After installation, however, the systems that most influence uptime, part finish, and operator acceptance are often the chip conveyor, the filtration.
When evaluating a CNC machine tool (Computer Numerical Control machine — a programmable machining center that removes material via rotating cutters), most procurement attention lands on spindle power, axis travel, and control brand. After installation, however, the systems that most influence uptime, part finish, and operator acceptance are often the chip conveyor, the filtration unit, and the coolant management loop. A machine that cuts well but floods the shop with swarf, or loses coolant concentration within a week, becomes a production liability regardless of its spindle specifications, a performance factor governed by the geometric accuracy standards in ISO 230-1.
This article walks through the three subsystems as they apply to Chinese CNC machine tools — what to specify, what benchmarks to expect, and where the technology has limits.
A chip conveyor is a mechanical transport device fitted to the base of a CNC machine that carries metal chips (small fragments removed during cutting) and coolant out of the work zone and into a collection bin. Without one, chips accumulate around the workpiece, interfere with probing, and force frequent manual cleanout.
The most common configuration. A hinged steel belt (overlapping steel plates hinged on pins) runs over sprockets at each end. Chips fall onto the belt, coolant drains through gaps between plates, and chips discharge at the top of the incline.
Typical specifications on Chinese-built machines: - Belt width: 200–600 mm - Speed: 1.5–3.0 m/min (fixed or VFD-adjustable — Variable Frequency Drive, a controller that varies motor speed electronically) - Load capacity: up to 500 kg/hr of steel chips for a mid-size VMC (Vertical Machining Center — a CNC mill with a vertically oriented spindle) - Incline angle: 30–45°
Hinged belt units handle stringy chips (long, curly chips common in steel turning) reasonably well, but fine cast-iron dust can pass through the hinge gaps and reach the coolant tank.
A magnetic conveyor uses a moving chain of permanent magnets beneath a stainless steel slide. Ferrous chips (chips containing iron, such as carbon steel or cast iron) adhere to the slide and are pulled up the incline. Non-ferrous materials — aluminum, brass, titanium — are not lifted and require a different conveyor type.
Typical use: cast iron machining, gear hobbing, grinding applications where chips are small and ferrous.
A scraper conveyor drags a series of flat blades (scrapers) along the bottom of a coolant trough. Chips settle, scrapers push them up an incline, and coolant drains back. This design handles fine chips and sludge better than hinged belt types but runs slower and is less tolerant of large, bulky chips.
An auger conveyor uses a rotating helical screw (like an Archimedes screw) in a trough at the bottom of the machine bed. Chips are pushed along the trough and discharged at one end. Common on smaller machines and turning centers.
Typical screw diameter: 100–200 mm; rotation speed: 10–30 rpm.
| Feature | Hinged Belt | Magnetic | Scraper | Auger |
|---|---|---|---|---|
| Ferrous chip handling | Good | Excellent | Good | Moderate |
| Non-ferrous chip handling | Good | Not suitable | Good | Moderate |
| Fine sludge handling | Poor | Moderate | Excellent | Poor |
| Stringy chip handling | Good | Moderate | Poor | Poor |
| Footprint | Medium | Compact | Medium | Compact |
| Maintenance burden | Medium (hinge pins) | Low | Medium (scraper wear) | Low |
| Typical machine class | VMC, HMC | Grinder, cast iron | Grinder, fine machining | Lathe, small VMC |
HMC = Horizontal Machining Center (CNC mill with horizontally oriented spindle).
Coolant (also called cutting fluid — a liquid that lubricates and cools the cutting zone) carries chips away from the cut, but it also picks up fine particles, tramp oil (lubrication oil that leaks into coolant from machine way lube systems), and bacteria. Filtration removes these contaminants before coolant returns to the cutting zone.
The benchmark for coolant cleanliness varies by application, with measurement and specification operators for such surface texture parameters defined in ISO 21920-3. - General milling/turning: 50–100 micron filtration - Grinding: 10–30 micron filtration - Honing / superfinishing: 5 micron or finer
Coolant flows through a disposable non-woven fabric media (paper roll). Particles are trapped on the media surface; clean coolant passes through. As the media loads, a float switch advances fresh media automatically.
Typical media roll width: 500–1,500 mm; filtration grade: 25–50 micron nominal; media consumption: 0.5–2.0 m² per shift depending on chip load.
Paper filtration is effective for fine particles but generates ongoing consumable cost and waste disposal volume.
