I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?

On Tue, 16 May 2017 15:47:13 +0800, Aussie wrote:

I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?
I have used a two part plastic glue to bond some hard to bond
plastics. I'm not sure if the glue is an epoxy. I do know that it is
waterproof though. I bought the glue at the local hardware store and
it is made by Henkel (I think). I'm pretty sure the brand was Loctite
(and Loctite is now owned by Henkel). To repeat, I have used this glue
on some pretty hard to bond plastics and it worked very well. In fact,
it exceeded the performance guaranteed on the package.
Eric

On Tuesday, May 16, 2017 at 3:46:47 AM UTC-4, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?

Watch out for silicone or any other intermediary. Silicone is used as a release surface for epoxy.

Epoxy-to-PVC was always a "medium-performance" plastic bond (I first reported on adhesive assembly in 1979, and the situation remained the same for decades). In recent years, epoxy formulators have developed a lot of specialized products, including for specific plastics. PVC is one of them.

Here's a brief article that talks about one of the newer ones:

http://epoxyworks.com/index.php/glui...h-gflex-epoxy/

--
Ed Huntress

Home Depot, a monster hardware store, has a dip type of elastic
encapsulent in a spray can. I bought a can and sprayed it on an empty pcb
and it looked good and felt slightly flexible. The can is now patiently
awaiting further testing.

Two part polyurethane might work also. Mix it and apply with a paint
brush. No idea how either of these handles immersion in water but it would
be nice to hear...

Hul


Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?

On Tuesday, May 16, 2017 at 3:46:47 AM UTC-4, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.


Any suggestions?


A good many years ago I was involved in something similar. Instead of dealing with water it was dealing with high voltages and vacuum. The first try was epoxy potting. It cracked in temperature cycling.

So somewhat flexible polyurethane potting was tried. It did not adhere well enough.

The solution was a metal box with a gasketed lid. It was great for reworking as in did not have any conformal coating to remove. The connectors did have to be a special design. They were kind of like morse tapers. Necessary because the voltage was about 2000 volts. Surprise , surprise the connector was designed on paper and worked without having to be revised.

Dan

On 16-May-17 10:56 PM, wrote:
On Tue, 16 May 2017 15:47:13 +0800, Aussie wrote:

I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?
I have used a two part plastic glue to bond some hard to bond
plastics. I'm not sure if the glue is an epoxy. I do know that it is
waterproof though. I bought the glue at the local hardware store and
it is made by Henkel (I think). I'm pretty sure the brand was Loctite
(and Loctite is now owned by Henkel). To repeat, I have used this glue
on some pretty hard to bond plastics and it worked very well. In fact,
it exceeded the performance guaranteed on the package.
Eric


Thanks. I'm kind of stuck with the bulk epoxy I have on hand.

On 16-May-17 11:59 PM, wrote:
On Tuesday, May 16, 2017 at 3:46:47 AM UTC-4, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?

Watch out for silicone or any other intermediary. Silicone is used as a release surface for epoxy.

Epoxy-to-PVC was always a "medium-performance" plastic bond (I first reported on adhesive assembly in 1979, and the situation remained the same for decades). In recent years, epoxy formulators have developed a lot of specialized products, including for specific plastics. PVC is one of them.

Here's a brief article that talks about one of the newer ones:

http://epoxyworks.com/index.php/glui...h-gflex-epoxy/



Thanks, that's an interesting article.

I thought silicone RTV rubbers were a different thing to the silicone
(oil?) used for mold release?

On 17-May-17 6:01 AM, Hul Tytus wrote:
Home Depot, a monster hardware store, has a dip type of elastic
encapsulent in a spray can. I bought a can and sprayed it on an empty pcb
and it looked good and felt slightly flexible. The can is now patiently
awaiting further testing.

Two part polyurethane might work also. Mix it and apply with a paint
brush. No idea how either of these handles immersion in water but it would
be nice to hear...

Hul



I'm kind of stuck with the epoxy I have on hand.





Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?

On 17-May-17 8:35 AM, wrote:
On Tuesday, May 16, 2017 at 3:46:47 AM UTC-4, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.


Any suggestions?


