Abstract:
The present invention relates to a bearing assembly, having at least one first bearing element and a second bearing element being movable relative to the first bearing element, wherein at least one of the bearing elements is made of ELTIMID.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a bearing assembly having at least one first bearing element and a second bearing element, being movable with respect to the first bearing element and to a method for the manufacture of such a bearing assembly, as well as the use of ELTIMID for the manufacture of at least one part of such a bearing assembly. 
       BACKGROUND 
       [0002]    Depending on the intended use, there are various prerequisites for such a bearing assembly, requiring different material properties. Ball bearings are already used for industrial applications of all kinds, which, apart from respective races made of anti-friction bearing steel, have bearing bodies made of a ceramic material (so-called hybrid bearings). They show specific improved properties over rolling bodies made of anti-friction bearing steel. Among technical ceramic materials, e.g. the silicon nitride Si 3 N 4  is a material suitable for anti-friction bearings due to its mechanical and physical properties. This material is characterized, among others, by high fraction strength, a low density and a high dielectric strength. These bearings are, e.g., suitable for use in electric machines. Rolling bodies made of ceramic material have a longer service life in comparison to rolling bodies made of steel; they are relatively inured to starved lubrication and are very well suitable for high-speed bearings, since these rolling bodies have a lower density than rolling bodies made of steel. 
         [0003]    Further important properties of such bearing elements are their weight, their wear, the resistance to chemically active or aggressive substances, the tensile and compressive strength, the specific electrical resistance, the density and the linear expansion coefficient. Another very important criterion for bearing elements is the manufacturing cost, especially since in bulk products minor price advantages already lead to considerable market advantages. 
         [0004]    For certain application purposes of bearing assemblies, it is desirable, also for configurations with no or only very bad lubrication possibilities, to obtain, despite said lubrication problems, sufficiently long service lives; that is to say to nevertheless obtain good wear characteristics with respectively low friction coefficients. 
         [0005]    Among the essential properties of respective bearing elements are a low density and hence low mass forces in order to obtain high revolution speeds, a great running smoothness, as possible, good wear characteristics and a small friction coefficient for a resistance-free bearing, as possible. 
       BRIEF SUMMARY 
       [0006]    According to the invention, at least one of the bearing elements, which form the bearing assembly, is made of ELTIMID. Several or even all parts of the bearing assembly, i.e. the bearing elements, can be made of ELTIMID. The plastic material ELTIMID is manufactured and sold by the company Albert Handtmann Elteka GmbH &amp; Co. KG in Biberach. “ELTIMID” is a registered trademark of the applicant. ELTIMID is a substance which is produced through press forming or moulding a powder which is a non-fusable plastic raw material. Such powder is an aromatic polyimide with the CAS-number 845621-44-5. The CAS Registry Number (CAS=Chemical Abstracts Service) is an international standard of nomenclature for chemical substances and is hence definite. For each known chemical substance, there exists (also biosequences, alloys, polymers), there exists an definite CAS number. Said powder, and, hence, ELTIMID, is therefore registered under such number and therefore identifyable by such number. 
         [0007]    The manufacturer of such powder with the CAS number 845621-44-5, the corporation Evonik Industries AG, from which the semi-finished products or the finished bearing assemblies are produced, calls such powder or such raw material, respectively P84 NT1. From such raw material said bearing assemblies, which form the present invention, are produced by press forming or moulding. Those assemblies or semi-finished products are then named ELTIMID and sold to customers who use them for other mechanical applications. 
         [0008]    The material ELTIMID has the following characteristics: 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Material Characteristics of ELTIMID for DF &amp; HCM parts 
               
             
          
           
               
                   
                   
                   
                   
                   
                 Eltimid 
                   
                 Eltimid 
                 Eltimid 
               
               
                   
                   
                 Test 
                   
                 Eltimid 
                 15G 
                 Eltimid 
                 15G 
                 15M 
               
               
                 Characteristic 
                 conditions 
                 standard 
                 unit 
                 (DF-part) 
                 (DF-part) 
                 (HCM-part) 
                 (HCM-part) 
                 (HCM-part) 
               
               
                   
               
             
          
           
