legendboy

Just curious if anybody here has any experience with this.

I am doing some work for my uncle. They build high performance filters for the food and beverage industry. Filters to remove ferrous metal. None of the local F&B welders have been able to do it. There is a hutterite that does some, and nice job but he is too busy and can't keep up.

Basically I weld .020 316 wall tubing to flanges and large steel threaded pipe plugs (fun lol), then put rare earth magnets and ss spacers inside the tube and weld a cap on the end. Lightly grind and polish to a shine.

Welding the tubing is fine but welding the stainless plug on the end is HELL!!!

First of all all molten metal; pool and filler being added instantly wants to flow counter clock wise around the pipe, and also torwards the middle. Also, it is extremely hard to establish even a semi stable arc in this enviornment. I have to me about 1-2mm away from the work peice. Then while welding, metal is flying around all over the place! Its really weird. Also the arc and heat from it fly back torwards my fingers lol.

I've managed to come up with something to help absorb some of the imeadite field close to where i'm welding but its still very tedious and frustrating. Also, with rare earth magnets, if you heat them up too much you kill their magnetic strength. So its an all round pita.

Anybody know anything about welding in magnetic fields??

kb58

You pretty much found out for yourself. Even using those 90 deg "welding helpers" will give you the same problem. No, AFAIK there's nothing you can do about it other then move the magnetic field away from your welding...

.RTErnie

a magnetic field affects charged particles...IE electrons. So how does your Tig welder arc to the metal? through electrons. So the path that your arc takes to get to the metal is being DIRECTLY affected by the magnetic field.

the only way would be to put it in a vacuum...but even then I don't think you could strike an arc in a real vacuum.

mopar junkie

would a lack of air pressure effect a magnetic field?

.RTErnie

no.... lack of air pressure wouldn't...but a "vacuum" would lol

BigMoose

Here, have fun guys and learn: http://hyperphysics.phy-astr.g...ml#c1

A magnetic field will always interract with a flow of electrons, whether it is in a vacuum or not. 30 years ago I steered a near relativistic beam of electrons to their target traveling down a vacuum line pumped to 1 x 10-6 torr with a magnetic field. The force on the electrons is B X V X is the vector cross product (right hand rule). Vacuum does not matter.

I have been thinking on your problem, and I don't have an easy solution. The approach would be to create an artifical field to counter the residual field in the part. But the fringes would be horendous, and I don't know how to do it cheaply and still have access.


Modified by BigMoose at 8:58 PM 12/17/2005

beepy

Some ideas:

1) Use friction welding
2) Use oxyacetylene welding
3) Hold the end caps on with high-strength epoxy
4) Thread the cap and pipe instead of welding

k24em2

I was gonna say oxy/acet as well.

.RTErnie

If you're in a true vacuum there are no electrons, just space. If you introduced electrons into the vacuum then yeah...but in an ideal vacuum there should be no electrons. btw I took E&M so I have a "decent" handle on it. Im not debating whether or not a magnetic field will affect the arc through the electrons...just that if we could get an idea vacuum there would be no affect from the magnet...because there are no electrons. Do you understand what Im trying to say? Im not sure if its correct, but do you understand?

rpm11

You're wrong about that, vacuum is no atmosphere, not electrons.
There would be no TV without vacuum tubes, right?

chsbldr

Over the years while welding on steel components when we would get to a corner area we would get the same effect of the feild drawing every which way... try taking a 10 gauge wire, and hook it to the ground of the welder wrap the wire around your tubing piece, several wraps then hook the other end of the wire to your component. make sure to also ground the unit as you would normaly.
We used this trick and it worked quit well.
let me know if you try this and if it worked for you.

.RTErnie

is that a neon cylinder head in your sig? Sure looks like it.

so...in a complete vacuum there is no atmosphere, but there are electrons? that doesn't make any sense...because ANY particle has at least one electron. And if there is no atmosphere...no particles...no nada...no electric fields etc.

