Patent Application
20100240463
The present application claims priority to German Patent Application No. 10 2009 007 993.9 filed on Feb. 2, 2009, the contents of which are fully incorporated herein by reference.
The invention relates to a rigid torque-transmitting connection, and more particularly to such a connection between two shaft members.
Connections or couplings between two members, such as shaft elements, are generally known and include some means for connecting end surfaces of each element.
An object of the invention, therefore, is to provide an improved rigid torque-transmitting connection, by means of which, in particular, high static friction coefficients can be achieved.
In one aspect, the present invention is a rigid torque-transmitting coupling comprising two members each having a connection face and either a coating disposed on one of the member connection faces or a coating carrier disposed between the two members. The coating carrier has opposing contact faces, each contact face being disposed against a separate one of the member connection faces, and at least one contact face having a coating. The coating includes a fixing layer disposed on the connection member face or one of the carrier contact faces, and a plurality of particles are disposed at least partially within the fixing layer so as to secure the particles on the member connection face or the carrier contact face. Each particle has a hardness of at least 9 on the Mohs hardness scale and at least twenty-five percent of the plurality of particles within any unit area of the coating extend outwardly from an outer surface of the fixing layer. Further, the two members are connected together such that each member contacts either the other member or the coating carrier with a pressure, the pressure having a value within a range of about 90 MPa and 180 MPa. Furthermore, each member connection face in contact with the coating is formed of a first material and the member connection face carrying the coating or the at least one carrier contact face having the coating is formed of a second material, the second material having a substantially greater hardness than the first material.
Consequently, especially advantageously, a connection is provided in which static friction coefficients greater than 0.7 and even above 0.8 can be achieved, which has not been possible hitherto to implement.
In an advantageous refinement, the fixing layer is formed from nickel applied by electroplating, so that, for example, at the same time an excellent protective layer against corrosion-causing and other environmental influences is generated for the coating carrier.
In an advantageous refinement, the coating carrier is designed with a greater Mohs hardness and/or a greater tensile strength than the connection partners, so that, as desired, when they are pressed against one another, those regions of the particles which project above the coating press into the connection partners, and the coating beneath the particles and the region of the coating carrier beneath the particles are deformed only insignificantly, as compared with pressing into the connection partners.
The foregoing summary, as well as the detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, which are diagrammatic, embodiments that are presently preferred. It should be understood, however, that the present invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:
At least one and preferably both axial end surfaces 31A, 31B of the carrier 30 are provided with the coating to ensure a firm connection between the shaft ends, and thus the two shaft elements 10, 12. The carrier disc 32 is preferably formed of a steel having a tensile strength with a range of about 600 MPa and 800 MPa. The end-face surfaces 31A, 31B of the coating carrier 30 are preferably ground to a surface roughness of Ra≦0.2 μm. Further, the grinding process preferably creates furrow-like depressions with a depth of less than or equal to 4 μm and with a width of less than or equal to 6 μm, and most preferably, the depressions have a depth of less than approximately ten percent (10%) of the coating thickness and/or with a width of less than approximately fifteen percent (15%) of the coating thickness. By providing depressions of such dimensions, the furrow-like depressions ensure optimal adhesion of the coating while reducing the chance that any coating particles disposed within the depressions do not extend above the fixing layer outer surface.
The coating preferably includes an undercoating formed of nickel with a thickness of, for example, approximately 5 μm, which is applied by electroplating to at least one and preferably both ground faces 31A, 31B of the coating carrier 30. A plurality of particles with a hardness of at least 9 on the Mohs scale, and most preferably a Mohs hardness of 10, and a grain size of between 40 μm and 90 μm, are disposed on the undercoating layer in a substantially single layer, but may form a plurality of layers. Preferably, each particle is provided by a sharp-edged or block-like grain of a monocrystalline diamond, for example of a natural diamond. Then, an overcoating of nickel is applied, preferably by electroplating, so that at least a lower region of the particles (i.e., the ends of the particles proximal to the contact surface) on the undercoating are surrounded by the overcoating. Thereby, the particles are fixed or secured in a substantially single layer, and if a plurality of layers have been applied to the undercoating, the outer, excess layers are removed, for example, by brushing after fixing/securing the particle layer with the overcoating.
As used herein, the term “a substantially single layer” is intended to mean that, in a predominant fraction of the coating, preferably greater than 75%, is actually one layer of particles, and in the remainder of the coating the particles may be adhered in multiple layers, particularly in two layers. Consequently, the coating is formed with more than 25% or even up to 40% of the particles projecting out of, or extending outwardly from, the outer surface of the nickel “fixing” layer, with the result that, ultimately, very high static friction coefficients can be achieved.
As mentioned above, both of the end faces or surfaces 31A, 31B of the coating carrier 30 are preferably provided with the coating as described in detail above. The flanges 12, 22 of the two shaft elements 10, 20 are preferably formed of a first material and the carrier faces 31A, 31B are formed of a second material, the second material having a substantially greater hardness than the first material, both in terms of Mohs hardness and tensile strength. Preferably, the shaft flanges 12, 22 are each formed of a grey cast iron, for example GG 40.3 with a tensile strength in the range of between 400 and 500 MPa. Each flange 12, 22 has a connection surface or face 13, 23, respectively, disposeable against or contactable with the carrier 30, each face 13, 23 preferably having a roughness Ra in the range of between 0.5 μm and 1.5 μm.
When the carrier 30 is disposed between the two shaft ends 10a, 20a and the flanges 12, 22 are fastened together, the diamond particles press into the grey cast iron during fastening such that the carrier 30 is connected inter-engagingly with the shaft ends 10a, 20a. Specifically, the two shaft ends 10a, 20a are preferably pressed against one another with a pressure per unit area of about 90 MPa to about 180 MPa. In other words, each shaft element 10, 20 contacts the coating carrier 30 with a pressure having a value within a range of about 90 MPa and 180 MPa. During fastening, the undercoating layer beneath the diamond particles is only slightly compressed in the direction of the carrier 30.
With this structure, the static friction coefficients between the shaft ends 10a, 20a and the carrier 30 greater than 0.7, and preferably greater than 0.8,are present within the coupling. Furthermore, the nickel undercoating provides excellent corrosion protection for the steel coating carrier 30, so that the carrier disc 32 is protected reliably against the most adverse climatic conditions. As a further result, with a connection having the above-described coating, the number of required fasteners can be reduced in comparison with conventional connections, while the strength of the connection remains the same.
Although the coupling is primarily shown and described as including the disc-like coating carrier 30, with the coating being applied to at least one and preferably both contact faces of the carrier 30, the coupling may alternatively be constructed without the carrier and instead have the coating, as described above, applied to the connection face of one of the two shaft elements 10 or 20.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as generally defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 007 993.9 | Feb 2009 | DE | national |