A good many years ago I was involved in something similar. Instead of dealing with water it was dealing with high voltages and vacuum. The first try was epoxy potting. It cracked in temperature cycling.

So somewhat flexible polyurethane potting was tried. It did not adhere well enough.

The solution was a metal box with a gasketed lid. It was great for reworking as in did not have any conformal coating to remove. The connectors did have to be a special design. They were kind of like morse tapers. Necessary because the voltage was about 2000 volts. Surprise , surprise the connector was designed on paper and worked without having to be revised.

Dan



A water proof enclosure would be nice but the price is waaay to high!

On Wednesday, May 17, 2017 at 5:41:13 AM UTC-4, Aussie wrote:
On 16-May-17 11:59 PM, wrote:
On Tuesday, May 16, 2017 at 3:46:47 AM UTC-4, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?

Watch out for silicone or any other intermediary. Silicone is used as a release surface for epoxy.

Epoxy-to-PVC was always a "medium-performance" plastic bond (I first reported on adhesive assembly in 1979, and the situation remained the same for decades). In recent years, epoxy formulators have developed a lot of specialized products, including for specific plastics. PVC is one of them.

Here's a brief article that talks about one of the newer ones:

http://epoxyworks.com/index.php/glui...h-gflex-epoxy/



Thanks, that's an interesting article.

I thought silicone RTV rubbers were a different thing to the silicone
(oil?) used for mold release?

Same chemical family, but someone with chemistry knowledge would have to weigh in here.

Silicone rubbers, RTV and otherwise, are widely used for making molds, for plaster, for thermoset plastics like epoxy, and even for low-temperature molten metals. (The latter are not RTV, but rather a hard, higher-temperature-cure type of silicone rubber.) Unless it's formulated specifically as an adhesive, it won't stick well to much of anything.

--
Ed Huntress

"Aussie" wrote in message
...
On 17-May-17 8:35 AM, wrote:
On Tuesday, May 16, 2017 at 3:46:47 AM UTC-4, Aussie wrote:
I'm playing around potting some electronics for immersion in water
up to
10 metres.


Any suggestions?


A good many years ago I was involved in something similar. Instead
of dealing with water it was dealing with high voltages and vacuum.
The first try was epoxy potting. It cracked in temperature
cycling.

So somewhat flexible polyurethane potting was tried. It did not
adhere well enough.

The solution was a metal box with a gasketed lid. It was great for
reworking as in did not have any conformal coating to remove. The
connectors did have to be a special design. They were kind of
like morse tapers. Necessary because the voltage was about 2000
volts. Surprise , surprise the connector was designed on paper and
worked without having to be revised.

Dan



A water proof enclosure would be nice but the price is waaay to
high!

Perhaps you could research high-performance professional and low-cost
educational solutions:
http://www.hydrogroupplc.com/pressur...netrators.html
http://oceanexplorer.noaa.gov/explor..._gr9-12_l4.pdf

I got a good deal on a vacuum oven that leaked through the wiring
feedthru. I replaced it with a solid plug and haven't found how to
make one. Here's one possibility for solid wires or sealed tubes:
http://www.omega.com/pptst/MFT.html

Light bulbs have wire leads that seal vacuum-tight in glass.
https://en.wikipedia.org/wiki/Fernico

-jsw

On 16/05/2017 17:47, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?


You can get cable that is filled with a hydrophobic gel, so that even if
the cable does have a leak somewhere along the length, water won't wick
along it.

If your device is being potted, you could put a short section of single
strand bare copper wire between the circuit board and each stranded
wire. The epoxy should form a good seal to the bare copper. Liquid water
in the stranded wire ought to stop at the solder joint between the
stranded and non-stranded wire. Probably some water will diffuse through
all of the plastics and resins eventually though.

You could try corona-treating the polyethylene and PVC which is much
like flame treating but may produce less heat.

