Walker Magnetics SMART-B SERIES - Manual (Page 10)

O.S. WALKER Co., Inc. SMART-B Control
SMART B MANUAL DD-14283J Rev J, March 30, 2011
4-1
4 OPERATING INSTRUCTIONS
4.1 Important Facts about Magnetic Holding
Workpiece characteristics must be considered in order to determine the magnetic holding
attraction that a magnetic chuck can provide.
This is true for all magnetic chucks because they all operate using the same fundamental
laws of physics. Magnetic power is often pictured as lines of magnetic force flowing from north
to south pole. Anything that limits the flow of these magnetic lines of force obviously reduces
the magnets holding capacity. There are many important factors that limit the flow of these
lines of force.
4.1.1 Surface Conditions
Magnetic lines of force do not flow easily through air. They need iron in order to flow
freely; therefore, anything that creates a space or an air gap between the magnet and the
workpiece limits the flow of magnetic lines of force and, thus, reduces the holding
capacity of a magnetic chuck.
• Magnetic Chuck Surface Condition -- The holding surface of a magnetic chuck must
be clean, smooth, flat, and free of nicks or burrs in order to minimize the air gap
between the chuck holding surface and the Workpiece. All Walker chucks are
designed with soft, low carbon steel magnetic poles in the top plate in order to
maximize the holding capacity; therefore, special care must be taken to protect these
areas.
• Workpiece Surface Condition -- The holding capacity of the chuck will be reduced if
certain surface conditions exist. A rough surface finish on the workpiece creates an air
gap as also foreign materials like dirt, paint, rust, paper, and rags.
4.1.2 Workpiece Thickness
The greater the number of lines of magnetic force flowing from a magnet into the
workpiece the greater the effectiveness of the magnetic chuck. The thicker the workpiece,
the more lines of magnetic force are able to flow. After a certain thickness of the
workpiece, no additional lines of force will flow because the magnet has reached its full
capacity.
• Thin workpieces mean less iron available, and thus fewer lines of magnetic force flow
from the magnet into the workpiece. Therefore, the chuck holding capacity is reduced.
• Typically, the minimum thickness of a workpiece required to reach full holding capacity
is the same as the thickness of the chuck major magnetic steel poles.
4.1.3 Portion of the Chuck Surface In Contact With the Workpiece
The full surface of the chuck top plate must be covered by the workpiece to achieve the
maximum holding capacity. The surface of the workpiece must contact equal areas of the
chuck opposite polarity major magnetic poles to obtain maximum holding force.