A METHOD OF PRODUCING A TUBE OR CONTAINER BY WINDING A THERMOPLASTIC MATERIAL

Abstract: A tube or container is formed by winding a strip (16) of thermoplastic material onto the surface of a drum (10) or of the mandrel. The drum (10) is first covered with a sheet or sheets (14) of lining material, preferably of the same thermoplastic material as the strips (16). Furthermore, the drum (10) or mandrel is not heated, but the winding strips (16) are preheated or may even be the output of a plastics material extruder.

Description: A METHOD OF PRODUCING A TUBE OR CONTAINER BY WINDING A THERMOPLASTIC MATERIAL This invention relates to a method of making tubes and containers of helically wound thermoplastic material. It has previously been proposed to make tubes or containers by winding a band of thermoplastic material onto the heated surface of a metal drum or other mandrel. The thermoplastic material is itself heated until it is in the plastic state so that adjacent edges fuse together to produce an unbroken cylindrical container wall. In a modification to this method, it has been proposed to cover the metal drum or mandrel with a heat insulating material, such as a layer of silicone rubber, so as to prevent heat loss therefrom. This method produced satisfactory cylindrical containers but was costly owing to the amount of heat needed to maintain the metal drum at the required elevated temperature. Furthermore, the interior surface of a container produced in this way would often have helical surface imperfections owing to its method of production and require to be surface finished prior to use. The invention seeks to provide a method of producing tubes or containers improved in the above respects. According to the present invention there is provided a method of producing a tube or container by winding a thermoplastic material onto the surface of a drum or other mandrel characterised in that the drum is first covered with a sheet or sheets of lining material and in that the drum or mandrel is not heated. The sheet or sheets of lining material will bond to the helically wound band of thermoplastic material during formation of the tube or container and will form the inner surface in the finished product. Since the sheet material is smooth the inner surface of the finished container or tube will also be smooth and no surface finishing will be required. It has futhermore been found that using the lining sheet in accordance with the method of the invention it is unnecessary to heat the drum or mandrel and thus considerable energy is saved. The lining sheet should preferably be of a heat insulating material, for example a plastics material, and will preferably be of the same plastics material as the thermoplastic band. This prevents the metal drum or mandrel leading the heat away too quickly from the heated band of thermoplastic material. The use of a lining sheet also means that the drum or mandrel may be of a lighter construction than would otherwise be necessary. The thermoplastic material employed may be any of the materials employed previously with this type of container, and polyolefin materials such as polyethylene are preferred, especially high density polyethylene. The invention will be described further, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a section through a winding drum ilustrating the method of the invention; and Figure 2 is a partial longitudinal section corresponding to figure 1. Referring to the drawings, a metal winding drum 10 of a suitable metal such as steel or aluminium is provided and has an outer surface 12 onto which a sheet or sheets of a thermoplastic lining material 14 may be affixed. A strip of heated thermoplastic, for example polyethylene, material 16 is fed onto the drum 10 over the lining sheet 14 where it is wound helically (as can be seen better from figure 2) . The strip 16 is preheated, or may even be the output of a plastics material extruder. The adjacent edges of the helically wound strip 16 bond or weld to one another and the strip also bonds to the lining sheet 14. Once the drum 10 has been completely wound and the strip 16 has cooled sufficiently, the tube or container may be removed therefrom in the conventional manner by ensuring that the cylinder is slightly undersize and is held open to its nominal diameter by a wedge segment which is removed after production allowing the cylinder diameter to be reduced once again. If the desired product is a container, once the formed tube is removed from the drum or mandrel a base may be affixed thereto e.g. by a plastic welding. The containers produced in accordance with the invention have smooth internal surfaces, owing to the presence of the lining sheets 14, and require less energy in their production.

Claims: CLAIMS 1. A method of producing a tube or container by winding a thermoplastic material onto the surface of a drum or other mandrel characterising that the drum is first covered with a sheet or sheets of lining material and in that the drum or mandrel is not itself heated. 2. A method as claimed in claim 1 in which the thermoplastic material is preheated. 3. A method as claimed in either of claims 1 or 2 in which the thermoplastic material is the output of a plastics material extruder. 4. A method as claimed in any of claims 1 to 3 in which the sheet of lining material has a smooth inner surface. 5. A method as claimed in any of claims 1 to 4 in which the lining material is produced from the same thermoplastic material as the windings. 6. A method as claimed in any of claims 1 to 5 in which the thermoplastic material is a polyolefin material. 7. A method as claimed in claim 6 in which the polyolefin is high density polyethylene. 8. A method as claimed in any of claims 1 to 6 which after in which once the formed tube is removed from the drum or mandrel a base is affixed thereto by plastic moulding. 9. A method as claimed in any of claims 1 to 8 in which the drum or mandrel is slighty under size and is held open to its nominal diameter by a wedge segment which is removed after production allowing the diameter to remove once again and the finished article easily removed therefrom.

Inventors: QUINN SEAMUS, QUINN, SEAMUS
Applicants: CHEM RESIST PLASTICS FABRICATI, CHEM-RESIST PLASTICS FABRICATIONS LIMITED
Application year: 1991
Main classification: B65D3
IPC codes: B29C53