Aluminosilicate Glass Sight Discs — Up to 70 MPa & 375°C, DIN 7080 Compatible
Lumiglas aluminosilicate glass sight discs: alkali-free RO-Al₂O₃-SiO₂ composition, rated 70 MPa & 375°C, 260–300 MPa bending strength. DIN 7080 compatible, Ø10–800 mm.
Description
Aluminosilicate glass is a high-performance technical glass that consists primarily of aluminum oxide (Al₂O₃) and silicon dioxide (SiO₂). Notably, it delivers exceptional mechanical strength, thermal shock resistance and softening points above 920 °C. As a sight glass material, alkali-free aluminosilicate glass provides observation windows for industrial applications where standard borosilicate glass cannot withstand the operating temperature, pressure or chemical environment.
Lumiglas manufactures aluminosilicate round sight glass discs from an alkali-free RO-Al₂O₃-SiO₂ system. Here, RO represents divalent metal oxides including MgO, CaO, BaO and ZnO. Because the composition contains no alkali metal ions, the glass delivers superior chemical stability, electrical insulation and bending strength of 260–300 MPa — 2 to 3× that of borosilicate. Moreover, the discs match DIN 7080 housing dimensions exactly and meet JC/T 891-2016, so engineers can use them as a direct upgrade for boiler sight windows, reactor viewports, autoclave observation ports and submarine equipment.
Aluminosilicate glass — quick facts
- Composition: Alkali-free RO-Al₂O₃-SiO₂ system, typically 10–25% Al₂O₃ by weight
- Continuous service temperature: ≤ 375 °C
- Pressure resistance: 1.0–70.0 MPa
- Bending strength: 260–300 MPa — 2 to 3× soda-lime and borosilicate
- Softening point: > 920 °C
- Density: 2.62 g/cm³
- Optical transparency: ≥ 90% at 400–2500 nm (5 mm thickness)
- Refractive index: 1.5472
- Primary variants: alkali aluminosilicate (consumer electronics) and alkaline-earth aluminosilicate (industrial high-heat) — Lumiglas produces the alkaline-earth grade for industrial sight glass
- Standards: JC/T 891-2016 · DIN 7080 housing compatible
Aluminosilicate vs borosilicate sight glass discs — when to upgrade
Three conditions trigger the upgrade from borosilicate sight glass discs to aluminosilicate: process temperature above 300 °C, pressure beyond the borosilicate limit, or contact with abrasive or chemically aggressive media. Aluminosilicate handles all three simultaneously. Furthermore, because the discs match standard DIN 7080 dimensions, your installer can swap them into existing housings without machining or rework. All performance data below comes directly from Lumiglas product specifications.
| Parameter | Borosilicate (DIN 7080) | Aluminosilicate (Lumiglas) |
|---|---|---|
| Continuous service temperature | ≤ 280 °C | ≤ 375 °C |
| Pressure resistance | Up to ~22 MPa | 1.0–70.0 MPa |
| Bending strength | > 160 N/mm² | 260–300 MPa |
| Alkali composition | Contains alkali | Alkali-free |
| Abrasion resistance | Standard | Superior |
| DIN 7080 housing fit | Standard | Direct compatible |
Composition and structure of aluminosilicate glass
Aluminosilicate glass derives its mechanical and thermal performance from the tight cross-linked atomic network. Specifically, aluminum oxide bonds into the silica matrix and stiffens the entire structure. Two industrial variants exist:
- Alkali aluminosilicate glass: contains alkali oxides (Na₂O, K₂O). Manufacturers chemically strengthen this variant for consumer electronics applications such as smartphone cover glass and display panels.
- Alkaline-earth (alkali-free) aluminosilicate glass: replaces alkali oxides with divalent oxides (MgO, CaO, BaO, ZnO). This is the grade Lumiglas produces for industrial sight glass discs. Because no alkali metal ions are present, the glass achieves higher chemical durability, lower dielectric loss and superior performance at elevated temperatures.
As a result, the Lumiglas industrial grade keeps optical and mechanical properties stable across the full operating range — from -196 °C cryogenic exposure up to 500 °C peak service.
Key performance characteristics
Pressure, temperature and mechanical strength
- Ultra-high pressure resistance — 1.0 to 70.0 MPa: Aluminosilicate sight glass discs handle pressure loads up to 70 MPa. Therefore, they suit high-pressure reactors, autoclaves and submarine viewports — a range that far exceeds what standard borosilicate sight glass discs can achieve.
- High-temperature service up to 375 °C: Process temperatures above 300 °C quickly exceed the capability of borosilicate. Aluminosilicate, however, runs continuously at up to 375 °C in boiler sight windows, steam vessel viewports and petrochemical reactor observation ports.
- Bending strength 260–300 MPa — 2–3× borosilicate: The alkali-free composition and thermal toughening together push bending strength 2 to 3 times higher than standard borosilicate. Consequently, the disc resists pressure cycling, thermal shock and mechanical impact far more effectively.
