Plate heat exchanger and edge seal
BACKGROUND OF THE INVENTION 
     This invention relates to a plate heat exchanger of the type comprising plates, which are joined in pairs closely adjacent each other and provided with corrugations forming passageways for the media flowing through the plate heat exchanger. 
     The plates joined in pairs closely adjacent each other are provided with grooves about their circumference and about the inlet and outlet portions. The grooves are intended to receive the gaskets, which in assembled state of the heat exchanger are pressed sealingly between the respective plate pair, thereby preventing leakage from the heat exchanger and distributing the media in the inlet and outlet portions. 
     At the type of plate heat exchanger comprising single plates, a gasket is attached between the plates, whereby each plate and therewith its gasket groove automatically rests against the gasket located behind in the assembled heat exchanger. At the heat exchanger comprising plates, which are arranged in pairs and already at the manufacture joined to each other, no gasket is provided between these two plates and, therefore, there is no support between them in the area of the gasket grooves. This involves the risk, that leakage arises in the heat exchanger between adjacent pairs of plates, due to the fact that the plates comprised therein and their gasket grooves can be pressed in against each other, for example at the mounting or due to the working pressure prevailing in the media in the heat exchanger. 
     When the joint between the two plates comprised in the pair is an edge weld or an outward directed folding, the space, which is located inside between the plates and compared to the heat exchanger with single plates has no gasket, permits a relatively free flow of the medium flowing between the plates arranged in pairs. This space, thus, acts in principle as a shunt line and lowers the effeciency degree of the heat exchanger. 
     SUMMARY OF THE INVENTION 
     The present invention as it is defined in the characterizing clauses of the attached claims renders it possible to eliminate the leakage problems between the plate packages arranged in pairs and at the same time to reduce the shunt effect of said space. 
     The invention relates to a plate heat exchanger of the type provided with plates (1,1) attached in pairs sealingly to each other, between which pairs of plates in the assembled state of the heat exchanger, gaskets (6) extend in grooves (3,4) embossed in the plates. The plates (1,1) attached in pairs to each other are connected to each other in the edge areas to be connected by a sealing folding (5,7), which extends inward between the individual plates and in between the embossings facing toward each other in the two plates and forming the grooves (3). 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is described in greater detail in the following by way of example and with reference to the accompanying drawing, in which 
     FIG. 1 is a general end side view of a plate package comprising a number of plates joined to each other in pairs to form a plate heat exchanger, and 
     FIG. 2 is a schematic partial section through the package according to FIG. 1 along the line II--II. 
    
    
     DETAILED DESCRIPTION 
     As should have become apparent without saying, the plates here concerned are comprised in a plate heat exchanger, which comprises a plurality of plate elements, which in advance have been sealingly joined to each other in pairs, and between which gaskets are provided. Said elements are clamped between two stand plates in a stand. This constitutes prior art and will not be described here in greater detail. 
     The heat exchanger plate 1 shown in FIG. 1 is provided in usual manner with inlet and outlet openings 2 and includes grooves 3 for field gaskets 6 extending about the circumference of the plate and the inlet and outlet opening of one medium, and grooves 4 for circular gaskets enclosing the inlet and outlet openings of the second medium. The heat exchanger plates 1 as mentioned above are sealingly jointed to each other in pairs along the circumference and along the edges of the inlet and outlet openings in question. According to the invention, this jointing is effected by folding inward the edges of the two plates 1 forming the pair, see FIG. 2. At said jointing one plate 1 at the edge is folded inward by a single folding 5 while the second plate is folded with a double inward folding 7, which embraces the free edge folded inward of the first plate 1. This is clearly shown in FIG. 2. The joint or folding extends inward between the individual plates in the pair a sufficient distance, so that the joint forms a support between the grooves 3 embossed in the plates. The gaskets 6 attached between the plate pairs 1,1 hereby can be pressed together with a sufficient force for bringing about a satisfactory and reliable sealing between adjacent plate pairs. 
     The aforementioned space 8 formed between the plates 1,1 of the pairs is filled partially by the joint or folding. The flow resistance in this space, therefore, is substantially increased, whereby shunting of the medium between the plates is substantially prevented. 
     Due to the fact that the joint is an inward directed folding of the plates, and the folding has been given the configuration described, the joint at increasing pressure between the pair of plates automatically is affected in sealing direction, i.e. pressed together. Hereby a further advantage of the present invention is obtained, as the pressure prevailing between the plate pairs does not tend to &#34;burst&#34; the joint. 
     In connection with the folding operation, a sealing agent can be applied in usual manner in the folding area of the plates. 
     The invention has been described above in principle. It is possible within its scope to carry out the folding for jointing the plates in other ways, but with regard paid to the above criteria.