Before starting work on site (morning and afternoon) and whenever there has been a change in the weather conditions, the welding parameters have to be verified and adjusted accordingly by carrying out a welding test. This is a site test and samples are torn by hand in the absence of a calibrated peel tester in the lab.
Width of the sample:
- Welding machine >50 mm
- Manual Hot air welders >20 mm
The requirement for a good weld is that the peel resistance / shear resistance is greater than the inter-laminar adhesion between the top and bottom PVC layers.
The peel test (by hand) shall not be carried out before the sample has cooled down to ambient temperature. Prior to performing the peel test, cut the sample material into strips 20 mm wide. The samples shall be torn by hand in lengthwise and crosswise direction respectively. When there is a delamination of either the top or bottom sheet the requirement is fulfilled and the welding parameters are set correctly.
The delamination means a controlled destruction of the product.
When the seam peels off without a delamination of the membrane layers, it is indicated that the welding parameters were insufficient. A visual check can give a lead to whether the air temperature was too low
Welds - checking of seams
Checking the seams is a compulsory action at the end of any area of work. The welded seams have to cool down to ambient temperature.
Tool: Seam probe. The tool shall slide along the seam with little pressure continuously. When a deficient weld is detected, it should be immediately visibly marked and repaired as soon as possible. Always use a patch of 100 x 100mm minimum with rounded edges. When the deficiencies are “long” cut the patch to the size of the problem zone plus a 50 mm perimeter overlap. Circular patches shall have a diameter of 100 mm min.
Never use liquid PVC to repair poor welds.
Wrinkles, capillaries and fish-mouths are to be avoided. When these deficiencies occur they shall be repaired immediately.