CN1180661C

CN1180661C - Thick film heater

Info

Publication number: CN1180661C
Application number: CNB00801678XA
Authority: CN
Inventors: C; 马丁·C·克里奇利; P��Ī��; 科林·P·莫顿
Original assignee: Strix Ltd
Current assignee: Strix Ltd
Priority date: 1999-08-13
Filing date: 2000-08-14
Publication date: 2004-12-15
Anticipated expiration: 2020-08-14
Also published as: AU6583000A; CN100396163C; ATE492139T1; ATE357832T1; GB2353457A; HK1040590A1; EP1713307B1; CN1523931A; EP1713307A3; DE60034019T2; EP1121835A1; DE60045400D1; CN1320355A; RU2001111004A; DE60034019D1; EP1713307A2; GB9919205D0; WO2001013680A1; EP1121835B1; ES2284516T3

Abstract

An electrical resistance or heater of the type comprising a thick film resistive track provided on an insulating substrate has two predetermined sections of said track (8d, 8e) with a predetermined current carrying capacity. These sections are bridged by a discrete bridge (22) of an insulating material, e.g. glass, which at a predetermined temperature becomes sufficiently conductive to cause a failure current to flow through one or both of said sections (8d, 8e). The resistive track (8) is protected from oxidation by a separate overglaze layer. Also disclosed is such an electrical resistance or heater wherein the track section (8d) passing the failure current is provided with means, such as an aperture (24) in the track, for concentrating locally the current flowing therethrough.

Description

Thick film heater

Technical field

The present invention relates to electric heater, relate in particular to the electric heater that on dielectric base, is provided with resistance track.

Background technology

This heater is employed or recommended use in the household implements of for example water heating vessels, water heater and flatiron.Usually, for example the insulating barrier of glass, pottery or glass ceramics (below be referred to as " glass ") is arranged on the metallic substrates (it can constitute the part of the substrate of heating vessel) such as metallic plate, and with printing technology resistance track is deposited on the insulating barrier.As a modification of metallizing substrate, this substrate can be hard ceramic body.Another metal level can cover on the resistance track to protect this track, to avoid it to be corroded and oxidation.This heater is said in the prior art " thick film " heater.

Obviously, heater does not allow exceedingly to be heated under the state of mistake, because this not only all can cause potential grievous injury to the device that is provided with heater or apparatus itself but also to the user of apparatus.

Many suggestions to this overtemperature protection have been proposed.In heating vessel, reducible overheat protector is set usually, when not having liquid or liquid to dryout in the container for example, during the overheated heater of container, overheat protector is connected also work.Typically, overheat protector comprises the bimetallic driver, and bimetallic driver and heater thermo-contact are also being worked under the fixed temperature, in the time of on being in the container normal working temperature, the bimetallic driver opens the winding point to heating installation power supply.But when this protector lost efficacy, also can provide the thermal cut-off of stand-by protection device, work when for example being provided at heter temperature and rising on the predetermined temperature.This structure is disclosed in applicant's the WO-A-94/18807 application.

In the applicant's U27 and U28 controller, two bimetallic drivers are set, they are standby mutually effectively, have exempted necessity that further serious overtemperature protection is provided.

But, preferred heater or the resistance that is provided with built-in protection.In WO97/39603, the applicant has proposed this structure.In this structure, the glass material bridge of selecting is arranged between the adjacent heating track, the material of the structure of track and track and the selection of position make the glass between the track region become fully under predetermined temperature, and thereby conduction makes the track region short circuit, so heater was controllably lost efficacy.Like this, this heater is known as does not need " self-shield " of external control heater.

The scheme of this " self-shield " heater is further specified among the WO99/02080 in application, wherein, in the structure of heater, the position of the bridge between the adjacent track from the end displacement of track in case when being short-circuited the electric current the restriction track.Can prevent the main fuse in the fault current fusing family like this.

Summary of the invention

The present invention does further to improve to said structure in all its bearings.

In WO97/39603, self-shield glass bridge is configured to cover the layer of whole heater traces.But find now, prevent the oxidized and corrosion of track if desired, discrete bridge preferably is set so that the glazed layer of separation is provided.

Therefore, according to first aspect, the invention provides a kind of resistance or heater, this resistance or heater comprise the thick-film resistor track that is located on the dielectric base, the discrete bridging that two fates with described track of predetermined current-carrying capacity are insulated material connects, this discrete bridge becomes under predetermined temperature, and fully conduction is so that fault current flows through from one or two described district, and the glazed layer of separation makes resistance track avoid oxidation.

