METHODS FOR INSTALLING BRAZETYTE FITTINGS
|The most effective means for making a stainless to stainless connection is by either|
soldering, brazing, welding, and epoxy. Such joints are strong, leak-tight, corrosion
resistant, economical and have a good appearance. BRAZETYTE tube fittings are
designed to provide for these assembly methods.
Soldered or brazed joints resist most corrosive media. The very nature of the process leaves only a small seam exposed to atmosphere. It is important to choose the proper solder or brazing alloy and this is usually determined by the application and environment of the assembly being fabricated. Certain alloys are formulated with precious metals which give them corrosive resistance equal to stainless steel itself. Soldered or brazed stainless steel connections are extremely strong in both tensile and shear strength. This high strength characteristic is based on the ability of molten brazing alloy to penetrate and fill the gap between bonding areas through "capillary action."CHOOSE THE PROPER ALLOY AND FLUX
The choice of a solder or a brazing alloy for stainless steel depends, of course, on the ultimate use of the installation. Ordinary "Soft Solders" may be satisfactory for use with stainless steel providing adequate cleaning is employed and the proper flux is used. Where extreme conditions exist involving corrosive media, high pressure, vibration and high or low temperature ranges which are not within the limits specified, a brazing expert should be consulted.
The extremely high corrosion resistance of stainless steel depends upon its naturally occurring oxide film which re-forms immediately when damaged by abrasion. To remove it by chemical means demands an aggressive flux which inevitably must be highly corrosive at the moment when the solder is required to wet the steel to make the joint.
Two Fluxes are commonly used for industrial soldering and brazing. Many companies produce these materials and have various trade names and/or nomenclature for their products. The American Welding Society designates them as follows:
1. AWS TYPE 3A FLUX-This Flux is used for low temperature silver brazing, (1050°F to 1600°F). it contains Boric Acid, Borates, Fluorides, Fluoroborates, and a wetting agent.
2. AWS TYPE 3B FLUX-This Flux is used in applications where high temperature silver brazing is required, (1350°F to 2100°F). The ingredients of this Flux are basically the same as the 3A type material except the formula is proportioned differently to accommodate high temperature.
The above fluxs enable joints to be made quickly and easily. The residues left after the joint is made, however, may continue to be highly aggressive towards stainless steel and involve some hazard of Flux corrosion. It is therefore necessary to remove all traces.of Flux from the outside of the tube as soon as possible and to flush through the system with water without undue delay. This may be accomplished by bushing with hot water or a boiling five percent caustic soda solution .
Where silver soldered joints are required, careful joint preparation is essential and the parts should be cleaned with a file or rough emery paper. Selection of the correct grade of silver solder is important when joining stainless steels and it is recommended that the alloy manufacturers be consulted.
The technique of applying the Flux and the Silver Solder is similar to that used for making joints in copper or copper alloys. A little care is necessary, however, in controlling the heat source to ensure that the temperature does not exceed that required to melt the Silver Solder and make it flow freely; otherwise a heat resistant black oxide film is formed anti the solder will not adhere to the metal. We recommend that the tube, or male portion of the joint, be brought up to a temperature where the alloy begins to flow and then the torch be moved to the female portion of the joint (The BRAZETYTE~ Socket), allowing "Capillary Action" to draw the alloy into the joint. It is also suggested that the brazing alloy be end-ted, as shown in the above photo .
The other means of making a permanent joint with BRAZETYTE fittings is by welding. Depending upon the configuration chosen, connections may be made by either of two basic methods, Butt or Lap welding. The technique chosen will be governed by the actual tubing application, the welding equipment available and the skill of the welding operator.
BRAZETYTE fittings can also be assembled using epoxy adhesives. Epoxy provides a permanent joint for low pressure assemblies and is an easy, inexpensive method to accomplish a connection. A joint may be made quickly, using unskilled labor and simple techniques. There are many types of commercial and industrial epoxy adhesives on the market. These usually are offered as two component kits, one part being the catalyst which activates the curing of the material. Curing methods of these epoxy adhesive materials vary. Some cure at room temperature and in other cases curing is accelerated by the application of heat. Properly prepared and fully cured, bonds are possible that will yield tensile shear strengths of up to 3,500 psi when tested at room temperature. Epoxy adhesive is not recommended for systems where temperatures exceed 200CF or for use with certain chemicals which might tend to attack the epoxy joint. The manufacturer usually supplies this type of information in the form of a chemical corrosion resistance table.