The flux-coated solder rod 10 is shown in FIG. 1 as having a core formed by a rod 12 of a suitable solder alloy, onto which a flux-containing material is applied so as to form a flux coating 14 that covers the entire circumferential surface of the rod 12. More specifically, the flux coating 14 is deposited on the rod 12 such that the coating 14 provides a continuous thermal-insulating barrier around the rod 12. According to this invention, the composition and thickness of the flux coating 14 must be sufficient to insulate the rod 12 during heating, such that the rod 12 does not melt until after the flux coating 14 has melted, at which time the rod 12 melts substantially simultaneously with the coating 14 or immediately thereafter. While the prior art relied on the use of flux compounds having melting temperatures lower than that of the alloys with which they were used in order to dislocate aluminum oxide on a surface prior to application of the molten alloy, investigations leading to the present invention unexpectedly showed that the near simultaneous melting of the solder alloy rod 12 and the flux coating 14 provided a sufficient cleansing action by the flux compound of the flux coating 14. Furthermore, and as is apparent from FIG. 1, the soldering rod 10 can be readily formed to contain predetermined amounts of flux compound and solder alloy that can be readily placed at a region to be repaired, thereby providing the solder alloy required to form the repair as well as the flux compound required to enhance the solderability of the region being repaired.
An improved method is provided for repairing aluminum alloy articles and structures, such as automotive heat exchangers including condensers used in automobile air conditioning systems. The method of the present invention is a soldering or low-temperature brazing operation that utilizes a soldering rod coated with a hard thermally-insulating flux coating. Importantly, the flux coating contains a flux compound having a higher melting temperature than the alloy of the soldering rod, and is present in a sufficient amount to maintain a thermal-insulating barrier around the rod until the flux compound melts, after which both the flux compound and alloy melt either simultaneously or in rapid succession. The relative amounts of flux compound and solder alloy present within the soldering rod are also at levels that ensure adequate dislocation of aluminum oxides on the repair surface for the amount of solder alloy being delivered with the flux compound to the surface.
In this soldering process, heat is applied to the parts to be joined, causing the solder to melt and to bond to the workpieces in an alloying process called . In stranded wire, the solder is drawn up into the wire by in a process called 'wicking'. Capillary action also takes place when the workpieces are very close together or touching. The joint's is dependent on the filler metal used. Soldering produces electrically-conductive, water- and gas-tight joints.
The above and other advantages of this invention will become more apparent from the following description taken in conjunction with the accompanying drawing, which shows a cross-sectional view of a flux-coated soldering rod in accordance with this invention.