STEAM GENERATOR

Abstract

The invention refers to a steam generator for household appliances. The steam generator comprises a container having an inlet for water and an outlet for steam, and an electrical heating element fixed to the container. The container comprises a first part and a second part which are connected along a joint such that a critical pressure inside the container causes a slit to appear in a predefined section of the joint, said slit providing a security vent for releasing pressure.

Description

The invention refers to a steam generator for household appliances like washing machines, laundry driers, electric irons, espresso machines or ovens.

Such steam generators have an inlet for water and an outlet for steam. If the outlet is clogged a continued steam generation might cause a dangerous increase of pressure and ultimately an explosion.

A steam generator suitable for household appliances is disclosed in DE 10 2006 020 280 A1. The known device generates steam inside a container consisting of a bottom part and a lid part which are clamped together by a threaded bolt extending through the container. The bolt head presses against the outside of the bottom part; a nut screwed onto the bolt presses against the outside of the lid part. A joint between the bottom part and the lid part is sealed by an elastic adhesive. If the pressure inside the container increases beyond a certain level the adhesive will fail and pressure vented through a rupture along the joint.

It is an object of the present invention to provide a steam generator for use in household appliances which is inexpensive to manufacture and prevents a dangerous increase of pressure by automatically venting of steam.

SUMMARY OF THE INVENTION

A steam generator according to the present invention comprises a container in which water is evaporated by means of an electrical heating element fixed to the container. The container has an inlet for water and an outlet for steam. The container comprises a first container part with a flange against which a second container part rests thereby covering the first part.

These two container parts are connected in such a way that a critical pressure inside the container forces them slightly apart such that a slit appears between the two container parts at a predefined location. This slit provides a security vent for releasing pressure. In the case that the steam outlet is clogged for any reason, even continued steam creation cannot lead to an increase of pressure beyond the critical level that causes the security vent to open. Therefore, the container cannot explode.

An important advantage of the present invention is that the slit or slits will open at a predefined location. Whereas prior art steam generators, like those known from DE 10 2006 020 280 A1, vent steam in a random direction where the steam may cause damage, such damages can be prevented according to the invention by choosing the predefined location accordingly.

In an embodiment of the invention the first and the second container part are fixed to each other along part of their circumference, for example by clamping, which may be achieved by at least one rim section of one of the container parts that is folded over a rim section of the other container part. In this way the two container parts are mechanically connected. However, according to the invention the two container parts are firmly connected only along part of their circumference. For example, along a first part of the circumference the rim of one of the container parts may be covered by a folded rim section provided at the other container part and along a second part of the circumference the rim of both container parts is not covered by such folded sections. Another possibility is to arrange a welded seam or a series of weld spots or rivets along a first part of the circumference, but not along a second part.

In the second part of the circumference the two container parts are therefore not fixed to each other and can be forced apart much more easily than in the first part. Should the pressure inside the container rise to an overly high level the container will therefore open slightly along the second part of the circumference enabling steam to escape. Advantageously, such venting may be achieved without destruction of the device.

In a preferred embodiment of the invention the security vent, which opens between the two parts of the container when the pressure in the container exceeds a critical threshold value, is used as a second safety feature in combination with a conventional overload valve at the steam generator.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will be better understood by the following description when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a side view of an embodiment of the present invention;

FIG. 2 a bottom view of the container of the steam generator shown in FIG. 1;

FIG. 3 is a cross section along line AA of FIG. 2; and

FIG. 4 is a cross section along line BB of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 shows a steam generator 1 comprising a disc-shaped container 2 and an electrical heating element 3 fixed to the outside of the container 2. The container 2 has an inlet 4 for water an outlet 5 for steam.

The container 2 comprises a bottom part 2a having a flange 6 and a lid part 2b resting against the flange 6 thereby covering the bottom part 2a. In the example shown these two container parts 2a, 2b are of substantially equal shape and the lid part 2b is also provided with a flange 7. Although in principle the lid part 2b might simply be a flat disc.

The two container parts 2a, 2b are fixed to each other by clamping. The clamping forces are caused by rim sections 8 of one of the container parts 2a, 2b which are folded over the rim of the other container part. In the example shown, rim sections 8 of the lid part 2b are folded over the rim of the bottom part 2a. Such rim sections 8 might just as well be provided on the bottom part 2a and folded over the rim of the lid part 2b. It is also possible to provide one or several folded rim sections 8 on both the bottom part 2a and the lid part 2b.

