Coating processes – Spray coating utilizing flame or plasma heat – Metal or metal alloy coating
Reexamination Certificate
2000-01-28
2001-12-11
Bareford, Katherine A. (Department: 1762)
Coating processes
Spray coating utilizing flame or plasma heat
Metal or metal alloy coating
C427S456000, C029S888090, C029S888091
Reexamination Certificate
active
06329022
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods for producing connecting rods having a thermally sprayed bearing layer.
Conventional connecting rods now in use, especially for internal combustion engines, are so-called cut or cracked connecting rods in which the large connecting rod eye that surrounds the crankshaft is cut or cracked to open it. As a rule, the small connecting rod eye does not need to be opened since it is connected to the piston by a straight bolt.
Depending upon the load applied to the bearing, connecting rod eyes are made with a variety of bearing shells providing the friction surface. In particular, supporting shell materials used in bearing shells are as a rule made of C 10 steel according to DIN 17210 or SAE 1010. Depending upon the particular design and application, the bearing shells may be cold hardened. The actual bearing surface layer, which may, for example, be white metal, leaded bronze, light metal, spatter coatings or the like depending upon the expected bearing load, may be applied to the supporting shell material. The bearing shells may be three-component, two-component or solid single component bearing shells. The shells are assembled to the connecting rod eye with an initial stress so that the bearing shells have a satisfactory, firm seat upon assembly.
Bearing shells not only constitute a substantial cost factor, but also complicate production and are a potential source of error. For example, the insertion of a bearing shell or bearing shell half may be overlooked in assembly, resulting in considerable engine damage.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a method for producing a connecting rod having a high strength bearing layer.
Another object of the invention is to produce a connecting rod bearing having a high strength bearing layer.
These and other objects of the invention are attained by thermally spraying a bearing material on the eye of a connecting rod using different thermal spray temperatures.
Thus, according to the invention, a bearing shell is no longer inserted into a connecting rod eye, either the large eye, or alternatively into both connecting rod eyes. Instead, a bearing layer is applied directly to the connecting rod eye by thermal spraying such as by plasma spraying. Specifically, the connecting rods made in this way are used in an internal combustion engine to connect the crankshaft to the pistons. To increase the adhesive strength of the bearing layer, the material of the connecting rod eye to be coated may be roughened by sandblasting with different particle size distributions. To increase the quantity of residual oil retained by the bearing layer, the applied bearing layer may have micropores and/or one or more groves.
In accordance with the invention, the bearing material is deposited on the substrate at different temperatures during the course of the thermal spraying, more particularly plasma spraying. The different temperatures can be achieved by a wide variety of parameter variations in which one or more parameters can be changed. The parameters to be changed in particular in order to achieve a temperature increase are an increase in the current or voltage at the burner, a reduction in the supply of cooling gas or carrier gas, an increase in the supply of fuel gas such as hydrogen, for example, a reduction in the mass flow of the bearing material to be supplied, a reduction in the particle size of the bearing material, or a change in the composition of the bearing material. To reduce the deposition temperature one or more of those parameters can be changed in the opposite direction.
It is especially advantageous to reduce the application temperature of the bearing material during the course of thermal spraying. The application temperature can in principle be increased again at a later time, but it is preferable for it to remain reduced. If the surface of the thermally sprayed bearing layer is to be subsequently removed, it is especially advantageous when the part of the bearing layer that is to be removed is sprayed at a low temperature, in which case it is desirable for the removal to extend into a region of the bearing layer that was deposited at a higher temperature. With this method it is especially advantageous that the temperature can be reduced during deposition to such a degree that the region of the bearing layer that is to be removed contains a relatively low-grade portion of the layer which is removed by subsequent machining of the bearing layer.
In the method according to the invention, the initial temperature at which the bearing material is applied to the connecting rod eye can be raised so that the processing temperature is high enough that it would cause annealing of the connecting rod material if all of the necessary bearing layer material were applied at that temperature. In this way, a particularly high bonding strength of the bearing layer to the substrate of the connecting rod eye and a desirable reduced porosity in the bearing layer can be achieved.
The various particle-size distribution curves that are advantageously used according to the invention are also known as mesh size classes, where according to the invention the classes from 16 mesh to 230 mesh i.e., 16, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 100, 120, 140, 170, 200 and 230 in particular are used. The mesh count specifies the number of holes per square inch, i.e., per 6.45 cm
2
in the screen used. For example, the individual particle-size distribution curves, including tolerances and sieve wire sizes, can be obtained from the Handbook of Chemistry and Physics, 64th Edition, 1983/1984, CRC Press Inc., Florida, p. F-114.
It has been determined by thermally coating a connecting rod eye that the usable bearing layers, which are made of aluminum bronze for example, have a high residual layer stress which in particular is increased by the fact that the material is deposited with a low porosity. Consequently, it is clear that measures to increase the bonding strength of the bearing layer are necessary. This is advantageously achieved in accordance with the invention in that, in addition to a high initial bearing layer application temperature, the connecting rod eye is sandblasted with successively different grain sizes including at least one fine and at least one coarse grain size distribution.
Operationally reliable connecting rod bearings require a wear-resistant design and construction in order to transmit the bearing forces reliably and at permissible operating temperatures. Wear resistance is always provided when the sliding surfaces are separated from each other by a lubricating film such as an oil film that is capable of bearing a load. Such a lubricating film is maintained in friction bearings by a slightly eccentric shaft mounting. With this arrangement, the rotating shaft has a pumping effect that feeds the lubricant such as motor oil into the eccentric bearing slot, and oil pressure is built up at the convergent surfaces of the bearing slot. In other words, the lubricant is pressed into the narrowest cross section of the space between the bearing surfaces. This results in a condition called “interfacial lubrication” in which there is interfacial friction of the bearing material on the journal when the rotary motion of the shaft begins or is very slow. An increase in rotation speed causes the oil film to assist in supporting the journal even though a coherent oil film has not yet been built up. This is a condition called “mixed friction,” i.e., simultaneous interfacial and floating friction. This condition exists chiefly when an engine is being started and stopped. An additional increase in the speed of rotation causes the development of the hydrodynamically supporting lubricating film layer having a thickness equal to half of the bearing clearance resulting in a condition called “floating friction.” With floating friction the bearing clearance is usually equal to about 15 &mgr;m to 60 &mgr;m.
When the surface of a connecting rod eye such as the large eye is plasma
Schlegel Udo
Vogelsang Reinhard
Baker & Botts LLP
Bareford Katherine A.
Volkswagen AG
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