to vacuum or not to vacuum... HEI epoxy potting?

On Friday, 1 November 2019 15:52:17 UTC, Jim Horton wrote:

On 11/1/19 9:34 AM, Bill Sloman wrote:


NT will never know. He can ask the questions, but doesn't seem to be much good at finding answers.

No disrespect, but I don't think that's a fair statement. Almost

true of most of his anti-personnel comments. People mostly ignore it

always, I DO research this stuff before asking here. The big problem I
have with Internet research is that there's too much information, so
trying to narrow down a specific thing for a specific task can take huge
amounts of time. I figured people here might have more experience in
many of the things I've done, or trying to do, to help me narrow it down
and save time.

Since posting here, and both with the group's help and my own, I've
found out some things about both mineral oil and wax potting:

1) Mineral oil can expand right out through the container if it can.
In this case, I wasn't aware how much it could expand/ contract with
environmental changes. The leakage I experienced with my ten year
stored spark device came from mineral oil expanding out from the
junction box cover. So, once rehoused, I took measures to both allow
for expansion and to compensate for any future leaks.

2) Paraffin wax probably isn't ideal for potting. My own experiments
cycling a block into and out of the freezer the last few days have
resulted in a block ending up with many cracks. However, now it's time
to remelt the block and repeat the same experiment cycling into and out
of the refrigerator since, after all, the device will never be stored
outside of this range. Then, I'll know for sure.

it's fine within temperature limits, but not for all jobs. The 1930s caps I redid (paper in wax in cans) showed no cracking but the paper caps were all leaky nonetheless. So I'm not certain what the degradation mechanism is.

3) I better think again before I use epoxy. Item will be
non-serviceable, vacuuming could be a problem with my limited equipment
available, and there is a lot of exothermic reaction with the 32 oz I
would need.

and of course a partial (or even a perfect) vacuum doesn't save you from that.

Such information can be hit and/or miss online, but the
group has been very helpful in helping me make the decision to probably
not try epoxy potting, especially for something this large. They just
helped me save $30 for the cheapest electronic epoxy I would have used.


Things inconclusive or I have not found out here (or anywhere else):

1) Ideal wax and additive mix ratios to better improve wax properties.
I did find information on wax-rosin ratios, but then controversial
performance if used in a heated circuit. Then there was machinable wax
(wax-LDPE), and wax-EVA mixes. Only information on machinable wax was
found and proper EVA ratios remain unknown.

2) I was not aware of RTV being used for anything other than small jobs
and/or automotive use. Now, if one wanted to criticize me, here is
where they could do it by the fact that I never specified an insulator
budget amount in which both the electronic RTV and most epoxy do not
fall.

So, again, I apologize if I haven't already found the answers I have
been looking for. I really enjoy reading this and the repair group's
posts especially since so much usenet has become useless.

Silly cone has a nice assortment of upsides for your job. Wax is still practical if there's not much temp swing.


NT

 

[Michael Terrell]

On Friday, November 1, 2019 at 6:57:57 PM UTC-4, tabb...@gmail.com wrote:

it's fine within temperature limits, but not for all jobs. The 1930s caps I redid (paper in wax in cans) showed no cracking but the paper caps were all leaky nonetheless. So I'm not certain what the degradation mechanism is.

Paper capacitors were made with cheap, high acid paper. Over time, it starts to disintegrate like an old newspaper.

 

[Bill Sloman]

On Saturday, November 2, 2019 at 11:16:01 AM UTC+11, Rick C wrote:

On Friday, November 1, 2019 at 7:56:30 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 1:34:44 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid..

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated?

Because that was the way it was done at places I've seen doing it.

All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

Getting the dissolved air out of the potting compound before it goes into the mold lets you do it when there's a lot more exposed surface for the bubbles to come out of, and can speed up the process a lot.

This is not a production run, no one cares if it takes a while. The process you describe is overly complex for a one-off.

It was a prototyping set-up. It was just complex enough to avoid inconvenient and time-consuming problems. People want prototypes as soon as possible, and they don't like hanging around when they don't have to.

