Cast Turrets and hulls...

Gryle some thoughts
I had a look at the pic. but I still tend to think it would be oil smoke, not steam.
Temper brittleness as they call it ( a term I had forgotten) is often caused by water temper, that is why they go to oil, as it is not as aggressive.
Comet fan;
Some body is dreaming if they think they can wait 12 months for a casting to cool.
There is, however a "weathering" process that casting used to to go through.
This did involve burying the castings in the ground for about a year (car engine castings used to be treated this way)
This was to allow a slow, natural stress relieving. Now days, and, I would imagine in ww2 due to production requirements, a heat treatment process is used. I cannot remember the temperatures involved, but it was basically heat up the casting to ?? and allow it to slowly cool, generally in the furnace. It can then be processed in the usual fashion.
As a matter of interest, the time taken to heat up steel things is usually rated at 1 inch (25.4 mm) per hour of heating. I guess atmospheric cooling rate would be about the same.
So for a 12" casting, heat up time would onlu be 6 hours. I cannot see a cooling time of a year?? :roll:
Hopefully I have added more mud to the clarity of the subject, guys. :kill:

 

Heating time can't be equalled to cooling time, since it's two completely different processes. One year sounds too long, but six hours will not be sufficient to cool down a six inch steel cast.

Consider the process of making ice cubes: The time it takes to freeze an ice cube, is significantly longer than the time it takes for it to melt.

 

Actually I agree with you that why I wrote the citation in bold.
Waiting at least 12 months is sort of ridiculous (spelling?), a controlled cooling process is surely important .
But (not knowing better) I would expect 1 or 2 weeks at the very most ?


This link http://www.combinedfleet.com/metalprp2002.htm

contains a lot of information, maybe someone more clever than me can evaluate this and draw a conclusion of how and where cast armour actually is usefull in tank production ?

It say amongst other things :
"Cast armor is only used when a somewhat lower grade product is acceptable and increased speed or reduced cost of manufacture is more important (for example, late- and post-World War II cast steel tank armor, though even here welded rolled steel armor was preferred) or there is no other way to manufacture the item "

I thought it was chosen for Chieftain for it superior protctection qualities !

 

Well, I would cast an uninformed guess that casting allows nice curvey shapes to be produced which can allow for better protection - no flat surfaces, no corners, etc. Check the shape of the Cheiftain turret.

 

Like Ricky said, smooth 3D curvatures are easier to achieve from a casting. And although cast armour may be of a lower quality that is more than made up for by the increases in thickness available.
Rolling sheet and plate requires complete new tooling to get different thicknesses (if over and above normal rolling processes).
If carefully controlled cast armour can be of equal quality to plate (except for heat treatment), but it's generally cheaper to allow for loss of quality by making it thicker.

 

Well if that's what you think, then that's what you think. However you are up against two separate sources that both say water, and a piece of film that shows the condensed steam coming off the hull evaporating again (not apparent in the still obviously).

Like I said, other castings I make no judgement about, but this one is water quenched.

 

Cooling periods can be very long, for example, the mirror for the 200-inch Hale telescope at Mt Palomar took some 8 months to cool to prevent cracking or distortion of the glass (http://www.britannica.com/eb/topic-252312/Hale-Telescope).

Yes, I know this isn't armour plate, but similar factors would, presumably, apply to ensure the homogeneity of the finished casting. Unfortunately googling for cast armour cooling brings this thread up as one of the top 10 hits!

 

Great feedback guys.
If I might summarize what I've learned so far...
Casting large steel components took very specialized facilities. Locomotive Works were often contracted due to their expertise in large castings. American and Russian industry was best equipped to take advantage of this manufacturing capability as it was both economical and efficient.
At one time the M4 Sherman hull-casting was the largest single casting ever done.
Cast armor is inferior to rolled homo-steel. However rolled steel must be welded--human error, tricky business eh?--and of course rivets weaken the entire structure and pose added dangers to crew.
Castings allow for more subtle angling and curves, thus better able to deflect a glancing-shot than RHS though the thickness must be increased to match the stopping-ability of rolled-steel.
Cast pieces can be cooled in the ground for a year, or dipped in a bath of whale-oil, or water and be ready in 6 days.

Thanks guys. I'm as confused as ever.

Tim

 

Only too pleased to help.

 

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casting is eminently suitable for manufacturing large serie in an unchanging design ,
the master pattern is carved , usually in hard wood , from a clay model .
It is advantageous to cast next to the steel mills in a continuous process
quality control is tight , the sand mold have to be heated if the metal has to flow evenly and vent properly , the cast has to cool evenly or micro-cracks will appear on the stress points
surface treatment can be water , oil quenching or nitrification ( the old medieval recipe of the urine of a redhead virgin , a cow's work fine too! )
the cast can then be machined for fitting , a mistake is a pain but less costly than with a mechanical riveted or welded one
there is substantial time and trained manpower saving , once the master pattern are made they can be kept years to be used when needed for a war

The strongest process would have been a hot forged turret , it is possible in theory but the mind recoil at the effort to get a consistent result


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I cannot imagine how difficult it would be to produce a forged turret, be it consistent or not.
the hollowed out form would be an absolute horror to make.

 

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Yes it would have to be with a rather hummungulous steam pile-hammer banging at a hot slab , the form and tool would wear rapidly ,
it would have been for the rought shape before a final machining
I rather fancy hot forming of the upper armor with a hydraulic press , as long as the shape is kept simple ,
it would have stretched the 40ies technologies ,would have been fun

.

 

Another approach is rough die forging and then manchining to the final shape. I'm not sure where 40's technology was with this, I remember reading Ed Heinemann's biography (designer of SBD, DB-7/A-20, A-26, A-1 and other notable military attack aircraft) talking about introducing die cast forging on a large scale for the A-4 Skyhawk, so it may have been beyond 1940 capabilities.

 

turrets.

I vaguely remember reading somewhere about some experimental tanks with a 'mild steel?' turret, was this a mistake or experiment, can't remember if they were Cents or Chieftains. Anyone else remember this, might not even have been on this forum.

 

Yeah, some one on this forum (waaay back) claimed he'd been in service in Vietnam in a Chieftain that turned out to be a mild steel prototype.

Mild steel was (maybe still is) used for engineering mock-ups, but not particularly for vehicles that are going to be made from cast armour - getting the curvature wouldn't work.
For flat plates MS would do to get the details right (interior fitting positions etc.)

 

Were Turrets cast as one piece? particularly the T-34

 

"The initial narrow, cramped turrets, both the cast one and the one welded of rolled armour plates bent to shape, were since 1942 gradually replaced with the somewhat less cramped hexagonal one; as it was mostly cast with only a few, simple flat armour plates welded in (roof etc.), this turret was actually faster to produce.."

T-34 - Wikipedia

 

A thread about cast WW2 tanks with no mention of Sentinel?
Tsk.

Cast to the tip of its thingy...