This just might be the question we receive most at Prince & Izant. When a customer receives a material lot with a slightly different color cast or tint from what they typically see, they often begin to question whether the material does, in fact, meet the required specification. The fact is, as long as the provided Certificate of Chemistry certifies the alloy to be within specification, these variations in color alone should cause no concern. There are many factors which may alter the physical appearance of a filler metal, while having absolutely no affect on its functionality or suitability to purpose. Just to list a few of the numerous things that we encounter - some quite frequently - which factor into an alloy's coloration and appearance: Annealing & Heat Treating. Mills often subject their alloy to an annealing or heat treating process as a normal course of events during the processing of an alloy lot. Quite often, this effects a minor color change to the alloy. Even minute variations in heat, length of cycle time, etc., can result in a visual difference in the color cast of various lots of alloy. Wire Drawing. The process of drawing wire from a larger diameter to a smaller one involves a lot of friction - and therefore, heat. Drawing the wire faster creates more friction and heat; slow down the process, less heat is generated. It's even quite possible to see a sudden color change right in the middle of a continuous coil of wire, if the drawing speed is slightly changed mid-run! Strip Slitting. This process is to strip-form alloy what drawing is to wire; you slit a wider width down to the size you need. Color differences can often be seen, especially in Trimet alloys, when looking at the slit edges of the strip. The original edges may display a slightly different hue from the freshly-slit edges. Variations in Composition. Some alloys are more color-sensitive to small variations in their elemental chemistry than others. A lot whose silver content runs just within the upper limit of the specification, for example, may seem to have a brighter finish than a lot whose silver content is closer to the lower limit. Cleaning Processes. Processes such as ultrasonic cleaning or bright-dip can have a significant effect on the surface finish and visual appearance of an alloy. If you weren't aware that a single lot of alloy had been split in half, with one half being ultrasonically cleaned and the other untouched, you may never guess by appearance alone that the two coils in front of you originated from the same lot. None of these factors will have any significant effect on the performance or usability of the alloy, only the appearance and tint. Minor color variations can be safely ignored if the Certifications demonstrate the alloy to test within specification.

The detection of trace elements in alloys is an inconsistent science, at best. When attempting to measure the impurities in an alloy where the content is measured in parts per million (ppm), it must always be remembered that one ppm is equivalent to .000001%, a very small percentage indeed. Expecting consistent repeatability of test results for trace elements is largely unrealistic using most commonly-accepted test methods. Advanced testing methods can produce better repeatability and more reliable results, but the time and expense involved makes this unfeasible in most cases. It is not uncommon that multiple tests on the same sample show some variances in the primary elements contained within the alloy; it is virtually guaranteed that, using standard methods, repeated tests will show what would appear at first glance to be large variations in trace elements! Even variations of 50 ppm (or more) are quite common – keep in mind that number represents only .00005% of the total composition. Always remember to expect some variations in trace elements in test results, and don’t give too much weight to what might appear at first glance to be inconsistent test results for an alloy sample. If a higher level of certainty is required on a particular element, it is always advisable to perform a specific test for the critical trace element in question. Take carbon as an example. If carbon cannot exceed a certain percentage in trace, the parameters for the test can be set accordingly to provide a more reliable result for that element. It also bears mentioning that it is not uncommon for the sum of elements in an alloy to add up to slightly less, or more, than 100%. That is due to the rounding up of percentages, in addition to the margin for error in test results.

The wire diameter and tolerance that the ring is to be manufactured from should be clearly stated. When calling out the ID / OD requirements, there are two acceptable methods: Either specify the required size range (i.e., ".245/.255 ID")... OR Specify a gap range as measured on a specific gage size (i.e., ".000-.015 gap when measured on a .245" plug gage"). This basically allows you to use either the ring diameter, or the gap size, as your tolerance when calculating alloy volume. We often see part drawings with both types of tolerance called out, which often results in either excessive or insufficient alloy volumes in a braze ring that technically meets the dimensional specification.

It all depends. No manufacturer lists the tensile strength of their brazing alloys. This is not to make life difficult for the ultimate consumer, it's because people tend to place too much emphasis on any number that might be published. Design engineers sometimes base designs on a number that's not appropriate for the ultimate use. In fact, the strength of a brazed joint depends more on the design and the brazing procedure then on the filler metal used. Furthermore, tensile strength numbers apply to material in the wrought state. When the filler metal is used in brazing, it is effectively recast. Recast metal has different properties from the wrought metal. Empirical testing of various brazed joints has shown that the PSI of the alloy does not correlate directly to the strength of the tested joint. We know some of the factors that influence this process. For example, if the alloy is overheated, the lower melting elements are burned off to a higher degree. This effectively changes the composition of the deposited metal. Thus, our advice is to encourage customers to do their own testing of the brazed joint. But there are some rules of thumb. If customers insist on a certain PSI number, we suggest a number ranging from 60,000-70,000 PSI when tested in the wrought state. Another rough guideline is that joints properly brazed with silver alloys have a shear strength that exceeds three times the shear strength of the thinner, joined metal.

Brazing has been defined as a group of joining processes specially arranged in a manner to produce coalescence of materials. The process involves heating of these materials at a brazing temperature by using a filler metal which has a liquidus above 840°F (450°C), and below the solidus of the base metals. Also, the filler metal is distributed in the joint by capillary action. In the case of soldering, the only fact which distinguishes it from brazing is the filler metal used, since, here the liquidus is below 840°F (450°C). Welding involves the process of fusion which takes place along with the melting of base metal and a filler metal.