To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

You are imagining that the encapsulant has a high vapour pressure component that boils at a specific pressure. Dissolved air doesn't work that way.. Any water in the encapsulant will boil at about 20 torr if the encapsulant is at room temperature, but there shouldn't be any.

I never mentioned any numbers.

Surprise, surprise.

> I'm not talking about foam from the air. I'm talking about the encapsulant forming enough vapor that the entire stinking mess expands out of the container and spills into the vacuum chamber making a huge mess that then has to be cleaned up so you can start over. This isn't imagination. This is experience.

You've had experience of doing it wrong, and you want to reject the experience of people who had done it often enough to do it better.

I didn't invent that set-up - I got to see it in use and more or less understood why it was set up the way it was, which you seem to be having a problem with.

--
Bill Sloman, Sydney

 

[Jim Horton]

On 11/1/19 8:09 PM, Bill Sloman wrote:

On Saturday, November 2, 2019 at 2:52:17 AM UTC+11, Jim Horton wrote:
On 11/1/19 9:34 AM, Bill Sloman wrote:


NT will never know. He can ask the questions, but doesn't seem to be much good at finding answers.

No disrespect, but I don't think that's a fair statement.

I apologize yet again. I thought "NT" meant me somehow. Not sure who
he/she is, but a big thank you for the clarification! I really do
appreciate this and the other groups.

Sadly, it's fair statement about NT. He does do the research - after a fashion - but has an unhappy knack of settling on the wrong answers.

Almost always, I DO research this stuff before asking here. The big problem I
have with Internet research is that there's too much information, so
trying to narrow down a specific thing for a specific task can take huge
amounts of time. I figured people here might have more experience in
many of the things I've done, or trying to do, to help me narrow it down
and save time.

The big problem with internet research is that there's a lot of false and misleading information, primarily designed to sell particular products rather than help the researcher.

Critical thinking is required.

Quite right and if you have a few extra funds to experiment without
putting yourself in the grave (i.e taking proper precautions), all the
better!

Since posting here, and both with the group's help and my own, I've
found out some things about both mineral oil and wax potting:

1) Mineral oil can expand right out through the container if it can.
In this case, I wasn't aware how much it could expand/ contract with
environmental changes. The leakage I experienced with my ten year
stored spark device came from mineral oil expanding out from the
junction box cover. So, once rehoused, I took measures to both allow
for expansion and to compensate for any future leaks.

2) Paraffin wax probably isn't ideal for potting. My own experiments
cycling a block into and out of the freezer the last few days have
resulted in a block ending up with many cracks. However, now it's time
to remelt the block and repeat the same experiment cycling into and out
of the refrigerator since, after all, the device will never be stored
outside of this range. Then, I'll know for sure.

3) I better think again before I use epoxy. Item will be
non-serviceable, vacuuming could be a problem with my limited equipment
available, and there is a lot of exothermic reaction with the 32 oz I
would need. Such information can be hit and/or miss online, but the
group has been very helpful in helping me make the decision to probably
not try epoxy potting, especially for something this large. They just
helped me save $30 for the cheapest electronic epoxy I would have used.

Things inconclusive or I have not found out here (or anywhere else):

1) Ideal wax and additive mix ratios to better improve wax properties.
I did find information on wax-rosin ratios, but then controversial
performance if used in a heated circuit. Then there was machinable wax
(wax-LDPE), and wax-EVA mixes. Only information on machinable wax was
found and proper EVA ratios remain unknown.

2) I was not aware of RTV being used for anything other than small jobs
and/or automotive use. Now, if one wanted to criticize me, here is
where they could do it by the fact that I never specified an insulator
budget amount in which both the electronic RTV and most epoxy do not
fall.

So, again, I apologize if I haven't already found the answers I have
been looking for. I really enjoy reading this and the repair group's
posts especially since so much usenet has become useless.

Some of our posters do get some of their information from deeply suspect sources. Cursitor Doom is a particularly horrible example, but he's also a particularly obvious example. None of the sane posters here take him seriously.

