<html><head></head><body><p dir="ltr">Makes sense. When I specify welds on drawings, I presume that the fabricator is not equipment limited. In the lab here at C-FER we have industrial feeds for both 600/347 VAC and 208/120 VAC, and equipment to match. Consumer equipment obviously imposes some constraints.</p>
<p dir="ltr">Sean<br>
</p>
<br><br><div class="gmail_quote">On September 19, 2017 9:56:54 AM MDT, Daniel Lance via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div dir="ltr">Sean,<div>GMAW commonly is utilised in two primary modes , " Short Arc " and " Spray Arc " . "Short Arc" equals lower amperage versus "Spray Arc" equals higher amperage . The amperage output and duty cycle of the welding machine determines what mode you would be capable of achieving . Lower amperage , lower duty cycle power sources will usually only run effectively in the "Short Arc" mode , some units in this class might be able to exhibit SA characteristics but only for a short period of time due to their limited duty cycle ( 10% - 20% ) at the higher amperage range necessary . Duty cycle is usually delineated as how many minutes in a 10 minute window the machine can maintain a rated amperage . "Short Arc" power sources are most commonly found in the consumer to light commercial markets . The primary determining factor being purchase price (a few hundred dollars to maybe a couple of thousand for a multi
purpose unit which could include smaw, gtaw and gmaw capabilities. "Short Arc" is fine for doing sheet metal work , custom car or custom motorcycle work in light gauge metals .</div><div>The use of GMAW in industry would be primarily focused on the " Spray Arc mode " . High amperages , much higher duty cycles ( at the least 60% to the prefered 100% ) , high deposition rates , and very robust weld integrity on thicker metals . Of course all of this comes at a cost . I haven't checked prices lately but the components I purchased to get in the "spray arc " mode cost me somewhere around 6k . This is definitely the low end of the price range in this category of welding , the sky is the limit when it comes to equipping an industrial facility .</div><div>When I build another submarine I will weld the root and the hot pass with GTAW ( TIG) and run the filler and cap passes with FCAW-G ( flux core with a cover gas) also commonly known as " dual shield
" In spray arc mode of course . I have complete confidence in this process . The alternative of course could be GTAW(TIG) root and hot pass and SMAW (stick) weld it out OR if a person has a lot of time on their hands they could GTAW(TIG) weld the joints completely out , root , hot , filler passes and cap .</div><div>To answer your question about which is the biggest concern , embrittlement or porosity . If you are welding with GMAW in the "short arc" mode then embrittlement is the issue . If you are welding with GMAW in the "spray arc " mode then porosity and blow thru on the root pass would probably be a problem unless you did the root and hot pass first with TIG . This is just a cursory overview because Industry has a lot of options at their disposal . Like using the Submerged Arc process with no gap for the root pass and getting 100% penetration running at 600 to 1000 amps . Not something someone can do at home in their garage ! Getting porosity
on the root pass while welding with GTAW ( TIG) on carbon steel is usually not a problem , Of course stainless steel is a completely different animal . Unless you purge with inert gas oxidation and porosity is standard procedure . </div><div>Dan</div><div><br /></div></div><div class="gmail_extra"><br /><div class="gmail_quote">On Tue, Sep 19, 2017 at 8:46 AM, Sean T. Stevenson via Personal_Submersibles <span dir="ltr"><<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>></span> wrote:<br /><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">Dan - I was under the impression that the issue with GMAW (MIG) was the risk of porosity due to ineffective purge (both purging the opposite side of the joint on the root pass, and back purging the puddle while filling), and that it is perfectly acceptable if 100% gas purge is ensured and low hydrogen electrodes are used? The
process is used in lots of pressure vessel manufacturing, but perhaps the pros have better control over this? </p>
<p dir="ltr">I like the idea of a GTAW (TIG) root pass. Doing the filling passes with SMAW (stick) seems tedious, particularly if there is a lot of filling to be done, but your message is making me think twice. Is the major problem the embrittlement, or the porosity?</p>
<p dir="ltr">Sean<br />
</p>
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