Armour vs. Armour.....

[robunos]

In the 'Indian Panzer' thread, here :-

http://www.secretprojects.co.uk/forum/index.php/topic,1863.0.html

it's stated that the Indian military chose the Vickers design over the German one
owing to the former's use of welded armour plates as opposed to cast armour,
in this case due to ease of licence manufacture.
This reminded me of a long-standing question I have,
which is superior, rolled, welded armour, or cast armour?


cheers,
Robin.

 

[Abraham Gubler]

This reminded me of a long-standing question I have,
which is superior, rolled, welded armour, or cast armour?

It’s not as simple as that, there are a lot more variables involved.

 

[overscan (PaulMM)]

The answer is "yes"

 

[mz]

Armour vs Amour... sometimes I read a little funny!

 

[robunos]

The answer is "yes"

It’s not as simple as that,...

Okay, I deserved that, I shall rephrase the question.
What are the strengths and weaknesses of rolled, welded armour,
as opposed to cast armour, and how do these influence the choice
of one type or the other for construction of an AFV.


cheers,
Robin.

 

[RyanC]

Oooh ooh can I help?

There are essentially several types of homogenous armor:

Cast Homogenous Armor (CHA) (MIL-DTL-11356)

It used to be used on a lot of tanks, due to the ease of casting it into shapes that had excellent ballistic qualities; like curved mantlets, boat shaped hulls, etc. Some armor quality was lost in the process however, since you could not be assured of uniform hardness throughout the entire casting process; but this was usually outweighed by the fact that you could make something like the IS-3's turret with it; presenting a very tough target for shot to penetrate.

Rolled Homogenous Armor (RHA) (MIL-DTL-12560)

Basically what it says. Your basic armor rolled by steel mills and put together by welding.

As the thickness of the armor increases, it's protective qualities decrease; e.g.

0.5" thick RHA has the following qualities:

Rockwell C Hardness: 37
Yield Strength: 938 MPa
Ultimate Tensile Strength: 1,111 MPa

while

1.5" thick RHA has the following qualities:

Rockwell C Hardness: 30.5
Yield Strength: 815 MPa
Ultimate Tensile Strength: 923 MPa

High Hardness Armor (HHA) (MIL-DTL-46100)

This was developed during the Vietnam War for protection against ball ammunition. The original USMC LAV uses this above the belt-line, and plain RHA under the belt line.

This is basically the ultimate extension of RHA; very thin rolled plates with extremely high hardness, allowing it to shatter small caliber ammunition. Mainly used in gun shields etc.

Dual-Hardness Armor (DHA) (MIL-DTL-46099)

This was developed to provide improved performance over HHA by incorporating a second layer of softer armor behind the main high hardness layer to trap fragments from the first layer.

 

[robunos]

Thanks for that......

I'm somewhat confused by the statement that :-

'As the thickness of the armor increases, it's protective qualities decrease'

Is this due to the hardening process being more effective in the surface layers
of the armour, and thus a thicker plate has a softer core?


cheers,
Robin.

 

[Just call me Ray]

Maybe it should be clarified, that a thicker piece of armor isn't going to be as efficient as a thinner piece in terms of armour protection.

 

[robunos]

Maybe it should be clarified, that a thicker piece of armor isn't going to be as efficient as a thinner piece in terms of armour protection.

Understood, but now I'm interested in why this should be so, is it a metallurgical
property of the armour, and linking back to my original question,do rolled and
cast armour differ in this property?

The cast armour by Bradford Kendall Ltd (still casting steel today) was one of the success stories of the program and enabled rapid design evolution compared to jigged welding or bolting production.

The Sentinel with its thick castings of softer but tougher steel alloy made it very resistant to spalling from blast effects.

The above quotes from Abraham Gubler, from the Sentinel ACIV thread,
see here :-

http://www.secretprojects.co.uk/forum/index.php/topic,8514.msg74873.html#msg74873

exemplify the kind of information I'm seeking.


cheers,
Robin.

 

[red admiral]

Understood, but now I'm interested in why this should be so, is it a metallurgical
property of the armour, and linking back to my original question,do rolled and
cast armour differ in this property?

It's difficult to ensure the same quality of material as the thickness increases. You get complex cooling gradients through the section, and these influence the material properties. As parts cool faster/slower you get a spread of properties away from the optimum.

 

[robunos]

Assuming you're talking about cast components here, would controlling the cooling process,
like is done when turbine blades, or even safety glass, is made, help to reduce this variation
in quality? it would be difficult, I know, due to the size of the castings involved.
Likewise, since rolled armour, I assume, is cast in ingots, and then rolled into plates, would
this be more homogeneous, with less quality variation within it?


cheers,
Robin.

 

[avatar]

well let me just state this,

The T-90 moved to an all welded turret with the Vladimir version.