Yes, one has to be careful. The 'net is getting better. An example of
really poor information out there relates to a guy wanting to build a
stun gun recently. Just out of curiosity, I decided to look up what
current stun guns are for sale on the web. The majority are being
falsely advertised! 9 billion or 9 million volts, yeah right, but
people seem to buy them like crazy. I doubt many of them would do much
other than cause a bit of pain. Videos I see of them produce maybe 1-2"
sparks across their electrodes which is maybe 25-50 KV max, a far cry
from their millions advertised. Not sure how they are getting away with
that.

 

On Friday, 1 November 2019 23:31:00 UTC, Jim Horton wrote:

On 11/1/19 7:23 PM, whit3rd wrote:
On Friday, November 1, 2019 at 4:14:54 AM UTC-7, DecadentLinux...@decadence.org wrote:

I would not recommend an epoxy unless you plan on zero
serviceablity. Use an RTV so you can service it if it fails.

Huh? RTV is 'room temperature vulcanizing' material, it sets up just as
irreversibly as epoxy does. How is that service-friendly?

I was wondering about that, but didn't know quite enough about
electronic RTV to ask.

it can be cut off easily


NT

 

[Bill Sloman]

On Saturday, November 2, 2019 at 1:34:44 AM UTC+11, Rick C wrote:

On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated?

Because that was the way it was done at places I've seen doing it.

> All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

Getting the dissolved air out of the potting compound before it goes into the mold lets you do it when there's a lot more exposed surface for the bubbles to come out of, and can speed up the process a lot.

> To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

You are imagining that the encapsulant has a high vapour pressure component that boils at a specific pressure. Dissolved air doesn't work that way. Any water in the encapsulant will boil at about 20 torr if the encapsulant is at room temperature, but there shouldn't be any.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Saturday, November 2, 2019 at 9:57:57 AM UTC+11, tabb...@gmail.com wrote:

On Friday, 1 November 2019 15:52:17 UTC, Jim Horton wrote:
On 11/1/19 9:34 AM, Bill Sloman wrote:


NT will never know. He can ask the questions, but doesn't seem to be much good at finding answers.

No disrespect, but I don't think that's a fair statement.

true of most of his anti-personnel comments. People mostly ignore it

NT certainly does. He's been indulging in his little ego trips for years, and seems to imagine that complaining about being slandered is an appropriate response to being jeered at for posting bad information.

<snip>

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Saturday, November 2, 2019 at 2:52:17 AM UTC+11, Jim Horton wrote:

On 11/1/19 9:34 AM, Bill Sloman wrote:


NT will never know. He can ask the questions, but doesn't seem to be much good at finding answers.

No disrespect, but I don't think that's a fair statement.

Sadly, it's fair statement about NT. He does do the research - after a fashion - but has an unhappy knack of settling on the wrong answers.

Almost always, I DO research this stuff before asking here. The big problem I
have with Internet research is that there's too much information, so
trying to narrow down a specific thing for a specific task can take huge
amounts of time. I figured people here might have more experience in
many of the things I've done, or trying to do, to help me narrow it down
and save time.

The big problem with internet research is that there's a lot of false and misleading information, primarily designed to sell particular products rather than help the researcher.

Critical thinking is required.

Since posting here, and both with the group's help and my own, I've
found out some things about both mineral oil and wax potting:

1) Mineral oil can expand right out through the container if it can.
In this case, I wasn't aware how much it could expand/ contract with
environmental changes. The leakage I experienced with my ten year
stored spark device came from mineral oil expanding out from the
junction box cover. So, once rehoused, I took measures to both allow
for expansion and to compensate for any future leaks.

2) Paraffin wax probably isn't ideal for potting. My own experiments
cycling a block into and out of the freezer the last few days have
resulted in a block ending up with many cracks. However, now it's time
to remelt the block and repeat the same experiment cycling into and out
of the refrigerator since, after all, the device will never be stored
outside of this range. Then, I'll know for sure.

3) I better think again before I use epoxy. Item will be
non-serviceable, vacuuming could be a problem with my limited equipment
available, and there is a lot of exothermic reaction with the 32 oz I
would need. Such information can be hit and/or miss online, but the
group has been very helpful in helping me make the decision to probably
not try epoxy potting, especially for something this large. They just
helped me save $30 for the cheapest electronic epoxy I would have used.

