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Technical Bulletins

Porcelain busing development

There has recently been a change to the profile of porcelain bushings used on the CBI-electric: african cables Outdoor seating ends. This bulletin serves to clarify the need and the consequences of the change.

Tapered porcelain profiles require a blank of abnormal proportions. The tube inner diameter needs to be small enough for the upper ID and an outer diameter large enough for the bottom OD. These thick walled tubes have a large rejection rate due to cracking during the initial green drying process. If insufficient extra blanks are planned there is a great impact on delivery (failure can occur at week 10 of a 12 week delivery).

By introducing a parallel profile the (narrow wall blank) rejection rate during green drying has been significantly reduced from some 60% to less than 10%. The financial savings have however been off set by the increased volumes of Polybutene compound and the significantly larger brass upper metal.

Notwithstanding the changes detailed above, the leading dimensions of mating components have remained unchanged. In essence if tapered porcelain were to be replaced with a parallel one, the only consideration would be the extra Polybutene compound needed.

Interchange ability and more reliability porcelain lead times makes the change to parallel porcelain strategically beneficial.