Can you explain it a bit better? In technical terms please.

BigMoose

Yep, get it, spot on. Pure vacuum = there is nothing there to effect. Therefore the magnetic field has not effect.

Niles

Perhaps the confusion is coming from studying how the movement of charged particles can create a magnetic field? Consider the practical example that in the vaccuum of deep space, magnetic fields exist. (i.e. motors on satellites work, even without atmosphere) So magnetic fields can cause charged particles to move, and charged particles that move create magnetic fields (look up maxwell's equations if you forgot)

rpm11's example shows that electrons can traverse a vacuum, because they are particles, they have mass, they can be ejected from an electrode and traverse a space to a point of lower potential energy, just like anything else. in this case a voltage applied across a vaccuum from the TV screen to the cathode ray tube causes the electrons to fall down a potential energy step.


Basically in technical terms the only particles relating to the immediate effects of a field would be theoretically propsoed quantum particles which are chargeless and massless (w bosons, mesons, etc) spontaneously ejected from matter to govern interactions we percieve as forces . So really if vacuum could stop a field from existing, the earth would not circle the sun, we would be flung off the surface, chemical bonds would be the only thing that could hold anything together etc etc etc because the vaccuum of space would stop gravity, but that doesn't make sense. obviously.

Cliff note's: Fields aren't made up of particles. They can affect each other, but you don't need one to have the other.

Niles

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BigMoose &raquo;</TD></TR><TR><TD CLASS="quote">Yep, get it, spot on. Pure vacuum = there is nothing there to effect. Therefore the magnetic field has not effect. </TD></TR></TABLE>

I love this guy!
So even if you removed the atmosphere, the field is still there, so when you start throwing electrons around (trying to weld) they will still, unfortunatley, be scattered.

I'm curious to see if that wrapping the ground wire around the pipe trick works, it should do something, but what that is I'm still thinking....

rpm11

Thanks Niles,

For explaining what I was too lazy to type...lol.
I used to operate a 30kW electron beam gun, it was used
to test cooled high energy laser mirrors, could not have thrown
those electrons around without a high vacuum.

Ernie,
That is an SRT-4 head that I ported, that guy just recently became the
first SRT-4 to crack the 500hp level in New Mexico, running a 50 trim.

.RTErnie

Ok I'm confused.

first you say this... " magnetic field will always interract with a flow of electrons, whether it is in a vacuum or not."

then you say "Pure vacuum = there is nothing there to effect"

which is it?

Niles Im not uber concerned about magnetic fields...Im talking about the presence of electrons(particles) in a vacuum. Are there electrons present in a pure vacuum? I say no.

The field may in fact be there, but it's not affecting anything(no particles/electrons etc). Just because its not causing any local effect doesn't mean it doesn't still exist.

So if you remove the atmosphere...you also remove the electrons...and with out electrons you can't strike an arc...or have an "effective" magnetic field. right?!?!? There are particles in space....just much less than here on earth.

Thank you for your patience!
-Eric

Niles

I think you would make a good physicist because you look for the holes in an argument, seriously.

So by example: In an absolute vaccuum there is by definition no pressure. This means no gas. There can still be particles, like dust, but they aren't really important. If they are charged, they will move around in a magnetic field, but there aren't many. Like you said there aren't any gas particles with thier electrons bouncing around. And like you said, even in space there is some garbage out there. (Convienently labeled "space dust")
So you are right in saying that if a space is clean and in absolute vaccuum there are no electrons, particles, or anything, but there can still be a field because of effects outside the chamber. (like from magnets)

