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Joining assembly including a plastic support member and a plastic threaded element

Joining assembly including a plastic support member and a plastic threaded element description/claims

The present invention relates to a joining assembly including a support member of plastic material and a threaded element of plastic material. The threaded element is threaded into a receiving bore of the support member and comprises a core and an external thread which when threaded into the receiving bore of the support member forms a counter-thread in the receiving bore of the support member. Furthermore, the present invention relates to a threaded element formed as a screw or a threaded sleeve for such a joining assembly, and a tool and method for making a joining assembly.

Such joining assemblies comprising a plastic support member and a plastic threaded element formed as a screw or a threaded sleeve with a self-tapping external thread have become known, see for example DE 42 27 272 A1, DE 42 27 274 C2, and DE 23 17 736. The threaded elements of these joining assemblies generally are provided with a specifically designed thread profile so as to enable them to perform their self-tapping function.

For example DE 42 27 272 A1 discloses a threaded element with a so-called round profile, wherein the thread in an axial cross-section is of a circular profile, the revolutions of the thread being spaced from each other, in an axial direction, by small gaps. DE 42 27 274 C2 discloses a threaded sleeve having an external thread of a height which increases from a minimal value to a maximal value in the threading direction so as to provide, at the maximal value of the thread height, a step intended to act as a disengagement lock. The thread is formed as a “triangular thread” in this case.

DE 32 01 846 A1 and DE 91 15 162 U1 disclose self-tapping threaded elements having threads of a profile specially designed to perform the self-tapping function. However, these threaded elements are not made of plastic material.

DE 23 17 736 discloses a self-tapping screw or bolt of plastic material which includes longitudinally extending grooves for providing a pair of diametrically opposite cutting edges in each thread revolution, which cutting edges act in the threading operation to cut an internal thread into the receiving bore of the support member when the screw or bolt is threaded into the receiving bore.

While self-tapping threaded elements of plastic material are being used in practice, further improvements are desirable. One drawback of the prior art threaded elements of plastic material is that they are generally suited only for support members of one specific plastic material while they are not suited for a great number of other plastic materials. Quite often the self-tapping qualities of the threaded element are poor. The strength and load capability of the threaded element and of the joining assembly may be detrimentally affected by notching and/or clamping effects during forming of the thread. Furthermore, deformation resistance and stability of the threaded element are not always satisfactory. Finally, even for small threading torques maximal security against inadvertent disengagement of the threaded element from the receiving bore of the support member should be ensured.

The above disadvantages and drawbacks of the prior art are to be overcome by the present invention. More particularly, it is a primary object of the present invention to provide a joining assembly, a threaded element formed as a screw or threaded sleeve, and a tool and method for making such a joining assembly which allow optimization of the joining assembly and its threaded element with respect to thread forming, mechanical strength, loading capability, deformation resistance, and safety against inadvertent disengagement.

According to one aspect of the present invention, the external thread of the threaded element is of a special thread profile as defined in claim 1, while special embodiments of this profile have been defined in claims 2 to 6. As defined in claims 7 and 8, the external threaded portion may be formed as a fine thread or as a multi-lead thread.

According to another aspect of the invention, the external thread of the threaded element is of a special cutting geometry as defined in claim 9. Specific embodiments of the cutting geometry have been defined in claims 10 to 14. Further details of the external thread of the threaded element have been defined in claims 15 to 17.

Preferably, the threaded element has a free end provided with a special tip area as defined in claims 18 to 22.

When the threaded element is a screw or bolt, the transition area between the shaft and the head thereof is designed in a special manner as defined in claims 23 to 27.

As an alternative the threaded element may be a threaded sleeve as defined in claims 28 and 29. A special tool as defined in claims 32 and 33 is preferably used to thread the threaded sleeve into the receiving bore of the support member.

According to a further aspect of the present invention the plastic materials of the threaded element on the one hand and the support member on the other hand are adapted to each other and selected such as defined in claims 30 and 31.

A method for making a specially designed joining assembly has been defined in claims 36 and 37.

As should be self-evident from the above, the present invention relates, additionally to the joining assembly and the tool and method for making the joining assembly, to the threaded element itself which may be a screw (bolt) or a threaded sleeve as defined in claims 34 and 35.

Further features and details of the present invention will be described in the following with reference to the accompanying drawings. In the drawings:

FIG. 1 is a cross-section of a joining assembly with one half of a threaded element formed as a screw;

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