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Specific gravity of steel

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Posted by: SFO

One of our new machinists wants to start making Ti parts for his race bike.
In an attempt to show him the real end result of his efforts I said he should weigh his steel component, then with the machinists handbook, he could compare the relative specific gravities of the materials to find the effective ratio of steel to Ti, or aluminum.
I went to my version 23 machinists handbook, and in the Specific Gravity and Properties of Metals chart it has a series of dots across the specific gravity of Steel, Carbon line.
Now, I was able to create the ratio from comparing the weight per cubic inch, so the question remains...
What is the specific gravity of carbon steel and why did the authors see fit to not add it.
Is steel the nominal or, value for 1?
This doesn't seem right...
Help me Mr. wizard.


Posted by: HLT

The standard for specific gravity is the weight of 1 cubic foot of water. About 64 lbs. Anything with a higher weight per cubic foot has a specific gravity in excess of one. Depending on the alloy, steel would have a spec. gr. around 3. It is a standard used to figure volume from weight, or vice versa. If you want to know the SG for any given material heavier than water, you use water displacement to find SG.


Posted by: SFO

Thank you for the specific gravity explanation...
But according to displacement, that would be a product of volume?
No?
My edification is a slow process, I appreciate your patience.
Bill


Posted by: Blue Smoke

I think what you're looking for is in the Handbook under 'weights' of materials. Carbon steel varies slightly, but is around .284- .287 lbs. per cubic inch. Aluminum is about .097 -.102 lbs. per cubic inch


Posted by: HLT

Yes, if you displace a measured amount of water, you will get the volume of your material. Then weigh it and find the difference between this and a like volume of water. This is used if it is a random shape or shapes. In your case, perhaps nuts and bolts. If you have a cube or something where the volume can be found from direct measurments, weigh it, multiply the weight by a value that would bring the VOLUME to one cubic foot. Divide that by 64, the weight of a cubic foot of water, (actually 63.7 if I remember correctly) and you will have your SG value. Also, I was wrong about the SG of steel. Since iron is it's major component, it will have a SG over 7. Use BlueSmoke's numbers and you'll get where you want to go for steel.



Posted by: viking2

The density of TI is about 0,6 of the density of steel. I would say there is not mutch use in making Ti parts unless you are making a frame. I would go for Al instead. A good and cheap way to save wheight is to call a flight mechanic and see if he can get you Ti-bolts. There are a lot of them in airplanes and they change them often.





Posted by: MikeT

Quote:
Originally posted by HLT:
The standard for specific gravity is the weight of 1 cubic foot of water. About 64 lbs. Anything with a higher weight per cubic foot has a specific gravity in excess of one. Depending on the alloy, steel would have a spec. gr. around 3. It is a standard used to figure volume from weight, or vice versa. If you want to know the SG for any given material heavier than water, you use water displacement to find SG.


Ahh, I just checked my Steel handbook

Steel SG 7.85
Aluminum SG 2.55-2.75

Don't have it for Ti though




Posted by: Ando

Don't you machinists ever use metric measurements?

One cubic centimer of water weighs one gram (at a specific temperature). This is the basis of the relative density of things.

------------------
Ando
Just another day in Paradise
Two Wheels, Kauai


Posted by: Buckholz

SFO, I recently went looking for the density's of Ti vs Stainless Steels for a problem here at work.

The previous poster was correct, Titanium has about 60% of the density (S.G.) of Steel so his parts will be about 40% lighter.

Better for your machinist to run at lunch during his freetime vs making dirtbike parts. Believe me, a couple of pounds off the rider is a much better hopup.


Posted by: SFO

I tried to disuade my minion, making ti parts is a pain in the butt, not to mention the gun drilling nightmare.
He is persistant.
I thank the forum for your assistance, I suspected you could help and you did.
Bill


Posted by: c3hammer

You guys are missing the point of using Ti in the first place. It's very stiff for it's weight. Thus you can come up with a fairly "tough" part that is equal stiffness to a steel part for much less than 0.6 the weight. Or conversely you can come up with a more flexible, very light weight part that won't fatigue as fast as the steel part. Ti is really cool stuff.

4130 steel has a flex modulus of about 19 mpsi. Aluminum's about 10 mpsi and Ti about 18 mpsi, I think. This whole discussion leads to what is called specific stiffness (modulus / weight).

Carbon fiber/epoxy parts are close to Ti, but lack the "toughness" factor. Ti is great for smacking against things and not coming apart.

Tell your best buddy (machinist) to thin the walls about 25% and double the corner radii, everywhere. His parts will be da bomb. Who cares if they don't help performance that much. They're the coolest looking things you can put on your toy.

After all, that's all these things are, toys http://dirtrider.net/ubb2/smile.gif

Pete
c3hammer@verts.com http://www.verts.com/dirt/





Posted by: SFO

[QUOTE]Originally posted by c3hammer:
[B]You guys are missing the point of using Ti in the first place. It's very stiff for it's weight. Thus you can come up with a fairly "tough" part that is equal stiffness to a steel part for much less than 0.6 the weight. Or conversely you can come up with a more flexible, very light weight part that won't fatigue as fast as the steel part. Ti is really cool stuff.

4130 steel has a flex modulus of about 19 mpsi. Aluminum's about 10 mpsi and Ti about 18 mpsi, I think. This whole discussion leads to what is called specific stiffness (modulus / weight).


