Author Topic: Cast iron ''SPRUES'' can they be of use to the model machinist?  (Read 15247 times)

Offline Jo

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #30 on: August 15, 2013, 11:41:39 AM »
Which reminds me I must put those two old sash weights in the bottom of the bonfire before I light it  :naughty:.

Jo
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Offline tel

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #31 on: August 15, 2013, 11:45:38 AM »
 :Lol: I'm a bit of a fan of sash weights - you get the odd unworkable one, but most are far better stuff than people are led to believe.
The older I get, the better I was.
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Online Dan Rowe

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #32 on: August 15, 2013, 02:55:11 PM »
Bob,
I see you slipped in a technical paper on ageing cast iron. Here is a brief overview of the same research.
http://www.e-smarrt.org/factsheets/aging_graphite.pdf

Dan
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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #33 on: August 15, 2013, 04:11:14 PM »
Thanks for pointing that out Dan, I didn't spot it before....Sorry Bob.

I'll read it tonight

Dave
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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #34 on: August 15, 2013, 11:44:25 PM »
Dan,

The age strengthening shown in the project proposal you attached shows a rise in tensile strength of Gray cast iron from 255 MPa to 275Mpa.
The strengthening was to be studied as part of a ongoing research project  as it appears that this was a proposal document for this research.

I did not see any statement regarding surface hardness, though they do claim that machinability was improved...but it did not state by how much.  However, the change in strength is not particularly large from a practical perspective...as parts are very rarely designed to tensile strength or even yield, but to a small fraction of the yield.  An exception to this would be a shear pin perhaps.

The rise in tensile strength is equivalent to a tensile strength improvement from 37000 psi to 40000 psi over a period of approximately 1000 hours. 
Dave
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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #35 on: August 16, 2013, 12:22:35 AM »
Hi Guys,

Without getting at all technical...............no major company seeking to maximise their profit margin is going to adopt a process which is not going to give a positive benefit, be it buying a field, producing parts 5 years in advance of them being required; etc.

For the technically minded.

http://www1.eere.energy.gov/manufacturing/resources/metalcasting/pdfs/age_strengthening.pdf

Best Regards
Bob

Hi Bob,

I did read your attached paper.   The observations were consistent with my own experience and "lore".  I have been told that the carbon will precipitate and be dispersed in solution over time.   I am astonished by the data showing a large improvement in machinability.   The strength improvement is as was described in the paper Dan described.    I didn't see any discussion of experimental error assessment.   

Your Friend

Dave
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Offline MuellerNick

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #36 on: August 16, 2013, 07:58:41 AM »
Quote
I have been told that the carbon will precipitate and be dispersed in solution over time.


No. In cast iron, the graphite is either spherical (GJS) or laminar (GJL). It is a wanted property that the carbon aggregates. Also, we have worm-shaped carbon (vermicular), called GJV.
The carbon lowers the melting temperature, that's a wanted property. It also increases the dampening, that's why CI is preferred for machinery.
Adding alloys influences the shape of the carbon "blobs".


Nick

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Offline Bezalel

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #38 on: August 20, 2013, 01:22:03 PM »
Trim>
The carbon lowers the melting temperature, that's a wanted property.
<trim

Hi Nick
 
The Iron Carbon phase diagram seems to contradict that statement.
I prefer to think of it as the right amount of carbon reduces the melting temperature of the alloy.

The Iron Carbon Alloy becomes Eutectic at 4.3% Carbon w/w . An Iron Carbon alloy with just 1% more carbon actually increases the melting temperature.

At 5.4% C w/w the alloy is not a liquid until it reaches a temperature grater than 1600 C.   Pure Iron becomes liquid at 1538 C.

Bez

« Last Edit: August 20, 2013, 01:33:36 PM by Bezalel »
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Offline firehazard

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #39 on: August 21, 2013, 01:09:35 AM »
Hi,

that's a very interesting diagram for those of us who don't have access to a cupola.

thanks

John

Offline MuellerNick

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #40 on: August 21, 2013, 11:48:38 AM »
Quote
The Iron Carbon phase diagram seems to contradict that statement.