On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan

On Wed, 17 May 2017 17:39:56 +0800, Aussie wrote:

On 16-May-17 10:56 PM, wrote:
On Tue, 16 May 2017 15:47:13 +0800, Aussie wrote:

I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?
I have used a two part plastic glue to bond some hard to bond
plastics. I'm not sure if the glue is an epoxy. I do know that it is
waterproof though. I bought the glue at the local hardware store and
it is made by Henkel (I think). I'm pretty sure the brand was Loctite
(and Loctite is now owned by Henkel). To repeat, I have used this glue
on some pretty hard to bond plastics and it worked very well. In fact,
it exceeded the performance guaranteed on the package.
Eric


Thanks. I'm kind of stuck with the bulk epoxy I have on hand.
I was thinking you could coat the PVC with the two part plastic glue
and then bond your epoxy to it.
Eric

On 18-May-17 12:03 AM, wrote:
On Wed, 17 May 2017 17:39:56 +0800, Aussie wrote:

On 16-May-17 10:56 PM, wrote:
On Tue, 16 May 2017 15:47:13 +0800, Aussie wrote:

I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?
I have used a two part plastic glue to bond some hard to bond
plastics. I'm not sure if the glue is an epoxy. I do know that it is
waterproof though. I bought the glue at the local hardware store and
it is made by Henkel (I think). I'm pretty sure the brand was Loctite
(and Loctite is now owned by Henkel). To repeat, I have used this glue
on some pretty hard to bond plastics and it worked very well. In fact,
it exceeded the performance guaranteed on the package.
Eric


Thanks. I'm kind of stuck with the bulk epoxy I have on hand.
I was thinking you could coat the PVC with the two part plastic glue
and then bond your epoxy to it.
Eric


OK, yep that would be an option. Thanks.

On 17-May-17 6:55 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
On 17-May-17 8:35 AM, wrote:
On Tuesday, May 16, 2017 at 3:46:47 AM UTC-4, Aussie wrote:
I'm playing around potting some electronics for immersion in water
up to
10 metres.


Any suggestions?


A good many years ago I was involved in something similar. Instead
of dealing with water it was dealing with high voltages and vacuum.
The first try was epoxy potting. It cracked in temperature
cycling.

So somewhat flexible polyurethane potting was tried. It did not
adhere well enough.

The solution was a metal box with a gasketed lid. It was great for
reworking as in did not have any conformal coating to remove. The
connectors did have to be a special design. They were kind of
like morse tapers. Necessary because the voltage was about 2000
volts. Surprise , surprise the connector was designed on paper and
worked without having to be revised.

Dan



A water proof enclosure would be nice but the price is waaay to
high!

Perhaps you could research high-performance professional and low-cost
educational solutions:
http://www.hydrogroupplc.com/pressur...netrators.html
http://oceanexplorer.noaa.gov/explor..._gr9-12_l4.pdf

I got a good deal on a vacuum oven that leaked through the wiring
feedthru. I replaced it with a solid plug and haven't found how to
make one. Here's one possibility for solid wires or sealed tubes:
http://www.omega.com/pptst/MFT.html

Light bulbs have wire leads that seal vacuum-tight in glass.
https://en.wikipedia.org/wiki/Fernico

-jsw




Thanks, I'll do some reading.

On 17-May-17 8:45 PM, Chris Jones wrote:
On 16/05/2017 17:47, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?


You can get cable that is filled with a hydrophobic gel, so that even if
the cable does have a leak somewhere along the length, water won't wick
along it.

If your device is being potted, you could put a short section of single
strand bare copper wire between the circuit board and each stranded
wire. The epoxy should form a good seal to the bare copper. Liquid water
in the stranded wire ought to stop at the solder joint between the
stranded and non-stranded wire. Probably some water will diffuse through
all of the plastics and resins eventually though.

You could try corona-treating the polyethylene and PVC which is much
like flame treating but may produce less heat.






I've not been able to find jelly cable or water block treated cable at a
viable price. The inexpensive type is solid core conductors and I need
multi-strand unfortunately.

I've left the insulation length long to provide a long sealing path,
three is an opportunity to strip the copper back so I will definitely do
that.


Corona treating - I'll check it out.

Thanks

On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

On Wednesday, May 17, 2017 at 9:32:23 PM UTC-4, Aussie wrote:
On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

The difficulty with epoxy bonding to many metals is that it's actually bonding to surface oxide. Depending on the metal and the thickness and nature of the oxide, this results in weak joints in stainless steel, aluminum, copper alloys, and, of course, anything containing lead. There are other problem metals.

