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Question What is a limitation in wrapping VRLA battery plates?

ANSWER: In prismatic VRLA construction, the surface quality and uniformity of the separator play a larger role than the tensile properties of the separator in limiting wrapping speed. The wrapping speeds can be limited by the plate stacking capabilities of the machine and alignment of the lugs in the group. Each wrapped plates ability to slide over another is influenced by the surface of the glass separator and which of the two separator surfaces is toward the plate. The coefficient of friction of the glass surfaces rubbing against each other determines the ease of slippage.  Among different separators, a 50% difference can be seen in coefficient of friction.

Adobe Photoshop ImageFigure 1. A coefficient of friction tester is used to determine the ability of two surfaces to slide over one another. +

A coefficient of friction test can provide values that would rate the separators resistance to sliding, which influences the aligning of plates. A lower coefficient of friction can help address proper plate movement. Most separators have two unique surfaces: a wire and felt surface. Generally, the wire surface of an AGM separator is smoother, has a lower coefficient of friction, and will provide for easier lug alignment. A 30% difference in coefficient of friction can exist between the wire and felt surfaces of the separator.

Adobe Photoshop ImageFigure 2. The resultant scuff or peel of a separator material is caused by a high coefficient of friction. +

Another issue may be the limitation of a separator in regards to scuffing. Figure 1 is a coefficient of friction tester and figure 2 demonstrates how this type of test equipment could detect separators that may scuff or peel.          BD