PVC Induction Heating Coil Design (early thoughts)

[RickDelta]

If your mesh has the overlaps in electrical contact, you might be able to get enough induced current to get resistance heating of the mesh.

You obviously have done a fair amount of research on the project. (more than most of us have!)

I'm curious how you can ensure 1/8" separation between the exciting coil and the mesh with different pipe diameters.
1) Are you assuming a different coil assembly for each pipe size?
2) What about buried pipes in a ditch?
3) How awkward would it be having to slide the coil assembly along a 20ft. pipe; say between floors in a building?

Possible workaround: make the coil assembly as a hinged item, like handcuffs.​

Please keep us updated an your progress and results, both success' and failures. We like to learn too!

Cheers,
Tom

@Tom.G
"If your mesh has the overlaps in electrical contact, you might be able to get enough induced current to get resistance heating of the mesh." - Tom.G

The manufacture of the micro-mesh screen is the next town over from me!
I met with the engineer there and he showed me that they can electronically weld the screens end to end and side to side without adding any additional metals or thickness!
I think this would meet your suggestion of an connected "overlap" now forming complete coils within the screen itself.

 

[Baluncore]

I think this would meet your suggestion of an connected "overlap" now forming complete coils within the screen itself.

I think you are using overlap in a different sense.

Where the individual wires cross, if they are to support eddy currents, and so be heated by the magnetic field, they must contact electrically. Unfortunately, that also reduces the compliance of the mesh to physically follow the joint surfaces.

Where the woven fabric screens are electrically welded, "end to end" and "side to side" without adding any additional metals or thickness, several smaller sheets are being joined to increase the total area. The cross wires will only be electrically connected where the sheets are welded at their edges. That will be too far apart to support eddy current heating.

PVC sheet is usually dielectrically welded, by clamping PVC between the plates of an RF capacitor. That employs the electrical field, not the magnetic field.
https://en.wikipedia.org/wiki/Radio-frequency_welding

 

[RickDelta]

" ......... several smaller sheets are being joined to increase the total area" - Baluncore

Don't understand what your saying here : (
Please explain in another way please.

 

[RickDelta]

A novel susceptor concept for metal-mesh susceptors, designed to achieve uniform in-plane temperatures during induction heating, is documented.

Metal-mesh susceptors require much smaller amounts of magnetic energy for heating compared to bulk materials and, in some cases, the distance problem can be overcome by increasing the input power to the coil.

 

[Baluncore]

Don't understand what your saying here : (

What size are the sheets of mesh you will cut your patches of susceptor from?
How will you treat the edges of the cut patches of mesh?

 

[RickDelta]

"What size are the sheets of mesh you will cut your patches of susceptor from?"
1" wide x 7.85" (circumference) long is the susceptor size for a 2" pipe.

"How will you treat the edges of the cut patches of mesh?"
Don't know yet! Not sure if I have to do anything! I can have welded the ends and sides ..... or have every crossover tack welded.


I'm thinking the steel mesh of the susceptor will have an added strength attribute to the joint itself ! (think: steel rebar) : )

 

[Baluncore]

"What size are the sheets of mesh you will cut your patches of susceptor from?"
1" wide x 7.85" (circumference) long is the susceptor size for a 2" pipe.

I asked for the raw sheet size, not the cut susceptor size.

I'm thinking the steel mesh of the susceptor will have an added strength attribute to the joint itself ! (think: steel rebar) : )

You mean like concrete cancer?
Or corrosion, because there is an electrical connection between the internal fluid and the outside at the pipe at the joint?

 

[RickDelta]

"I asked for the raw sheet size, not the cut susceptor size."
What I saw in a walk thru of the manufacturing plant was metal screen coming off the loom around 8ft wide and ..... by how long? ...... a mile?? no clue!

" ..... because there is an electrical connection between the internal fluid and the outside at the pipe at the joint?"
How so? .... the susceptor is fully embedded within the polymer.

 

[Baluncore]

How so? .... the susceptor is fully embedded within the polymer.

Not so. The ends of the wires cannot be heated because they are not part of the eddy current circuit. They will be exposed to the environment, in and out.

