Page 133 - Electromechanical Devices and Components Illustrated Sourcebook

Chapter 5 Magnetic Components 95

My father used to tell a story of how he and his friend built Iron Core
an electromagnet in their high school industrial arts class. The Push Button
idea was that they would place the magnet on top of the glass
of a pinball machine and move the ball in order to rack up
points. The sandwich shop down the road from the school
would give a free sandwich to anyone who got a score above
Field Lines
a certain level. My father and his friend thought that this
would be a good way to get free sandwiches. They hauled the + −
19 pound electromagnet down to the sandwich shop and,
somehow, slipped in unnoticed. His friend carried a book bag
with six dry cell batteries connected in series. They placed the
magnet on top of the pinball machine, slid it over the ball and
connected it to the batteries. The magnet was so strong that it Battery
sucked the ball up and shattered the glass. It took them six
weekends to work off the repair costs and their shop-teacher
never gave the magnet back.
Cup-style electromagnets can produce very high flux den-
sities at their poles. For this reason they are commonly used Figure 5-44 “C” Style Electromagnet
in mechanisms that require mechanical high loads. A com-
mon use for these magnets is as door locks. The locking force
is so strong that the door cannot be opened, even with con-
siderable force, until the power is turned off. Figure 5-43
shows a cup-style electromagnet.
Figure 5-44 shows a “C” style electromagnet. By manipu-
lating the gap spacing extremely high fields can be produced
with relatively low power and coil sizes.
Figure 5-45 shows a typical commercial application of a
cup-style electromagnet for scrap recycling. These mag-
nets can be seen in action at nearly every scrap yard in the Lift Cable
nation.

Iron Core

Coil
Coil Form
Cable Clamps Power Cable

Thimble

Field Lines

+ − Chain Sling

Connector
Push Button Lifting Lugs

Battery
Cup-Style Cup

Figure 5-43 Cup-Style Electromagnet Figure 5-45 Electromagnet for Scrap Recycling