GB2137133A

GB2137133A - Moulding of Plastic Articles

Info

Publication number: GB2137133A
Application number: GB08308815A
Authority: GB
Inventors: Wolfgang Ernst Schedel
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-03-30
Filing date: 1983-03-30
Publication date: 1984-10-03
Also published as: GB2137133B

Abstract

This invention relates to a method of and apparatus for moulding, from an expandable plastics material such as polystyrene beads, an elongate article which has a length greater than the length of the mould. The method includes the steps of introducing the unexpanded plastic material into a mould (10), expanding the material in the mould in such a manner that the material at one article is not fully expanded, moving the article along the mould through an opening in its end, introducing fresh material into the mould to be in contact with the partially expanded material at one end of the article and fully expanding and bonding the fresh and partially expanded material in the contact zone between the two. The apparatus includes a mould (10), means (18) for introducing the unexpanded plastic material into the mould and means (12) for expanding the material in the mould (10) with the material expanding means (12) being adapted only partially to expand the material at one of the ends of the mould (10). <IMAGE>

Description

SPECIFICATION Moulding of Plastic Articles Field of the Invention This invention relates to a method of and apparatus for continuously moulding elongate articles from an expandable plastics material such as polystyrene or the like.

Background to the Invention An article which is moulded from polystyrene beads cannot be welded to another by means of steam as the steam will cause the fully expanded and welded beads, and so the portions of the articles exposed to the steam, to collapse to about two thirds of their fully expanded volume.

Object of the Invention It is the object of this invention to provide a method of and apparatus for welding expandable plastics material which will overcome the above problem.

Summary of the Invention A method of moulding an elongate article from expandable plastics material according to the invention includes the steps of introducing the plastics material into a mould, expanding the material in the mould in such a manner that the material at one end of the article is not fully expanded, introducing fresh material into the mould to be in contact with the partially expanded material at the one end of the article and fully expanding the fresh and partially expanded material in the contact zone.

The plastics material may be polystyrene in bead form.

Apparatus for moulding elongate articles from an expandable plastics material according to the invention includes a mould, means for introducing the material in an unexpanded state into the mould and means for expanding the material in the mould with the material expanding means being adapted only partially to expand the material at one end of the mould.

In one form of the invention the mould is open ended and the apparatus includes means for moving the article being moulded through the mould as it is being progressively moulded.

Brief Description of the Drawings An embodiment of the invention is now described by way of example with reference to the drawing which is a schematic side elevation of the moulding apparatus of the invention.

Detailed Description of the Invention The apparatus of the invention is shown in the drawing to consist of an elongate open ended mould 10, a steam jacket 12 which surrounds the mould, a slide gate 14 and a pusher 16.

The mould 10 has a cavity shape which is of constant cross-section over the length of the mould in a direction normal to the axis of the mould. Within the steam jacket 12 the mould is perforated by conventional steam ports which are evenly spaced over its length with the important exception of the ports at the left hand end of the jacketed mould which are spaced further apart than the remaining ports or may be omitted altogether. The mould includes an inlet port 18 through which polystyrene beads are fed into the mould.

In use, the left hand side of the mould is closed by the slide gate 14. Polystyrene moulding beads are fed into the now closed mould through the port 18 and steam is introduced into the jacket 12 through a port 20 through which air, displaced from the mould by the beads, is initially expelled.

The beads in the mould are expanded in the mould and are welded by the steam in the conventional manner. However, the shortage of ports on the left hand side of the mould starves the beads at this end of the mould of steam and so retards their expansion and welding relatively to those in the remaining portion of the mould.

After a short cure time the gate 14 is removed from the mould and the pusher 16 is activated to move the incomplete article to the left in the mould until the incomplete end of the article is well clear of the inlet port 18 to the left in the drawing. The pusher is then retracted to the position illustrated in the drawing. The mould is again charged with beads which are steamed as described above again leaving the beads at the right hand end of the mould partially welded to each other.

The partially welded beads at the right hand end of the previously moulded portion of the article are, with the second steam application, fully expanded and bond with the fresh beads in the mould during the second steaming operation.

In the meantime, the leading portion of the article is cooled and so cured in the mould to left of the gate 14. The process is repeated until the article being moulded has reached the required length.

In an example of the invention, the cavity of the mould 10 is substantially U-shaped in crosssection with a cross-sectional area of approximately 4,364 mm2. The spacing between the mould ports is 25 mm with about 350 mm of the right hand end of the mould having no ports at all. The polystyrene beads used in the process are block or conventional moulding beads which have a density of between 12 and 80 grams per litre.

The beads in the mould are steamed at a pressure of about 0,5 bar at 1 00C for approximately ten seconds during each moulding operation of the process. The partially moulded article is allowed to cure for about twenty five seconds before being moved by the pusher 16 to the left in the drawing and the commencement of the second moulding operation.