There are ways around it. One is to abrade the surface of the metal while it's coated with the mixed epoxy. This is sometimes called "scratch-in" preparation. I use it all the time, and it works great on stainless and aluminum.

I don't know for sure about copper. I've been asked about it before but I never tried it or looked into it, but I suspect it will be the same as for other metals.

This abrasion method is not practical in most commercial applications: aluminum aircraft wing skins being a prime example. To work fast and to get more reliable results, industrial users have worked out various conversion coatings and etches for specific metals that need to be bonded with epoxy and other adhesives. On aluminum, for example,they use phosphoric acid anodizing, PAA, and I've heard there are newer, better conversion coatings for aluminum.

There is an entire literature on this, but when I have a question, I just call 3M or Loctite, or whomever, and ask to speak to an engineer. Or I did. I was a trade magazine editor and I could use that leverage to get through. Now that I'm retired, they might just tell me to go **** up a rope. d8-)

--
Ed Huntress

Aussie wrote:
I'm playing around potting some electronics for immersion in water up
to 10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected
to a circuit board are embedded in some rigid setting epoxy.

I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the
circuit board?

I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.

Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that
might form an intermediary seal?


Use a heated plate to melt a rolled lip on the end of the poly tubing.
The lip will give the epoxy a mechanical bond. To ensure it doesn't leak
you could put a common O ring that fits the tubing above the lip. The
epoxy then encapsulates the ring and the lip.

--
Steve W.

"Steve W." wrote in message
news
Aussie wrote:
I'm playing around potting some electronics for immersion in water
up
to 10 metres.

A cable with a polyethylene sheath and PVC insulated wires
connected
to a circuit board are embedded in some rigid setting epoxy.

I know I'm not going to get the epoxy to adhere to the
polyethylene.

What can I do to enhance the bond between the epoxy and the PVC
wire
insulation to keep the water from wicking along the wire to the
circuit board?

I've read that brushing with PVC pipe glue primer (MEK) can help,
as
well as flame treating.

Flame treating is impractical as the job is too small & tight to
get
into the area where the PVC insulation is.

Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that
might form an intermediary seal?


Use a heated plate to melt a rolled lip on the end of the poly
tubing. The lip will give the epoxy a mechanical bond. To ensure it
doesn't leak you could put a common O ring that fits the tubing
above the lip. The epoxy then encapsulates the ring and the lip.

--
Steve W.

I haven't had much luck sealing tube feedthrus with O rings unless
there was a threaded packing nut to compress them.

On 18-May-17 9:47 AM, wrote:
On Wednesday, May 17, 2017 at 9:32:23 PM UTC-4, Aussie wrote:
On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

The difficulty with epoxy bonding to many metals is that it's actually bonding to surface oxide. Depending on the metal and the thickness and nature of the oxide, this results in weak joints in stainless steel, aluminum, copper alloys, and, of course, anything containing lead. There are other problem metals.

There are ways around it. One is to abrade the surface of the metal while it's coated with the mixed epoxy. This is sometimes called "scratch-in" preparation. I use it all the time, and it works great on stainless and aluminum.

I don't know for sure about copper. I've been asked about it before but I never tried it or looked into it, but I suspect it will be the same as for other metals.

This abrasion method is not practical in most commercial applications: aluminum aircraft wing skins being a prime example. To work fast and to get more reliable results, industrial users have worked out various conversion coatings and etches for specific metals that need to be bonded with epoxy and other adhesives. On aluminum, for example,they use phosphoric acid anodizing, PAA, and I've heard there are newer, better conversion coatings for aluminum.

There is an entire literature on this, but when I have a question, I just call 3M or Loctite, or whomever, and ask to speak to an engineer. Or I did. I was a trade magazine editor and I could use that leverage to get through. Now that I'm retired, they might just tell me to go **** up a rope. d8-)



Thanks Ed, this stuff is too small to abrade manually. The wires cores
are ~0.3mm diameter.

On 18-May-17 10:47 AM, Jim Wilkins wrote:
"Steve W." wrote in message
news
Aussie wrote:
I'm playing around potting some electronics for immersion in water
up
to 10 metres.