               
                 Density 
                   
                 DIN 53479 
                 g/cm 3   
                 1.282 
                 1.365 
                 1.38 
                 1.46 
                 1.54 
               
               
                 Shore D 
                   
                 DIN 53505 
                 — 
                 84 
                 83 
                 90 
                 87 
               
               
                 hardness 
               
               
                 Rockwell 
                   
                 ISO 2039-2 
                 RH 
                 R 60 
                 R 63 
               
               
                 hardness 
                   
                 “R” 
               
               
                   
                   
                 ISO 2039-2 
                 RH 
                   
                   
                 E 94 
               
               
                   
                   
                 “E” 
               
               
                 Water 
                 24 h/80° C. 
                 ISO 62 
                 % 
                 2.6 
                 1.6 
                 1.7 
               
               
                 absorbtion 
                 48 h/80° C. 
                   
                   
                 3.3 
                 2.2 
                 2.2 
               
               
                   
                 3 weeks 
                   
                   
                 4.5 
                 3.7 
                 3.2 
               
               
                   
                 80° C. 
               
               
                 Dimensional 
                   
                 Method Af at 
                 ° C. 
                 310 
                 351 
                 325 
               
               
                 stability 
                   
                 1.8 MPa 
               
               
                 temperature 
                   
                 Method B at 
                   
                 356 
                 382 
                 373 
                 384 
               
               
                 HDT 
                   
                 0.45 MPa 
               
               
                 Glass 
                  1 Hz 
                 DTMA (main 
                 ° C. 
                 391.8 
                 383.5 
                 370 
               
               
                 transition 
                   
                 max. of tan δ) 
               
               
                 temperature T G   
                   
                 Dynamic 
                   
                 325.6 
                   
                 337 
               
               
                   
                   
                 differential 
               
               
                   
                   
                 calometry 
               
               
                   
                   
                 (DDK) 
               
               
                 Resistance to 
                 Testcyclus:+80° 
                 PV 1200 
                 % 
                 Ø + 0.2 
                 Ø + 0.2 
               
               
                 atmospheric 
                 C./−40° C. 
                   
                   
                 hight + 
                 hight + 
               
               
                 changes 
                 bei 50 Zyklen 
                   
                   
                 0.6 
                 0.4 
               
             
          
           
               
                 Electrical Characteristics 
               
             
          
           
               
                 Dielectric 
                   
                 ISO 60243-1 
                 kV/mm 
                 34.4 
                   
                 21.8 
                   
                   
               
               
                 strength (DC) 
               
               
                 Dielectric loss 
                  50 Hz 
                 IEC 60250 
                 — 
                 3.4 
                   
                 4.2 
               
               
                 factor 
                   
                   
                   
                 (4*10 −3 ) 
               
               
                   
                  1 kHz 
                   
                 — 
                 3.4 
                   
                 4.2 
               
               
                   
                   
                   
                   
                 (4*10 −3 ) 
               
               
                   
                  10 kHz 
                   
                 — 
                 3.4 
                   
                 4.1 
               
               
                   
                   
                   
                   
                 (8*10 −3 ) 
               
               
                   
                 100 kHz 
                   
                 — 
                 3.4 
                   
                 4.1 
               
               
                   
                   
                   
                   
                 (10*10 −3 ) 
               
               
                 Surface 
                   
                 IEC 60093 
                 Ω 
                 4.6*10 15   
                   
                 5*10 15   
               
               
                 Resistivity 
               
               
                 Volume 
                   
                 IEC 60093 
                 Ω*m 
                 1.5*10 13   
                   
                 8*10 13   
               
               
                 Resistivity 
               
               
                 Creep 
                   
                 IEC 60112 
                 — 
                 200 
               
               
                 Resistance 
               
               
                 (CTI) 
               
             
          
           
               
                 Mechanical Characteristics 
               
             
          
           
               
                 Tensile 
                   
                 ISO 527 
                 MPa 
                 74 
                 65 
                 107 
                   
                 92 
               
               
                 Strength 
               
               
                 Elongation 
                   
                 ISO 527 
                 % 
                 3.3 
                 2.8 
                 3.7 
                   
                 3.2 
               
               
                 E-tensile 
                   
                 ISO 527 
                 MPa 
                 3095 
                 3939 
                 3400 
                   
                 4112 
               
               
                 modulus 
               
               
                 Bending 
                 at 23° C. 
                 ISO 178 
                 MPa 
                 102 
                 91 
                 177 
                 126 
                 146 
               
               
                 strength 
                 at 200° C. 
                   