A rotating drum with internal permanent magnets attracts ferrous fines from the coolant flow. Used as a pre-filter ahead of paper or cartridge stages. Typical separation efficiency: 95%+ for ferrous particles above 30 micron; negligible effect on non-ferrous fines.
A hydrocyclone is a conical device that uses centrifugal force (the outward force generated by rotational motion) to separate particles from liquid. Coolant enters tangentially, heavier particles spiral to the wall and exit the bottom (underflow), clean coolant exits the top (overflow).
Typical separation cut point: 10–20 micron for ferrous; 20–40 micron for non-ferrous. No consumables, but efficiency drops with low-density particles and viscous coolants.
Coolant passes through fabric bags or pleated cartridges. Filtration grade: 5–50 micron depending on media. Higher pressure drop than paper systems; bags/cartridges require periodic replacement. Common on grinding machines and EDM (Electrical Discharge Machining — a process that removes material via electrical sparks in a dielectric fluid).
| Method | Filtration Grade | Consumables | Flow Rate Range | Best Application |
|---|---|---|---|---|
| Paper media | 25–50 µm | Yes (media rolls) | 50–500 L/min | General milling, turning |
| Magnetic separator | 30 µm+ ferrous | No | 50–300 L/min | Pre-filter, ferrous machining |
| Hydrocyclone | 10–40 µm | No | 100–1,000 L/min | High-flow, mixed materials |
| Bag filter | 5–50 µm | Yes (bags) | 50–200 L/min | Grinding, fine finishing |
| Cartridge | 5–25 µm | Yes (cartridges) | 50–300 L/min | EDM, honing |
µm = micrometer (one thousandth of a millimeter).
Filtration removes solids. Coolant management addresses the broader questions of concentration, temperature, biological growth, and tramp oil — all of which affect tool life and part quality.
Most CNC machining uses water-soluble coolant: a concentrate (the chemical additive package) mixed with water, typically at 5–10% concentration by volume. Too low a concentration reduces tool life and allows corrosion; too high a concentration can cause skin irritation, residue buildup, and foaming.
Concentration is typically measured with a refractometer (a handheld optical instrument that measures refractive index — how much light bends when passing through a liquid, which correlates to dissolved solids), a process that should be verified against the conformity rules in ISO 14253-1. Concentration drift of ±1% within a week is normal; drift beyond ±2% indicates a problem with mixing, leakage, or evaporation.
Automatic coolant mixers (proportioners) blend concentrate and water at a set ratio. Specifying one at procurement avoids manual mixing errors.
Coolant temperature affects dimensional accuracy. As coolant warms, it expands slightly and changes viscosity, which alters flow rates and cutting performance. For precision work (tolerances tighter than ±0.02 mm), a coolant chiller (a refrigeration unit that maintains coolant temperature within a set band) is specified, as thermal stability is critical for the geometric accuracy of axes of rotation defined in ISO 230-7.
Typical chiller setpoint: 22–24°C; stability: ±1°C for general machining, ±0.5°C for precision grinding.
Without a chiller, coolant temperature in a recirculating system can climb 5–10°C above ambient during continuous operation.
Tramp oil (hydraulic and way-lube oil leaking into the coolant) forms a film on the coolant surface, blocks oxygen transfer, and promotes bacterial growth. A tramp oil separator — typically a belt skimmer (a rotating hydrophobic belt that picks up oil) or a coalescing unit (uses media that oil adheres to, allowing it to separate from water-based coolant) — removes this oil.
Benchmark: tramp oil content below 0.5% by volume is acceptable; above 2%, coolant life drops sharply and odor problems begin.
Bacteria and fungi grow in water-soluble coolants, producing "Monday morning smell" (hydrogen sulfide odor after weekend stagnation) and breaking down the coolant chemistry. Management approaches include: - Biocide dosing (adding antimicrobial chemicals on a schedule) - Aeration (running coolant pumps during idle periods to oxygenate the fluid) - UV treatment (passing coolant past ultraviolet lamps to kill microorganisms)
A well-maintained coolant charge lasts 6–12 months. A neglected one may require disposal within 4–8 weeks.
Tank capacity should be sized to allow chips and fines to settle and to provide thermal mass. A common rule of thumb: tank volume equals 3–5× the coolant flow rate per minute. A machine with 100 L/min pump flow typically needs a 300–500 L tank.
