The heating phase is controlled within zones in the oven and the temperature controls ensure that the glass is always heated correctly to the right parameters by directing heated air from above, below and at the linear edges of the glass substrate.

 

The big advantage that Smartglass has, is that this full convection process is necessary to be able to temper the latest and most sophisticated high

performing low emissivity * glasses and solar control glasses, in fact all high performing soft coated products.

 

*(Low E or low emissivity glass, has a coating that increases its heat flow resistance.  A Smart-Glaze low E Insulated Glazing Unit allows light to pass through but reflects back radiant heat, keeping the window surface and the building a more comfortable temperature in both hot and cold weather.)

 

Many furnaces in the industry are unable to do this.  Our equipment thus ensures clarity and minimal distortion.

 

1. Fully Tempered Glass

 

Once the glass has been heated it is rapidly quenched or cooled by blasts of air delivered to the top and bottom surfaces of the glass, which then puts the surfaces into a state of compression.

 

The cooling (or chilling) phase is as crucial as the heating process to minimize distortion both physically and aesthetically.  This minimal distortion after tempering is a sign of a premium product to experienced building professionals.  

 

When one adds the very large sizes of glass we can temper, up to 6000 mm x 2500 mm, then one can see that Smartglass out performs all its competitors.

 

Smart- Temp tempered glass also has greater thermal resistance than Smart- Heat, heat strengthened or ordinary annealed glass.

 

 

Heat Strengthened Glass

The process used for manufacturing heat strengthened glass is similar to tempering but the cooling process is done at a slower rate, which results in lower compressive stress.   Thickness for thickness heat strengthened glass is approximately twice as strong as ordinary annealed glass.  However with the exception of its’ strength and breakage characteristics, heat strengthened glass retains the normal properties of annealed glass including chemical resistance, hardness, expansion and deflection.  It should be noted that unlike tempered glass, heat strengthened glass is not a safety glass.

 

 

Comparison between Fully Tempered Glass and Heat Strengthened Glass.

 

Characteristics	Fully Tempered Glass	Heat Strengthened Glass
Thicknesses	4 mm to 19 mm	4 mm to 10 mm
Maximum sizes	6000 x 2500 mm	On application
Minimum sizes	350 x 350 mm	350 x 350 mm
Mechanical strength	4 to 5 times stronger Than annealed glass	Twice as strong than annealed glass
Surface compressive tress in Mpa	80 to 150	25 to 52
Resistance to thermal Stress	More than 6 times that of annealed glass	More than twice that of annealed glass
When broken	Breaks into small relatively Harmless pieces	Breaks similar to   annealed glass and is Not a safety glass
Maximum  Operating Temperature	300 deg C	150 deg C

 

Heat soak test

Sometimes any fully tempered glass may break spontaneously due to inclusions in the raw glass mix, mostly Nickel Sulphide (NiS).  Spontaneous breakage in heat strengthened glass (see below) is virtually unknown.  Although the incidence of Nickel Sulphide inclusion is low in good quality float glass, it is not considered a float glass product defect by the manufacturer.  Smart-Temp tempered glass can be tested to destruction by a process known as heat soaking.

 

This test is carried out at customer’s request.  Although not an absolute guarantee, the majority of panes of glass with an inclusion will break during the test.  Our test is carried out in accordance with the European standard EN 14179.