MAGNABEND – FUNDAMENTAL DESIGN CONSIDERATIONS(6)


Duty Cycle

The concept of duty cycle is a very important aspect of the design of the electromagnet. If the design provides for more duty cycle than is needed then it is not optimum. More duty cycle inherently means that more copper wire will be needed (with consequent higher cost) and/or there will be less clamping force available.

Note: A higher duty cycle magnet will have less power dissipation which means that it will use less energy and thus be cheaper to operate. However, because the magnet is ON for only brief periods then the energy cost of operation is usually regarded as being of very little significance. Thus the design approach is to have as much power dissipation as you can get away with in terms of not overheating the windings of the coil. (This approach is common to most electromagnet designs).

The Magnabend is designed for a nominal duty cycle of about 25%.

Typically it takes only 2 or 3 seconds to make a bend. The magnet will then be off for a further 8 to 10 seconds while the workpiece is repositioned and aligned ready for the next bend. If the 25% duty cycle is exceeded then eventually the magnet will get too hot and a thermal overload will trip. The magnet will not be damaged but it will have to be allowed to cool for about 30 minutes before being used again.

Operational experience with machines in the field has shown that the 25% duty cycle is quite adequate for typical users. In fact some users have requested optional high power versions of the machine which have more clamping force at the expense of less duty cycle.