Disappointed in the non-ferrous yield of your eddy current separators? Not achieving maximum belt coverage? Material sticking to or accumulating in the vibratory feeder? Interested in super-efficient magnetic separation in combination with a ballistic trajectory? Then read our blog.
Eddy current separators
First of all, a brief introduction to eddy current separators, also called non-ferrous separators. Eddy current separators consist of a conveyor belt system with a rapidly rotating magnetic rotor at the end. The rotation speed of the magnets generates an induction field, creating a rapidly changing magnetic field. See this animation about Eddy Current non-ferrous separators .
The separation is based on the principle that every electrically conductive particle located in an alternating magnetic field temporarily becomes magnetic. Simply put: For a brief moment all non-ferrous metals that pass the magnetic roller become magnetized themselves, causing them to be ejected. This enables us to separate a huge number of non-ferrous metals and their alloys, including aluminium, copper and brass. For a more detailed explanation of how non-ferrous eddy current separators work, see: general explanation Goudsmit's eddy current separators.
What is a mono-layer?
This is a product layer that has a maximum thickness of one particle. In other words, in an ideal mono-layer none of the particles are on top of each other. This is important for eddy current separation, because the non-ferrous particles in the product flow are 'ejected'. For example, if a metal particle is covered with sand or stones (in a non-mono-layer situation) it is unlikely that the EC separator will eject the metal part with enough velocity to separate it from the product flow. Particularly for the 'fine fractions' (particle size 0-10 mm) it is extremely important to create a mono-layer for maximum recovery of non-ferrous material.
Why is full belt coverage important?
There are a number of reasons:
- For maximum utilization of the capacity of your machine
- To create a mono-layer
- A longer residence time on the conveyor belt
As a bulk processor, you no better than anyone that every percent counts. Therefore you want to get the most out of your product flow. The two examples above show situations in which 20% of the belt is not covered. The difference in volume of the product flow is offset somewhere else. As a consequence, somewhere else in the flow there is no mono-layer, which ultimately results in a lower recovery yield of your non-ferrous metals.
Problems with mono-layers and/or incomplete belt coverage can occur as a result of sticky or moist product flows, such as IBA (incinerator bottom ash) and RDF (refuse-derived fuel). An example of this is that the cement-like mass in IBA adheres to the surface of vibratory feeders. This prevents the vibratory feeder from distributing the product evenly.
The product assumes a uniform orientation (the path of least resistance). In practice, this problem is solved by cleaning at weekly or monthly intervals. This does, however, mean unnecessary downtime and extra maintenance. The true cause of the problem is the encrusted vibratory feeder, and you need to tackle the problem at the source by implementing a permanent, maintenance-free solution.
Solution: conveyor belt feeder with product distributor
At Goudsmit we are familiar with your problem, and we have developed a proven solution: a conveyor belt feeder with product distributor. This feeder module replaces the vibratory feeder and thus solves the problem. But how does this module work? The feeder module actually consists of two conveyor belts, each with its own task.
The first conveyor belt (product distributor)
is at an angle and feeds the material up until it reaches the product distributors. These product distributors (also called ‘churners’), which look like large hand mixers, spin in the material to distribute it evenly. If the amount of material being fed in exceeds the capacity, the excess material slides back down. This ensures a constant volume and continuous flow to the next processing step. Therefore, the task of the first conveyor belt is to distribute the material to form a mono-layer and ensure full belt coverage.
The second conveyor (magnetic separator)
is flat and transports the material towards the end: the magnetic head pulley of the conveyor belt. This magnetic head pulley can be fitted in any of four different strengths (option):
- Magnetic head pulley 1800 gauss;
for steel and iron particles from 1 to 100 mm
- Magnetic head pulley 3000 gauss;
for steel and iron particles from 0.5 to 100 mm
- Magnetic head pulley 6000 gauss;
for steel, iron and stainless steel particles from 0.5 to 100 mm
- Magnetic head pulley 9000 gauss;
for steel, iron and stainless steel particles from 0.1 to 30 mm
We strongly recommend the inclusion of a magnetic head pulley, because it significantly improves the eddy current separation and a magnetic head pulley will boost your ferrous yield.
The third conveyor belt (eddy current separator)
now receives an optimal material flow: a mono-layer, perfectly spread across the entire width of the belt and free from fluctuations in density. The ferrous metals are also removed so they do not interfere with the eddy current separation step. The material is now perfectly prepared for the powerful 38HI eddy current rotor, with 3500 gauss at the belt.* A high magnetic force is required for the heavy non-ferrous metals, such as copper and brass. This machine distinguishes itself quite clearly from all others in this regard.
The end result of the complete machine: optimal ferrous and non-ferrous separation without time-consuming downtime for cleaning encrusted vibratory feeders. Simply put: a highly efficient solution to your problem.
*) flux density at 3 mm thickness on the belt and tolerance of ±10%
Conveyor belt vs. vibratory feeder?
Is a vibratory feeder always inferior to the conveyor belt system? The answer is no. After all, this entirely depends on your product flow. In some cases, a conveyor belt feeder is actually a less desirable solution and a vibratory feeder is the better choice. For example, when processing WEEE flows, which contain many sharp parts.
These parts would quick damage a conveyor belt, resulting in considerable maintenance and downtime for the necessary conveyor belt replacements. Moreover, such flows are not moist and do not adhere to the vibratory feeders. Furthermore, the conveyor belt feeder is a more expensive solution than a simple vibratory feeder. But in the right application the extra cost will quickly be compensated by the additional non-ferrous recovery. The following comparison will help you quickly grasp the pros and cons of a conveyor belt feeder:
Summing up: the conveyor belt feeder module is an excellent solution for moist or sticky product flows, such as:
- IBA (incinerator bottom ashes)
- RDF (refuse-derived fuel)
- ASR (automotive shredder residue)
The fraction must be between 0 and 50 mm so the product distributors can spread the material evenly over the belt.