                   
                   
                   
                 136 
               
               
                 Bending 
                 at 23° C. 
                 ISO 178 
                 % 
                 3.6 
                 2.8 
                 6.1 
                 3 
                 4.6 
               
               
                 elongation 
                 at 200° C. 
                   
                   
                   
                   
                 8.2 
               
               
                 E-bending 
                 at 23° C. 
                 ISO 178 
                 MPa 
                 2994 
                 3577 
                 3750 
                 4850 
                 3788 
               
               
                 elongation 
                 at 200° C. 
                   
                   
                   
                   
                 3090 
               
               
                   
                 at 250° C. 
                   
                   
                 2062 
                 2768 
                 2300 
               
               
                   
                 at 300° C. 
                   
                   
                 1841 
                 2542 
                 2150 
               
               
                 Compression 
                 at 1% load 
                   
                 MPa 
               
               
                 strength 
                 at 10% load 
                   
                   
                 128 
                 127 
                 105 
                 83 
                 164 
               
               
                 Pressure 
                   
                 ISO 604 
                 MPa 
                 392 
                 189 
                 470 
                 209 
                 296 
               
               
                 resistance 
               
               
                 E-pressure 
                   
                 ISO 604 
                 MPa 
                 1648 
                 1686 
                 1960 
                 2111 
                 2047 
               
               
                 modulus 
               
               
                 Pressure 
                   
                 ISO 604 
                 % 
                 59 
                 30 
                 58 
                 23 
                 46 
               
               
                 Elongation 
               
               
                 Impact 
                 Charpy- 
                 ISO179-1/1eA 
                 kJ/m 2   
                 3.1 
                 1.6 
                 5.9 
               
               
                 Resistance 
                 impact 
               
               
                   
                 strength 
               
               
                   
                 Charpy- 
                 ISO179-1/1eU 
                   
                 18.3 
                 11 
                 40 
               
               
                   
                 impact 
               
               
                   
                 resistance 
               
               
                 Adhesion 
                 v = 
                 ASTM D1894 
                 μ H   
                 0.29 
                 0.23 
               
               
                 Friction factor 
                 0.0025 m/s; 
               
               
                   
                 hardened 
               
               
                   
                 against 
               
               
                   
                 steel and 
               
               
                   
                 grinded 
               
               
                 Slip Friction 
                 v = 
                 ASTM D1894 
                 μ G   
                 0.25 
                 0.20 
               
               
                 factor 
                 0.0025 m/s; 
               
               
                   
                 hardened 
               
               
                   
                 against 
               
               
                   
                 steel and 
               
               
                   
                 grinded 
               
             
          
           
               
                 Thermal Characteristics 
               
             
          
           
               
                 Thermal coef- 
                  50-200° C. 
                 DIN 53752 
                 10 −6 /K 
                 53 
                 40 
                 54 
                 41 
                   
               
               
                 ficient of linear 
                 200-300° C. 
                   
                   
                 66 
                 50 
                 61 
                 45 
               
               
                 expansion 
               
               
                 Heat capacity 
                   
                 ISO 527 
                 J/g*K 
                 0.98 
                 0.97 
                 0.925 
                 1.046 
               
               
                 Heat co- 
                   
                 ISO 8302 bei 
                 W/m*K 
                 0.23 
                 0.49 
                 0.22 
               
               
                 efficient 
                   
                 40° C. 
               
