarily low coefficient of friction and its high corrosion and thermal resistance is preferred. However, this polymer tends to  so-called "cold river" and points among all thermoplastics the highest Wear at higher loads. Polytetrafluoroethylene can therefore only be used in combination with fillers.

From DE-PS 11 32 710 it is known to be PTFE Powder, paste or dispersion under low pressure into the pores of the sintered layer and then to sinter. Contains the PTFE material Additives to solid lubricants and wetting agents.

In DE-OS 114 94 078 a storage material described that from a mixture of one or several thermoplastics, u. a. PTFE and additives Phosphates, Pb, PbO or graphite.

DE-PS 9 62 561, DE-AS 10 35 415, DE-PS 10 65 182 and DE-PS 14 94 079 describe Plain bearings in which in the PTFE matrix different fillers such as sulfides, selenides, Telluride or molybdenum, tungsten and titanium, indium or tantalum are included.

In the case of the PTFE sliding layers provided with metallic lead as filler, however, it has been shown that under high load at sliding speeds and specific loads they correspond to a PV value of 1500 kg / cm ² × m / min, their pressure and the temperature on the sliding surface rise far enough to melt the metallic lead, the melting point of which is only 327 ° C. Such a sliding layer cannot withstand high PV values such as 3000 kg / m ² × m / min. In addition, since the lead can only be distributed very poorly in a uniform manner in the PTFE matrix, the metal loss through melting does not occur evenly, so that local areas are already free of lead at loads of 1500 kg / cm ² × m / min are so that the load can no longer be absorbed evenly, which leads to locally progressive wear. The plastic sliding layers are literally shattered. Particularly under conditions such as those found in shock absorbers and struts, the metal-plastic composite bearings used here as guide bushings with a plastic matrix made of PTFE fail in series regardless of the type of filler, since they are subject to high local side loads, high piston rod speeds and are not up to the cavitative and erosive demands. Efforts to remove the solid lubricant, e.g. B. Adding lead in thinly rolled form flat or scale-like to the PTFE matrix did not bring any significant improvement, since the achievement of such a particle shape in the solid lubricants mentioned in DE-OS 35 16 649 such as metals (Pb), oxides, fluorides, boron nitride first is not feasible and, where it is possible, for example, in the case of metallic lead, the relatively low melting point of the same cannot be raised.

In the course of the search for improved sliding layers with otherwise the same structure you have that Polytetrafluoroethylene u. a. Calcium fluoride added. This is described in GB 21 66 142. The Practice has shown, however, that initially the Laboratory tests emerging improvements Model test benches not confirmed in practice.  

In order for the previously formed areas of application Bonds of the PTFE particles to each other and to Substrate (e.g. porous bronze sintered structure) improve, you have in DE-PS 32 29 667 suggested that the PTFE 0.1 to 50 vol .-% Tetrafluoroethylene perfluoroalkyl vinyl ether Add copolymer resin. From DE-OS 41 05 567 is known an impregnation coating composition from 0.5 to 30 vol .-% of a material from the group PFE, FEP, EPE and 5 to 30 vol .-% lead with the rest of PTFE to use.

These additives to meltable fluoropolymers but brought no noticeable improvements towards the cavitative and errosive Stresses in practice. The replacement of the Sliding layers continued to appear. The coefficient of friction the PTFE rose and the otherwise high thermal Resilience of the PTFE has been reduced.

From DE-PS 30 50 056 is a Multi-layer composite material known in the a steel support layer forms a matrix Polyimide layer is applied, which is preferred consists of a polyester imide. In this matrix are low molecular weight PTFE particles as self-lubricating additive finely dispersed.

A slide bearing is known from DE-AS 28 18 184, with a sliding layer on a rough surface PTFE, high temperature resistant, thermosetting Polyimide and up to 20% by volume of cavitation and Additives that increase wear resistance is applied.  

The use of this as well as others Polymer matrix materials such as PEEK (DE-PS 22 21 785) or PES (DE-PS 33 43 309) with different Fillers brought about an improvement the cavitative and erosive stresses, however showed that the coefficient of friction of such Sliding materials even when adding friction reducing additives is too high and the requirements not on the driving comfort of automobile manufacturers enough. In addition, when necessary Slitting the coated broad bands and the Stamping the boards to form the bushings constantly due to the brittleness of the sliding layers significant spalling occurs, resulting in leads to unusually high reject rates.

