The present invention relates to a gas burner membrane comprising a woven textile fabric and to a method to provide such membrane. It further relates to a method to provide a gas burner membrane.

Background of the invention.

Woven gas burner membranes are known in the art, e. g. from US5165887 and others.

Gas burner membrane comprising metal fibers are known from W09704152. Such gas burner membranes have the disadvantage that, when apertures occur due to the membrane which is worn out, these apertures tend to enlarge spontaneously. The yarns present in the surroundings of the aperture are no longer permanently fixed in the fabric structure and will further tend to unravel.

These apertures are of great danger, since they may cause sudden back flashes or local spots on the burner with increased combustion rates.

Summary of the invention.

It is an object of the invention to provide a gas burner membrane, which does not have this disadvantage. A method to manufacture such gas burner membrane is also provided.

A gas burner membrane as subject of the invention comprises a woven fabric, which is characterized by the fact that the woven fabric has more than one layer of weft yarns. Warp yarns connect the different layers of weft yarns to each other.

Since this woven fabric is to be used as a gas burner membrane, a first outer surfaces faces the supply of gas-air mixture of the burner. This surface is called hereafter the gas supply surface of the gas burner membrane. The second outer surface is used as the surface of the gas burner membrane, on which the combustion action starts. This surface, also called the combustion or radiant surface is hereafter called burner surface.

The layer of weft yarns, used to provide the burner surface of a textile woven fabric, on its turn used to provide a gas burner membrane as subject of the invention, is provided by heat resistant fibers such as ceramic fibers and/or heat resistant metal fibers. Possibly, yarns comprising metal and ceramic fibers may be used.

Metal and ceramic fibers may be provided as filament fibers. Filament fibers are understood in the textile art as endlessly long fibers, usually several meters to several kilometers long.

In case both metal and ceramic fibers are staple fibers, both fibers may be transformed into one yarn by intimately blending the fibers.

Alternatively, for staple fibers and filaments, each fiber type may be used to provide spun yarns comprising only that type of fiber. These yarns on their turn may be plied together to provide a plied yarn, which comprises metal and ceramic fibers.

According to the present invention, it is not necessarily so that the burner surface and the gas supply surface comprises both metal and ceramic fibers. The burner surface may comprise mainly or only ceramic fibers or heat resistant metal fibers. The gas supply surface may comprise mainly or only metal fibers. However, when metal and ceramic fibers are used to provide the burner surface, preferably the burner surface has a metal fiber content of more than 5 vol%, and has a ceramic fiber content of

more than 30 vol% ceramic fibers. Preferably, a ceramic fiber content of more than 70 vol%, e. g. between 75 and 90 vol% is to be used.

When metal and ceramic fibers are used to provide the burner surface, preferably the gas supply surface of the textile fabric has a metal fiber content of at least 5vol% to provide a gas burner membrane. More preferably however, a metal fiber content of the gas supply surface of more than 12 vol% or even more then 50% are to be used. Best results are obtainable using a metal fiber content of more than 75 vol%.

A visible yarn length L at surface S of the textile fabric is defined as the length of the yarns, which are present and visible at this side S. The total volume of fibers Vtotal of the visible yarn length L, is the volume of all the fibers, which are present in the length L of those yarns. A metal fiber content at a surface S of X vol%, is to be understood as X vol%= 100*VmfNtotal Wherein Vmf is the volume of metal fibers, being present in the visible yarn length L. A ceramic fiber content at a surface S of Y vol%, is to be understood as Y vol% = 1 OO*Vcf/Vtotal Wherein Vcf is the volume of ceramic fibers, being present in the visible yarn length L.

Ceramic fibers may e. g. be AI203 based fibers, further comprising SiO2.

NEXTEL@-fibers are such fibers which may be used. Ceramic fibers based on Al203 may be used, e. g. fibers comprising 62 % by weight Al203, 24 % by weight SiO2and 14% byweight B203. Preferably

however, Si02-based fibers are used, such as QUARTZELO fibers from Quartz & Silice, which comprises more than 99. 99% Si02.

Metal fibers, provided by any known production method may be used to provide the burner surface, provided that the metal alloy used is resistant to the temperatures used during appropriate radiation. Different alloy- types, such as stainless steel alloys, nickel alloys and other specific types of steels containing, for example, chromium, aluminum and/or nickel and 0.05 to 0.3% by weight of yttrium, cerium, lanthanum, hafnium or titanium may be used, such as FECRALLOYO. The latter steel alloys are very resistant to high temperatures and are preferably used on the burner surface. Other alloys suitable are INCONEL and Nichrome- steels.

The second and further layers of weft yarns may be provided by identical yarns, or may be provided by less heat resistant yarns such as e. g. glass fiber yarns or metal fibers from less temperature resistant alloys such as AISI-300 or-400 series alloys e. g. AISI 316 or AISI 316L.

