The present invention refers to rolling bearings incorporating outer race ring, inner race ring and rolling bodies arranged therebetween and which furthermore has a retainer mainly consisting of plastic material or the like.
Different types of rolling bearings with retainer of plastic material are earlier known. The plastic retainer is less expensive than retainers made of more conventional materials such as brass and steel. The reason for plastic retainers to be cheaper than retainers made from the other mentioned materials is primarily that the manufacture will be simpler. The plastic retainer is thus molded directly, and there is no final treatment of importance. Further advantages with retainers made from plastic material are that they are lighter than the other retainers and give the bearing a more quiet operation.
Retainers made of plastic material have unfortunately also their drawbacks. These are primarily that the mechanical strength of the plastic retainer is lower than that of the conventional retainers. This depends often on the fact that boundary layers are formed in the retainer during the molding when flows of plastic from different casting gates meet. Cracks can easily come up in such boundary layers. The plastic material is also more sensitive to high temperature than e.g. steel and brass.
The biggest disadvantage with retainers made of plastic material is, however, probably that the coefficient of thermal expansion of plastic material is considerably higher, about three times, than that of e.g. steel, from which material the bearing otherwise is made. The diameter of a retainer will therefore at a temperature rise increase more than the diameters of the outer race ring and the inner race ring respectively. If the retainer is centered on the inner race ring, it will therefore get a too big play relative to this; if it is centered on the outer race ring, it may happen that it gets a too small play and press against this ring. And if it is roller centered, a more wobbly and inferior guiding of the rollers will result.
It has therefore since long been a desire to produce retainers from plastic material which have the excellent properties of the plastic but which at the same time have the thermal expansion properties and strength of e.g. steel.
This desire has been satisfied with the present invention, and a rolling bearing has been provided which incorporates outer race ring, inner race ring, rolling bodies and retainer, and possibly guiding ring and which is characterized thereby that the retainer and possibly the guiding ring incorporates rings made from a material which has mainly the same coefficient of thermal expansion as the material in the outer and inner race rings, e.g. steel, and being embedded in another material e.g. plastic, which can have another coefficient of thermal expansion than that of the material in the rings. PG,4
According to the invention, the embedding material shall be applied in such a manner or in such a small quantity that the thermal expansion is controlled by means of the embedded rings.
The rings may be divided and joined by means of the embedding material.
The rings should be provided with projections or indentations, for securing a safe attachment of the embedding material.
In order to avoid strains in the retainer, it is possible to let the embedding material be so loosely attached in certain areas that a sliding between this and the ring can occur.
The safe attachment of the embedding material should e.g. at a window type retainer be made at the connections between the webs and the annular parts of the retainer.
It is possible to let the embedding be thinner between the areas of safe attachment than in these areas.