CA1237570A - Process for the production of molded items and a model for completing the process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to a process for the production of molded items and a pattern for carrying out the process.
Vapourizable pattern parts are used to configure irregular shapes and reusable pattern parts are combined with the vapourizable parts to form a complete pattern. Once the mold has been shaped, the reusable pattern parts are removed from the mold, whereupon the vapourizable pattern parts are destroyed during the pouring of molten metal in the mold.

Description

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The present invention relates to a process for the production of molded items and a pattern for carrying out the process.
In order to mold shapes that are not regular, i.e., of cutbacks on patterns, it is customary to work with loose parts. When the main section of the pattern is removed, these are then used in the resulting hollow mold space and then removed, so as to be combined with the main portion of the pattern once again. In the case of relatively small patterns it is not possible to work with loose parts since there is not a sufficiently wide hollow space in the mold. In such a case, separate cores have to be inserted into the mold that is produced.
Another possibilitv for molding irregular shapes is offered by the full-mold technique using patterns that can be vapourized. When this technique is used, the pattern that is formed is destroyed just prior to or during the molding process.
The use of this process is limited by the stability of the foamed plastic that ca~ be used, that has a mold density consolidation of relatively low resistance. This can lead to faulting or to dimensional deviations. A new pattern has to be produced for each pouring, and this is then completely vapourized. Relatively large quantities of gas have to be cleared away during the molding process. The residues on the surface of the molded item can reduce the quality of the product.

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'~, , 37~i70 In the present application a process is disclosed which permits the production of molded items having irregular shapes, this being possible without any of the disadvantages outlined above.
The present invention may generally be defined as a process forthe production of molded items with partially irregular contours, characterized in that a pattern made up of vapourizable pattern parts and reusable pattern parts is used in order to configure irregular shapes, and in that, after being used to shape the mold, the reusable model parts are removed from the mold, the vapourizable model parts being destroyed during the molten metal pouring stage.
Of the two known molding processes using reusable and vapourizing patterns, the appropriate advantages are exploited.
Compared to the pure full pattern technique, the required accuracy is maintained because the functional scale, the accurate shapes and the supporting parts for the vapourizable pattern parts are of material that is stable with regard to shape. It is not necessary to vapourize very large volumes during the molding process. This leads to an improvement in the pour behaviour of the metal since gas pressures are lower and the gases can be exhausted easier. There are also fewer residues in the cavities of the hollow mold, and this results in a considerable improvement in the surface quality of the molded items. In addition, there is a considerable reduction in costs and the expenses associated with the production of the ~ ' ; 2 . .

1~3'757~3 full patterns required up to now.
Compared to the customary molding technique utilizing reusable patterns, the proposed process offers greater configuration possibilities that are the equal of much greater stresses, since one is no longer restricted by the requirement for great accuracy in the mold. Loose parts that can be removed subsequently from the mold can be dispensed with. Difficult contours can be produced very easily without the use of cores. This leads to a reduction in costs and at the same time eliminates a source of error.
The process of the present invention achieves its special advantages in conjunction with ~7acuum molding technology. This molding process is suitable for the production of molded items that require a high level of dimensional accuracy, even in the case of large dimensions, since the mold material can be shaken down very easily to the most dense core pack because there are no binders. This high density does not permit the use of large full patterns.
The instability of this pattern material leads to inaccuracy in the molding process.
The vacuum molding process is extremely well-suited for the combined technique herein proposed. The relatively small, vapourizable patterns are deformed only minimally by the high pressures involved. On the other hand, they make it possible to achieve a form that has no loose parts or core, which is connected with certain problems in the vacuum molding process.

~23'7570 An exemplary version of the present invention is shown in the drawings appended hereto. These drawings are as follows:
Figure 1 is a cross-section of a pattern for a double sink;
Figure 2 is a cross-section through a mold with the pattern of Figure 1 place;
Figure 3 is a cross-section through a lower mold during removal of the pattern; and Figure 4 is a cross-section through a prepared mold prior to pairing.
The double sink has a rib structure consisting of ~-shaped and T-shaped ribs. The regualr shapes of the vertical rib cross members are configured as reusable parts 1 of the pattern. The irregular shapes of the horizontal rib flanges are formed by vapourizable parts 2 of the pattern. The vapourizable parts 2 are so disposed relative to the other parts 1 that these can be removed from the mold vertically after the pattern has been formed. The double sink that is shown merely illustrates on presently preferred application.
Of course, other types or shapes of the pattern parts 1 and

2 are possible. Thus, for example, the vapourizable parts 2 can be located at one si.de of the reusable parts , or else surround these in sections.
; The pattern according to Figure 1 is used in a mold

3, as is shown in Figure 2. In order to use the vacuum molding process, the pattern is covered with a film 4. A
vacuum source is then connected to the mold 3.

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According to Figure 3, only the reusable parts 1 of the pattern are removed from the mold. The vapourizable parts 2 remain in the mold 3, and these are shown in their final positions in Figure 4. They are then destroyed by the molten metal during the pouring stage.
In the molding processes known up to now, one either had to develop a regular design or else work with loose parts or cores. Pure full-shape patterns all entailed the disadvantages set out above. ThuS, they were far too costly for large scale production.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of molded items with partially irregular contours, characterized in that a pattern made up of vapourizable pattern parts and reusable pattern parts is used in order to configure irregular shapes, and in that, after being used to shape the mold, the reusable model parts are removed from the mold, the vapourizable model parts being destroyed during the molten metal pouring stage.

2. A process according to claim 1, characterized in that a model for producing a double sink has rib flanges which are L- or T-shaped in cross-section extending vertically from a horizontal base, in which connection, after the mold has been formed, only the vertical ribs and base are removed from the mold as reusable parts, the rib flanges being destroyed during the pouring stage through vapourization.

3. A process according to claim 1, or 2, characterized in that the pattern of vapourizable and reusable model parts are covered by a film and then imbedded in molding material that contains no binders, and in that the mold so produced is connected to a vacuum source prior to the removal and the destruction of the model parts.

4. A model for the completion of the process as in claim 1, characterized in that it consists of vapourizable model parts used to configure irregular shapes, and of reusable model parts.

5. A model as in claim 4, characterised in that it has a rib structure consisting of L- and T-shaped ribs for the production of a tubbing, in which connection vapourizable model parts form the horizontal rib flanges and reusable model parts form the vertical rib webs.

6. A model according to claim 4, characterized in that the vapourizable model parts are supported in vertical guides on the reusable model parts.