Magnetic chip conveyor: a key equipment to improve machining efficiency
A magnetic chip conveyor removes ferrous swarf continuously, so the machine keeps cutting instead of waiting for a manual clean-out. This page explains the separation mechanism, the boundary conditions where it stops working, and the checks that keep it running on a 24-hour spindle schedule.
What a magnetic chip conveyor actually does
A magnetic chip conveyor is a separation device, not a transport device. Its job is to pull ferrous swarf out of the coolant stream before the coolant reaches the tank, the pump, or the nozzles. The transport is a side effect. If you evaluate one as a conveyor belt with magnets on it, you will size it wrong and blame the machine when fines still reach the pump.
The working surface is a set of stationary or rotating magnetic elements behind a stainless steel plate. Swarf lands on the plate, the field holds it, and a scraper or an endless hinge belt drags it up an incline and out of the coolant. Coolant drains back through the plate. The gap between the plate and the scraper sets the smallest particle the unit can discharge, and that gap is the number that decides whether your pump lasts.
Separation is not filtration. A magnetic element captures iron, low-carbon steel, and most alloy steels. It ignores aluminium, brass, titanium, and stainless grades that are only weakly magnetic. A shop cutting 6061 and 304 on the same cell gets the aluminium and the 304 fines through to the tank no matter how strong the magnets are.
Field strength falls off fast with distance. At 10 mm from the pole face a magnet might hold a chip firmly; at 40 mm through a layer of wet swarf it holds almost nothing. That is why a mat of chips sitting on the plate is the normal failure mode. The unit is not broken. It is full.
Which machining setups benefit and which do not
The clearest case is a cast iron or carbon steel cell running long unattended shifts. Grey iron and ductile iron produce short, broken chips that flow well and hold a magnetic charge. One unit can pull that stream continuously while the operator loads the next part. The payback comes from spindle uptime, not from the conveyor itself.
A second case is fine swarf that would otherwise blind a cartridge filter. Turning and drilling steel at higher feeds makes small particles that pass a coarse screen and pack a filter element in hours. A magnetic stage ahead of the filter cuts the load on the element, so change intervals stretch out.
Where it stops working: aluminium-intensive cells, mixed-metal cells with no segregation, and any process producing long stringy chips that bridge the inlet. A magnetic unit will not lift aluminium at all, and long birds-nesting chips wrap the scraper and stall it.
Size matters more than brand. A 4,000 mm machining centre with heavy roughing can push a volume of swarf per hour that a compact unit cannot clear. Undersize the unit and chips back up into the machine enclosure, which is worse than having no conveyor.
- 1Good fitCast iron, carbon steel, alloy steel, unattended shifts
- 2Good fitFine ferrous swarf ahead of a filter element
- 3Poor fitAluminium, brass, titanium, austenitic stainless
- 4Poor fitLong stringy chips from soft gummy steel
Where the mechanism breaks down
Three failure families cover most complaints. The first is material: non-ferrous or weakly magnetic workpieces. No adjustment fixes this. The correct answer is a different separation principle, such as a scraper or a centrifugal unit, or segregation of the ferrous work on a dedicated machine.
The second is loading. Swarf arrives faster than the scraper can discharge it, the plate saturates, and the field cannot reach the incoming stream. Symptoms show up as chips in the coolant tank, rising pump pressure, and a warm smell from the tank. The fix is throughput, not magnet strength.
The third is coolant chemistry. Heavy tramp oil coats the chips and the plate, and oil films reduce the effective holding force. Fine swarf then slides back down the incline during the drain-back phase. A skimmer or an oil separator upstream usually restores performance without touching the conveyor.
Temperature and grit wear the scraper over time. Cast iron dust is abrasive, and the clearance between the scraper and the plate opens up. Once that clearance exceeds roughly the target particle size, fines pass through and the unit looks like it has stopped working when it is simply worn.
Five checks that protect machining efficiency
Check one is the material mix on the cell. List every workpiece material the machine will run in the next quarter. If ferrous content is below roughly 80 percent of swarf volume, a magnetic unit is the wrong primary separator. This check takes ten minutes and prevents the most expensive mistake.