A cable with a polyethylene sheath and PVC insulated wires
connected
to a circuit board are embedded in some rigid setting epoxy.

I know I'm not going to get the epoxy to adhere to the
polyethylene.

What can I do to enhance the bond between the epoxy and the PVC
wire
insulation to keep the water from wicking along the wire to the
circuit board?

I've read that brushing with PVC pipe glue primer (MEK) can help,
as
well as flame treating.

Flame treating is impractical as the job is too small & tight to
get
into the area where the PVC insulation is.

Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that
might form an intermediary seal?


Use a heated plate to melt a rolled lip on the end of the poly
tubing. The lip will give the epoxy a mechanical bond. To ensure it
doesn't leak you could put a common O ring that fits the tubing
above the lip. The epoxy then encapsulates the ring and the lip.

--
Steve W.

I haven't had much luck sealing tube feedthrus with O rings unless
there was a threaded packing nut to compress them.




I did read that to seal some potted sonar assemblies a couple of tight
large section o-rings are placed on the cable inside the potted volume.

The o-ring material is selected to bond well to the potting material.


The theory is the o-ring tension provides a seal against the cable
sheath and the potting compound to o-ring bond seals the ingress path
around the outside.

It sounds viable but I'm a little skeptical about long term sealing.

"Aussie" wrote in message
...
On 18-May-17 10:47 AM, Jim Wilkins wrote:
"Steve W." wrote in message
news
Aussie wrote:
I'm playing around potting some electronics for immersion in
water
up
to 10 metres.

A cable with a polyethylene sheath and PVC insulated wires
connected
to a circuit board are embedded in some rigid setting epoxy.

I know I'm not going to get the epoxy to adhere to the
polyethylene.

What can I do to enhance the bond between the epoxy and the PVC
wire
insulation to keep the water from wicking along the wire to the
circuit board?

I've read that brushing with PVC pipe glue primer (MEK) can help,
as
well as flame treating.

Flame treating is impractical as the job is too small & tight to
get
into the area where the PVC insulation is.

Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that
might form an intermediary seal?


Use a heated plate to melt a rolled lip on the end of the poly
tubing. The lip will give the epoxy a mechanical bond. To ensure
it
doesn't leak you could put a common O ring that fits the tubing
above the lip. The epoxy then encapsulates the ring and the lip.

--
Steve W.

I haven't had much luck sealing tube feedthrus with O rings unless
there was a threaded packing nut to compress them.




I did read that to seal some potted sonar assemblies a couple of
tight large section o-rings are placed on the cable inside the
potted volume.

The o-ring material is selected to bond well to the potting
material.


The theory is the o-ring tension provides a seal against the cable
sheath and the potting compound to o-ring bond seals the ingress
path around the outside.

It sounds viable but I'm a little skeptical about long term sealing.

I needed to contain internal pressure that expands the O ring while
you have external pressure compressing it. It sounds like you found a
proven solution.

10 meters deep is the same pressure differential as a vacuum, which
these are thick enough to resist:
http://www.apiezon.com/

On Thursday, May 18, 2017 at 12:33:53 AM UTC-4, Aussie wrote:
On 18-May-17 9:47 AM, wrote:
On Wednesday, May 17, 2017 at 9:32:23 PM UTC-4, Aussie wrote:
On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

The difficulty with epoxy bonding to many metals is that it's actually bonding to surface oxide. Depending on the metal and the thickness and nature of the oxide, this results in weak joints in stainless steel, aluminum, copper alloys, and, of course, anything containing lead. There are other problem metals.

There are ways around it. One is to abrade the surface of the metal while it's coated with the mixed epoxy. This is sometimes called "scratch-in" preparation. I use it all the time, and it works great on stainless and aluminum.

I don't know for sure about copper. I've been asked about it before but I never tried it or looked into it, but I suspect it will be the same as for other metals.

This abrasion method is not practical in most commercial applications: aluminum aircraft wing skins being a prime example. To work fast and to get more reliable results, industrial users have worked out various conversion coatings and etches for specific metals that need to be bonded with epoxy and other adhesives. On aluminum, for example,they use phosphoric acid anodizing, PAA, and I've heard there are newer, better conversion coatings for aluminum.