So conventional glazed layer can be given track and appropriate insulation material, for example provide normal corrosion protection for the selected suitable glass material of the serious overheat protection of heater.

In a preferred embodiment, serious overheat protection bridge also is used as the glaze of this suitable track region of bridge joint.This bridge preferred orientation is above near the track region end.

The time of " self-shield " heater self-shield under serious superheat state is depended on the temperature of the heater in the material bridge zone.It is hot more that heater becomes, and then bridging must be warm more, and it is just fast more to reach the time of flowing through fault current.In described water heating vessels, avoid the initial failure of heater, particularly avoid extremely important such as the fault in the time before the main overheat protection part work of bimetallic driver such as kettle.

This problem can be according to a further aspect of the invention, material bridge is set in the district of the heater by being lower than adjacent region in power density is reduced.According to second aspect, the invention provides a kind of resistance or heater, this resistance or heater comprise the thick-film resistor track that is located on the dielectric base, have predetermined current-carrying capacity described track two fates by the bridge of electrical insulating material partly bridging connect, the bridge of electrical insulating material becomes under predetermined temperature and fully conducts electricity so that fault current flows through from one or two described district, described resistance heating track has variable power density, and described material bridge is arranged in the heater traces zone with lower-wattage density.

By for example glass bridge being arranged on the low power density district of heater, the temperature in superheat state district rises to rise than the temperature in adjacent high power density district and lags behind, so the time of length can be arranged before breaking down.Certainly, the position of this bridge is still position rather than the other places that heater breaks down.Therefore, be arranged on the heater traces, then should select the position of glaze so that puncture and at first take place in other position of track if separate glaze.

In a preferred embodiment, the lower-wattage density region is centered on by the higher power density district.In specific preferred embodiment, the lower-wattage density region is arranged on the radially mesozone of heater traces, and the radially outer district of track has higher power density at least.The advantage of this structure is to be suppressed at the tendency that insulating material under the serious overheated condition produces microfissure, at the trial, microfissure makes heater produce fault.This effect is illustrated in greater detail in copending application, agents document 74.46.70570, the denomination of invention of applying for same date with the application also are the file of " electric heater ".The present invention described here may be used in the structure of above-mentioned application.

In the disclosed international application of above-mentioned " self-shield " heater and applicant's early reference, the track fault is owing to raise and bridging gets when fully conducting electricity, flow through track region above the electric current of track current-carrying capacity produces in temperature.Discover in this state, how track region all can deposit exactly and melt along any point of its length based on for example this track.In addition, when breaking down, track can produce electric arc.This electric arc is highly conductive and easily changes in magnetic field, so this electric arc can be by drawing to other parts such as control assembly.This electric arc even can damage the insulating barrier that is provided with track makes that heater is charged after breaking down.This potential danger system that makes can not satisfy existing safety standard.

Therefore, special hope can make fault exist in the precalculated position of track, so that make location of fault away from such as other parts such as control assemblies.The present invention realizes above-mentioned purpose by the device that provides a kind of electric current that will flow through the track that may break down to carry out concentration of local.

So, according to another aspect, the invention provides a kind of resistance or heater, this resistance or heater comprise the thick-film resistor track that is located on the dielectric base, two fates with described track of predetermined current-carrying capacity are connect by for example electrical insulating material bridging of glass, electrical insulating material becomes under predetermined temperature, and fully conduction is so that fault current flows through a described district at least, and wherein, described track region is provided with a device that will flow through the electric current concentration of local of track region.

This aspect of the present invention allows more effectively to control the inefficacy of track.The current concentration device is preferably away from any current-carrying part or grounded parts, parts relevant with the control of heater for example.

Current concentration can be accomplished in several ways.But preferably reducing track width by the part realizes.In one embodiment, obtain required concentrating, but preferably the hole of passing track, for example circular hole are set and realize this effect by reducing track width.The focus that will lose efficacy as track in this hole.

Described in above-mentioned embodiment, this bridge can be arranged between the adjacent track district partly or cover whole track.

It should be noted that various aspects of the present invention are separate basically.So described low power density and current concentration characteristic can be applied to the described structure of WO97/39603, for example, the fusing glass bridge in this structure is used as the glaze of whole track.

