The various fibres which are available for filtration come in a range of diameters. Traditionally in the textile industry the term denier is used to define them. Effectively, 9000 metres of any 1 denier fibre, will weigh 1 gram. 9000 Metres of any 5 denier fibre weighs 5 grams etc.
Diameter (in microns) is related to denier:
This table demonstrates how fibre diameters change with denier for various fibre types:
| Diameter in microns compared with fibre type and denier | ||||||||
|---|---|---|---|---|---|---|---|---|
| DENIER | ||||||||
| FIBRE | SG | 0.5 | 1 | 1.5 | 2.2 | 3 | 5 | 15 |
| POLYPROPYLENE | 0.91 | 8.8 | 12.5 | 15.3 | 18.5 | 21.6 | 27.9 | 48.3 |
| ACRYLIC | 1.15 | 7.8 | 11.1 | 13.6 | 16.4 | 19.2 | 24.8 | 42.9 |
| POLYESTER | 1.38 | 7.2 | 10.1 | 12.4 | 15.0 | 17.5 | 22.6 | 39.2 |
| PPS | 1.34 | 7.3 | 10.3 | 12.6 | 15.2 | 17.8 | 23.0 | 39.8 |
| M ARAMID | 1.38 | 7.2 | 10.1 | 12.4 | 15.0 | 17.5 | 22.6 | 39.2 |
| POLYIMIDE | 1.41 | 7.1 | 10.0 | 12.3 | 14.9 | 17.3 | 22.4 | 38.8 |
| PTFE | 2.30 | 5.5 | 7.8 | 9.6 | 11.6 | 13.6 | 17.5 | 30.4 |
So in terms of diameter a 1½ denier acrylic fibre is the same as a 3 denier PTFE.
Based on the above, if you consider any polyester filter felt at 500 g/m² it will contain 362 cm³ of fibre, if the fibre is 2.2 Denier, then its length will be 2045 km. If it were produced from 1 denier fibre, the length would rise to 4500 km.
All this additional fibre length is contained in the same volume of felt and so the spacing between adjacent fibres must be smaller inside the finer denier medium. This is the first reason why finer denier fibres give improved fine dust collection. Quite simply the pores inside the felt are reduced in size so it is easier for the fibres to catch particles.
A second benefit is found because the total surface area of the fibres inside the felt increases as the denier is reduced:
| Surface area in square metres per 500 grams of fibre | ||||||||
|---|---|---|---|---|---|---|---|---|
| DENIER | ||||||||
| FIBRE | SG | 0.5 | 1 | 1.5 | 2.2 | 3 | 5 | 15 |
| POLYPROPYLENE | 0.91 | 8.8 | 12.5 | 15.3 | 18.5 | 21.6 | 27.9 | 48.3 |
| ACRYLIC | 1.15 | 7.8 | 11.1 | 13.6 | 16.4 | 19.2 | 24.8 | 42.9 |
| POLYESTER | 1.38 | 7.2 | 10.1 | 12.4 | 15.0 | 17.5 | 22.6 | 39.2 |
| PPS | 1.34 | 7.3 | 10.3 | 12.6 | 15.2 | 17.8 | 23.0 | 39.8 |
| M ARAMID | 1.38 | 7.2 | 10.1 | 12.4 | 15.0 | 17.5 | 22.6 | 39.2 |
| POLYIMIDE | 1.41 | 7.1 | 10.0 | 12.3 | 14.9 | 17.3 | 22.4 | 38.8 |
| PTFE | 2.30 | 5.5 | 7.8 | 9.6 | 11.6 | 13.6 | 17.5 | 30.4 |
Halving the denier increases the fibre surface area by just over 40%. This isn't just a theoretical difference between materials as the following images show:
0.7 Denier
2.2 Denier
It is very evident that the distances between the fibres in the fine denier felt are smaller and that the structure is finer. Almost all routine filtration can be handled by 'normal' fibres (2 to 2½ denier). When higher efficiency or reduce emissions are specified, then it is normal practice to change the fibres to 1½ denier. Media as fine as 0.7 Denier are in regular use in demanding applications.
Andrew Webron Limited has a range of products designed to satisfy the BGIA specified performance levels. BGIA is a German Testing and Safety House which sets performance standards. They have performance levels, 'L' and 'M', the latter being more demanding.
Our products include:
| PRODUCT | CLASSIFICATION |
|---|---|
| MICROWEB I | M |
| MICROWEB MW2 | M |
| TPX352P1G | L |
| PX401P1G | L |
| PX502P1G | L |
| P0502SPS | L |
| PX552P1G | L |
When the filtration demands are even higher, other options come into play such as membranes, on the left below is a picture of a PTFE membrane at the same magnification as the 2 felts above on the right is the same membrane material magnified a further 10 times:
The huge redution in fineness is very clear.
Typical applications for fine filtration are:
| Combustion | Incineration | Pigments |
| Industrial Vacuums | Metal Processing | Coal |
| Food | Toxic Chemicals | Minerals |
