The following Brazing Q & A articles were published in the Welding Journal and are available online.
- August 2013 by Alexander E. Shapiro
Q: We need assistance to design and manufacture a structure for cryogenic work that will be immersed in liquid nitrogen with the upper tubing staying at ambient temperature. The application of low-weight metals is very desirable but the bottom plate or cup should be made from copper as the metal with the best thermal conductivity. The cylinder can be made of aluminum, titanium, or magnesium alloys. As any combination of these metals with copper is not weldable, we have to join the cylinder, the bottom, and tubing by brazing or soldering. But we cannot find any data about the mechanical behavior of brazed joints of dissimilar metals at cryogenic thermal cycling. How should we select a filler metal or solder for this job? What would be the best material combinations to provide reliable work for at least 2000 hours?
A: You are right, the properties of brazed joints subjected to low temperatures are not known for many base metal/filler metal combinations. Some data were published for brazed joints designed for use in nuclear industry applications, but the joining technique is definitely not suitable in your case. Read More
- June 2013 by Tim P. Hirthe
Q: We manufacture an aluminum heat exchanger for an automotive application. It is of a round tube-to-fin design. The open ends of the tubes in the circuit are joined with a U-bend, and are brazed with a flux bearing aluminum-zinc braze alloy. We use a relatively simple fixture with four torches. We have set up to use natural gas and oxygen. The design of the heat exchanger includes a mounting bracket that makes it difficult to heat the entire circumference of one of the braze joints. We are having significant leak issues in the area where accessibility is hindered. Is there equipment available or some technique that will allow us to get a quality braze in this joint?
A: To state the obvious, the best situation would be to not have the bracket in the way in the first place. You mentioned that it is an automotive application, so the odds of removing it from the design are probably quite low. Read More
- April 2013 by Dan Kay
Q: Our brazing shop has been doing nickel brazing in our vacuum furnaces for a number of years. I heard recently that I can use isothermal solidification in some high-temperature brazing processes in order to significantly raise the remelt temperature of a nickel brazement in subsequent service. How is this accomplished?
A: Yes, isothermal solidification can be a very useful brazing process for some brazing filler metals (BFMs), and can result in a significant increase in the re-melt temperature of the BFM in that brazed joint. Read More
- February 2013 by Alexander E. Shapiro
Q: We are very interested in brazing titanium products. My question concerns brazing titanium with steel. Basically, we would like to join titanium Grade 5 plate with stainless steel 304 round bars (1 or 7⁄8 in. in diameter) and require a strength of 40 ksi at the joint. Please suggest a suitable filler metal and a brazing process for us to try.
A: Technically, vacuum brazing of titanium Grade 5 (Ti-6Al-4V alloy) to stainless steel is not a problem. Read More
- December 2012 by Tim P. Hirthe Kay
Q: We are manufacturing refrigeration lines consisting of a variety of copper tubing joints. The joints are primarily copper to copper but we do have some brass valves and steel connections. We employ dozens of hand brazers over several shifts and have a tremendous variation in quality. We are using oxyacetylene torches. It seems that everyone makes the joints their own way. One of the most aggravating issues is that we have a great deal of braze alloy teardrops and spatter. I amsure we are using more braze alloy than is necessary. I have included a photo for your reference – Fig. 1. My preference is to find some other method of making these joints. We are continually told that we need to improve our training but it seems to me to be a training nightmare. There must be equipment we can use to minimize our brazer variation. What can we do to take the manual aspects out of the operation to try to get some consistency?
A: In my experience, manual torch brazing is the most difficult brazing process to get under control. Generally, the process and resultant quality are in the hands of the operator. Read More
- October 2012 by Dan Kay
Q: I am wondering whether there is an industry standard dealing with the shelf life of brazing pastes. I notice that manufacturers of brazing pastes seem to use different statements on their products, some giving a shelf life of up to two years, while others merely specify a date of manufacture. Since I'm working in a critical environment, how can I know when a brazing paste is actually no longer good or out of date if the manufacturer doesn't print an actual shelf life date on their containers?
A: I am not aware of any industry standard that has guidelines dealing with the shelf life or expiration dates of brazing pastes. Read More
- August 2012 by Alexander E. Shapiro
Q: Many times in our repair business, we encounter the problem of brazing steel tubes that have deviations in diameters, so there is no consistency in the size of the joint clearance of the joints to be brazed. Sometimes the tubes match each other and the joint clearance is small, but often they do not match and the joint clearances are extensive, and often the centering of tubes is far from symmetrical. In these cases, we get voids on the side of the wider joint clearance. What can be done to braze wide nonuniform joint clearances properly, without these voids that cause leakages and require rebrazing after testing under pressure? We use torch and induction brazing with BAg-1a for carbon steel tubes and BAg-22 for stainless steel tubes.
A: Successful brazing or soldering requires a capillarity force in the joint clearance between the parts to be joined. Read More
- June 2012 by Tim Hirthe
Q: We are brazing an assembly fabricated from 439 stainless steel and are encountering a severe problem with failure due to corrosion. The parts are showing rust at the fillet edges between the braze alloy and the stainless parts. The braze alloy is BAg-24 and the joints are made using torch heating and a black brazing flux. We had an understanding that by selecting a braze alloy that contains nickel we would not have a problem with corrosion. I have included photos showing the problem and our attempt at a solution using BAg-21 as an alternative. These parts are subjected to moisture in service and the corrosion appears after only a short time in tap water. We also find that the steel rusts on the surface well away from the joint after thoroughly removing the flux. The BAg-21 joints are better but it is a difficult alloy to work with. What is causing this condition and are there any other remedies we can try?
A: Every once in a while a classic brazing problem rears its head and that's what we see here. What you are experiencing is called interfacial corrosion. Read More
- April 2012 by Dan Kay
Q: We are brazing high-temperature alloys together with nickel-based brazing filler metals (AMS 4777), and have had problems with parts failing in service due to cracks right through the brazed joints. The vacuum furnaces we use for brazing appear to be fine, and cross-section evaluation of the failed parts showed that joint clearances were about 0.006 in. (0.15 mm) in the joints before they cracked. Why are these joints failing in service if we're doing our best to keep the parts really clean before and during brazing, and our vacuum brazing cycle appears to be correct according to our customer specification requirements?
A: You are experiencing a problem that many brazing shops face, namely that of correctly dealing with joint-clearance issues during nickel-brazing processes. Read More
- February 2012 by Alexander E. Shapiro
Q: We want to braze a 1/16-in.-diameter tungsten rod into a quartz glass tube about 11/2 in. in diameter. The rod will work as an electrode inside the glass tube. A similar device that we have used for many years looks like it was made using a glass solder. How do we select the correct glass solder? What is the soldering technique that is applicable for use in a university lab? In other words, how can we make a sealed joint between the quartz glass tube and the tungsten rod?
A: Brazing or soldering glass to metals has a long history of applications. Since ancient times, they were used for decoration of glassware, in jewelry, and later, in the manufacture of optical and chemical devices. Read More
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Welding Journal
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