Can anyone help me on this?
I have structure where blocks, approx 6" lg x 4" high x 4" thick, are welded to . Currently a 3/4" fillet weld runs continually around the base of these blocks. These blocks are prone to shock loading in use and we have experienced fatigue cracks and in some places complete weld failure resulting in loss of some blocks. To address this we have been able to incorporate shear blocks in the design and in some cases weld blocks to each other to distribute the load over a wider area. My question ( eventually! ): would a 3/4" x 45degree weld prep around the base of the blocks be stronger than the 3/4" fillet weld?
Thanks.
The short answer is, YES, it would be stronger, but the 45 degree weld prep may not be enough. I'm not an engineer, but it may also get into design issues with the amount of force, etc., and you may even want to consider a higher tensile strength weld metal. If you provide your material grades, welding process, and electrode information, there's many welding professionals in the Forum, and someone should be able to help you.
Just a thought. Do you preheat your material before welding?
My question would be - what loads are imposed on these blocks? You can't properly size the weld or the blocks without determining the loads. A 3/4" deep groove with at 3/4" reinforcing fillet would definitely carry more load than the 3/4" fillet, but who knows how much is needed.
PNM,
You haven't gone into details regarding the application (which is fine with me...) but if nothing else, blocks as big as that are dangerous as projectiles. Assuming your weld process is in control and you are following your WPS then you should hire a Structural Professional Engineer to analyze and redesign if needed. If you already are that PE and you understand the loading conditions then hire a Welding Engineer to evaluate the weld process.
Good Luck,
By PNM
Date 11-14-2005 09:01
Thanks for the responses.
To add a little more info, the structure is an underground cutting auger, 58" dia x 12' wide rotating at 45rpm,cutting through potash and salt but with intrusions of boracite(?) which is 'uncuttable'. The blocks I mention are holders which carry the cutting picks. The forces can vary on these cutting picks, as cutting condition change and the carbide wears on the cutting tip - in theory one pick could take the full load of the 140ton, 400kw machine. This is usually the case where the cutting pick shears, not the holder, or the weld attaching the holder to the main body.
We have had welding engineers address similar problems before and after calculating the maximum forces acting on the unit (smaller than in this case) arrived with a fillet weld of 2" - totally impractical.
The answer is to ensure the shear strength of the replaceable cutting picks is stronger than the structure and the weld of the pick holder. I naively thought that by applying a fillet weld would ensure a longer length of weld than an inset prepped weld and also the fillet would act as a 'gusset' support. I do understand that a fillet covering the prep would be stronger, but we are trying to keep costs to a min.
Thanks for all your answers.
