Cad Welding..how done?
TJS
works. Is it a chemical thing? I see the term "shots" used, is there a
explosive thing to drive the conductors together?
I'm sure others reading the NG are curious too
Anybody
Tim KF8XW
Louis Bybee
made out of a carbon or graphite (I'm not sure) composite material, over
the wires, ground rod, building steel, or combinations of the previous.
Depending on the age or tightness of the mold around the components, a
sealing putty is often used. The mold is then filled with a "shot", a
combination of a gunpowder type material, and metallic powder. Lighting
the shot causes the gunpowder to ignite, heating the components to be
joined, and melting the metal powder allowing it to flow around the
components to be joined.
The above process is an expedient way to field join grounding components
in a manor similar to hard soldering (brazing).
It is not a difficult process to learn. The shots are somewhat
expensive, and the molds are VERY expensive. There are some safety
procedures that MUST be followed, such as insuring NO moisture is inside
the area where the shot will be active. Can you say flaming, molten
material on everyone within ten feet!
Louis
Barry L. Ornitz
described the process but got the chemistry wrong. The reaction looks like
ignited gunpowder, but is entirely different.
CADWeld is basically copper thermite - a mixture of copper oxide and
aluminum powder. Once ignited, the two react to reduce the copper oxide to
metallic copper and oxidize the aluminum to its oxide. The process is
quite exothermic (liberates lots of heat) and the metallic copper that is
produced is white hot. This flows to the bottom of the mold and slightly
alloys with the metal being connected. The bond is somewhat like brazing,
but since it is done at a much higher temperature, more alloying of the
base metal occurs. It is an exceptionally effective bond for grounding and
power connections. [Iron thermite, made with iron oxide and aluminum is
often used to weld railroad rails. It takes a huge acetylene torch or a
big arc welder to produce this much heat.]
I am surprised that a CADWeld joint could be a significant source of
intermodulation distortion if the joint is prepared properly. There are
some intermetallic species produced such as aluminum, iron, carbon and
silicon alloys - especially if the joint is not cleaned before "firing".
These could certainly have nonlinear voltage/current curves. I would think
that these could be minimized by carefully controlling the CADWeld process,
however.
But I am even more surprised that mechanical bolted stainless steel
hardware is suggested as the replacement. From a chemical corrosion
standpoint, connecting copper and steel together mechanically - even with
stainless in between, is asking for corrosion. In fact, stainless steel
can be both anodic and cathodic to ITSELF. This means that a single piece
of stainless can act as a galvanic battery and promote its own corrosion.
Dr. Barry L. Ornitz WA4VZQ orn...@dpnet.net
KQ6UV
Cadweld makes a variety of reusable graphite molds for different situations.
One shot molds are also available. After clamping the mold to the conductors
to be welded, you pour a powdered weld metal into the crucible. There's an
explosive powder that is sprinkled on top of the metal, and in the mold
opening. Once this is done, and the mold is closed, and you use a flint
igniter to set it off. It quickly gets hot enough to weld everything
together.
Jim Smith, KQ6UV
TJS wrote in message <367E71...@mk.com>...
Gray Frierson Haertig
could be significant IM gemerators. Remember, you can have all the
dirty oxide infected joints you want around and none will generate any
IM until there is an AC voltage across whatever is acting like a
semiconductor. Any oxide inclusions in a CADWELD joint are imbedded
inside or along side massive amounts of highly conducting copper. Hard
to develop a voltage across anything with all that copper.
Some ferromagnetic materials, such as nickel, can produce IM. This is
why current practice calls for the elimination of nickel plated
connectors in or near sensitive receive operations.
Remember also, even if there were an intermod generator built into a
CADWELD joint, in order to generate much intermod, you have to have
significant current flowing through the joint. Certainly in VHF and UHF
installations where there is very little RF current flowing in building
ground systems, any IM generated is going to be very low, and far away
from the antennas. Since at these frequencies, building grounds are not
part of the antenna circuit, there is no path into the receiver except
via radiation and pick-up by the antennas.
