Stress relief / Bronze castings

[emma55]

Well I have a stack of Slic. Bronze parts fresh from the foundry , What are the concepts of stress relief?

[the_gr8t_waldo]

i'm an home hobbist and not an expert but......when casting metals stresses are created when the various elements of the casting,welding quickly cool. some of these stresses are relived as well, during the cooling. never tottally gone though. the usual fix is to place the casting/weldment into an oven and reheat to a temp. just below the melting point, an over a long period of time, slowly decressing the temp. allowing most of the stresses to work themselves out of the casting, untill room temps are reached. how long and what temps to use, depends on the metal. i'm sure that there's probably some that don't even respond to this

[paulf]

Hi Emma,
I would contact the foundry and find out if they stress relive all their work, they might.
Depending on the size of the castings, this might require a sizable furnace.
@500 deg for 1hour for each 1" of material thickness.

The concept is to allow the metal to cool slowly from near critical temp allowing the recrystalization to sort it's self out in the most anealed condition.
This however may not be what tha part was designed for.
If the foundey knows what they are doing you should get the castings in working condition needing only cosmetic brushing and slight sanading.

I'll bet if you called the foundry forman he/she could really bend your ear about whats hapening at a molecular level. Bring a beer if they allow such things and then you could fill all of us in!!
http://www.eriebronze.com/uploads/me...tasheet-16.pdf

[emma55]

Maybe I missed spoke , What I mean is in the file work along the edge of a casting

[wizbang 13]

I thought you were relieved to have your new jewelry!

[emma55]

I thought you were relieved to have your new jewelry!

Nice

[emma55]

I thought you were relieved to have your new jewelry!

Well in all truth it is not all for me , First for Emma and then for the next Gen.

[paulf]

making us jump through the hoops??...

[emma55]

making us jump through the hoops??...

At least we are jumping .

[paulf]

Ya got a point there.

[Gold Rock]

Maybe I missed spoke , What I mean is in the file work along the edge of a casting

Are you talking about the flash or extra metal left on the rough castings along the parting line? If so, the technique varies depending on the amount of metal to be removed. Large amounts in areas that allow sufficient work room are dealt with using an angle grinder and a hard abrasive wheel. For lesser amounts also in sufficiently accessable areas you can change the hard abrasive disc to a sanding disc or flap wheel. 60 grit offers a good compromise between aggressive removal and an acceptable finish. For tighter areas, a die grinder and burr are a good tool. If the shape of the part allows, you can get excellent control using a bench mounted, or free standing disc sander with an attached work platform. Hand files are of course always useful. If you're using hand held power tools take care to exert control. They can get away from you quickly and mar the work.

[emma55]

Are you talking about the flash or extra metal left on the rough castings along the parting line? If so, the technique varies depending on the amount of metal to be removed. Large amounts in areas that allow sufficient work room are dealt with using an angle grinder and a hard abrasive wheel. For lesser amounts also in sufficiently accessable areas you can change the hard abrasive disc to a sanding disc or flap wheel. 60 grit offers a good compromise between aggressive removal and an acceptable finish. For tighter areas, a die grinder and burr are a good tool. If the shape of the part allows, you can get excellent control using a bench mounted, or free standing disc sander with an attached work platform. Hand files are of course always useful. If you're using hand held power tools take care to exert control. They can get away from you quickly and mar the work.

Thank you that helps big time CW

[Thad Van Gilder]

I remove the flash from my casting with a flap sander. about 80 grit. i usually finish
with a random orbital, but i recently heard of a local non ferrous foundry cleaning up castings with a sand blaster.

i may try that...

-Thad

[emma55]

I remove the flash from my casting with a flap sander. about 80 grit. i usually finish
with a random orbital, but i recently heard of a local non ferrous foundry cleaning up castings with a sand blaster.

i may try that...

-Thad

my next door mate [ A real metal worker } Had just told me about a sandblaster . Sets me thinking

[Gold Rock]

I remove the flash from my casting with a flap sander. about 80 grit. i usually finish
with a random orbital, but i recently heard of a local non ferrous foundry cleaning up castings with a sand blaster.

i may try that...

