Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means to heat or cool
Reexamination Certificate
1999-04-30
2001-07-17
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means to heat or cool
C264S106000, C425S810000
Reexamination Certificate
active
06261083
ABSTRACT:
In an injection molding machine heated, liquid plastic molding compound is injected through an injection molding nozzle into an injection mold where it cools down and stiffens. Normally the plastic molding compound reaches an entry channel of a mold from a heated nozzle-body via a cylindrical or disc-shaped outlet. The outlet is located on the axis of the nozzle and the flow direction of the plastic molding compound when leaving the nozzle is identical to the axis. The plastic compound is only distributed in the actual forming cavity of the injection mold after it has flowed through the mold entry channel.
Apart from the actual molded part in the forming cavity a sprue in the mold-entry-channel is also formed; this sprue must later be separated from the molded part and removed. Especially with molded parts with a bore, e.g. compact disc carrier discs this sprue has a negative effect on the production process. The removal of the sprue and possibly of a bore necessitates additional production steps. The sprue and possibly the bore lead to unwanted losses of material; even if the material can be processed into plastic granulate and melted this recycling means effort which increases the production cost and the production time.
Due to losses of heat because of thermal conduction, convection and radiation the temperature of the plastic molding compound in the head of the nozzle decreases. In the region of the outlet of the nozzle head the temperature can be considerably lower than in the heated region of the body. This kind of temperature drop in the nozzle is not wanted and can lead to fatal disturbances of the whole course of processing. A first possibility to reduce the decrease in temperature is direct heating of the nozzles. This, however, is connected with further disadvantages: The heating of the thermal sensors required for control and the necessary electric lines and contacts are sensitive to disturbances and require a large amount of space in the dipping region.
A second possibility for reducing the temperature drop in the nozzle is the employment of an indirectly heated thermally conducting torpedo, as is e.g. known from “Technische Kunststoffe C.2.1: Heisskanalsystem indirekt beheizter Wärmeleittorpedo” Ed. Hoechst Aktiengesellschaft, 1982. This kind of thermally conducting torpedo is substantially a bar with a high thermal conductivity immersed in the plastic molding compound in the part of the nozzle which is not heated. It conducts heat from the heated part of the nozzle to the region of the outlet. In many known nozzles the thermally conductive torpedo is bolted to the nozzle body or the nozzle head. The bolted connection has disadvantages: it does not guarantee an optimal heat transmission into the thermally conducting torpedo and its production is complicated and costly. Publications U.S. Pat. Nos. 4,787,836, 4,266,723 and 4,652,230 avoid this problem by clamping the thermally conducting torpedo in-between base and nozzle head. Admittedly, this kind of thermally conducting torpedo so far seemed unsuitable for molding of flat molded parts with bore.
A further possibility for reducing the temperature decrease in the nozzle is to attach a temperature-equalization-element around part of the nozzle which is not heated. This kind of temperature equalizing element reduces the temperature drop by means of heat conduction, heat isolation and/or heat reflection. It can be employed in combination with a thermally conducting torpedo. An example for this is revealed in publication WO 97/02129.
In publication WO 92/08597 an injection mold for injection molding of disc shaped molded parts is revealed which comprises a first and a second part; These two parts define a disc-shaped cavity together and can be shifted relatively to each other. A third cylindrical part protrudes through the disc-shaped cavity in order to define a hole in the center of the part to be molded. The third part consists of a core and a jacket between which a cylindrical channel for feeding of molding compound is located. The core is equipped with electrical heating means on its inside. The injection mold has different disadvantages. Firstly, the heating means require a lot of space such that the thickness of the core cannot be smaller than a determined size. This means that only discs with relatively large central holes can be molded. Secondly, the heating means in the core need a gauge in order to be able to supply the required temperatures which makes operation complicated and sensitive to disturbance. Thirdly, it is not guaranteed that the heat reaches the molded part from the heating means. Fourthly, the production of the mold according to WO 92/08597 with its many parts to be matched is complicated and costly.
The invention now has the object to develop a nozzle for injection molding of disc-shaped molded parts which does not have the above disadvantages, i.e. especially has thermal characteristics, is more simple to be assembled and simpler and more robust in operation. This object is solved by the nozzle and the method as it is defined in the independent claim.
In the inventive nozzle, one or several outlets in the nozzle head are arranged at a distance to the axis of the nozzle. The outlets must not necessarily be disc-shaped but can have other geometrical forms of cross section; they can e.g. be designed as lengthy slots, the length of which is a multiple of their height. The direction of flow of the plastic molding compound when leaving the nozzle must not necessarily be identical with the direction of the axis of the nozzle but can e.g. be at a right angle to the nozzle axis.
For guidance of the plastic molding compound to at least one outlet, it is advantageous to provide an adapter at the end of the nozzle. The adapter is e.g. fastened to the torpedo. The thermally conducting torpedo is, according to the invention, merely clamped in-between the nozzle body and the nozzle head. The nozzle thus is assembled by inserting the thermally conducting torpedo into the body and by clamping or pressing it with slight initial tension respectively into position in the nozzle body by means of bolting the nozzle head down. This kind of press fit is simple to produce and, moreover, guarantees a very good heat transmission into the thermally conductive torpedo and through the thermally conductive torpedo into the adapter or to the at least one outlet respectively. The manufacture of the inventive nozzle is considerably more simple than and less costly than the manufacture of known nozzles. The inventive nozzle is thermally advantageous as well as mechanically.
In the inventive method the plastic molding compound is ejected out of the nozzle through at least one outlet at a distance from the nozzle axis into an injection mold. After injection of the plastic molding compound into the injection mold the molded part is separated from the plastic molding compound in the nozzle head in a still warm condition, by means of shifting the nozzle and the injection mold in relation to each other. This shifting substantially takes place in parallel to the area of the nozzle outlet.
A further advantage of the invention is that the molded parts can be produced in an almost unlimited variety of forms, whereby losses due to sprue and bore are prevented. Examples for parts produced according to the inventive method and/or with the inventive nozzle are plates with bores, especially compact disc carrier discs, hollow structures such as tubes, cups or funnels and also plates without bores, e.g. credit card carrier plates.
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patent: 4771164 (1988-09-01), Gellert
patent: 4787836 (1988-11-01), Osuna-Diaz et al.
patent: 4900560 (1990-02-01), Trakas
patent: 5268184 (1993-12-01), Gellert
patent: 5324190 (1994-06-01), Frei
patent: 0051252 (1982-05-01), None
patent: 0075043 (1983-03-01), None
patent:
Heitbrink Tim
Lacasse & Associates
Luk Emmanuel S.
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