CN2461236Y

CN2461236Y - Electric heater

Info

Publication number: CN2461236Y
Application number: CN00255073U
Authority: CN
Inventors: M·C·克里特克利; C·P·穆顿
Original assignee: Strix Ltd
Current assignee: Strix Ltd
Priority date: 1999-08-13
Filing date: 2000-08-12
Publication date: 2001-11-21
Anticipated expiration: 2010-08-12
Also published as: GB2353457A; CN1320355A; DE60045400D1; DE60034019D1; EP1121835A1; ES2284516T3; EP1121835B1; AU6583000A; WO2001013680A1; EP1713307A3; ATE492139T1; EP1713307A2; GB2353457B; GB9919205D0; CN100396163C; HK1040590A1; EP1713307B1; RU2001111004A; CN1523931A; DE60034019T2

Abstract

The utility model provides an electric heater, relating to a resistor or a heater which has a thick-film resistance groove arranged on an insulating substrate. The utility model is characterized in that two predetermined sections of grooves 8d, 8e have predetermined current-carrying capacity for current; the sections are connected with each other by separated insulating material, such as a glass bridge; the bridge has sufficient conductivity under certain temperature, resulting in that failure current pass through one to two sections of the 8d, 8e; the oxidation of a resistance groove 8 can be prevented by a separated outer-layer enamel layer. The utility model provides a resistor or a heater which also has the characteristics that a groove section of the 8d which the failure current can pass through is provided with a device used for the local current to pass through in centralization, such as a hole in the groove.

Description

Electric heater

The present invention relates to electric heater, relate in particular to the sort of electric heater that the resistance groove is arranged on dielectric base.

This heater is used in or has been proposed and is used in various occasions, household electrical appliance for example, and as water heating vessels, water heater or electric iron.Insulating barrier, usually be arranged on the metallic substrates as glass, pottery or glass ceramics (below be referred to as " glass "), as (for example forming the part of heating vessel substrate) on the plate, utilize printing technology that the resistance groove is arranged on this insulating barrier usually.As the replacement to the substrate of one deck metallizing, this substrate can be a solid ceramic body.Can another electric insulation layer be set on this groove and protect groove, prevent its corrosion and oxidation.In the art, this heater is called " thick film " heater.

Obviously under situation about breaking down, do not allow overheated heater very important,, and may cause suitable infringement the user because this not only can be to equipment or the electrical equipment that is using.

Several suggestions that this overtemperature protection is provided have been proposed.In heating vessel, resettable overheat protector is provided usually, turn round during the overheated heater of this protector in container, for example in container, do not have liquid and be energized or running when the liquid in container evaporation is done.Usually, this comprises a bimetallic trigger of being arranged to the heater thermo-contact, and this trigger moves under given temperature, when being higher than the natural running temperature of container, starts the cover contact in the heater power source.But if this protector can not move, it also is known that an alternative protector is provided, and thermo-fuse for example, this thermo-fuse rise in the temperature of heater and work when being higher than predetermined temperature value.Such scheme is described among the applicant's the patent application WO-A-94/18807.

In the applicant's U27 and U28 control, be provided with two bimetallic triggers, they are used alternatingly mutually, just needn't use serious overheat protector.

But, a kind of heater or resistance with inherent protection preferably is provided.The applicant has proposed a kind of like this scheme in WO97/39603.According to this scheme, the bridge of selecting glass material is set between adjacent heating tank, selects the shape of groove and the position and the material of groove, so that the glass between the groove section has enough conductivity under predetermined temperature, make the short circuit of groove section, thereby cause the controlled inefficacy of heater.Therefore this heater can be described as " self-protection ", does not need external control.

A kind of " self-protection " heater also is provided in the applicant's application WO99/02080, has wherein stipulated the position deviation groove end of the bridge between the adjacent slot, so that the electric current when short circuit occurring in the limiting groove.Purpose is to prevent that fault current from blowing the fuse of domestic power supply.

The present invention has done to further develop to above-mentioned application in all fields.

In WO97/39603, proposition self-protection glass bridge preferably is set to the one deck on whole heater pocket.But, find the bridge that bridge is preferably discrete now, and if make this groove exempt from oxidation and corrosion, provide one deck independent outer glaze layer.