               
                 Flammability 
                   
                 UL 94 
                 — 
                 V 0 
               
               
                   
               
             
          
         
       
     
         [0009]    The designation 15G means that the material has an addition of 15 wt.-% graphite, the designation 15M means that the material has an addition of 15 wt.-% molybdenum disulphide (MoS 2 ). Both are additions to the aromatic polyimide with the CAS Number 845621-44-5 and serve as lubricants. A lubrication of the bearing is then no longer necessary as the bearing is then self-lubricating. 
         [0010]    The press forming of ELTIMID-parts works generally in two ways: Either by Hot Compression Moulding (HCM) or by Direct Forming (DF). When HCM is used, the powder used is subjected to pressure and temperature but it does not melt, the powder grains rather bake together. A certain time is also needed. It is advisable to use temperatures in the range of 300° C. bis 400° C. and a pressure of between 300 kg/cm 2  and 500 kg/cm 2  nd a duration of app. 5-15 hours. When DF is used, the grains of the powder are pressed together under a very high pressure at room temperature, e.g. at 1,0 bis 5,0 t/cm 2 , wherein a kind of sintering, agglomeration or baking takes place. The grain particles hold together through adhesion. ELTIMID therefore is composed of an aromatic polyimide with the CAS number 845621-44-5, which has been hot compression moulded or direct formed, thereby including these powder grains being baked or pressformed together. 
         [0011]    The term “bearing element” in this connection relates the various parts of a bearing and a bearing assembly, respectively. They comprise outer rings and inner rings of a radial bearing, bearing shells of an axial bearing, rolling bodies like e.g. balls, needles or the like, cages for rolling bodies, etc. The entire bearing assembly gets more light-weighted since at least one of the two bearing elements, which are movable relatively to each other, is made of ELTIMID having a lower density than anti-friction bearing steel or, for example, ceramic material, like, e.g., silicon nitride (Si 3 N 4 ) which is used for the manufacture of bearings. As a result of the thus reduced mass forces, for example, high speeds of the bearing assembly can be realized. 
         [0012]    The invention can advantageously be used as a slide bearing in an embodiment of the bearing assembly. Furthermore, the invention can be perfectly used in large bearing assemblies, like, e.g., the bearing of a conveyor belt or a component or the like. Such a movably supported part will normally be supported on a roller, said roller being located on a respective support bearing and able to roll thereon. Due this more light-weighted design, realized by using ELTIMID for the manufacture of one of the bearing elements, the overall weight of the bearing assembly can be reduced. Such bearings, used in construction, are particularly beneficial in that they are light and low-priced (in comparison to steel) and do not corrode. 
         [0013]    A particularly preferred field of application of the present invention comprises the manufacture of anti-friction bearings which are provided with at least one rolling body. Preferably ball bearings, needle bearings, roller bearings or barrel bearings are counted among them. With regard to such bearings, which are produced in large quantities, there is a cost-reducing effect in at least one bearing element being made of ELTIMID. 
         [0014]    A special advantage resides in that at least one rolling body made of ELTIMID is provided in the bearing assembly. This can improve the running smoothness of the rolling bodies, especially if all rolling bodies are made of ELTIMID, because both lower density and lower mass forces of the rolling bodies have a positive effect on the running smoothness. This advantage especially influences groove ball bearings which are not run with steel or ceramic balls, but with ELTIMID balls. If the rolling bodies, in particular balls as rolling bodies, are made of ELTIMID, this also produces less material waste than in the manufacture of steel balls—which are manufactured by grinding—since the ELTIMID rolling bodies can be manufactured in a pressing machine. This leads to significant cost savings. 
