Background

Mechanical fibrous filters including Hepa H13 can achieve very high filtration efficiency. However, hepa filters have no drainage and the high concentration of oil mist in industrial machining processes, makes the efficiency of drainage filter cassettes upstream of the hepa filter critical to achieve long changing intervals. Fibre diameter is a critical parameter that greatly influences both efficiency and pressure drop. The effect of reducing the fibre diameter from 10 µm to 8 or 6 µm was therefore investigated in this study.

Objective

Is it preferable to use a smaller fibre diameter to increase the efficiency, even if this reduces the oil drainage capacity? Will the pressure drop increase more than the efficiency by using thinner fibres?

Method

Experiments were carried out on four fibre cassettes loaded with oil mist (63 mg/m³). Three different glass filter materials were tested with fibre diameters of 10 µm, 8 µm and 6 µm. The three needle mat materials had different thicknesses (10, 7.5 and 5 mm) but quite similar pressure drops (118, 109 and 105 Pa). The 6 µm material was also tested in a thicker version (10 mm). Efficiency, pressure drop and oil accumulation in the cassettes were monitored until steady state was reached.

Main results

The oil trapped in the cassettes caused a continuous increase in ... After 19 to 25 days, the cassettes reached a steady state where the drainage of oil was similar to ... The pressure drop then stabilised ...