Electrical conductive graphite & copper

Hello Guest,

"<As the , then hoe come it is used in heaters ? Graphite electrodes are used to heat the crucibles & copper heaters used for water heating ?">

<"Graphite & copper are the best electrical conductive materials"> = Untrue, because at room temperatures, Silver is the best Conductor.

Because graphite is not a perfect conductor (it has Resistance), and it becomes heated when electrical current passes through it.

Graphite is manufactured to varying specifications, for use in large electrical heating applications, such as metal smelting crucibles (aluminium, steel etc), because it is cheap.

Read about the relationship here: http://amasci.com/elect/vwatt1.html

Kind Regards....

Another primary application of graphite electrodes is non-sparking contacts; such as motor brushes, load-break contacts, etc. because the graphite does not spark or pit in those applications.

Hello Bluestone

<"the graphite does not spark or pit in those applications.">

Surely you jest

Kind Regards....

Surely I do. What I was trying to say is that graphite electrodes are less affected by sparking because it doesn't pit or erode as readily as other conductors. It also imparts some lubricity to sliding contacts.

We use graphite electrodes to create sparks!!!

One of the most interesting and educational aspects of this forum are the responses of people from around the globe with different backgrounds, experience, and interests. This is a classic case. I'm a graduate EE who has spent a lifetime in electrical product design, testing, applications, etc. so when I see a title like this, I immediately think of graphite electrodes in electrical apparatus; not high temperature arc furnaces and crucibles.

Obviously, I need to expand my thinking.

Thanks for taking the time to correct me.

I was being a little 'tongue in cheek' in the context of this post, what we do is to use a graphite electrode to create a spark gap in vacuum to sputter graphite on to an aluminium coated phosphor layer. This gives us an anti-reflective coating.

Re: Electrical conductive graphite & copper

In response to Bluestone:

Truth telling time.

Truth be to say that I have said here on at least one occasion I attended Brooklyn Technical H.S. in N.Y.C. The measure and quality of that school is that although I did not graduate, due to an impossible home life, the nature of that pre-engineering high school was such that all my life, a good part of it as a printer or an industrial maintenance tech, I have drawn on what I learned there from the git-go.

Consider! Entering freshman encounter straight off courses in chemistry and Industrial Processes. Whilst in chemistry we are reducing iron oxide in a test tube, in Industrial Processes we are studying the extraction of iron ore, in all its various forms from iron oxide to magnetite, its transportation to the steel mill, and there the various parts of that process, manufacture of coke from coal, mixture of ore, coke, and lime in the blast furnace, etc.

We knew intimately the parts of that furnace so that years later I could see the remaining carcass of such a mill in Birmingham, Alabama, and point out not just the furnace sections but as well the soaking pits (For those not knowledgeable, heat soaking of the iron billet product of the furnace to relieve and equalize internal stresses prior to rolling), the coke ovens and so on.

But that wasn't all. Simultaneously we were learning to operate metal lathes, milling machines, drill presses, etc.

As if that wasn't enough we were making wooden patterns, green sand molds from the patterns in the foundry, and casting them in iron from the cupola furnace which was one of the three, the other two being a resistance furnace and an arc furnace, i.e., furnaces using carbon rod electrodes.

And that was not an industrial arts school but rather a full pre-engineering school with math, language, physics, etc., and the city's WNYE studio and FM transmitter and tower on the roof.

Pity is they have dropped the industrial aspects in favor of digital stuff rather than do what they should have done, i.e., add it in so that students would leave with the full scope.

Years later, installing central office switching equipment, it became clear that the engineers designing the stuff had never actually worked in a switch room. If you work on your own cars, the newer transverse engine ones in particular, you know that whilst the engineers crammed all that stuff under the hood they never had to do repairs on it.

So Bluestone, although I could go on in this vein, I am curious; no offense meant or intended. How much of the stuff I just mentioned are you familiar with. It is a serious mistake, even if basic manufacturing and production have fled this country for cheaper labor, when everybody, not just engineers, are not intimately familiar with this stuff. Believe it or not it has a cumulative cognitive effect that goes way beyond just industry because its product is all around us, a part of our everyday lives.

Besides which, it makes for much more interesting conversation than most of the silly stuff most people talk about.

j.

J:

Truth-telling time. I'm familiar with most of it (including Sloss Furnaces in Birmingham, AL, which still offers iron and bronze casting workshops, by the way).

I take your point. Lots of times, I'll answer a question, using my personal experience to interpret the question, and it'll turn out the poster had something else in mind. Oh well, being wrong toughens me up for the Pirates' inevitable head-long dash into the cellar.

Do you really use copper heaters for water? How long do they last? Have you tried nichrome?

Hi all,

Some clarifications if you allow me: (Otherwise you can score "off politeness")

Both graphite and copper can be used for electrical and thermal uses. The main difference are that they have quite different electrical resistivity and thermal conductivity.

Graphite has (at room temperature) about 25% of thermal conductivity of pure copper and about 1000 times the resistivity of copper (100% IACS).

So, copper is best thermal conductor and much better electrical conductor than graphite.

The problem with crucibles is that you need to produce heat by passing a current through an electrode and get very high temperatures. In electric furnaces used to melt metals, graphite electrodes burn and you need to feed them more or less continuously. The result of heating graphite at electric arc temperatures is producing CO₂ which usually doesn't contaminate the metal as it goes with fumes, but you cannot use copper electrodes because it can melt and form undesired alloys or intermetallic compounds with the main melted metal, affecting the quality of product.

And without taking into consideration power consumption: due to the great difference in resistivity, power needed is more or less proportional to V²/R, so as greater the resistance, the lower voltage needed.

Cheers

As has been said, graphite electrodes are used in arc and resistance furnaces for melting metals, one reason is the carbon vaporizes and goes off as a gas.

But, it took a second read to see you were not asserting carbon rod is used in water heaters. Rather you are talking about copper.

I suspect you don't realize the copper tube coils you see in water heaters are not themselves the current carriers that do the heating.

Inside those tubes there is a nichrome wire which is the current carrier and is insulated from the copper tube, usually with ceramic beads. It would be possible to heat water by directly immersing a nichrome wire in the water but then if would, and this I suspect is the reason underlying at least the water heater part of your question, conduct electricity into the water putting at risk anybody using the water or touching any part of the often connecting metal piping.

That does not take place in water heaters because the beads that support the nichrome in the center of the copper tube are insulators as is the sealing material at the ends of the tubing where the nichrome get connected to the electricity supply.

j.

Thanks Jack.

Rating to your answer no. 1

I need to check my water heater.