Abstract:
Fittings made of copper, brass, red brass or steel are provided with an inside coating of a flux and a solder layer. By this technique, the soldering process is simplified, damages caused by overheating of the flux are avoided and the amount of the solder used is reduced.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to fittings used for brazing and soldering of tubes. 
     Various techniques for brazing and soldering tubes are conventional and known. In one such technique, the tubes are first cut square and the burr is removed. Pipe ends are mechanically cleaned until the oxides are removed, and then a flux paste is applied with a small brush or a clean cloth. The parts are pushed into the fitting and the surplus paste should be wiped off. The joint is then heated. As soon as the soldering temperature is reached, additional solder is added by hand until the capillary space is filled. 
     Usually, the plumber cuts the tubes, assembles the pipe with the fittings and attaches the system to a wall until the entire network of pipes is complete. Before soldering, the pipes must be removed and put into pieces in order to enable the addition of the flux. 
     The fluxes are corrosive, therefore, they should not come into direct contact with the human body. 
     To prevent the fluxes from fast settling and to adjust the viscosity of the fluxes, organic substances are added. However, the use of these organic additives during the soldering process has many disadvantages. The additives burn, have a disagreeable odor, produce carbon black, and cause pores in the soldering seam. These disadvantages are especially evident when the solders ar overheated. It is very difficult for even an experienced plumber to determine when the proper soldering temperature is reached. 
     An improvement can be realized if a solder powder is added to the flux. By watching the flux carefully during the heating process, the user can realize when the solder powder melts. That gives him an indication that the optimal soldering temperature is close. The amount of solder powder present in such pastes is too small to completely fill the capillary space; therefore, it is necessary for the user to feed additional solder by hand. Penetration of the solder around the joint must be visually observed, and a fillet should form between the pipe and the fitting. 
     Flux residues are corrosive. They must be completely removed by rinsing the tubes with water. Fluxes with organic additives have created a great corrosion problem. Organic components which were not completely soluble in water, incorporated halogen containing flux residues. These covered flux residues have caused severe pitting corrosion in the copper tubes. 
     When adding solder by hand, it is not possible to exactly measure the amount added. Normally, the operator uses much surplus solder, which ca then penetrate into the tube and block it. 
     If the tubes are laid into a wall, it is not possible to add the solder from the back. It is this situation which is often the reason for an incomplete filling of the capillary space. This results in leaky fittings. 
     SUMMARY OF THE INVENTION 
     It is one objective of this invention to develop fittings for brazing and soldering metal tubes which require less handling by the user. 
     It is another objective of this invention to provide fittings wherein the optimal amount of flux and solder or braze are included. 
     It is another object of the invention to provide a process suitable for mass production of the fittings for brazing and soldering tubes. 
     The invention includes providing a coating of a thin flux layer on the inside walls of a fitting. Inside the flux layer, a thin braze or solder layer (braze or solder cylinder) is provided, which is preferably connected with a braze or solder deposit (braze or solder ring). It is preferred that the braze or solder cylinder and the braze or solder ring are formed into a single, unitary construction, i.e. a single piece. 
     Production of the fittings in accordance with this invention can be accomplished in the following manner. A ring of solder is formed into a thin walled cylinder. The outer diameter of this cylinder is somewhat small than the inner diameter of the fitting. The cylinder is coated on its outside with a flux. The flux-coated solder cylinder is then placed into the fitting and pressed against the fitting wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantageous aspects of this invention will be more fully appreciated from the following detailed description, and further in view of the appended drawings, wherein: 
     FIG. 1 shows the solder cylinder and thin flux layer used in accordance with the invention; 
     FIG. 2 shows the solder cylinder inserted into a fitting; 
     FIG. 3 shows two pipes connected within a fitting prior to heating the joint; and 
     FIG. 4 shows the joint after the soldering process is complete. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The process in accordance with this invention will be described in detail below, in conjunction with the Figures. 