         [0015]    A special field of application of the present invention concerns hybrid bearings in which at least one of the bearing elements is made of steel, ceramic, ELTIMID or a combination thereof. By the combination of different materials, the particular advantages of the individual materials can be combined. For example, the presence of a ball made of ceramic can cause a certain “self-healing” in polluted surroundings. Already one single ceramic ball can free the track from smaller solid impurities by grinding said impurities thanks to its hardness. The remaining balls can, for example, be made of ELTIMID, wherein, for example, the other bearing components are then made of anti-friction bearing steel. 
         [0016]    It is much preferred if at least one of the ELTIMID bearing elements has a content of up to 15 wt.-% molybdenum disulfide (MoS 2 ). This leads to improved wear characteristics and a lower friction coefficient, because said molybdenum disulfide, released by friction, incorporates into the surface of the counter-direction partner—e.g. steel or ceramic—and thereby smoothes a possibly rough surface. That is to say—in other words—the wear is relatively high at first, but decreases strongly with an increasing running period, until the incorporation into the surfaces of the counter-direction partners has reached a saturation level. This effect will be particularly significant, if either an otherwise desired lubrication fails, or a lubrication, e.g. with grease, is not desired, because this will lead to undesired impurities. Possible fields of application are, for example, in food industries or plant engineering. 
         [0017]    The effects achieved by adding molybdenum disulfide to ELTIMID can even be enhanced or optimized, if, instead of 15 wt.-%, there are comprised 25 wt.-% or 40 wt.-% of molybdenum disulfide in ELTIMID. 
         [0018]    A similarly enhanced lubricating effect can be achieved in that at least one of the ELTIMID bearing elements has a content of 15 wt.-% or 25 to 40 wt.-% of graphite. A suitable combination of the graphite content and the content of molybdenum disulfide might possibly help to optimize the friction and wear properties and, as a result, increase the operating time of a respectively formed bearing element. 
         [0019]    The invention also manifests in a novel method for the manufacture of a bearing assembly in that ELTIMID is used as a material for the manufacture of at least one of the bearing elements, like e.g. a bearing shell, bearing bodies or cages for such bearing bodies. Respective bearing elements can then be manufactured by a pressing operation in a press and, unlike steel, need not be produced by cutting processing. The press forces, which—for example—arise or have to be applied in the manufacture of balls, are different and depend on the geometry of the balls. In practice, balls with a diameter of 11.3 mm, for example, could be produced in a press with a pressure of approximately 200 MPa and show a very good quality. 
         [0020]    An essential idea underlying the present invention is, not least, based on the fact that ELTIMID is used for the manufacture of at least one part of the bearing assembly. Up to now, it has nowhere been suggested using ELTIMID for the manufacture of a bearing element or even entire bearing assemblies. There are no respective hints or suggestions to have someone skilled in the art use ELTIMID for the manufacture of bearing assemblies or elements thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Further advantages, features and characteristics of the present invention are evident from the following description of preferred embodiments of the invention. In the drawing: 
           [0022]      FIG. 1  shows a schematic sectional drawing through a first embodiment of the invention in the form of an axial angular ball bearing, 
           [0023]      FIG. 2  shows a schematic sectional drawing through a second embodiment of the invention in the form of a radial groove ball bearing, 
           [0024]      FIG. 3  shows a schematic sectional drawing through a third embodiment of the invention in the form of a slide bearing, and 
           [0025]      FIG. 4  shows a schematic sectional drawing through a forth embodiment of the invention in the form of a bridge bearing. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  depicts an axial angular contact ball bearing  10  with a bearing shell  21  shown on the left and a second bearing shell  24  shown on the right. The two bearing shells  21 ,  24  are made of anti-friction bearing steel or ball bearing steel and form a ball track  28 , in which balls  22  can roll off. The balls  22  are made of ELTIMID having a content of 15 wt.-% molybdenum disulfide. The balls  22  show a density of approximately 1.3 g/cm 3 , which is considerably less than the one of steel (7.85 g/cm 3 ) and ceramic (3.2 g/cm 3 ). As a result, less mass forces work upon rotation of the axial bearing  10 , allowing for high revolution speeds of the bearing. In addition, the running smoothness of such balls is very high. The content of molybdenum disulfide in the balls  22  results, even in case of lubrication failure, in that good running properties of the bearing are maintained over a longer period of time. Molybdenum disulfide, released by the initial abrasion of the balls  22 , builds up on the surfaces of the ball track  28  in the bearing shells  21 ,  24  and causes a low-wear, low-abrasion rolling of the balls  22  on the ball track  28 . 