The folded rim sections 8 cover only part of the circumference of the container 2. Therefore the clamping forces act only on a part of the flanges 6, 7, i. e. on first sections but not on second sections adjacent to the first sections in a circumferential direction. This can be seen especially well in FIG. 2 which shows a bottom view of the circular container 2 without the heating element. There is a series of sections of the flanges 6, 7 where folded rim sections 8 are provided, by which the flanges 6 and 7 are clamped together. Sections 9 and 11 in between the folded rim sections 8 are not clamped together.

Partly the circumference of the device 1 is covered by folded rim sections 8 and therefore is clamped as illustrated in FIG. 3 showing a cross section along line A-A of FIG. 2. Along at least one second part of the circumference there are no folded rim sections, i.e. neither the rim of the bottom part 2a nor the rim of the lid part 2a is covered by a folded rim section as illustrated in FIG. 4 showing a cross section along line B-B of FIG. 2. No clamping forces act on this at least one second part of the circumference.

In the example shown, this at least one second part of the circumference comprises two larger venting sections 9 between folded sections 8. These venting sections 9 are indicated in FIG. 2 by dotted lines enclosing an angle α.

The venting sections 9 provide a security feature preventing a dangerous build up of pressure in the container 2. If the steam outlet 5 is obstructed for any reason, continued steam generation causes pressure in the container 2 to increase. Unchecked, such an increase might eventually cause the container 2 to explode. This is prevented by the venting sections 9. As the bottom part 2a and the lid part 2b are not fixed to each other along the venting sections 9, an increase in pressure beyond a certain level will force the bottom part 2a and lid 2b slightly apart elastically in this venting section 9 of the circumference. Thus a critical pressure inside the container 2 causes a slit to appear in a predefined venting section of the joint along which the two container parts 2a, 2b are connected. This slit provides a security vent for releasing pressure which will always open elastically when needed and will close when the pressure dropped to an uncritical value.

In order to open reliably without damaging the container 2, the venting sections 9 preferably should have a length of at least one eighth of the total length of the circumference. In the example shown, each venting section 9 has a length of about one seventh of the total length of the circumference. The smaller sections 11 between the folded sections 8 of the illustrated container 2 are too small to enable venting and are not necessary. In principle a single large folded section 8 covering a sufficiently large part of the rim would be sufficient. However, it is easier to fold several smaller sections 8 instead of one larger section.

In principle, one sufficiently large venting section 9 is sufficient to prevent a dangerous increase of pressure. In general, the venting section 9 should have a length of at least one tenth of the circumference and at most one third of the circumference. Larger venting sections 9 could cause the container to open too easily. Preferably, the venting sections 9 have a length of not more than one quarter of the total length of the circumference. Preferably, the venting sections 9 should have a length of one eighth to one quarter of the circumference.

The bottom part 2a and the lid part 2b are made of sheet metal, for example by deep drawing of a sheet of stainless steel. Therefore, the container 2 should have rather thin walls of less than, 0.7 mm, preferably less than 0.6 mm, most preferably 0.4 to 0.5 mm. As a consequence, the container 2 has a favourably low heat capacity and can be heated up quickly for steam generation. The volume of the container 2 is about 50 ml to 400 ml, preferably 150 ml to 300 ml. To obtain such a volume the overall diameter of the container 2 may be 10 cm to 20 cm and preferably is selected to be 13 to 15 cm.

To seal the container 2 during normal operation, a seal 10 is compressed between the flange 6 of the bottom part 2a and the lid part 2b. The seal 10 may be a gasket, for example an O-ring as shown in FIGS. 3 and 4. Alternatively, the seal 10 may be a strand of adhesive. In the embodiment shown, the seal 10 is arranged in a groove of the flange 6 of the bottom part 2a. The flange 7 of the lid part 2b may also have a groove which encloses an upper part of the gasket seal.

Claims

1. Steam generator comprising

a sheet metal container having an inlet for water and an outlet for steam, and an electrical heating element fixed to the container,

the container comprising a first container part and a second container part which are clamped together,

the first part having a flange against which the second part is clamped covering the first part, and

a seal arranged on the flange, said seal being compressed between the first container part and the second container part,

wherein the first container part and the second container part are clamped together by clamping forces acting on at least one first section of the flange but not on at least one second section of the flange adjacent in circumferential direction to the at least one first section,

the clamping forces being applied such that a critical pressure inside the container causes a slit to appear between the at least one second section of the flange and the second container part, said slit providing a security vent for releasing pressure.

