Apparatus and Method for Reducing Neck Waste in a Cast Vinyl Shell

(1) Field of the Invention

This invention relates to an apparatus and a method for molding hollow thin-walled articles from a gellable material such as vinyl plastisol.

Various vinyl plastisol compositions are known which can be used in various powdered vinyl molding processes. Typically, an open hollow mold is covered by dry plastisol and heat is applied to the mold surface and transferred to the dry plastisol to gel a layer of plastisol adjacent the mold surface. The thickness of the gelled layer depends upon the temperature to which the plastisol layer is subjected and the time the plastisol is maintained at that temperature. After the layer adjacent the mold surface is gelled, the ungelled plastisol is poured out of the mold. In such processes, certain mold configurations may have surfaces thereon in which deposited material is later disposed of as scrap or trim waste.

(2) Description of the Prior Art

Articles which are manufactured by vinyl cast on a heated mold often include salvage or trim areas which are not used in the final product and therefore do not require the thickness of the other finished areas in the product. Yet, when the entire mold surface is heated uniformly the entire finished article has approximately the same thickness even though some areas are trim or non-usable. There is known in the slush molding art the technique of varying the thickness by heating different areas of the mold to a higher degree to increase the thickness of the article in certain areas. Such a technique is exemplified in U.S. Pat. No. 2,588,571 granted to Sydney Porter on Mar. 11, 1952. That patent discloses the technique of slush molding a boot by utilization of infrared lamp heating and shielding the heating from certain portions of the mold to prevent the build-up of the plastisol thickness and to increase the thickness of the sole of the boot by increased heating.

Another apparatus for controlling waste build-up on a mold is formed in a mold having first and second groups of liquid passages disposed adjacent the mold surface for controlling the temperature over respective first and second areas of the mold surface as set forth in U.S. Pat. No. 4,217,325 granted to D. E. Colby on Aug. 12, 1980 with a common assignee. The first group of liquid passages are disposed adjacent the first area of the mold surface where it is desired to increase the thickness of the finished article whereas the second group of passages is disposed adjacent the second area of the mold surface where the material in the finished article is scrapped and/or will be trimmed and therefore the desired thickness is desirably less. Both the first and second groups of passages are supplied with liquid to maintain the temperature of the first and second areas of the mold surface at a non-gelling temperature as liquid plastisol is disposed over the mold surface to define a coating or layer. This very thin coating of plastisol is applied to be free of surface blemishes. Thereafter, additional liquid plastisol is provided for increasing the thickness only over the first area of the mold surface. To accomplish this, the first group of passages is supplied with a liquid at a temperature higher than the non-gelling temperature of the liquid in the second group of passages for heating the first area of the mold surface to a higher temperature than the second area so as to gel the liquid plastisol over the first area of the mold surface which is heated with the heat supplied by the liquid in the first group of passages. After the desired gelled thickness is attained, all passages are supplied with liquid at a temperature sufficient to heat the first and second areas of the mold to a cure temperature for curing all of the plastisol. Accordingly, the finished article will have a greater thickness over the first area which defines the finished area of the article whereas the thickness of the article over the second area of the mold surface will be much thinner and define the scrap or trim areas. Consequently, significant amounts of material are saved.

Still another method of controlling the build-up of gelled material on a mold surface is set forth in U.S. Ser. No. 673,810 filed Nov. 21, 1984 for Gas Conditioned Modular Slush Molding Machine. In the '810 case, the control of waste build-up is accomplished by selective control of air flow from a heated plenum through elongated tubes with nozzles that impinge heated air onto exposed surfaces of the mold.

U.S. Pat. No. 3,698,849 discloses an injection molding nozzle with an insulating gasket that enables the nozzle to remain seated on a sprue bush during the whole of a molding cycle.

The subject invention provides an improved method and apparatus to eliminate neck waste on an article made by a powdered vinyl molding process by use of a heated mold having an inlet neck through which powder is cast onto the mold surface. A powder box has an insulated pour spout which shields the inlet area of the mold so that waste neck material in the finished article to be scrapped or to be trimmed will be reduced. The mold is heated to a gelling temperature. Plastisol is distributed from the spout over the heated mold surface to produce a coating or layer of gelled material on the mold surface. A heat resistant liner on the spout covers the inlet neck so that no waste build-up occurs.

The U.S. Pat. No. 3,698,849 discussed above discloses a thermal gasket in an injection mold nozzle but there is no suggestion of utilizing a barrier of heat resistant material on a powder box pour spout located to shield a neck area of the mold for preventing material waste build-up on the mold and to eliminate neck scrap on the finished part. The above-mentioned U.S. Pat. No. 3,680,629 suggests the use of liquid passages adjacent the mold surface for controlling the temperature of the mold, however, there is no suggestion in that patent of the apparatus or method of the present invention. As alluded to above in regard to U.S. Pat. No. 2,588,571, the technique of varying the thickness by differential heating is known in the slush molding art, however, such is accomplished by infrared heating. There has been no recognition in the prior art of the advantages of utilizing a thermal barrier of heat resistant material on a powder box pour spout to prevent waste on an adjacent mold surface. Other processes using hot gas to mold plastic parts are set forth in U.S. Pat. Nos. 3,578,066; 3,590,435; 3,492,307; 3,416,913 and 3,388,429. However, none of the processes use the system of the present invention to reduce the waste neck area in dry vinyl casting process.

