Material selection of thermal protectors

Thermal protector contact

Gold Au has excellent corrosion resistance and is suitable for small loads. Due to its soft texture (Vickers hardness HV25-65), it is more prone to adhesion (joint adhesion), and the joint is prone to indentation under high contact forces.

Gold and silver alloys AuAg. 90% gold and 10% silver alloys have excellent corrosion resistance, with a hardness of HV30-90, which is higher than gold. Therefore, they are widely used in switches for small loads.

Platinum, gold, and silver alloys PGS69% gold, 25% silver, and 6% platinum have excellent corrosion resistance and the same hardness as gold and silver alloys. They are widely used in switches for small loads. It is called "alloy 1".

Silver and palladium alloys AgPd have good corrosion resistance, but are more prone to adsorbing organic gases to form polymers. In the case of 50% silver and 50% palladium, the hardness is HV100-200.

Silver Ag has high conductivity and thermal conductivity in metals. Although exhibiting lower contact resistance, its disadvantage is that it is more prone to generate a sulfide film in the environment of sulfide gas, and is more prone to poor contact in small load areas. The hardness is HV25-45. Commonly used for switches for general loads.

The conductivity of silver and nickel alloys AgNi90% silver and 10% nickel is similar to that of silver, and they exhibit excellent resistance to arc and melting. The hardness is HV65-115. Silver, indium, and tin alloys AgInSn have high hardness, melting point, superior arc resistance, and are not easy to melt or transfer.

The phosphorus bronze C5210 used for movable springs and movable leaf springs has excellent compression ductility, fatigue resistance, and corrosion resistance. Annealing treatment has been carried out. If the critical value of the spring (Kb0.075) C5210-H is above 40kgf/mm2 and C5210-EH is above 47kgf/mm2, it is lower and widely used as a movable piece for small micro switches.

Used for aging hardening treatment of beryllium copper (time hardening treatment type) C1700C1720 after rolling processing for springs. The conductivity is high, and after hardening treatment, if the critical value of the spring (Kb0.075) C1700-H is above 90kgf/mm2 and C1720-H is above 47kgf/mm2, it is very high. Therefore, it must be used for microswitches with high critical values for springs.

When the spring is made of beryllium copper (mille hard material) C1700- □ MC1720- □ M, the material manufacturer has already undergone age hardening treatment (called mille hard material), and there is no need for age hardening treatment after the parts are processed (rolled). If the critical value of the spring (Kb0.075) is above 65kgf/mm2 (reference value), it will be higher than that of phosphorus bronze used in springs, and it is widely used as a movable spring for small micro thermal protection switches.

Stainless steel (austenitic series) SUS301-CSPSUS304-CSP for springs has excellent corrosion resistance. The critical value (Kb0.075) of SUS301-CSP-H is above 50kgf/mm2, and SUS304-CSP-H is above 40kgf/mm2.

Shell, protective cap, phenolic resin PF heat hardening resin. Widely used as casing material for micro switches. UL temperature index is 150 ℃, UL flame retardant level is above 94V-1, and water absorption rate is 0.1-0.3%. Micro switches often use ammonia free materials.

PBT resin PBTP thermoplastic resin. Fiberglass reinforced materials are commonly used as casing materials for micro switches. UL temperature index is 130 ℃, UL flame retardant level is above 94V-1, and water absorption rate is 0.07-0.1.

PBT resin, PETP thermoplastic resin. Glass fiber reinforced shell material for micro switches. UL temperature index is 130 ℃, UL flame retardant level is above 94V-1, and water absorption rate is 0.07-0.1.

Polyamide (nylon) resin PA thermoplastic resin. Compared with PBT and PET, glass fiber reinforced materials have better heat resistance. Due to its high water absorption rate, please try to choose varieties with lower water absorption rates. UL temperature index is 180 ℃, UL flame retardant level is above 94V-1, and water absorption rate is 0.2-1.2. Polyphenylene sulfide PPS thermoplastic resin. Compared to PA, it has superior heat resistance. UL temperature index is 200 ℃, UL flame retardant level is above 94V-1, and water absorption rate is 0.1.

Aluminum (cast) ADC is commonly used as a material for switch boxes of limit switches. There are standards in JISH5302.

Compared with aluminum castings, zinc (casting) ZDC is suitable for thinner areas and has superior corrosion resistance. There are standards in JISH5301.

Sealed rubber nitrile rubber NBR has excellent oil resistance and is widely used in limit switches. According to the amount of bound nitriles, the grades of nitriles are divided into 5 categories, namely extremely high (over 43%), high (36-42%), medium high (31-35%), and low (below 24%), with slightly different oil resistance, heat resistance, and cold resistance. The temperature range for use is -40~130 ℃.

Silicone SIR is heat-resistant and has excellent cold resistance, with a temperature range of -70-280 ℃, but its oil resistance is poor. Compared with nitrile butadiene and silicone, fluorinated rubber FRM has excellent heat resistance, cold resistance, and oil resistance. However, in terms of oil resistance, it may sometimes be worse than nitrile butadiene depending on the composition of the oil.