Where
the pump shaft enters the molten solder surface on many
wave soldering machines, a fine powdery dross is likely
to form. Unless taken off, this dross can build up into
a thick layer, which spreads through the bath.
A small
quantity of waxlets placed on the molten metal surface in
the pump, provide a cover to prevent dross formation.
After
initial re-melting at 250ºC (482ºF), this wax
gives off little noticeable fume and does not ignite or
evaporate. In time the fused layer thickens and turns brown.
It is not practical to use it at temperatures over 250ºC.