Metal fiber equivalent diameters may range between 5 and 150pm, preferably between 25 and 50um, e. g. 25um, 30um or 35um. These metal fibers may be bundle-drawn, shaved from a coil as described in W09704152 or obtained by any other metal fiber production process known in the art. With equivalent diameter is meant, the imaginary diameter of a fiber with a circular radial section, with equal surface of this radial section as the surface of the radial section of the metal fiber.

In order to improve the weaving process, metal yarns and/or ceramic yarns may substantially be surrounded with polymer or natural fibers, before they are used to provide the woven fabric. One or more metal and/or ceramic yarns are e. g. ; wrap spun or core spun, providing an outer layer of polymer or natural fibers around one or more metal and/or

ceramic yarns, being located in the core of such core spun or wrap spun yarn.

The different layers of weft yarns are connected to each other with one or more warp yarns. Further some warp yarns may only be used to connect the different weft yarns in the same layer of weft yarns. The warp yarns which are present in the burner surface of the textile woven fabric, are to be provided by fibers, similar to the fibers which are to be used to provide the weft yarns being present at the burner surface. Warp yarns, which are not incorporated in the burner surface, may be provided by less temperature resistant fibers, as described for the weft yarns of layers, other than those present at the burner surface.

A gas burner membrane as subject of the invention is provided using such a woven textile fabric. The advantages of a gas burner membrane as subject of the invention over the presently known gas burner membrane, are when the burner surface is damaged or used, the danger on sudden flash-backs is minimized, if not avoided. When the burner surface is damages, e. g. by a subject which has scratched the surface, an object has dropped on the surface or the thermal resistant fibers are used, a small aperture may be observed on the surface. When such aperture is met on a presently known gas burner membrane, this aperture may easily expand since the warp and weft yarns which are damaged, e. g. broken on this spot are no longer fixed into the woven structure, causing sudden flash-backs. The woven structure of the textile fabric providing such a gas burner membrane will tend to curl upwards, away from the burner surface. When objects pass near the burner surface, the curling of the woven fabric may hinder them.

When such an aperture is met on a gas burner membrane as subject of the invention, this defect can be seen during an inspection of the burner

surface, but the additional layers under the aperture will act as a barrier for the temperature to rise beyond the gas burner membrane (causing flash-backs). It will also prevent the aperture from expanding, since the warp yarns, which are also fixed in the layer or layers underneath the burner surface, hinder the expansion and curling of the fabric. Further, the layers underneath the burner surface will act as a support layer, supporting e. g. a ceramic burner surface or a metal burner surface. It is generally known that in time, metal burner surfaces loose gradually their strength since they oxidize.

Gas burner membranes as subject of the invention are also more self supporting, so the used of a supporting screen may be avoided. The used of such supporting screens does not provide the advantages of the invention, since e. g. it does not prevent the expansion from the apertures.

By varying the warp and/or weft density, or by using different warp and/or weft yarns, one may vary the air permeability of the textile woven fabric over its surface. This provided different combustion zones to the gas burner membrane during operation.

Embodiments of a burner membrane as subject of the invention, comprising metal and ceramic fibers both at burner surface and gas supply surface, with preferred metal and ceramic fiber content as specified above, have additional advantages.

Compared to a similar fabric out of 100% metal fibers, the radiation temperature of a gas burner membrane is increased by using ceramic fibers on the burner surface, without causing too quick wear of the metal fibers. On the other hand, such burner membrane has the advantage to be weldable compared to 100% ceramic membranes. By welding the

gas burner membrane to the frame of the gas burner, a seal between frame and membrane, which has an outstanding lifetime, is obtained.

The metal fibers present further offer mechanical strength to the gas burner membrane.

Brief description of the drawings.

The invention will now be described into more detail with reference to the accompanying drawings wherein -FIGURE 1 shows a cross-section of a woven fabric, to be used as a gas burner membrane as subject of the invention.

-FIGURE 2 shows another cross-section of a woven fabric, to be used as a gas burner membrane as subject of the invention.

-FIGURE 3 shows a gas burner membrane as subject of the invention, used on a gas burner.

-FIGURE 4 shows a gas burner membrane as subject of the invention, showing a defect.

-FIGURE 5 shows a gas burner membrane as known in the art, having a similar defect as the gas burner membrane as subject of the invention of FIGURE 4.

Description of the preferred embodiments of the invention.

FIGURE 1 shows a cross section of a woven fabric 10, to be used as a gas burner membrane as subject of the invention. A burner surface 11 and a gas supply surface 12 is provided. The fabric 10 comprises two layers of weft yarns. First weft yarn layer 13 is provided by weaving warp yarns 14 and weft yarn 15. A second weft yarn layer 16 is provided by weaving warp yarns 17 and weft yarns 18. Both layers are connected to each other with warp yarns 19.

