Manufacture of two part mold

#The present invention relates to a mould part which is intended to be brought together with at least one other mould part, to form a mould cavity for shaping plastics articles and objects. The present invention also relates to a method in the manufacture of such a mould part, and to a method in the manufacture of shaped, plastics articles and objects while using said mould part.

#Such objects as the hulls of boats, cisterns, car-body components, and other similar objects are being made to an ever increasing extent from fibre-reinforced plastics materials, and particularly from polyester resin reinforced with glass-fibre. The normal method of manufacture is one in which the fibre-reinforcement and the plastics material are placed in layers on a mould, whereupon the plastics material is pressed into the fibre-reinforcement with the aid of a roller, or corresponding device for moistening the reinforcement throughout and for removing air inclusions. In an alternative method, plastics material containing chopped reinforcing fibres is injected, under high pressure, directly into the mould cavity, until a layer of the desired thickness is obtained.

#Both of these methods represent serious health hazards especially when using polyester resins which contain harmful styrenes, these styrenes being released during the moulding process, to mix with the air in the workshop. Attempts have been made to overcome this problem, by installing powerful ventilating systems. Among other things, this has proved to be relatively expensive, since in addition to the costs involved in the actual ventilating apparatus, heating costs are also increased. In addition to costs, such systems create irritating noise and raise the level of draughts in the workshop.

#FIG. 1 is a sectional view of a model and a female mould-section constructed thereupon.

#FIG. 2 is a sectional view of the resultant female mould-section with replaceable mould shell, turned through 180.degree..

#FIG. 3 is a sectional view of the female mould-section and a male mould-section built in said female section.

#With reference to the Figures, it is assumed that an elongate, substantially U-shaped shell is to be moulded from a reinforced plastics material. In this respect, there is shown in FIG. 1 a rigid model 1 having a surface whose shape conforms to the object being moulded. In accordance with the invention, a female mould-section adapted to the model is manufactured in the following manner. Firstly, a gel-coating is applied to the model 1, either with the aid of a brush or by spray. This layer will form the actual moulding surface of the female mould-section. Fibre-reinforced polyester is then applied to the gel-coating in a conventional manner. In the illustrated case, two layers 2, 3, each having a thickness of about 2 mm are applied, in order to obtain the desired thickness and rigidity of the ultimate mould shell. The polyester should be heat resistant, and able to withstand temperatures of at least 100.degree. C. In the illustrated embodiment, a thin layer 4 of polyester, having a thickness of about 0.5 mm, is applied to the outermost layer of layers 2, 3, for a reason hereinafter made apparent. The outer layer is rubbed down and any remaining cracks or crevices filled in, whereafter the surface is waxed and polished and the model, together with the applied layers, is placed on a plate 5, which serves to provide a parting plane and which is provided with walls 6.

#A mixture of resin and filler is then prepared, and a gel-coating is applied to the waxed layer 4, either by brush or by spray. A coupling layer of fine filler is optionally brushed onto the gel-coating. The cavity defined by the layer 4, the plate 5 and the walls 6 is then filled with a plastics mixture, which is packed hard and allowed to harden to form an extremely rigid support body 10. The plate 5, with walls 6, and the model 1 are then removed, the result being a female mould-section according to FIG. 2, having an extremely fine inner moulding surface comprising a replaceable mould shell.

#As schematically illustrated in FIG. 3, the female mould-section produced in accordance with the aforegoing can be used to manufacture a male mould-section which conforms to the female mould-section. In this respect, the steps taken are substantially the same as those previously described with reference to FIG. 1. In this case, however, there is first applied to the waxed moulding surface of the female mould one or more plastics layers 11 having a thickness corresponding to the desired thickness of the object to be formed. The layer 11 is rubbed down, and any remaining cracks or crevices filled in, whereafter the surface is waxed and polished. A gel-coating is then applied, to form the moulding surface of the male mould, to which surface there is applied, for example, two plastics layers 12, 13 each having a thickness of about 2 mm, to obtain the desired thickness of the mould shell. Applied to this layer is a further thin layer of plastics 14, having a thickness of about 0.5 mm. This layer is then rubbed down and any cracks or crevices filled in, whereafter the surface is waxed and polished and a gel-coating applied thereto. Walls 15 are arranged adjacent the support part of the female mould, and the female mould and the space between said walls are filled with a filler which contains a hardening agent. Optionally, a coupling layer of fine filler is first brushed onto the gel-coating.