Dear Shri Banerjee,

Please inform whether the magnetic separator would be operating in conjunction with metal detector i.e. separator will have full magnetic strength when there is signal from metal detector. Or whether magnetic separator will be separating tramp iron and metal detector will be utilised for signaling the presence of non-magnetic metal and stopping the conveyor for manual removal of non-magnetic metal.

Your clarification as above shall enable you to get the right answers from various people.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Dear Shri Banerjee,

If you are planning to use magnetic separator operating in conjunction with metal detector, following are my views.

As I know, the magnetic separator operating in conjunction with metal detector had been experimented / used quite frequently, about 1.5 decades back in India. The basic principle for this type of system is as below :

1) The metal detector is located some meters before the magnetic separator.

2) The magnetic separator is under energized (i.e. less DC Current) most of the time. So, it is comparatively less hot.

3) The metal detector on sensing the presence of tramp-iron gives signal / command to magnetic separator DC Supply system, which increases the DC current to very high value to create powerful magnetic separation.

As the magnet is less hot most of the time, the allowable current value as per serial no. 3 is more compared to full value continuous energizing of magnet. The high DC Current is present for fraction of minute, during which the heating of magnet starts. However, this being for short duration; the magnet temperature will still remain within allowable limit. Thus, this system simply increases the thermal rating of the magnet during action period.

However, if there is repetitive arrival of tramp-iron, the magnet temperature will cross the limit. If the temperature safety sensor device fails (which is quite probable by various reasons) the magnetic winding will get damaged and the system will fail.

So, the system life and guarantee / warranty becomes subject of dispute between seller and buyer because nobody can prove the actual status of tramp-iron, when the magnet had failed. In view of such problems, as I know, I have not come across such specification at least during last decade in India.

The magnetic separator cum metal detector system results into following outcome :

- It can result into smaller size magnet and consequent economy (to seller / buyer)

- Alternatively, same magnet can create more powerful magnetic effect.

Regarding metal detector on steel cord belt, I have my doubts about its performance reliability on steel cord belts. The metal detector primarily functions on the principle of “Disturbance in magnetic flux” due to tramp-iron presence. In steel cord belt, the presence of splice creates an abnormality. If this abnormality is bypassed in metal detector circuit, and if tramp-iron happens to be in this zone, then metal detector will fail to signal its presence. I will prefer to avoid metal detector on steel cord belt. However, you can interact with the metal detector suppliers and if they have solution you can think about its application.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■