A Scrap Heap Magnet can only pick up metals that are magnetic.
If the metals are not magnetic then the scrap heap magnet cannot pick the metals up.
A scrap heap magnet can only pick up metals that are Ferrous metals which are Iron, Steel, Tin and some types of stainless steel.
Regular Stainless Steel is not magnetic but some grades of stainless steel are magnetic.
Non Ferrous Metals are Brass, Copper, Aluminum which are not magnetic and cannot be picked up by a scrap heap magnet.
The Scrap Heap Magnetic uses electricity to create the magnetic field.
When the electricity is turned off the metals are released and when the electricity is turned on to the magnet the magnet picks the material up.
Inside the scrap heap magnet there is a wound of copper wire that creates the magnetic field.
And in the crane or track hoe there's a generator and transformer that creates the voltage needed for the scrap heap magnet to work.