Overview of Limit Switches Technical Guide for Limit Switches

PartMaterialSymbolCharacteristicsContactsGoldAuGold is extremely resistant to corrosion and is used for microloads. It is soft (Vickers
strength: HV25 to HV65), which easily results in adhesion (e.g., contacts sticking
together) and the contacts are easily dented if the Contact force is large.Gold-silver
alloyAuAgThis alloy of 90% Au and 10% Ag is extremely resistant to corrosion, and its hardness
(HV30 to HV90) is higher than that of gold, and so it is often used in switches for
microloads.Platinum-gold-
silver alloyPGSThis alloy of 69% Au, 25% Ag, and 6% Pt is extremely resistant to corrosion, its hardness
(HV60) is similar to AuAg, and it is often used in switches for microloads.Silver-
palladium
alloyAgPdThis alloy has good resistance against corrosion but it easily generates polymers if it
adsorbs organic gases.
With 50% Ag and 50% Pd, it has a hardness of HV100 to HV200.SilverAgSilver has the highest rate of electrical conductivity and heat transfer among metals. It
exhibits low Contact resistance, but has the disadvantage of easily generating a sulfide film
in environments with sulfide gas, and so Contact faults easily occur in microload ranges.
The hardness is HV25 to HV45. Silver is used in almost all switches for standard loads.Silver-nickel
alloyAgNiWith 90% Ag and 10% Ni, this alloy has electrical conductivity about equal to Ag, and it has
excellent resistance to arcing and welding.
The hardness is HV65 to HV115.Silver-indium-
tin alloyAgInSnThis alloy is very hard, has a high melting point, and exhibits excellent resistance to arcing,
welding, and Contact transfer.Movable
springs
and
armaturesPhosphor
bronze
for springsC5210Phosphor bronze is very ductile and has resistance against fatigue and corrosion. It is
annealed at low temperatures. The spring limit (Kb0.075) is somewhat low at 390 N/mm2
minimum for C5210-H and 460 N/mm2 minimum for C5210-EH, but it is often used for
armatures of miniature basic switches.Age-hardened
copper
beryllium
for springsC1700
C1720Copper beryllium is pressed and then age-hardened. It has a high rate of electrical
conductivity, and the spring limit (Kb0.075) after age hardening is extremely high at
885 N/mm2 minimum. for C1700-H and 930 N/mm2 minimum for C1720-H.
It is used for basic switches that require a high spring limit.Mill-hardened
copper beryllium
for springsC1700-[]M
C1720-[]MThis copper beryllium is age hardened by the materials manufacturer before shipment (i.e.,
mill hardened). Pressing after age hardening is not required. At 635 N/mm2 minimum
reference value) for C1700-HM and 635 N/mm2 for C1720-HM, the spring limit (Kb0.075)
is higher than with bronze phosphor for springs. Mill-hardened copper beryllium is often
used for the movable springs in basic switches.Stainless steel
for springs
(austenite)SUS301-CSP
SUS304-CSPAustenite stainless steel has excellent resistance against corrosion.
The spring limit (Kb0.075) is 490 N/mm2 minimum for SUS301-CSP-H and 390 N/mm2 for
SUS304-CSP-H.Cases and
coversPhenol resinPFPhenol resin is heat hardened. It is often used as the material for the casings of basic
switches.
Phenol resin has a UL heat index of 150°C, a UL fire-retardant grade of at least 94V-1, and
a water absorption coefficient of 0.1% to 0.3%. Material without ammonia is used for basic
switches.Polybutylene
terephthalate
resinPBTPThis resin is thermoplastic. A glass-reinforced epoxy type of this resin is often used as the
material for the casings of basic switches.
The resin has a UL heat index of 130°C, a UL fire-retardant grade of at least 94V-1, and a
water absorption coefficient of 0.07 to 0.1.Polyethylene
terephthalate
resinPETPThis resin is thermoplastic. A glass-reinforced epoxy type of this resin is used as the
material for the casings of basic switches.
The resin has a UL heat index of 130°C, a UL fire-retardant grade of at least 94V-1, and a
water absorption coefficient of 0.07 to 0.1.Polyamide
(nylon)
resinPAThis resin is thermoplastic. A glass-reinforced epoxy type of this resin has heat resistance
that is superior to PBT and PET. The absorption coefficient is large. Select a grade for use
with a the lowest possible absorption rate.
The resin has a UL heat index of 180°C, a UL fire-retardant grade of at least 94V-1, and a
water absorption coefficient of 0.2 to 1.2.Polyphenylene
sulfidePPSThis resin is thermoplastic. It has heat resistance that is superior even to PA.
The resin has a UL heat index of 200°C, a UL fire-retardant grade of at least 94V-1, and a
water absorption coefficient of 0.1.Switch
boxesAluminum
(die-cast)ADCAluminum is often used as the material for the switch box (case) of Limit Switches.
Standards are specified in JIS H5302.Zinc
(die-cast)ZDCDie-cast zinc is more suitable than ADC for thin-walled objects, and its resistance to
corrosion is also superior to ADC.
Standards are specified in JIS H5301.Rubber
sealsNitrile-
butadiene
rubberNBRThis rubber has excellent resistance to oil, and it is often used for Limit Switches. It is
classified into five nitrile levels according to the amount of combined nitrile: Very high
(43% or higher), high (36% to 42%), mid-high (31% to 35%), medium (25% to 30%), and low
(24% or lower). Resistance to oil, heat, and cold somewhat vary with each level. The
ambient operating temperature ranges from -40 to 130°C.Silicon rubberSIRSilicon rubber has excellent resistance to heat and cold, and the ambient operating
temperature ranges from -70 to 280°C. Its resistance to oil, however, is inferior.Fluorine
rubberFRMFluorine rubber has resistance to heat, cold, and oil that is superior even to NBR and SIR.
Depending on the constituents of the oil, however, the oil resistance may be inferior to NBR.Chloroprene
rubberCRChloroprene rubber has good resistance against ozone and climatic conditions. It is often
used as the material for basic switches that require resistance against climatic conditions.