         [0027]      FIG. 2  depicts a radial groove ball bearing  11  with an outer bearing shell  31  and an inner bearing shell  32 . The two bearing shells  31 ,  32  together form a ball track  38  on which the balls  22  can roll. While the outer bearing shell  31  and the balls  22  in this second embodiment are made of anti-friction bearing steel, the inner bearing shell  32  is made of ELTIMID which contains 40 wt.-% of molybdenum disulfide. This radial ball bearing  11  is run without grease lubrication. By rolling off the steel balls  22  on the ball track  38  of the inner bearing shell  32 , the latter is initially slightly abraded so that molybdenum disulfide is released. Said molybdenum disulfide builds up on the balls  22  and the ball track  28  of the outer bearing shell  31  and results, after a short period of time, in excellent low-friction and—as a result—low-wear roll characteristics of the balls  22  in the ball track  38 . 
         [0028]      FIG. 3  depicts a radial slide bearing  12  with an outer slide bearing shell  41  and an inner slide bearing shell  42 . The inner slide bearing shell  42  is made of anti-friction bearing steel, whereas the outer slide bearing shell  41  is made of ELTIMID. Said ELTIMID has a content of 15 wt.-% graphite and a content of 15 wt.-% molybdenum disulfide. After an initial abrasion of ELTIMID, the equally abraded weight proportions of graphite and molybdenum disulfide result, after a short period of time, in an optimum lubrication when the outer bearing shell  41  is rotated with respect to the inner bearing shell  42 . 
         [0029]      FIG. 4  depicts a bearing assembly  13  for bearing a component  55  on a bearing  52 , e.g., the supporting of a pivoting machining table in a machine. On the surface of the bearing  52  is provided a bearing layer  51  which is made of ELTIMID. In said ELTIMID, there may be comprised contents of molybdenum disulfide and/or graphite, so that a lubrication of said bearing assembly  13  by means of grease can be avoided. Between the bearing layer  51  and the component  55 , there is provided a roller  53  which is, for example, made of steel. When the component  55  moves to the left or the right, e.g. caused by an elongation or a load applied, the component can roll on the roller  53 , thereby setting the roller  53  in a rolling motion which is carried out by the roller  53  on the bearing layer  51 . Said bearing assembly  13  is low maintenance, because it needs not be lubricated and—hence—needs also not be relubricated. The assembly can be manufactured at low cost, easily built in and does not corrode. 
         [0030]    Graphite has “greasing” properties similar to those of molybdenum disulfide. However, the better adhesion of molybdenum disulfide to metallic surfaces as compared to graphite has to be pointed out. This is due to the secondary valencies of sulphur. However, it has to be stressed in this regard that this is not about free sulphur and its known unpleasant side effects. The sulphur is fixedly bonded in the molybdenum disulphide molecule so that it is under no circumstances released, unless at a decomposition temperature of approximately 450° C. at full access of air. 
         [0031]    Another advantage over graphite is that graphite, in general, only shows its lubricating effect at higher temperatures or in a vacuum. One reason is that the bonding of the graphite to metallic surfaces takes place adsorptively with liquid films. Hence, it could be proven that completely degasified graphite has no lubricating effect. Its friction coefficient of approximately 0.1 then increases to values as usual with metals. 
         [0032]    Furthermore, molybdenum disulphide is absolutely nontoxic. On the basis of thorough scientific studies and tests, it has been found that molybdenum disulfide is one of the most insoluble compounds at all, which is only affected by chlorine, fluorine, aqua regia and boiling hydrochloric acid or nitric acid. Hence, when using molybdenum disulfide as a lubricant, no special protection measures are needed. The storing of these substances poses no danger. 
         [0033]    The material properties of ELTIMID are listed in the following table: 
         [0000]    
       