Tell your best buddy (machinist) to thin the walls about 25% and double the corner radii, everywhere. His parts will be da bomb. Who cares if they don't help performance that much. They're the coolest looking things you can put on your toy.

I have heard and experienced the flexability of ti after attempting a long turn machining exercise on ti.

Ti will deflect away from your cutting tool as much as .005" on a 6" span. Ti acts so springy, unlike steel which machines much deader, deflecting less than a thou...
The stiffness modulus means naught in the real world of training a newby in the intricasies of ti.
Let alone trying to tap and drill it.
Tricks are hard fought, I guess, I have learned to conserve my grey matter for easier modes of result gaining.
I do not look forward to the edification of an apprentice in regards to superalloys.
Production and results are valued in my eyes at a time vs. results quotient.
It just seems like I could spend countless hours teaching him my hard fought results of maching ti for a negligble result.
2 f'in grams?
Is this worth 10 hours of my time?
Plus all of the cutting tools that are certainly going to be smoked?
I am having a little reality check here.
There are things I want my employees to grok.
Spinning out on maching knarley material seems counterproductive.
Yet, I am still open to the mastery of ti.
If any ti machinist want to email their secrets I will listen.


Posted by: Norm

C3hammer,

You might want to do a couple of quick calculations to verify your statements about specific stiffness. It turns out many engineering metals have very similar specific stiffness (modulus/specific gravity) values. Here's a few examples.

Steel: 210 GPa / 7.85 = 26.75 GPa
Aluminum: 70 GPa / 2.70 = 25.92 GPa
Titanium: 114 GPa / 4.43 = 25.73 GPa

As you see they're all about the same. Ti and Al can be used to make lighter stiffer structures compared with steel, but they need to be designed with the material in mind to get any benefit.

BTW, carbon fiber/epoxy composites blow metals out of the water in terms of specific stiffness (can be over 100 GPa or about 4 times that of metals listed above), but you're right about them not being very tough.

Norm




Posted by: motopuffs

I hate it when Rich tells me I'm generalizing too much.

I gotta say this,you guys are generalizing WAY bad!

Al and Ti are elements, while steel is a solid solution composed of iron, manganese, silicon, and other elemencts.

Al and Ti are rather unimpressive unalloyed.

There are limitless alloys of each, with a wide range of properties. This is without even considering heat treatment.

Same deal with steel. Even considering just 4130, annealed has a hardness of <20 RC while hardened and untempered is over 50 RC.
So you can see where just the heat treat alone can make a huge difference in the properties of these materials.

The most popular titanium alloy is called Ti6Al4V, which is composed of six percent Al, four percent vanadium, and the balance titanium.

My turn to generalize. Heat treatment of titanium is difficult and weird. It is no fun to machine. Funny colored sparks and strange smells when grinding. Tends to have poor wear resistance (especially considering its hardness).

Titanium alloys can be ion nitrided, which will produce a gold surface appearance, and a very thin (<.0001") but exremely hard surface composed of TiN and Ti2N.

Right, most steels weigh about .284 pounds per cubic inch.

To sum up, steels and certain other alloys, due to chemistry and heat treatment, can have properties ranging from "peanut butter" to "hard as glass".

Not only are there many apples and oranges in the fruit basket, but they are of various sizes, shapes, and ripenesses.



[This message has been edited by kookooformotopuffs (edited 04-03-2001).]


Posted by: SFO

The fact that Ti and Al are elements and that Steel is an alloy would explain why its specific gravity is not on the chart in the machinists handbook.
My curiousity is finally sated.
Thanks Gents.


Posted by: c3hammer

Norm:

DOH!!! I've always compared carbon/epoxy parts to aluminum and the difference depending on layup can be huge in specific stiffness. I guess I never actually calc. the specific stiffness of the different metals and indeed they are about the same.

By the way most carbon/epoxy parts (using 33 mpsi fiber) exhibit significantly lower modulus than you've stated. The flex modulus (not tensile module) of a quasi isotropic layup will be about 7 mpsi. 3/4 the stiffness of aluminum and about 1/3 the stiffness of 4130 steel. The specific gravity of a 32% epoxy and 68% carbon fiber layup is about 1.8 or so. For practical purposes carbon fiber / epoxy parts are nowhere near as stiff as the theory would say unless talking about a flat plate make of all uni carbon fiber. The higher modulus fibers will yield better numbers as well, but layup makes a huge difference.

SFO:

120 surface feet:
1/4" carbide endmill = 0.0009 chip load.
1/2" endmill = 0.0012 chip load
3/4" endmill = 0.0018 chip load.

In otherwords, push it really hard at a slow rpm. Ti doesn't like being nitpicked at.

Pete


Posted by: agmjr

Quote:
Originally Posted by SFO
One of our new machinists wants to start making Ti parts for his race bike.
In an attempt to show him the real end result of his efforts I said he should weigh his steel component, then with the machinists handbook, he could compare the relative specific gravities of the materials to find the effective ratio of steel to Ti, or aluminum.
I went to my version 23 machinists handbook, and in the Specific Gravity and Properties of Metals chart it has a series of dots across the specific gravity of Steel, Carbon line.
Now, I was able to create the ratio from comparing the weight per cubic inch, so the question remains...
What is the specific gravity of carbon steel and why did the authors see fit to not add it.
Is steel the nominal or, value for 1?
This doesn't seem right...
Help me Mr. wizard.




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