Walker Magnetics TURBOMILL 40B - Manual (Page 13)

O.S. WALKER Co. Inc., Turbomill Electroperm Chucks
DD15508M.doc Rev. ~, September 17, 2002
4-2
4.3.2 Workpiece Surface Condition
The holding capacity of the chuck will be reduced if certain surface conditions exist. A
rough surface finish on the work piece creates an air gap. Foreign materials such as dirt,
paint, rust, paper, and rags will create an air gap.
4.3.3 Workpiece Thickness
The greater the number of lines of magnetic force flowing from a magnet into the work
piece the greater the effectiveness of the magnetic chuck. The thicker the work piece,
the more lines of magnetic force are able to flow. After a certain thickness of the work
piece, no additional lines of force will flow because the magnet has reached its full
capacity.
Thin work pieces mean less iron available, and thus fewer lines of magnetic force flow
from the magnet into the work piece. Therefore, the chuck holding capacity is reduced.
Typically, the minimum thickness of a work piece required to reach full holding capacity
is the same as the thickness of the chuck major magnetic steel poles.
4.3.4 Portion of the Chuck Surface In Contact With the Workpiece
The full surface of the chuck top plate must be covered by the work piece to achieve the
maximum holding capacity. The surface of the work piece must contact equal areas of
the chuck opposite polarity major magnetic poles to obtain maximum holding force.
4.3.5 Workpiece Material
Low carbon steel such as SAE 1020 steel, are nearly as good conductors of magnetic
lines of force as pure iron. However, many other alloys contain non-magnetic materials,
which reduce the ability of magnetic lines of force to flow. An alloy such as SAE 300
series stainless steel is almost as poor a conductor of magnetic lines of force as air.
Type 416 stainless steel is considered magnetic, but it contains enough chromium so
that a magnet can develop only about one half as much magnetic force as it can on an
SAE 1020 steel work piece. In addition, because of the carbon content, the force
developed on typical cast iron is less than one half that developed on SAE 1020 steel.
(Chilled cast iron further reduces the force to less than one quarter.)
Additional concerns regarding Magnetic Holding should be forwarded to O. S. Walker,
Inc.