There is an entire literature on this, but when I have a question, I just call 3M or Loctite, or whomever, and ask to speak to an engineer. Or I did. I was a trade magazine editor and I could use that leverage to get through. Now that I'm retired, they might just tell me to go **** up a rope. d8-)



Thanks Ed, this stuff is too small to abrade manually. The wires cores
are ~0.3mm diameter.

I get started on this subject and off I go on a tangent. g Yes, I realize it probably wouldn't help your situation. The point is that no, epoxy won't bond to solder unless you take special steps.

--
Ed Huntrress

On 18-May-17 6:39 PM, wrote:
On Thursday, May 18, 2017 at 12:33:53 AM UTC-4, Aussie wrote:
On 18-May-17 9:47 AM, wrote:
On Wednesday, May 17, 2017 at 9:32:23 PM UTC-4, Aussie wrote:
On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

The difficulty with epoxy bonding to many metals is that it's actually bonding to surface oxide. Depending on the metal and the thickness and nature of the oxide, this results in weak joints in stainless steel, aluminum, copper alloys, and, of course, anything containing lead. There are other problem metals.

There are ways around it. One is to abrade the surface of the metal while it's coated with the mixed epoxy. This is sometimes called "scratch-in" preparation. I use it all the time, and it works great on stainless and aluminum.

I don't know for sure about copper. I've been asked about it before but I never tried it or looked into it, but I suspect it will be the same as for other metals.

This abrasion method is not practical in most commercial applications: aluminum aircraft wing skins being a prime example. To work fast and to get more reliable results, industrial users have worked out various conversion coatings and etches for specific metals that need to be bonded with epoxy and other adhesives. On aluminum, for example,they use phosphoric acid anodizing, PAA, and I've heard there are newer, better conversion coatings for aluminum.

There is an entire literature on this, but when I have a question, I just call 3M or Loctite, or whomever, and ask to speak to an engineer. Or I did. I was a trade magazine editor and I could use that leverage to get through. Now that I'm retired, they might just tell me to go **** up a rope. d8-)



Thanks Ed, this stuff is too small to abrade manually. The wires cores
are ~0.3mm diameter.

I get started on this subject and off I go on a tangent. g Yes, I realize it probably wouldn't help your situation. The point is that no, epoxy won't bond to solder unless you take special steps.



There's nothing wrong with the tangential stuff - it might come in handy
some day & it costs nothing to carry the knowledge around!

On 18-May-17 6:39 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
On 18-May-17 10:47 AM, Jim Wilkins wrote:
"Steve W." wrote in message
news Aussie wrote:
I'm playing around potting some electronics for immersion in
water
up
to 10 metres.

A cable with a polyethylene sheath and PVC insulated wires
connected
to a circuit board are embedded in some rigid setting epoxy.

I know I'm not going to get the epoxy to adhere to the
polyethylene.

What can I do to enhance the bond between the epoxy and the PVC
wire
insulation to keep the water from wicking along the wire to the
circuit board?

I've read that brushing with PVC pipe glue primer (MEK) can help,
as
well as flame treating.

Flame treating is impractical as the job is too small & tight to
get
into the area where the PVC insulation is.

Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that
might form an intermediary seal?


Use a heated plate to melt a rolled lip on the end of the poly
tubing. The lip will give the epoxy a mechanical bond. To ensure
it
doesn't leak you could put a common O ring that fits the tubing
above the lip. The epoxy then encapsulates the ring and the lip.

--
Steve W.

I haven't had much luck sealing tube feedthrus with O rings unless
there was a threaded packing nut to compress them.




I did read that to seal some potted sonar assemblies a couple of
tight large section o-rings are placed on the cable inside the
potted volume.

The o-ring material is selected to bond well to the potting
material.


The theory is the o-ring tension provides a seal against the cable
sheath and the potting compound to o-ring bond seals the ingress
path around the outside.

It sounds viable but I'm a little skeptical about long term sealing.

I needed to contain internal pressure that expands the O ring while
you have external pressure compressing it. It sounds like you found a
proven solution.

