Bending rectangular copper waveguides

[Rene Tschaggelar]

During my work I came across several way to
bend a rectangular waveguide. The copper is
best softened before by a heat treatment.
Then the choices are :
- fill it with sand and heat while bending
- fill it wit water, freeze it with LN2 and bend
- fill it with Wood metal melting at 60 Celsius
and bend at room temperature
- fill with brass strips and bend at room
temperature

Short of trying all, what are the better choices?
Yes, I'm aware there are rectangular cast bends
to solder in. They are limited the rectangular
though.

Rene

 

[_]

cross-posted to r.c.m. as the level of practical experience therein is
likely to be high. r.c.m.'ers should note that for wave-guides maintaining
the (x-section?) dimension following the bend may be quite important.

 

[Jim Wilkins]

cross-posted to r.c.m. as the level of practical experience therein is
likely to be high.  r.c.m.'ers should note that for wave-guides maintaining
the (x-section?) dimension following the bend may be quite important.







- Show quoted text -

Avoid them if possible. Semirigid coax and SMA connectors work to at
least 20 GHz.

 

[[email protected]]

During my work I came across several way to
bend a rectangular waveguide. The copper is
best softened before by a heat treatment.
Then the choices are :
- fill it with sand and heat while bending
- fill it wit water, freeze it with LN2 and bend
- fill it with Wood metal melting at 60 Celsius
   and bend at room temperature
- fill with brass strips and bend at room
   temperature

Short of trying all, what are the better choices?
Yes, I'm aware there are rectangular cast bends
to solder in. They are limited the rectangular
though.

Rene

HAVE YOU TRIED URI GELLER?

 

[Rene Tschaggelar]

- Hide quoted text -

Avoid them if possible. Semirigid coax and SMA connectors work to at
least 20 GHz.

We use the WR28 at 35GHz and the attenuation
in a coax is dramatic. 5dB for a single meter
are common. Even if the plumbing appears crude
and tiring, we prefer waveguide if possible.

Rene

 

[[email protected]]

- Hide quoted text -



We use the WR28 at 35GHz and the attenuation
in a coax is dramatic. 5dB for a single meter
are common. Even if the plumbing appears crude
and tiring, we prefer waveguide if possible.

Rene

What are the dimensions and wall thickness?

How long are the pieces you wish to bend, what's the angle, and what's
the radius?

Can your application withstand a few failed attempts (mismatch)
without self-destructing?

We use some flexible waveguide here at work (corrugated) for some low-
power radar stuff. Is that an option?


Dave

 

[[email protected]]

- Hide quoted text -



We use the WR28 at 35GHz and the attenuation
in a coax is dramatic. 5dB for a single meter
are common. Even if the plumbing appears crude
and tiring, we prefer waveguide if possible.

Rene

Some flexible '28 stuff here

http://www.rflambda.com/product_list.jsp?catalog=5003&sort=fq&dir=down

Dave

 

[[email protected]]

- Hide quoted text -



We use the WR28 at 35GHz and the attenuation
in a coax is dramatic. 5dB for a single meter
are common. Even if the plumbing appears crude
and tiring, we prefer waveguide if possible.

Rene

More flexible stuff

http://www.advancedmicrowave.com/products/flex_twists.htm

http://www.advancedmicrowave.com/products/double_flex.htm

Dave

 

[Bruce L. Bergman]

cross-posted to r.c.m. as the level of practical experience therein is
likely to be high. r.c.m.'ers should note that for wave-guides maintaining
the (x-section?) dimension following the bend may be quite important.

Electrician's perspective: If it's a one-off (prototype or custom
project) for a complex bend like an offset, or a J-bend...

I'd consider taking sheet copper, cutting the four sides with all the
flat curves needed for each face, cut the flanges, bend in all the
required squiggles and turns with a forming roller, and then braze or
TIG weld it together.

You leave two opposing faces a bit wide so they overlap on the
outside for easier assembly - make a fillet weld rather than acute on
the outside corner - the weld penetration on an acute corner will mess
up the profile of the inside corners of the waveguide.

