Author Topic: Reproduction 2 piece rotor review  (Read 3284 times)

bergy

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Re: Reproduction 2 piece rotor review
« Reply #15 on: May 14, 2017, 01:39:04 PM »
Automotive gray cast iron was either class 25 or class 30 depending on the application.  That would be 25,000 or 30,000 psi ultimate tensile strength with very little deformation before breaking (brittle).  Automotive ductile iron was typically 65-45-12.  That is 65,000 psi ultimate tensile strength, 45,000 psi yield strength, and 12% minimum deformation before failure.  The problem with using gray cast iron for wheel hubs is that it's weaker, but (more importantly) it fails traumatically without deformation (snaps).  A ductile iron hub will bend when hit hard - allowing the driver to control the car after impact.

Mike S

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Re: Reproduction 2 piece rotor review
« Reply #16 on: May 14, 2017, 01:54:03 PM »
It sounds like then that anyone who sells these rotors, including the main distributor, can be liable if indeed these hubs are not meeting MVSS specs and are the root cause for an accident. I assume then that parts manufacturers  must provide some sort of proof of certification that they meet requirements?
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67 NOR SS/RS L35 Convertible - Under restoration

x66 714

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Re: Reproduction 2 piece rotor review
« Reply #17 on: May 14, 2017, 03:32:10 PM »
Sounds more & more like I'll need to buy the rotor assms & put the rotor itself on my hubs....Joe
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

x66 714

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Re: Reproduction 2 piece rotor review
« Reply #18 on: May 15, 2017, 03:12:07 PM »
Well it's true. They are not available. I ask if they would be returning as they could be a high demand item. His answer was "I have no clue".  Lovely. Back to the drawing board....Joe 
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

z28z11

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Re: Reproduction 2 piece rotor review
« Reply #19 on: May 16, 2017, 12:30:03 AM »
Well it's true. They are not available. I ask if they would be returning as they could be a high demand item. His answer was "I have no clue".  Lovely. Back to the drawing board....Joe 


Don't go too far - I've got a line on the rotors only, not terribly expensive, either. Let you know when I receive them and check them out - want to make sure these work before I release the source.

Regards,
Steve
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1969 Z28 X77/M20/VE3 LeMans/W
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x77-69z28

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Re: Reproduction 2 piece rotor review
« Reply #20 on: May 16, 2017, 03:19:36 AM »
Awesome!
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x66 714

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Re: Reproduction 2 piece rotor review
« Reply #21 on: May 16, 2017, 02:34:25 PM »
Great Steve. Looking forward to your research results....Joe
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

jdv69z

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Re: Reproduction 2 piece rotor review
« Reply #22 on: May 16, 2017, 07:22:40 PM »
Gray iron is very brittle. If you drop it, I think it will crack. Ductile iron takes the gray iron and introduces other molecules, (primarily molybdenum I think) which acts to block cracks and stops them from continuing. Thus, you can make a crankshaft from ductile iron, but a gray iron one would crack immediately.
Jimmy V.

bergy

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Re: Reproduction 2 piece rotor review
« Reply #23 on: May 17, 2017, 08:21:19 PM »
Oh my Jimmy - that ductile iron explanation/comment is incorrect on so many levels!

BULLITT65

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Re: Reproduction 2 piece rotor review
« Reply #24 on: May 17, 2017, 08:35:07 PM »
Bergy your going to have to explain why he is wrong, if your going to call him on it.

Level 1 ?

Level 2?

thanks
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-Looking for 3192477 (front) spiral shocks 3192851 (rear)
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cook_dw

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Re: Reproduction 2 piece rotor review
« Reply #25 on: May 17, 2017, 11:09:37 PM »
Darrell Cook

Contact me if you have a 68 L78/L89 Camaro to add it to my database.

bergy

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Re: Reproduction 2 piece rotor review
« Reply #26 on: May 17, 2017, 11:44:25 PM »
OK - but the answer gets kinda far into the weeds!  The foundry that I owned made 100% of the Motor Wheel hubs that they supplied to Ford & Chrysler passenger cars in the 80s.  Also, I'm a metallurgical engineer - so here goes.