Description of drawings

In the mode of example the preferred embodiments of the present invention are described below in conjunction with accompanying drawing, in the accompanying drawings:

Fig. 1 is the plane graph of heater of the present invention;

Figure 1A is the cutaway view of being done along Fig. 1 center line A-A;

Fig. 2 is the form of record heater related data shown in Figure 1.

Embodiment

Fig. 1 represents to implement thick film plane heater 2 of the present invention.This heater comprises the stainless steel-based end 4 that 0.5mm is thick, depositing insulating layer 6 and heating track 8 in a usual manner in substrate 4.In this specific embodiment, insulating barrier 6 is made by Du Pont (Dupont) 3500 printing ink and thickness is 85 microns (+/-10 microns).Be deposited on that resistance heating track 8 on the insulating barrier 6 is made by the mixture of the F/612F/629 of Du Pont (Dupont) resistance printing ink and thickness is 13 microns (+/-2 microns).

As shown in the figure, resistance heating track 8 is made up of 8 concentric arcs track region of

row

8a, 8b...8h, and the end of concentric arcs track region is connected by silver-colored line 10.This track configuration is illustrated with general terms in applicant's WO98/366182.

Track region

8a, 8b, 8c and 8h are basically fully around heater, and other track position is subdivided into semicircle position roughly.The end of track 8e is connected to the silver-colored pad 16 that is used to receive the silver tipped contact (not shown) by silver-colored track 14, and the end of track 8d is connected to another contact by silver-colored track 20 and receives pad 18.Utilize as receive the voltage of 230V (or other voltage) with the contact of welded and installed on pad.The external diameter of outermost track 8a is about 60mm, and the gap between the adjacent track is about 0.5mm.

The gross power of this element is the AC power of the 230V of 1000W, and the power division of each track part provides in Fig. 2.

From Fig. 1 and 2 as can be known, the width of track part 8a-8h changes from the element edge to its center.Particularly, 8a is the narrowest for outermost track part, and track width increases towards

track

8e and 8f before reducing once more towards the most inboard track part 8h, in the radial center district.Because power density and track width are inversely proportional to,, then be increased to second local maximum at track 8h so power density is reduced to the minimum value of track 8e-8f from the maximum of track 8a.The effect that this width distributes is the tendency that has reduced insulating barrier 6 generation microcrack under serious overheated condition.

Referring again to Fig. 1 as can be known, be printed with " self-shield " glaze bridge 22 of wide 7mm, long 4mm by the opposed end of the track 8d of silver-

colored line

10a and 10b bridge joint and 8e.This bridge 22 is by ESL 4771G materials, printed on and about 13 microns of thickness (+/-2 microns).As can be seen, bridge 22 is arranged on the track position that connects track 8 respective end, so can produce bigger voltage drop by bridge 22.In fact, this bridge is apart from the about 61mm in the end of track 8e, apart from the about 30mm in the end of track 8d.This can produce the voltage difference of 208V on bridge 22.

As can be seen from Figure 1, the hole 24 of the about 1mm of diameter is set in place in bridge 22 and is connected in the zone of the track 8d between the track 8d end of contact pad 18.

Whole element be printed with thickness for example be 13 microns ,+/-2 microns Du Pont 3500 protection glazes.

In use, shown heater is installed in the bottom such as the heating vessel of kettle.Boil dry or in kettle, do not have water and when switching on, at kettle because the temperature of the high rated power of heater and its low heat capacity, heater is with fast rise.If the main overheat protector of bimetallic driver lost efficacy, so the temperature of heater continues to rise.But at a certain predetermined temperature, the conductance of self-shield glaze bridge 22 will rise to a bit, put the most of track of short circuit effectively at this, cause very big electric current to flow through the track region 8d and the 8e of track bridge joint.In specific embodiment, the resistance of these track region is about 5 Ω, makes about 46 amperes electric current flow through this track region, 4.35 ampere the electric current of this electric current during obviously greater than normal running, and surpassed the current capacity of this track region.Therefore, one or two this track region will lose efficacy.But this electric current is small enough to avoid the fusing or the earth leakage protector action of family expenses fuse when operate as normal.It is generally acknowledged, 10 and 15A/mm between breaking current produce satisfied opening circuit.

