Joules to Degrees

Date 04-14-2004 22:29

Like you said, joules are an energy input, but they do not "directly" relate to temperature. For instance, it takes so many joules to boil 1 gallon of water. This is because of the specific heat of the material (for instance, I see for 1020 steel, specific heat is about .5 Joules per gram per degree Celcius), so, to raise 1 gram of steel 1 degree C, it takes a half a joule. Two grams up 1 degree C or 1 gram up 2 degrees C takes 1 joule, ect. All specific heats are characteristic of each material, and all are most likely very different. This, however, considers that all parts of the system are isolated and the energy that is being imputed is going to and staying exactly where it is intended, and why I said joules don't exactly relate to temperature directly. Energy moved from one place to another is never fully accounted for in the end product due to losses, sinks, ect.

This is where the issues of power and efficiency come in but i wont elaborate unless necessary. Hope that helps!

G. L.

By OSUtigger (**)

Date 04-14-2004 22:42

Sorry, also was gonna say that the specific heat of materials is not constant either...the .5 j/g-C stated earlier is for somewhere in between 50 and 100 C, but above that temperature, it bumps up to .52 j/g-C until 200C, and then it jumps again. I'm not positive that steels have significant latent heats when they melt, but it would make sense if they did- latent heat is the little bit of extra energy it takes to change the phase of the material. Ice and water can both coexist at 0 degrees C because of this concept. I don't think that these two things were what you were asking, but another tricky little concept that'll screw any of your numbers up if you are actually trying to calculate something.

By MBSims

Date 04-14-2004 23:14

Other units of energy that can be converted to joules are calories or Btu. 1 Btu = 1055.056 joules, or 1 cal = 4.184 joules. The joule is a measure of work and can be defined as force times distance, or in metric terms 1 joule = 1 newton x 1 meter (or 1 newton-meter).

By jwright650 (*****)

Date 04-14-2004 23:37

Hi Brian,
There are lots of conversions and I had this chart filed away, check it out.
http://www.simetric.co.uk/si_hij.htm#juliet
John Wright

By G.S.Crisi (****)

Date 04-15-2004 00:20

After all of the excellent replies that have been posted before this one, all I can say is that converting joules to degrees Celsius is the same thing than trying to convert BTU to degrees Farenheit, i.e., an impossible thing, because joule (and BTU) is a unit of energy and degree Celsius (or Farenheit) is a unit of temperature.
Giovanni S. Crisi
Sao Paulo - Brazil

By bmaas1

Date 04-15-2004 05:00

Ok,
Given all the responses I am trying to understand the relationship of heat input to temperature if there is one.

Example:

On a welding job the wps calls for a maximum heat input per inch of weld, amps x volts x 60 divided by travel speed = joules/inch of weld. With this said can I somehow determine approximately what the interpass temp will be on any given material? Or would this just be trial and error?

Brian J. Maas

By Tim Buyle (**)

Date 04-15-2004 08:30

To determine the interpass temperature, you can not base upon the max. heat input. It depends on the type of steel. Each type of steel has different metallurgical properties due to cooling effcts, resulting in possible different material structures for the same base material.
example : carbon steels can become brittle after welding by cooling to fast : the microstructure can contain brittle martensite, etc.

For almost every type of steel, the manufacturer has a CCT or TTT diagram, in wich the effect of cooling rates can be studied. Based on critical temperatures ("Ms" for martensite formation, ...) you can determine the max. interpass temperature. Steel manufacturers do also indicate interpass temperatures for special steels, based on their experience.

Conclusion : when welding with the same heat input, but different interpas temperatures, you can influence the microstructure of the steel, resulting in different mechanical properties (impact, hardness, ...)

By OSUtigger (**)

Date 04-15-2004 16:57

In short, yes, you could get a good estimate of interpass temps, but you might as well begin on the drawings for a new type of space shuttle, because it is going to be more in depth that that. Different coefficients of heat transfer, surface areas, shapes and too many other things would make just estimating this more rocket science than curiosity. It would be easier to just use a thermometer...

G. L.

By Niekie3 (***)

Date 04-19-2004 20:48

Hi Brian

This is a complicated subject to understand in detail, but let me give it a go. (Maybe I am misunderstanding your question. If so, let me know.)

The term heat input, as used in welding, is a "handy" way of describing how much energy (basically in the form of heat) is entering your weldment for any given length of weld. (In the metricated world we would look at Joules (or kilojoules) per mm. In the imperial world, people generally work with joules per inch or BTU per inch.)

Given that a certain amount of energy is transferred into the weldment, we could theoretically calculate the temperature that the entire weldment would reach after each weld. On a small regularly shaped weldment, this would not be too difficult, but on a complex shaped and large weldment this becomes a very big problem. Keep in mind that not all the energy stays in the weldment. Some is constantly being lost to the surrounding air. It also takes time for the energy to be conducted away from the weld area to the adjacent cold base metal.

The use of the "heat input" is therefore not really to calculate interpass temperatures or anything simmilar. Rather, it is used to get a feeling of how rapidly a weld will cool down and how wide the HAZ will be. The higher the heat input, the slower the cooling and the wider the HAZ.

All-in-all, energy input would be a better term than heat input!

Hope this helps.

Regards
Niekie Jooste
Fabristruct Solutions

By Lawrence (*****)

Date 04-15-2004 11:36

So, let me see if I have this right.

A calorie is a specific measurement of temperature.

So if I keep my twinkies in the freezer they will be free of calories and as long as I scarf em while they are cold I won't get any fatter?

