Composite gear blank

摘要

Composite gear blanks are manufactured by placing a rigid centerpiece in a mold, optionally inertizing the mold, filling the mold by adding a liquid reactive mixture around the centerpiece, applying static pressure to the mold and polymerizing the reactive mixture so as to form a plastic outer part surrounding the centerpiece. The composite gear blanks thus made have improved values of normal and shear adhesion strength both at room temperature and at elevated temperatures of up to 120° C. and are particularly suited for making worm gear parts of automotive electronic power steering systems.

主权项

1. A method of manufacturing a composite gear blank, comprising a rigid centerpiece and an outer part made of a plastic material, said centerpiece being substantially disk-shaped with two disk-faces substantially parallel to each other, said outer part being cast around a peripheral surface of said centerpiece, wherein said composite gear blank has the following properties:
a) when determined at a temperature of up to 25° C.:
a normal adhesion strength SN between outer part and centerpiece of at least 17 MPa;a shear adhesion strength SS between outer part and centerpiece of at least 16 MPa; and b) when determined at a higher temperature of up to 120° C.:
a normal adhesion strength SN between outer part and centerpiece of at least 11 MPa;a shear adhesion strength SS between outer part and centerpiece of at least 16 MPa; wherein said normal adhesion strength SN is determined by applying a radially outward load with a constant velocity of 5 mm/min and wherein said shear adhesion strength SS is determined by taking the lower value of: i) a tangential adhesion strength ST obtained by applying a tangential load with a constant velocity of 3 rad/min, and ii) an axial adhesion strength SA obtained by applying an axial load with a constant velocity of 1 mm/min, comprising the steps of:a) providing at least one rigid centerpiece having a structured peripheral surface to be surrounded by said plastic material;b) surface roughening said peripheral surface;c) surface conditioning the centerpiece;d) placing the centerpiece in a mold;e) optionally inertizing the mold by flushing with an inert gas;f) adding a liquid reactive mixture into the mold until the liquid reaction mixture at least partially surrounds the centerpiece;g) applying a static pressure to the mold containing the liquid reactive mixture;h) polymerizing the reactive mixture to form said outer part;wherein surface conditioning comprises applying an organofunctional silane compound onto the peripheral surface and wherein, after step h), the centerpiece is subjected to a controlled heating step so as to locally melt the plastic material in a region adjacent to the centerpiece, followed by forced cooling of the centerpiece.