DE4227909C2 - Metal-plastic composite bearing material and process for its production - Google Patents

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 top of that Metal back applied porous Metal sintered layer and one on top of 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 for the production of such Metal-plastic composite bearing materials in which 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 composite materials are known and essentially consist of a porous sintered layer applied to a steel support made of, for example, CuSn8, CuSn10 or CuPb10Sn10 alloys, with mixtures of fluoropolymers with a wide variety of active fillers such. B. Pb, PbO, metallic sulfides, MoS ₂ are incorporated so that a sliding layer covering the sintered structure of 10 to 30 microns is obtained.

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

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

In DE-OS 14 94 078 a storage material described that consists of a mixture of one or several thermoplastics, including 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 where 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 a filler, however, it has been shown that under high loads at sliding speeds and specific loads ^{corresponding to a PV value of 1500 kg / cm 2} × m / min, their pressure and temperature on the sliding surface are as follows rise so far that the metallic lead, whose melting point is only 327 ° C, is brought to melt. Such a sliding layer cannot withstand high PV values such as 3000 kg / m ^{2 × m / min.} In addition, since the lead cannot be distributed uniformly in the PTFE matrix, the metal loss by melting does not occur evenly, so that locally already surface areas with loads of 1500 kg / cm ² × m / min are free of lead are, so that the load can no longer be evenly absorbed, which leads to locally progressive wear. This literally shatters the plastic sliding layers. Particularly under conditions such as those found in shock absorbers and spring struts, the metal-plastic composite bearings used here as guide bushes with a plastic matrix made of PTFE fail in series regardless of the type of filler, as they cope with the high local side loads, the high piston rod speeds and are not able to withstand the cavitative and erosive stresses. Efforts to use the solid lubricant, e.g. B. adding flat or flaky lead to the PTFE matrix in thin-rolled form did not bring any significant improvement, since the achievement of such a particle shape in the solid lubricants mentioned in DE 35 16 649 A1 such as metals (Pb), oxides, fluorides, boron nitride, firstly, does not is to be accomplished 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 and others. Calcium fluoride added. This is described in GB 21 66 142 A. the However, practice has shown that the initially in Laboratory tests showed signs of improvement Model test stands not confirmed in practice.

In order to use the Bonds of the PTFE particles to each other and to Substrate (e.g. porous bronze sintered framework) improve, one has in DE 32 29 667 C2 suggested adding 0.1 to 50% by volume to the PTFE Tetrafluoroethylene perfluoroalkyl vinyl ether Add copolymer resin. From DE 41 05 657 A1 is known, an impregnation coating composition from 0.5 to 30% by volume of a material from the group PFE, FEP, EPE and 5 to 30 vol .-% lead with the remainder PTFE to use.

These additives of fusible fluoropolymers however, brought no noticeable improvements compared to the cavitative and errosive ones Stresses in practice. The replacements of the Sliding layers continued to occur. The coefficient of friction of the PTFE rose and the otherwise high thermal The load-bearing capacity of the PTFE has been reduced.

From DE 30 50 056 C1 is a Multi-layer composite known in which on a steel support layer forming the matrix Polyimide layer is applied, which is preferably consists of a polyesterimide. In this matrix are low molecular weight PTFE particles than finely dispersed self-lubricating additive.

From DE 28 18 184 B2 a plain bearing is known, in which a sliding layer is formed on a rough ground PTFE, high temperature resistant, thermosetting Polyimide and up to 20% by volume of the cavitation and Additives that increase wear resistance is upset.

As in DE 28 18 184 B2 and in DE-OS 22 06 400 Thermosetting polyimides are used, a porous one Formed matrix structure in which the additives are incorporated. There Such a porous structure does not have the desired resistance to cavitation has, other additives such. B. MoS₂ required.

A multilayer composite material is known from DE 86 01 948 U1, whose matrix consists of polyetherimide, in which, inter alia, as active fillers. PTFE particles are embedded. This polyetherimide is an amorphous one Material that is said to be advantageous over partially crystalline material. There are no indications of an improvement in the cavitation resistance given.

