Spark Testing?

[Hulagrub]

Have been lurking and reading posts, I think I know what spark testing is, but could someone elaborate for me.
All I have heard is that the smaller the spark the more carbon. Is this true? And what exactly does this tell you?
Thanks, Dave

[RustyLaidlaw]

Hi Dave!
I use spark testing to help get a general idea, and I'm stressing general, of what grade of steel I'm working with. The spark test doesn't tell you anything specific, but can give you a good basic bit of information to go forward with. All spark testing tells you is carbon content, and can be figured as four groups:

1. Wrought Iron
2. Mild Steel
3. Medium Carbon Steel
4. High Carbon steel
Any more information than that warrants a metallurgical analysis in a lab.

I use an aluminum oxide wheel, 6 inch on a 1/4 hp motor spinning roughly 1750 rpm. This is important because sparks look different depending on what you're grinding with.

To start, you'd do best to have a control piece of steel to compare results. I use a piece of known 1018 (low carbon), and 4140 (medium carbon).

Wrought iron is almost no carbon and gives off all straight streaks with no bursts, typically.

Low carbon is "mild steel" and gives off straight-looking streaks with bright tips and a couple bursting sparks.

Medium carbon is more active with much longer streaks and lots of bursting sparklers forking off the main sparks. See the attached pic Sparks 1. That was done on a 1" belt grinder but you can see the streaks and forking.

High Carbon is just beautiful bright fizzly sparks with no streaks. The pic Sparks 2 shows this pretty good.

Aside from that, if you ever grind high speed steel you'll see very little streaks of a kinda dull orange color. It's hard stuff, and usually only in smaller bits for lathes and other machine tooling so it should be obvious if you ever run across any.
Hope that helps!
- Rusty

[Hulagrub]

Thank you Rusty.

[Ted T]

I second that! "Thank You Rusty"
That was the most simple, shortest and most informative explaination I have heard.
I have written many pages about the subject!
I wish you would have been here sooner! :)

[ianinsa]

Rusty,
A+ on that answer!
Ian

[Frank Turley]

Good show, Rusty. I might add that one should not press hard on the wheel. A light touch will be easier to read.

http://www.turleyforge.com Granddaddy of Blacksmith Schools

[RustyLaidlaw]

Thanks for the responses guys, I'm glad to help. The wife says I should write a book. I love teaching and helping folk out, so I appreciate your encouragement. Especially from someone like you Mr. Turley!
Thanks again.
- Rusty

[Jeff Seelye]

Sparks are very interesting indeed. It is cool to check out the different sparks from different metals. Always looking for the 1. color of the spark 2. The length of the streamer and the burst at the end. For instance,Titanium has a white spark, short bursts. Niobium has a white spark. Cast Iron has very dark red sparks best seen in very dim light and medium length streamers. If you want to compare different metals it is good to have an assortment of alloy steels to compare them to. The longer the length,and fewer bursts, the lower the carbon content . It takes years of practice to identify alloy steels.It is an art all in itself The above explanation was awesome.

[Marksnagel]

Thanks Rusty!

I have found some new (to me) scrap and never worried about spark testing before. I always felt it was something the rocket surgeon smiths did and not little ole me.

Now to test the steel.

Thanks again,
Mark<><

[Ten Hammers]

" It takes years of practice to identify alloy steels.It is an art all in itself "

I live near a Deere plant. I am told by old retired folks that in years past men would climb railcars full of steel with a shadowbox and hand held grinders to spark test. Yes after random samples full cars were rejected on occasion. I have no idea what goes on today although one of my son-in laws welds there. I witnessed a man doing a spark test in his garage ( he was the (retired) plant metallurgist and I took him some samples ) on a bench grinder. He has since passed away. His skills were awesome and I sincerely miss his knowledge. This area is really a tech area that needs a good teacher in my thinking. The above posted suggestions about what to look for are great, thanks. Franks suggestion about pressure is I think the most important along with controlled light. I should add that if I have a specific need I try and get a specific pedigree steel ( known alloy ). Read h-13 or s-7 as examples. Otherwise, sucker rod or med to high carbon steel are my choices when using scrap. The chopsaw will give me a fair indication on spark testing but I have never really developed the skill. Try common manurealloy steel, some leaf spring, some PTO shafting, a piece of grey iron casting and some known wrought iron as controls for just messin around.

[MOONY]

hi all
spark test is a very simple way to tell if the steel is a low carbon steel or higher carbons , but if you have samples of steels you know exactly what they are, you can get a accurate test , by testing the known piece against the unknown piece , it is best done with a lite press on the wheel and in a darken area , i have used this method of testing now from when i was shown how to do it in my training an a kid smith
keep up the interest
moony

[ThomasPowers]

Well simple steels, you can't tell much from the high alloy things as you can get HSS that is over 1.5% C but sparks like cast iron...