GB2229667A - Petal mould and moulding process - Google Patents

Abstract

A mould made from flexible moulding material e.g. silicone rubber consists of a number of leaves or petals which are flexibly pivotable about a common base. The mould is particularly useful in the casting of thin walled fine detail objects where minimum air entrapment is required e.g. a model plaster building, and also facilitates the mould release of undercut article configurations. During mould filling with a liquid material, one or an opposed pair of mould sides (3) are sealingly engaged between an opposite pair of the mould sides (2) which are maintained at a constant separation distance and act as a seal against the sides (3), as at least one of them is progressively inwardly flexed towards a closed position during filling with the liquid, so that air can move towards the liquid surface and entrapment against the mould sides is avoided. Article release is effected by outward flexing of the mould walls. <IMAGE>

Description

TITLE: Petal Mould and Moulding Process.

INTRODUCTION: This invention relates to a petal or shell moulding process, and to a mould for use i- such a process.

When casting fine detail into objects there are usually problems associated with delicate features and undercuts.

Unless overcome these problems will result in air entrapment or breakage of the cast. The usual meth od of overcoming such problems is to "design them out". This usually results in lost definition and the rounding of a form to accomodate the casting process.

The following describes a mould which is particularly suitable for use with delicate shell like forms where a high degree of detail and tolerance is needed in a production situation. Solid forms may also be cast using this method. The example gives one idea of how this mould technology might be applied.

The mould described below allows air to escape easily whilst the mould is in use. It also enables the operator to physically remove air from the inside surface of the mould whilst casting is in progress. This might be done by brushing or using a related method.

In addition the invention allows the final cast to be released easily from the mould once it has cured, hardened etc.

The main advantages of using this type of mould are that - firstly the process lends itself to the reproduction of very fine detail whilst retaining a long mould life, i.e. mould stress and wear is minimalised.

- secondly the process can accomodate features which would normally be designed out, e.g. undercuts or fine detail etc.

- thirdly the mould design facilitates easy release of the cast from the mould. This means the petal mould process should be considered especially when thin delicate articles are to be cast.

The use of this type of mould would normally be associated with cold setting fluids such as plaster or resins but it may also be used with other casting materials.

The mould should preferably be made from one of the flexible moulding materials available as characterised by the family of silicon rubbers.

A specific embodiment of the invention will now be described by way of example with reference to drawings Fig. 1 to 5.

Figure 1 Shows a model building (cast in plaster). The building is shown upside down, i.e. the position in which it would be cast. Alongside is a small sketch of the finished cast from the front. Figures 2 to 5 show the detail of a mould suitable for the production of Figure 1.

Figure 2 Shows a general view of the basic mould with no additions.

Please find on the diagram Mould body 1. Side cheeks 2.

AAK and BB' refer to sections illustrated in Figure 4 and Figure 5 respectively.

Figure 3 Shows the mould set up prior to pouring. Side cheeks 2 are now supported by Side jaws 5. The Inner arms 3 are in an open position held in place by pressure through the Side cheeks. A Cradle 4 supports the mould before during and after use. The mould itself is only held in this cradle by a press fit.

The top arrows indicate the directions in which pressure is applied while casting is in progress. The Cross Hatched area 6 shows a Block which is inserted prior to casting in order to maintain the inner cavity shape. The block is removed prior to releasing the cast.

Figure 4 Shows section AA (see Fig 2). The mould is shown in an open postion as in Figure 3.

Figure 5 Shows section BB (see Fig 2). The mould is shown in a closed position as in the final position of the moulding process. The insert block is shown as a dotted area' The Final cavity space 7 is also seen clearly.

The rotation arrows show the arc travelled by the Inner arms 3 when moving from an open to a closed position, i.e.

Figure 4 position to Figure 5 position.

GENERAL DESCRIPTION, OPERATION: The invention essentially consists of a single unit of flexible oul ai n nateri l . This unit consists of preferably four flaps or leaves which flex outwards from one another ano have a common base, analogous to the petals of a flcwer.

Two of the sides are extended to form retaining cheeks between which the remaining two sides may move in a pincer movement. These inner sides are called the.

Inner Arms in this description. The retaining cheeks are at a constant width apart so that the Inner Arms maintain a constant seal as they close in towards one another. The Inner Arms can move from an open V section where the mould faces are upwards to a position where the faces are opposed to one another. The retaining cheeks have additional internal stiffening added during the manufacture of the mould. Perforated steel sheet can be used for this but this is only one of a range of suitable materials. The inclusion of stiffeners is not always necessary.

Direct pressure exterted via Jaws on the retaining cheeks ensures a seal is made between all sides of the mould.

In the example described by the drawings the fluid is poured into the mould in its open position, i.e. Inner Arms inclined outwards. The majority of any air within the mould whether entrapped or introduced will rise unimpeded to the surface. A major advantage of the mould being open is that air bubbles may be brushed from the mould face. The Inner Arms are slowly brought together and clamped into the final setting position.

It may not be necessary to use the mould in this way if there is little or no trouble with air entrapment.

The decision on whether inner arm movement is necessary will vary with the type of article which is being moulded and the material in which it is being cast.

When the material has set within the mould release is brought about by simply splitting the leaves from the cast. In the example shown the block insert would be withdrawn prior to release of the cast.

Note that although a rectangular example is shown the mould type may also be used in a number of situations where concave or convex shapes are reproduced.

Claims (1)

1. CLAIMS: 1. A mould made from flexible moulding material which

   consists of a number of leaves or petals which are joined at a common base.

   t. A mould as claimed in claim 1 where two of the opposing petals are parallel to one another and extend to form flat cheeks between which inner arms may move from an inclined to a closed position.

   3. A method of moulding employing a mould as claimed in any preceding claim.

   4. A method as claimed in claim 3 in which, while casting is in progress, at least one of the leaves or petals is moved inwardly from an initial outward position to a final position.

   5. A method as claimed in claim 4 in which a pair of opposite leaves or petals are moved inwardly from the initial outward position to a final position.

   6. A method as claimed in claim 4 or 5 in which movement of the or each petal comprises a pincer movement in which a root end of the petal remains stationary and the free end moves inwardly.

   7. A mould as claimed in any preceding claim where the principal form of seal between the individual leaves is by direct pressure through opposing cheeks.

   8. A method of moulding substantially as described herein with reference to Figures 1 - 5 of the accompanying drawing but with additional provisions as described in the text.