Patent Application
20100034526
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.
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.
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:
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
Partly the circumference of the device 1 is covered by folded rim sections 8 and therefore is clamped as illustrated in
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
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
