BOROFLOAT® & Sight glass: A Union of Inspiration & Quality

BOROFLOAT® - The sum of its properties is what makes it unique for sight glass applications!

  • Outstanding thermal resistance
  • Exceptionally high transparency
  • High chemical durability
  • Excellent mechanical strength

BOROFLOAT® 33 glass sight glasses stand up to high thermal loads

A particularly low coefficient of thermal expansion makes BOROFLOAT® remarkably resistant to high temperature levels. Our borosilicate glass is proven to stand up to not only high, but also fluctuating temperatures which are typical for sight glass windows used in chemical, pharmaceutical, food & beverage and many other industries. Even with applications where rapid cooling from higher temperatures is the requirement, BOROFLOAT® easily passes the test.
Thermal properties
Coefficient of Linear Thermal Expansion (C.T.E.) α (20 - 300 °C)
3.25 x 10-6 K-1 *
Specific heat capacity cp (20 - 100 °C) 0.83 kJ/(kg·K)
Thermal conductivity λ (90 °C) 1.2 W/(m·K)

* According to ISO 7991.
Maximum operating temperatures
For short-term usage (< 10 h)
500 °C
For long-term usage (≥ 10 h) 450 °C
The maximum operation temperatures for BOROFLOAT® should be seen in conjunction with RTG (Resistance to Temperature Gradients) and RTS (Resistance to Thermal Shock) values. Such values and test methods are available on request.
Working Point (104 dPas)
1270 °C
LITTLETON temperature / Softening Point (107,6 dPas) 820 °C
Annealing Point (1013 dPas) 560 °C
Strain Point (1014,5 dPas) 518 °C
Transformation temperature (Tg) 525 °C

BOROFLOAT® 33 sight glasses are extremely resistant to chemical attack

Acids, alkalis and organic substances have virtually no negative impact on BOROFLOAT® glass. Its high resistance to water is another important performance benefit for many industrial applications. Such exceptional chemical resistance is the reason why this type of borosilicate glass has been successfully used in the chemical, pharmaceutical and food industry for over 130 years as annual edge sight glasses, laboratory glassware, chemical reactors, vials, ampules and even cookware.
Chemical durability
Hydrolytic resistance (according to ISO 719 / DIN 12 111)
(according to ISO 720) HGA 1
Acid resistance (according to ISO 1776 / DIN 12 116) 1
Alkali resistance (according to ISO 695 / DIN 52 322) A 2

BOROFLOAT® 33 sight glasses stand up to high mechanical loads

Thermally toughened BOROFLOAT® glass is characterized by high bending strength, in combination with outstanding abrasion and scratch resistance. These properties are particularly crucial when high pressure and mechanical loads play an important role. The material’s low inherent weight makes it ideal for lightweight glazings and applications in modern high-tech facilities. BOROFLOAT® delivers lightweight resistance! To further increase strength, BOROFLOAT® glass can be thermally toughened to allow it to withstand even higher
pressure loads.
Mechanical properties
Density ρ (25 °C)
2.23 g/cm3
Young’s Modulus Ε (according to DIN 13316) 64 kN/mm2
Poisson’s Ratio μ (according to DIN 13316) 0.2
Knoop Hardness 0.1/20 (according to ISO 9385) 480

BOROFLOAT® 33 sight glasses guarantee clear views

Essential for view ports and sight glasses are outstanding visual quality along with high clarity and excellent transmission. BOROFLOAT® glass outperforms many soda-lime glasses due to its low iron content which results in exceptional UV and light transmission and has made BOROFLOAT® glass the material of choice for many optical applications.

BOROFLOAT® 33 sight glasses – your choice for any harsh environment

Elevated temperatures, chemical attack and high pressure – alone or in combination – need to be considered when specifying a material that can safely resist such environments. The thickness and diameter of a sight glass must be determined in order to be able to satisfactorily meet the expected pressure and thermal loads. SCHOTT has years of experience and supports sight glass fabricators in designing safe and lightweight products. Please request our technical paper „BOROFLOAT® & Sight Glass: A Union of Inspiration & Quality“ to learn more about sight glass calculations. It contains calculation examples and pressure charts allowing you to easily determine which glass thickness and diameter to use for your specific application.
SCHOTT North America supplies BOROFLOAT® 33 borosilicate glass in raw sheet form only. Secondary processing is performed by others who cut and finish the glass to end user specifications. The finishing process, combined with the strengthening process (if applied), has a significant influence on thermal shock resistance and mechanical properties that affect the maximum usable pressure. Therefore, determining the suitability of our product and any product specifications or requirements necessary for your particular application(s) remain(s) entirely your responsibility. SCHOTT assumes no responsibility or liability and makes no warranty or guarantee with respect to any suggestion, advice or information related to the use of sight glasses or any reliance on this website. Sight glass calculations are to be seen in conjunction with AD 2000-Merkblatt N4: Pressure vessels made of glass, Published by German Technical Inspection Agency VdTÜVstandards. The reader is required to refer to and obey by such standards. Design of mounting, characteristics of gasket material and assembly procedures must be considered.
Exhibitions & Events
Exhibition CIOE - China International Optoelectronic Exposition, Shenzhen, China, 09-01 to 09-03-2021
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