-Thad

Most castings produced in the sand cast method are sandblasted prior to cut off, but sand blasting won't do much for you in terms of cleaning up the parting lines or gate or riser connections. Sand blasting is indiscriminate and wears down everything over a relatively large area. If you try to blast off a bump you just wear down the bump but also all of the area surrounding the bump. The traditional steps to produce a finshed (albeit unmachined) sand casting are: 1) pouring which is self explanitory, 2) breakout, this is the destruction of the mold to separate the raw casting, 3) sand blasting or media tumbling depending on the operation, this removes all traces of mold sand, scale, and mold residue, 4) cutoff, this is the separation of the cast part from the gating/risering/venting system, 5) grinding, this is the stage at which much happens - vestiges of gates, risers, and vents are ground off to varying degrees of finish depending on the machining requirement, excess material may be removed that was added for molding purposes, parting flash is ground off, again to varying degrees of finish depending on machining requirements, and much more, and if no further machine work is required the final step in a proper foundry would be, 6) media tumbling, this is a process where the casting is placed in what amounts to a giant rock tumbler (if you remember those from your childhood). It evens out, removes, and/or blends together left over grinding marks, machined surfaces, and small surface irregularities and imperfections. So for your parting line removal stick to the grinding, sanding, buffing wheel techniques. If you apply these simple techniques carefully and thoughtfully you will get the results you desire.

[emma55]

Most castings produced in the sand cast method are sandblasted prior to cut off, but sand blasting won't do much for you in terms of cleaning up the parting lines or gate or riser connections. Sand blasting is indiscriminate and wears down everything over a relatively large area. If you try to blast off a bump you just wear down the bump but also all of the area surrounding the bump. The traditional steps to produce a finshed (albeit unmachined) sand casting are: 1) pouring which is self explanitory, 2) breakout, this is the destruction of the mold to separate the raw casting, 3) sand blasting or media tumbling depending on the operation, this removes all traces of mold sand, scale, and mold residue, 4) cutoff, this is the separation of the cast part from the gating/risering/venting system, 5) grinding, this is the stage at which much happens - vestiges of gates, risers, and vents are ground off to varying degrees of finish depending on the machining requirement, excess material may be removed that was added for molding purposes, parting flash is ground off, again to varying degrees of finish depending on machining requirements, and much more, and if no further machine work is required the final step in a proper foundry would be, 6) media tumbling, this is a process where the casting is placed in what amounts to a giant rock tumbler (if you remember those from your childhood). It evens out, removes, and/or blends together left over grinding marks, machined surfaces, and small surface irregularities and imperfections. So for your parting line removal stick to the grinding, sanding, buffing wheel techniques. If you apply these simple techniques carefully and thoughtfully you will get the results you desire.

Thank you Chuck The tumbler sounds like the way to go . I will look into that CW

[rregge]

Residual stresses build up in casting due to:


During solidification the thin parts of the casting typically solidify before the heavier sections...During solidification the material experiences expansion or contraction due to solidification and phase transformation in the material. The parts that are solidified first are stressed as the rest of the casting solidiffies and expands-contracts.

The objective of stees relief is to remove the residual stresses through heating to allow the atoms to rearange themselves.

Russell

[Gold Rock]

Residual stresses build up in casting due to:


During solidification the thin parts of the casting typically solidify before the heavier sections...During solidification the material experiences expansion or contraction due to solidification and phase transformation in the material. The parts that are solidified first are stressed as the rest of the casting solidiffies and expands-contracts.

The objective of stees relief is to remove the residual stresses through heating to allow the atoms to rearange themselves.

Russell

True. These kinds of stresses however only manifest themselves if the part is subjected to sufficient loads or conditions. For instance an exhaust manifold may not have a large amount of post cast finish machining but the thermal stress it will be subjected to in use may be enough to induce distortion due to stress realease. Alternatively, a part that is subjected to large amounts of post cast machining may experience distortion due to stress release. Most bronze, brass, or aluminum marine castings though, are of relatively simple shape and are rarely subjected to the kinds of conditions that would induce stress release distortion.