Method for production of drawn seals

The tongue material (2) is shaped, in a hot state, immediately after the extrusion thereof, preferably by means of a gear wheel acting upon the tongue material. The tongue material (4) is preferably longitudinally drawn after cooling below the solidification point thereof, with preferably a doubling in length. The final tongue profile (7) is thus achieved which displays a higher stiffness due to the stretching and may be adjusted to length or cut to length. The tongue (7), produced in the above manner, is finally mounted on the base body (8) of the drawn seal (1) by a spray application and forms the final drawn seal (1), together with the sealing body, also preferably mounted to the base body (8) by a spray application. The above is characterized not only by the good stability, but by the adjustable length of the tongue (7) and also a high security on manipulation. The final drawn seal (1) cannot be cut and resealed after installation, without leaving traces on the object to be sealed.

The present invention relates to a method for the manufacture of drawn seals according to the preamble of claim1.

Drawn seals made of plastic are usually manufactured via an injection molding method. Molds, as a rule metal molds, are manufactured for this purpose, into which molds is subsequently injected under high pressure the plastic in a liquid form, and the drawn seal is manufactured in one piece in one operation.

Such a drawn seal is designed with a base body having a sealing body mounted thereon and a tongue projecting, respectively leading away, from the base body, the tip of which tongue can be placed during use through the sealing body. The tongue has thereby as a rule hold-back means in the form of nubs or teeth which permit the guiding of the tongue through the sealing body in one single direction. However, a pulling back of the tongue is impossible in the opposite direction due to blocking means which are arranged in the sealing body and which act onto the hold-back means of the tongue. Such drawn seals are thus so-called one-way means, namely they can as a rule be only used one time and the seal can be released only through destruction.

The size of the tongue and the type of the sealing body are chosen depending on their use.

The problem now exists that when a long tongue is needed the respective tool, that is the respective shape must be designed relatively large which, on the one hand, results in high costs, and, on the other hand, can result in problems relating to the complete and homogeneous filling of the mold, which in turn cause complicated manufacturing methods, which also result in an increase in the manufacturing costs and thus an increase in the cost of the product.

The purpose of the present invention is to provide a method for the manufacture of drawn seals made of plastic, which method makes it possible to manufacture tongues with practically any desired dimensions without any extra expenses.

This purpose is attained according to the invention by the method defined in claim1.

Preferred embodiments of the method of the invention can be taken from the further claims2to8.

By manufacturing the tongue of the drawn seal via the extrusion method, practically any desired dimensions, in particular in length, can be advantageously achieved. Furthermore higher strength values are achieved regarding the strength after the profiling and lengthening of the tongue body than is available in common seal tongues manufactured via the injection molding method. Instead of manufacturing many different molding tools for each needed dimension, it is possible to cover with one single extrusion tool and the use of a standardized base body practically all demands on the drawn seals at an expense which is less in comparison to the common method.

A further advantage lies in the possibility of using polyethylene as the plastic for the manufacture of the drawn seal, since through the lengthening operation the orientation of the plastic molecules is changed thereby resulting in an increase of the strength characteristic, and practically the same values as is available in common drawn seals made of polyamide are achieved at much reduced costs.

One exemplary embodiment of the invention will be discussed in greater detail hereinafter in connection with the drawing figures, which show in

FIG. 1schematically illustrates the inventive manufacturing process of a drawn seal1made of plastic. The tongue of the drawn seal is manufactured in a first process group by preferably extruding a trapezoidally-shaped profile2, which is profiled directly after the extrusion. The cross section of the profile strand2is illustrated inFIG. 2.

The profiling is preferably done by a profiled wheel3, which is preferably rollingly pressed onto the short upper side of the extruded profile strand2. A rack-shaped profile strand4is in this manner created, as it is illustrated inFIG. 3. The profile protrusions4′ are preferably spaced apart at a regular distance A.

These two process steps can be carried out advantageously continuously, in contrast to common pressure injection molding methods in molds, which must be carried out individually for each piece. This means that tongues of any desired length can be manufactured with the extrusion method by subsequently cutting the profile strand4to the needed length.

This profile strand4is thereafter fed to a lengthening process5, which preferably doubles the length of the profile strand4. This can advantageously again occur continuously, or can be applied individually as an alternative for the profile pieces already lengthened to the needed dimension. The lengthening process5applied to the profiled profile strand4leads on the one hand to an orientation of the plastic molecules to effect an increase in the strength characteristic. Thus polyethylene can advantageously be used as the plastic, which is less expensive than polyamide commonly utilized in pressure injection molding methods, however, achieves due to the lengthening ability practically the same strength values as polyamide. This is achieved preferably by lengthening the profile at a temperature of approximately 60° C. A further advantage of this method is that the material upon tensile load breaks practically without expansion when reaching the breaking limit, which makes a nonvisible manipulation of the drawn seal practically impossible.

On the other hand, the tapered sections4″ of the profiled profile strand4are in particular lengthened during the lengthening process, and a final profile shape6is created which fit together ideally with the resilient hold-back means of the sealing body of the drawn seal.FIG. 4illustrates the view of a section of such a final profile shape6, where the profile protrusions6′ preferably are now spaced at twice the distance2A or more in comparison to the profiled profile strand4. This enables the drawing in one direction through the sealing body, whereas a pulling back into the opposite direction is made impossible by engagement of the hold-back means against the profile edges of the tongue, as this is known for drawn seals.

The finish profiled tongues7, which are subsequently cut to the needed length, are now injection molded onto the base body8of the drawn seal1at the area suitably provided therefor. This creates a strong and tamper-free connection. A further advantage of this method is the possible use of differently colored material for the base body8and the tongue7, which results in additional design freedoms when manufacturing drawn seals1.

The base member8can in a common manner be manufactured, for example, by pressure injection molding methods and can thereby either be equipped in one piece already with the sealing body9, or same is injection molded in a separate additional process step onto the base body analogously to the tongue7. This latter method step permits preferably again an increased freedom in design when designing drawn seals1, in that the sealing body9can consist, for example, of many parts and in particular not only of one material but of a combination of various materials. Thus it is possible in particular to use a sealing body9with a metal insert, which has an increased drawing resistance to provide assurance against manipulation.FIG. 5illustrates the view onto a drawn seal1manufactured in this manner.

A drawn seal1manufactured in this manner has a very high assurance against manipulation since after one manipulation, as for example the cutting open of the tongue7, this manipulation cannot simply be reversed or cannot be made to be not visible. When preferably polyethylene is used, a cut area cannot again be connected simply by invisible gluing. When heat is used, the material will simply melt and cannot be simply welded as a strong connection.

The introduced manufacturing process can thus be universally utilized for the manufacture of drawn seals1with varying tongue lengths and, if necessary, varying sealing bodies9, and requires merely a minimal number of tools. Of a particular advantage is that it is not necessary to manufacture a separate, special mold for each demanded different length of tongues, and thus the method is also suited for the inexpensive and economical manufacture of small amounts in special sizes or designs. In addition it is also possible to utilize a less expensive plastic, such as polyethylene with non-reduced strength values of the drawn seal1, than is necessary in the common injection molding method of manufacture with the use of polyamide.