Therefore a first aspect of the present invention has provided a kind of resistance, perhaps this have a heater that the thick-film resistor groove on the dielectric base is set, two predetermined sections of described groove have scheduled current current-carrying flux, separate the spanning mistake by insulating material, this bridge has enough conductivity under predetermined temperature, cause that fault current passes through one or two described section, utilize independent outer glaze layer to prevent the oxidation of resistance groove.

Like this, can use traditional outer glaze, for the resistance groove provides normal corrosion protection and a kind of suitable insulation material, for example the glass material of suitably selecting is used for the serious overheated protection of heater.

In a most preferred embodiment, serious overtemperature protection bridge is also as the outer glaze that strides across suitable groove section.Preferably also make bridge location in top, adjacent slot section end.

The time of " self-protection " heater self-protection under serious overheat condition is depended on the temperature in heater material bridge zone.Heater is warm more, and bridge is warm more, can more quickly reach the temperature above fault current.In the said water heating vessels of context, for example in the kettle, especially in a period of time before carrying out the protection of any overtemperature protection first time such as bimetallic trigger, prevent that the heater premature failure from being crucial.

According to another aspect of the present invention, in the low zone of a power density ratio adjacent area by material bridge being placed on heater, can alleviate this problem.Therefore a second aspect of the present invention provides a kind of resistance or this heater that the thick-film resistor groove is set on a dielectric base, two predetermined sections of described groove have the predetermined current current-carrying capacity, the spanning mistake of making by electrical insulating material, this bridge has enough conductivity under predetermined temperature, make fault current pass through described one section or two sections, described resistance heating groove has transformable power density, and described material bridge is arranged on the lower heater pocket zone of power density.

By the glass bridge being placed on the low power density zone of heater, temperature that should the zone under the superheat state temperature that will lag behind adjacent high power density zone that rises rises, and therefore provides the long time to fault.Certainly, still keep the position of bridge, so that heater is in this position rather than other position fault.Therefore,, can select like this, so that fault can at first not occur in other place of groove if independently outer glaze is provided on heater pocket.

In this most preferred embodiment, the lower-wattage density area is positioned at next door, higher power density zone.In a particularly preferred embodiment, the lower-wattage density area is arranged in the radially middle part of heater pocket, has higher power density in the radially outer zone of groove at least.This layout has in the advantage that stops formation slit in the substrate under the serious overheated situation, and slit may cause heater failure.This effect is described in the applicant's application on the same day more fully, and promptly procuratorial proxy number is that its title also is an electric heater in 744670570 the patent application.Invention described herein can be applied in the scheme of that application.

Described in the above and the applicant is early stage with reference in " self-protection " heater alleged in the disclosed international patent application; when bridge raises and after having enough electric conductivities in temperature; because the electric current that passes through one section groove surpasses the ampacity of groove, groove just breaks down.Have been found that in this case the groove section may be along the fusion of place, the arbitrfary point of its length direction, for example depend on exactly standing groove etc.In addition, when groove lost efficacy, will produce electric arc.This electric arc conductivity is strong, has variable magnetic field, in addition near other parts, such as control assembly.This arc even damage are provided with the insulating barrier of resistance groove, may cause heater to activate after fault.This may be dangerous, and this system can not satisfy current safety standard.

Therefore, wish most to make fault occur in the precalculated position of groove, so that can be arranged on position away from miscellaneous part such as control assembly.By using the device that can make the electric current concentration of local that flows through the groove section that can break down, the present invention has just reached above-mentioned purpose.

Therefore, another aspect of the present invention provides a kind of resistance or thisly has a heater that is arranged on a thick-film resistor groove on the dielectric base, two predetermined sections of described groove have a predetermined current ampacity, and stride across by a kind of electrical insulating material, glass for example, this material has enough conductivity under predetermined temperature, cause fault current to pass through at least one described section, and wherein said groove section is provided with the device of concentration of local electric current.

Therefore this aspect of the present invention allows the controlled more inefficacy of groove.This current concentration device preferably is set to away from any electric current carrying or earth element, for example a controller relevant with heater.

Can reach concentrating of electric current in several modes.But, preferably obtain by the part width that reduces groove.In one embodiment, this groove can be restrained, so that concentrating of needing, but preferably reaches this effect by a hole is set, for example the circular hole by this groove.The focus that will lose efficacy as groove in this hole.