I have seen it asserted here that there is a problem with CADWELD, but I
haven't seen any citations as to where one can find out how this was
determined and what kind of levels are being generated. Until I see
some fairly conlusive research as to the inadvisability of using CADWELD
connections in communications sites ground systems, I will continue to
spec them for my clients. I KNOW and have seen what poor pressuure
connections can do trying to conduct a big lightning hit, and its
consequences are far worse than the level of intermod that is likely
being generated by CADWELD.
Gray
--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
g...@haertig.com
DMartin560
Cadweld is the manufacturers trade name for exothermic weld connections.
These connections are superior to any known mechanical or pressure type surface
to surface contact connector. Because of it's molecular bond, the welded
connection will not loosen or corrode, even in the harshest conditions.
The connection is preformed by clamping a mold similar to a ceramic craft-type
two-piece mold to the top of the ground rod. Holes in the side of the mold
accept the ground wire which is in contact with the top of the rod. A two-part
weld metal (the "shot") is then poured into the top of the mold and ignited
with a flint igniter. The reaction heats to 4000 degrees and welds the wire to
the rod.
There are many molds for many different applications: 1,2 and 3 wires to rod;
to vertical pipe, bar, etc.
The molds are about $80. The clamp handle is about $75. The molds last for
about 50 welds then you buy new ones. The shots range $3 - $8 ea.
There is also a "mini mold" which is a disposable mold and weld metal kit
called a "One-Shot". These work very well, they are about $6 each and are just
for wire to top of rod.
This system of ground connections is the industry standard for communications
facilities.
Cadweld products can be obtained at commercial/industrial electrical supply
houses.
Info might be obtained by searching the web for "Cadweld", I don't know if they
have a web site.
Hope this was informative,
Dwayne
N GA
TJS
>
> I agree with you, Barry. It seems unlikely that CADWELD connections
> could be significant IM gemerators. Remember, you can have all the
> dirty oxide infected joints you want around and none will generate any
> IM until there is an AC voltage across whatever is acting like a
> semiconductor. Any oxide inclusions in a CADWELD joint are imbedded
> inside or along side massive amounts of highly conducting copper. Hard
> to develop a voltage across anything with all that copper.
>
Thanks very much to the fine group of responders. I found this very
informative.
I had little idea that this was done. The idea of an exothermic chemical
reaction
I think is not well grasped by most non-engineer persons. Its hard to
conceive the
great release of chemical energy that results from placing a couple
different
powders in a chamber and adding a little heat to touch it off. Even more
unbelievable
is the idea of welding a railroad rail by this method...I'd like to see
that!
Thanks
Tim KF8XW
Barry L. Ornitz
Just one correction, Jim.
CADWeld is not a mixture of metals. It is copper OXIDE and aluminum.
Likewise iron thermite is either red or black iron OXIDE and aluminum. The
reaction takes place when the aluminum strips the oxygen from the less
reactive metal to oxidize itself.
There are exothermic alloying reactions between pure metals, however.
Aluminum/palladium is one such reaction that is of commercial use. A
co-extruded wire of the one metal clad over the other is manufactured by
Pyrofuze corporation. It is used in a number of special purpose aerospace
applications and in some ordnance. Once heated to the alloying
temperature, the reaction continues on its own liberating large quantities
of heat, but no gases.
Barry WA4VZQ orn...@dpnet.net
N2EY wrote in message <19981222203726...@ngol03.aol.com>...
>What's even more amazing is that the powders are not explosives or highly
>flammable, but merely finely ground metals.
N2EY
>Subject: Re: Cad Welding..how done?
>From: "Barry L. Ornitz" <orn...@dpnet.net>
>Date: Mon, 21 Dec 1998 22:12:17 -0500
wrote:
>Tim Shearer asked how CADWelding was done. Louis Bybee physically
>described the process but got the chemistry wrong. The reaction looks like
>ignited gunpowder, but is entirely different.
