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snowman
05-26-2010, 04:39 PM
There are a lot of different grades of cast iron. What is the appropriate grade for sliding surfaces? I want to make a couple of dovetail slides, but want to do it right. These will be controlled with an air cylinder and see a lot of strokes, but I don't want to use the now traditional ball bearing slide.

Oldbrock
05-26-2010, 04:44 PM
Continuous cast would be my choice such as Durabar.

snowman
05-26-2010, 04:48 PM
Guess I should be more specific. From the durabar website, these are the available grades.

Ductile
65-45-12
80-55-06
100-70-03
65-45-12 HRDS
Gray
G2
G1
G2A
G1A
Ni-Resist
201 Type 1

Oldbrock
05-26-2010, 05:09 PM
One of the grey's, but I don't know which one. Peter

bob_s
05-26-2010, 05:21 PM
Go with the Ni-resist as it is a grey cast iron with nickel added, that should increase the wear resistance of the contact surface.

Nickel alloyed cast iron is used in engine blocks to increase the wear resistance.

Oldbrock
05-26-2010, 05:29 PM
Thanks bob, I'll file that info for myself too. Peter

lazlo
05-26-2010, 06:03 PM
Ductile has about 50% higher tensile strength than grey. Grey has superb self-damping characteristics, which probably doesn't matter for your application. Never heard of the Ni-Resist.

pcarpenter
05-26-2010, 06:47 PM
Are you going to scrape these sliding surfaces to flatness? If so, think twice about something really hard...you will curse yourself forever.

Additionally, the rule of thumb for sliding way surfaces is that you can make one side hard if you want, but you never do hard-on-hard as it leads to galling.

I can't really answer your question overall since I don't know that a lot of machine tool makers publish the specific grade of grey iron used. I do know that, as mentioned, grey iron has a higher damping factor due to it's structure than say one of the varieties of ductile iron. That having been said, I have a picture somewhere from Monarch sales literature where they demonstrate the characteristics of the iron used in their castings, by making a "spring" out if it and then bending that spring into a U shape. They take a round bar of the stuff, cut what would appear to be highly pitched square threads on it and then bore out the center till it looks like a spring made of flat wire....and it bends without breaking. This, to me, implies that they must have been using some variety of ductile iron.

Paul

lazlo
05-26-2010, 07:09 PM
Are you going to scrape these sliding surfaces to flatness? If so, think twice about something really hard...you will curse yourself forever.

Good point! If you pick the Ni-Resist, you'd better plan on surface grinding it :)


I have a picture somewhere from Monarch sales literature where they demonstrate the characteristics of the iron used in their castings, by making a "spring" out if it and then bending that spring into a U shape. They take a round bar of the stuff, cut what would appear to be highly pitched square threads on it and then bore out the center till it looks like a spring made of flat wire....and it bends without breaking. This, to me, implies that they must have been using some variety of ductile iron.

I'd love to see that Paul. I have a copy of the American Machinist article that someone posted on PM where they're hardening a Monarch leadscrew by lowering it through an inductive coil and right into a vat of quench oil.

Quality indeed!

BobWarfield
05-26-2010, 07:40 PM
I have a copy of the American Machinist article that someone posted on PM where they're hardening a Monarch leadscrew by lowering it through an inductive coil and right into a vat of quench oil.

Quality indeed!

Isn't it a pity the Internet and cheap video didn't exist back then so we could see all that work being done?

It would be fascinating stuff.

Best,

BW

wierdscience
05-26-2010, 09:29 PM
Definately one of the greys,don't remember which,but the more graphite the better.

Robin R
05-26-2010, 09:46 PM
It might be worth using the Ni-resist for one part and a softer grey cast iron for the other part.

oldtiffie
05-27-2010, 02:33 AM
I'd be more concerned about machinability, ability to scrape if needed and probably most importantly, lubrication - depending upon speed and load - or perhaps an auto/self-oiler?

pcarpenter
05-27-2010, 12:03 PM
Sorry about the late reply. I barely have any time to read here lately, much less post. Here is that page from a Monarch ad. I am pretty sure I found it from someone else's posting either here or on PM, but I can't give credit because I don't know who it was.

http://i108.photobucket.com/albums/n16/pfcarpenter/Machinery/monarchsemi-steel.jpg switch_body(0);

rowbare
05-27-2010, 01:10 PM
OP, Is using adding a layer of turcite an option? That would take care of much of your wear issue while reducing friction.

bob