As above-mentioned embodiment was described, bridge can a part be arranged between adjacent two grooves, perhaps on whole grooves.

Obviously, various aspects of the present invention are separate basically.Therefore, low power density and current concentration characteristic can be applied in the scheme of WO97/39603, and for example those fusing glass bridges are as the place of whole rooved face glaze.

A most preferred embodiment of the present invention is described below with reference to accompanying drawings.Wherein:

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

Figure 1A is the profile along A-A line among Fig. 1;

Fig. 2 is the relevant data table of heater among Fig. 1.

With reference to Fig. 1, represented that is embodied a thick film plane heater 2 of the present invention.This heater has the stainless steel-based end 4 that 0.5mm is thick, and insulating barrier 6 and heating tank 8 are arranged in the substrate in a conventional manner.In this certain embodiments, insulating barrier 6 is made by Dupont3500 printing ink, about 85 micron thickness (+/-10 microns).This resistance heating groove 8 is arranged under the insulating barrier 6, is mixed and made into by the DupontF/612/F629 resistance printing ink, thick about 13 microns (+/-2 microns).

Obviously, resistance heating groove 8 is by 8

concentric arcwall groove

8a, 8b ... 8h forms, and its end connects silver-colored connecting rod 10.A kind of like this groove of shape is disclosed among applicant's the patent application WO98/366182.

Groove section

8a, 8b, 8c and 8h all extend around heater basically, and other groove section further forms semi-circular portions.The end of groove 8e is connected to silver-colored groove pad 16 by a silver-colored groove 14, and this groove pad is used to hold silver-colored groove contact (not shown), and the end of groove 8d connects another contact by silver-colored connecting rod 20 and holds pad 18.In use, for example hold a 230V (or other voltage) power supply by the contact of welded and installed on pad.The external diameter of the groove 8a of ragged edge is about 60mm, and the gap between adjacent two grooves is about 0.5mm.

The gross power of this element is 1000W, the 230V alternating current, and the distribute power of each groove section is seen Fig. 2.

Can find out obviously that from Fig. 1 and 2 the width of

groove section

8a and 8h is for to change to the center from the element edge.Especially the groove 8a of ragged edge is the narrowest, and before reducing once more towards interior groove section 8h, the width of groove is towards radially middle

section groove section

8e and 8f increase.Because power density and well width are inversely proportional to, power density is decreased to the minimum value of groove 8e-8f from the maximum of groove 8a, then is increased to one second local minimum at groove 8h place.The purpose of this width distribution is the tendentiousness that microcrack appears in minimizing insulating barrier 6 under serious overheat condition.

Again with reference to Fig. 1, obviously the opposed end of

groove

8d and 8e is connected by silver-colored connecting rod 10, and is printed with " self-protection " glaze bridge 22, and about 7mm is wide for bridge, and 4mm is long.This bridge 22 is by the printing of ESL4771G material, about 13 micron thickness (+/-2 microns).Obviously bridge 22 is arranged on the groove section that is connected to groove 8 each end, so that bigger voltage drop occurs on bridge 22.In fact, this bridge is apart from the about 61mm in groove end, apart from the about 30mm in the end of bridge.This has just produced the pressure reduction of about 208V on this bridge.

As can be seen from Fig. 1, the diameter in hole 24 is near 1mm, and the bridge 22 and this groove section 8d that are provided with among the groove section 8d connect between the end of contact mat 18.

Whole element all is printed with the protection glaze, Dupont3500 for example, and thickness is 13 microns+/-2 microns.

In use, heater as shown in the figure is installed in the heating vessel bottom, for example in kettle.When this kettle dryouied or kettle in still be switched on without any water, then because the heater power height, and it is poor to conduct heat, so heter temperature will rise very fast.If an any elementary overtemperature protection for example bimetallic trigger was lost efficacy, heter temperature will continue to rise so.But under a certain predetermined temperature, the conductivity of the outer glaze bridge 22 of self-protection will be brought up to that makes the most slot short circuit effectively, cause among the groove section 8d that connected by groove and the 8e by very high electric current.In this certain embodiments, the resistance of these groove sections is about 5 Ω, causes reaching about 46 amperes by the electric current of these groove sections, far above the normal running electric current of about 4.35amps, considerably beyond the electric current carrying capacity of slot part.Therefore, there are one or two groove sections to lose efficacy in these grooves.But electric current is enough low, is enough to prevent that the family expenses fusible link from blowing, and perhaps prevents the operation of earth leakage switch.Usually can find also that the fault current between 10 to 15A/mm can produce satisfied fault.