Safety, optical clarity and surface durability
- Explosion-proof certified: Lumiglas tests each disc thickness to defined impact energy thresholds — 10 mm discs achieve ≥ 10 J, 15 mm ≥ 20 J, and 20 mm ≥ 40 J. These ratings confirm safe fragmentation behavior in the event of breakage and satisfy the safety requirements for industrial pressure equipment.
- Distortion-free optical clarity: The disc transmits ≥ 90% of light across the 400–2500 nm wavelength range at 5 mm thickness. In addition, a refractive index of 1.5472 and polished parallel faces guarantee undistorted visual inspection of process conditions through the sight window.
- Superior abrasion and scratch resistance: Sight windows in slurry lines, particulate-bearing flows and corrosive environments degrade standard borosilicate surfaces rapidly. Aluminosilicate, however, resists surface wear far better and extends service life between maintenance intervals.
Technical specifications (JC/T 891-2016)
The table below lists the full material data for Lumiglas aluminosilicate sight glass discs. All values come directly from the Lumiglas technical datasheet and reflect the standard production grade for the alkaline-earth (alkali-free) industrial variant.
| Parameter | Value |
|---|---|
| Executive standard | JC/T 891-2016 · DIN 7080 housing compatible |
| Continuous service temperature | ≤ 375 °C |
| Maximum service temperature (short term) | 500 °C |
| Minimum service temperature | -196 °C |
| Thermal shock resistance | ≤ 300 °C differential |
| Pressure resistance | 1.0–70.0 MPa |
| Bending strength | 260–300 MPa |
| Coefficient of thermal expansion | 42–46 × 10⁻⁷ /°C |
| Density | 2.62 g/cm³ |
| Young’s modulus | 84.5 GPa |
| Poisson’s ratio | 0.24 |
| Glass transition temperature (Tg) | 715 °C |
| Sagging temperature (Ts) | 791 °C |
| Softening point | > 920 °C |
| Optical transparency | ≥ 90% at 400–2500 nm (5 mm thickness) |
| Refractive index | 1.5472 |
| Explosion-proof rating | 10 mm ≥ 10 J · 15 mm ≥ 20 J · 20 mm ≥ 40 J |
Standard sizes and dimensions
Round disc diameters run from Ø10 mm to Ø800 mm, covering the full range of standard sight glass fitting sizes. Common thicknesses include 12.7 mm, 16 mm, 17 mm, 19 mm and 21 mm. Additionally, Lumiglas produces non-standard diameters and custom thicknesses to customer specifications. For example, we regularly deliver both compact high-pressure viewports and large-diameter reactor observation windows. Contact us with your dimensions, pressure rating and temperature conditions for a direct quotation.
Applications & industries
Aluminosilicate sight glass discs cover a wide range of high-demand industrial environments. In particular, they excel wherever high temperature, high pressure or abrasive media rule out standard borosilicate sight glass discs.
- Boiler Sight Windows
- Petrochemical Reactors
- Autoclave Viewports
- Submarine Equipment
- Power Generation
- Slurry & Abrasive Lines
- Optical Instruments
- Iron & Steel Metallurgy
Process equipment and pressure vessels
- Boiler and steam vessel sight windows above 300 °C — this is the primary application, where aluminosilicate discs replace borosilicate in existing DIN 7080-compatible housings. Therefore, you avoid any housing modification because the discs match the standard dimensions exactly.
- High-pressure reactor and autoclave observation ports — engineers across petrochemical and chemical processing specify these discs when pressure reaches 70 MPa, covering the full range of reactor operating conditions without special housings.
- Power generation and iron & steel metallurgy — boiler and furnace viewports for heavy industrial heat processes.
Marine and corrosive environments
- Submarine and marine high-pressure viewports — engineers specify alkali-free sight glass here for the certified explosion-proof ratings. Moreover, the absence of alkali ions improves long-term corrosion resistance in marine environments.
- Sight windows in slurry or particulate-bearing process lines — abrasive contact rapidly degrades standard borosilicate surfaces. Aluminosilicate, however, keeps optical clarity and surface integrity over far longer service periods.
Precision viewports and optical instruments
- Precision optical instrument windows and sensor covers — the stable refractive index of 1.5472 and superior scratch resistance make aluminosilicate a reliable choice. For example, specialty instrument manufacturers rely on it where surface quality must remain consistent over extended service.
Manufacturing and quality standards
Our Nanjing facility produces every batch of Lumiglas aluminosilicate glass discs under JC/T 891-2016 and ISO 9001:2015 quality systems. Every production batch passes hydrostatic pressure testing, optical transmission verification and impact-energy fragmentation testing — therefore confirming compliance with the published explosion-proof ratings. Moreover, we dimensionally control all discs intended for pressure vessel installation to DIN 7080 tolerances, so they drop directly into standard sight glass fittings without machining. For current third-party test records and material traceability documentation, see our certifications page.
