Thermostatic bimetals (temperature-sensitive materials)

Thermostatic bimetal (TB)is a metal composite with several layers with different TLEC. These materials are tightly welded along the contact surface. The component with a high TLEC is active, the one with a low TLEC is passive.

Thermal sensitivity is the main property of the material, i.e. ability to bend under the change of temperature. TB thermal sensitivity is proportional to the differential of component TLEC and is characterized by the nominal bending value - change of the flexure of the thermobimetallic plate of unit thickness with the temperature change by 1 °К.

Thermostatic bimetals are divided into 6 groups according to their physical and mechanical properties.

• High-sensitivity
• With increased thermal sensitivity
• With medium and low thermal sensitivity
• With low nominal resistance
• With high nominal resistance
• Special-purpose

Materials of the first froup from Classification section have a high nominal bending, high and increased nominal resistance. 75MnNiCu and 70 MnNiCr high-manganese alloys with a high TLEC, nominal resistance, low modulus of elasticity, low corrosive stability are active components of thermostatic bimetals. TiNb2013 grade has the highest thermal sensitivity, TiNb1613 grade has the nominal resistance.

Thermostatic bimetals with increased thermal sensitivity have increased nominal bending (А=15-12·10-6 К^-1), nominal resistance and high modulus of elasticity. 20NiMn, 24NiCr, 19NiCr, 27NiMo alloys are active components of these thermostatic bimetals, 36Ni is the passive component. TiNb1523, TiNb1423, TiNb1323, TiNb1224 grades have linear properties under 200 °С.

The third group of materials (TiNb1132, TiNb1032, etc.) has medium and low nominal bending, medium resistance, high modulus of elasticity and medium corrosive stability.

Low nominal resistance of thermostatic bimetals that belong to the fourth group (TiNb1353, TiNb1254) is determined by an intermediate nickel-copper layer.

Thermostatic bimetals of the fifth group have high resistance (1.3-1.5 µΩ·m). Their thermal sensitivity is lower than one of TiNb2013 and TiNb1613 by 20-30%; the modulus of elasticity is slightly lower.

Special-purpose materials have good technological properties. The nominal bending calculated on the basis of the transition in the temperature range of maximum sensitivity (120-170 °С) is higher than the nominal bending of the most highly-sensitive TiNb2013 thermostatic bimetal and is А = (40-60)·10^-6 К^-1. The drawbacks of Mn-Cu system alloys applied as thermally sensitive elements are low modulus of elasticity (80-90 hPa) and insufficient thermal stability (up to 200 °С). TiNb20P grade properties: nominal bending within 20-150 °С (5±10)·10^-6 К^-1 and within 150-200°С (18-20)·10^-6 К^-1, modulus of elasticity E=110 hPa.

Described according to the types given in Classification section.

• TiNb2013, TiNb1613, TiNb1821, TiNb1624. High-manganese 75MnNiCU и 70MnNiCr alloys serve as active layers.
• TiNb1523, TiNb1423, TiNb1323, TiNb1224. 20NiMn, 24NiCr, 19NiCr, 27NiMo grades are active layers, 36Ni is the passive layer.
• TiNb1132, TiNb1032, TiNb0921, TiNb0831. Fe-Ni alloys with 18-27 % of Ni serve as the active components, Fe-Ni alloys with 42-50 % of Ni serve as the passive layer with low TLEC under 330-480 °С.
• This group includes standard TiNb1353 and TiNb1254 grades. Low-resistant materials - L62 and L90 brasses so as TiNb1243 and TiNb1253 serve as the active layer.
• TiNb 150/140, TiNb 120/145, TiNb140/140, TiNb110/150. Based on TiNb2013 and TiNb1613 grades due to increasing the thickness of the active layer - high-resistance 75MnNiCu alloy.
• Materials based on Mn-Cu, Mn-Ni, Ni-Ti and other systems.

Thermostatic bimetals are applied for producing temperature compensators, sensitive parts of thermometers, thermal regulators (including those working under temperatures up to 400-450 °С), circuit breaker assemblies, thermal elements of thermal (including those for low current ratings) and current relays so as breakers.

Thermostatic bimetals are produced in form of strips.