How to Use a Glass Annealing Temperature Tester Correctly

During glass forming, rapid temperature changes create temperature gradients between the inner and outer layers. The shape and thickness of the product and the degree of cooling can also create irregular thermal stresses. These stresses reduce mechanical strength and thermal stability and can affect optical uniformity. If stress exceeds the product’s strength limit, the glass may fracture spontaneously; non-uniform thermal stress is therefore a serious defect in glass products.

Annealing is a heat-treatment process that removes or reduces residual thermal stress in glass to an acceptable level. Except for glass fibers and small, thin-walled hollow products, nearly all glass products require annealing. A glass annealing temperature tester detects the annealing point and strain point and is used primarily for quality control in glass production.

Operating procedure

Preheat the equipment: Set the tubular resistance furnace to the required temperature, usually up to a maximum of 1,200 °C, and allow the high-purity corundum furnace tube to heat uniformly.

Place the specimen: Position the glass specimen at the center of the furnace’s uniform-temperature zone so that it is heated evenly.

Heat synchronously: Use the controller’s programmed curve and record the relationship between temperature and stress in real time.

Collect data: The wireless transmission system records temperature data every 2 s and generates a complete temperature–stress curve.

Precautions

Check that the instrument is level before testing. Otherwise, the heated glass fiber may adhere to the furnace and cause the test to fail. Pass the specimen fiber through the small hole in the fixture and suspend it freely at the center of the furnace; make sure it does not touch the furnace wall. Set the tubular electric furnace to heat at (5 ± 1) °C/min.