         
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Eltimid ® 
                 Eltimid ® 15G 
                 Eltimid ® 
                 Eltimid ® 15G 
               
               
                 Property 
                 (DF part) 
                 (DF part) 
                 (HCM part) 
                 (HCM part) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 General Properties 
               
             
          
           
               
                 Density [g/cm 3 ] 
                 1.282 
                 1.365 
                 1.38 
                 1.46 
               
               
                 Shore D hardness 
                 84 
                 83 
                 90 
                 87 
               
               
                 Rockwell hardness 
                 R 60 
                 R 63 
               
               
                 [RH] 
               
               
                 Water absorption [%] 
                 4.5 
                 3.7 
                 3.2 
               
               
                 3 weeks at 80° C. 
               
               
                 Dimensional stability 
                 356 
                 382 
                 373 
                 384 
               
               
                 temperature HDT 
               
               
                 [° C.] at 0.45 MPa 
               
               
                 Glass transition tem- 
                 391.8 
                 383.5 
                 370 
               
               
                 perature T G  [° C.] 
               
               
                 Resistance to at- 
                 Ø + 0.2 
                 Ø + 0.2 
               
               
                 mospheric changes 
                 height + 
                 height + 
               
               
                 [%] 
                 0.6 
                 0.4 
               
             
          
           
               
                 Electric Properties 
               
             
          
           
               
                 Dielectric strength 
                 34.4 
                   
                 21.8 
                   
               
               
                 (DC) [kV/mm] 
               
               
                 Relative dielectric 
                 3.4 (4*10 −3 ) 
                   
                 4.2 
               
               
                 coefficient (at 50 Hz) 
               
               
                 Specific surface 
                 4.6*10 15   
                   
                 5*10 15   
               
               
                 resistance [Ω] 
               
               
                 Specific transition 
                 1.5*10 13   
                   
                 8*10 13   
               
               
                 resistance [Ω] 
               
               
                 Creep strength 
                 200 
               
             
          
           
               
                 Mechanical Properties 
               
             
          
           
               
                 Tear strength [MPa] 
                 74 
                 65 
                 107 
                   
               
               
                 Elongation [%] 
                 3.3 
                 2.8 
                 3.7 
               
               
                 Tensile modulus of 
                 3095 
                 3939 
                 3400 
               
               
                 elasticity [MPa] 
               
               
                 Bending strength at 
                 102 
                 91 
                 177 
               
               
                 23° C. [MPa] 
               
               
                 Bending strain at 
                 3.6 
                 2.8 
                 6.1 
               
               
                 23° C. [MPa] 
               
               
                 Flexural/bending 
                 2994 
                 3577 
                 3750 
               
               
                 modulus of elasticity 
               
               
                 at 23° C. [MPa] 
               
               
                   
               
               
                 “ELTIMID 15G” is an ELTIMID material with a graphite content of 15%. A “DF part” is a part obtained by direct forming, whereas a “HCM part” is a part which was formed by means of press forming at a higher temperature (Hot Compression Moulding). 
               
             
          
         
       
     
         [0034]    ELTIMID is resistant to a plurality of chemicals, like, e.g., gasoline, diesel, motor oil, cooling fluid, antifreeze, brake fluid, sulphuric acid, spirit etc. ELTIMID has an amorphous structure and is equally resistant to high temperatures. ELTIMID also resists continuous use temperatures of up to 260° C. and, for a short time, is resistant to up to 400° C. It has excellent mechanical and tribological properties and—as evident from the above tables—stands out due to its high strength and good ductility, and it is an excellent electric insulator. The resistance to atmospheric changes and the chemical resistance are also outstanding in comparison to a plurality of other plastic materials. In many fields of property, ELTIMID shows values similar to metal, ceramic or silica and therefore is suitable as a substitute for them. Due to the additive molybdenum disulfide, the plastic material additionally achieves the excellent storage properties. 
         [0035]    In comparison to anti-friction bearings made of steel or silicon nitride, ELTIMID is characterized by a lower specific electrical resistance and a lower density. Hence, ELTIMID has a specific electrical resistance below 10 12  Ωm and a density below 3.2 g/cm 3 , namely approximately 1.3 g/cm 3 . 
         [0036]    It has to be stated that the features of the invention, which are mentioned with reference to the depicted and described embodiments, like the kind and the specific design of the individual bearing assemblies, the addition of lubricating components like graphite and molybdenum disulfide, as well as the choice, which one of the bearing elements is made of ELTIMID, can also be present in other embodiments, unless stated otherwise or out of question for technical reasons. 
         [0037]    Two preferred embodiments of how to produce parts of ELTIMID are now explained: A preferred Hot Compression Moulding method uses temperatures in the range of 200° C. to 400° C., preferably 280° C. to 380° C., even more preferred about 350° C. A preferred pressure is around 400 kg/cm 2  and a preferred duration is app. 7-12 hours, even more preferred about 9 hours. When DF is used, the grains of the powder are pressed together under a very high pressure at room temperature, e.g. at 3,0 bis 5,0 t/cm 2 , preferably around 3,5 t/cm 2 . It is advisable to also put such material into a furnance with a temperature of about 300° C. for a period of time of 1 to 10 hours, preferably around 7 hours. These powder grains are then being baked or pressformed together. If lubrication additions such as graphite or molybdenum disulfide are used, these are added in form of a powder prior to press forming the raw powder with the CAS Number 845621-44-5.