Determining the best location to remove metal in a Plastics Processing plant can be difficult. To assist plastics engineers, Bunting has released a Typical Plant Flowsheet showing optimum locations for metal separators. This blog focuses on the locations, designs and types of Magnetic Separator and Metal Detector commonly used in plastics plants.
On the flowsheet, the Plastics plant is divided into different areas and identifies optimum locations to remove metal. In many cases, a combination of Magnetic Separator and Metal Detector is recommended as the Magnet captures and holds ferrous metal (the vast majority of metal contamination in any plant). This leaves the Metal Detector to focus on removing the more difficult non-ferrous metals whilst minimising product loss and production downtime.
The type and suggested location of Metal Separation equipment is as follows:
Tramp metal commonly enters the process with the raw material feed. Subsequently, it is good practice to position metal detectors and magnetic separators on the pneumatic line feeding the primary storage silo. This reduces the level of tramp metal introduced to the process from external sources.
The key in preventing equipment damage or causing defects in the end plastic product is to continually identify and trap any metal contamination. Metal contamination arises within a plant from fatigued equipment (e.g. screens, pumps), general wear and tear (e.g. of silos, pipes, etc), and accidental introduction from personnel when conducting maintenance and other work. Subsequently, several stages of metal removal are required.
When the raw material leaves the storage silo, the feed passes through a gravity fed HF Drawer Filter or Pneumatic Inline Magnets.
Metal contamination entering the moulding lines causes costly damage to machinery affecting productivity, as well as increasing the percentage of finished product rejects. A combination of metal detectors and magnetic separators prevents such issues, with the final combination determined by the installation. The options include:
Metal contamination also damages the extruder. Once again, a combination of a magnetic separator and metal detector provide important protection.
Metal contamination entering the hot runner system, which is an assembly of heated components used in plastic injection molds that inject molten plastic into the cavities of the mold, can cause catastrophic and costly damage. If the system is fed pneumatically, the optimum metal separation equipment includes:
Within any plastic manufacturing process, a proportion of the production will be rejected (i.e. by metal detectors) and there will be off-cuts and pre-production runs that produce recoverable waste. Metal contamination in this 'waste' is more likely, due to the collection process and also as some materials will have already been rejected with such contamination.
The three recycling processes include:
The process stands for Post Industrial Regrind, or PIR and essentially describes the process of recapturing scrap plastics and resins from any manufacturing process. These processes happen, for example, when lids are being made for bottles and plastic containers. There is a wide range of metal detectors and magnetic separators used including:;
Previously rejected material is reprocessed to recover any entrapped good material, initially passing through a magnetic separator followed by a metal detector.
In some operations, the waste plastic is immediately extruded for future use in the plant or on-sale. Metal separation equipment is vital to protect the extruder and can include:
The type and design of Magnetic Separator and Metal Detector and the recommended locations has been determined following several decades of working with plastics producers and processors all over the world. There are always variations to plant designs and layouts that mean different types of Metal Separation equipment is needed and an onsite review by a Bunting engineer will help ascertain the best solution.
For further information on removing metal from a plastics processing plant using Magnetic Separators and Metal Detectors, please contact the Bunting technical sales team on:
For additional information on removing metal from plastic please contact us on:
Email Gordon: gkerr@buntingmagnetics.com
Telephone: +44 (0) 1527 65858
All product photographs by Paul Fears Photography
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