GB2202486A - Improvements in vacuum formed plastics articles - Google Patents

Abstract

A peripheral reinforcing frame (12, to 22), for a vacuum formed plastics sheet, is located around the mould on which the hot soft sheet is draped, and the mould is then evacuated to conform the sheet to the mould contour, the sheet also being caused to at least partly embrace the frame, so as to locate the frame in position relative to the formed sheet. The frame preferably rests upon castellations around the mould periphery and, after the application of the vacuum, mould elements press the sheet on opposite sides of the reinforcement together, between the castellations, where opposed recesses (34,36) are formed and the sheet (30) completely embraces the frame (18). The frame may comprise tubular pieces (12,14,16,18,20) aligned end-to-end at loose spigot & socket joints (22), allowing telescopic sliding movement during shrinkage of the plastics sheet. The formed article may comprise a boat (10), or the chute (52, Fig 4) of a childs slide, to which is attached a ladder. The frame prevents distortions, which would otherwise arise when the article is removed from the mould. <IMAGE>

Description

IMPROVEMENTS TN VACUUM FORMED PLASTICS ARTICLES The technique of vacuum forming involves taking a suitably dimensioned sheet of a thermoplastics material, heating it to a temperature at which it is softens locating the soft hot sheet on a mould, and evacuating the mould cavity so as to cause the sheet to drap and conform to the mould contours.

When this well known technique is applied to large articles it is sometimes found difficult to maintain a desired shape after removal from the mould, because stresses set up by the shape changes cause distortion.

Whilst this may be controlled to some extent by allowing complete cooling and hardening of the material on the mould, this involves undesirably long mould occupancy and hence low output from a mould. Since the mould cost is a significantly large part of the total manufacturing cost, this tends to make the process uneconomic.

An alternative approach, especially where a particular structural stiffness or strength is required is to control the distortion by means of an added frame.

The frame may be for example steel tube or the like.

However. the attachment of the formed sheet to the frame can be time consuming and hence expensive. and any distortion occurring after separation from the mould and before attachment to the frame may create problems in correction. The object of the invention is to provide a solution to these difficulties.

According to the invention, a method of making an article comprising a reinforcing frame and a vacuum formed plastics moulding comprises locating the reinforcing frame on the mould, draping the plastics material over the mould and reinforcement and causing the plastics material to part encircle the reinforcement so as to fix the two together.

Preferably the frame is a steel tube which extends about the periphery of the mould and hence about the periphery of the sheet. The steel tube may be a continuous loop. Preferably the loop is made of a series of pieces located end to end connected by sliding spigot and socket joints which allow for dimensional changes during cooling of the sheet.

One example of an article for which the process of the present invention is particularly suitable is boats.

Another example is chute or slide portion of large playground toys. Examples of these will now be more particularly described with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a pram dingy Figures 2 and 3 are sections taken on the lines 2-2 and 3-3 of Figure 1 Figure 4 is a perspective view of a child's slide or chute.

Referring first to the boat shown in Figure 1, the hull comprises a one-piece vacuum moulding of a suitable plastics material. The forming is made in a mould having a cavity conforming to the desired external shape of the hull at 10, and the cavity face and also an external face of the mould around the rim of the cavity form a castellated upper edge.

Before placing the sheet on the mould, the steel reinforcing frame is assembled to form a continuous loop but with a number of spigot and socket joints, and the frame is placed to rest on the castellations around the periphery of the cavity. As seen in Figure 1, the loop frame comprises a first part 12 located so as to extend across the stern of the boat, a pair of like parts 14 16 each extending part way along the length of the boat at the gunnel, and a further pair of the tubular parts 18 20 also forming part of the gunnel and which together extend to the bow of the vessel. Each of the parts make a spigot and socket joint with a reinforcing tube 22, and it will be appreciated that with five such parts forming the loop, five sockets are required. However the number can be varied according to requirements.The ends of the tubes are spaced from one another in the sockets, in the original assembly so that as the draped material cools and contracts, the peripheral frame can accommodate and itself shrink in size.

Figures 2 and 3 show cross sections through the finished boat showing the way the plastics material 30 has been caused to drape around and embrace the tube at different points. Figure 3 shows in broken line the location of one of the mentioned mould castellation 32 and shows how the tubular frame was supported on that castellation during the moulding process.

In general, the plastics sheet is placed in a generally planar condition to rest on the tubular frame which in turn is supported by the plurality of castellations located around its periphery. As the mould cavity is evacuated, the plastics within the loop sinks to the mould wall to form the boat shape, and because -of the softness of the hot material it also drapes over the tubular rail. In a final operation, the material is displaced by further movable mould elements for separate pliers-like tools to create a series of recesses opening from the interior of the boat as at 34 Figure 1 and Figure 2 matched with complementary recesses 36 on the outside, each of these pairs of recesses 34 36 being located between two of the castellations, and causing the adjacent material to substantially completely encircle the tube as seen in Figure 2.At the intervening points, as seen in Figure 3, the material may be lightly indented as at 38. For neatness and to provide a rubbing strake, the material may be formed by an additional mould element into the generally radially outwardly projecting flange 40 with a finished bead 42, by a further mould element (not shown).

The manufacturing process thus far described may produce a virtually finished boat requiring merely the addition of the thwarts 44 placed in position and or possibly adhered in the required locations to rest upon an internal shoulder formed as part of the moulding step and indicated by the reference numeral 46.

Figures 4 shows a child's slide for use in a childrens playgound or the like and consisting of a ladder 50 and a chute 52. The chutes may be made by the same technique but in this case it is preferred to provide a smooth continuous channel section interior comprising faces 54 which are generally planar, and with indentations 54 between appropriate mould castellations to cause a peripheral reinforcing frame element to be made captive with the plastics material.

Claims (6)

1. A method of making an article comprising a reinforcing f frame and a vacuum formed plastics moulding comprises locating the reinforcing fram on the mould, draping the plastics material over the mould end reinforcement nj causing the plastics material to part encircle the reinforcement so as to fix two together.

2. A method as claimed in Claim 1 wherein the frame is 2 steel tube extending about the periphery of the forming mould.

3. A method as claimed in Claim 1 or Claim 2 wherein the frame forms a loop of a series of pieces located end-to-end and connected by sliding joints.

4. A method as claimed in any preceding claim wherein the plastics material is caused to substantially encircle the reinforcement at a plurality of spaced portions along the length of the reinforcement and to embrace the reinforcement less completely at intervening points.

5. A method of making a boat as claimed in Claim 1 and substantially as described with reference to Figures 1 to 3 of the accompanying drawing.

6. A nethud of making 2 chute or slide as claimed in Claim 1 and substantially as described with reference to igure 4 of the accompanying drawings.