By CHGuilford (****)

Date 04-15-2004 13:26

Gee, Lawrence! Why don't you test that out and report back to us on your findings?
But be careful! All that sugar hitting your bloodstream........
Sorry, I couldn't resist. I appreciated your joke.
Chet

By jwright650 (*****)

Date 04-15-2004 17:04

That's the whole idea L, eat em' fast!
John Wright:)

By G.S.Crisi (****)

Date 04-15-2004 19:07

To answer your first doubt, no, Lawrence, a calorie is a unit of HEAT, not TEMPERATURE. The unit of temperature is degrees Celsius in old metric units and degreees Farenheit in Imperial units.
The unit "calorie" has been banned from the new metric system (SI system of units) and replaced by the Joule. 1 kilocalorie = 4,13 joules.
Regarding the second doubt, I can't answer it. It's written in such a terrific slang that I don't understand a word of it.
Giovanni S. Crisi

By Lawrence (*****)

Date 04-15-2004 19:35

Prof. Crisi

Thank you for the correction. I was too busy thinking about the twinkies to be bothered with accuracy.

Up north here "terrific" is generally used to describe something well done. So thank you.

Let me try to interpret the slang for you.

"Twinkie" is a fattening snack with 150 calories and 5 grams of fat. Here is a link that describes just how far we Americans are willing to be influenced by snack food
http://www.snopes.com/legal/twinkie.htm

So the joke goes; If you put high calorie food in the refrigerator you bypass the calories.

This is a tough room!

By jwright650 (*****)

Date 04-15-2004 20:52

L,
You should also note, "this is a tough room" is a comedian's slang for a hard audiance to get a laugh out of. Where do you find all these off the wall links? Don't get me wrong, I enjoy them, keep them coming.:)
John Wright

By bmaas1

Date 04-15-2004 23:30

Don't think I'm crazy but I am just trying to understand how it relates to welding not being an engineer myself.

Brian J. Maas

By jwright650 (*****)

Date 04-16-2004 10:47

Brian,
I'm not certain I fully understand it and how it should be applied either. You know, there are lots of "units" that I don't have any clue how or why they are used. They show up in formulas and they get used, but many can't be converted and have to be used as they are. I suppose, that joules fit into that category to some extent. Did you check out that conversion chart I supplied a link to earlier? If you did, you will quickly realize just how many "units" there are and that some of them relate to each other and some don't.
John Wright

By G.S.Crisi (****)

Date 04-15-2004 23:37

OK, since "terrific" means "excellent" up north, I'll correct the phrase and write "horrible slang" instead of "terrific".
John Wright, you're from Virginia, is that also the meaning of terrific down in Dixie?
I wish I was in Dixie, hurra! hurra!
Away, away, away on south in Dixie!
Giovanni S. Crisi

By jwright650 (*****)

Date 04-16-2004 10:39

Hi Giovanni,
I would have to say that the word "terrific" can mean "excellent" if you used it in this fashion...
"That is an "excellent" way of describing the word "terrific", or "That is a "terrific" way of describing the word "excellent".

I'm certainly not the one to ask to critique the use of the English language. I make a mess more often than not of English grammer, and I'm sure my ignorance lets me use it in ways that it was never intended for it to be used. However, at this point I'm not going to get into any North/South issues. Some may still carry a chip on their shoulder about Northerners or Southerners, so I'll dodge that one. I was born and raised in Virginia, and it happens to be below the Mason-Dixon line that was distinguished several years ago to seperate the country in a civil war.

And ever since I read your post, I can't get that little tune you started (one that we were taught as children) out of my head.
...Do da, Do da. I will be singing that all day now! :)
John Wright

Sorry Brian, we have strayed way off of the course you were on.

By CHGuilford (****)

Date 04-16-2004 13:06

John, the antidote to having that song running around on your head all day is to replace it with "Yankee Doodle Dandy". Just thought I'd help.
Chet

By jwright650 (*****)

Date 04-16-2004 15:30

Here you go Chet, I don't want to be the only one singing today.

http://my.homewithgod.com/heavenlymidis/USA/dixie.html

http://my.homewithgod.com/heavenlymidis/USA/yankee.html

John Wright

By ssbn727 (*****)

Date 04-16-2004 20:59

Hi Giovanni!
Over here in THE UNITED STATES of AMERICA, there is an evolutionary process that's ongoing as far as the language we speak... Sort of like a work in progress. Contrary to what the rest of the world may think, we DO NOT speak the same type of english that the english do. In fact, I believe we speak an AMERICAN form of english with a variety of dialects much like the english themselves only alot different and with alot more variety... There are many reasons for the differences as I'm sure you're aware of so, I wo'nt go into them...

I must say to you that it sure is enlightening and refreshing to hear from someone that lives outside of this country regarding the use of "slang" in the way we americans communicate with each other...

I hope that we are'nt unique in that aspect because if that were the case, the rest of the world would be too predictable and we would'nt have a problem communicating with each other or worse, not having to disseminate the slang used in a variety of languages would probably discourage more people in their desire to learn more about the different cultures that exist in countries that are known to use similar languages.
(approaching CRUSH DEPTH!!!) I'll stop here before I get too confusing!!!

One thing that fascinates me is the fact that when it comes to mathematics, engineering & sciences, we all strive very much to speak the same language. Thank goodness for that!!!

Respectfully,
SSBN727 Run Silent... Run Deep (but not too deep)!!!!