One such method is described in EP-A1-0 315 052. According to this known method the channel plates are treated in a manner to cause respective end portions of the outer walls of the individual channel plates of the heat exchanger to bend outwardly, such that the edges of said outwardly bent end portions will lie in contact with one another or in the vicinity of one another, and are then mutually joined by a weld seam, by gluing or by a U-shaped section fitted over said edges, so as to close the channels in the transverse channel system, formed with the aid of spacer members, at the side edges of said channels. The heat exchanger may be coupled for parallel current, counter current or cross current flow of the heat-exchanging fluids, which may be liquids or gases.
According to one preferred alternative proposed in the aforesaid publication, a part of the end portions of the intermediate walls is milled away prior to mutually assembling the channel plates together with intermediate spacer members, so as to expose a desired length of the end portions of the outer walls, these exposed end portions then being bent outwards. According to another alternative proposed in the aforesaid publication, the intermediate walls are configured at the channel-plate manufacturing stage such that the height of the end-portions of said intermediate walls becomes succesively greater the closer to the edge of the channel plates at the same time as the end portions of the outer walls are given a correspondingly, outwardly curved or bent form.
This pre-forming of the channel plates involves additional work and therewith higher manufacturing costs.
Another method of manufacturing a heat exchanger comprising plastic channel plates is described in EP-0-226 825. The end portions of the channel plates are fitted into openings provided in two plastic end plates and are therewith held parallel with one another in given space relationship. The channel plates are then heat treated so as to melt the ends of the narrow long sides and the broad long sides of said plates, causing the channel walls to expand and to fuse to the inner defining surfaces of said openings. Alternatively, the channel plates may extend slightly freely above the openings in the end plate, so as to enable the ends of the channel plates to expand during the heat treatment and thereby lock the channel plates in the end-plate openings. Thus, in order to produce a separate heat exchanger it is necessary to use two end plates provided with openings in which the end portions of the channel plates shall be fitted to desired positions. The end plates together with their accurately disposed and configured openings involve additional costs, as does also the task of fitting the channel plates in the openings provided in said two end walls.
U.S. Pat. No. 4,733,718 and DE-A-2 751 115 describe methods which are even further distant from the inventive concept than EP-A-226 825, and consequently the methods taught by these publications will not be discussed in detail here.