WO1995022722A1 - Allumeur a surface chaude - Google Patents

Allumeur a surface chaude Download PDF

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Publication number
WO1995022722A1
WO1995022722A1 PCT/GB1995/000329 GB9500329W WO9522722A1 WO 1995022722 A1 WO1995022722 A1 WO 1995022722A1 GB 9500329 W GB9500329 W GB 9500329W WO 9522722 A1 WO9522722 A1 WO 9522722A1
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WO
WIPO (PCT)
Prior art keywords
oxide
binder
composition
hot surface
high temperature
Prior art date
Application number
PCT/GB1995/000329
Other languages
English (en)
Inventor
Mark Fabian Hall
Christopher John Hampson
Original Assignee
Morgan Matroc S.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB9403121A external-priority patent/GB9403121D0/en
Application filed by Morgan Matroc S.A. filed Critical Morgan Matroc S.A.
Priority to AU16696/95A priority Critical patent/AU1669695A/en
Publication of WO1995022722A1 publication Critical patent/WO1995022722A1/fr

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
    • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
    • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
    • H05B3/141—Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23Q—IGNITION; EXTINGUISHING-DEVICES
    • F23Q7/00—Incandescent ignition; Igniters using electrically-produced heat, e.g. lighters for cigarettes; Electrically-heated glowing plugs
    • F23Q7/22—Details