>CADWeld is basically copper thermite - a mixture of copper oxide and
>aluminum powder. Once ignited, the two react to reduce the copper oxide to
>metallic copper and oxidize the aluminum to its oxide. The process is
>quite exothermic (liberates lots of heat) and the metallic copper that is
>produced is white hot. This flows to the bottom of the mold and slightly
>alloys with the metal being connected. The bond is somewhat like brazing,
>but since it is done at a much higher temperature, more alloying of the
>base metal occurs. It is an exceptionally effective bond for grounding and
>power connections.
Hello Barry,
That's exactly what I learned. The igniting powder is usually magnesium.
Several companies make kits that are designed for this purpose. Some use
reusable mold assemblies, while others use one-time molds. For example, Erico
makes a "One-Shot" kit that is meant for cadwelding #6 or larger ground wires
to the end of a ground rod.
Successful cadwelding requires several factors. First, the surfaces to be
welded must be shiny and clean - this is usally done by grinding and
sandpapering. Second, everything must be kept absolutely dry - wet powder
either wont work, or will explode violently when the water boils. Third,
protective clothing and eyewear is mandatory, and fire prevention must always
be considered. Fourth, the correct molds and charges must be used.
> [Iron thermite, made with iron oxide and aluminum is
>often used to weld railroad rails.
Most railroad field welds are made this way. (Rail is supplied in sections
about a quarter mile long, and the sections welded using the thermite method.)
Shop welds are done by special electric welders that pass truly amazing
currents through the rail joint. Either method produces a joint that is as
strong as the rail itself, if done properly.
> It takes a huge acetylene torch or a
>big arc welder to produce this much heat.]
Acetylene and electric welding is used by rail workers mostly for cutting rails
and building up worn spots in frogs.
Cadwelding (on a much smaller scale) is also used to attach wires to the rails
for signaling purposes.
73 de Jim, N2EY
N2EY
>Subject: Re: Cad Welding..how done?
>Date: Tue, 22 Dec 1998 12:22:54 -0500
wrote:
>Thanks very much to the fine group of responders. I found this very
>informative.
>I had little idea that this was done. The idea of an exothermic chemical
>reaction
>I think is not well grasped by most non-engineer persons. Its hard to
>conceive the
>great release of chemical energy that results from placing a couple
>different
>powders in a chamber and adding a little heat to touch it off.
Hello Tim,
What's even more amazing is that the powders are not explosives or highly
flammable, but merely finely ground metals. It seems unbelievable that a
mixture of powdered iron and powdered aluminum will burn - until you see it.
> Even more
>unbelievable
>is the idea of welding a railroad rail by this method...I'd like to see
>that!
It is truly spectacular - particularly at night. Fireworks seem quite dull
afterwards.
The molds are clamped to the rail, and the "crucible" (shaped like a funnel) is
attached to the top. The crucible has a hole in the bottom, and is filled with
the aluminum/steel mixture, then topped with a little magnesium powder. The
whole thing is ignited, and becomes white hot. There is a metal plug in the
bottom of the crucible that melts when the correct temperature is reached, and
the weld metal flows into the gap between the rail ends. After things cool
down, the molds and crucible are removed and reused. Cheaper, stronger and
safer than using bolted joints.
73 de Jim, N2EY
n2...@aol.com
"Barry L. Ornitz" <orn...@dpnet.net> wrote:
>
> Just one correction, Jim.
>
> CADWeld is not a mixture of metals. It is copper OXIDE and aluminum.
> Likewise iron thermite is either red or black iron OXIDE and aluminum. The
> reaction takes place when the aluminum strips the oxygen from the less
> reactive metal to oxidize itself.
Hello Barry,
Thanks for the clarification! I was under the mistaken impression that all of
the oxygen in the reaction came from the surrounding air.
>
> There are exothermic alloying reactions between pure metals, however.
> Aluminum/palladium is one such reaction that is of commercial use. A
> co-extruded wire of the one metal clad over the other is manufactured by
> Pyrofuze corporation. It is used in a number of special purpose aerospace
> applications and in some ordnance. Once heated to the alloying
> temperature, the reaction continues on its own liberating large quantities
> of heat, but no gases.