About Lumiglas — manufacturer expertise
Lumistar Special Glass Technology Co., Ltd. (Lumiglas® brand) is a specialist industrial sight glass manufacturer in Nanjing, China, with over a decade of dedicated experience in high-pressure and high-temperature observation windows. Our portfolio covers aluminosilicate, borosilicate (DIN 7080 / DIN 7081), sodium-calcium silicate, quartz and sapphire viewports for pressure vessels, pipelines, reactors and marine equipment. Furthermore, we design every product to comply with international standards (DIN 7080, DIN 28120, DIN 28121, NB/T 47017, ANSI flange) and ship worldwide with full material traceability.
Frequently asked questions
Properties and composition
What is aluminosilicate glass?
Aluminosilicate glass is a technical glass that consists primarily of aluminum oxide (Al₂O₃) and silicon dioxide (SiO₂), typically containing 10–25% Al₂O₃ by weight. The interwoven cross-linked atomic network delivers bending strength 2–3 times higher than soda-lime glass, softening points exceeding 920 °C and excellent thermal shock resistance. Two main industrial variants exist: alkali aluminosilicate for electronics, and alkaline-earth (alkali-free) aluminosilicate for industrial high-pressure, high-temperature applications.
What makes aluminosilicate glass alkali-free?
The industrial-grade Lumiglas aluminosilicate composition replaces alkali oxides (Na₂O, K₂O) with divalent oxides such as MgO, CaO, BaO and ZnO. Because no alkali metal ions remain in the matrix, the glass achieves superior chemical durability, electrical insulation and stability at elevated temperatures — properties that boiler, reactor and submarine viewport applications require.
Is aluminosilicate glass stronger than soda-lime glass?
Yes. Aluminosilicate glass is 2 to 3 times stronger than standard soda-lime glass thanks to its higher Al₂O₃ content and tight cross-linked atomic network. Bending strength of 260–300 MPa compares with roughly 30–90 MPa for soda-lime. For this reason, engineers select aluminosilicate for high-pressure sight windows and high-stress display applications.
Selection and comparison
What is aluminosilicate sight glass used for?
Aluminosilicate round sight glass discs serve as high-temperature, high-pressure observation windows in industrial pressure vessels, reactors, boilers and sight glass fittings. Specifically, engineers specify them when process temperatures exceed 300 °C or when pressure loads exceed the capability of standard borosilicate sight glass. Typical installations include boiler sight windows, petrochemical reactor viewports, autoclave observation ports and submarine equipment viewports.
What is the difference between aluminosilicate and borosilicate sight glass discs?
Aluminosilicate sight glass discs withstand continuous operating temperatures up to 375 °C, compared with 280 °C for standard borosilicate. Furthermore, their pressure resistance reaches 70 MPa versus approximately 22 MPa for borosilicate, and their bending strength of 260–300 MPa is 2 to 3 times higher. Therefore, engineers upgrade to aluminosilicate when borosilicate sight glass can no longer meet the temperature or pressure requirements of the application.
Do aluminosilicate discs fit DIN 7080 sight glass housings?
Yes. Lumiglas aluminosilicate round sight glass discs match standard DIN 7080 sight glass housing dimensions exactly. As a result, they serve as a direct high-temperature upgrade for borosilicate DIN 7080 discs in existing installations — installers need no housing modification.
Pressure, safety and sizing
What is the maximum pressure rating for aluminosilicate sight glass discs?
Lumiglas aluminosilicate sight glass discs carry a pressure resistance rating of 1.0 to 70.0 MPa, depending on disc dimensions and installation configuration. Therefore, this range covers standard industrial pressure vessels as well as high-pressure reactors, autoclaves and submarine viewports.
What explosion-proof rating do aluminosilicate sight glass discs carry?
Lumiglas tests each disc thickness to defined impact energy thresholds. Specifically, 10 mm discs achieve ≥ 10 J, 15 mm discs achieve ≥ 20 J, and 20 mm discs achieve ≥ 40 J. As a result, these ratings confirm safe fragmentation behavior in the event of breakage — therefore satisfying the safety requirements for industrial pressure equipment.
What sizes are available for aluminosilicate round sight glass discs?
Standard round diameters run from Ø10 mm to Ø800 mm. Common thicknesses include 12.7 mm, 16 mm, 17 mm, 19 mm and 21 mm. Beyond these, Lumiglas produces non-standard diameters and custom thicknesses to customer specifications. For example, we regularly deliver both compact high-pressure viewports and large reactor observation windows. Contact us with your requirements for a direct quotation.
Sources and references
- JC/T 891-2016 — Chinese industry standard for aluminosilicate glass.
- DIN 7080 — Plane glass discs without screening for pressure equipment (housing compatibility standard).
- SCHOTT AG — Technical documentation on aluminosilicate optical glass: schott.com
- ScienceDirect — Aluminosilicate glass overview: sciencedirect.com
- Lumiglas technical datasheet — Aluminum Silicon Round Glass Datasheet (PDF)
Downloads & Technical Documentation
Download the full aluminosilicate sight glass disc datasheet, or send us your dimensions, pressure rating and temperature conditions for a direct quotation.
