327
Understanding Magnets for Catches & Latches
Types and Properties of Magnets
Demagnetization Recovery Temperature
Corrosion Resistance (No Plating)
Mechanical Strength (Brittleness)
Heat Resistance
Magnet Strength (image)
Magnet
Features
•Rust-resistant magnet made mainly from iron oxide •Prone to breaking and chipping •Strongest magnetic force in the world •Cheaper than other rare earth magnets •Breakage-resistant •Vulnerable to heat •Prone to rusting, requiring plating (nickel plating normally in use) •Low thermal demagnetization even in high- temperature environments (approx. 250°C), with high magnetic force •Rust-resistant •Prone to breaking and chipping •Expensive due to the use of rare earths
Ferrite (sintered)
Approx. 200°C
OK
OK
NO
Neodymium (sintered)
Approx. 80°C
Possible
NO
OK
Samarium-cobalt (sintered)
Approx. 300°C
Good
Good
Possible
[Magnets’Thermal Demagnetization Properties]
100 (%)
80
Ferrite (sintered) Neodymium (sintered) Samarium- cobalt (sintered)
60
40
0
20°C
50°C
100°C
200°C
Role of the Yoke
•Through use in combination with iron rather than on their own, magnets form magnetic circuits, increasing their magnetic force and notably improving their performance. This iron is called the yoke.
Magnet used alone
Used with yoke
Yoke
S
N
Yoke
N
S
S
N
N
N
Concentrated
S
Contact surface
Contact surface
Magnetic flux is not concentrated: weak magnetic force
Magnetic flux is concentrated: strong magnetic force
Magnetic Catches / Magnetic Latches: Precautions for Use
•Magnetic force varies. Confirm with the actual product. •For some strike plates in countersunk specifications, add screw and rivet relief as shown in the figure at right.
[Machining and Mounting Examples] With M3 screws
90°
Mounting Surface
Relief machining
Product
M3 machine screw
M3 female screw machining
No.500 Catalogue
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