Neat! What surprises most people, I think, is the idea of ordinary metals
suddenly "burning" at extremely high temperatures in such simple setups as a
CADweld bonding mold. (You dump this powder that is just ground-up metals and
metal oxides into a mold, shoot a couple of sparks from a flint/steel igniter
at it, and you get white hot molten metal in a matter of seconds.
>
> Barry WA4VZQ orn...@dpnet.net
>
> N2EY wrote in message <19981222203726...@ngol03.aol.com>...
> >What's even more amazing is that the powders are not explosives or highly
> >flammable, but merely finely ground metals.
>
Thanks again,
73 de Jim, N2EY
-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Tom McDermott
reaction.
The temperature required to start the exothermic rection is quite high - and it
takes something
like magnesium burning to create enough heat to start the process. In high-school
chemistry
we would use a magnesium strip to start an iron-oxide/aluminum THERMITE reaction.
Thermite
was the main component used in WW2-era incendiary bombs. It is most impressive in
that
white-hot iron can be produced by the reaction.
If you attend a telephony trade-show (such as Supercom) there is almost always a
company
or two present that markets CAD-weld products for telephone central-office
grounding. Look
for those shows that market to outside-plant engineering for the telephone
operators. Normally the
people at the trade show booth will be happy to demonstrate the CAD welding process
to you
right then and there - either via videotape, or a couple of times a day via a live
demo. Well
worth your time to watch - I've seen it live, and the process is very dramatic and
entertaining.
CAD welding produces an extremely low resistance ground that is primarily designed
for
lightning protection. The advantage of CAD-welding is that the ground connection
is not likely
to fail after a lightning strike. Other types of ground connection can fail after
a 'hit', soldering being
exactly one of those connections that is prone to failure. The heat produced by the
first 'hit' causes
thermal expansion of the joint, leaving a much higher-resistance connection. A
subsequent 'hit' encounters
a higher-resistance connection which dissipates a catastrophic amount of energy in
the high resistance.
Solid mechanical connections are the only NEC-allowed grounding connections.
CAD-welding usually
produces a joint that is much less likely to fail than the interconnecting
grounding conductor(s).
Of course it requires that proper design for the ground system be performed first,
this consisting of
eliminating all ground loops, and bringing all grounds through the ground-window
that is less than
meter in diameter. CAD welding is used to assure the proper connections whose
resistance should
not degrade with time.
Bellcore has produced good documentation on the theory of grounding telephone
central offices and the
concept of the ground window. It relates the inductance of the steel members in a
building to the voltage
expected to be generated across any given amount of inductance. Recall that
lightening is, for all practical
purposes, a current source of 10,000 to 100,000 amperes with about a 200 Khz
frequency copmponent.
The voltage induced across an inductance is L di/dt. So the physical dimensions of
the grounding member
determine both it's inductance and thus the voltage dropped. If all grounds within
the central office pass
through the same 1-meter diameter circle, then the inductance across that circle
should lead to non-destructive
voltage gradients across that diameter.
N2EY wrote:
> >Subject: Re: Cad Welding..how done?
Louis Bybee
past a stunt we used to pull in a school shop class. It would be
interesting to have described in technical terms what took place.
We used to take a large hand full of the iron dust from beneath the
grinding wheel, and throw it up in the air above the Bunsen burner.
Sometimes the result would be a twinkling flame ball. If you got the
iron powder dispersed just right in the air, a significant flaming
rapport was the result. The end result was a very frustrated shop
teacher who couldn't figure out what was going on, and kids who were
fascinated to discover that metal would burn.
Thank you.
Louis
Robert H. Penoyer
Apparently the fine pieces of iron are able to oxidize enough to burn.
I recall putting the tip of a red hot metal (iron? steel?) rod into a
small pile of iron dust and the whole pile burned.
Steel wool will burn. Just hold some over the burner on a stove, or
maybe a match will work.
ajw
the mixture is right and some source ignites it. Lots of energy is
released when something like iron, for example, gets rusty. The
configuration you suggested gets it rusty all at once!