10 meters deep is the same pressure differential as a vacuum, which
these are thick enough to resist:
http://www.apiezon.com/



Am I understanding correctly?
You think a smidge of thick vacuum grease on the embedded wires might
block the water??
Thats an interesting idea.

"Aussie" wrote in message
...
On 18-May-17 6:39 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
On 18-May-17 10:47 AM, Jim Wilkins wrote:
"Steve W." wrote in message
news Aussie wrote:
I'm playing around potting some electronics for immersion in
water
up
to 10 metres.

A cable with a polyethylene sheath and PVC insulated wires
connected
to a circuit board are embedded in some rigid setting epoxy.

I know I'm not going to get the epoxy to adhere to the
polyethylene.

What can I do to enhance the bond between the epoxy and the PVC
wire
insulation to keep the water from wicking along the wire to
the
circuit board?

I've read that brushing with PVC pipe glue primer (MEK) can
help,
as
well as flame treating.

Flame treating is impractical as the job is too small & tight
to
get
into the area where the PVC insulation is.

Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone
that
might form an intermediary seal?


Use a heated plate to melt a rolled lip on the end of the poly
tubing. The lip will give the epoxy a mechanical bond. To ensure
it
doesn't leak you could put a common O ring that fits the tubing
above the lip. The epoxy then encapsulates the ring and the lip.

--
Steve W.

I haven't had much luck sealing tube feedthrus with O rings
unless
there was a threaded packing nut to compress them.




I did read that to seal some potted sonar assemblies a couple of
tight large section o-rings are placed on the cable inside the
potted volume.

The o-ring material is selected to bond well to the potting
material.


The theory is the o-ring tension provides a seal against the cable
sheath and the potting compound to o-ring bond seals the ingress
path around the outside.

It sounds viable but I'm a little skeptical about long term
sealing.

I needed to contain internal pressure that expands the O ring while
you have external pressure compressing it. It sounds like you found
a
proven solution.

10 meters deep is the same pressure differential as a vacuum, which
these are thick enough to resist:
http://www.apiezon.com/



Am I understanding correctly?
You think a smidge of thick vacuum grease on the embedded wires
might block the water??
Thats an interesting idea.

Or maybe chain lube. Perhaps you could adapt pipe fittings to compress
on one end of a wire sample, apply likely diluted or melted greases to
the other and see if they block bubbling when pressurized.
-jsw

On 18/05/2017 11:47, wrote:
On Wednesday, May 17, 2017 at 9:32:23 PM UTC-4, Aussie wrote:
On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

The difficulty with epoxy bonding to many metals is that it's actually bonding to surface oxide. Depending on the metal and the thickness and nature of the oxide, this results in weak joints in stainless steel, aluminum, copper alloys, and, of course, anything containing lead. There are other problem metals.

There are ways around it. One is to abrade the surface of the metal while it's coated with the mixed epoxy. This is sometimes called "scratch-in" preparation. I use it all the time, and it works great on stainless and aluminum.

I don't know for sure about copper. I've been asked about it before but I never tried it or looked into it, but I suspect it will be the same as for other metals.

This abrasion method is not practical in most commercial applications: aluminum aircraft wing skins being a prime example. To work fast and to get more reliable results, industrial users have worked out various conversion coatings and etches for specific metals that need to be bonded with epoxy and other adhesives. On aluminum, for example,they use phosphoric acid anodizing, PAA, and I've heard there are newer, better conversion coatings for aluminum.

There is an entire literature on this, but when I have a question, I just call 3M or Loctite, or whomever, and ask to speak to an engineer. Or I did. I was a trade magazine editor and I could use that leverage to get through. Now that I'm retired, they might just tell me to go **** up a rope. d8-)



Ok, then I wonder whether epoxy will bond to the urethane enamel of
solderable magnet wire instead, used in the same way.

On 18/05/2017 11:31, Aussie wrote:
On 17-May-17 8:45 PM, Chris Jones wrote:
On 16/05/2017 17:47, Aussie wrote:
I'm playing around potting some electronics for immersion in water up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?


You can get cable that is filled with a hydrophobic gel, so that even
if the cable does have a leak somewhere along the length, water won't
wick along it.