In described embodiment, track region 8d will in fact open circuit because of there being hole 24.Thereby existing hole 24 to make electric current concentration of local ground flow through this track makes and produces the possibility that opens circuit around the zone in hole 24 greater than other zone among the track region 8d.

It shall yet further be noted that bridge 22 is arranged between the track region of broad.The power density that this will reduce in this bridge zone this means, this bridge can be not warm as the peripheral region.This reaches the time of the fracture temperature of this bridge 22 with increase, so prolonged the time before the heater failure.Its advantage is to have reduced the main overheat protector work possibility of heater failure before.

As can be known, the self-shield time of heater is about 8 seconds in described embodiment.This is obviously greater than the desired 4 seconds bimetallic operating time of main overtemperature protection, so be under the overheat condition of dry combustion method or the logical state of stem grafting at kettle or similar device, heater can premature failure.But, within the heater insulation substrate is with the breakdown time, can realize safe failure mode.

Obviously, can carry out various improvement to the foregoing description without departing from the scope of the invention.For example, the current concentration device more than can be set, for example in

track

8d and 8e, all be provided with one.Though can be preferred, also needn't bridge 22 be set, so that track 8a-8h can have identical width at low density area.In addition, bridge 22 can be to cover the glaze of whole track 8 and be not only discrete bridge.The invention is not restricted to disclosed particular track size, in certain embodiments, according to the size and the required power of heater of heater, track width can be greater than or less than disclosed width.

As seen from the above description, various aspects of the present invention allow heater under serious overheated state, controllably lost efficacy to reduce the mode that heater punctures the possibility of center line or ground connection.

Obviously, for a person skilled in the art, an example of the present invention is just implemented in above-mentioned explanation.Given size, parameter and the tolerance of this example do not limit the present invention.

Claims

1. resistance, it comprises: be arranged on the thick-film resistor track on the dielectric base, two fates of described track with predetermined ampacity are by the discrete bridge institute bridge joint of glass material, this discrete bridge under predetermined temperature, become abundant conduction, flow through the fault current in one or two described district with generation, prevent that with the glazed layer that separates with discrete bridge above the track described resistance track is oxidized at discrete bridge.

2. resistance as claimed in claim 1, wherein, described bridge applies with the form of the glaze of the described track region of bridge joint.

3. resistance as claimed in claim 1, wherein, described spanning is connected on the end of adjacent track region.

4. resistance as claimed in claim 1, wherein, the bridge of described material is arranged on the zone of the lower-wattage density of resistance.

5. resistance as claimed in claim 4, wherein, relatively low power density district is centered on by higher power density district institute both sides.

6. resistance as claimed in claim 5, wherein, the lower-wattage density region is arranged on the radially middle region of resistance.

7. resistance as claimed in claim 6, wherein, the radially outer district of described at least resistance track has higher power density.

8. resistance as claimed in claim 1, wherein, setting device in described track region is when this device makes the electric current of concentration of local flow through described track region, this track region lost efficacy.

9. a resistance as claimed in claim 8 wherein, reduces described track region width by the part and makes current concentration.

10. resistance as claimed in claim 9 wherein, passes described track region and a hole is set.

11. heater, it comprises: be arranged on the thick-film resistor track on the dielectric base, two fates of described track with predetermined ampacity are by the discrete bridge institute bridge joint of glass material, this discrete bridge under predetermined temperature, become abundant conduction, flow through the fault current in one or two described district with generation, prevent that with the glazed layer that separates with discrete bridge above the track described resistance track is oxidized at discrete bridge.

12. the heater as claim 11, wherein, described bridge applies with the form of the glaze of the described track region of bridge joint.

13. the heater as claim 11, wherein, described spanning is connected on the end of adjacent track region.

14. the heater as claim 11, wherein, the bridge of described material is arranged on the zone of the lower-wattage density of heater.

15. the heater as claim 14, wherein, relatively low power density district is centered on by higher power density district institute both sides.

16. the heater as claim 15, wherein, the lower-wattage density region is arranged on the radially middle region of heater.

17. the heater as claim 16, wherein, the radially outer district of described at least heater traces has higher power density.

18. the heater as claim 11, wherein, setting device in described track region is when this device makes the electric current of concentration of local flow through described track region, this track region lost efficacy.

19. the heater as claim 18 wherein, reduces described track region width by the part and makes current concentration.

20. the heater as claim 19 wherein, passes described track region and a hole is set.