Physical properties

of Micro Glass Tubes

 

Mean linear thermal coefficient of expansion
at (20 °C; 300 °C) in compliance with DIN ISO 7991
 3.3 · 10-6 K-1
Transformation temperature Tg  525 °C
Temperature of glass at viscosities η in dPA · s:
1013 (upper cooling temperature)
107,6 (softening temperature)
104 (processing temperature)

560 °C
825 °C
1260 °C
Temporary max. permissible service temperature 500 °C
Density ρ at 25 °C  2.23g · cm-3
Elasticity module E (Young's modulus)  63 · 103N · mm-2
Poisson's ratio μ 0.20 
Thermal conductivity λw at 90 °C 1.2 W · m-1· K-1 
Temperature for specific electrical resistance
of 10 Ω · cm (DIN 52 326) t k 100
250 °C
Logarithm of electrical volume resistivity (Ω · cm)
at 250 °C
at 350 °C

8
6.5
Dielectric properties (1 MHz, 25 °C)
Dielectric constant ε
Dielectric loss factor tan δ

4.6
37 · 10-4
Refractive index (λ = 587,6nm)nδ 1.473
Spannungsoptischer Koeffizient (DIN 52 314) K 4.0 · 10 -6 mm 2 · N -1

The following values relate to stress-free tubes and hollow cylindrical bodies with a round profile, uniform wall thickness and open ends, free of thermal stress, with positive internal and negative external pressure.

 

Calculation of compressive strength (p) at specified wall thickness (Wd) and specified outer diameter (Ad):

p = Ad - Wd
Wd · 20 · KS

 

Calculation of wall thickness (Wd) at specified compressive strength (p) and specified outer diameter (Ad):

Wd = Ad · p
20 · KS + p

Ad = outer diameter in mm
Wd = wall thickness in mm
p = compressive strength in bar
KS = permissible stress = mm²
7 N

 

Compressive strength (p) is also influenced by:

  • Temperature difference between inner and outer wall
  • Surface quality
  • Treatment of ends
  • Adherence to installation conditions conforming to Pressure Vessel Ordinance (Druckbehälterverordnung)
  • Tube length

 Please contact us if you require precise calculations.

 

 The following should also be taken into consideration:

  • AD 2000 Leaflet N 4, Issue 2000-10: pressure vessel made of glass with Appendix 1, Issue 2000-10: evaluation of errors in walls of glass pressure vessels
  • AD 2000 Leaflet B 1, Issue 2000-10: Cylindrical and spherical shells subject to internal overpressure

 

The temperature change resistance based on DIN ISO 718 is the temperature difference between the hot sample body and cold water bath (room temperature) at which 50% of samples indicate initial cracks if immersed rapidly in the water bath. The temperature change resistance of tubes, capillaries and rods depends on the wall thickness, shape and size of quenched surface, surface condition, current tension and treatment of ends. Uneven, rapid heating or cooling can easily lead to breakage, due to the resulting tensile stress.

It is recommended that a temperature difference of 120 °C should not be exceeded. The temperature difference is limited to lower values in the case of greater wall thicknesses. A few measurement values are detailed below as examples of the temperature change resistance of DURAN® borosilicate glass 3.3 tubes and rods. These values are only intended as reference values, as considerable deviations are possible between workpieces.