Definitions

  • This invention relates to an electrically resistive hot surface igniter particularly, though not exclusively, usable in lighting gas appliances such as pilots, heaters and cookers.
  • an ignition device For use in gas appliances, especially domestic appliances such as cookers, an ignition device must heat up within 30 seconds and preferably in less than 10 seconds. It must have the ability to function between -15% and +10% of design voltage for periods of fluctuating voltage supply and preferably have the potential to work from mains voltage (e.g. 220/240V ac. in Europe) thus eliminating the need for voltage transformation. It must be of comparable size to a spark igniter and have fairly simple control circuitry. It must not degrade easily. For convenience of volume manufacture and cost it should encompass well understood methods of processing using a minimum of specialised machinery.
  • Previous and existing hot surface igniters have generally been made from silicon carbide and derivatives thereof. Pure silicon carbide devices suffer from low density and therefore low strength as it is difficult to sinter silicon carbide. Such pure silicon carbide devices are easily damaged or degraded.
  • Current devices using this technology can include strengthening rods made from materials such as alumina (e.g. the spiral SiC element on alumina rod igniters as manufactured by The Carborundum Company, Niagara Falls, New York, USA). Efforts to overcome the low density of these materials have produced more dense components by mixing with other non-oxide ceramic materials such as silicon nitride, boron nitride, aluminium nitride or other carbides. Manufacture usually includes a hot pressing step and the products often have poor electrical properties and degrade quickly in use. Any new device should address the question of fragility which has dogged the development of ceramic hot surface igniters from inception.
  • a significant problem in such hot surface igniters is that whereas the ignition surface must reach an elevated temperature ⁇ e.g. 1050°C or more) the parts to which electrical contact are made are preferably at a lower temperature.
  • One means that has been employed to effect this is to provide an igniter formed of material comprising an electrically conductive material or materials and an electrically insulating material.
  • the resistance can be varied so that the terminal parts of the igniter have a low resistance and the ignition surface has a high resistance. See, for example, GB-A-1492672, US-A-3974106, US-A-5191508 US-A-5045237 and EP-A-0486009. More than two zones can be employed if a gradation of resistivity is required.
  • This technique may also be used to reduce differential thermal expansion effects, however such effects are not eliminated as the change in chemical composition from the terminal parts to the ignition surface is gross in nature.
  • GB-A-2015986 discloses an igniter comprising a ceramic block having an enclosed chamber with openings through which a medium to be ignited may pass. Within the chamber is mounted an electrically conductive heating element comprising lanthanum chromite or a doped lanthanum chromite. Variation in resistance of the heating element is not discussed in GB-A-2015986 but the drawings show variation in cross section .
  • a hot surface igniter comprising a unitary body having an electrically conductive resistance heatable ignition surface in electrical contact with electrically conductive te ⁇ ninal portions of the body having a higher electrical conductivity than the ignition surface, the ignition surface and terminal portions comprising a doped oxide having differing levels and/or species of dopant.
  • doped oxide an oxide material comprising small amounts of an oxide or other material (the dopant) that alters the electrical conductivity of the oxide material by donating electrons to, or accepting electrons from, the oxide material.
  • the dopant is an oxide material comprising small amounts of an oxide or other material (the dopant) that alters the electrical conductivity of the oxide material by donating electrons to, or accepting electrons from, the oxide material.
  • the exact chemical formulation of the dopant is not critical but oxides are convenient
  • the preferred oxide is tin oxide, doped with an oxide of an element with fewer or more valence electrons than tin.
  • the best dopant appears to be antimony oxide.
  • the igniter according to the present invention has an electrical path from an electrically conductive terminal portion of high electrical conductivity, through a zone of lower electrical conductivity (i.e. higher electrical resistivity ) providing the ignition surface, to a further electrically conductive terminal portion of high electrical conductivity , the electrical path being substantially in the shape of a hairpin (or "U") having two legs joined by a connecting section, the legs comprising the electrically conductive terminal porr.ons, the connecting section comprising the zone of lower electrical conductivity, and a space between the legs comprising a substantially electrically non-conducting material.
  • the hot surface igniter described may be manufactured by traditional ceramic processing methods (therefore relatively cheaply) with closely controlled electrical properties, good thermal expansion properties, high strength, and suitable for a wide range of voltages.
  • Tin oxide has advantages over materials known to be used in the manufacture of hot surface igniters as it densities by simple powder compaction and sintering in air rather than by hot pressing and/or sintering in a reducing atmosphere. It is also relatively cheap.
  • Fig. 1 shows schematically in front cross-section and side view an igniter according to the present invention.
  • Fig. 2 shows schematically in front cross-section and side view a disc-shaped igniter according to the present invention.
  • Figs. 3-11 show schematically in cross-section nine steps in the manufacture of an igniter according to the present invention using a pressing tool.
  • Fig. 12 shows a plan view of a filler shoe which is used in combination with the pressing tool of Figs. 3-11.
  • Fig. 13 and Fig. 14 show the relationship between resistivity and % conducting phase as modelled by D K Hale (described below).
  • Fig. 15 shows the order of resistance typically required for a hot surface igniter, depending on the applied voltage.
  • the igniter shown in Fig. 1 (best seen in front cross-sectional view) comprises electrical leads (2, 2 1 ) at terminal ends of zones A and A 1 which have high electrical conductivity.