The use of this as well as others Polymer matrix materials such as PEEK (DE 32 21 785 A1) or PES (DE 33 43 309 C3) with different Fillers did bring an improvement over the cavitative and erosive stresses, however showed that the coefficient of friction of such Sliding materials even with the addition of friction reducing additives is too high and the requirements on the driving comfort of the automobile manufacturer enough. In addition, the necessary Slitting the coated broadband and the Punching the blanks to form the sockets all the time due to excessive brittleness of the sliding layers significant flaking occurs, leading to unusually high reject rates.

The object of the present invention is therefore a metal-plastic composite bearing material to provide the complex Sufficient operating conditions, especially high ones Running speeds and high specific Withstands loads, the coefficient of friction being low and the wear and cavitation resistance at least no worse than the materials according to the Should be state of the art. In addition, should problem-free processing should be possible.

This task is accomplished with a composite bearing material solved according to claim 1. The inventive The method is the subject of claim 7.

It has been shown that while retaining PTFE as a matrix material in connection with Mixed polyimides with a proportion of 10 to 40% by weight fully meet the above requirements could be met. Here has found that from about a share of 10% by weight of mixed polyimides reduce the brittleness of the Materials lowered and the cavitation resistance and Resistance to erosion compared to a pure PTFE layer could be improved without the The coefficient of friction increases and the thermal load capacity sinks.

By using mixed polyimides, on the addition of further the cavitation and Additives that increase wear resistance, such as z. B. molybdenum disulfide can be omitted. the However, the invention includes the addition of such Fillers are not sufficient 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 Molybdenum sulfide or graphite, so that the Scrap 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 Represents compromise. When the mixed polyimide content is over 40 wt .-%, the wear increases continues to decrease, but the coefficient of friction increases significantly on, 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)

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 themselves well, which has the general structural formula (Formula 2)

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.

Also, mixed polyimides are common with Structural formula (formula 3)

Formula 3

preferred, where z = 0.1 to 0.9.

It turned out that the Material properties are particularly good when z between 0.15 and 0.25 with respect to the the aforementioned structural formulas is selected. at Try on model wear apparatus of the types Pen-washer and pen-roller as well Original shock absorber and pump test benches were made also good properties in terms of coefficient of friction, Wear and cavitation resistance as well Get brittleness similar to that of the foregoing mentioned mixed polyimides are comparable.

Mixed polyimides according to formula 3 and their preparation are described in DE 21 43 080 C3. as advantageous properties of these mixed polyimides over homopolyimides will improve the High temperature stability without loss of desired structural strength highlighted, so Properties that are also beneficial for plain bearings are. An indication that these mixed polyimides in Plain bearings are not used as a matrix material, but as a filler to be used, especially together with However, PTFE is not in this prior publication to find. Rather than being preferred Areas of application of the mixed polyimides, among others. Brake liners, clutch surfaces and Grinding wheel called where it's straight on high Coefficient of friction matters. It was therefore all the more surprising that these known mixed polyimides work together with PTFE the coefficient of friction of the sliding layer does not or only insignificantly, at least not so much increased, as is the case with other fillers and that at the same time the wear of the sliding layer high speeds and high specifics Loads could be reduced significantly.

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

This procedure is described for everyone Mixed polyimides applicable.

Thus the favorable coefficient of friction of the PTFE to a large extent remains, it is advantageous if that Mixed polyimide that is finely dispersed in the PTFE matrix is distributed, with grain sizes from 5 µm to 75 µm is added. Here grain sizes are around 12 µm preferred.

For coagulation, one is used in the PTFE dispersion corresponding amount of wetting agent contained Aluminum nitrate solution added.

The paste application is preferably such carried out that the later sintered out Sliding layer a layer thickness d of 5 to 100 µm having a layer thickness of 5 to 20 µm is preferred.

The sintering temperature and the sintering time are determined depending on the mixed polyimides used. Preferably the temperature is around 375 ° C.

Examples of making the PTFE / mixed polyimide paste

In the mixing container of a Colette mixer (type MP 900) are 34 g of PTFE dispersion with a Given solids content of 35%. While stirring at approx. 500 rpm are then 1.3 / 4 / 7.9 kg accordingly 10/25/40% by weight 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 of aluminum nitrate solution to the Contains 0.34 kg aluminum nitrate nonahydrate per liter, coagulated for 1 min stirring time. By adding 1 liter of toluene is used for processing advantageous consistency achieved.