2. Steam generator according to claim 1, wherein the clamping is effected by sections of the first container part folded over a rim of the second container part.

3. Steam generator according to claim 1, wherein the clamping is effected by sections of the second container part folded over a rim of the flange of the first container part.

4. Steam generator according to claim 1, wherein the seal is a gasket.

5. Steam generator according to claim 4, wherein the gasket is arranged in a groove of the flange.

6. Steam generator according to claim 1, wherein the second container part comprises a flange which rests against the flange of the first container part.

7. Steam generator according to claim 1, wherein the container is a circular disc.

8. Steam generator according to claim 7, wherein the at least one second section has a length of one eighth to one quarter of the circumference of said circular disc.

9. Steam generator according to claim 7, wherein the at least one second section has a length of one seventh to one fifth of the circumference of said circular disc.

10. Steam generator according to claim 1, wherein at least one of the container parts is made of a sheet metal.

11. Steam generator according to claim 7, wherein the container has an overall diameter of 10 cm to 20 cm.

12. Steam generator according to claim 7, wherein the container has an overall diameter 13 cm to 15 cm.

13. Steam generator according to claim 1, wherein the heating element is fixed to the outside of the container.

14. Steam generator according to claim 17 wherein the at least one second section of the flange has a length of at least one twelfth of the circumference the flange.

15. Steam generator according to claim 1, wherein the at least one second section of the flange has a length of at most one quarter of the circumference the flange.

16. Steam generator according to claim 1, wherein the first container part and the second container part are of equal shape.

17. Steam generator comprising

a container having an inlet for water and an outlet for steam, and

an electrical heating element fixed to the container,

the container comprising a bottom part as a first container part and a lid part as a second container part which rests against a flange of the bottom part,

wherein these two container parts are fixed to each other along part of their circumference by at least one rim section of one of the two container parts that is folded over a rim section of the other container part, such that along a first part of their circumference the rim of one of the container parts is covered by the other container part and along a second part of their circumference the rim of both container parts is uncovered,

wherein the second part of their circumference comprises a venting section having a length of at least one tenth of the circumference and at most one third of the circumference, said section providing a vent which opens in the case of the pressure exceeding a critical threshold.

18. Steam generator according to claim 17 wherein the venting section has a length of one eighth to one quarter of said circumference.

19. Steam generator according to claim 17, wherein the venting section has a length of one seventh to one fifth of said circumference.

20. Steam generator according to claim 17, wherein the container part comprising the folded rim section or sections is made of a sheet metal.

21. Steam generator according to claim 17, wherein both the lid part and the bottom part are made of a sheet metal.

22. Steam generator according to claim 17, wherein the container has an overall diameter of 10 cm to 20 cm.

23. Steam generator according to claim 17, wherein the container has an overall diameter of 13 cm to 15 cm.

24. Steam generator according to claim 17, wherein the container has a wall thickness of less than 0.7 millimeters.

25. Steam generator according to claim 17, wherein the container has an wall thickness of 0.4 mm to 0.5 mm.

26. Steam generator according to claim 17, wherein the container has a volume of 50 to 400 milliliters.

27. Steam generator according to claim 17, wherein the container includes a volume of 150 to 300 ml.

28. Steam generator according to claim 17, wherein the bottom part and the lid part are of equal shape.

29. Steam generator according to claim 17, wherein a gasket is placed between the flange of the bottom part and the lid part.

30. Steam generator comprising

a container having an inlet for water and an outlet for steam, and

an electrical heating element fixed to the container,

the container comprising a first container part and a second container part which are connected along a joint,

the first container part having a flange against which the second container part rests covering the first container part, and

a seal compressed between the first container part and the second container part, wherein the first container part and the second container part are connected such that a critical pressure inside the container causes a slit to appear in a predefined section of the joint, said slit providing a security vent for releasing pressure.

31. Steam generator according to claim 30, wherein said slit in the joint occurring between the first container part and the second container part responsive to a critical pressure inside the container opens as a result of an elastic deformation of at least one of said first container part and said second container part and will close again by the container parts reducing their elastic deformation as the pressure in the container decreases to an uncritical value.