Tubing Glass is formed by a continuous draw process using either the Danner or Vello processes to achieve the correct diameter and thickness. The glass is drawn over a line of support rollers by a drawing machine.
Blow and Blow Process - compressed air is used to form the gob into a parison, which establishes the neck finish and gives the gob a uniform shape. The parison is then flipped to the other side of the machine, and air is used to blow it into its desired shape.
Press and Blow Process-
a plunger is inserted first, air then follows to form the gob into a parison.
At one point this process was typically used for wide mouth containers, but with the addition of a Vacuum Assist Process, it can now be utilized for narrow mouth applications as well.
Strength and distribution is at its best in this method of glass formation and has allowed manufacturers to “lightweight” common items such as beer bottles to conserve energy.
- no matter the process, once
the blown glass containers are formed, the containers are loaded into an Annealing Lehr, where their temperature is brought back up to approximately 1500° F, then reduced gradually to below 900°
This reheating and slow cooling eliminates the stress in the containers. Without this step, the glass would easily shatter.
Surface Treatment - external treatment is applied to prevent abrading, which makes the glass more prone to breakage. The coating (usually a polyethylene or tin oxide based mixture) is sprayed on and reacts on the surface of the glass to form a tin oxide coating. This coating prevents the bottles from sticking to one another to reduce breakage.
Tin oxide coating is applied as a hot end treatment. For cold end treatment, the temperature of the containers is reduced to between 225 and 275° F before application. This coating can be washed off. Hot End treatment is applied before the annealing process. Treatment applied in this fashion actually reacts to the glass, and cannot be washed off.
Internal Treatment - Internal Fluorination Treatment (IFT) is the process that makes Type III glass into Type II glass and is applied to the glass to prevent bloom.
Quality Inspections - Hot End Quality Inspection includes measuring bottle weight and checking bottle dimensions with go no-go gauges. After leaving the cold end of the lehr, bottles then pass through electronic inspection machines that automatically detect faults. These include, but are not limited to: wall thickness inspection, damage detection, dimensional analysis, sealing surface inspection, side wall scanning and base scanning.
To learn more about Lab Glass Defects & How to Inspect Glass Packaging, please contact us to read more and download a reference guide to help determine whether or not you need to be concerned with a defect.