Glass - Back to the Future!

Presenting Author:
Fikret Hacizade

article posted 22 March 2016

Fikret Hacizade received MSc and PhD degrees in Quantum Electronics and Nonlinear Optics from Moscow State University, Moscow, USSR, in 1977 and 1982, respectively. He received the Prof. Degree in Laser Physics in Condensed Media from the USSR Academy of Sciences in 1992. Between 1973-1980 he worked at Moscow State University and between 1980-1991 in the Semiconductor Physics Research Institute of Baku State University (Baku, Azerbaijan, USSR). From 1991 to 2015 he worked at various institutes of TUBITAK (The Scientific and Technological Council of Turkey). His interests include optoelectronic control measurement devices, digital/optical signal and image processing, hyperspectral image analysis, high spectral and space spectroscopy systems. He is the author and co-author of more than 70 published papers and a number of international Patents. Most recently he has joined TLSE Ltd. where he leads optoelectronical projects for the glass industry.

A Validation Of Area Stress Measurements
in Float Glass Manufacturing

Fikret Hacizade* & Midiya Hacizade
TLSE Ltd, Istanbul, Turkey,

Excessive stress of float flat glass can cause cutting difficulties and reduced production yields. Glass manufacturers have used quantitative measurements of online area stress measurements (ASM) mainly for proper cooling of the ribbon in the annealing zone. In this article, it is proposed to locally heat the moving web upstream of the ASM position and run an analysis of the induced temporary compression according to the photoelastic reaction of the float glass for validation of the ASM device.

Any imbalance between the compressive stress at the surface and the tensile stress in the mid-plane will weaken the glass, often causing it to rupture unpredictably and dangerously. Area stress in the ribbon near the cutting station is a combination of permanent and temporary stress. On lines where there is no washing machine, the stress is made up of permanent area stress plus a significant amount of temporary area stress.

Fig. 1 demonstrates the Total Retardation, Hot Stress, Temperature and Thickness distribution on the float line, which is manufactured of 3.8 mm thickness flat glass. It is possible to observe the near periodical and opposite sign distribution of temperature and total optical retardation distributions. Downstream of the annealing zone there are no different contact points with the ribbon except the rollers of the conveyor. The surface of rollers absorbs the heat from the surface of the ribbon more effectively than air and makes it possible to detect some relative minimums of temperature profile due to the rollers. It is possible to detect some maximums of hot stress on the same places on the ribbon which correspond to minimums of temperature distribution. For example, we detect a ~1.6 degree difference and the corresponding compression total retardation peak is around 10 nm in a red elliptical position. The stress optical constant for float glass is 1.6 nm/degree/mm. Calculation of temporary retardation due to the local temperature difference is DR = 9,73 nm. The difference between calculated and measured retardation is within accuracy of amplitudes of temperature and the corresponding retardation peaks.

Local heating is an effective way for inducing temporary compression stress in the float glass and validates the properly working ASM. Additionally, we locally heat the moving glass for verification of the ASM measurements using an industrial hot air tool. Corresponding distributions are demonstrated in Fig. 2. Glass surface is heated continuously on a distance of 2m before measurement line. Retardation is calculated as DR = 35 nm and the correspondent retardation is 35 nm too.

On lines where the washing machine is in use, the total stress demonstrates permanent area stress and very little temporary stress. The temperature profile is practically flat and the ribbon is nearly isothermal, excluding edge effects. Validation of online ASM is more accurate on lines where washing machines are used.