  • Zone B connects the ends of zones A and A 1 remote from the leads and has a lower electrical conductivity (i.e. higher electrical resistivity) than zones A and A 1 .
  • Zone C lies between zones A and A 1 and is substantially electrically non-conducting.
  • the igniter comprises an electrical path from lead 2 through zone A, zone B and zone A 1 to lead 2 1 .
  • zones A and A 1 conduct the electricity to and from zone B.
  • zones A and A 1 are highly conductive, they remain relatively cool while zone B, having a lower conductivity and hence higher resistivity, heats up to the temperature required for ignition.
  • zones A and A 1 are legs (4, 4 1 ) of the electrical path and the legs are joined at the end opposite the terminals by a connecting section 6.
  • the legs (4, 4 1 ) are separated by space (8) which comprises the non-conducting material.
  • the non-conducting material may be air, providing an igniter having a hairpin-shaped cross-section or may be, for example, an essentially non-conductive oxide ceramic such as non-doped tin oxide or tin oxide doped with a material which further reduces its conductivity such as Ti0 2 , so providing an igniter of substantially rectangular cross-section. .An igniter of substantially rectangular cross-section (i.e. bar-shaped) is considerably less prone to accidental breakage than one of hairpin shape.
  • Fig. 2 shows an igniter in the form of a disc (best seen in front cross-sectional view).
  • the disc can be seen to provide zones A and A 1 , B and C with relative conductivities as defined above.
  • Electrical leads are shown attached to zones A and A 1 at 12 and 12 1 .
  • the electrical path is provided from lead 12 to 12 1 via zones A, B and A 1 .
  • Significant current does not flow through zone C because it is formed of a substantially non-conducting material.
  • the igniters shown in Fig. 1 and Fig.2 may have tapered widths as shown in side view so providing a smaller cross-section (and hence higher resistance) to zone B in comparison to zones A and A 1 than if a constant section were used throughout.
  • the preferred material for the igniter is doped tin oxide. Doping of tin oxide with an oxide of atoms of a valency other than four will result in either a surplus of electrons from dopant donor atoms creating an n-type semiconductor, or a deficit of electrons from dopant acceptor atoms creating a p-type semiconducting material The greater the number of dopant atoms the greater the number of charge carriers (electrons or "holes") free to conduct. .
  • Antimony oxide is the preferred dopant but other dopants such as oxides of arsenic, bismuth, gallium, or indium may be used. This technology is well understood in the semiconductor industry. An article that has discussed the effect of antimony oxide on tin oxide is "Contributions to the study of SnC -based ceramics", M.Zaharescu et al. Journal of Materials Science, 26 (1991) 1666-1672.
  • any oxide or other material that alters the electrical conductivity of the oxide material by donating electrons to, or accepting electrons from, the oxide material may be usable.
  • the resistivity (and therefore conductivity) of the doped oxide used in the igniter of the present invention may be controlled by altering the amount of dopant in the oxide, i.e. in the preferred case, the ratio of tin oxide : antimony oxide.
  • the most conductive combination has a tin oxide : antimony oxide ratio of about 15: 1 (weight: weight). In this instance compositions with a ratio as low as about 824 : 1 (weigh weight) have been tested to produce highly resistive materials.
  • the relationship between resistivity and antimony oxide content is described, for example, in British Patent No. 1 213 621 (STEATITE AND PORCELAIN PRODUCTS LTD.).
  • Doping of tin oxide can provide resistivities varying over many orders of magnitude providing resistivities from under lCTOhm.m to over 10 5 ohm.m.
  • Previous systems using mixtures of resistive and insulating phases and relying on variation in volume fraction of the insulating phase for resistivity offer a more limited range of resistivity and become very sensitive to variations in mixing efficiency when the volume fraction of the resistive phase approaches the percolation limit (i.e. the volume fraction at which only the insulating phase is continuous). This problem is especially significant when the two phases have vastly different resistivities.
  • a mathematical model due to D K Hale J.Mat. Sci. 11 2105-2141 (1976) illustrates the effect well as shown in the graphs in Fig. 13 and Fig. 14 [Note Y axis scale is logarithmic].
  • the shape of the igniter itself can vary widely.
  • a popular shape is a U-shape or hairpin.
  • Another shape successfully manufactured is a disc or thin plate.
  • the igniter can be made in other shapes: the present invention is not limited to the particular shape of the igniter.
  • Enhanced strength is achieved by manufacturing the device as a monolith, for example as shown in Fig. 1, with a non-conducting solid centre portion. Using the same oxide throughout and reducing the dopant level of the centre portion to zero (impurities excepted) results in the centre portion having the conductivity of undoped oxide material which if sufficiently low will cause the current to pass through the high resistivity zone at the tip.
  • Certain dopants such as Ti0 2 increase the resistivity of sintered tin oxide substantially and are therefore suitable for use in the centre portion. This design gives a much stronger device which is less susceptible to arbitrary damage than a U-shaped or hairpin shaped igniter.
  • Pure tin oxide is a relatively inactive material and does not density well when fired, except at very high temperatures (e.g. in excess of 1600°C).
  • a dense material is required for component strength but commercial considerations dictate a lower preferred firing temperature.
  • Various substances can be added to tin oxide to promote densification, often referred to as sintering aids. Examples of such materials are, for example, oxides of copper, zinc or manganese. Addition of these materials, in small quantities, has the effect of lowering the firing temperature required for densification.
  • Another method of lowering the required firing temperature is to introduce a bonding phase.
  • Glass containing or glass forming materials can be used to bind the tin oxide together in a glassy matrix.
  • doped tin oxide is bonded with a high temperature glaze which is suitable for firing in the temperature range 1100-1400°C producing a strong glass bonded material.
  • any glass forming or glass containing material may be used (for example, borosilicate glass).
