Posted by Bengt Blomberg on November 23, 2000 at 14:55:01:
You are a bit confused about the HYAB technique. The so
called hyper absorbtion is caused by heating an about 15 cm
circle with about 200 degrees hot air, not a flame as you
mention. The heated spot is surrounded by a strong fast flow of
colder air. This is what causes the evaporation and the movement
of fluids inside the laminate. The effect is accelerated by also
alternating heating of the centre with periods of cooler air only.
However this as well as the Hotvac can not remove
the deeper enclosures of hydrolysis formed acid, The heat only changes
the colour to dark brown which shows clearly through the glass clear
laminate. Mostly one can find about 1 - 20 such enclosures / square meter
each of them affecting about 5 cm diameter circles of the laminate.
Like cancer tumors being cut out with a laser knife without hurting
the tissuer around it, we have to heat each such spot to the melting point
with a very tiny but hot little flame tip, also surrounded by a strong flow
of cold air, and let the air blow away all solid material
above the acid + the acid itself leaving the dry fibreglass mats dry and
disrupted only. As some of the blown away substances actually burns, this phase
of the treatment causes a very sticky smell.
Afterwards each such treated spot must be repaired by adding some extra fibre
glass and a special epoxy resin.
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