Machine elements consisting of a glass/plastic compound

The invention relates to machine elements, such as bearings and toothed wheels.

A number of plastics are used as material for machine elements. In addition to good mechanical properties such as high stiffness and toughness, good tribological properties and a good to very good resistance to chemicals are required for such materials. In addition, the materials have to prove themselves in a harsh environment and they are often subjected to continuous use temperatures of more than 140 ° C.

The group of plastics which are used for machine elements under high stresses include duromers, such as epoxy resins, phenol-formaldehyde resins and polyimide resins, as well as high-temperature thermoplastics such as polyphenylenesulfide, polyetheretherketone, polyetherimide, polyethersulfone, polysulfone and liquid-crystalline polymers and also technical thermoplastics such as polyamide and polyoxymethylene . In the case of the last-mentioned materials, however, the application area is limited in terms of the temperature to the top: T_Max <125 ° C. The high-temperature thermoplastics used in machine elements are predominantly glass or carbon fiber-reinforced or supplemented with mineral fillers, but are also used unreinforced or unfilled. Especially for bearing applications, these thermoplastics are often modified with graphite, molybdenum disulfide or polytetrafluoroethylene in order to improve the tribological properties (see: Gunter Erhard and Erich Strickle "Machine elements made of thermoplastics - bearings and drive elements", 2nd edition, VDI-Verlag GmbH , Dusseldorf 1985, pages 7 to 9).

Compared with metallic materials, unreinforced or unfilled thermoplastics show an approximately 10-fold greater thermal expansion, usually a lower strength and, consequently, a low load-bearing capacity, as well as a lower modulus of elasticity and limited heat resistance. Corresponding machine elements can therefore only be used at comparatively low temperatures and low loads. The addition of reinforcing agents and fillers can improve the property profile.

When used in machine elements, the fluidity and abrasion resistance as well as the dimensional stability and the dimensional stability of the materials play a decisive role. In all materials, however, the contamination of particles is found to be problematic, for example, in the manufacture of bearings and gear wheels, as well as the abrasion behavior during operation. In addition, in the case of an injection-molding-technological production of the machine elements, glass fibers are partially pressed against the component surface or protrude from it. During subsequent working and / or installation steps, the protruding glass fibers then break off and can settle on the surface of the machine elements and then intensify the friction and the wear. Furthermore, the orientation and the position of the fibers opposite the direction of loading and movement, especially in bearings, is decisive for the tribological behavior. An optimum wear and wear behavior is only achieved if the fibers are parallel to the load and movement direction. However, this can not be ensured, in particular, in the case of complicated components, and regions are formed in which the fibers are perpendicular to the direction of loading and movement; This results in a much inferior tribological behavior. The introduction of fibers also results in a highly anisotropic material behavior during processing, which manifests itself during the production of components and test specimens in a different shrinkage behavior and, associated therewith, in a distortion of the parts. The reason for this is the alignment of the fibers during the filling process. The fibers are oriented in the direction of flow of the melt stream, which results in a significantly smaller shrinkage on the finished part in the direction of the fiber than transversely to the fiber direction. In order to mitigate this anisotropic behavior, fiber / mineral mixtures are often used as a reinforcing system. Frequently, the thermoplastics must also be processed into composite elements in which the plastic parts are combined, for example, with a steel shell or a steel ring for support. The plastic surface must then be extensively reworked and lubricated.

WO 01/44 361 discloses medium-tight contact guides for plastic components consisting of a glass / plastic compound based on thermoplastics, which has a low-melting sulfophosphate glass of the following composition:<ul><li>4 to 10% Li₂O, 4 to 10% Na₂O, 4 to 8% K₂O,</li><li>1 to 2% CaO, 35 to 37% ZnO, 0 to 3% La₂O₃,</li><li>19 his 22% P₂O₅ And 19 to 22% SO₃ And a high-performance thermoplast.</li></ul>

The object of the invention is to design machine elements such that they are stable and highly load-bearing, the materials used for this purpose having favorable tribological properties and good dimensional stability.

This is achieved according to the invention by the fact that the machine elements consist of a glass / plastic compound on a thermoplastic resin base,<ul><li>A low melting sulfophosphate glass of the following composition (in mol%): 4 to 10% Li₂O, 4 to 10% Na₂O, 4 to 8% K₂O, 1 to 2% CaO, 35 to 37% ZnO, 0 to 3% La₂O₃, 19 to 22% P₂O₅ And 19 to 22% SO₃ as</li><li>a high-performance thermocouple</li></ul>.

The use of the special glass / plastic compound from a low-melting sulfophosphate glass and a high-performance thermoplast is used to obtain machine elements which have a long service life, in particular at higher temperatures. The new materials also show good mechanical properties such as high stiffness, dimensional stability and compressive loadability. Therefore, the corresponding machine elements no longer have to be supported by expensive metal inserts.

