SERRATED STRAPPING SEALS
Serrated strapping seals are essential for joining polyester strapping assuming the friction weld method is not used. In fact they are the only metal seal that can be safely used with this strapping material, although it should be noted that not all serrated seals perform to the same efficiency and therefore safety levels. Many copies of the original seal are now manufactured from varying grades of steel and with different serration patterns, and there is a considerable difference in their load bearing capability.
Apart from the physical construction of the seal the other major factor affecting seal performance is the tendency to use straps that are too thick such that the seal does not lock off correctly, a concept seldom understood by general packaging and strapping material distributors. The sketches below illustrate how straps that exceed the recommended max thickness de-rate the seal efficiency.
The seal is shown without it's serrations for clarity. The first three drawings show the normal closing procedure for a serrated seal and the important thing to note (Fig 3) is how the short right hand 'leg' of the seal is folded neatly folded over - flat - the long top horizontal leg. This will be an effective joint. Note what happens in the last sketch (Fig 4) however where the effect of exceeding the strapping tool manufacturers max strap thickness is exceeded. It can be seen that two thicker straps in effect foreshorten the length of the short seal leg making it very difficult for the action of the strapping tool to close it properly. Similarly, the top section of the seal is foreshortened adding to the incorrect closure of the seal.