Is it necessary to choose full top and bottom force convection system for glass tempering furnace?

Is it necessary to choose top and bottom force convection system for glass tempering furnace?

Not necessary

Force convection system is mainly used to temper the coating glass, especially for procesing Low-e glass.because there is one coating layer for coating glass, and this coating layer is upper surface, so during being heating, the coating layer will reflect the heat. Thus the heating speed of upper is slower than that of bottom. So the glass will be bent upward. Then we need the force convection at the top oven to blow hot air onto the upper surface of glass to make the heating speed faster.

But for the bottom, you know, during the heating process of tempered glass, there is radiation heating from heating elements and conduction heating from ceramic rollers, and when glass is moving onto the ceramic roller which would give enough heating through conduction. So normally, we should reduce the heating temperature of bottom side to avoid the glass bent upward.

The disadvantage of bottom force convection system:

1. If the heating speed of bottom is too fast, the glass would bent upward, and there would be white haze at the middle of glass.

2. Lower force convection will increases the probability of thick glass broken inside heating oven

3. Lower force convection will increase the marks/pitting on the lower surface of the glass

4. The furnace wire is easier to ground

5. Glass broken piecess is not easy to be cleaned, and after long time, the air flow is uneven. The nozzle is easy to be blocked, and the thermocouple is too close to the glass

6. The machine cost will be higher

So now, after few years using for top/bottom force convection glass tempeirng furnace, most customers don’t choose this type, and only top force convection is enough.

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