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic view of an assembly constructed in accordance with the subject invention;

FIG. 2 is an enlarged sectional view taken along line 2--2 of FIG. 1 looking in the direction of the arrows;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2 looking in the direction of the arrows; and

FIGS. 4-7 show various steps in the operation of the apparatus of FIGS. 1-3 .

FIG. 1 shows an assembly generally indicated at 10 and constructed in accordance with the subject invention. The assembly 10 includes a stationary pedestal generally indicated at 12 for rotatably supporting a mold support box generally indicated at 14. The pedestal 12 rotatably supports the mold support box 14 for rotation about the axis A--A. The mold support box 14 receives and supports a mold 16. The mold 16 has a mold surface 18 and includes a waste inlet neck 20.

The assembly 10 also includes a movable modular unit generally shown at 22 with a powder box 21 for supplying gellable material such as plastisol or powder material to the open mold 16. The unit 22 is supported on a plurality of rollers 24. The entire unit 22 and is normally disposed under the mold support box 14 when the unit 22 is in the operating position illustrated in FIG. 1 relative to the pedestal 12 for receiving plastisol emptied from the mold 16 as the mold 16 is rotated for dumping or emptying into the unit 22. As alluded to above, the mold 16 may be supplied with a different plastisol or the same plastisol of a different color merely by moving the modular unit 22 away from the mold and inserting or placing a different modular unit in position having a different plastisol.

The modular unit 22 includes a powdered plastisol supply for supplying plastisol to the mold surface 18 of the mold 16 and for retrieving plastisol emptied or dumped from the mold 16. The rollers 24 define a conveyance means for facilitating the movement of the unit 22 away from the pedestal 12 and the mold support box 14.

The mold 16 is heated by suitable means, not shown, so that the plastisol deposited thereon will gel.

The mold box, supported by rotary joints at each end, bears the electroform mold 16 in the same manner as in U.S. Pat. No. 4,217,325 and is designed to accommodate a variety of molds. Further, the gellable material can be in the form of a powder as set forth more specifically in U.S. Pat. No. 4,562,025, issued Dec. 31, 1985 for Mold Method and Apparatus for Multi-Color Plastic Shells.

The waste inlet neck 20 is defined by a pair of divergent walls 26, 28 arranged at an angle that accommodates a thermally insulated pour spout 30 on the modular unit 22. The pour spout is maintained at a non-gelling temperature below that required to gel any appreciable thickness of material thereon.

More particularly, the insulated pour spout 30 includes a pair of convergent walls 32, 34 that are dimensioned to cover the inside surfaces 36, 38 of each of the walls 26, 28 when the modular unit 22 is joined to the heated mold 16.

A liner gasket 40 of heat insulating material such as silicone or polytetra fluoroethylene covers the outside surfaces of the pour spout 30. The liner gasket 40 defines a sealing surface between the pour spout 30 and the neck 20.

The powder box 21 of the modular unit and the silicone liner gasket 40 are at room temperature when they are joined to the heated mold. Consequently, powder distributed through the mold will not gel on the waste inlet neck 20 of the mold. For purposes of this description, the mold surface 18 represents a finished polyvinyl cast product such as an automotive armrest, headrest or parts of similar construction. The elimination of gel material on the waste neck area of the heated mold reduces material usage and also reduces labor required to trim waste from the finished part. The saved material and labor for trim represent a considerable cost savings.

The process of the invention is set forth in FIGS. 4-7. FIG. 4 shows the mold 16 separated from the powder box 21 and with a finished vinyl part 42 released from the mold surface 18. The part 42 includes marginal edges 44, 46 that do not need to be trimmed.

At the start of the next process sequence, mold 16 is preheated and the powder box 21 is raised from the lowered position in FIG. 4 and is joined to the heated mold 16 at the pour spout 30 and waste neck 20, as shown in FIG. 5. The joined box 21 and mold 16 are then rotated on suitable trunnions 48 by suitable drive means 49 (FIG. 1) and inverted as shown in FIG. 6. This causes powder in the box 21 to be cast onto the mold surface 18. The preheated mold is maintained at a temperature in the range of 250.degree. F. to 290.degree. F. for gelling the gellable material over the mold surface 18.

In the illustrated arrangement, a perforated air fluidizer tube 50 is carried on the powder box 21. It has an inlet 52 connected to an air source 53 which will direct air flow through the perforations in tube 50 to assist in distributing the powder evenly across the mold surface 18. The insulated pour spout 30 will prevent the powder from gelling on the waste neck 20 of the mold 16 to reduce costs of material and trim.

Following the distribution of material, the powder box 21 and heated mold are inverted so that excess nongelled powder will be dumped into the powder box 21 (FIG. 7) for recycling in subsequent process cycles. The gelled material remains on the mold surface 18 and the mold is then reheated to a temperature in the range of 350.degree. F. to 400.degree. F. for curing the gelled material.