ISO 4790:1992 pdf download.Glass-to-glass sealings - Determination of stresses
I Scope
ISO 4790:1992 pdf download describes the test method for determining the stresses which may occur after the sealing of two glasses by means of stress birefringence.
2 Normative references
The following standards contain provisions which, through reference In this text, constitute provisions of this International Standard. At the time of pubUcation, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 10345-11992, Glass — Determination of stress- optical coefficient — Part 1: Tensile test.
ISO 10345-2:1992, Glass — Determination of stress- optical coefficient — Part 2: Bending test
FEPA-Standard 43-GB-1984,1 Standard for coated abrasive grains of fused alumina and silicon carbide.
3 PrincIple
If two glasses are sealed together, stresses can persist in them after cooling. The value of these stresses depends on the differences in the thermal, elastic and viscous properties of the glasses.
5.2 CondItion of glass pieces
The glass pieces shall be free of strlae, gaseous and solid Inclusions In the vicinity or the surfaces to be sealed.
The surfaces of the glass pieces to be sealed shall be flat, with a roughness less than that achieved by polishing with an abrasive of particle size P 240 according to FEPA-Standard 43-GB.
5.3 PreparatIon of the test specimen
5.3.1 Seal two glass pieces completely together. on the surfaces prepared for sealing, to form one test specimen (see figure 1). During this procedure, any deformation of the flat sealed surface shall be avoided.
5.3.2 Since the result of the measurement can be affected by the cooling rate applied to the test specimen in the visco-elastic range of the glasses, the test specimen shall be cooled at a rate or (2 ± 0,2) °C per mm, within the following temperature range:
— the upper limit of temperature range is determined by the temperature at which the glass of the test specimen which has the higher viscosity has reached a dynamic viscosity of 10’3dPas;
— the lower limit lIes 150 C below the temperature at which the glass with the lower viscosity has a dynamic viscosity of 1O(13)dPa.s.
6.5 When the surfaces of the test specimens through which the light passes are not sufficiently smooth for the stress picture to be clear, it is advis-able to place the test specimen in an immersion fluid, for example water in the case of fine polished surfaces. The bottom of the immersion vessel itself shall not have any interfering birefringence and op-tical path difference.ISO 4790 pdf download.