Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
1999-07-20
2001-05-29
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S046500, C264S046800, C264S154000, C264S259000, C264S291000
Reexamination Certificate
active
06238604
ABSTRACT:
The present invention relates to a method for producing a composite tub consisting of at least one steel tub and at least one acrylic tub, which are firmly connected with each other, wherein in a first step a deep-drawn acrylic blank is inverted over a core.
A method for producing composite tubs of the above mentioned type is known from DE 195 44 426 C1, for example. In this known method an inner shell made of acrylic (acrylic blank) is connected with an outer shell made of steel, wherein a two-component plastic material is injected into the space between the two shells as a filler, so that after the latter has cured, a three-layered tub is created, having an outer layer of steel, which stabilizes the tub, an inner layer of acrylic, which represents the usable layer of the finished tub, and an intermediate layer created from the two-component liquid plastic material, which provides a satisfactory bond between the two other layers.
A disadvantage of this known method lies in that the outer steel skin must respectively be of identical shape with the acrylic shell to a large degree. Because of this, there is either a fixed limited number of composite tubs of different designs, or a large number of variously shaped steel blanks must be stored. This is naturally connected with increased expenses for the manufacturer, since the individual steel blanks also must be initially produced, which generally are made of sheet steel also in a deep-drawing process.
It is therefore the object of the present invention to create a method for producing composite tubs of the type mentioned at the outset which also permits changes in the shapes of the outer steel blank and the inner acrylic shell.
This object is attained by means of a method in accordance with the invention for producing composite tubs of the species mentioned at the outset, having the characterizing features of the main claim. The method in accordance with the invention is such that initially the deep-drawn acrylic blank is again inverted over the core. But thereafter, an outer mold shell is placed at a defined distance over this acrylic blank. The outer mold shell and the acrylic blank are sealed against each other, and a suitable reaction resin is injected into the space between the outer mold shell and the acrylic blank. After the reaction resin has cured, the outer mold shell can be removed. An intermediate product is obtained in this way which, on the one side, has the interior shape of the acrylic blank, which was the starting point, and on the other side has an outer layer as a coating made from the reaction resin, which stabilizes the acrylic layer. Thereafter it is possible to apply a steel blank of a shape which differs from that of the initial acrylic blank. The steel blank and the acrylic blank (intermediate product) are again sealed against each other. A space is left free between the steel blank and the intermediate product (acrylic blank with a coating), into which a polymer foam is injected. A composite tub, which can be unmolded, results after the polymer foam has been cross-linked. This composite tub is a product whose acrylic component which, when the tub is used, constitutes the inner skin and can have a shape different from that of the steel tub which, when the tub is used, constitutes the outer skin and is used as a stabilizing support.
Regarding the difference of the respective shapes, the distance between the acrylic blank and the steel blank is of course important. This distance, which is determined by the respective production techniques, can vary and can be up to approximately 50 mm or more, for example. As a rule, in molding the acrylic shell which determines the desired design of the end product, the designer can use the distance between the two shells to a large percentage, for example up to approximately 80%. Thus, an essential advantage of the method in accordance with the invention lies in that the same steel blank can be used for several acrylic blanks of designs which vary within defined limits.
Preferred further developments of the above mentioned method in accordance with the invention are hereafter described.
A plastic on the basis of methyl methacrylate or polyurethane or an epoxy or polyester is preferably used as the said reaction resin. A polyurethane foam system is preferably employed for the polymer foam.
It is possible to utilize a drain or overflow bore of the tub, or respectively the tub blanks, for injecting the polymer foam, or respectively the reaction resin, into the respective space. The drain and/or overflow bores are preferably cut into the finished tub following unmolding.
In accordance with a variation, the invention furthermore relates to the production of a composite tub comprising at least one support and at least one acrylic shell, which are firmly connected with each other, wherein in a first step a deep-drawn acrylic blank is inverted over a core, while the following steps are initially performed in the same way as in the method mentioned at the outset. Thus, subsequently an outer mold shell is placed at a distance over the acrylic blank. Then the outer mold shell and the acrylic blank are sealed against each other and a suitable reaction resin is injected into the space between the outer mold shell and the acrylic blank. After the reaction resin has cured, the outer mold blank is removed and then an acrylic blank is obtained, which is provided with a coating on the outside (underside).
However, in a change from the method mentioned at the outset, after removing the first outer mold shell a new outer mold shell of the exterior measurements of a tub support, which is a part of the tub, is placed instead of the steel blank. This method has the advantage that it makes it possible to produce a tub (preferably a bathtub or shower tub) which immediately following the production has an integrated tub support below the actual tub body, which is connected with the latter.
Preferably, a seal toward the newly placed outer mold shell is first provided after placement. Moreover, a polymer foam is preferably injected into the space between this tub and the new outer mold shell and, after it has been cross-linked, a finished tub with an integrated tub support is removed.
Again, the drain or/respectively overflow bores are preferably made in the finished tub.
It has been shown that within the scope of the present invention a foam is used as a polymer foam, which has a foam density within a range between approximately 40 kg and 60 kg, preferably in the range of approximately 50 kg. A polyurethane foam is also preferably used here as the polymer foam.
A method for producing such a composite tub with an integrated tub support is described. Furthermore, a composite tub with or without an integrated tub support is also a subject of the present invention, which was produced in accordance with the method of one of claims
1
to
12
. Further advantages of the present invention ensue from the following detailed description.
REFERENCES:
patent: 4289717 (1981-09-01), Bortz
patent: 4731213 (1988-03-01), Klepsch
patent: 4822652 (1989-04-01), Sempio et al.
patent: 4938825 (1990-07-01), MacDonald
patent: 5300531 (1994-04-01), Weaver
patent: 5534216 (1996-07-01), Kamiyama
patent: 43 38 963 (1995-05-01), None
patent: 195 44 426 (1997-04-01), None
patent: 904763 (1962-08-01), None
Franz Kaldewei GmbH & Co.
Kuhns Allan R.
Pauley Petersen Kinne & Fejer
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