How to Adjust Air Separation and Mesh Size for Higher Copper Purity

Published in News & Insights · Tech & Maintenance

By Henan Jiacui Intelligent Equipment Co., Ltd.

Copper purity is not a property of the granulator; it is a property of the separation stage. Two yards running identical machines on similar cable routinely produce different grades of product, and the difference is almost always the mesh aperture and the air velocity — two settings that are adjusted in a few minutes and yet are left untouched for months.

This article explains what each setting does physically, how they interact, and a procedure you can follow to tune them on your own material. It deliberately includes the honest complication: mesh and air cannot be optimised separately, and chasing the last tenth of a percentage point of purity has a real cost in throughput.

Where purity is actually lost

Before adjusting anything, it helps to know which of three losses you are trying to fix. They have different causes and different remedies.

The physics, briefly and usefully

Air separation exploits the density difference between copper (about 8,900 kg/m³) and PVC or PE insulation (roughly 1,300–1,400 kg/m³ — about one-seventh the density). In a rising airstream, the upward force on a particle depends on its projected area, while its weight depends on its volume and density. For particles of the same size, the plastic is lifted much more easily than the copper.

The complication is particle size. A large, flat piece of plastic has a high surface area to weight ratio and is easily lifted. A very small copper particle has a low mass but also a small projected area, and in a high-velocity airstream it can be entrained and lost. This is precisely why mesh size and air velocity must be considered together: the mesh decides which particle sizes reach the separation stage, and the air velocity decides which of those sizes are lifted.

What mesh (screen) aperture actually does

The screen sits between granulation and final classification. Its aperture sets the upper size limit of what passes, and it therefore controls the size distribution entering separation and the size distribution of the finished product.

The practical conclusion is that mesh selection is a trade between throughput and uniformity, not a purity dial as such. Its purity effect comes through controlling what the separation stage has to deal with.

What air velocity actually does

Air velocity is the purity dial, within limits. Raising it lifts more material into the plastic outlet, which reduces plastic contamination in the copper product but risks losing fine copper. Lowering it retains copper but allows plastic into the copper fraction.

• Variable-frequency fan control is what makes this adjustable in practice. A fixed-speed fan leaves you with one setting for a feed mix that changes every day.
• A second, gentler separation pass over the plastic outlet is the cheapest purity upgrade available on a machine that has only single-stage separation. It lets you run the first pass conservatively — biased toward retaining copper — and recover the remaining copper in the second pass where the material is already largely plastic.
• Velocity is not the same as volume. Ductwork leaks, partial blockages and dirty filters all change the velocity reaching the separation chamber even if the fan setting is unchanged. This is why a machine that worked well for months can gradually drift for no apparent reason.

The interaction that catches people out

Mesh and air are usually adjusted by two different people at two different times, and that is where problems start. Changing the mesh changes the size distribution reaching the separation stage, which changes the air velocity that is correct. Fitting a finer mesh and leaving the air setting alone will lose fine copper. Fitting a coarser mesh and leaving the air setting alone will push plastic into the copper product. Any change to one requires a retune of the other.

A tuning procedure you can run in half a day

1. Run a baseline test. With everything as found, feed a weighed batch of representative material — at least 200 kg — and collect and weigh all three outputs: copper product, plastic product and dust. Record the feed rate you actually achieved. This is your reference point.
2. Sample and assess purity. Take a representative 2–3 kg sample of the copper product and inspect it. A practical field method is to spread it on a clean sheet and count or separate by eye, then weigh the plastic you pick out. You already have accurate scales, so precise counting matters less than doing the same measurement every time.
3. Check the mesh first. Inspect for blockage, wear, distortion and tears. Clean or replace before touching the air setting — you cannot tune separation through a worn screen.
4. Adjust air velocity in small steps. Change the fan setting by a small increment, feed the same material at the same rate, and sample the output again. Move in one direction until you see copper appearing in the plastic outlet, then come back one step. That is your upper limit.
5. Watch the mass balance, not just the appearance. The correct setting is the one where the copper product is clean and the plastic fraction is light and low in copper. A setting that improves copper appearance but increases total copper in the plastic has made things worse, not better.
6. Record the setting against the material type. Write down the fan setting, mesh and observed purity for each feed type — household wire, communication cable, harness, fine wire. You now have a starting point next time instead of a day of trial and error.
7. Repeat after any change. New blade set, new mesh, different material supplier, or a freshly cleaned dust system all shift the optimum. Retune rather than assuming last month's setting is still right.