The object of the present invention is therefore a metal-plastic composite bearing material to provide the complex Operating conditions are sufficient, especially high ones Running speeds and high specific Withstands loads, the coefficient of friction is low and the wear and cavitation resistance at least not worse than the materials after State of the art. Beyond that problem-free processing may be possible.

This task is done with a composite bearing material solved according to claim 1. The invention Process is the subject of claim 7.

It has been shown that while maintaining PTFE as a matrix material in connection with Mixed polyimides in a proportion of 10 to 40% by weight fully meets the above requirements  could be fulfilled. Here has pointed out that from about a share of 10 wt .-% of mixed polyimides the brittleness of Material lowered and the cavitation resistance and Erosion resistance compared to a pure PTFE layer could be improved without the The coefficient of friction increases and the thermal resilience sinks.

By using mixed polyimides it was possible on the addition of further the cavitation and Wear resistance increasing aggregates, such as e.g. B. molybdenum disulfide. The However, the invention includes the addition of such Fillers do not work for certain applications.

The brittleness of the sliding layers thus obtained was significantly lower than with the sliding layers that for example a polyimide matrix or the known high temperature resistant polyimides in the PTFE matrix in the presence of, for example Have molybdenum sulfide or graphite, so that the Reject rates when processing the Plain bearing material could be significantly reduced.

With a proportion of 25 to 35% by weight of mixed polyimides a composite bearing material is obtained which the best in terms of complex requirements Compromise. If the mixed polyimide content is more than 40% by weight, the wear decreases continue to decrease, but the coefficient of friction increases significantly so that the requirements of the automotive industry in terms of driving comfort at higher Mixed polyimide proportions no longer fully met can be.  

Mixed polyimides are preferably used which following general structural formula (Formula 1)

have, where X ¹ and X ^{2 are the} following intermediate members -O-, -CH ₂ -, -SO ₂ -, -C (CF ₃ ) ₂ -, -C (CH ₃ ) ₂ -, -S- and z = Is 0.1 to 0.9.

Any combinations of the intermediate links X ¹ and X ² are possible.

Mixed polyimides have also proven successful, which the general structural formula (Formula 2)

have, where X ^{2 represents the} following intermediate members -O-, -CH ₂ -, -SO ₂ -, -C (CH ₃ ) ₂ -, -C (CF ₃ ) ₂ -, -S-, and z = 0, Is 1 to 0.9.

In addition, mixed polyimides with the general Structural formula (Formula 3)

preferred, wherein z = 0.1 to 0.9.

It has been found that the Material properties are particularly good if z between 0.15 and 0.25 in relation to the aforementioned structural formulas is selected. At Try on model wear apparatus of the types Pin-disc and pin-roller as well Original shock absorber and pump test benches were also good properties in terms of coefficient of friction, Resistance to wear and cavitation as well Get brittleness equal to that of the above Mixed polyimides mentioned are comparable.

Mixed polyimides according to formula 3 and their preparation are described in DE-PS 21 43 080. When advantageous properties of these mixed polyimides compared to homopolyimides, the improvement in High temperature stability without loss of desired structural strength highlighted, so Properties that are also beneficial for plain bearings are. An indication of these mixed polyimides in Use plain bearings, especially together with However, PTFE is not in this prior publication  to find. Rather be preferred Areas of application of mixed polyimides u. a. Brake linings, clutch surfaces and Called grinding wheel where it just goes to high Coefficients of friction arrive. So it was all the more surprising that these known mixed polyimides work together with PTFE the friction coefficient of the sliding layer is not or only insignificantly, at least not so far raised, as is the case with other fillers and that at the same time the wear of the sliding layer high speeds and high specific Loads could be significantly reduced.

The inventive method for producing the Metal-plastic composite bearing materials insist that powdered in a PTFE dispersion Mixed polyimide is entered and dispersed. Then the dispersion thus obtained is added coagulated by aluminum nitrate. After weaning of the coagulate, this is used as a paste on the metallic sintered layer with a given Supernatant applied. The sliding layer is at 360 sintered up to 390 ° C.