  • the composition and quantity of bonding phase may have an effect on the resistivity of the material. Glasses are normally considered to be non-conducting (depending on composition) and as such become a resistive phase within the material. Generally, the higher the proportion of non-conducting phase present the higher the overall resistivity of the material. Controlling the amount of glassy phase or other non-conducting additive (e.g. alumina) is a method of controlling the resistivity, up to the percolation limit, as already explained. The percolation limit is, in practice, about 80% by volume of non-conducting phase. A complication to the model occurs if a conducting glass composition is used, or if the doped oxide dissolves significantly in the glass phase leading to conduction through the glass. In the preferred embodiment it is thought that the glaze acts as a reacting bonding phase which attacks the tin oxide causing some dissolution and forms a conducting glass.
  • the glaze acts as a reacting bonding phase which attacks the tin oxide causing some dissolution and forms a
  • the composition of the glassy phase affects its softening and melting temperatures. If the firing temperature is too high then the glass will melt and the compact will loose its shape. If it is too low then the bonding ability will be restricted and the resultant glassy composite will be weak. In the preferred embodiment it is found that the firing temperature also affects the resistivity. Generally, the higher the firing temperature the lower the resistivity. This effect can be used to advantage to control the resistivity of the material.
  • the igniter is made of parts having compositions which are very similar, i.e. in the preferred form in which tin oxide with a glass containing material is used, the amount of binder (glaze) is preferably constant, the tin oxide having small variations in dopant level and/or including non-conductive additives to achieve different resistivities.
  • the different sections of the device thereby have near identical thermal expansion characteristics and so the device should not suffer from differential effects. This is particularly useful when the igniter is in the form of a monolith where any mismatch of thermal conductivities would put the igniter under considerable internal stresses.
  • the resistance of a heater depends on its geometry and the resistivity of the material used. For a simple shape of uniform section:
  • A is the area of the surface ( ⁇ r) T 0 is the ambient temperature (K) e is the emissivitv of the surface.
  • emissivity is lower (tin oxide is a characteristic blue-grey colour and is not black like all other hot surface igniters) and ii) thermal conductivity of tin oxide material is lower than for silicon carbide.
  • the different zones (A, A 1 , B, C) preferably have the compositions (where Ti0 2 is not used as a dopant for the central portion C):-
  • zones A, A 1 , B and C may be made in the following way:
  • Raw materials are weighed in the required portions and placed in a ball mill with water, mill balls and an organic binder to impart green strength to the pressed article. Milling can be from 1 to 24 hours or until the required properties are achieved. The parameters of milling are well understood by those skilled in the art. Additional ingredients such as binders, deflocculants and lubricants may be added before or after milling - this is also well known.
  • the slip can be spray dried or filter pressed or, on a laboratory scale, tray dried in an oven before crushing and sieving.
  • the dry powder may be pressed in a suitably shaped press tool using, for example, a standard ceramic hydraulic or mechanical press. These processes are known to anyone skilled in the art.
  • the use of a suitably segregated filling device can enable co-pressing of more than one material in the same press tool.
  • the electrical properties of the material may be substantially affected by the method of processing and some degree of experimentation will be necessary to obtain optimum results.
  • the green article After pressing, the green article is sufficiently strong to allow machining, as may be necessary.
  • Conventional hairpin-shaped igniters can be made in this way by producing the green article in the shape of a bar and then machining out a longitudinal space between what become the legs of the igniter.
  • a hairpin-shaped press tool may be employed to produce the part in the required shape without machining.
  • the article can then be fired in ordinary air or in an oxygen atmosphere kiln to 1200°- 1400°C, depending on the properties required.
  • a rectangular shaped pressed article can be made by pressing the above mentioned three distinct powders in one die cavity. There are many ways of arranging this but one such method is detailed here.
  • the press tool is filled from a specially constructed filler shoe which permits the three different materials to be loaded into the tool without undue mixing.
  • Figs. 3-1 1 show schematically nine sequential steps in the manufacture of an igniter according to the present invention using a pressing tool (22).
  • the pressing tool (22) comprises a cavity (26) formed by a die (28), which defines walls of the cavity (26), and a plunger (30), which defines a floor to the cavity (26).
  • Fig. 12 shows a specialised filler shoe (20) in plan view for use with the tool (22) shown in Figs. 3-11.
  • the filler shoe has 3 or 4 compartments, separated by dividers (24 and 24 1 ).
  • One compartment contains a Material A, as described in relation to Fig. 1 above, another contains a Material C and one compartment B (which may be divided into two smaller compartments Bl and B2 as shown) contains Material B, as also described above.
  • the shoe (20) sits on the tool (22) so that as shown in Figs. 3-11 the compartment(s) containing material B lie behind the page.
  • Tlie shoe (20) is then displaced sideways to the position shown at Fig. 3 (see Fig. 6) and the plunger (30) lowered further so that materials from compartments A and Bl may enter the cavity (26) (see Fig. 7).
  • the shoe (20) is then moved aside (Fig. 8) and the material in the cavity (26) pressed between plunger (30) and upper plunger (32) to form a green body (Fig. 9).
  • the green body is ejected from the cavity (26) by withdrawing the plunger (32) and raising plunger (30) to be flush with the surface of the die (28) (Fig. 8).
  • the shoe (20) sideways Fig. 11
  • the green body is displaced sideways and on lowering the plunger (30) the tool returns to the position shown in Fig. 3.
  • This process provides a bar with a composition as shown in Fig.l.