Or combine both - TIG to tack it together and make sure it fits,
then silver-braze so you don't spend all day on sealing it all up -
brazing temperatures don't reach the melting point of the parent
metal, so they won't make the TIG tack welds come apart.

And brazing metals can bridge gaps and fill grooves, almost like
Bondo filler putty - just have to be delicate with the heat to stay in
the plastic state.

Another possibility is to section the tubing and make a segmented
bend, expand one side slightly with a flanging tool to make a step
overlap for mechanical strength, and then braze the pieces together.

If it fits and works as expected /then/ you can tool up molds to
cast them, or figure out another way to mass produce.

--<< Bruce >>--

 

[tom koehler]

- Hide quoted text -


We use the WR28 at 35GHz and the attenuation
in a coax is dramatic. 5dB for a single meter
are common. Even if the plumbing appears crude
and tiring, we prefer waveguide if possible.

Rene

in any effort to bend a tube, the metal on the outside curve wants to
stretch, the metal on the inside of the curve wants to compress. Any of the
various things to fill a tube are attempting to keep the tube from
collapsing. If the filling material is sufficiently non-compressible, the
metal on the outside of the curve must stretch. If it is not ductile enough,
it will tear.

This is way out there, but could you make a dummy waveguide from solid
plastic rod of the proper cross-section, and then plate a metal layer onto
the plastic?

tom koehler

 

[Ned Simmons]

cross-posted to r.c.m. as the level of practical experience therein is
likely to be high. r.c.m.'ers should note that for wave-guides maintaining
the (x-section?) dimension following the bend may be quite important.

I think the Wood's metal or brass strip methods would work best. The
problem with sand is that it relies on the fact that the geometric
shape with maximum area relative to its perimeter is a circle. If you
pack a circular tube with sand and bend it, the cross section can't
deviate from a circle because, assuming the circumference remains
constant, any change would reduce the section's area and the sand is
incompressible. A rectangular section can distort into a more circular
shape while allowing the sand to become loose. I imagine the ice would
behave somewhat like the sand as it fractures.

The brass strips idea is clever, as long as you can pull the strips
out after bending. It simulates the ID mandrels used for sharp bends
in production.
http://www.toolsforbending.com/mandrels.asp

 

[Clifford Heath]

- fill it with Wood metal melting at 60 Celsius
and bend at room temperature
Short of trying all, what are the better choices?

I think there's little doubt that using a solid metal
filling is the best option. Wood's metal is expensive
due to the indium content. That might not worry you,
but if it does, there's another eutectic alloy I've
been meaning to try; you should be able to make it
yourself. Bismuth (perhaps buy bismuth shot?) with
tin and lead in the right ratios will melt near 94 C,
i.e. in boiling water. You'll have to look up the
exact ratios, but I recall that the tin/lead ratio
is just below 60/40 which is convenient; just add
lead to standard solder. Check the purity of the
bismuth shot, but as long as the ratios are close,
the alloy should still melt below 120 degrees or so.

Clifford Heath.

 

[NoSPAM]

During my work I came across several way to
bend a rectangular waveguide. The copper is
best softened before by a heat treatment.
Then the choices are :
- fill it with sand and heat while bending
- fill it wit water, freeze it with LN2 and bend
- fill it with Wood metal melting at 60 Celsius
and bend at room temperature
- fill with brass strips and bend at room
temperature

Short of trying all, what are the better choices?
Yes, I'm aware there are rectangular cast bends
to solder in. They are limited the rectangular
though.

Rene

Many folks have suggested flexible waveguide, which is probably the simplest
method. I'll present two other alternatives.

You can design a mitered joint using only pieces of rectangular waveguide
cut at the correct angles and soldered or brazed together. The design of
both E-plane and H-plane corners of arbitrary angle is covered in
Marcuviitz' "Waveguide Handbook". This was one of the volumes in the MIT
Radiation Laboratory series published after WWII. The book was reprinted in
1986 by the IEE.

