Thermostatic bimetal strip
Thermostatic bimetal is a specialist type of clad strip. It is composed of two or more metals or alloys with different expansion coefficients that are firmly compounded along the entire contact surface. It has a layered metal composite functional material that changes shape with temperature.
1>According to the use temperature
· High temperature type such as 5J1070
· Medium temperature type such as 5J1480, 5J1580, etc.
· Low temperature type, such as 5J20110, etc.
2>According to heat sensitive characteristics
· Highly sensitive type (temperature curvature above 30 × 10-6 / ℃)
· Medium sensitive type (temperature curvature is in the range of 15 ~ 30 × 10-6 / ℃)
· Low sensitivity type (temperature curvature below 15 × 10－6 / ℃)
3>According to resistance characteristics
· Low resistance series
· Medium resistance series
· High resistance series
During manufacture the material is subjected to continuous control. The extensive and thorough final control includes a check of dimensions, surface finish, straightness and flatness. Laboratory tests include a check of hardness, resistivity and deflection. is certified according to EN ISO 9001–2000.
3-What is a bimetal
A bimetal or thermostatic metal is a sheet or strip of two or more composite materials having different coefficients of linear thermal expansion bonded by riveting, brazing or welding. The material with the larger coefficient of thermal expansion (CTE) is considered as the active component, and that of smaller CTE is the passive component. The active component usually has alloys containing iron, manganese, nickel, or chrome in varying amounts. Whereas on the passive side, invar is often chosen, an iron-nickel alloy containing 36% nickel. Some bimetals include a third layer of copper or nickel in between the active and passive sides in order to increase thermal conductivity and decrease the material’s electrical resistivity [1, 2].
4-Properties of bimetal
Bimetals work with the propensity of metals to expand when heated, and contract when cooled. The resulting change of curvature, or bending, in response to temperature change, is a fundamental property of all thermostatic bimetals. In effect, the temperature change is converted into mechanical displacement. The behaviour of bimetals is predictable and repeatable. The components used for bimetals are selected for their temperature characteristics as well as their thermal conductivity, stability, strength, workability, and electrical properties.
The fundamental characteristic of a bimetal is flexivity, also known as specific curvature. It is an important property of bimetals that is defined by the curvature change along its longitudinal axis. To clearly define flatness and straightness a special terminology is normally used which is visualized in the illustrations below.
· Regulate and control temperature on clothes irons, toasters, toaster ovens, coffee makers, ovens, clothes dryers, hair dryers, deep fat fryers, electric blankets, electric frying pans and tea kettles, rice cookers, griddles, grills, and waffle irons, just to name a few
· Protect fluorescent light ballasts from overheating
· Regulate room temperature
· Turn automotive fans on or off
· Record the temperature of sensitive cargo in transport to assure it has not varied from the desired range
· Protect home, office, factory electrical circuits
· Protect aircraft electrical circuits
· Open/close crawl space and attic vents
· Regulate electric range burner temperatures
· Protect electric motors from overloading
· Protect circuitry in computer and peripheral surge protectors
· Provide anti-scald protection in hospital and nursing home showerheads
· Keep self-adjusting drum brakes from over adjusting at elevated temperatures
· Compensate for ambient temperature variations in car and SUV hatch and hood struts
· Compensate for viscosity variations due to temperature changes in automatic transmissions
...And much more