Diff. between "Cold Finish" & "Hot Rolled" steel?

[beppington]

What's the difference?

I need a 4' round bar I can use to manually manipulate my 3PH auger.

I bought a 4'L x 3/4" diameter Hot Rolled round bar, but it bends too easily.

Turns out I can fit a slightly larger, about 7/8" bar in the auger's hole, but should I get Cold Finish or Hot Rolled, so it doesn't bend (so easily)?

Thanks ...

 

[Danno1]

.


Cold finished is a rolling/forming operation done after the hot rolling. It has a smoother surface finish and improved thickness tolerances. Some materials get slightly stronger due to work hardening. However, the grade of the steel has more effect on the strength. IE. 4140 is much stronger than A36.


.

 

[dynasim]

A piece of pipe with a stub welded on the end would be better. The pipe diameter helps a bunch in stiffness, without adding the weight.

Heat treating also helps.


Chris

 

[jmc]

Yield strength is the number you want to be comparing between steels.You need to know the type of steel that bent in the 3/4 diameter. The most common hot finished would probably be A36 which has a minimum yield strength only 36,000 psi.

The most common cold finished (cold rolled) steel is 1018, which has a yield strength of 53,000 psi so that substitution will be about 50% stronger.

Now, since bending strength is proportional to the cube of the diameter, moving up from 3/4 to 7/8 in the same steel will add another 50%.

Then, by going to a 100,000 psi steel (yield), like pre-harden 4140, you get another 250% or so over A36. You can get this at Speedy Metals for about $25/4ft plus shipping, and in any other length.

You can't really harden either 1018 or A36 except for case hardening, which just hardens the surface.

A pipe with stub will be more rigid but the stub will still yield at the same load as a solid bar, right where the stub enters the auger.

 

[Gary Fowler]

Pound for pound a pipe will withstand more bending force than solid rod.

 

[Argosy]

Pound for pound a pipe will withstand more bending force than solid rod.

The only problem with that is to get a pound of tube the diameter will have to be way bigger than he can fit into a 7/8" hole.

I've got to wonder how you're bending this? 3/4" should be strong enough to position the auger before you start. If you're trying to 'wobble' out a bigger hole with a 4' long bar I think you're going to bend it if you really lean into it unless you get some really hard steel like mentioned above.

 

[rrrkkk]

I would suggest a DOM (drawn over mandrel) tube. They come in various sizes and it would be stronger than you can bend at that length and size

 

[rjmack]

this type of wrench might be the answer... not sure what the name of it is. easy enough to make though.

 

[beppington]

Wow, thanks for all the great info!

The auger has probably 4" of side-to-side play, & even 1" roots or limerock can deflect it out of plumb while drilling, so my dad uses the bar to try to keep it plumb (the bar bends almost every time, but he just flips it over & lets it bend back the other way on the next one). The first set of 50 holes we drilled without the bar required manual post hole digging in just about every hole to get the holes where they needed to be after the auger had gone off line. Since using the bar they're much better; Now most holes just need the loose dirt cleaned out.

I think the first thing I'll do is check Home Depot for a pipe.

I don't understand the "stud" welded to the end of a pipe idea ...?

 

[lucky llama]

Truckers use a whinch bar to stap down loads on flat bed trailers. It is a large pipe with a tappered end. this should fit in the 7/8 hole. you can find them at industrial supply stores and also any truck parts store or online.