Even in a vaccuum however, you can move electrons by creating a high enough voltage between two points (or using photoelectric effects, thermionic emmision, etc etc). For Example when I worked for GE we would put a lamp in a high vaccuum chamber then apply a voltage across the two points of a lamp (basically imagine a wire with a little gap in it). Electrons move because electrons jump from one point to the other through the vaccuum so that they can be at a lower potential energy. The Electrons weren't there, we put them into the vaccuum chamber by applying the voltage across the two points, and allowing the current to flow somewhere. When they start to jump across the gap, that's a flow of electrons and thus electricity with a well defined current and voltage.
What this means is that even in an absolute vaccuum, where you remove all the gas, you can still put just electrons in by playing with the voltage, and giving the electrons somewhere to go! Electricity amazes me. Now if I were to put magnets on the outside of the vaccuum chamber, they would make a magnetic field, and affect the flow of electrons. I also probably would have been fired.
In this thread that means that even if they put the magnet and pipe in a vaccuum, they could still weld it but the magnet would still mess with the electrons. This is because when you strike the arc, all of a sudden you introduce electrons in the area of the magnet, and now the magnet has something to affect, and it happily does.

So the cliff note's version: In a clean absolute vaccuum there is nothing, no particles, no electrons, nothing. There can be a field, because that doesn't depend on particles being there. We can put electrons in by putting a voltage across two points, and giving the electrons somewhere to go. (Like applying voltage from a TIG electrode to the ground clamp/work piece) The surprise is that you can move electrons around in a vaccuum!

For the non scientists out there, voltage refers to how much energy an electron has, amperage refers to how many electrons are flowing.

Does that help? I'm not the best at explaining things, but I bet there's people learning by reading this thread, and more importantly learning critical thinking by reading this discussion.

Also this gets even more fun when you realize that in normal welding the gas (argon/CO2 etc, plays a role in arc starting because you can ionize the gas! (arcing) welcome to the world of Neon lighting)
Speaking of Neons, 500HP? wow nice work.


Modified by Niles at 5:24 AM 12/21/2005

legendboy

Thanks for the replies everybody, seems like this is a fairly complex problem

chsbldr, i will try this and let you know how it works

.RTErnie

I'm an applied physics student at Linfield college...getting a major in math too so thats why I *should* be a physicist lol.

ok thats makes a lot more sense...I had these questions tho.

When you worked for GE did you ever graph the potential difference versus vacuum? focusing on the ability to strike an arc?

And from what I learned in E&M electrons don't actually move when electricity flows, they just transfer the charge. instead of people running sand bags to the dam...they are passing the sand bags from person to person. so how is it that the potential difference will cause these electrons to form a line and then pass the current? Or is this some basic physics principle that I fell asleep during lecture? lol

thank you sooo much! makes tons more sense now.

rjay8604

Hey, this is pretty cool thread i should have looked at sooner. keep talking guys.

DaveF

battle it out

i want to know what wrapping the pipe with a ground wire will do to the puddle/arc. Will the magnentic feild be "contained" within the ground ???

RMF

Have you guys ever been welding into a corner ,Like on a piece of angle and it just won't go in .It just wants to go back the way you came in .Thats called arc spray.And most of the time you can put the ground on the other end and it will weld the other way.Sounds weird but it works.

Niles

Hahaha, This is excellent, it seems we have gained an audience!
I'm not an electrical engineer, so correct me please on anything!

RTErnie:
Applied physics is sweeeet, I have a good friend doing solid state electronics physics something or other, its very interesting.

OK, I'm learning here too, some of the things I said earlier are not absolutley correct. Why? I'm an idiot. moving on....

I'm sure that the electrical engineers have a better understanding of the potential vs. pressure. I can tell you that electrons can happily be ejected and transverse small spaces when given enough energy (its how a TV 'cathode ray tube' works, or the photoelectric effect, or thermionic emmission), I was in fact wrong earlier if I called a smiliar phenomenon arcing, your definition is closer in that "arcing" depends on the pressence of a gas. because arcing is the electrical ionization and de-ionization of a gas.(as in a neon light)

The ability of electrons to move I belive is governed by the dielectric constant of the material the elctrons are moving through, and any physics book should have a table of relative constants for different materials.