  • leg A of the bar could have a composition that differs from leg A 1 , or, more than one composition could be used in each leg so that a gradation of resistivity from connection end to ignition surface may be provided
  • Igniters according to the present invention could alternatively be made by extrusion, tape casting, isostatic pressing or injection moulding or otherwise.
  • a coating e.g. zone B
  • a coating could be obtained by flame spraying or other well known methods of deposition such as plasma vapour deposition or chemical vapour deposition.
  • the electrical connections may be made as follows:
  • silver-palladium-platinum metallising paint Before firing it is possible to apply silver-palladium-platinum metallising paint to the terminal areas which is then co-fired with the article.
  • another type of silver palladium paint can be applied after firing followed by a second firing to about 750°C to achieve good adhesion between metal paint and ceramic.
  • the wires are subsequently connected using high temperature solder.
  • Yet another method of connection involves tamped flexes. Small holes approximately 1.5mm in diameter and 5mm deep are formedin the legs of the igniter. Using tamping apparatus as used in the carbon brush industryfor example silver coated copper wire flexes are fixed into the holes.
  • the fixing may be by use of resinated silver coated copper powder requiring the application of heat at 105°C for 1 hour. More preferably fixing is by a mixture of graphite and copper oxide powders with formaldehyde resin set by doping with a mixture of acetic acid and phosphoric acid and baking in an oven at 95°C for VA hours (see for example EP-A-0148035).
  • a preferred method of making electrical connections is by applying a metal deposit, preferably flame sprayed, to the terminal regions of the legs, these regions preferably having first been roughened by abrasive or chemical means.
  • the metal deposit is preferably copper but could be other conducting metals, e.g. nickel.
  • a low temperature brazing alloy is then used to join a metal tab to the deposit on each leg. Electrical leads are subsequently soldered to the tabs by conventional means. Connections made in this way have good electrical conductivity and thermal shock resistance as well as adequate mechanical strength.
  • Material A consisting of 75% by weight SnO, (e.g. SuperliteTM from Keeling and Walker, Stoke-on-Tren England) 7.5% S ⁇ b,0 3 (e.g. P3400TM from Potterycrafts, Stoke-on-Trent, England) and 17.5% high temperature transparent lead free glaze (e.g. P2048TM from Potterycrafts) was mixed in a rubber mill with 50% by weight of water, 5% by weight of Polyethylene Glycol 20000TM (from Hoechst (UK), Hounslow, England), and 0.5% Dispex A40TM (from Allied Colloids, Bradford. England) deflocculant. Tlie mill also contained steatite milling balls. After milling for 3 hours the mixture was emptied into a glass drying tray and dried for 24 hours in an oven set to 70°C. The dried cake was pestled and sieved to less than 0.355 mm.
  • SnO e.g. SuperliteTM from Keeling and Walker, Stoke-on-Tren
  • Material B was prepared in the same way but contained 82.25% Sn0 2 , 0.25% Sb,0 3 and 17.5% glaze.
  • a split feeder system was used to load the powders to a rectangular die such that Material A occupied three quarters of the length of the die and Material B the remaining quarter.
  • a load of approximately 250 kg/c ⁇ was applied to produce a rectangular pressing.
  • the green article was then sliced along the centre line, longitudinally, to produce a hairpin shape with legs made from Material A and a tip made from Material B; the two legs of Material A being joined only by Material B.
  • the machined article was then placed in a furnace and fired to 1360°C with a one hour dwell.
  • the ends of the legs then had silver palladium metallising paint applied (e.g. El 140TM from Johnson Matthey, Royston, England) and was fired to 780°C for 30 minutes. Connections were made by soldering wires to the metallised points of the igniter.
  • the device was manufactured as in example 1. Before it was placed in the kiln a silver/palladium/platinum metallising paste was applied to the ends of the legs by screen printing (e.g. Metech-Ronal type 3160TM from Metech-Ronal (UK) Ltd., Buxton, England) and was co-fired with the ceramic at 1360°C.
  • the resultant metallised pad can have solder applied to produce electrical connections.
  • the device was manufactured as in example 1. Before firing a hole approximately 5mm deep and 1.5mm diameter was drilled in the end of each leg portion. After firing tl e device was placed on a flex tamping machine and silver coated copper flex was tamped into the holes using resinated silver coated copper powder. The tamping powder was set by heating to 105°C for 1 hour.
  • the tamping powder used was 50% graphite, 48% copper oxide and 2% urea formaldehyde resin. A few drops of acetic/phosphoric acid mixture were added to the tamped area and the whole device was cured at 95°C in an oven for 90 minutes.
  • Materials A and B were prepared as in example 1 and a third material, C, was prepared from 75.5% SnO,, 17.5% glaze and 7% TiO, (R-SM2 grade from Tioxide Ltd., Billingham, Cleveland, UK) using the same methods as described for Material A.
  • the third material is incorporated into a more complex filling device, as described with reference to fig 3 and Fig. 4, such that the die cavity is filled to produce a component in space 8 as shown in Fig. 1.
  • Material C is non-conducting and therefore materials A and B form, around material C, a conducting path which is hairpin shaped Once sintered at 1360°C the igniter is extremely strong. Electrical connections can be made by any one of the four methods mentioned in examples 2, 3, 4 and 9.
  • a device was made as in Example 1 except that electrical connection was by way of spring loaded clips attached to the metallised areas 10 shown hatched in Fig.1.
  • the device had the dimensions :-a, 5mm; b, 26mm; c, 21.5mm; d, 8mm; e, 7.5mm; f, 1.7mm; g, 3.7mm; and h, 2mm.
  • Tlie taper at the top of the igniter was obtained by grinding after firing.
  • the space 8 was empty.
  • Tlie surface of the hot zone, made from material B, can be calculated as approximately 125 mnf. Using the heat loss formula shown above losses at 1000°C should be about 12W.
  • the device could be run off 110 V ac at 1.34A using a circuit with a compensating resistance of about 20 ohm, the power consumption of the igniter being approximately 100W.
  • Material A was found to have a cold (room temperature) resistance of 0.007ohm.m while material B was measured at 0.18ohm.m. the cold resistance of the whole device was approximately 120 ohm.