In the above-described embodiments, owing to hole 24 occurs, in fact groove section 8d lost efficacy.Can concentration of local electric current by groove so that the zone around the hole 24 is more greater than other zone that causes in the groove 8d losing efficacy and taking place.

It may be noted that also bridge 22 is arranged between the groove section of broad.Help to reduce the power density in bridge zone, this means that the bridge zone can not become the same with zone on every side hot.Just having increased bridge 22 effectively reaches the time that the fault temperature is changed for this, thereby has prolonged the time before the heater failure.This reduced the similar fault of heater to thermal protector before first running favourable.

In described embodiment, have been found that the time of heater self-protection is about 8 seconds.Better 4 seconds bimetallic durations of runs than wishing elementary overtemperature protection, so as this heater not can said kettle dryout with anhydrous connection situation under first fault.But,, all caused a safety failure pattern no matter how few the time of heater insulation substrate fault is.

Obviously, the various improvement that the foregoing description is carried out do not break away from the spirit and scope of the present invention yet.For example, more than one current concentration device can be set, for example in each groove, all be provided with one.In addition, although be best, also can bridge 22 be set, so that groove 8a-8h all has identical width at low power section.In addition, bridge 22 can be set to all on the grooves 8 outer glaze is being set, and not be one independently on the bridge.The invention is not restricted to the specific groove size that discloses among some embodiment, but depend on the size of heater and the power that heater requires, groove can be wideer or narrow than the size that discloses.

As seen from above-mentioned, various aspects of the present invention all allow under serious overheat condition, and heater reduces the controlled inefficacy of mode that similar heater failure is neutrality or ground connection with a kind of.

To those skilled in the art, obviously specification only relates to an enforcement embodiment of the present invention.Particularly, can not limit the present invention only according to the given various sizes of example, parameter and tolerance limit.

Claims

1, a kind of resistance or thisly have a heater that is arranged on a thick-film resistor groove on the dielectric base, two predetermined sections of described groove have the predetermined current current capacity, glass material bridge joint by a separation is logical, this bridge has enough conductivity at a certain temperature, cause fault current to pass through described one or two section, the outer glaze layer independent by one deck prevents the oxidation of resistance groove.

2. resistance as claimed in claim 1 or heater, its jackshaft is as the outer glaze of a crossed slot section.

3. resistance as claimed in claim 1 or 2 or heater, its jackshaft are arranged on the adjacent groove section end.

4. described resistance of any one claim or heater as described above, wherein material bridge is arranged on the lower zone of heater power density.

5. a resistance or thisly have a heater that is arranged on a thick-film resistor groove on the dielectric base, two predetermined sections of described groove have the predetermined current current capacity, glass material bridge joint by a separation is logical, this bridge has enough conductivity at a certain temperature, cause fault current to pass through described one or two section, described resistance heating groove has variable power density, and described material bridge is arranged on the lower zone of heater power density.

6. as claim 4 or 5 described resistance or heaters, wherein the zone that power density is lower is other in the higher zone of power density.

7. as claim 4,5 or 6 described resistance or heaters, wherein the zone that power density is lower is arranged on radially middle body of heater.

8. resistance as claimed in claim 7 or heater, wherein the radially outer zone of heater pocket has higher power density at least.

9. described resistance of any one claim or heater as described above, wherein in described one the groove section that will lose efficacy, be provided with can concentration of local device by the electric current of this groove section.

10. a resistance or thisly have a heater that is arranged on a thick-film resistor groove on the dielectric base, two predetermined sections of described groove have the predetermined current current capacity, glass material bridge joint by a separation is logical, this bridge has enough conductivity at a certain temperature, cause fault current to pass through described one or two section, wherein said groove section is provided with the device of the electric current that concentration of local passes through.

11. as claim 9 or 10 described resistance or heaters, wherein the width by part minimizing groove section obtains concentrating of electric current.

12. resistance as claimed in claim 11 or heater, wherein the groove section is provided with a through hole.