The present invention relates to such combustion chambers as are disclosed in the preamble to the following claim 1. A combustion chamber of the kind in question is disclosed _/ e.g. in the U.S. patent 3 853 453.

If the combustion chamber has four side chambers, the partition wall will be in the shape of a cross. The ends of the cross are free in the side chambers, while the side edges of the cross are attached to the inside of the combustion chamber. The combustion chamber and the partition wall are usually cast in one piece, but it is also possible to manufacture the partition wall as a separate part and weld it in the combustion chamber. The combustion chamber is intended to dissipate heat to the surroundings for heating. In most cases, known combustion chambers of the kind in question are surrounded by water in a hot water installation, e.g. hot water for a dwelling house. If cracks occur in the wall of the combustion chamber, the result can be that water comes into the combustion chamber and causes operational disturbances and stoppages. It has been found that this can occur due to the combustion chamber and the partition wall expanding differently when starting and stopping the apparatus, resulting in tensional stresses at the attachments of the partition wall to the combustion chamber, in some cases causing cracks in the wall of the combustion chamber. With respect to partition walls which are integrally cast with the combustion chamber, there are pores in the cast steel material, and when said tensional or heat stresses exceed certain values, cracks are obtained in the pores of the combustion chamber walls with the resulting risk of water leaking into the combustion chamber.

The object of the present invention is to eliminate this risk. In order to solve this problem, the invention is based on the knowledge that cracks in the combustion chamber wall must . be prevented, while it is possible to allow cracks of a certain width in the partition wall without this the function of the apparatus.

From this starting point, the problem is solved in accordance with the invention such that in the manufacture of the partition wall, said wall is already provided with stress concentration locations or indications of fracture at predetermined places for providing desired cracks in the partition wall when said wall and the walls of the side chambers are subjected to heat stresses during the first runs as well as heatings during starting and coolings during stopping the apparatus. The partition wall thus cracks into two parts in each side chamber, so that these parts can move freely relative each other during heating and cooling. The cracks which occur will, however, be so narrow that they do not affect the course of combustion.

A suitable embodiment of the combustion chamber in accordance with the invention is illustrated as an example in the appended drawings.

Fig. 1 is a side view of the combustion chamber in accordance with the invention. Fig. 2 is a view from above. Fig. 3 is a section along the line 3-3 in Fig. 1, Fig. 4 is a section along the line 4-4 in Fig. 2, and Fig. 5 is a section along the line 5-5 in Fig. 2.

The whole combustion chamber is integrally cast steel, and consists of identically similar side chambers 10,12,14,16 which are uniformly distributed around the central axis of the combustion chamber.

As is illustrated, the side chamber 12, for example, has two opposing side walls 12a,12b and an arcuate outer wall 12c so that the side chambers will be substantially half- cylindrical. The side walls of the side chambers merge into each other and form corners 18 in the central space of the combustion chamber, to which the side chambers are connected.

The outer walls of the side chambers run together in an upper end wall 20 and in a lower end wall 22. An inlet port 24 is made in the end wall 20 for accommodating an axial inlet pipe (not shown) .

The end wall 22 is formed with an axial outlet 26, to which an exhaust pipe is to be connected.

The central zone of the combustion chamber is /'iυK ^. E.A

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a partition wall 28 preventing straight through-flow from the inlet port 24 to the outlet 26.

The partition wall 28 is extended with side portions 28a at the side chambers, said portions extending as projections into the respective side chamber and are terminated with an end edge 28b situated at a predetermined distance from the outer wall of the respective side chamber, e.g. the outer wall 12c of the side chamber 12. In this manner there is obtained a through-flow opening 30 in each of the side chambers. The part of the combustion chamber including the side walls, lying above the partition wall, form a first chamber 32 in which the fuel-air mixture is ignited and combusted, where¬ after the combustion gases flow, with a certain amount of terminating combustion, down through the openings 30 to the subsequent second chamber 34 situated under the partition wall.

The illustrated combustion chamber is usually intended to be kept immersed in a container with water which is to be heated. Since the partition wall 28,28a is cast in one piece with the rest of the combustion chamber, the edge portions of the partition wall will be rigidly attached to the walls of the combustion chamber and to the side walls of the side chambers. This signifies, inter alia, that considerable heat stresses can be obtained at the side edges 28c of the wall portions

28a. When the combustion chamber is started up, and during its heating to normal operational temperature, the walls of the side chambers will expand more rapidly than the partition wall, and the partition wall will be cooled more quickly than the side walls when the apparatus is shut down, which results in that tensional stesses can occur, especially at the side edges of the wall portions. Since the casting has a certain porosity, it can thus happen that cracks occur in the side walls of the side chambers if particular measures have not been taken. Such measures have been taken in the embodiment illustrated, these measures consisting in that each wall portion has a stress concentration location at its middle in the form of grooves 36,38,40,42 on the upper side of the partition wall.

The stress concentration locations illustrated in the example extend out to the respective end edge 28b and meet at the centre 44 of the partition wall.

The stress concentration locations are formed as V-shaped grooves, the depth of which is substantially greater than the thickness of the partition wall at the stress concentration. In the example illustrated, the depth of the groove is about 85% of the thickness of the partition wall at the stress concentration. When the combustion chamber is started the first few times after manufacture and is heated to normal operating temperature, the heat and tensional stresses mentioned are obtained. Since the remaining material thickness in the bottom of the grooves 36,38,40,42 is comparatively small, a desired rupture of the material is obtained at the bottom of the grooves. The partition wall 28 is thus separated into four parts, resulting in that the tensional stresses are entirely eliminated at the side edges of the wall portions, and thereby the risk of ruptures and cracks occurring in the walls of the combustion chamber and in the side walls of the side chambers. The cracks which are obtained have no significance, however, for the function of the apparatus as a combustion apparatus, since the stress concentration locations can be made with such, accuracy that the cracks will be commonly just as great and narrow.

As will be seen from the drawings, the side portions have a thickness increasing from the middle and out towards the side edges, where the wall portions connect via a softly rounded junction to the side walls of the side chamber. Within the scope of the invention according to the following patent claims, the stress concentrations can naturally have a plurality of other locations than those illustrated in conjunction with the described embodiment.

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