  • a device was made according to example 1 with connections made according to example 4. The whole device had a cold resistance of 130 ohm. This device was operated at 220V ac and 2A in a circuit with a compensating resistance of approximately 90 ohm. The power consumed by the igniter was estimated at 120W.
  • a device is made from Materials A, B and C (C having the composition 82.5% SnO, and 17.5% glaze) to the disc shape shown in Fig. 2.
  • the disc is made by pressing the raw materials into a disc-shaped die partitioned by a removable spacer. The materials may be loaded by hand into four compartments defining areas .A, A 1 , B, and C and the spacer then carefully removed before compacting the materials in the die.
  • the pressed component is then fired to 1360°C in an oxygen-containing atmosphere. The component is then ground to remove surface cross-contamination.
  • the article could be manufactured by co-extrusion of the different materials as a rod followed by slicing of the extruded rod to form discs.
  • the disc shaped igniter is inherently strong due to its shape and has a larger hot zone than the hairpin. Both examples 6 and 7 show that igniters can be made on a prototype basis of similar power consumption to known igniters. Optimisation may lead to lower power consumption.
  • a hairpin shaped igniter was made according to Example 1 except that after firing at 1360°C the termination areas on the leg portions were roughene4 by rubbing on silicon carbide paper, then flame sprayed with copper metal (the other portions of the device being masked) to a thickness of approximately 0.1mm.
  • a metal tab was attached to the copper deposit on each leg by means of a low temperature alloy braze (e.g. silver brazing paste 1802PA from Eutectic Company Ltd of Redditch, England) using an oxyacetylene torch. Leads were attached to the tabs by conventional soldering. No deterioration in the joint could be detected, either electrical or mechanical, after subjecting the device to 20000 ignition cycles.
  • a low temperature alloy braze e.g. silver brazing paste 1802PA from Eutectic Company Ltd of Redditch, England
  • Material A was made by measuring 77.5g of SnO, (Superlite from Keeling and Walker, Stoke-on-Trent, England) into a porcelain pot mill (half litre capacity) with 5g of Sb,0 3 (P3400 from Potterycrafts, Stoke-on-Trent, England) and 17.5g of high temperature, transparent, lead-free glaze (P2048 from Potterycrafts). 150ml of water was added with 0.5ml of Dispex A40 (Allied Colloids, Bradford, England) and 3g of a solution containing 50% by weight of polyethylene glycol 20000 (Hoechst (UK), Hounslow. England) and water. The mill also contained 500g of cylindrical alumina milling media ( 10mm diameter, 10mm high).
  • Tlie mixture was milled for 16 hours on a mill bank at 92revolutions per minute.
  • the slip was emptied from the mill into a glass drying dish and the media strained off.
  • the dish was placed in a fan assisted oven at 70°C for a further 16 hours after which time the water had evaporated.
  • the dried cake was broken up in a mortar and pestle and sieved to less than 0.355mm. When pressed into a compact at 250 kg/cm 2 and fired to 1360°C in an electric kiln the resultant material has a resistivity of about 0.25 ohm.cm at room temperature.
  • Material B was made from 82.25g of SnO,, 0.25g of Sb,0 3 and 17.5g of glaze (P2048). These powders were placed in a rubber mill (one litre capacity) with 150ml of water, 0.5ml of Dispex A40 and 3g of polyethylene glycol solution (50% water). The milling media used was lOOg of half inch steatite balls and 200g of 3/8 inch steatite balls. The mixture was milled for 3 hours at 60 revolutions per minute. The resultant slip was drained from the milling media into a glass drying dish which was placed into a fan assisted oven for 16 hours at 70°C to evaporate the water. The dried cake was pestled and sieved to less than 0.355mm. When pressed into a compact at 250 kg/cm 2 and fired to 1360 C C in an electric kiln the resultant material had a resistivity of 18 ohm.cm at room temperature.
  • the two materials were loaded into a split feeder system in order to fill a rectangular die (60mm x 6mm) such that material A occupied one part of the die and material B another part, with the join occurring approximately 12mm from one end.
  • a load of 250 kg cm 2 was applied to produce a pressing approximately 60 x 6 x 5mm.
  • the article was fired to 1000°C to remove organics and impart sufficient strength to allow it to be sliced longitudinally to produce a hairpin shape with legs made from material A and a tip made from material B; the two legs of material A being joined only by material B.
  • the machined article was then placed in a furnace and fired to 1360°C with a one hour dwell.
  • the terminal portions of the legs were lightly roughened by grit blasting with fine silicon carbide grit.
  • a layer of copper metal was deposited on the roughened terminal portions by flame spraying.
  • a metal tab was attached to the copper deposit on each leg by means of a low temperature alloy braze (silver brazing paste 1802PA from Eutectic Company Ltd of Redditch, England) using an oxyacetylene torch. Leads were attached to the tabs by conventional soldering.
  • the device had a room temperature resistance of 80 ohms and when a voltage of 48V was applied it heated to over 1000°C at the tip in less than 5 seconds.
  • Material A was manufactured in the same way as described in example 10 with the composition 79.5% SnO,, 3.0% Sb,0 3 , and 17.5 % P2048 glaze giving a material which after compaction at 250 kg cm 2 and firing to 1360°C had a cold resistivity of about 0.3 ohm.cm.
  • Material 3 was made in the same way as material A but had a composition of 43.5% SnO,, 4.3% Sb,0 3 , 17.5 % P2048 glaze, and 34.7 % A1 > 3 (AES11C grade of Sumitomo Corporation, Japan). When compacted at 250 kg/cm 2 and fired to 1360°C this material had a cold resistivity of about 160 ohm.cm.
  • the two materials were loaded into a split feeder system for filling a rectangular die, as described in example 11 , and a hairpin shaped igniter manufactured in the way described in example 11.
  • the above description has been based on the same dopant (albeit at differing levels) being used throughout the conductive parts of the igniter. It will be clear to the person skilled in the art that in appropriate circumstances (e.g. for doped oxides other than tin oxide) different dopants for different parts of the igniter may also be used (e.g. antimony in the terminal portions and bismuth in the ignition surface, or antimony in one terminal portion and bismuth in the other).