1. A method of moulding an elongate article from expandable plastics material including the steps of introducing the plastics material into a mould, expanding the material in the mould in such a manner that the material at one end of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Moulding of Plastic Articles Field of the Invention This invention relates to a method of and apparatus for continuously moulding elongate articles from an expandable plastics material such as polystyrene or the like. Background to the Invention An article which is moulded from polystyrene beads cannot be welded to another by means of steam as the steam will cause the fully expanded and welded beads, and so the portions of the articles exposed to the steam, to collapse to about two thirds of their fully expanded volume. Object of the Invention It is the object of this invention to provide a method of and apparatus for welding expandable plastics material which will overcome the above problem. Summary of the Invention A method of moulding an elongate article from expandable plastics material according to the invention includes the steps of introducing the plastics material into a mould, expanding the material in the mould in such a manner that the material at one end of the article is not fully expanded, introducing fresh material into the mould to be in contact with the partially expanded material at the one end of the article and fully expanding the fresh and partially expanded material in the contact zone. The plastics material may be polystyrene in bead form. Apparatus for moulding elongate articles from an expandable plastics material according to the invention includes a mould, means for introducing the material in an unexpanded state into the mould and means for expanding the material in the mould with the material expanding means being adapted only partially to expand the material at one end of the mould. In one form of the invention the mould is open ended and the apparatus includes means for moving the article being moulded through the mould as it is being progressively moulded. Brief Description of the Drawings An embodiment of the invention is now described by way of example with reference to the drawing which is a schematic side elevation of the moulding apparatus of the invention. Detailed Description of the Invention The apparatus of the invention is shown in the drawing to consist of an elongate open ended mould 10, a steam jacket 12 which surrounds the mould, a slide gate 14 and a pusher 16. The mould 10 has a cavity shape which is of constant cross-section over the length of the mould in a direction normal to the axis of the mould. Within the steam jacket 12 the mould is perforated by conventional steam ports which are evenly spaced over its length with the important exception of the ports at the left hand end of the jacketed mould which are spaced further apart than the remaining ports or may be omitted altogether. The mould includes an inlet port 18 through which polystyrene beads are fed into the mould. In use, the left hand side of the mould is closed by the slide gate 14. Polystyrene moulding beads are fed into the now closed mould through the port 18 and steam is introduced into the jacket 12 through a port 20 through which air, displaced from the mould by the beads, is initially expelled. The beads in the mould are expanded in the mould and are welded by the steam in the conventional manner. However, the shortage of ports on the left hand side of the mould starves the beads at this end of the mould of steam and so retards their expansion and welding relatively to those in the remaining portion of the mould. After a short cure time the gate 14 is removed from the mould and the pusher 16 is activated to move the incomplete article to the left in the mould until the incomplete end of the article is well clear of the inlet port 18 to the left in the drawing. The pusher is then retracted to the position illustrated in the drawing. The mould is again charged with beads which are steamed as described above again leaving the beads at the right hand end of the mould partially welded to each other. The partially welded beads at the right hand end of the previously moulded portion of the article are, with the second steam application, fully expanded and bond with the fresh beads in the mould during the second steaming operation. In the meantime, the leading portion of the article is cooled and so cured in the mould to left of the gate 14. The process is repeated until the article being moulded has reached the required length. In an example of the invention, the cavity of the mould 10 is substantially U-shaped in crosssection with a cross-sectional area of approximately 4,364 mm2. The spacing between the mould ports is 25 mm with about 350 mm of the right hand end of the mould having no ports at all. The polystyrene beads used in the process are block or conventional moulding beads which have a density of between 12 and 80 grams per litre. The beads in the mould are steamed at a pressure of about 0,5 bar at 1 00C for approximately ten seconds during each moulding operation of the process. The partially moulded article is allowed to cure for about twenty five seconds before being moved by the pusher 16 to the left in the drawing and the commencement of the second moulding operation. CLAIMS

1. A method of moulding an elongate article from expandable plastics material including the steps of introducing the plastics material into a mould, expanding the material in the mould in such a manner that the material at one end of the article is not fully expanded, introducing fresh material into the mould to be in contact with the partially expanded material at the one end of the article and fully expanding the fresh and partially expanded material in the contact zone.

2. A method as claimed in Claim 1 in which the plastics material is polystyrene in the form of moulding beads which, when the beads at one end of the mould are not fully expanded, they are also not fully welded and when fully expanded are fully welded.

3. Apparatus for moulding elongate articles from an expandable plastics material including a mould, means for introducing the plastics material into the mould and means for expanding the material in the mould with the material expanding means being adapted only partially to expand the material at one of the ends of the mould.

4. Apparatus as claimed in Claim 3 in which the material to be moulted is polystyrene in bead form and the means for expanding and welding the beads in the mould is a steam jacket which surrounds the mould over a substantial portion of its length and ports in the wall of the mould through which steam may enter the mould from the jacket.

5. Apparatus as claimed in Claim 4 in which the end of the mould at which the beads are to be partially expanded and welded contains fewer ports than the remaining portion of the mould.

6. Apparatus as claimed in Claim 4 in which the end of the mould at which the beads are to be partially expanded and welded has no ports.

7. Apparatus as claimed in Claim 6 in which the unported length of the mould is between 300 and 400 mm in length.

8. Apparatus as claimed in any one of Claims 3 to 7 in which the end of the mould remote from the end at which the material is to be partially expanded is open and the apparatus includes means for moving the article through the open end of the mould as the article is being progressively moulded.

9. Apparatus as claimed in Claim 8 including a gate adapted to open and close the open end of the mould.

10. Apparatus as claimed in either one of Claims 8 or 9 including a movable pusher which is located at the end of the mould opposite the open end for moving the article through the mould as it is being progressively moulded.

11. A method of moulding an elongate article from expandable plastics material substantially as herein described.

12. Apparatus for moulding elongate articles from expandable plastics material substantially as herein described with reference to the drawing.