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Posted on June 27, 2016
Unlike mechanically switchable permanent lifting magnet and electro lifting magnet, the actual lifting capacity of an electro permanent lifting magnet is influenced by more conditions, such as the magnitude of the magnetizing current pulse, the properties of the permanent magnets and the reversible magnets, in addition to the load thickness, the air gap between the load and the magnet, and so on.
Since electro permanent lifting magnet has been invented for lifting and moving ferromagnetic workpiece decades ago, engineers have come up with different ways for maximum safety of lifting. One patented technology is to detect the shape of the magnetizing current impulse in order to determine full magnetization of the electro permanent lifting magnet. In another patent, electro permanent lifting magnet was installed with coils around the steel pole heads as for measuring total flux through them and thus for attracting force to the load lifted. These methods involve high accurate measure means and complex installment of the safety devices.
Compared to the above mentioned methods for maximum safety of lifting by electro permanent lifting magnets, Armstrong's Twice Magnetizing (Partial and then Full magnetizing) mechanism should be simple and reliable.
Twice Magnetizing is based on a simple logical thinking: If A>B>C, thus A>C. Here C is the weight of the load being lifted, B is holding force of the electro permanent lifting magnet to the load after partially magnetized. A is the holding force to the same load after another but more strongly magnetization. Normally we adjust some of electrical parameters of the electro permanent lifting magnet to make B equal to 1/3 - 1/2 of A.
When operating an Armstrong Electro Permanent Lifting Magnet, it is partially magnetized and thus has partial lifting capacity after pressing the MAG button. A few seconds after the hoist rope is tensioned or the lifting magnet attracting the load is hoisted off the floor, a full magnetizing current takes place automatically and a stronger attracting force to the load can then be achieved.
If an electro permanent lifting magnet partially magnetized and with partial lifting capacity is lifting a load, why would you be worried about the lifting safety after it gets another but stronger magnetization and thus has more lifting power?