The Institute for Glass and Raw Materials Technology (IGR) outlines how it can help glass manufacturers analyse seeds and blisters during production.
The IGR is a global service provider for the glass industry, raw material producers, and food technology.
Its services support manufactures of hollow, flat, and specialty glass.
As a testing laboratory, the institute offers routine seed and blister content analyses for its customers.
Blisters and seeds are among the most common and costly defects in glass production.
The typical blister content analysis is performed using gas chromatography, mass spectroscopy and/or Raman spectroscopy.
It covers the gases H2, Ar, O2, N2, CO2, SO2, CO, CoS, H2S, CH4 as well as H2O.
In this context, it is particularly important that all gases, explicitly including the above-mentioned sulphur modifications, as well as the pressure, are analysed during the blister content analysis, as this is the only way to obtain a meaningful interpretation of the origin.
In addition to gas content analysis, the institute also uses microscopy to examine the inner surface (e.g. crystals or droplets) as well as the shape, size and location of the seeds or blisters, enabling it to provide tips on how to avoid these gas inclusions in the future.
If other abnormalities such as streaks or particles are found in the surrounding area of the blisters and seeds, it also carries out an SEM-EDX examination to obtain additional information about the cause of the blister formation.
The IGR interprets the results based on the macroscopic and microscopic examinations it has carried out, the results of the blister content determination and the information received from the client, such as melting tank and raw material parameters and cullet qualities.
This enables it to interpret the origin of the blisters formation so that it can develop and communicate suggestions on how to modify the melt to prevent blister formation in the future.
The institute can also analyse special blisters, known as vacuum blister (also called vacuoles), which are blisters without crystalline or gaseous content.
They occur when the glass cools too quickly during production.
These special blisters are not present during the forming process and only develop afterwards.
Physically and chemically dissolved gases in the glass have no way (high viscosity, low temperature, no time) to diffuse into this cavity.
These blisters can also no longer float up (viscosity > log 10^7.6).
The analyses revealed no crystals and no gas content, so they are empty.
Another special feature of the vacuoles is that they disappear immediately when the glass is reheated to a temperature of approximately 650 °C – 680 °C.
An IGR customer provided the institute with a video in which this process can be observed in detail (see below).
When watching the video, pay attention to the two bright spots on the left and right.
The first blister (left) disappears at 16 seconds, the second (right) is no longer visible at 28 seconds.