This procedure is described for everyone Mixed polyimides applicable.

So that the favorable coefficient of friction of the PTFE largely is preserved, it is advantageous if that Mixed polyimide that is finely dispersed in the PTFE matrix is distributed, with grain sizes from 5 microns to 75 µm is added. Here grain sizes are around 12 µm preferred.

Coagulation is carried out in the PTFE dispersion amount of wetting agent contained Aluminum nitrate solution added.  

The paste application is preferably such performed that the later sintered Sliding layer a layer thickness d of 5 to 100 microns has a layer thickness of 5 to 20 microns is preferred.

The sintering temperature and the sintering time are adjusted the mixed polyimides used. The temperature is preferably around 375 ° C.

Examples for the production of the PTFE / mixed polyimide paste

In the mixing container of a Colette mixer (type MP 900) 34 g PTFE dispersion with a Given solids content of 35%. With stirring approx. 500 rpm will then be 1.3 / 4 / 7.9 kg accordingly 10/25/40 wt .-% of the polyimide powder in grain sizes of <0.075 mm, or <0.045 mm, but preferably <0.012 mm entered and over a period of Dispersed for 10 min. After that, the approach is through Add 0.75 l aluminum nitrate solution, the Contains 0.34 kg aluminum nitrate nonahydrate per liter, coagulated during 1 min stirring time. By adding of 1 liter of toluene becomes one for processing achieved advantageous consistency.

The manufacturing process and the one obtained End products are exemplified using the following Figures explained in more detail.

Show it:

Fig. 1 shows a schematic representation of a plant for the manufacture of semi-finished product,

Fig. 2 is a photomicrograph of the material according to the invention,

Fig. 3 is a Reibwertdiagramm,

Fig. 4 shows the wear coefficient for different materials, and

Fig. 5 is a graph representing the results of an ultrasonic cavitation for various materials.

The coating with a paste according to Example 1a on a copper-plated steel / CuSn10 sintered strip or CuPb10Sn10 sintered strip in a system according to FIG. 1 is described below. For this purpose, coils 2 with a band width of 250 mm and a band length of approximately 1200 m are placed. The tape 1 runs from the decoiler 3 via a straightening machine 4 , a pair of hand scissors 5 for cutting and a welding device 6 to the paste application station 7 . The Pastenauftragestation 7 consists of a knurled roll 8 a smooth lower roller 8b and a downstream smooth roller pair 8c to smooth the plastic layer. The application takes place in such a way that a later sintered sliding layer of 5 to 50 μm, preferably 5 to 100 μm, is obtained. After the paste has been applied, the belt 1 runs over a roller table into the continuous sintering furnace 9 , so that residual water and wetting agent are expelled. The sintering temperature is 360 to 390 ° C, preferably 375 ° C. The first rolling mill 10 downstream of the sintering furnace 9 rolls to pre-dimensioning, the second rolling mill 12 to final size. A measuring device 11 is provided between the two rolling mills. The tapes of the take-up reel 14 are fed via a measuring and registration device 13 and a deflection roller with a tachometer drive.

This coil coating process is for everyone Mixed polyimide examples described can be used.

Fig. 2 shows a section through the produced according to the process just described composite bearing material 20th The porous sintered layer 22 is applied to the copper-plated steel layer 21 . The paste forming the sliding layer is applied in such an amount that the sintered layer has a protrusion d. The mixed polyimide particles 24 can be seen in the PTFE matrix 23 in a finely dispersed distribution.

Composite plain bearings (V-VII) produced from the composite bearing material were subjected to a comparative test for determining the coefficient of friction, the results of which are shown in FIG. 3. The load was 900 N, the sliding speed 0.01 m / s, the path + 20 mm and the sliding path 36 m / h.

The inventive and the comparison materials are summarized in the following table:

The selected materials of Examples I-III have in the examined cases as most reasonable compromise between coefficient of friction and Wear and tear.

A mixed polyimide was used for Examples V-VII selected according to structural formula 3 with Z = 0.8.

The curve V shows only a slightly higher one Coefficient of friction compared to curve IV, however lower coefficients of friction than with composite plain bearings with other matrix materials.

