Iron removal growth introduction
PTMS magnetic separation
Which metal cannot be separated by magnetic separation?
Magnetic separation systems, also known as (iron removers), were first found in scrap mills for heavy-duty shredders for grinding cars. Early magnetic separation systems were primarily electromagnetic iron removal; as ceramic materials became available and the cost of producing them was significantly reduced, permanent magnets began to enter the field to provide the same magnetic strength as their electromagnets. In addition, permanent magnet separators do not have to rely on external power sources, and there is no problem with overheating of electromagnets. These early electromagnets were often expensive and cumbersome.
With the development of the scrap industry, magnetic separation systems are also evolving. By the end of the 1970s, three main types of magnetic separation systems were common: top magnets; magnetic pulleys; and drums. By the end of the 1980s, another form of magnetic separator, eddy current, has become increasingly popular among used processors and municipal recyclers. Although eddy currents are not discussed here, its contribution to the recycling industry is significant. The eddy current typically applies a magnetic charge to the non-ferrous metal material through a rotating alternating magnetic pole magnet below the conveyor belt and below the head pulley. When charged particles are in contact with the field of the opposite pole, it is rejected and classified.
Today, magnetic separation is still the primary way for processors to remove iron from non-ferrous metals. Although permanent magnets are a popular choice, advances in electromagnets have made them competitive again.
Top magnet
The first type of iron removal device is an overhead magnet. These are stationary magnets with self-cleaning straps that can be rotated around the magnet assembly. The wedge belt moves the attracted ferrous material and discharges it out of the magnetic field. These magnets can be configured in two main ways - parallel to the conveyor, called in-line; or perpendicular to the conveyor, called the cross-belt. Other configurations are actually variations of overhead magnets in which multiple magnets are used to transfer ferrous material from one magnet to another. These magnets are referred to as "multi-stage" magnets.
In online applications, the magnet is typically located at the end of the conveyor above the head pulley. The main advantage of positioning the magnets in this manner is that the entrainment of the iron sheets and particles is reduced. Once the material leaves the conveyor belt, it is released and the magnet extracts the suspended iron material from the air.
If the conveyor is in an inclined state, the momentum of the particles leaving the conveyor belt will result in an upward trajectory towards the magnet. Therefore, the closer the material is to the magnet, the easier the iron-containing particles are picked up.
A magnetic device manufacturer said: "No matter how hard the processor tries to prevent it from getting stuck, it always happens with overhead magnets." However, it does not happen in an online configuration as it does in a crossover strap. ”
It is particularly difficult to remove iron from a wet, broken wood stream with overhead magnets as the debris begins to interlock and collect. Suppliers say that wet wood and any other wet materials are more difficult to process and, if possible, should be avoided when applying magnetic separation. However, the online configuration can release more ferrous material for separation.
For online applications, the magnet should be the width of the conveyor. Some manufacturers have square magnets. Others offer rectangular magnets in which the longer length of the magnet is parallel to the conveyor belt, providing more belt coverage.
Another application for overhead magnets is the cross-belt structure. This is a popular installation because it is not always practical to place the magnet directly on the head pulley - there may be other equipment at the end of the conveyor belt, such as a magnetic pulley or eddy current separator. In addition, materials such as cross-belt configurations are equipment recovery operators because the magnets can be placed close to the manual picking station and the efficiency of the magnet is increased due to the slower belt speed.
In in-line and cross-belt configurations, overhead magnets are resistant to gravity, so they must work harder and must generally be more powerful than magnetic pulleys or rollers. However, the in-line arrangement requires less field strength than the cross-belt because it does not have to be stuck with the wire mesh and does not have to change the direction of the ferrous material. Therefore, the cost of an in-line overhead magnet may be lower than the cost used in a cross-belt configuration.
Variants of overhead magnets include single and tertiary magnets. In a single-stage magnet, the ferrous material is transported by a magnetic field and unloaded onto another conveyor, while the non-ferrous material falls into the container.
In a three-stage configuration, the ferrous iron passes through three separate magnets that are contained in one housing. When a ferrous material is transferred from one magnet to another, the particles will flip and any remaining non-ferrous materials will fall off, resulting in a cleaner final product. Both single- and three-stage variants are powerful magnets that pick up black blocks of heavy metal.
Although many manufacturers sell permanent and electromagnetic configurations, one manufacturer recommends using an electromagnet at the overhead position when the distance between the magnet and the conveyor must be greater than 12 inches.
Most overhead applications have permanent magnets, but the processor also likes electromagnets because they adjust the strength and turn it off even when there is no need to separate the iron.
Magnetic plush
Another type of magnetic separator is a magnetic pulley. In this configuration, the magnet is embedded in the head pulley of the conveyor. As the pulley rotates, the magnetic force captures the ferrous particles and brings them around and under the pulley until the natural band separation on the surface of the pulley forces the particles to fall into a separate bin. Although suppliers are reluctant to recommend pulleys and overhead magnets, unless they know the specific application, most people think that the pulleys usually pull out finer iron particles than the overhead magnets.
This better sorting is possible because the material is closer to the magnet located directly below the belt. Moreover, the gravity of the pulley is advantageous for it. However, this method may not effectively remove larger iron-containing materials or substances trapped on top of the material stream.
Another disadvantage of the magnetic pulley is that the strength of the magnet is limited by the size of the pulley. According to one supplier, magnetic pulleys typically only have a penetration depth of 6 to 7 inches.
Magnetic pulleys can also be configured with overhead magnets. These combinations are recommended when the material stream contains ferrous metal advantages. Once this is done, make sure that the two magnetic devices are sufficiently separated - in some cases up to 8 feet or more - to avoid magnetic interference.