The simple answer to the above question is: each has its place and there are situations where one or the other is a clear preference.
In recent years the separating of ferrous contamination from food, grain and plastic products has tended to favour the use of 1 Tesla (10,000 Gauss) grate magnets whereas a decade or two ago, magnetic drums were very widely used.
The rationale among users seems to have been that magnetic grates at a surface strength of 10,000 Gauss must be better than a magnetic drum with a surface strength of say 4000 – 5000 gauss. However, this is certainly not necessarily the case.
As suppliers of both magnetic drums and grates we at Serpent & Dove – Applied Magnetics believe it is important for users to understand that each product has its place and each offers features appropriate to specific situations.
For a start, there is nothing particularly ‘magical’ about 10,000 Gauss. It happens to be what is relatively easily achieved on the surface of a grate magnet with the state of current rare earth magnet technology. While it is true that 1 Tesla (10,000 Gauss) on the surface of a grate magnet tube can be quite good for the recovery of fine iron and some feebly magnetic iron (such as work-hardened stainless steel), it is not a number that is particularly necessary for the removal of iron contamination. .jpg)Once a piece of iron (regardless of size) is magnetically saturated (that is, as magnetised as it’s possible for it to be), no amount of stronger magnetic field strength will make any difference. And – it does not require a ‘magic’ number of 10,000 Gauss.
That is why magnetic drums at say, 5000 Gauss on the surface, but offering a much longer residence time for particles within the magnetic field, as well as some opening up of the product over the face of the drum, can be the most effective separator in many applications.
Add to this the fact that drums are continuously self-cleaning and allow for larger product particles and/or difficult materials to be processed and it can be seen that in some applications, magnetic drums have distinct advantages over grate magnets. Moreover, for processing more abrasive materials drums are likely to give longer wear because of the shell thickness and the rotation of the drum compared to the static nature of grate magnets and very thin tube walls.
A further factor for consideration is of course, available head-room. As a general rule a double row self-cleaning grate magnet may occupy a little less vertical space than a drum for the same duty. Lastly, self-cleaning grate magnets (which are cyclically cleaned and are not continuously self-cleaning as is a drum) can be the more expensive option.
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