Undersized tanks cause short-circuiting (coolant returns and is immediately pumped back without settling), which degrades filtration performance.
Modern Chinese CNC machine tools (using Fanuc, Siemens, Mitsubishi, or domestic controls such as Guangzhou CNC, Syntec, and others) typically provide M-code (auxiliary function codes in CNC part programs) and PLC (Programmable Logic Controller — the machine's internal sequence controller) interfaces for conveyor and coolant system control, which must comply with the electrical equipment requirements of EN 60204-1.
Common interface points: - M-code activation of conveyor forward/reverse - Coolant on/off (M08/M09 in most control dialects) - Low coolant level alarm (digital input to PLC) - Conveyor overload alarm (motor current sensor) - Filter clog alarm (differential pressure switch)
Specifying these interfaces at procurement ensures the peripheral systems are integrated into the machine's alarm and safety architecture rather than running as standalone islands.
Not every application benefits from the full suite of coolant management technology. Honest limitations:
Low-volume job shops running mixed materials may find automatic paper filtration wasteful — the media advances based on level, not chip load, so a light-cutting shift can consume media with little benefit. A simple hinged belt plus mesh basket may suffice.
Cast iron machining generates graphite fines that paper media captures poorly and that pass through most cartridge filters. Magnetic separation works, but only if the iron is ferrous enough. Some cast irons (austenitic grades) are weakly magnetic.
Small machines under 10 kW spindle power often ship with auger conveyors and simple mesh filtration. Upgrading to a full filtration loop may cost more than the machine itself and rarely pays back for low-utilization operations.
Coolant chillers add heat load to the workshop. A chiller rejects heat to ambient air; in a small, poorly ventilated shop, this can raise ambient temperature by 2–4°C. In tropical climates, the additional HVAC load can offset the precision benefit.
Tramp oil separators require maintenance. Belt skimmers need periodic cleaning and replacement; coalescing media loads and must be serviced. Shops without a disciplined maintenance schedule often install these units and then ignore them until they fail.
Refractometer-based concentration control assumes a single coolant product. Shops that mix coolant brands or change formulations will get misleading refractometer readings, since refractive index varies by product. In such cases, titration (a chemical analysis method) provides more accurate concentration measurement but requires lab capability.
High-pressure coolant systems (70 bar and above) used in deep-hole drilling and aggressive aluminum machining generate fine foam and aerosol mist that standard filtration cannot address. These applications require mist collection (air filtration units above the machine enclosure) as a separate system.
Before issuing an inquiry or PO (Purchase Order) for a CNC machine tool, the following items can be verified with the supplier:
Chip Conveyor - [ ] Conveyor type specified (hinged belt, magnetic, scraper, auger)? - [ ] Belt width and incline angle confirmed? - [ ] Chip discharge height matches collection bin height? - [ ] Conveyor motor VFD-controlled or fixed speed? - [ ] Reverse function available for chip jam clearing? - [ ] Overload alarm wired to CNC PLC?
Filtration - [ ] Required filtration grade (micron) defined for the workpiece material and tolerance? - [ ] Filtration method selected (paper, magnetic, hydrocyclone, bag, cartridge)? - [ ] Consumable replacement interval estimated (media rolls, bags, cartridges)? - [ ] Pre-filter stage included if ferrous fines expected? - [ ] Differential pressure alarm specified?
Coolant Management - [ ] Coolant tank capacity confirmed (3–5× pump flow rate)? - [ ] Automatic coolant mixer / proportioner included? - [ ] Refractometer supplied with machine? - [ ] Tramp oil separator specified (belt skimmer or coalescer)? - [ ] Coolant chiller required? If yes, setpoint and stability specified? - [ ] Low coolant level alarm wired to CNC? - [ ] Biocide dosing or aeration strategy defined?
Integration - [ ] M-codes for conveyor and coolant documented in machine manual? - [ ] PLC alarm list includes conveyor overload, filter clog, low coolant? - [ ] Coolant system compatible with intended coolant brand and type (soluble oil, semi-synthetic, synthetic)?
Site Readiness - [ ] Workshop floor can support conveyor and tank weight when full? - [ ] Coolant disposal route compliant with local environmental regulations? - [ ] Ventilation adequate for coolant mist and chiller heat rejection?
For specific machine configurations and conveyor/filtration packages available with GreeCNC machine tools, the engineering team can be reached through the inquiry form on greecnc.com.
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