thermal properties
resistance to temperature variations
Resistance to temperature variations corresponds according to ISO 718 to the thermal difference between the hot test piece and the cold water bath (room temperature), where the first cracks appear on 50 per cent of samples, when these will have been quickly dipped into the water bath. Resistance to temperature variations of tubes, capillaries and rods depends on the wall thickness, shape and size of the cooled surface, surface condition, tension and final working. Uneven, flash heating or fast cooling may easily lead to cracking due to the resulting tension. It is recommended not to exceed the thermal difference of 120°C. At thicker walls, this thermal difference is limited to lower values. As for examples of resistance to temperature variations of tubes and rods made of SIMAX borosilicate glass 3.3 some values measured have been specified hereinafter. These values may be considered indicators, because considerable differences may exist among parts of the same sizes:
The manufacturer may perform an exact calculation, where necessary.
instructions for porcessing
SIMAX tubes, capillaries and rod material properties guarantee a very good workability in glass forming and dividing, which is usual with technical glass. To remove temporary stress, which originates in processing, it is appropriate to warm the glass through well up to a temperature of 550°C, and, to leave it at this temperature over a period of time of at maximum 30 minutes; as a rule, in thin-walled products a fraction of this time would suffice. With regard to glass chemical durability the stabilization time should be as short as possible. For subsequent cooling down, the cooling speeds have been recommended in the point below.
cooling speed
In the event that it is necessary to cool the product down several times, the sum of all the stabilization times at 550°C should not exceed two hours. SIMAX glass may be melted and joined with other brands of borosilicate glass of the same type, without stress, and processed and stabilized at the same temperatures. SIMAX tubes, capillaries and rods may be printed using silver- and copper-based diffusion colours and silk-screen-printing colours.
