What properties does long borosilicate glass according to DIN 7081 have?
These long sight glass panes made of thermally tempered borosilicate glass are particularly suitable for applications under pressure as well as for thermal and chemical stress. They offer high temperature cycling resistance and chemical durability and undergo strict production and quality inspections.
Specifications of long borosilicate glass
Product specification: Long sight glass plates
Material: Borosilicate glass tempered
Etching rates and further information about the glass can be found in our info data sheet and in our brochure
MAXOS® Borosilicate glass safety sight glasses are required wherever visual inspection of processes in containers must be ensured under pressure, with thermal and chemical stress.
The high safety is achieved through a special borosilicate glass with good chemical resistance, extraordinary purity, and homogeneity. In combination with the characteristic low thermal expansion of this borosilicate glass, thermal pre-stressing (hardening) results in particularly high temperature cycling resistance.
Through production and quality checks in the process flow, the property values of the glasses and the tight dimensional tolerances are guaranteed. With these excellent safety properties, MAXOS® safety sight glasses can be used for extreme conditions.
Operating Conditions:
The pressure-temperature rating in the INFO data sheet must be observed! The following table is for orientation only.
Calculation of pressure resistance: TOOL - Glass Advisor Borosilicate Glass DIN 7081
| Operating Type | Maximum Working Pressure | Maximum Operating Temperature |
|---|---|---|
| Unprotected reflective and transparent sight glasses at saturated steam or hot water pressure | 35 bar / 500 psi | 243 °C / 470 °F |
| Mica-protected transparent sight glasses at saturated steam or hot water pressure | 103 bar / 1500 psi | 320 °C / 608 °F |
| Reflective sight glasses in operation without steam and without technically significant glass attack | 280 bar / 4000 psi | 38 °C / 100 °F |
| For media without technically significant glass attack for transparent sight glasses | 345 bar / 5000 psi | 38 °C / 100 °F |
| High-pressure transparent sight glasses in special fittings | 414 bar / 6000 psi | 38 °C / 100 °F |
Chemical Resistance:
Water resistance DIN ISO 719/720: Hydrolysis class 1
Acid resistance DIN 12116: Acid class 1
Alkali resistance DIN 52332: Alkali class 2
Technical Information:
Coefficient of expansion at 20 °C/300 °C: 4.1 x 10–6 K–¹
Modulus of elasticity: 67 x 103 N/mm²
Thermal conductivity at 90 °C: 1.2 W/(m·K)
Photoelastic coefficient K: 3.2 x 10–6 mm²/N
Temperature cycling resistance: 265 °C
Permissible material defects:
Round bubbles enclosed in the glass may have a maximum diameter of 2 mm. Oval bubbles must not exceed the value (length + width)/2 = 2 mm. Tapered bubbles are not permissible.
| Bubble diameter (d3) | Bubble frequency | Bubble frequency |
|---|---|---|
| ≤ 250 mm | > 250 mm | |
| d3 < 0.3 | 3 pieces per cm² of sight area | 3 pieces per cm² of sight area |
| 0.3 ≤ d3 ≤ 0.5 | 10 pieces per glass | 15 pieces per glass |
| 0.5 < d3 ≤ 1 | 4 pieces per glass | 6 pieces per glass |
| 1 < d3 ≤ 2 | 2 pieces per glass | 3 pieces per glass |
Dimensional tolerances:
The dimensional tolerances are based on DIN 7081 for sight glass plates made of Borosilicate glass. The parallelism for standard sight glasses is ≤ 0.08 mm and for high-pressure sight glasses is ≤ 0.05 mm.
Dimensional tolerances according to DIN 7081
Dimensional tolerances for longitudinal glasses width 34 mm:
| Tolerance | |
|---|---|
| Length (95 ... 400 mm) | + 0 mm / – 1.5 mm |
| Width (34 mm) | + 0.2 mm / – 0.8 mm |
| Thickness (17.5 mm) | + 0 mm / – 1.0 mm |
Dimensional tolerances for longitudinal glasses width 30 mm:
| Length (115 ... 340 mm) | Tolerance |
|---|---|
| up to 250 mm | ± 0.8 mm |
| over 250 mm | ± 1.0 mm |
| Width (30 mm) | + 0.5 mm / – 0.8 mm |
| Thickness (17.5 mm) | + 0 mm / – 1.0 mm |
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