An embodiment is obtained by using metal fiber yarns for both layers 13 and 16. Yarns 14 and 15 are metal fiber yarns, comprising AISI 316L stainless steel fibers. Yarns 17,18 and 19 are Fecralloy metal fibers, which are stainless steel fibers, resistant against high temperatures.

Preferably a FecralloyE metal fiber yarn with metrical number 3/1 Nm (= 333 Tex) is used, comprising Fecralloy metal fibers with equivalent diameter of 35um or 22um.

Alternatively, ceramic fiber yarns may be used for yarns 17 and 18, and eventually for yarn 19. Preferably a QuartzelE filament yarn with metrical number 30 Nm (=33 Tex) is used, comprising fibers with diameter of 9um. Most preferably, this yarn is a double plied yarn, comprising two single yarns of metrical number 59 Nm (=17 Tex).

Another woven fabric, to be used as a gas burner membrane as subject of the invention is shown in FIGURE 2. The fabric 200 has a burner surface 201 and a gas supply surface 202. Fabric 200 comprises three layers of weft yarns. A first layer 203 is provided by weaving warp yarns 204 and weft yarn 205. A second layer 206 is provided by weaving warp yarns 207 and weft yarns 208. A third layer of weft yarns 209 is provided by weaving warp yarns 210 and weft yarns 211. layers 203 and 206 are connected to each other with warp yarns 212. Layers 206 and 209 are connected by warp yarn 213.

An embodiment is obtained by using metal fiber yarns for both layers 203,206 and 209. Yarns 204,205 and 212 are metal fiber yarns, comprising AISI 316L stainless steel fibers. Yarns 207,208,210,211 and 213 are FecralloyX metal fibers, which are stainless steel fibers, resistant against high temperatures.

Preferably a FecralloyX3 metal fiber yarn with metrical number 3/1 Nm (= 333 Tex) is used, comprising FecralloyE metal fibers with equivalent diameter of 35um or 22um.

Preferably, AISI 316L metal fiber yarns with metrical number 11/2 Nm are used. This is a double plied yarn, comprising two single yarns of metrical number 11 Nm (=91 Tex). AISI 316L metal fiber equivalent diameter is preferably 12, um.

Alternatively, ceramic fiber yarns may be used for yarns 210 and 211, and eventually for yarn 213.

Preferably a Quartzel0 filament yarn with metrical number 30 Nm (=33 Tex) is used, comprising fibers with diameter of 9um. Most preferably, this yarn is a double plied yarn, comprising two single yarns of metrical number 59 Nm (=17 Tex).

A person skilled in the art understands that other combinations of metal fibers and ceramic fibers may be used to provide other embodiments of this invention. Preferably, the warp and/or weft yarns are substantially surrounded with viscose fibers, to improve the weaving behavior of the warp and weft yarns. If two or more metal or ceramic yarns are to be woven into the fabric in an identical way (e. g. these yarns form part of one warp or weft element, following the same path through the fabric), they may be comprised in one core spun or wrap spun yarn, having these metal and ceramic yarns in its core, said core being substantially surrounded with polymer or natural fibers, such as viscose fibers.

FIGURE 3 shows a woven fabric as subject of the invention, used as a gas burner membrane. A fabric 31 is used in such a way that the fabric's surface, which is most resistant against high temperatures is used as burner surface 32. The other surface, pointing towards the gas supply, is then used as gas supply surface 33. The fabric 31 is mounted, e. g. welded in case the woven fabric comprises sufficient metal fibers, on the frame 34 of the gas burner.

Suppose a defect is observed on the gas burner membrane at the burner surface. FIGURE 4 shows that a small perforation 43 is observed in the weft layer 41, the closest to the burner surface. The other weft layer 42 (or layers in case more than two layers are used) does not show this perforation. Since warp yarn 44 keeps both layers together, the ends of the yarns, pointing towards the perforation will not tend to curl up, and cover to some extend the perforation 43. Since yarn 44 keeps the layers together, the temperature of the layer 42 does not rise to such an extend that the risk on flash-backs is increased. The perforation however will be visible. In case objects are to move closely to the burner surface, these objects will not be hindered since the burner surface does not tend to curl.

In FIGURE 5, the same situation is shown for a perforation on a gas burner membrane, as known in the art. A woven fabric 51, provided using the same material as layer 41 of FIGURE 4, is mounted on a supporting layer 52, provided out of the same material as layer 42. When a perforation 54 occurs on the fabric 51, the fabric will tend to curl away from the perforation as indicated with arrows 53. The perforation area will be enlarged, and the supporting layer 52 underneath the perforation 54 will be heated to such an extend, that a real danger for flash-backs occurs. E. g. hot spots can be met on the supporting layer or the supporting layer starts to oxidize locally underneath the aperture. If no such supporting layer is used, it is clear that the risk on flash-backs is even higher.

A gas burner membrane as subject of the invention clearly has the advantage of reducing the risk on flash-backs. In case objects are to move closely to the burner surface, they may be hindered by the edge of the perforation that curls away from the burner surface.