Things inconclusive or I have not found out here (or anywhere else):

1) Ideal wax and additive mix ratios to better improve wax properties.
I did find information on wax-rosin ratios, but then controversial
performance if used in a heated circuit. Then there was machinable wax
(wax-LDPE), and wax-EVA mixes. Only information on machinable wax was
found and proper EVA ratios remain unknown.

2) I was not aware of RTV being used for anything other than small jobs
and/or automotive use. Now, if one wanted to criticize me, here is
where they could do it by the fact that I never specified an insulator
budget amount in which both the electronic RTV and most epoxy do not
fall.

So, again, I apologize if I haven't already found the answers I have
been looking for. I really enjoy reading this and the repair group's
posts especially since so much usenet has become useless.

Some of our posters do get some of their information from deeply suspect sources. Cursitor Doom is a particularly horrible example, but he's also a particularly obvious example. None of the sane posters here take him seriously.

--
Bill Sloman, sydney

 

[Rick C]

On Friday, November 1, 2019 at 7:56:30 PM UTC-4, Bill Sloman wrote:

On Saturday, November 2, 2019 at 1:34:44 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of..

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated?

Because that was the way it was done at places I've seen doing it.

All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

Getting the dissolved air out of the potting compound before it goes into the mold lets you do it when there's a lot more exposed surface for the bubbles to come out of, and can speed up the process a lot.

This is not a production run, no one cares if it takes a while. The process you describe is overly complex for a one-off.

To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

You are imagining that the encapsulant has a high vapour pressure component that boils at a specific pressure. Dissolved air doesn't work that way. Any water in the encapsulant will boil at about 20 torr if the encapsulant is at room temperature, but there shouldn't be any.

I never mentioned any numbers. I'm not talking about foam from the air. I'm talking about the encapsulant forming enough vapor that the entire stinking mess expands out of the container and spills into the vacuum chamber making a huge mess that then has to be cleaned up so you can start over. This isn't imagination. This is experience.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Friday, November 1, 2019 at 8:32:39 PM UTC-4, Bill Sloman wrote:

On Saturday, November 2, 2019 at 11:16:01 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:56:30 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 1:34:44 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated?

Because that was the way it was done at places I've seen doing it.

All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

Getting the dissolved air out of the potting compound before it goes into the mold lets you do it when there's a lot more exposed surface for the bubbles to come out of, and can speed up the process a lot.

This is not a production run, no one cares if it takes a while. The process you describe is overly complex for a one-off.

It was a prototyping set-up. It was just complex enough to avoid inconvenient and time-consuming problems. People want prototypes as soon as possible, and they don't like hanging around when they don't have to.

To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

You are imagining that the encapsulant has a high vapour pressure component that boils at a specific pressure. Dissolved air doesn't work that way. Any water in the encapsulant will boil at about 20 torr if the encapsulant is at room temperature, but there shouldn't be any.

I never mentioned any numbers.

Surprise, surprise.

I'm not talking about foam from the air. I'm talking about the encapsulant forming enough vapor that the entire stinking mess expands out of the container and spills into the vacuum chamber making a huge mess that then has to be cleaned up so you can start over. This isn't imagination. This is experience.

You've had experience of doing it wrong, and you want to reject the experience of people who had done it often enough to do it better.

I didn't invent that set-up - I got to see it in use and more or less understood why it was set up the way it was, which you seem to be having a problem with.

The only problem is that you insist on making it many steps when those extra steps add nothing of benefit. Now that we have gotten to the root of the issue you stop talking about the issue and attack the person.

Bottom line is there is no need to pump the epoxy first and then again when adding it to the mold. At least you haven't talked about any reason to do that and you have mentioned the absurd complexity of adding a mechanism to the vacuum chamber to manipulate the ingredients while inside.

Just give it up. You never admit when you are wrong. You just have a compulsion to argue with people here, mostly the idiots who can barely put words on a page... as if that were an accomplishment.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Bill Sloman]

On Saturday, November 2, 2019 at 12:01:48 PM UTC+11, Rick C wrote:

On Friday, November 1, 2019 at 8:32:39 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 11:16:01 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:56:30 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 1:34:44 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated?

Because that was the way it was done at places I've seen doing it.

