[PSUBS-MAILIST] Heads Question

Tue Sep 19 13:57:05 EDT 2017

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.

Sean

On September 19, 2017 9:56:54 AM MDT, Daniel Lance via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Sean,
>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 .
>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 .
>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 .
>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 .
>Dan
>
>
>On Tue, Sep 19, 2017 at 8:46 AM, Sean T. Stevenson via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>> 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?
>>
>> 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?
>>
>> Sean
>>
>> _______________________________________________
>> Personal_Submersibles mailing list
>> Personal_Submersibles at psubs.org
>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>
>>
>
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20170919/607e234f/attachment.html>