The invention relates to a method of compacting a non woven sintered metal web. The invention also relates to a non woven sintered metal web obtained by said method. Such a non woven metal web may be used in filters and in radiant surface combustion burners.
By non woven metal web is meant a web consisting of metal fibers having a diameter of less than 100 micrometer, preferably less than 60 micrometer. e.g. 25 .mu.m, 15 .mu.m, 2 .mu.m or 1.5 .mu.m. These metal fibres have rough outer surfaces and are randomly distributed in the web and are interlocked in an intermingled relationship substantially solely by means of the rough outer surfaces thereof in a frictional engagement. A non woven metal web may comprise two or more layers wherein each layer comprises metal fibres of about the same diameter and wherein the diameters of the different layers are not necessarily equal to each other. By a non woven metal web is also meant a non woven metal web reinforced by one or more wire meshes. A non woven metal web may be produced by a rando-feeder-webber apparatus which is disclosed in GB 1.190.844.
This non woven metal web may be sintered or not, but relating to this invention the sintered form is to be preferred. By sintering a bond is created at the points of crossing of the different fibers.
It is well known to use non woven metal webs in filters. The pore size is one of the most important characteristics of a filter. It determines the size of the particles which will be kept by the filter. In order to obtain a specified limited pore size the non woven metal web has been compacted by pressing or rolling up to now. However, these conventionally compacted non woven webs have some limitations. The density, i.e. a measure For the compactness (for correct definition, see below), corresponding to a specified pore size is quite high. This causes relatively higher pressure drops over the filter or necessitates the use of larger filter surfaces or the use of ventilators and pumps with more power.
It is also known to use non woven metal webs as panels in radiant surface combustion burners. These burners can have a true radiant surface combustion, i.e. no blue flame patches or no free flame, with a thermal output up to 900 kW m.sup.-2. However, until now this has only been possible with non woven webs having a limited surface of about 40.000 mm.sup.2 or less (and this not on a constant basis), or, if one desires to use surfaces greater than 40.000 mm.sup.-2, with thermal outputs which are limited to 500 kW m.sup.-2 or less. This represents a severe restriction for the application of these burners.