A FILTER RESISTANT TO HIGH TEMPERATURES AND A METHOD FOR MANUFACTURING IT

Abstract: The object of the invention is a method of manufacturing a filter resistant to high temperatures and mechanical stress, in which the filter is formed from a fibre net by securing it to a suitable framework. In accordance with the invention a double-sided knitted fabric is knitted from a fibre resistant to high temperatures, e.g. Nomex <R> fibre (7), on a knitting machine with two rows of needles, and a reinforcing fibre resistant to high temperatures, e.g. Aramid <R> fibre (1) is fed on top of the fabric, and on top of this a new double-sided fabric, when the reinforcing fibre (1) remains in the channels formed by the transverse loops (2, 3, 4) of the knitted structure, after which a piece of this fibre structure is secured to a suitable frame.

Description: A Filter resistant to High Temperatures and a Method for Manufacturing it The object of the invention is a filter resistant to high temperatures, and a method for manufacturing it, in which method the filter is formed from a fibre net by securing it to a suitable framework. Often the temperature resistance of dust filters that are at present used limits the temperature of processes disadvanta- geously. It is possible to achieve high temperatures by using steel net, but this does not withstand corrosive substances. Nets of other metals can also be used, but these are quite expensive. The filter must withstand abrasion and pressure impacts, which are used at regular intervals to clean it. International Patent Application PCT/FI89/20 presents a method of manufacturing an oriented fibre structure, in which it is most advantageous to use a double disc knitting machine, on account of its great manufacturing output. In accordance with this two rows of needles knit loops in different directions, which form lateral channels, into which it is possible to feed reinforcing fibres. A corresponding textile product, the struc¬ ture of which is similar to that shown in this international application, is known from British application publication 2 121 837. The intention of this invention is to create a new type of filter, which withstands pressure impacts and high temperatures, as well as being highly resistant to abrasion. The characteristic features of a filter in accordance with the invention appear in Patent Claim 2, and the features of the method of manufacturing this appear in Patent Claim 1. The main principle of the invention is to use the oriented fibre structu¬ re known from the aforementioned international application publication and fibre materials that are resistant to high temperatures. The filter can also be advantageously made to conduct electricity by adding carbon fibres, which conduct electricity, to the oriented fibres. In what follows, the invention is illustrated by means of the accompanying example, which depicts the knitted structure applied to a filter. The knitted fabric in Figure 1 is created by a so-called double disc knitting machine, in which there are cylinder needles in the vertical direction and disc needles in the horizontal. Nomex or Aramid fibres, which withstand high temperatures, are used as the reinforcing fibres 7 i.e. as loop filament. The needles on the cylinder side are set to knit loops 2 in each feed in different systems. The disc needles, on the contrary, are set to the so- called Interlock setting, when the knitting takes place alternately in each sequential feed. The loops knitted by the disc needles are marked with the reference numbers 3, 4. The Aramid fibres 1 are fed on every second system, and they remain in the channels formed by the loops 2, 3, 4 running in different directions. The Aramid fibres 1 remain transverse in relation to the wales 10 of the fabric. Due to the Interlock setting, the fabric tends to shrink longitud.inally, when the reinforcing fibres become very dense. In this was the filter also becomes tight. Nomex fibres can also be used in place of Aramid fibres as the oriented fibres. As a second example, reference can be made to two trial runs, in which the following materials and machine settings were used. Example 1: Surface 25 Tex Nomex. Infill 2 x 25 Tex Nomex, every sixth infill thread Aramid 142 Tex. 10 17 10 System 1. B 2. B 3. A k.c. -pass k.c. 15 15 k.c. = knit close Example 2: Surface 25 Tex Nomex. Infill 2 x 25 Nomex, every sixth infill thread 200 Tex Carbon. Syst. 17 10 l.pass 2. A 3. B 4. pass 5. B 6. A B pass all A pass all 15 15 In the latter example carbon fibre, which conducts electricity, is used as a component. The carbon fibres are connected to a common electrode, in which case the filter can either be effec¬ tively earthed, or else it may be used as part of an electric filter. It is also possible to use two electrodes in such a way that some of the fibres are connected to the first electrode, and the remainder to a second electrode. It is advantageous to use partly Aramid filament fibres and partly spun fibres as the oriented fibres. The filament fibres provide the fabric with stiffness, and the spun fibres make the filter as dense as desired, i.e. determine the size of penetra¬ ting particles.

Claims: Patent Claims 1. A method for manufacturing a filter resistant to high temperatures, in which the filter is formed of a fibre net by securing it to a suitable framework, characterized in that a double-sided fabric is knitted on a knitting machine equipped with double rows of needles from a fabric that withstands high temperatures, e.g. Nomex fibre (7) , and a high temperature resistant reinforcing fibre e.g. Aramid fibre (1) is fed on top of this fabric, and on top of this a new double-sided fabric, in which case the reinforcing fibre (1) remains in the channels formed by the transverse loops (2, 3, 4) of the knitted struc¬ ture, after which a piece of this kind of fibre structure is secured to a suitable frame. 2. A filter resistant to high temperatures, which is formed of a net-like fibre structure set in a frame, characterized in that the filter section is formed from double-sided knitted fabric, the main material of which is Nomex or other fibre resistant to high temperatures and Aramid or other corresponding reinforcing fibre set in the channels formed by the transverse loops of the fabric. 3. A filter in accordance with Patent Claim 2, characterized in that carbon fibres, which are connected to a suitable electrode at the edges of the filter, are used among the oriented fibres. 4. A filter in accordance with Patent Claims 2 or 3, characterized in that both filament and spun fibres are used as the oriented fibres.

Inventors: SAARIKETTU JUKKA ELIAS, SAARIKETTU, JUKKA, ELIAS
Applicants: SAARIKETTU JUKKA ELIAS, SAARIKETTU, JUKKA, ELIAS
Application year: 1990
Main classification: B01D39
IPC codes: B01D39, D04B1