All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

Getting the dissolved air out of the potting compound before it goes into the mold lets you do it when there's a lot more exposed surface for the bubbles to come out of, and can speed up the process a lot.

This is not a production run, no one cares if it takes a while. The process you describe is overly complex for a one-off.

It was a prototyping set-up. It was just complex enough to avoid inconvenient and time-consuming problems. People want prototypes as soon as possible, and they don't like hanging around when they don't have to.

To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

You are imagining that the encapsulant has a high vapour pressure component that boils at a specific pressure. Dissolved air doesn't work that way. Any water in the encapsulant will boil at about 20 torr if the encapsulant is at room temperature, but there shouldn't be any.

I never mentioned any numbers.

Surprise, surprise.

I'm not talking about foam from the air. I'm talking about the encapsulant forming enough vapor that the entire stinking mess expands out of the container and spills into the vacuum chamber making a huge mess that then has to be cleaned up so you can start over. This isn't imagination. This is experience.

You've had experience of doing it wrong, and you want to reject the experience of people who had done it often enough to do it better.

I didn't invent that set-up - I got to see it in use and more or less understood why it was set up the way it was, which you seem to be having a problem with.

The only problem is that you insist on making it many steps when those extra steps add nothing of benefit.

It's one extra step. Letting the encapsulant liquid froth out before you put it into the mold gives you better control of the degassing process.

I don't insist on it - I'm just pointing out that the prototyping set up I saw allowed you to do it that way.

Now that we have gotten to the root of the issue you stop talking about the issue and attack the person.

Bottom line is there is no need to pump the epoxy first and then again when adding it to the mold.

You can get away with not doing it, but out-gassing the encapsulant in the mold takes longer than doing it in an open beaker, and works better.

> At least you haven't talked about any reason to do that and you have mentioned the absurd complexity of adding a mechanism to the vacuum chamber to manipulate the ingredients while inside.

The mechanism just let you tilt the beaker through the vacuum wall. It was a conical hole in the side of the chamber, plugged with a ground glass plug which had been lubricated with vacuum grease. Demountable laboratory glass-ware uses standard range of cones and sockets, which you can buy off the shelf.

Back when I was doing the glass-blowing on my vacuum line (as a graduate student) I could have whipped something up in a few minutes.

The chemistry department stores had all the parts I would have needed.

> Just give it up. You never admit when you are wrong.

Actually I do. It doesn't happen often, but the posts where I've done it tend to contain the word "oops" which makes them easy to find.

I'm not wrong all that often, and I'm fairly sure that I'm not wrong here.

> You just have a compulsion to argue with people here, mostly the idiots who can barely put words on a page... as if that were an accomplishment.

I'm just as happy to argue with intelligent people - it isn't necessary nearly as often.

You are confusing "arguing" and "disagreeing". I do tend to point out when people get things wrong, and our crew of idiots do that a lot.

--
Bill Sloman, Sydney

 

whit3rd <whit3rd@gmail.com> wrote in
news:87c37d58-86ae-4210-a7e6-2677f51f6b29@googlegroups.com:

On Friday, November 1, 2019 at 4:14:54 AM UTC-7,
DecadentLinux...@decadence.org wrote:

I would not recommend an epoxy unless you plan on zero
serviceablity. Use an RTV so you can service it if it fails.

Huh? RTV is 'room temperature vulcanizing' material, it sets up
just as irreversibly as epoxy does. How is that
service-friendly?

Well, son... it ain't yer tube of window caulk. ;-)

RTV for HV potting is 100% serviceable. It shears easily.

Epoxy, on the other hand cures usually quite rigid.

Remember "Stycast"?

 

[Peter]

Many years ago I worked at a UK firm making HV power supplies.

We always prepared both epoxy and silicone in vacuum. It went into a
bucket and into a vacuum chamber, whose evacuation rate was manually
controlled (via a glass window) so the material didn't "boil" over the
edge. Quite a fun job!

Eventually it would be evacuated fully and then poured into the mould
(containing the electronics) and then the whole mould would be
evacuated again, to remove bubbles which got in during the pouring
process.

The company is long gone. They specialised in precision (ppm grade) DC
power supplies for all kinds of applications.