A "low-melting" sulfophosphate glass is used as a glass with a low glass transition temperature T_G In particular a glass with T_G &lt;About 500 ° C. A "high-performance thermoplast" is a high-performance polymer, in the present case a "high-temperature resistant polymer" ( "heat-resistant polymer"). This is important because both the temperature during the production of the compound and the processing temperature (of the compound) is&gt; 300 ° C.

The sulphophosphate glass contained in the glass / plastic compound has a glass transition temperature in the range from 250 to 280 ° C; At the processing temperature it is therefore in the flowable state. The compound preferably has a sulfophosphate glass of the following composition (in mol%): 4.9% Li₂O, 9.4% Na₂O, 7.1% K₂O, 1.6% CaO, 36.6% ZnO, 20.0% P₂O₅ And 20.4% SO₃. Such a glass has a glass transition temperature of 268 ° C. Another glass has, for example, the following composition (in mol%): 9% Li₂O, 5% Na₂O, 7% K₂O, 1.6% CaO, 37% ZnO, 20.4% P₂O₅ And 20% SO₃ (T_G = 280 ° C). Another glass has, for example, the following composition (in mol%): 4.8% Li₂O, 9.2% Na₂O, 6.9% K₂O, 1.6% CaO, 35.9% ZnO, 2.0% La₂O₃, 19.6% P₂O₅ And 20.0% SO₃ (T_G = 275 ° C).

As a high-performance thermoplast, the glass / plastic compound preferably contains one of the following polymers: a polyetheretherketone (PEEK), a polyetherimide (PEI), a polyphenylene sulfide (PPS), a polyaromatic polyamide such as polyphthalamide (PPA) and polyamide (PA) 6 / 6T , Or a liquid crystal polymer (LCP). In these polymers, the glass transition temperature of the glass component is adapted to the processing temperature of the thermoplastic material. Further high-performance thermoplastics which can be used are polyarylether ketones (PAEK) in general, for example polyether ketones (PEK), as well as polysulphones (PSU), in particular polyethersulfones (PES) and polyphenylenesulfones (PPSU).

The proportion of the compound on the glass component, ie on the sulfophosphate glass, is generally from 15 to 80% by weight, preferably from 25 to 60% by weight. The processing temperature of the compound is about 320 to 420 ° C. Despite the high proportion of glass, the compound has a high flowability or a very good flow behavior.

The glass / plastic compound is advantageously produced, for example, in such a way that a masterbatch with a glass content of 60 to 90% by weight is obtained from the two components, ie, sulfophosphate glass and high-performance thermoplastics, at an elevated temperature (preferably about 320 to 420 ° C.) -% will be produced. Surprisingly, it has been found that, in the case of the use of glass particles (glass grains) with a diameter ≤ 1.5 mm in the masterbatch, glass structures in the μm and sub-μm range are obtained which are distributed evenly.

The further processing then takes place in such a way that the glass content is reduced to 25 to 60% by weight, for example, by adding further high-performance thermoplast to the masterbatch at elevated temperature (preferably about 320 to 420 ° C.). The structure and the homogeneous distribution of the glass particles are not affected, ie they are retained. In the case of control experiments, it was surprisingly found that the structure size and distribution of the described type are not obtained when starting directly from a batch, for example with a glass fraction of 15%. Uniformly distributed glass structures, even in the nm range, can only be achieved by a masterbatch with a high proportion of the special sulfophosphate glass in a high-performance thermoplast.

As already stated, the compound is in the flowable state at the processing temperature. A new, virgin glass surface is always produced by the melting process during processing. Therefore, a very smooth surface is obtained, and the bonding of the glass particles to the plastic matrix is ​​very good. Compared to conventional fiber-reinforced compounds, no exposed glass fibers or glass fibers are formed, and the formation of particles by abrasion is drastically reduced.

Machine elements made from the new materials, which have good tribological and good shrink properties, are in particular bearings, such as plain bearings, and gear wheels. Further applications for these materials are, for example, rollers, pulleys, couplings, joints, hinges and spring elements.

The invention is to be explained in more detail with reference to exemplary embodiments. The sulfophosphate glass used in the tests has the following composition (in mol%): 4.9% Li₂O, 9.4% Na₂O, 7.1% K₂O, 1.6% CaO, 36.6% ZnO, 20.0% P₂O₅ And 20.4% SO₃.

example 1

Friction and wear

The friction and wear behavior is tested in a pin / disc arrangement.

