Why Cast Iron?

[4GSR]

Cast Iron , Cheap? Has anyone tried to buy dura- bar lately???

When you have a close friend in the cast iron business, be amaze what I can get my hands on! Dead stock, short ends, stuff cut wrong, etc.

Billy, if you were a little closer or have a USA address, I'll be glad to try getting you a piece of D.I. Ken

 

[blaser.306]

Glad to hear some have availability, I was just quoted $130.00 CAD for 12" of 3" material and a $25.00 sawing charge! Guess I won't be using cast for anything.

 

[GarageGuy]

Cast Iron , Cheap? Has anyone tried to buy dura- bar lately???

I don't know if it was "Dura-bar" brand or not, but I bought a foot long piece of 3" diameter cast iron from Speedy Metals for $12. That's cheap compared to most other materials, and that was "walk in the door full retail price".

GG

 

[blaser.306]

Pricing from the suppliers here are all over the board! I asked the boss to add a length of 5/8" cold rolled hex to a $3000.00 dollar steel order ( Russel steel ) for the shop I work at , he was given a price of $55.00 a foot, $660.00 for a 12' length! needless to say I passed on the "opportunity" I bough from one of the buy what you need suppliers and paid $62.00 for a 12' piece!

 

[John Hasler]

as far as I understnd it is because cast iron absorbs vibration and is pretty hard, a cheaper alternative i've heard good things about is granite resin
Its fairly difficult to find something that dampens vibrations /and/ is hard enough to not wear out quickly

In most cases you would not want to make a granite resin direct replacement for a cast iron part. The resin materials are stiff but not nearly as strong or dense as cast iron. You can make machine parts out of resin but they must be designed with the limitations of the material in mind.

 

[HBilly1022]

When you have a close friend in the cast iron business, be amaze what I can get my hands on! Dead stock, short ends, stuff cut wrong, etc.

Billy, if you were a little closer or have a USA address, I'll be glad to try getting you a piece of D.I. Ken

Ken, not sure if that was addressed to me or BL, since you quoted him. But if it was intended for me, thanks for the generous offer but I do not have a US address and don't need any cast iron just yet.

John

Pricing from the suppliers here are all over the board! I asked the boss to add a length of 5/8" cold rolled hex to a $3000.00 dollar steel order ( Russel steel ) for the shop I work at , he was given a price of $55.00 a foot, $660.00 for a 12' length! needless to say I passed on the "opportunity" I bough from one of the buy what you need suppliers and paid $62.00 for a 12' piece!

I have a similar issue here and there are no walk in steel places. I have found a welding shop that will sell me small quantities but they do not have a great selection and their prices aren't the best. But they are better and nicer to deal with than the 2 steel suppliers in town, who act as though us small buyers are a PITA and treat us that way. Their prices also reflect that attitude. I understand business and if a small purchaser is not wanted because of the disruption caused by dealing with small orders, the company can politely state that they don't sell small orders. Last year I wanted to buy some steel for a grapple I was building and the local suppliers cost was over $800 for the steel I wanted. I drove 4 hours to another supplier and got the same order for just over $400 and I got to visit my kids while I was there. Living in the boonies has its downside but I still love it out here.

 

[eeler1]

Cast iron don't bend much, it breaks if stressed. So if you have an application that can use the "brittle" that cast iron brings, go for it!

 

[MozamPete]

My understanding is cast iron is also somewhat self lubricating so sliding/bearing surfaces wear less (ways, dovetails, etc) than a a stright steel on steel interface. For that reason I would be reluctant to replace any moving cast iron part with a steel replacement.

 

[cjtoombs]

It's mostly used because it is cheap. I say cheap when talking about that applicaiton. Iron castings can be very expensive in small quantities, but in large quantities (the amount being done for mass market machine tools) it is probably the cheapest thing available. As far as replacement of cast iron components, you just want to avoid steel on steel sliding components. Steel on cast iron is fine, as is cast iron on cast iron. I suspect that the gibs on most of those machines is already steel.

 

[Engineer61]

Grey Cast Iron has a very high carbon content (4-7%), which when cooled slowly precipitates out of solution with the iron and forms little flat flakes of graphite between the iron crystals. This creates it's many properties.
It's brittle because every graphite flake is not just a very easy path for cracks to split apart the iron crystals, but a place for such cracks to get started.
It has low tensile strength as the graphite flakes don't "stick" the iron crystals together well, making the whole structure fairly easy to pull apart.
It machines well because every graphite flake is a place for the chips to break - that's why you get that fine "dust" for chips, and the graphite provides lubrication for the cutting tool.
It doesn't transport vibrations well because the graphite flakes, not sticking well to the iron crystals, provides an energy absorption barrier to the vibration. It can't take large amplitude vibrations (like from a hammer blow) because they will cause cracks, but small amplitude vibrations from a motor running or cutting tool do get absorbed.
If given a simple heat-treatment (i.e. induction or flame-hardened, basically heated and held at temp long enough for the carbon to dissolve into the iron, then cooled quickly to prevent it from precipitating out again) it will become extremely hard due to the very high carbon content.
The graphite flakes do pierce the surface and provide a surface lubrication as well, so it slides easily on most other materials without a lot of wear occurring to either surface.
If given a complex heat-treatment and a very small amount of alloy material (0.10% magnesium) you can transform the graphite flakes into spherical carbon nodules, turning it into a material with much higher tensile strength referred to as Ductile Iron, Nodular Iron etc depending on trademarks. Yes, the material the auto industry calls nodular iron used in crankshafts is the exact same stuff machinists call ductile iron used in vises.