 

[RickDelta]

"Not so. The ends of the wires cannot be heated because they are not part of the eddy current circuit"

....... and why cant they be heated? ... even if the flux couldn't reach the very tip tip ends ...... think : thermal conduction thru the steel! we only need around 385 degrees F !!

 

[RickDelta]

I just now center heated the metal susceptor screen , trust me ..... almost an instant hot at the ends!! .... I had to drop it on the table! : (

 

[Baluncore]

....... and why cant they be heated? ... even if the flux couldn't reach the very tip tip ends

The flux could reach there, but the end of a .0065" wire has insignificant area, so, insignificant heating. It requires a larger closed loop to generate heat from an eddy current.

...... think : thermal conduction thru the steel! we only need around 385 degrees F !!

The 0.0065" wire has insufficient section to conduct sufficient heat. Heat will be lost to the PVC before it gets to move along the wire. The heating time is insufficient.

I just now center heated the metal susceptor screen , trust me ..... almost an instant hot at the ends!! .... I had to drop it on the table! : (

It was not instant. The temperature sensing nerves in your fingers are slow. You would need to explain how you heated it. By induction? From a coil of what size? Spaced how far away?

If I were to reverse engineer your idea, I could make several improvements, but I would still expect to go broke before I got it to work reliably. I am going to stick with the PVC glue, and avoid the insurance and legal problems of faulty welds.

 

[RickDelta]

"If I were to reverse engineer your idea, I could make several improvements"

well ...... I'm sure we'd all would love to hear them! ( but haven't heard any as of yet) : (

Will you share these great ideas with us?

 

[RickDelta]

"Now is my way clear, now is the meaning plain:
Temptation shall not come in this kind again.
The last temptation is the greatest treason:
To do the right deed for the wrong reason."

- T.S. Eliot - Murder in the Cathedral

 

[RickDelta]

This is another possibility for the susceptor .......
Particle "Curie" bond temperature control

 

[RickDelta]

This looks to be the best method for the PVC susceptor :

A special property of magnetic materials is the presence of a Curie temperature, which marks the transition of the material from a ferromagnetic or ferrimagnetic state to a paramagnetic state. A material which is above its Curie temperature loses its magnetic properties, and can
no longer generate hysteresis heating. Therefore, if magnetic particulate susceptors can be designed which possessa Curie temperature and do not heat due to eddy current effects, they cannot be heated inductively above their Curie temperature.

This property allows the creation of specialized susceptors which “automatically” maintain a desired processing temperature without the need for external control.

In this situation all of the heating is due to hysteresis effects.

 

[renormalize]

My quest is to develop an alternative to the conventional method of "primer and cement" bonding of typical pressure PVC pipe and fittings.
I want to effect a molecular PVC (polymer to polymer) bond only ....... without any chemical priming or cementing.
To achieve this inductively, I must insert an "susceptor" between the interfacial contact area of the joining pipe and the receiving socket of the fitting.

You've expounded at length in this thread regarding inductive/RF bonding of PVC pipes using a susceptor. Can you articulate your best-use case for this rather exotic and comparatively expensive approach to joining plastic tubes? How would it be superior to the current most-used alternative to pipe gluing, namely heat welding?

It's hard to beat the simplicity and efficiency of resistive heating, especially when you can buy the pipe welder shown above on Amazon for less than $50 US.

 

[RickDelta]

@renormalize

Hi! : )

"Can you articulate your best-use case for this rather exotic and comparatively expensive approach to joining plastic tubes?" - renormlize

Sure! : )

It's a special OEM product design (TAC media filtration system) i'm doing for the commercial hotel/motel & laundromat industry.
This system requires the assembly of large complex pressure PVC manifolds (elbows,"T"s, crosses, etc) in very close proximity to each other.

With the conventional "primer & cement" process, you can't prime and cement, lets say, 80 fittings all at the same time. You have to work each fitting one at a time, and then hold pressure on each joint for 30 seconds min. as the joint will walk itself apart if you don't!

