Analytical systems are assembled using many types of joints ranging from compression fittings, VCR, VCO, up to KF and conflat flanges. In order to make a system inert and to assure a consistent and thorough coating throughout the system, we ask customers to send in parts disassembled.
SilcoTek will then coat the individual components and then ship the parts back to the customer for assembly into an inert high performance analytical system. But often individual components are assembled with brazed or soldered joints. Can SilcoTek make a brazed or soldered joint inert or corrosion resistant? And is one joint better than another in regards to coating quality and analytical performance?
The short answer to "can we make a a solder or brazed joint inert or corrosion resistant" is a qualified yes. OK I'll stop dancing around the issue and give you the longer version of what type joint is coatable.
Some Background About Brazing And Soldering
There are three main concerns when considering whether a brazed or soldered joint is coatable:
It's always best to consult with the customer to communicate what we know, & what we don’t know about potential coating issues, and to establish proper customer expectations before coating parts.
Brazing and soldering are typically defined by the melting temperature of the filler material:
One common misnomer, however, is “silver soldering”. Typically, silver soldering is actually a silver braze process and should withstand temperatures of 450°C.
Brazing: An excellent primer on brazing can be found in the Oerlikon Brazing Guide. Brazing is a joining process where metals are bonded together using a filler metal with a lower melting point than the base material. Heat, via torch or furnace, is used to liquefy and allow the flow of filler metal (via capillary action), which then cools, solidifies, and joins the base material. Additional materials, such as flux, may be used to prevent the accumulation of oxides and other undesirable contaminants in the filler metal.*
The following materials may be present in filler metal. Formulation is highly variable and unique between most suppliers:
Possible Base Materials: Nickel, Cobalt, Silver, Gold, Aluminum, Copper
Possible Alloying Materials: Nickel, Cobalt, Manganese, Boron, Silicon, Iron, Chromium, Tungsten, Aluminum, Copper, Molybdenum, Carbon, Titanium, Niobium, Germanium, and Rare Earth elements such an Lanthanum, Yttrium, etc.
The presence of some of these materials in higher concentration may pose a reason for concern. For example, we know that high levels of copper can cause contamination issues with our processing systems and affect the inertness of the coating, particularly SN2000.
Soldering: The soldering process has similarities to brazing but is generally a less challenging process. Solder filler material may have some of the same materials as found in braze materials, such as silver and copper, but it is also alloyed with metals such as tin, bismuth, indium, zinc, antimony, gold, lead and manganese to yield lower melting points (lead is being phased out but is still available). **
Recommendations for Braze Joints:
Recommendations for Solder Joints:
With a proper joint, the entire analytical flowpath can be successfully coated. The result? More consistent test results, less analytical time and improved profits!
Want more tips on how to improve analytical sampling, processes and products? Get 7 great tips on how to improve anaytical sampling.
*Image courtesy of http://www.free-ed.net.
** Image courtesy of http://canada.newark.com/solder-and-soldering-guide