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Overband magnetic separator

Application

An overbelt magnet is suitable for removal or separation of high volumes of iron or steel and hangs above a flat- or trough-shaped conveyor. This type of magnet is self-cleaning and continuously separates (ferromagnetic) Fe parts from material streams. The deferrization efficiency of overbelt magnets varies from 70 to 90%; this depends on magnet design, product flow and placement.

Automatic self-cleaning overbelt magnet separators are suitable for both the recovery (recycling) of ferrous parts and the removal/elimination of impurities (iron contaminants).

These magnets are mainly suitable for coarser fractions with pieces larger than 10 mm. Thanks to the robust, reliable technology, these magnets have applications in many industries. Putting a permanent overbelt magnet in service requires nothing more than four suspension points, sufficient space and power to drive the conveyor belt.

Transversely mounted electromagnetic overbelt magnet

Operation

Conveyor belt speed

To remove ferrous or iron parts from a material flow, they must remain in a magnetic field for between approximately 0.3 and 0.5 seconds, where they are magnetized. To achieve maximum separation, it is important to optimally match the size of the block magnet (main pole) and the belt speed.

This means that with a narrow overbelt magnet the conveyor belt beneath it must run at lower capacity (m/s) than with a wider magnet at the same suspension height. The following formula provides an indication of the maximum conveyor belt speed:

Maximum conveyor belt speed (b) = block magnet width (a) / 0.3 (sec.)

As an example, this has been calculated for two Goudsmit overbelt magnets:

Type: ROP-F1-C

Block magnet width (a): 0.470 m

Type 1 overbelt magnet

Results in max. conveyor belt speed of the material (b): 1.6 m/s

Type: ROP-F3-C

Block magnet width (a): 0.615 m

Type 3 overbelt magnet

Results in max. conveyor belt speed of the material (b): 2.0 m/s

The formula above is a rule of thumb and does not guarantee perfect separation. Longer residence time in the magnetic field always has a positive effect on the degree of separation. If there are long or large ferrous parts in the product flow or the conveyor belt speed cannot be lower than 3 m/s, we recommend an inline type magnet.

Magnet type

Overbelt magnets can be divided into three main types. There are various materials and versions that can serve as a suitable magnet system. Each type has its advantages and disadvantages and therefore its own specific application:

Specification

Ferrite

Neodymium

Electromagnetic

Max. mounting height [mm]*

230 - 450

300 - 350

360 - 600

Magnetic field

Permanent

Permanent

Switchable

Number of magnet poles in main pole

3

2

3

Ferro (iron) separation

Yes

Yes

Yes

Weakly magnetic and stainless steel separation

No

Yes

No

Compact design

No

Yes

No

Lightweight

No

Yes

No

Price

$

$$

$$$

 

 

 

 

*) depending on the selected version; low-budget types have a lower maximum mounting height.

Placement

The distance between a magnet and the conveyor belt must be as small as possible; the magnetic force decreases exponentially with increasing distance. There is, however, a minimum distance required so the rubber cleats safely remove all the ferrous parts from the material flow.

There are two methods for use/placement of overbelt magnets: transverse and inline. Goudsmit has a specific, optimum magnet configuration for both mounting options.

Transverse ('Cross')

In practice, transverse placement is most common, because it is easier to install in an existing line. An additional advantage is a ferrous discharge to the side, which from the logistical perspective is easier to process.

Inline

If you have the option to place your overbelt magnet in line with the conveyor belt, this is always preferred. The advantage of this is that the transported material ‘breaks open’ at the end of the belt (head pulley) and is therefore suspended in midair for several milliseconds. As a result, the magnet can easily pull the ferrous metal out of the product flow.

Transversely and inline mounted overbelt magnets

Non-magnetic zone

Note: when positioning the magnet, the construction below the magnet—such as the frame, bearing rollers and reversing rollers—must be made of non-magnetic material. This is because steel parts will become magnetized, which will adversely affect the separation performance of the overbelt magnet. Goudsmit uses the following rule of thumb: keep the area extending a distance of 1/3 of the magnet's width (shown below as 'a') on all sides free of magnetic material. For the area below the magnet, maintain a non-magnetic zone that is twice the height of the block magnet ('b'). It is important that all components in this zone be made of stainless steel, plastic or other non-magnetic material.

Viewing direction

Inline mounting

Transverse mounting

Front view

Inline mounted overbelt magnet

Transversely mounted overbelt magnet

Side view

Inline mounted overbelt magnet

Transversely mounted overbelt magnet

 

 

Separate particles
Max. installation height

Products

Ferrite overband magnets

Suitable for thin to thick layers and do not require a control box. Very reliable and available in many belt widths. Transverse or inline installation above your conveyor belt.

More information

Neodymium overband magnets

Suitable for fine fractions in thin layers; also separate weakly magnetic particles. No control box required. Transverse or inline installation above conveyor belt. Also for mobile applications.

More information

Electro overband magnets

Electromagnetic overband magnets have a deeply penetrating magnetic field and are therefore suitable for very thick layers. A control box is required. Installation perpendicular to or in line with conveyor belt.

More information