Patent ID: 8776371

Claim:
A method of joining thin heat exchanging plates comprising the steps of; providing plates of an iron-based material, the plates having port holes and a pressing pattern of elevations and depressions over a heat exchanging area of the plates and, if present, over a distribution area to a plate heat exchanger; providing a braze material which contains iron-based braze filler and melting point lowering elements prior to brazing; coating 5-40% of the heat exchanging area and distribution area of the plates with the braze material so that both the iron-based braze filler and melting point lowering elements are coated on the 5-40% of the heat exchanging area and distribution area of the plates, or coating 5-40% of the heat exchanging area of the plates, wherein the plates are coated with the braze material so that both the iron-based braze filler and melting point lowering elements are coated on the 5-40% of the heat exchanging area of the plates, prior to the joining; arranging the plates in such way that a direct interfacial contact between adjacent elevations and depressions defines a plurality of contact points; creating brazed joints by brazing the plates together at the contact points and wherein the braze material is present in the brazed joints; wherein the contact points include at least one of point shaped contact points and lined formed contact points; and wherein the melting point lowering elements of the braze material have diffused into the iron-based plate material, which changes the melting interval of the material in the brazing joint.