A Mould for Moulding of a Thermosetting Substance.

Field of the invention:

The present invention relates to a mould for casting a hardenable substance within a space between at least two separable mould halves.

Technical background:

Mass production of precision cast parts of a hardenable substance, e.g. synthetic resin, is traditionally made using metal moulds, e.g. moulds made from aluminum or steel.

If the hardenable substance is concrete, corrosion problems may occur in the aluminum. Therefore, moulds made from steel are usually used in these conditions. A problem with this kind of mass production, is that the concrete needs a relatively long time for hardening, in order to reach sufficient strength, so that the moulded part can be removed from the mould and then cure, e.g. under supply of heat. On account of the long time for hardening, the number of moulds usually has to correspond to the daily output. If a product comprises several different separately made moulded details, the number of moulds thus has to be multiplied with the number of details. A steel mould is very expensive to manufacture. For this reason, the investments in moulds will be very high when a mass production of moulded concrete products is started.

Attempts have been made to produce moulds from a more inexpensive material, for mass production of concrete components. For example, it has been attempted to produce moulds from concrete with an inner surface of a plastics substance. However, those attempts have failed because the bond often is as good between the plastics substance and the moulded component, as between the plastics substance

and the concrete mould. This results in problems when separating the two mould halves from the moulded component, because unforeseeable tensile stresses occur in the moulded component and in the concrete mould. Therefore, it is difficult to maintain a low rate of cassation and simultaneously maintain a high production rate.

The technical problem:

One object of the present invention is therefore to provide a simple and cheap mould which does not present the above described disadvantages.

The solution:

This object is achieved according to the invention, because the inside of each mould acts as a support surface for an plastics insert which abuts said mould inside. Since the insert is a loose part, the separation of the mould halves from the moulded component is surprisingly facilitated.

According to one preferable embodiment of the invention, the insert consists of a heat formed plastics sheet. Such inserts can be mass produced at a very low cost.

Preferably, the moulds are made from a hardenable substance, e.g. concrete. These moulds can be produced at a very low cost.

In order to facilitate the handling of the mould halves, they can be provided with a reinforcing frame, e.g. made from metal beams.

Preferably, the moulds and the insertable inserts are provided with a profiled seal which forms a sealing in the joint between the moulds.

Briei description of the drawings:

One embodiment of the invention will now be described in more detail with reference to the accompanying drawing, in which Fig. 1 is a perspective view showing the two mould halves separated from each other, Fig. 2 correspondingly shows a free insert, and Fig. 3 is a section along the line the line III-III through the two separated mould halves.

Preferred embodiments of the invention:

In the drawing, two mould halves 10 and 11 are shown, each comprising a steel frame 12 manufactured from welded L- beams and a mould bed 13 placed within said frame.

A number of bolts 14 are welded to one of the frames 12, said olts being arranged to be received in a corresponding numbe of sleeves 15 which are welded to the other frame 12. nen the two mould halves 10, 11 have been moved togetxer, nuts which are not shown in the drawing can be entered upon the bolt ends and tightened, so that the mould halves are held together with a certain pretension.

Preferably, the mould beds 13 are manufactured from concrete which is cast between the beams of the steel frame and will be rigidly connected to the frame by adhesion. The connection can be made completely secure by suitable design of the frame, e.g. with across beams.

The inside of the mould is cast in such a way that it will be adapted to the form of the object which will be moulded. In this connection, consideration must be taken to an insert 16 (see Fig. 2) which shall be placed in each mould halve.

The insert 16 is manufactured from a thin sheet of plastics which preferable has been produced by heat forming, so that its inside exactly corresponds to the shape of the object which shall be cast in the mould. The heat forming of the sheet of plastics, which may have a thickness of 0,5 - 1 mm, is made in the conventional manner by heating the sheet of plastics to a suitable temperature and subsequently forming it by means of different air pressures on the two sides of the sheet, so that it is drawn towards a form face corresponding to the object to be moulded. Then when the sheet is cooled down to normal room temperature, it will maintain its given shape.

Fig. 3 shows how each of the two mould halves 10, 11 are provided with an insert 16 which has recesses and elevations 16a which are supported by corresponding recesses and elevations 13a in the mould beds 13.

In order to prevent mastic from forcing its way out between the two mould halves 10, 11, the mould bed and the insert 16 in the mould halve 11 has been provided with a protruding V-shaped lip 17, while the other mould halve 10 has been provided with a correspondingly shaped slot 18. At suitable places, these sealing means are broken by openings 19 enabling the supply of moulding mastic and evacuation of air.

When the moulding mastic has hardened sufficiently for the separation of the two mould halves, it will be simple to separate the two mould halves since the plastic insert 16 has no tendency to adhere either to inside of the mould or to the moulded object.

It has been verified that cassation caused by problems during separation of the mould halves almost will be negligible by means of the above described arrangement. It

is possible to use the inserts several times which can be desirable from the ecological viewpoint, but because the cost of each mould insert is very low, it is possible from the economical viewpoint to change inserts often or even for every new moulding.

The invention is not limited to the above described embodiment, but several modifications are possible within the scope of the accompanying claims. For example, the arrangement according to the invention can also be used for moulds where more than two mould halves are used. The steel frame 12 is not necessary for the invention, but when a frame is used, it may naturally differ very much from the described embodiment.