Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – Mold having movable core or movable pin
Reexamination Certificate
2000-01-14
2002-03-26
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
Mold having movable core or movable pin
C249S175000, C249S184000, C425SDIG001, C425SDIG005
Reexamination Certificate
active
06361309
ABSTRACT:
This application is based on and claims priority under 35 U.S.C. §119 with respect to German Application No. P 199 01 282.2 filed on Jan. 15, 1999, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention generally relates to linear bearings. More particularly, the present invention pertains to a rolling bearing cage for a linear bearing and an injection molding tool for producing a cage for a linear bearing.
BACKGROUND OF THE INVENTION
Injection molding tools for producing linear bearing cages are known. A rolling bearing cage made of an injection-moldable material is described in German Offenlegungsschrift 36 35 261 and is made in one piece of an endless strip injection-molded in sections in a tool. The recesses for receiving rolling bodies are provided with protrusions extending out of the base element of the cage and extend around the balls inserted into the cage to prevent the balls from falling out of the cage.
A similar version of a rolling bearing cage is known from DE 37 22 651 A1. Here, the base element of the cage is also provided with recesses which are intended to prevent the inserted balls from falling out.
One type of known linear bearing cage construction is illustrated in FIG.
1
. The illustrated cross roller cage halves
11
′ are provided with openings for receiving rollers, with pairs of adjacent or successive rollers being offset by 90° with respect to each other. The cage
2
′ is shown in the disassembled state in FIG.
1
and in the assembled state in FIG.
2
. The two parts
11
′ of the cage that are visible in
FIG. 1
are connected, and for this purpose appropriate clip pins are provided. The receiver pockets
10
′ for the rolling elements as well as the holding protrusions
12
′ are thus formed, thereby preventing the rolling elements from falling out of the cage.
Another known version of a cage is illustrated in
FIGS. 3 and 4
. In this version, individual receiver elements
11
′ for individual rollers are injection-molded. A plurality of these individual elements
11
′ which are shown in
FIG. 3
are clipped together to create the entire cage arrangement which is depicted in FIG.
4
. The individual cage elements also have holding protrusions
12
′ which prevent the rolling body from falling out of the cage element.
On the one hand, the above mentioned cages are frequently needed in a very long one-piece version. On the other hand, the cages are also needed for quite small and numerous balls for increasing the support. It has been found that problems can arise when injection molding the cage.
The thermoplastic material injected into an injection molding tool must fill the entire mold cavity. This can cause problems, particularly in connection with cages for small balls, because the plastic material cools too rapidly and “freezes”. Thus, the protrusions needed for holding the balls are not shaped with sufficient accuracy. Easy-flowing plastic materials, for example LCPs (liquid crystal polymer plastics), are as a general rule very expensive and typically do not have the required elasticity to be used in this context.
Furthermore, multiple cross roller cages are also known. However these cages must be connected by an additional assembly process. This means higher production costs because of the assembly tools, as well as specially formed snap-together elements on the cage. The snap-together elements also increase the division between the rolling bodies and therefore reduce the support capability.
Sheet metal cages are also known which typically do not have these same problems in connection with their production. However, the disadvantage of metal cages is that the production costs associated with manufacturing metal cages are relatively high, they display relatively low elasticity and typically provide a ball guidance that is not as good as a plastic cage.
Known injection molding tools for producing cages for linear bearings have the further disadvantage that it is frequently necessary to accomplish the shaping of the holding protrusions for the rolling elements by way of complicated injection molding tools designed with movable slider elements. Although it is possible by way of these tools to relatively precisely produce the desired shape of the holding protrusions as well as the stop faces of the rolling bodies, the required injection molding tool is quite complicated and therefore rather expensive.
In light of the foregoing, a need exists for an injection molding tool that is able to produce a relatively exact shaping of the holding projections as well as the stop faces for the rolling bodies.
A need also exists for an injection molding tool having a design that is more simple than other known injection molding tools to thereby produce cages in a more cost effective manner.
It would also be desirable to produce rolling bearing cages for use in linear bearings in such a way that relatively long cages, particularly suited for receiving very small balls or respectively rollers, can be reliably and reproducibly made, without the problems associated with other known injection molding techniques.
SUMMARY OF THE INVENTION
One aspect of the invention involves an injection molding tool for producing a one-piece cage for a linear bearing in which several rolling elements are positioned in the one-piece cage in a direction along a longitudinal extent of the one-piece cage. The injection molding tool includes first and second tool halves between which is defined a cavity of the tool which receives injection molding material during injection molding of the one-piece cage. The first tool half is provided with a plurality of first protrusions fixedly connected with the first tool half and extending into the cavity of the tool during the injection molding of the one-piece cage, and the second tool half is provided with a plurality of second protrusions fixedly connected with the second tool half and extending into the cavity of the tool during the injection molding of the one-piece cage. Each of the first and second protrusions form a portion of a receiver pocket which is adapted to receive one of the rolling elements. The first and second protrusions are configured to form holding projections associated with each receiver pocket and integrated with the cage for holding the rolling elements in the cage.
The injection molding tool is embodied in such a way that a linear bearing cage can be produced by injection molding having guide faces as well as holding projections or protrusions for the individual rolling elements which do not project out of the basic geometry of the cage such as is the case with the construction described above in German Offenlegungsschrift 36 35 261. Moreover, the protrusions on the tool halves work together in such a way that they form receiver pockets for receiving the rolling bodies in the cooperating position and in the process also define the required holding protrusions for the rolling bodies.
An alternative version of the injection molding tool which is suitable for linear bearing cages which are provided with rolling elements in the form of rollers is designed to produce a one-piece cage, with the one set of protrusions being fixedly connected with one tool half and the other set of protrusions being fixedly connected with the other tool half. The protrusions on the tool halves are shaped in such a way that, when acting together, they form holding protrusions or elements for the rollers in the cage when the injection molding tool is closed, with such holding protrusions being integrated into the basic geometry of the cage. The protrusions on the tool halves are divided from one another, on the surface on which they lie next to each other when the injection molding tool is closed, at an angle of greater than zero degrees with respect to the closing direction of the injection molding tool.
In accordance with this aspect of the invention, the protrusions are in contact at a defined contact angle on the surface with which they come into
Burzynski Albert
Edelmann Ludwig
Geyer Andreas
Glöckner Hermann
Jeschka Erwin
Heitbrink Tim
SKF Linearsysteme GmbH
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