Curve VI also shows a very good one Coefficient of friction, but here is the Wear resistance impaired. A Increasing the proportion of mixed polyimides causes Raising the coefficient of friction, which is clear from curve VII emerges.  

In FIG. 4, the wear coefficient k is shown to VII for various materials according to the examples I. In addition, a composite material with only PTFE was examined. The test method was carried out in accordance with DIN ISO 7148 part d on a pin and disc test machine (test condition: technically dry against AlSn20). The wear coefficients are comparable to the values in Examples I to IV and are significantly cheaper than for a composite plain bearing with a pure PTFE sliding layer.

In FIG. 5, the results of the Ultraschallkavitationstests are shown, wherein the average relative wear volume β, which is normalized to the example V, is applied. The average values from 10 tests were determined. Except for the lowest mixed polyimide content of 10% by weight (curve VI), better values were achieved compared to Examples II to IV.

Reference numerals

1 steel band with sintered layer
2 coil
3 decoiler
4 straightener
5 scissors
6 welding device
7 paste application station
8 a knurled roller
8 b smooth bottom roller
8 c pair of smooth rollers
9 sintering furnace
10 first rolling mill
11 measuring device
12 second rolling mill
13 measuring and registration station
14 take-up reel
20 composite bearing material
21 steel support layer
22 sintered layer
23 PTFE matrix
24 mixed polyimide particles

Claims (13)

1. Metal-plastic composite bearing material with a metal back, in particular made of steel or copper-plated steel, a porous metal sintered layer applied to the metal back and a sliding layer material applied to the metal sintering layer, the sliding layer material having PTFE as the matrix material and a polymer additive contained in the matrix material, characterized in that the polymer additive has at least one mixed polyimide which is contained in the PTFE matrix material in a fraction of 10 to 40% by weight in fine distribution. 2. Composite bearing material according to claim 1, characterized characterized in that the mixed polyimide 25th is up to 35% by weight. 3. Composite bearing material according to claim 1, characterized in that the mixed polyimide has the general structural formula (Formula 1) has, where X ¹ and X ^{2 are the} following intermediate members -O-, -CH ₂ -, -SO ₂ -, -C (CH ₃ ) ₂ -, -C (CF ₃ ) ₂ -, -S- and z = Is 0.1 to 0.9. 4. Composite bearing material according to claim 1 or 2, characterized in that the mixed polyimide has the general structural formula (formula 2) has, where the following intermediate members are -O-, -CH ₂ -, -SO ₂ -, -C (CH ₃ ) ₂ -, -C (CF ₃ ) ₂ -, -S-, and z = 0.1 to Is 0.9. 5. Composite bearing material according to claim 1, characterized in that the mixed polyimide has the general structural formula (Formula 3) has, where z = 0.1 to 0.9. 6. Composite bearing material according to claim 5, characterized characterized in that z = 0.15 to 0.25.   7. A method for producing a metal-plastic composite bearing material, in which a metal sintered layer is applied to a metal back and the sliding layer material is then applied as a paste to the metal sintered layer and sintered,
characterized,
that powdered mixed polyimide is introduced and dispersed in a PTFE dispersion to produce the paste,
that this dispersion obtained in this way is coagulated by adding aluminum nitrate solution and, after the coagulate has settled, it is applied as a paste to the metallic sintered layer with a predetermined excess, and
that after the paste application the sliding layer is sintered at 360 to 390 ° C. 8. The method according to claim 7, characterized characterized in that the sliding layer at 375 ° C. is sintered. 9. The method according to claim 7 or 8, characterized characterized in that mixed polyimide with grain sizes from 5 to 75 µm is added. 10. The method according to claim 9, characterized characterized in that mixed polyimide with grain sizes of 12 µm is added.   11. The method according to any one of claims 7 to 10, characterized in that the paste application in such a way that the later sintered Sliding layer a layer thickness d from 5 to 100 µm. 12. The method according to claim 11, characterized characterized in that the paste application such takes place that the later sintered Sliding layer a layer thickness d from 5 to 20 µm. 13. The method according to claim 12, characterized characterized in that the paste application such takes place that the later sintered Sliding layer a layer thickness of 12 µm having.