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How does a lifting magnet work?

 

city-machine-technologies-inc-57-inch-scrap-handler-magnetIn the next few weeks, we will take an in-depth look at lifting magnets. Lifting magnets are magnets that are used in scrap handling operations and in steel mills. Some lifting magnets can move cars and several pieces of steel and can be as big as queen-size beds.

Most lifting magnets are designed to operate in a 250-volt direct current system. A magnet, in its simplest form, is nothing more than a string of wire wrapped around a magnetic core. This string of wire has resistance (ohms) that govern what current (amps) flows at a given voltage (volts). All DC magnets obey Ohm’s law.

A magnet at room temperature, also called ambient temperature, has the greatest lift capability since its resistance is at its lowest point. The time in use, also called duty cycle, affects its strength.

When a magnet is used, or energized, it warms up.  The internal temperature rises quickly, and because of the size and construction of the magnet case, the heat is released slowly.
The internal temperature increases and so does the conductor resistance.  Therefore, as the temperature continues to increase, current will decrease, and so will the magnet’s lifting strength.

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