Glass defects
Glass defects are defects in the finished product of glass manufacture . These can be bubbles, stones, streaks or cracks. Glass defects can render the product unusable or severely limit its use. Some products like optical glasses are very sensitive to glass defects.
The cause of the glass defects may lie
- in the raw material : impurities, unfavorable grain sizes; Errors in the disposal of old glass
- In the melt : incomplete melting, recrystallization, corrosion and flaking of the lining or the electrodes
- when standing still: reboil (aftergassing) due to strong temperature fluctuations, fluctuations in the redox state of the melt, incorrect fire setting or direct current flow in the glass bath
- During molding : contamination from mold lubrication, mold temperature that is too high or too low, incorrect machine setting
- During cooling : Stress cracks due to incorrect temperature profile in the cooling path or insufficient cooling path running time
- in post-processing : defective coating
The glass defect analysis tries to identify the cause of the respective defect in order to be able to act specifically on the cause.
In order to ensure the quality of the glass, extensive tests must be carried out regularly, including:
- Online control in the glassworks (optical checks of all individual glass products for dimensional accuracy, cracks, relics, contamination, etc.)
- daily or weekly chemical glass analysis with the ICP-OES to a. also monitor the heavy metals in the packaging glass (requirement of the packaging ordinance)
- Weekly or monthly Fe 2+ analysis and analysis of the redox state in order to assess the melting unit and the quality of the recycled glass grades used
- Daily voltage tests with 1st order red light under the microscope to reduce breakage problems
- If necessary, fracture analyzes with the SEM-EDX
literature
- H. Jebsen-Marwedel, R. Brückner (Hrsg.): Glass-technical manufacturing defects - Pathological exceptional states of the material glass and their elimination . 3. Edition. Springer, 1980.