Technical Field

This invention relates in general to extrusion blow processing, and more particularly to a process for creating internal structures within blow extruded products. Background Art

It is often desired to create internal structures within blow extruded plastic products. For example, plastic vehicle fuel tanks often require a fuel reservoir in the form of a circular ridge projecting from the inside wall of the tank for accommodating a fuel pump. Also, baffle walls are sometimes required to ^' prevent excess sloshing of fuel within the fuel tank. Prior art techniques for creating such internal structures involve creating a plastic mould with such structures embossed on the surface. Thus, upon blow extrusion of a parison plastic tube in accordance with such prior art techniques, the tube is expanded against the mould such that the required structure (i.e. reservoir walls, baffle walls, etc.) is formed. However, since the entire wall of the plastic product is moulded to the internal structure shape, a specially machined or adapted mould is required to form the structure resulting in significant waste in volume. Also, it has been discovered that plastic products manufactured in accordance with such prior art processes are subject to increased probability of failing required Government flame tests due to resulting insufficient product wall thickness to sustain such tests. Disclosure of the Invention

According to the present invention, a process is provided for creating internal structures within blow extruded products while maintaining the outer surface

flush, thereby overcoming the prior art disadvantages of poor flame test performance and excess wasted volume.

In accordance with an aspect of the present invention, there is provided a method for creating a blow moulded product comprising the steps of extruding a parison tube (13) into a cavity formed between opposite halves of a mould (15) , pinching off a topmost portion of said parison via crimping apparatus (17 and 19), admitting high pressure compressed gas into the inner portion of said parison tube via a blow pin (14) for inflating the tube against said opposite halves of said mould thereby creating said blow moulded product, the improvement comprising the step of securing a frame" (1) to an inside wall of at least one of said opposite halves of said mould, said frame being provided with one or more apertures through which said parison tube passes responsive to inflating of said parison tube, such that said parison forms around and encapsulates said frame to form an internal structure of said blow moulded product. Brief Description of the Drawings

Figure 1 is a perspective view of a frame for implementing the process of the present invention;

Figure 2 is a cross-sectional view of a blow moulding machine and the frame of Figure 1 implementing the process of the present invention;

Figure 3 is an enlarged cross-sectional view of the frame within the machine of Figure 2 during moulding; and

Figures 4 and 5 are perspective views of injected moulded parts substituting for the frame in accordance with alternative embodiments of the invention. Best Mode For Carrying Out the Invention

Turning to Figure l, a frame 1 is shown comprising a pair of parallel loops 3 and 5 and a

plurality of connecting foot members 7 extending between the loops 3 and 5.

Turning to Figure 2, the frame 1 is shown inserted into the mould 15 of a blow extrusion moulding machine by means of securing the foot members 7 into the wall of the mould 15, although other means for securing the frame 1 thereto may be provided.

In operation, a parison 13 is extruded from the accumulator head 11 of the apparatus into the cavity formed by both halves of the mould 15. The parison 13 is pinched off at top and bottom portions via crimping apparatus 17 and 19. High pressure compressed gas is admitted into the inner portion of tube 13 via blow" pin or needle 14 for inflating the tube 13 against the walls of mould 15 and consequently also against the wire frame 1.

As shown in Figure 3, the plastic 13 bends or forms around the frame 1 thereby completely encapsulating the frame 1 within the parison 13. Finally, the mould 15 is opened and the final plastic product is removed. Any excess material (i.e. flash) 7 is then snapped or cut off leaving a smooth outer surface.

Thus, in accordance with the present invention, internal structures such as walls, reservoirs, etc. may be created without the requirement of specially machined mould walls. The final product includes all necessary structures internally thereof yet exhibits a smooth outer surface, resulting in substantial increase in container volume. In addition, superior performance is achieved in flame safety testing over prior art techniques, due to uniform wall thickness.

Other embodiments and variations of this invention are contemplated.

For example, instead of using a wire frame as shown in Figure 1, other internal designs may be utilized as shown in Figures 4 and 5 for creating internal structures within blow extruded products. Figure 4 shows a plastic injection molded part

21 having windows 23 disposed within cylindrical portion 24 which projects from an annular base portion 26. The plastic 13 bends or forms around the windows 23 as discussed with reference to Figure 3, thereby completely encapsulating the part 21 within the plastic parison tube for forming a fuel reservoir as an internal structure within a fuel tank fabricated from the plastic tube 13. The base portion 26 may be removably secured to the inside wall of mould 15 using one of a number of well known techniques (e.g. provision of a vacuum at the surface of the wall to thereby retain the base portion 26) .

Figure 5 shows a further plastic injection molded part 25 having a U-shaped portion 28 defining an aperture 27 around which the blow extruded plastic effectively bends or forms for completely encapsulating the part 25 within the parison tube 13, for creating an internal baffle structure. The U-shaped portion 28 projects from a generally rectangular base 30 which may be removably secured to the inside wall of the mould 15. The internal structure forming parts illustrated in Figures 1, 4, and 5 are representative of the varieties of designs contemplated. However, numerous other such designs are possible for creating internal structures.

All such embodiments and variations are believed to be within the sphere and scope of the present invention as defined by the claims appended hereto.