Robert H. Penoyer
C. Joy
>
> What I have learned from this thread on CADWelding brought back from the
> past a stunt we used to pull in a school shop class. It would be
> interesting to have described in technical terms what took place.
>
> We used to take a large hand full of the iron dust from beneath the
> grinding wheel, and throw it up in the air above the Bunsen burner.
> Sometimes the result would be a twinkling flame ball. If you got the
> iron powder dispersed just right in the air, a significant flaming
> rapport was the result. The end result was a very frustrated shop
> teacher who couldn't figure out what was going on, and kids who were
> fascinated to discover that metal would burn.
>
>
> Louis
Its just like a dust bomb. grain silo's sometimes explode because of this. you
can make a dust bomb out of a paint can that has been thoroughly cleaned out.
you mount a small funnel inside so that the small end sticks out of the bottom
of the can near the bottom rim. connect a tube to that. fill the funnel with
flour and put a small candle inside..light the candle and close the lid with a
hammer. Then blow into the tube. The lid will be blown off the can into the
sky. try it with fine iron powder.
Louis Bybee
would have been punished for, er-- perform a valid, point proving,
scientific experiment. I'm wondering about the advisibility of including
a check valve in the line before you blow into it?
Thank you.
Louis
Beau Schwabe
wrote:
With Iron powder, YES...with flower I wouldn't worry...but as for the
"experiment" the main reason this works, is because of the increased surface
area of the powder vs. the solid form. Increasing the surface area of almost
everything/anything will allow it to become more combustible when exposed to
a flame or heat source. BTW) Fireworks use different metal powders to
produce different colors as they burn with Carbon, Sulfur, and Phosphorus (Gun
Powder)
Gary Tait
oxygen.
Robert H. Penoyer wrote:
> Louis Bybee <lou...@datacomm.com> wrote:
>
> >What I have learned from this thread on CADWelding brought back from the
> >past a stunt we used to pull in a school shop class. It would be
> >interesting to have described in technical terms what took place.
> >
> >We used to take a large hand full of the iron dust from beneath the
> >grinding wheel, and throw it up in the air above the Bunsen burner.
> >Sometimes the result would be a twinkling flame ball. If you got the
> >iron powder dispersed just right in the air, a significant flaming
> >rapport was the result. The end result was a very frustrated shop
> >teacher who couldn't figure out what was going on, and kids who were
> >fascinated to discover that metal would burn.
>
phat phreddie
>
> A teacher demonstrated burning iron,by burning some steel wool in a jar of
> oxygen.
> >
> > Steel wool will burn. Just hold some over the burner on a stove, or
> > maybe a match will work.
You can also ignite steel wool by using it to short a 9-volt battery.
Very good fire starter for campfires, great survivalist trick. The
finer the better.
jh
Fred
that ran on a plastic track with inbedded power rails to power the cars.
The rails would get dirty causing the cars to stall at that point.
We would clean the rail with steel wool. All went well until I found that
if you left the transformer on... you can light up the steel wool and watch
it burn. Pretty soon I lost interest in the cars and invested in a
plumbers supply of steel wool to "Clean the tracks" so to speak. All I can
say is thank God we had a full concrete basement or I would have burned
that house down. ( I dont know what happened mom, I was just cleaning my
tracks)
Gary Tait <ta...@zdnetmail.com> wrote in article
<36891035...@zdnetmail.com>...
> A teacher demonstrated burning iron,by burning some steel wool in a jar
of
> oxygen.
>
>
> Robert H. Penoyer wrote:
>
> > Louis Bybee <lou...@datacomm.com> wrote:
> >
>
>---------------------------------snip--------------------------------------
----------------
> > Apparently the fine pieces of iron are able to oxidize enough to burn.
> > I recall putting the tip of a red hot metal (iron? steel?) rod into a
> > small pile of iron dust and the whole pile burned.
> >
David Cole
them at www.harger.com. I've bought a lot of grounding materials from them. They
are knowledgable and very helpful.
Regards,
David
WD5BZY
N2EY wrote:
> >Subject: Re: Cad Welding..how done?
