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70 RBSM Separators 080801
Question: What is the standard density for RBSM (AGM) separators?

Answer: There is no standard density. Density of the separator - (Grammage of thickness - gsm/mm ) varies rather broadly. Densities can range from 110 to over 200 gsm/mm. The density is influenced by the fiber furnish. Based on the fibers used, an ultimate low density can be obtained for each former and fiber blend combination. Lower surface area tends to provide a loftier sheet, especially at very low loads. Fillers (particles, such as silica) will tend to densify the sheet based on classical packing theory. This variation in density has persisted since early development times. Even Dexter’s samples in the early 80’s had a range of density (at 0.7 psi -their standard pressure at the time, per Dexter’s data sheets). Dexter’s Grade showed a data sheet density of 138 gsm/mm for X8993 while X4225 showed a density of 215 gsm/mm. Recently, reported ALABC work by Dr. McGregor of CSIRO demonstrated the benefit of higher separator density with regards to battery cycle life and retained force amongst the plates. A typical range could be said to be in the 140 to 160 gsm/mm range. Higher density, although helpful for battery life, can negatively impact the assembly of the cell. Higher density will affect filling, stuffing the group into the case and even sealing the lids. Therefore, one must always consider the system when specifying a separator.
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