Plastic and nonmetallic article shaping or treating: processes – Forming electrical articles by shaping electroconductive... – Conductive carbon containing
Patent
1995-04-05
1997-05-20
Fiorilla, Christopher A.
Plastic and nonmetallic article shaping or treating: processes
Forming electrical articles by shaping electroconductive...
Conductive carbon containing
26433111, C04B 3500
Patent
active
056309732
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for producing sliding bodies for electric collectors, contact brushes, current collectors and the like. It involves placing a powder mass which includes at least graphite and one synthetic resin binder in a mold having at least one press die for pressing the powder into a shaped body. The body is thereafter heat treated by subjecting it to a sintering temperature at which the binder softens and binds the powder mass together.
When practicing such a method it has been noted that the press dies become quickly fouled and require cleaning after short time intervals to remove residues from the die. The reason for this is that during pressing heat is generated between the press die and the powder particles on which it acts which melts the resin binder in the vicinity of the press die. Thus, the binder adheres to the surface of the die, which in turn can cause other constituents of the powder mass to adhere to the die. A press die to which such residue clings cannot press-form bodies which have a clean surface. Press dies therefore require frequent cleaning.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of the above-mentioned type which significantly lengthens the time intervals before the pressing tools must be cleaned while producing sliding bodies which have an improved surface quality.
In accordance with the present invention a method of the above-mentioned type is characterized in that a parting compound which is free of synthetic resin is placed between the powder mass in the mold and the press die. It has been discovered that an appropriately selected parting compound effectively completely eliminates the adhesion of residue on the press die. Consequently, the heretofore common, frequent cleaning of the press die can by and large be eliminated.
It is particularly advantageous to use a powder-like parting compound because it can be placed in the mold with equipment already available on the pressing machine for placing the powder mass that is to be pressed into the mold. The parting compound placed into the mold combines with the powder mass during pressing and forms a thin sheath over the surface of the press-formed body.
It is preferred to use a powder of an electrically conductive material as the parting compound. Thus, pure graphite, for example, can be used as a parting compound. It is particularly advantageous to use a material having a very high electric conductivity, such as copper, as the parting compound. When copper powder is applied as a parting compound layer and the required electric lead is extended through the compound layer into the powder mass in the mold, the lead is pressed with and into the powder mass. This has the additional advantage of a significant reduction in the electrical resistance between the sliding body and the lead pressed into it.
Alternative embodiments of the invention contemplate to use foil-like materials as the parting compound. The foil material is either removed from the formed body after completion of the pressing and before the former is heat treated, or it can remain on the body during heat treatment. In the latter case, care must be taken that the parting compound does not include substances which are released during the heat treatment, and can then enter the pressed body and, for example, change its porosity. It is also possible to use, for example, paper as the parting compound, which, during the heat treatment, incinerates substantially completely without leaving any residues.
An embodiment of the invention will be described with reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically shows a section through a press mold during the fabrication of a sliding body in accordance with the invention.
FIG. 2 schematically shows a finished sliding body made according to FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to FIG. 1 the press comprises a mold 1 and an upper and a lower press die 3, 5. In use a powder mass 7 is filled
REFERENCES:
patent: 3510710 (1970-05-01), McCafferty
patent: 4055615 (1977-10-01), IKeda
patent: 4359438 (1982-11-01), Hoggins et al.
patent: 4822538 (1989-04-01), Yoshida et al.
Patent Abstracts of Japan, vol. 13, No. 142 (E-793) (3490) Apr. 7, 1989 & JP, A, 63 302 744 (Hitachi Chem Co. Ltd.) Dec. 9, 1988.
Patent Abstracts of Japan, vol. 16, No. 285 (E-1222) (5328) Jun. 24, 1992 & JP, 04 071 177 (Shin Etsu Polymer Co. Ltd.) Mar. 5, 1992.
Japanese Patents Gazette, Section Ch, Week 8630, Sep. 3, 1986, Derwent Publications Ltd., London, GB; Class L, P. 12, AN 86-192435/30 & JP, A, 61 124 080 (Hitachi Chemical K.K.) Jun. 11, 1986.
Grabner Herbert
Hoell Johann
Fiorilla Christopher A.
Hoffman & Co. Elektrokohle Ges. mbH
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