Fume and Oil Mist Extraction Systems

What problem it solves

Unlike dust, welding fume and oil mist consist of very fine particles. They stay airborne for a long time, spread through the whole space and, when inhaled, reach deep into the lungs. The visible blue smoke is only part of it; most of the exposure comes from the invisible fine fraction.

Oil mist forms in machining when coolant is atomised inside the machine. Once it spreads into the room it causes two problems: operator exposure, and an oil film that builds up on floors, surfaces and electrical panels. The oil film increases the risk of slips and shortens the life of electronic equipment.

In both cases the same principle is at the centre of the solution: capture the contaminant at source. If the fume is caught at the torch and the oil mist inside the machine, both the required airflow and the filter load stay small. Trying to clean the room air in general gives the same result later and at a much higher energy cost.

Applications

• Welding shops and robotic welding cells
• CNC machining centres and lathes
• Laser and plasma cutting machines
• Heat treatment and hardening lines
• Soldering and electronics production areas
• Foundry and mould preparation areas

Solution types

Extraction arms at source

Articulated extraction arms that hold their position. The operator pulls the arm next to the workpiece and the fume is captured as it forms. This is the solution with the highest efficiency for the lowest airflow. Its effectiveness depends directly on how the operator uses the arm, so it is important that the arm moves easily and stays where it is put.

Machine-mounted oil mist separators

Units connected to the machine enclosure that extract from the closed volume. Separation is usually in three stages: a mechanical pre-separator catches large droplets, the main filter handles fine mist, and the final stage is HEPA where needed. The captured oil can be drained back to the machine.

Central filter units

A layout where many stations are connected to a single filter. Cartridge units with pulse-jet cleaning are used. This reduces equipment clutter in the shop and concentrates maintenance in one place. In return it needs ductwork, and if diversity is not calculated correctly it ends up either undersized or oversized.

Ceiling-mounted ambient filtration

Units that circulate and filter room air where source capture cannot be applied. They reduce exposure but do not replace source capture; they should be seen as a complementary solution.

Filter selection

Activated carbon only makes sense for gases and odours; it does not capture particles. If it is placed before the particle filter it fills quickly and stops working. The correct order is always particles first, then carbon.

Points to watch

Sparks. In welding and cutting, hot particles can enter the duct. A spark arrestor or drop-out box should be provided before the filter; cartridge filters are combustible.

Capture velocity. If the capture velocity at the hood is insufficient, fume escapes past the opening. This effect grows in shops with cross-draughts; the positions of doors and fans must be taken into account.

Recirculation or exhaust. Returning filtered air to the room lowers heating costs in winter. But this is acceptable only if filtration efficiency is sufficient and there are no gas-phase contaminants in the room. If gas phase is involved, air is exhausted outside and replaced with fresh air.

Operator habits. The success of source capture depends on positioning the arm correctly. A short briefing for the team during commissioning has a lasting effect on system performance.

Maintenance

In cartridge filter systems, differential pressure is monitored. Moisture and oil in the compressed air line reduce the effect of the cleaning pulse. In oil mist separators, the drain line is checked regularly; a blocked drain lets the captured oil return to the filter.

How airflow is determined

For source capture, the required airflow depends on the distance between the hood and the source and on how fast the contaminant spreads. The size and geometry of the opening matter too: a plain pipe end draws air from all directions and its effect drops off quickly; a flanged or funnel-shaped hood reaches further with the same airflow.

A common situation in practice is the operator leaving the extraction arm away from the workpiece. Even if the system is sized correctly, the fume is then not captured. The solution is not more airflow but choosing the right arm reach and ease of movement.

Robotic welding cells are different: since the cell is enclosed, extraction is calculated from the cell volume, and the cell is kept at slight negative pressure so that fume does not escape when the door opens.

Diversity in central systems

In welding shops with many stations, not all stations work at the same time. The system is sized for the number of stations actually operating at once. Each extraction arm gets an automatic damper; when the arm is not in use the damper closes and extraction power is directed to the working stations.

This reduces both fan size and energy consumption. Combined with a variable speed fan, the system adjusts its own airflow to the number of open arms.

Legal framework and measurement

Welding fume and oil mist are contaminants tracked in workplace exposure monitoring. Keeping concentrations in the air below the limit values is the employer's obligation. Having workplace air measured after the extraction system is installed both documents that the obligation is met and shows that the system really works.

If the measurement is higher than expected, the problem is usually in one of three places: the hood is too far from the source, the airflow is insufficient or the filter is clogged. All three are measurable and fixable.

What we deliver at handover

During commissioning, the capture velocity at each extraction point is measured, the filter differential pressure is recorded as the initial value and the fan current is noted. These three values describe the system on day one. When performance drops later, comparison is made against these records and the cause is found by measurement, not guesswork.