Once the glass enters the furnace, the heating speed is quite fast because of the large temperature difference between the glass and glass tempering furnace. With the decrease of the temperature difference between the glass in the chamber and the furnace, the heating speed will slow down. When the temperature difference between the inner layer and the outer layer of the glass tends to zero, the heat transfer in the furnace will considerably slow down.

- If the heating temperature of the tempering furnace is too high or the temperature of the glass in the furnace exceeds its softening point, the glass is easily deformed in the furnace, seriously affecting the surface quality of the tempered glass.

- On the contrary, if the heating temperature of the tempering furnace is too low and the temperature of the glass inner layer fails to reach its desired temperature within the set time to completely relieve residual internal stresses, it will affect the redistribution of the stresses after cooling and result in easy breakage in the quenching process. Besides, the fragmentation performance of the tempered glass will be poor and the tempered glass will shatter into larger particles when it breaks.