Think of the fitting to fitting alignment nightmare of assembling all those joints to form a perfect manifold plane and orientation.
With this chemically (prime/cement) bonded joint, you cannot put the connections under test water pressure (120psi) for at least 12 hours of its full cure time!

With an inductive PVC susceptor bonding method, I create a 100% "polymer to polymer" joint the full length of the fittings socket (as opposed to only 1/3 of the socket depth bonding with the primer and glue).

With my proposed system, you fully assemble the entire 80 to 120 piece manifold all at once .... un-bonded!

Only then, do I inductivally bond the entire assembled manifold! (each bond only takes 3 seconds and can be fully pressure tested immediately!)

..... your heat "welding" suggestion suffers much the same attributes as the primer and cement unfortunately.

 

[RickDelta]

@renormalize

"How would it be superior to the current most-used alternative to pipe gluing, namely heat welding?" - renormalize

A great example of this is from another project i've design. "trenchless sewer lateral relining"

I always get a good laugh at my competitor's advertising of their "trenchless" or "no-dig" sewer lateral repair system ........ and the first thing that shows up at your home ....... is a backhoe!! : )

Their epoxy impregnated fiberglass sock sewer liner can't negotiate around the lawn trap underground! ...... so they have to dig a 4ft x 4ft hole in your front yard to cut out the entire sewer trap!

My system "threads" down a 2" "rigid" schedule 80 PVC pipe from the yard sewer vent, thru the trap and out to the townships sewer main sewer pipe (typically an 80 ft run) ..... in a Truly "No-Dig" system!

With my 2" PVC repair liner in place inside the existing 4" damaged sewer lateral, ....... I expand the new liner's diameter out to 4", .... lining the damaged lateral with solid PVC pipe.

The longest length of 2" PVC pipe you can get is 20ft , so, I needed to be able to join multiple lengths of pipe together.

I couldn't use a standard PVC pipe "coupler"..... as this would double the wall thickness at the joints. When I would expand the entire pipe from 2" to 4" inches, the joints would remain "necked down" at the couplers.

If I were to use your suggested "heat welding" to join the pipes butt ends , that process creates a large melt "bead" both on the outside and inside of the pipe! ...... again, doubling the pipes wall thickness.

The best solution looks to be an inductively heated Particle "Curie" bond susceptor. It creates a bonding as strong as the pipe itself and expands like there is no joint even there!

 

[Tom.G]

A case of "Nothing new under the Sun"?

Around 15 to 20 years ago I watched a city work crew "repair" a storm drain a few hundred feet long. The drain was a few feet in diameter and ran underneath a city street. It was all done thru a couple of manholes.

They pulled a steel cable thru the pipe to the next manhole using a small motorized vehicle.

The cable was then used to pull a flexible plastic liner thru the damaged pipe. The liner was somewhat smaller than the pipe, flattened, and wound on a reel on a separate trailer.

Next step was to pump very hot water into the plastic liner, thus expanding the plastic to line the pipe. They had a good-sized boiler on a separate truck.

There was apparently a another drain pipe emptying into the one just repaired/re-lined. So another small vehicle was sent into the drain to clear things up. This vehicle had a video camera and a blow torch, which made short work of clearing the connection.

Cheers,
Tom

 

[RickDelta]

Hi Tom.G! : )
Yep! I know the system well!

The major difference here, ..... they have access at each end of the pipe!
Many options are then available with that kind of access. You could even slide in an entire preformed pipe liner like that ..... easy!

I don't : (

I had to design a system were the entire process could only be done from one end only (ie: typical residential sewer lateral)

 

[RickDelta]

@Tom.G
An interesting point:
Somewhere in the world (not sure) they do have what's called "the Berlin system" ..... residential sewer laterals. All the residential sewer laterals terminate to a shared manhole in the street! (maybe 5 homes into the one manhole).

The problem is, .... if my toilet backs up from a cracked lateral, typically, my lateral would run from my house, underneath your driveway, across your lawn and out to the common manhole. Can you imagine waking up to a backhoe digging up your front yard?

That's why we don't do that here in the states! : )