Not that much.
Not so much, because carbon steels stops at 2.06% of carbon. Not so much, because the diagram is misleading. Right of the eutectic, the solid line going upwards is NOT where you have molten metal. The dashed line that stops at 1253 C and the solid horizontal line is liquid too.


"L + C(graphite) is liquid plus primary Fe3C.
The section (roughly) lined out by 0.16, 2.1 and 4.2 is liquid too (liquid + gamma-mc (mixed crystals)).
So above 2.06 % C, you have won and a constant melting temperature of 1153 C.




Nick

Offline firehazard

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #41 on: August 22, 2013, 01:18:04 AM »
Hi,

it might be worth mentioning that 4% carbon is regarded as the practical maximum of carbon solubility in iron. You would need to be doing something a bit special to exceed that.

The problem for small scale casting is getting enough carbon into the metal.

I have personally smashed up modern engine blocks with a sledgehammer and, unlike classical grey iron, a Ford or VW block will bend before it breaks.

take care

John


Offline Bezalel

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #42 on: August 24, 2013, 06:31:39 PM »
Quote
The Iron Carbon phase diagram seems to contradict that statement.


Not that much.
Not so much, because carbon steels stops at 2.06% of carbon. Not so much, because the diagram is misleading. Right of the eutectic, the solid line going upwards is NOT where you have molten metal. The dashed line that stops at 1253 C and the solid horizontal line is liquid too.


"L + C(graphite) is liquid plus primary Fe3C.
The section (roughly) lined out by 0.16, 2.1 and 4.2 is liquid too (liquid + gamma-mc (mixed crystals)).
So above 2.06 % C, you have won and a constant melting temperature of 1153 C.




Nick

Hi Nick

That's an very interesting way to interpret a binary phase diagram.

I'll explain for those not familiar with them a few aspects of the PD.

Since the other one was misleading  here is one from a different university.



Each line represents the temperature at which the rate of temperature change stops momentarily during heating or cooling due to latent heat.

This equates to the energy absorbed or released during a change of state or crystal structure.   

The top line from 1535oC through E to 1837oC is known as the liquidus. above which the alloy is termed a liquid solution i.e it is a liquid.
Latent heat is released as the metal cools at this temperature solid crystals form. In many alloys not all the metal will solidify at that temperature. 

The solidus line is a line below which the alloy is a solid which here runs from C to B through E at 1130oC

Between those two lines it is known as a solid solution,  because contains solids at that temperature.

A solid solution is NOT a liquid.

Solubility of carbon in iron is very temperature dependent and you can use heat treatment to change the numbers below via quenching, tempering or annealing. But in general;

At room temperature ( assume very slow cooling to establish Body Centered Cubic crystal formation- alpha Iron) solubility of carbon in Iron is  around 0.008%

At 723oC solubility of carbon in Iron is around 0.022% ( assume very slow cooling Body Centered Cubic crystal- alpha Iron)
At 723oC solubility of carbon in Iron is  around 0.83% ( Face Centered Cubic crystal- gamma Iron)
At 1130oC solubility of carbon in Iron is  around 2.2% ( Face Centered Cubic crystal- gamma Iron)

Solubility of Carbon in Iron as Fe3C is  around 6.7%

John
I know all this hasn't answered your original question,

So IMHO the answer is....... If the sprues machine nice, use them...  if they don't, toss em out.
Depending on what the castings were for, that the sprues came off, they could be made of who knows what.

Bez
« Last Edit: August 24, 2013, 06:37:17 PM by Bezalel »
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Offline Jo

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #43 on: August 24, 2013, 06:48:28 PM »
All of these numbers are a bit technical for me busy relaxing at home... All I can say is the latest two sash weight have been recovered from the ashes of the bonfire and they cut on the mechanical hacksaw like butter  8)

Which is some what different from when they started  :facepalm2:

Jo
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Offline Bezalel

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Re: Cast iron ''SPRUES'' can they be of use to the model machinist?
« Reply #44 on: August 25, 2013, 12:32:53 AM »


Sumarises it nicely Jo.

Probably all John wanted to know. 

I wasn't expecting to hear back on the annealing in a bonfire plan until after November 5.

Who needs a TTT chart?
 :cheers:
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