Check two is swarf volume per hour at the heaviest roughing condition. Collect the chips from one hour of the worst case and measure the volume. Compare that against the unit rating with margin, not against the average shift. Peak load is what jams the inlet.
Check three is particle size. Measure the fines that reach the tank today. If the smallest fraction is near the scraper-to-plate clearance, the unit will not capture it and you will need a secondary stage. Filtration and magnetic separation are complementary, not alternatives.
Check four is coolant condition. Look for tramp oil, a low concentration refractometer reading, and foam. Dirty coolant reduces holding force and increases chip adhesion to the plate. Fix the coolant before you replace hardware.
Check five is the discharge path. The chip bin must be reachable without stopping the machine, and the incline must drain back into the tank rather than onto the floor. A conveyor that works but cannot be emptied on schedule becomes a manual process again. In practice, checks one, two, and five decide whether the installation improves machining efficiency at all.
Separation method by swarf type
Match the method to the material and chip form, not to the machine size.
| Swarf type | Magnetic conveyor | Best alternative | Why |
|---|---|---|---|
| Grey cast iron | Strong fit | — | Short broken chips, high magnetic response |
| Carbon and alloy steel | Strong fit | — | Reliable capture across turning and milling |
| Fine steel swarf | Good with a filter stage | Centrifugal separator | Particles near scraper clearance can pass |
| Aluminium 6061 or 7075 | No capture | Scraper or hinge belt | Non-magnetic, no field response |
| Austenitic 304 or 316 | Weak capture | Scraper conveyor | Low permeability, poor retention |
| Titanium and Inconel | No capture | Hinge belt plus filter | Non-magnetic, abrasive fines |
| Long stringy chips | Jams the scraper | Hinge belt with breaker | Bridging at the inlet stalls the drive |
When to specify one, and when to walk away
If your cell runs mostly ferrous work with broken chips and you want the spindle cutting instead of the operator shovelling, a magnetic chip conveyor is the right first stage. If aluminium, titanium, or austenitic stainless dominates the mix, specify a scraper or hinge belt instead and add a filter downstream.
Questions engineers ask before specifying
Can a magnetic chip conveyor handle stainless steel?
It depends on the grade. Ferritic and martensitic grades such as 430, 420, and 440C respond to a magnetic field and are captured reasonably well. Austenitic grades such as 303, 304, and 316 have low permeability and are mostly lost to the tank.
If the cell runs both families, treat the austenitic work as non-ferrous for sizing purposes and plan a second separation stage.
Does magnet strength decide capture performance?
Rarely. Field strength at the pole face is usually sufficient. The limiting factor is the distance between the magnet and the incoming chip, which grows as swarf builds on the plate.
A stronger magnet behind a saturated plate does not help. Throughput and clearance matter more than grade.
Will it remove aluminium fines from coolant?
No. Aluminium is not ferromagnetic, so the field has no effect on it. Aluminium fines will pass straight through to the tank and the pump.
For mixed cells, the practical options are segregating the aluminium work onto a machine with a scraper conveyor, or adding a filtration stage after the magnetic unit.
How does tramp oil affect separation?
An oil film on the chips and the plate reduces the effective holding force and lets fine swarf slide back down the incline. The conveyor is not at fault.
Skim the tank, correct the coolant concentration, and clean the plate on a schedule. Most field complaints disappear after that.
Where does the conveyor sit relative to filtration?
Put magnetic separation first, immediately after the chip flush, then filtration. The magnetic stage removes the bulk ferrous load so the filter element sees far less solids.
Reversing the order blinds the filter with iron and wastes the magnetic unit's capacity.
What maintenance interval is realistic?
Check the scraper-to-plate clearance and the incline drain path monthly on a two-shift cell. Inspect the drive and the chain or belt for wear quarterly.
Abrasive cast iron dust opens the clearance gradually, so record the measurement rather than judging by eye.
Send us the swarf mix and we will size the stage
Tell us your workpiece materials, heaviest chip volume per hour, and target particle size. Our engineers come back with a separation layout that fits the machine, not a catalogue number.
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