> >From: TJS <Timothy...@mk.com>
> >Date: Tue, 22 Dec 1998 12:22:54 -0500
>
> wrote:
>
> >Thanks very much to the fine group of responders. I found this very
> >informative.
> >I had little idea that this was done. The idea of an exothermic chemical
> >reaction
> >I think is not well grasped by most non-engineer persons. Its hard to
> >conceive the
> >great release of chemical energy that results from placing a couple
> >different
> >powders in a chamber and adding a little heat to touch it off.
>
> Hello Tim,
>
> What's even more amazing is that the powders are not explosives or highly
Reb Ruster
>When I was a Kid, (about 10) we played with "HO Cars" Small electric cars
>that ran on a plastic track with inbedded power rails to power the cars.
>The rails would get dirty causing the cars to stall at that point.
>
>We would clean the rail with steel wool. All went well until I found that
>if you left the transformer on... you can light up the steel wool and watch
>it burn. Pretty soon I lost interest in the cars and invested in a
>plumbers supply of steel wool to "Clean the tracks" so to speak. All I can
>say is thank God we had a full concrete basement or I would have burned
>that house down. ( I dont know what happened mom, I was just cleaning my
>tracks)
Heck, when I was a kid, we used to tie steel wool on long sticks and
use them as sparklers on July 4th.
kim...@couriernet.infi.net
Ruster) wrote:
>On 30 Dec 1998 17:27:16 GMT, "Fred" <Boc...@Aol.com> wrote:
>
>>When I was a Kid, (about 10) we played with "HO Cars" Small electric cars
>>that ran on a plastic track with inbedded power rails to power the cars.
>>The rails would get dirty causing the cars to stall at that point.
>>
>>We would clean the rail with steel wool. All went well until I found that
>>if you left the transformer on... you can light up the steel wool and watch
>>it burn.
Heck, that's an old Boy Scout survival item we were taught to
carry with us on camping trips. I used to make sparkler bombs: scrape
all of the combustable material, and put into a cylindrical aluminum
foil form, put a sparkler in the top as a fuse, and watch it melt. Not
satisfied with that, I added contents of a road flare, magnesium
shavings, etc to it. We once put a nearly-empty Bic lighter in it. How
we survived that stupidity, I'm not sure, but we did. Never did it
again. I eventually saved up paper-towel cores, which made for better
bombs. But I digress. Steel wool burns quite well.
Pete.
FDecker
especially well also with electricity since they heat instantly and vaporize,
as is used in flashbulbs.
Of course, you were NEVER supposed to use the steel wool on your cars. I still
have my childhood sets and use them and the newer TYCO stuff with my kids. You
use very, very fine sand paper and pencil erasers. The steel wool gets in the
car and shorts it out the same way. <g>
KE4IXL
Fred
Please remember to remove the
<<NOSPAM>> from my email address
when replying.
Bill Nelson
:
: With Iron powder, YES...with flower I wouldn't worry...but as for the
: "experiment" the main reason this works, is because of the increased surface
: area of the powder vs. the solid form. Increasing the surface area of almost
: everything/anything will allow it to become more combustible when exposed to
: a flame or heat source. BTW) Fireworks use different metal powders to
: produce different colors as they burn with Carbon, Sulfur, and Phosphorus (Gun
: Powder)
Phosphorus is not used in fireworkks, nor is it a component of gunpowder.
Gunpowder (black powder) is composed of potassium nitrate, sulfur and
charcoal (not the same as carbon - which is much less reactive).
--
Bill Nelson (bi...@peak.org)
Bill Nelson
: Iron filings are used in a lot of old chemical explosives. They react
: especially well also with electricity since they heat instantly and vaporize,
: as is used in flashbulbs.
Actually, iron filings were NOT used in old explosives - too expensive, and
they would not give a more powerful explosive.
Nor are the filings used in flashbulbs - that metal is more likely to be
zirconium.
Both magnesium and aluminum were used in the old photographer's flash
powders - usually magnesium.
--
Bill Nelson (bi...@peak.org)