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Resistance Heating (AREA)

Abstract

L'allumeur à surface chaude décrit comprend un corps unitaire possédant une surface d'allumage susceptible d'être chauffée par une résistance à conduction électrique, cette surface étant en contact électrique avec les parties d'extrémité du corps possédant une conductivité électrique supérieure à celle de la surface d'allumage, la surface d'allumage et les parties d'extrémité comprenant un oxyde dopé possédant différents niveaux et/ou espèces de dopant. De préférence, l'oxyde dopé est de l'oxyde d'étain et le dopant préféré est de l'oxyde d'antimoine. Les parties d'extrémité peuvent être séparées par un oxyde non conducteur approprié qui peut être de l'oxyde d'étain dopé à l'oxyde de titane. L'invention se rapporte également aux procédés de fabrication de tels allumeurs.
PCT/GB1995/000329 1994-02-18 1995-02-16 Allumeur a surface chaude WO1995022722A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU16696/95A AU1669695A (en) 1994-02-18 1995-02-16 Hot surface igniter

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB9403121.8 1994-02-18
GB9403121A GB9403121D0 (en) 1994-02-18 1994-02-18 Hot surface igniter
GB9423361.6 1994-11-18
GB9423361A GB9423361D0 (en) 1994-02-18 1994-11-18 Hot surface igniter

Publications (1)

Publication Number Publication Date
WO1995022722A1 true WO1995022722A1 (fr) 1995-08-24

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Family Applications (1)

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PCT/GB1995/000329 WO1995022722A1 (fr) 1994-02-18 1995-02-16 Allumeur a surface chaude

Country Status (2)