If your device is being potted, you could put a short section of
single strand bare copper wire between the circuit board and each
stranded wire. The epoxy should form a good seal to the bare copper.
Liquid water in the stranded wire ought to stop at the solder joint
between the stranded and non-stranded wire. Probably some water will
diffuse through all of the plastics and resins eventually though.

You could try corona-treating the polyethylene and PVC which is much
like flame treating but may produce less heat.






I've not been able to find jelly cable or water block treated cable at a
viable price. The inexpensive type is solid core conductors and I need
multi-strand unfortunately.

I bought some UV sensors from this Australian company:
http://www.monitorsensors.com/
and they came with stranded gel-filled cable IIRC.

They seem to be a small company so maybe they will sell you some cable
if the minimum order quantity is too large from usual suppliers.

I'm not sure I would take their advice on waterproofing though: one of
the UV sensors went intermittent and then stopped working not long after
it was installed outdoors.

On Thursday, May 18, 2017 at 8:05:00 PM UTC-4, Chris Jones wrote:
On 18/05/2017 11:47, wrote:
On Wednesday, May 17, 2017 at 9:32:23 PM UTC-4, Aussie wrote:
On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

The difficulty with epoxy bonding to many metals is that it's actually bonding to surface oxide. Depending on the metal and the thickness and nature of the oxide, this results in weak joints in stainless steel, aluminum, copper alloys, and, of course, anything containing lead. There are other problem metals.

There are ways around it. One is to abrade the surface of the metal while it's coated with the mixed epoxy. This is sometimes called "scratch-in" preparation. I use it all the time, and it works great on stainless and aluminum.

I don't know for sure about copper. I've been asked about it before but I never tried it or looked into it, but I suspect it will be the same as for other metals.

This abrasion method is not practical in most commercial applications: aluminum aircraft wing skins being a prime example. To work fast and to get more reliable results, industrial users have worked out various conversion coatings and etches for specific metals that need to be bonded with epoxy and other adhesives. On aluminum, for example,they use phosphoric acid anodizing, PAA, and I've heard there are newer, better conversion coatings for aluminum.

There is an entire literature on this, but when I have a question, I just call 3M or Loctite, or whomever, and ask to speak to an engineer. Or I did. I was a trade magazine editor and I could use that leverage to get through. Now that I'm retired, they might just tell me to go **** up a rope. d8-)



Ok, then I wonder whether epoxy will bond to the urethane enamel of
solderable magnet wire instead, used in the same way.

I wonder, too.

Urethances are formulated in so many different ways that I can't begin to guess. FWIW, the conventional wisdom is that epoxy will bond to urethane (and to polyester and methacrylate) better than any of them will bond to epoxy.. Just watch out for the extreme elongation (ductility) of most polyurethanes, compared to the low elongation of epoxy. The difference can result in shear failure right where they're bonded.

--
Ed Huntress

On 19-May-17 8:08 AM, Chris Jones wrote:
On 18/05/2017 11:31, Aussie wrote:
On 17-May-17 8:45 PM, Chris Jones wrote:
On 16/05/2017 17:47, Aussie wrote:
I'm playing around potting some electronics for immersion in water
up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?


You can get cable that is filled with a hydrophobic gel, so that even
if the cable does have a leak somewhere along the length, water won't
wick along it.

If your device is being potted, you could put a short section of
single strand bare copper wire between the circuit board and each
stranded wire. The epoxy should form a good seal to the bare copper.
Liquid water in the stranded wire ought to stop at the solder joint
between the stranded and non-stranded wire. Probably some water will
diffuse through all of the plastics and resins eventually though.

You could try corona-treating the polyethylene and PVC which is much
like flame treating but may produce less heat.






I've not been able to find jelly cable or water block treated cable at a
viable price. The inexpensive type is solid core conductors and I need
multi-strand unfortunately.

I bought some UV sensors from this Australian company:
http://www.monitorsensors.com/
and they came with stranded gel-filled cable IIRC.

They seem to be a small company so maybe they will sell you some cable
if the minimum order quantity is too large from usual suppliers.

I'm not sure I would take their advice on waterproofing though: one of
the UV sensors went intermittent and then stopped working not long after
it was installed outdoors.


Thanks Charis, I'll have a look.