The research we were doing was for something similar. The pheonomenon I witnessed would better be described as thermionic emmision, or basically electron ejecting.
Because electrons can flow, or be thrown around in small free spaces, if you can get enough of them to flow, it should heat up whatever they hit and flow through, making it possible to weld, but that might not be entirely practical. (things can get hot though, which is why vaccuum breakers often use carbon points to prevent heat wear)
I do know that electrodes used for this kind of work wear because of microscopic local vaporization and deposition of material, which is why some of this stuff runs on AC waveforms, to prevent one electrode from doing all the wearing out.... I'm not sure of the wear rate however, maybe applied physics journal can help us?

I'm pretty sure that normally the conduction model used follows your understanding, where electrons are not necessarily flowing like cars on a highway but "displacing" one another, or being handed off like you said. The only way atoms can pass along charge is by passing along electrons (or protons, but that won't happen outside of a really wierd particle decay and re-absorbtion and I know I don't have an atom smasher to cause that kind of thing) The net effect is the same though, electrons in one end of a wire, electrons out the other.

I would think that arcing would be made easier in the pressence of large atoms that have a relatively large electron cloud (xenon comes to mind, this could also be one reason why argon works well for welding, the big cloud makes them easier to ionize)

I should edit my earlier post to read that electron movement is possible, but arcing, as we know it is dependant on a gas.

Electrictity scares and confuses me, I'm a mechanical engineer

Dturbocivic:

Wrapping a current carrying wire around a pipe should, based on my understanding, have the following effect:

If you look down a straight length of wire the way you would look through a tube and it is carrying current away from your eye, the movement of current would generate a magnetic field that goes clockwise around the wire. (The Right hand rule). (If you put a compass near a wire that carries alot of current, the needle will move away from north (unless the field points exactly north))
Wires that carry alot of current and run side by side can affect each other through thier magnetic fields, if you've ever seen very high current wires turned on and off, they look like they "jump" or "jerk" around, this isn't from the electrons or anything, but from the magnetic field generated by the current.

Anyway, by wrapping a high current carrying wire (your torch wire or ground clamp) around a pipe, you'll create a field when you stike the arc. On the inside of the pipe, the field is pretty much straight (if the pipe is straight) and follows the axis of the pipe wherever there are windings of current carrying wire.
The outside of the pipe would be more complicated, basically the field would still follow the axis of the pipe wherever there were current carrying wire windings, but the field would point in the opposite direction as the inside of the pipe. (so if you were looking at the pipe from the side, wrapped the whole thing in current carrying wire and the field on the inside carried positive charge to the left, then the field on the outside would send it to the right.)

At the ends of the section where there is current carrying wire wound around the pipe, the field would kind of "diffuse" but its not exactly a neat and predictable effect (at least with the math I have, maybe it is, but I haven't studied it, Kurt knows maybe?)
If you change the direction you wind the wire, you change the direction of the field (ie what was right to left inside the pipe becomes left to right if you reverse the direction of the winding)
The more wire you wrap around in a small space the stronger and more uniform the field will be.
(this is the principle behind the operation of soleniods btw, like starter soleniods, fuel injectors, etc etc)

So in conclusion I talk too much, and I'm still not sure how the magnet is set up on the pipe to be welded, but because you don't really want ot have your torch wire or ground wire too close to your hot metal I'm not sure this would work safely, the possibility of accidentally welding into or melting a high current wire scares me.

Sorry for the long post, I got back from working super late and just started typing, have a good night everyone!

Cliffs: "arcing" is the ionization of a gas, electrons can be moved about in vaccuums or in air etc, wrapping a pipe with a current carrying wire will create a magnetic field (well defined inside the coils, hazy outside that area)

DaveF

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Niles &raquo;</TD></TR><TR><TD CLASS="quote">Hahaha, This is excellent, it seems we have gained an audience!
I'm not an electrical engineer, so correct me please on anything!
</TD></TR></TABLE>

thanks for answering my previous question. school is amazing(just wish i woulda had more motivation to stay in school) you sir have my respect, as well as anyone else on here that is going to school.