Patent Application
20070266811
The individual planet wheel is manufactured from, e.g., steel and is nitrided.
To receive the pin 40, the individual planet wheel 30 has a cylindrical through-hole 32, which is oriented in the longitudinal direction. The pin 40 has a cylindrical cross-section with a diameter of, e.g., 5 mm, at least in the area where the planet wheel is received.
The pin 40 consists of a hard metal. The hard metal is a compound material, consisting of hard material—e.g., tungsten carbide, tantalum carbide, titanium carbide, etc.—and of a binding agent, e.g., cobalt. In the exemplary embodiment, the hard metal pin 40 consists of 90.5% by weight tungsten carbide and 9.5% by weight cobalt. Other hard materials are not incorporated. The structure is non-reactive to foreign matter.
The portion of the hard material(s) in the work material can lie, e.g., between 70% and 94% by weight. The portion of the binding agent accordingly lies between 30% and 6% by weight.
For hard metals, the portion of hard material determines the hardness of the work material and the wear characteristics. The binding agent gives the compound material its toughness. Thus the hard metal pin 40 of the exemplary embodiment has a high degree of hardness, e.g., 1230 HV, and a high toughness.
In the exemplary embodiment, the employed grain size of the hard metal pin 40 is 8 micrometers. The hard metal pin 40 thus has a density of 14,500 kg/m3. It reaches a bending strength of at least 2000 N/mm2, ideally greater than 2800 N/mm2, and a compressive strength of 3800 N/mm2.
If the hard metal pin 40 should have a high thermal resistance, it may exhibit, in addition to the hard tungsten carbide, a portion of titanium carbide of up to 12% by weight. This reduces the effect of the binding agent, however, which in turn reduces the toughness.
The use of, e.g. tantalum carbide has a smaller influence on the effect of the binding agent. This hard material can accompany tungsten carbide in a portion of up to 8% by weight. This only slightly changes the effect of the binding agent, while simultaneously raising the toughness of the material. Operating safety is further enhanced as a result.
Through a combination of all three indicated hard materials and the binding agent the physical characteristics of the hard metal can be finely adjusted.
The hard metal pin 40 can also have surface coating. This might be, e.g., a thin layer of titanium carbide, titanium nitride, or titanium. The layer thickness is, e.g., between 5 and 15 micrometers. This coating is either separated from the gas phase in the so-called CVD process or produced in the PVD process by means of ions in an electrostatic field. Of the indicated coatings, those of titanium carbide and titanium carbide have the highest resistance to wear.
Upon assembly, the planet wheel 30 is pushed onto the pin 40. The pin 40 and the through-hole 32 have a loose fit. After assembly, the toothings 21, 31 are lubricated, e.g., with oil.
When the wheels 20, 30 turn, the planet wheel 30 rotates on the pin 40. These two parts 30, 40 form a radial sliding bearing 40 with a sliding mount 51.
During operation the through-hole 32 of the planet wheel 30 slides on the hard metal pin 40 in the circumferential direction. The through-hole 32 is subjected here to a circumferential load and the hard metal pin 40 to a lumped load. The lumped load on the hard metal pin 40 takes effect in the radial direction of the planetary gear 10. Because of its high hardness and high toughness, the surface of the hard metal pin 40 is resistant to the wear caused by this pressure load.
During operation of the planetary gear 10, changes in load from the output end (block travel) may occur in sudden bursts. Here there is a change in the ratio of the output torque to the driving torque of the planetary gear 10. The hard metal pin 40, which is resistant to bending, prevents the pin from cracking. In addition, the nitriding of at least the through-hole 32 (for example) contributes to the robust combination of materials in the sliding joint 51.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 023 390.5 | May 2006 | DE | national |
