Gantry Base Plates

[WoodyBurn]

Hi all,
I'm having difficulty with welding a circular base plate onto a circular column for a gantry leg.

Circular column is approx 508mmø and base plate is about 50mm thick.

Gussets welded around top of the base plate.

Due to the amount of welding on 1 side, the base plate is becoming deformed and basically starting to "dome".

I am trying to find a suitable method of stopping this happening as sometimes 2 plates have to be positioned back to back and they wont sit flat against each other.

Thanks Woody

 

[Ron]

What is the weld profile? How is it being put in (number of passes, size of each pass, any pre-heat/post-heat treatment, any pass grinding)?

Also, does the circular baseplate have a hole in its center, and if so, how large?

Is the assembly restrained during welding?

When is the deformation noticed...during or after welding?

 

[WoodyBurn]

Thanks, it's welded using Mig Process, no preheat used.
There is a hole approx 150mmø in the centre but this is to allow service cables to run up through a pipe welded into this hole. Deformation noticed during and after welding. Workshop foreman has tried restraining with "strongback" flat bars but bot making any difference.
Only suggestion we have at the minute is to machine the plates with a milling machine but this in turn will reduce their thickness and weaken the plate.
Have tried heating the back of the weld but no real difference achieved.

 

[Ron]

Try using a process that puts less heat into the assembly. Increase the number of passes and decrease the size of each pass (smaller electrode, less current, etc), using SMAW instead of GMAW. You might also consider welding the section in quadrants, alternating to opposite quadrants with each couple of passes.

With the thicknesses involved, why is there no pre/post heat?

 

[WoodyBurn]

Can't imagine preheat helping, all welds get tested and usually no issues with the welding, therefore no need to pre-heat. Thanks

 

[metengr]

Three suggestions come to mind;

1. Apply a general preheat of 200 deg F to the base plate to reduce thermal gradients. The preheat would also be required by most Codes to avoid problems with the weld heat affected zone in the base plate and to reduce distortion by slowing the rate of cooling.

2. Use a solid strong back plate not bars and fillet weld completely around the base plate. When welding is completed cut the strong back plate loose.

3. Agree with welding in quadrants.

 

[WoodyBurn]

thanks, had thought about welding similar temporary piece of tube of the same diameter before welding the actual part and then removing after. Might give that a go.