Finally you can mill out two halves with a CNC milling machine and bolt or
braze the two pieces together. The seam does not have to be perfect if it
is parallel to the E-field. Again see the "Waveguide Handbook" for a
discussion of symmetrical slotted waveguide.

Both of these methods are easy with rectangular waveguide. If you use
ridged waveguide, they are still possibilities, but you would need a good
machinist!

Dr. Barry L. Ornitz

 

[NoSPAM]

I think there's little doubt that using a solid metal
filling is the best option. Wood's metal is expensive
due to the indium content.

Indium? Wood's metal is approximately: tin, 12.5%, lead, 25%, bismuth.
50%, and cadmium, 12.5%. And it is cheap - cheap enough to be used
extensively in temperature controlled baths for organic chemistry. Of
course the cadmium is quite toxic but the baths were always in fume hoods.
For EE's and others not familiar with working with this stuff, I suggest
reading the J/ T Baker (Mallinckrodt-Baker Inc.) MSDS at
http://www.jtbaker.com/msds/englishhtml/w3500.htm.

Dr. Barry L. Ornitz

 

[amdx]

During my work I came across several way to
bend a rectangular waveguide. The copper is
best softened before by a heat treatment.
Then the choices are :
- fill it with sand and heat while bending
- fill it wit water, freeze it with LN2 and bend
- fill it with Wood metal melting at 60 Celsius
and bend at room temperature
- fill with brass strips and bend at room
temperature

Short of trying all, what are the better choices?
Yes, I'm aware there are rectangular cast bends
to solder in. They are limited the rectangular
though.

Rene

HAVE YOU TRIED URI GELLER?

Working at 35Ghz is REAL magic!

Mike

 

[[email protected]]

* This works with round and rectangular waveguide.


* Never heard of this "trick"; would seem to require more bending force
and not as easy to impliment as #1 above.

snip

That is how they do when building trumpets, the trick is they use soap
water
because it doesn't freeze as hard

-Lasse

 

[Rich Grise]

Working at 35Ghz is REAL magic!

At what point do you switch to fiber optics? ;-)

Thanks,
Rich

 

[Rich Grise]

Indium? Wood's metal is approximately: tin, 12.5%, lead, 25%, bismuth.
50%, and cadmium, 12.5%. And it is cheap - cheap enough to be used
extensively in temperature controlled baths for organic chemistry. Of
course the cadmium is quite toxic but the baths were always in fume hoods.
For EE's and others not familiar with working with this stuff, I suggest
reading the J/ T Baker (Mallinckrodt-Baker Inc.) MSDS at
http://www.jtbaker.com/msds/englishhtml/w3500.htm.

I just went to McMaster and searched on "bismuth":
http://www.mcmaster.com/#catalog/114/3532

158F? That's not even BOILING! =:-O

Hope This Helps!
Rich

 

[Clifford Heath]

Indium? Wood's metal is approximately: tin, 12.5%, lead, 25%, bismuth.
50%, and cadmium, 12.5%. And it is cheap

Ahh, must be a different low-melting point alloy I was thinking of. Thanks.

 

[Rene Tschaggelar]

Jim Wilkins wrote: [snip]

Avoid them if possible. Semirigid coax and SMA connectors work to at
least 20 GHz.

We use the WR28 at 35GHz and the attenuation
in a coax is dramatic. 5dB for a single meter
are common. Even if the plumbing appears crude
and tiring, we prefer waveguide if possible.

Rene

What are the dimensions and wall thickness?

7.xx by 3.5xx mm, with a wall about 1.2mm

How long are the pieces you wish to bend, what's the angle, and what's
the radius?

less than 90 degrees, otherwise we're flexible.

Can your application withstand a few failed attempts (mismatch)
without self-destructing?

Yes, it can. We also have a network analyzer to
measure some parameters

We use some flexible waveguide here at work (corrugated) for some low-
power radar stuff. Is that an option?

We have the corrugated stuff here too.

Rene