Heat Soak Ovens

EFCO manufactures Heat Soak Ovens (heat soak test ovens).

When toughened glass is put into controlled temperature environment of an EFCO Heat Soak Oven the unstable examples will break, thus reducing the risk of potential field breakages and ensuring that only the best glass is shipped.

Why does this happen?

For years it has been known that toughened glass can be subject to spontaneous disintegration.

Studies have shown that one cause is the inclusion in the glass of Nickel Sulphide NiS.

During the toughening process the glass is heated up to temperatures of 620°C. The NiS changes at 380°C from the beta phase which in turn changes in volume. When the glass is rapidly cooled during the air quench, the NiS does not have time to return to the beta phase and is therefore 'frozen' in an unstable form.

Over a period of time alpha phase will slowly convert to the beta phase with an increase in volume of about 2-4%. If the NiS is in the central tensile zone and the increase in size is big enough it will propagate a crack which will cause glass breakage.

At the rate of change from alpha - beta phase is temperature/time dependent, the hotter the glass the quicker the reaction takes place and the sooner breakage will occur (this is the philosophy of the Heat Soak Test).

When toughened glass is put into controlled temperature environment of an EFCO Heat Soak Oven the unstable examples will break, thus reducing the risk of potential field breakages.

Experience has shown that a thermal cycle which takes the glass uniformly to a temperature of 209°C, and then holds it there for a period of time followed by a controlled cool, provides glass suppliers and hence customers with a confidence that a better product has been supplied.

The length of the 'Soak' period determines the expected conversion rate.

More information about testing toughened glass:
      
Download datasheet
   

NEWS

Pilkington takes delivery
of heat soak oven

Furnace specialist EFCO Furnaces, Waterlooville, Hampshire, delivers a Heat Soak oven to the Pilkington Group.

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