The manufacturing process as well as the one obtained Final product are exemplified by the following Figures explained in more detail.

It shows

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 following describes the coating with a paste according to Example 1a on a copper-plated steel / CuSn10 sintered belt or CuPb10Sn10 sintered belt in a system according to FIG. 1. For this purpose, coils 2 with a band width of 250 mm and a band length of about 1200 m are placed. The strip 1 runs from the decoiler 3 via a straightening machine 4 , hand shears 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 is carried out in such a way that a later sintered-out 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 the remaining 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-dimension, the second rolling mill 12 to final dimension. A measuring device 11 is provided between the two rolling mills. The tapes are fed to the take-up reel 14 via a measuring and recording device 13 and a pulley with a speedometer drive.

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

FIG. 2 shows a section through the composite bearing material 20 produced by the method just described. 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-out layer has a protrusion d. In the PTFE matrix 23 , the mixed polyimide particles 24 can be seen in a finely dispersed distribution.

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

The materials according to the invention and the comparison materials are compiled in the following table:

The selected materials of Examples I-III have proven to be most sensible compromise between coefficient of friction and Proven 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 However, the coefficient of friction compared to curve IV is clear lower coefficients of friction than with composite plain bearings with other matrix materials.

Curve VI also shows a very good one Friction coefficient curve, however, here is the Impaired wear resistance. One Increasing the mixed polyimide content causes a Increase in 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 investigated. The test method was carried out in accordance with DIN ISO 7148 part d on a pin-and-disk testing machine (test condition: technically dry against AlSn20). The wear coefficients are comparable to the values in Examples I to IV and are significantly more favorable than in the case of a composite plain bearing with a pure PTFE sliding layer.

The results of the ultrasonic cavitation test are shown in FIG. 5, the average relative volume wear β, which is normalized to Example V, being plotted. The average values from 10 tests each were determined. Except for the lowest mixed polyimide content of 10% by weight (curve VI), better values compared to Examples II to IV were achieved.

Reference number

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 recording 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 sintered layer, the sliding layer material having PTFE as the matrix material and a polymer additive contained in the matrix material, characterized by
that the polymer additive has at least one mixed polyimide in powder form, which is contained in the PTFE matrix material with a proportion of 10 to 40 wt .-% in fine distribution. 2. Composite bearing material according to claim 1, characterized in that that the mixed polyimide content is 25 to 35 wt .-%. 3. composite bearing material according to claim 1, characterized in that the mixed polyimide has the general structural formula (formula 1) formula 1 where X ¹ and X ^{2 represent 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) Formula 2 where X² is the following intermediate members -O-, -CH ₂ -, -SO ₂ -, -C (CH ₃ ) ₂ -, -C (CF ₃ ) ₂ -, -S-, and z = 0.1 to 0.9. 5. composite bearing material according to claim 1, characterized in that the mixed polyimide has the general structural formula (formula 3) Formula 3 where z = 0.1 to 0.9. 6. composite bearing material according to claim 5, characterized in that 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 then the sliding layer material is applied as a paste to the metal sintered layer and sintered,
characterized,
that for the production of the paste powdered mixed polyimide is added to a PTFE dispersion and dispersed,
that this dispersion thus obtained is coagulated by adding aluminum nitrate solution and, after the coagulate has settled, this is applied as a paste to the metallic sintered layer with a predetermined supernatant, and
that after the paste application, the sliding layer is sintered at 360 to 390 ° C. 8. The method according to claim 7, characterized in that the Sliding layer is sintered at 375 ° C. 9. The method according to claim 7 or 8, characterized in that Mixed polyimide with grain sizes of 5 to 75 microns is added. 10. The method according to claim 9, characterized in that Mixed polyimide with grain sizes of 12 microns is added. 11. The method according to any one of claims 7 to 10, characterized characterized in that the paste is applied in such a way that the later sintered sliding layer a layer thickness d of 5 to 100 µm. 12. The method according to claim 11, characterized in that the Paste is applied in such a way that the later sintered out Sliding layer has a layer thickness d of 5 to 20 µm. 13. The method according to claim 12, characterized in that the Paste is applied in such a way that the later sintered out Sliding layer has a layer thickness of 12 µm.