Process for the production of wear-protected and corrosion-prote

Details Process for the production of wear-protected and corrosion-prote Process for the production of wear-protected and corrosion-prote

1997-05-30

1999-10-19

Bell, Janyce

Coating processes

Spray coating utilizing flame or plasma heat

Nonuniform or patterned coating

427449, 427450, 427451, 427455, 427456, 427555, 427556, 427282, 427287, 427405, 427292, 4274197, 427261, B05D 132

Patent

active

059686030

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for producing wear-protected and corrosion-protected surfaces on plasticizing screws for injection molding machines, wherein wear-resistant layers are produced in two process steps on the entire surface of a plasticizing screw.
In order to improve the wear resistance of plasticizing screws, the conventional state of the art provides that the plasticizing screws are hardened or coated by means of flame spraying with subsequent heat treatment. Both can result in deformation of the screw, while in the case of flame spraying, cracks can occur in the coating in the subsequent operation of straightening the plasticizing screw. A plasticizing screw of that kind is therefore not resistant to corrosion.
An object of the present invention is to provide an improved process for coating plasticizing screws, by means of which it is possible to produce a wear-resistant and corrosion-resistant coating, which is operative to produce a conveyor effect, on the surface of the plasticizing screw.
The object in accordance with the invention is attained in that additive substances are fused into the top side of the screw flight by means of laser technology and the flight flanks and the screw bottom are coated with metal, carbide-metal and/or ceramic materials by means of high-speed flame spraying.
The process according to the invention does not involve distortion of the screw main body after the high-speed flame spraying procedure, whereby cracks in the coating are avoided.
It is advantageously provided that additive substances are fused into the top side of the screw flight by means of a laser beam on a cylindrical steel main body in a helical configuration, that thereafter the screw geometry is mechanically finished and that then the flight flanks and the screw bottom are coated by means of high-speed flame spraying.
An embodiment of the invention is described hereinafter with reference to the Figures of the accompanying drawing.
FIGS. 1a, 1b and 1c show parts of the screw main body in various stages of the processing procedure and FIG. 2 shows a part of the cylindrical blank from which the screw is worked.
An additive substance is fused on to the screw blank 1' by means of a nozzle 7 in the region of the top side 3' of the flight, in a helical configuration, by means of a laser beam 8.
The screw geometry is then mechanically finished, with the screw bottom 5 and the flight 2 being shaped out of the screw blank 1'. The shaping operation is preferably effected by a cutting machining procedure such as milling, turning and grinding.
After the actual screw main body 1 has been produced the flight flanks 4 and the screw bottom 5 are coated by means of high-speed flame spraying.
The operation of coating the flight flanks 4 of the screw bottom 5 is effected by means of a burner or torch nozzle 6 by means of which a spray jet of metal, hard-metal or carbide-metal, or ceramic material is applied using the high-speed flame spray process.
The burner nozzle 6 is moved axially a plurality of times over the screw main body 1, with the screw main body 1 being rotated about its longitudinal axis. In that respect the forward feed movement of the burner nozzle 6 corresponds to the pitch of the screw flight. The burner nozzle 6 is oriented at an angle A of 0.degree.-60.degree. relative to the line n normal to the flight flank 4 of the screw flight 2.
At each reversal point the burner nozzle 6 is pivoted in order to spray the oppositely disposed flight flank 4 of the screw flight 2 and likewise at each reversal point the direction of rotation of the screw main body 1 is changed.
After the flanks 4 of the screw flight 2 have been coated the screw bottom 5 is also coated by means of the high-speed flame spray process, in which case, as shown in FIG. 1c, the burner nozzle 6 is oriented at an angle of 90.degree. relative to the longitudinal center line of the screw main body.
It is also possible for the flight flanks 4 to be coated in such a way that the burner nozzle 6 is pivoted at the reversal points, but the dir

REFERENCES:
patent: 4233072 (1980-11-01), Watanabe et al.
patent: 5135378 (1992-08-01), Catton
Schlei B-und, Korrosionsschutz durch Laserstrahlbeschiechten, Jun. 1995.

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