Country Link
AU (1) AU1669695A (fr)
WO (1) WO1995022722A1 (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998033017A1 (fr) * 1997-01-27 1998-07-30 Saint-Gobain Industrial Ceramics, Inc. Allumeur en ceramique a chaleur adaptee et methode d'utilisation
WO2001016528A1 (fr) * 1999-08-27 2001-03-08 Robert Bosch Gmbh Bougie crayon de prechauffage en ceramique
WO2001043506A1 (fr) * 1999-12-10 2001-06-14 Bdsb Holdings Limited Procede de fabrication d'elements chauffants a resistance electrique composes d'oxydes metalliques semi-conducteurs et elements a resistance ainsi fabriques
WO2001055645A1 (fr) * 2000-01-25 2001-08-02 Saint-Gobain Ceramics And Plastics, Inc. Allumeurs en ceramique, procedes d'utilisation et de production correspondants
EP1812754A2 (fr) * 2004-10-28 2007-08-01 Saint-Gobain Ceramics & Plastics, Inc. Allumeur en ceramique
EP1846695A2 (fr) * 2005-02-05 2007-10-24 Saint-Gobain Ceramics & Plastics, Inc. Allumeurs ceramiques
EP1533571A3 (fr) * 2003-11-19 2008-01-02 Beru AG Procédé de fabrication de bougies de préchauffage en céramique
CN102515694A (zh) * 2011-12-29 2012-06-27 浙江晟翔电子科技有限公司 一种绝缘填料的制备方法

Citations (5)

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DE2642161A1 (de) * 1975-12-08 1977-06-30 Popov Stromleitender film fuer elektrische heizgeraete
GB1492672A (en) * 1974-01-10 1977-11-23 Honeywell Inc Igniter elements
JPS6433877A (en) * 1987-07-28 1989-02-03 Kubota Ltd Ceramic resistance heating element and manufacture thereof
FR2640803A1 (fr) * 1988-12-15 1990-06-22 Neiman Sa Resistance en ceramique a haute temperature
US5191508A (en) * 1992-05-18 1993-03-02 Norton Company Ceramic igniters and process for making same

Patent Citations (5)

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Publication number Priority date Publication date Assignee Title
GB1492672A (en) * 1974-01-10 1977-11-23 Honeywell Inc Igniter elements
DE2642161A1 (de) * 1975-12-08 1977-06-30 Popov Stromleitender film fuer elektrische heizgeraete
JPS6433877A (en) * 1987-07-28 1989-02-03 Kubota Ltd Ceramic resistance heating element and manufacture thereof
FR2640803A1 (fr) * 1988-12-15 1990-06-22 Neiman Sa Resistance en ceramique a haute temperature
US5191508A (en) * 1992-05-18 1993-03-02 Norton Company Ceramic igniters and process for making same

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 13, no. 220 (E - 762) 23 May 1989 (1989-05-23) *

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998033017A1 (fr) * 1997-01-27 1998-07-30 Saint-Gobain Industrial Ceramics, Inc. Allumeur en ceramique a chaleur adaptee et methode d'utilisation
US6660970B1 (en) 1999-08-27 2003-12-09 Robert Bosch Gmbh Ceramic sheathed element glow plug
WO2001016528A1 (fr) * 1999-08-27 2001-03-08 Robert Bosch Gmbh Bougie crayon de prechauffage en ceramique
WO2001043506A1 (fr) * 1999-12-10 2001-06-14 Bdsb Holdings Limited Procede de fabrication d'elements chauffants a resistance electrique composes d'oxydes metalliques semi-conducteurs et elements a resistance ainsi fabriques
GB2378748B (en) * 2000-01-25 2004-06-16 Saint Gobain Ceramics Ceramic igniters
GB2378748A (en) * 2000-01-25 2003-02-19 Saint Gobain Ceramics Ceramic igniters and methods for using and producing same
WO2001055645A1 (fr) * 2000-01-25 2001-08-02 Saint-Gobain Ceramics And Plastics, Inc. Allumeurs en ceramique, procedes d'utilisation et de production correspondants
ES2237252A1 (es) * 2000-01-25 2005-07-16 Saint-Gobain Industrial Ceramics And Plastics, Inc. Ignitores ceramicos y metodos para utilizarlos y producirlos.
EP1533571A3 (fr) * 2003-11-19 2008-01-02 Beru AG Procédé de fabrication de bougies de préchauffage en céramique
EP1812754A2 (fr) * 2004-10-28 2007-08-01 Saint-Gobain Ceramics & Plastics, Inc. Allumeur en ceramique
EP1812754A4 (fr) * 2004-10-28 2012-02-22 Saint Gobain Ceramics Allumeur en ceramique
EP1846695A2 (fr) * 2005-02-05 2007-10-24 Saint-Gobain Ceramics & Plastics, Inc. Allumeurs ceramiques
EP1846695A4 (fr) * 2005-02-05 2012-09-19 Saint Gobain Ceramics Allumeurs ceramiques
CN102515694A (zh) * 2011-12-29 2012-06-27 浙江晟翔电子科技有限公司 一种绝缘填料的制备方法

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