Seal welding thin plastics sheet e.g. polyethylene - involves clamping the sheet between moving chain belts and welding by hot air blowing

摘要

A device for welding together two lapped strips of plastics sheet, esp. the edges of a packaging sheet, comprises two endless belts, running with one side of each belt adjacent to one side of the other. These two sides grip the thermoplastics sheet between them and advance at the same speed. Each belt consists of a series of rollers interconnected by links and they run so that the thermoplastics sheets are gripped between the links of the two belts only and are not in contact with the rollers. Air is blown onto the thermoplastics sheets from both sides simultaneously, thus forming a weld seam between the two sheets. As the sheets move forward with the belts, they then pass between two cold air blowing devices, also situated on both sides. Used esp. for forming a continuous seam weld at the lapped of a sheet folded around an article to be packed, so that the sheet forms a closed tube. By pressing the sheets together only with the links of the belts and not with the rollers, it is found that an effective seal weld can be produced with thin thermoplastics material, e.g., polyethylene, which does not possess a backing sheet.