How to measure purity without a laboratory

You do not need analytical equipment to manage purity; you need consistency. Three field methods are enough for day-to-day control:

• Visual spread and pick. Spread a sample thinly, pick out visible plastic by hand, and weigh it against the total. Repeatable to within a fraction of a percentage point if you always take the same sample size.
• Water float test. Copper sinks and most insulation plastic floats. Submerging a sample in water separates the fractions instantly and is a fast check on gross contamination — though not on fine contamination, and it is a check, not an assay.
• Mass balance. The most powerful tool you have. If feed in minus copper out minus plastic out does not account for the difference as dust, the missing material is a loss. Track it daily and you will see a separation problem developing before it reaches your buyer.

Common mistakes when tuning separation

1. Tuning air separation on a machine with worn blades or an open blade gap — fix the cutting chamber first, then tune.
2. Chasing maximum purity regardless of throughput. Going from 99% to 99.7% copper content while cutting output by a third may lose more money than it earns.
3. Adjusting mesh and air at the same time, then being unable to tell which change helped.
4. Judging the setting by the copper product alone and never inspecting the plastic fraction.
5. Leaving a machine with a dusty, partially blocked duct or filter and expecting the fan setting to behave as it did when clean.
6. Never recording the settings, so every material change means starting over.

When to accept lower purity

Higher purity is not automatically more profitable. Separation consumes energy, and running the fan and feed rate at the edge of the setting costs throughput and increases the risk of losing fine copper. The sensible approach is to establish what your buyer actually requires — often a contractual minimum copper content per shipment — and to tune to clear that specification comfortably rather than to maximise a number nobody is paying a premium for. On difficult fine wire, a well-tuned 98–99% product delivered reliably usually beats a 99.5% product produced in half the volume.

Frequently Asked Questions

Does a finer mesh always give higher copper purity?

Not directly. A finer mesh gives a more uniform particle size, which makes the separation stage easier to tune and therefore usually improves achievable purity — but only if air velocity is retuned to match, and only if the additional fines generated are recovered by the dust system rather than lost. A finer mesh left with an unchanged air setting will lose fine copper.

How do I know if my air separation is set too high?

Look at the plastic outlet. If the plastic fraction is heavy for its volume, contains clearly visible bright or pinkish copper, or if your mass balance shows copper unaccounted for, the velocity is too high or the feed rate is too aggressive for the separation stage. Reduce fan speed in small steps and re-check the plastic fraction each time.

What mesh size should I use for fine and capillary wire?

The mesh must be small enough to prevent long strand fragments reaching the separation stage, because those fragments are the hardest particles to separate cleanly. At the same time it must not be so fine that throughput collapses and fines generation rises. Because the right aperture depends on your specific strand sizes, the practical method is to test two adjacent mesh sizes on a representative batch and compare both purity and measured throughput.

How often should I check and clean the screen?

Inspect it weekly as part of the normal maintenance routine, and clean it whenever throughput or power draw changes noticeably. Screen apertures block gradually, and a partially blocked screen changes the size distribution reaching separation — so it will quietly degrade purity without any obvious symptom until someone inspects the plastic fraction.

Can I improve purity on a machine that only has single-stage air separation?

Often yes, without replacing the machine. Running the first separation pass slightly conservatively — biased toward retaining copper rather than removing every trace of plastic — and then reprocessing the plastic fraction through the same separation stage a second time usually recovers most of the remaining copper. It costs an extra pass over the material and is far cheaper than a new machine.

Get a Separation Tuning Recommendation

If you tell us your granulator model, your feed mix and the purity your buyer requires, our engineers will give you the recommended mesh aperture and air-separation procedure for that material — and, if you can send a sample, we will test it and report the settings we would use.

Send us your material description, daily tonnage and target output, and our engineering team will respond with a model recommendation, a capacity calculation and a quotation. You are also welcome to book a live video walk-through of the Henan Jiacui Intelligent Equipment Co., Ltd. factory in Zhengzhou, Henan, China, or request a reference list of installations running comparable cable or waste streams.

About the Author and the Manufacturer

This article was prepared by the technical sales and engineering team of Henan Jiacui Intelligent Equipment Co., Ltd. (brand name JIACUI). Founded in 2015 in Zhengzhou, Henan Province, China, JIACUI designs and manufactures solid waste recycling equipment and copper wire granulation systems in a 5,000 m² factory with more than 100 employees. Our equipment holds CE, ISO and CSA certification, uses ABB and Siemens control components built to European design standards, and has been delivered to more than 400 customers in over 100 countries. Factory audits have been completed with SGS, BV and TÜV. We hold 27 patents covering shredding, granulation and separation technology. Where this article quotes performance figures, those figures come from our published model specifications and from commissioning tests on real installations; actual results depend on cable composition, feed preparation and operating practice.