Test parameters:

<tables id="tabl0001" num="0001"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="61mm" colsep="0" /><colspec colnum="2" colname="col2" colwidth="17mm" colsep="0" /><thead><row><entry namest="col1" nameend="col1" align="left" valign="top">Friction disc:</entry><entry namest="col2" nameend="col2" align="left" valign="top">steel</entry></row></thead><tbody><row><entry namest="col1" nameend="col1" align="left" valign="top">Surface roughness of the friction disc:</entry><entry namest="col2" nameend="col2" align="left" valign="top">0.8 μm</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Surface pressure:</entry><entry namest="col2" nameend="col2" align="left" valign="top">4 N / mm²</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Friction speed:</entry><entry namest="col2" nameend="col2" align="left" valign="top">0.5 m / s</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Temperature:</entry><entry namest="col2" nameend="col2" align="left" valign="top">23 ° C</entry></row></tbody></tgroup></table></tables>

Wear (in μm) and coefficient of friction are determined on injection-molded test specimens (base area: 10 mm × 4 mm) taken from a shoulder bar. At the end of the running-in phase, the test time is 15 h. A compound based on PPS with a glass content of 60% by weight is mixed with a commercially available PPS with 40% by weight of glass fibers (PPS Gf 40).<tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="3" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="29mm" colsep="1" /><colspec colnum="2" colname="col2" colwidth="35mm" colsep="1" /><colspec colnum="3" colname="col3" colwidth="26mm" colsep="1" /><thead><row><entry namest="col1" nameend="col1" align="left" valign="top">material</entry><entry namest="col2" nameend="col2" align="center" valign="top">Wear in 15 h μm</entry><entry namest="col3" nameend="col3" align="center" valign="top">Coefficient of friction</entry></row></thead><tbody><row><entry namest="col1" nameend="col1" align="left" valign="top">PPS Gf 40</entry><entry namest="col2" nameend="col2" align="center" valign="top">950</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="54">0.32</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">PPS + 60% glass</entry><entry namest="col2" nameend="col2" align="center" valign="top">20</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="54">0.30</entry></row></tbody></tgroup></table></tables>

Example 2

Dimensional stability and shrinkage

The shrinkage behavior of injection-molded plates is measured longitudinally and transversely to the direction of flow:<ul><li>A) Processing shrinkage: 24 h after injection (storage: 23 ° C., 50% relative humidity);</li><li>B) Post-shrinkage: After subsequent heat storage at 180 ° C. (2 h).</li></ul>

Process parameters:

<tables id="tabl0003" num="0003"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="36mm" colsep="0" /><colspec colnum="2" colname="col2" colwidth="30mm" colsep="0" /><tbody><row><entry namest="col1" nameend="col1" align="left" valign="top">Plate size:</entry><entry namest="col2" nameend="col2" align="left" valign="top">130 mm x 100 mm</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">thickness:</entry><entry namest="col2" nameend="col2" align="left" valign="top">1 mm</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Mass temperature:</entry><entry namest="col2" nameend="col2" align="left" valign="top">330 ° C</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Tool temperature:</entry><entry namest="col2" nameend="col2" align="left" valign="top">150 ° C</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">injection pressure:</entry><entry namest="col2" nameend="col2" align="left" valign="top">700 bar</entry></row></tbody></tgroup></table></tables>

A compound based on PPS with a glass content of 40% by weight and a corresponding compound with a glass content of 60% by weight are mixed with a commercially available PPS containing 40% by weight of glass fiber (PPS Gf 40) and a commercially available PPS 65% by weight glass fiber / mineral fraction (PPS Gf / M 65, low distortion optimized). <tables id="tabl0004" num="0004"><table frame="all"><tgroup cols="3" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="29mm" colsep="1" /><colspec colnum="2" colname="col2" colwidth="63mm" colsep="1" /><colspec colnum="3" colname="col3" colwidth="51mm" colsep="1" /><thead><row><entry namest="col1" nameend="col1" align="center" valign="top">material</entry><entry namest="col2" nameend="col2" align="center" valign="top">Processing shrinkage in% longitudinal / transverse</entry><entry namest="col3" nameend="col3" align="center" valign="top">Post-shrinkage in% longitudinal / transverse</entry></row></thead><tbody><row><entry namest="col1" nameend="col1" rowsep="1" align="left" valign="top">PPS + 40% glass</entry><entry namest="col2" nameend="col2" align="center" valign="top">&lt;0.5 / &lt;0.6</entry><entry namest="col3" nameend="col3" align="center" valign="top">&lt;0.4 / &lt;0.4</entry></row><row><entry namest="col1" nameend="col1" rowsep="1" align="left" valign="top">PPS + 60% glass</entry><entry namest="col2" nameend="col2" align="center" valign="top">&lt;0.4 / &lt;0.5</entry><entry namest="col3" nameend="col3" align="center" valign="top">&lt;0.2 / &lt;0.3</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">PPS Gf 40</entry><entry namest="col2" nameend="col2" align="center" valign="top">&lt;0.85 / &lt;0.2</entry><entry namest="col3" nameend="col3" align="center" valign="top" /></row><row><entry namest="col1" nameend="col1" align="left" valign="top">PPS Gf / M 65</entry><entry namest="col2" nameend="col2" align="center" valign="top">&lt;0.7 / &lt;0.2</entry><entry namest="col3" nameend="col3" align="center" valign="top" /></row></tbody></tgroup></table></tables>