Influence of storage conditions of PVC rooftop sheets on the hot air welding process

Abstract

One of the common welding methods for polymer rooftop sheets is the overlap welding by hot air. For this method two rooftop sheets are put over each other with a certain overlapping part and then a hot air fan, followed by a pressure role is lead through the overlap. The surfaces of the sheets are melted and the pressure of the role bonds them together. This welding method depends on some different parameters to achieve a good welding quality. The main parameters are the welding temperature, the welding speed and the pressure applied to the rooftop sheets. However, as the sheets are used to cover roofs outside, there are a lot of other influences on the weldability of the sheets and the quality of the weld itself. For example, the ambient temperature during the welding process, the intensity of the sun or the humidity of the air. Another influence on which this work is focused, is the effect of the storage temperatures of rooftop sheets. There is no common guideline how storing temperatures effect the welding as producers of rooftop sheets usually only recommend a dry storage. To analyze and characterize this effect, a common PVC rooftop sheet is stored under different temperatures and welded directly after the temperature treatment. The welded samples are tested according to the DIN EN 12317-2 to determine the shear resistance of the weld as it is an important mechanical property and a good indicator for the quality of the weld.