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The
basic principle of the holding or pot magnet is to direct and
concentrate the flux from both magnetic poles to one active face. This
is usually achieved with steel pole pieces or a steel-backing cup.
The
standard selection can be broken down into three material types and
there is a great variety of systems available. The following data should
act as a simple guide:
1)
Sintered Ferrite, this material offers a good performance from an
inexpensive magnet, however, they tend to be bulky and are not always
suitable where space is an important factor. The steel parts are plated
& the Ferrite is inert thus corrosion is limited. Maximum operating
temperature is +120 °C.
2)
Cast AlNiCo, offers a better holding force than Ferrite systems and is
the only pot magnet that can be heated to extreme temperatures. However,
the high cost of the Cobalt content in the cast magnet makes the price
prohibitive unless the application requires temperatures over +120°C up
to a maximum of +500°C.
3)
Rare Earth Samarium & Neodymium, pots and assemblies can offer up to
eleven times the performance of a Ferrite system in a comparable size.
Applications tend to be specialized engineering projects where
performance and available space are key factors. Maximum operating
temperatures are +60°C for the Neodymium and +150°C - +250°C for the
Samarium depending on the design configuration.
When
considering your selection, please be aware of the following factors:
The stated Kg Pull (holding/gripping force) is based on the magnets
retaining force against a direct pull when offered to a clean ground
mild steel surface with a minimum thickness of 6mm. Painted or un-ground
surfaces will reduce this force, assemblies working in shear will
support approximately 1/3 of the stated value. |