Ductile iron should be made from its own base iron.  High production gray iron base has too many tramp elements in it which can hurt the elongation of as cast ductile iron.  Also, gray iron melters often use scrap iron for melt stock that has too many tramp elements in it.  Melt stock that contains thing like old bathtubs and steam radiators contains relatively high amounts of phosphorous.  If used for ductile iron, phosphorus in the metal raises the brittle transition temperature too much.  In which case - ductile iron becomes strain rate sensitive and can experience brittle failure at room temperature.  Even at lower phosphorus levels - traumatic brittle impact can occur in severe cold weather environments.

The excellent elongation of ductile iron (versus gray cast iron) is achieved by adding magnesium as an alloy to the liquid iron post melt.  The magnesium causes the graphite that precipitates out of the liquid iron as it goes through the solidification process to have a spheroidal morphology (round "nodular" graphite in the ferritic matrix).  These spheroids of graphite don't interrupt the metal matrix of the iron as much as the "flake" graphite that is seen in gray iron.  As a result - ductile iron can stretch before fracture a lot more than gray iron.

Gray typically has more pearlite stabilizers in the chemistry.  So in addition to the graphite "flakes" interfering with its ability to "stretch", it also has a matrix that is just not conducive to ductility to begin with.

We didn't cast cranks, but to my knowledge - GM crankshafts from the late 60s were either cast or forged.  Actually, one of the advantages of cast iron is that it has great anti vibration qualities.  Also, after a million cycles (doesn't take long for a reciprocating part) it generally has an infinite fatigue life.  Steel, on the other hand, will continue to propagate fatigue cracks to eventual failure even after a million cycles.  I'm sure that many of you have noted these fatigue cracks when crack detecting old forged cranks.  So, don't use forged cranks with significant cracks thinking that they aren't too bad.  Steel fatigue cracks will continue to propagate to eventual failure.  Cracks in cast cranks generally stop propagating when they hit the flake graphite structure (kinda like drilling a hole at the end of a crack to stop it from propagating).

Mike S

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Re: Reproduction 2 piece rotor review
« Reply #27 on: May 18, 2017, 12:24:23 AM »
 Bergy,

  Can you tell the difference between gray and ductile iron by looking at them side by side?

Mike
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67 NOR SS/RS L35 Convertible - Under restoration

BULLITT65

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Re: Reproduction 2 piece rotor review
« Reply #28 on: May 18, 2017, 12:42:25 AM »
Great explanation Bergy. (you were the right guy to have on this thread!)

If I saw cracks on either cast, or steel that would be worrisome. But I understand the common thinking that the steel would continue to hold up, when actually the cast may last longer before failure.
1969 garnet red Z/28 46k mile unrestored X77
-Looking for 3192477 (front) spiral shocks 3192851 (rear)
-Looking for an original LOF soft ray windshield
-Looking for original Delco side post negative battery cable part # 6297651AV

bergy

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Re: Reproduction 2 piece rotor review
« Reply #29 on: May 18, 2017, 01:07:27 AM »
It's hard to tell the difference visually unless you know what to look for at the parting lines and in the size of the "in gates".  Ductile iron requires larger feed gates and also needs larger risers to adequately supply iron to the solidifying casting.  To tell if a casting is gray or ductile.... remember that those same flakes in cast iron that stop cracks from propagating also interfere with sound waves traveling through the matrix.  So, if you tap a nodular casting with a hammer - it tends to ring like a bell.  Gray iron just yields a dull thud.  Sounds like a crude test, but we used the same principal to ultrasonic test 100% of the ductile hubs that we produced to make sure that they had acceptable nodular microstructure.