     Starting with a solder ring, the final preform can be produced in a one step process by a conventional compressive forming process. The shape of the final solder preform can be described as a ring of solder with an attached thin cylinder of solder which is 1-2 cm high and 20-50 micrometer thick. A thin flux coating is applied to the solder preform. This flux coating may be applied to the solder cylinder by standard coating techniques known to those skilled in the art. The flux is preferably mixed with a solvent, such as methanol or ethylene glycol, and then coated onto the outer surface on the cylinder. The flux coated solder preform is dried until the solvent from the flux is completely evaporated, or it may even be heated to the melting point of the flux. The flux coated preform is then placed inside the fitting and pressed against the wall of the fitting with a special precision tool. Optionally, prior to pressing the flux coated cylinder against the fitting body with the precision tool, an additional deposit of solder or braze may be coated over the flux layer. Such precision tools are commercially available under the brand name Rotherberger. The tool is conventionally used by plumbers to expand the ends of copper tubing to a larger diameter. The tool comes with a set of changeable heads to facilitate different diameter tubes. 
     FIGS. 1-4 show longitudinal sections of a flux coated solder preform and an example of the assembly before and after the soldering process. 
     As shown in FIG. 1, the ring of solder (1) is preferably connected to a thin cylinder of the same solder (2). This cylinder of solder (2) is coated with a thin layer of flux (3). Two of these flux coated preforms are put into a fitting (4) with the solder ring (1) end placed into the fitting (4). This is shown in FIG. 2. A precision compression tool, as described above, is used to press the preform against the wall of the fitting (4). 
     FIG. 3 shows two tubes o pipes (5) pushed into the fitting (4). In the preferred embodiments of this invention, the fittings are made from copper, brass, red brass or steel. It is possible to push the tubes (5) into the fitting (4) because the ductile solder preform is pressed onto the fitting wall with the precision tool. 
     In FIG. 4 the soldered joint is shown. During heating, the solder becomes molten and due to capillary action, it is sucked into the capillary space, thereby forming a fillet (6) between the pipe or tube (5) and fitting (4). 
     All dimensions and shapes mentioned in this specification are included for purposes of illustrating the invention, and should not be construed as limiting the invention. Various modifications in size and shape may be made without departing from the invention. The following is a list of dimensions corresponding to a preferred embodiment of the invention for purposes of illustration: 
     
         ______________________________________a)  inside diameter of the solder cylinder 2                       14.6      mm;b)  thickness of the walls of the solder                       0.03-0.04 mm;    cylinder 2c)  height of the solder cylinder 2                       12.5      mm;d)  inside diameter of the fitting 4                       15        mm;e)  thickness of the walls of fitting 4                       1         mm;f)  overall length of the fitting 4                       24        mm;g)  inside diameter of solder ring 1                       9.5       mm;h)  outside of diameter of solder ring 1                       14.63     mm;i)  overall thickness of the solder ring 1                       0.8       mmj)  thickness of the flux coating 3                       0.01      mm;k)  distance between flux coating and fitting                       0.2-0.3   mm;    before compressionl)  outside diameter of pipe 5 to be                       15        mm.    inserted into the fitting______________________________________ 
    
     The fittings in accordance with this invention have many advantages, including the following advantages. No personal handling of the corrosive and environmentally harmful fluxes or pastes by the user is required. Pitting corrosion and hygiene problems can be avoided. Overheating or cold soldered joints are not a problem because the proper amount of flux and solder is optimally positioned at the joint. 
     This invention may be used with various solder compositions, flux compositions, and types of pipe and fitting materials. The following examples of various particular embodiments of these materials are given to illustrate the invention and should not be construed as limiting the same. 
     For copper piping in cold and warm water plumbing, a preferred solder contains 97 wt% Sn and 3 wt% Cu, or 96 wt% Sn and 4 wt% Ag. As a flux, a mixture of 85 wt% ZnCl 2  and 15 wt% NH 4  Cl, or 82 wt% SnCl 2  and 18 wt% NH 4  Cl 2  can be used. ZnCl 2  is hygroscopic, therefore, if the fittings are to be stored for a long period of time, it is better to use the SnCl 2  containing flux. 
     For cooper and steel tubes, a preferred braze contains 45 wt% Ag, 27 wt% Cu, 3 wt% Sn and 25 wt% Zn, and the fluxes which could advantageously be used are specified in the German standard DIN 8511 in class F-SHl. 
     The optimal amount of solder or flux depends on the size of the fittings. It is believed that the determination of these optimal amounts is a matter of routine experimentation, well within the level of ordinary skill in the art.