 

Peter <nospam@nospam9876.com> wrote in
news:qpm34h$3jt$1@dont-email.me:

Many years ago I worked at a UK firm making HV power supplies.

We always prepared both epoxy and silicone in vacuum. It went into
a bucket and into a vacuum chamber, whose evacuation rate was
manually controlled (via a glass window) so the material didn't
"boil" over the edge. Quite a fun job!

I noticed that most RTVs evacuate pretty quick. The Polyurethanes
were a lot more 'airy'. But the worst is transformer varnish. It
'boils' seemingly forever, but finally gets done and can be used for
sealing up transformers.

Eventually it would be evacuated fully and then poured into the
mould (containing the electronics) and then the whole mould would
be evacuated again, to remove bubbles which got in during the
pouring process.

Yeah, there is air trapped in the PCB layers that gets released as
well. The low pressure also vaporizes any water, which PCBs also
have an affinity for, especially in typically non-masked HV sections.

The company is long gone. They specialised in precision (ppm
grade) DC power supplies for all kinds of applications.

A big UK HVPS maker is HiTek Power in Littlehampton, West Sussex.
Now part of Advanced Energy group.

Lots of precision DC supply expertise.

 

[Peter]

DecadentLinuxUserNumeroUno@decadence.org wrote

A big UK HVPS maker is HiTek Power in Littlehampton, West Sussex.
Now part of Advanced Energy group.

Lots of precision DC supply expertise.

There are several around, probably offshoots from the old Wallis
Electronics. Applied Kilovolts is a good one.
https://www.appliedkilovolts.com/

It was a fun business. One of the projects done at Wallis was a 500kV
unit with 1ppm-grade wirewound resistors (lots of them) for the
feedback network. The whole multiplier stack was in a huge steel
cylinder with some gas inside; probably sulphur hexafloride or some
such. Mann Components (long gone too) made the resistors. I have a few
of their 0.01% resistors still, 1972 date codes, and all are well
within 0.01% now.

Brandenburg was another old one but they used air insulation. It's not
as good; you get corona so a bit of noise.

 

[Jim Horton]

Appreciate everyone's info on the epoxy. I still think if I ever went
the route with the HEI's, I probably wouldn't do the vacuum because the
HEI transformers themselves appear to already be potted, so it would
have just been a matter of insulating HV to ground and core. However, I
have decided not to try it.

The paraffin is holding up lots better cycling into and out of the
refrigerator as opposed to the freezer. The freezer bottoms out at 0 F
while the refrigerator at 36 F. The house is cooling fast though at 57
F now, so will probably have to continue cycling tests next spring and
summer when it could reach 87 F.

 

[Rick C]

On Sunday, November 3, 2019 at 11:47:49 AM UTC-5, Jim Horton wrote:

Appreciate everyone's info on the epoxy. I still think if I ever went
the route with the HEI's, I probably wouldn't do the vacuum because the
HEI transformers themselves appear to already be potted, so it would
have just been a matter of insulating HV to ground and core. However, I
have decided not to try it.

The paraffin is holding up lots better cycling into and out of the
refrigerator as opposed to the freezer. The freezer bottoms out at 0 F
while the refrigerator at 36 F. The house is cooling fast though at 57
F now, so will probably have to continue cycling tests next spring and
summer when it could reach 87 F.

Do you really think you need to test at higher temps? The stuff was poured at some 120+F. It is the low end where it gets brittle. The high end makes the wax pliable. They use paraffin wax for dental uses and it has to be warmed a bit in your hand to make it soft enough to form. That's all it takes to get soft, body temperature around 98°F.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

 

[Jim Horton]

On 11/3/19 12:19 PM, Rick C wrote:

Do you really think you need to test at higher temps? The stuff was poured at some 120+F. It is the low end where it gets brittle. The high end makes the wax pliable. They use paraffin wax for dental uses and it has to be warmed a bit in your hand to make it soft enough to form. That's all it takes to get soft, body temperature around 98°F.

Probably not. The second HEI coil assembly had already been potted in
the wax last week and has been sitting on the shelf ever since. These
are just small, separate blocks I made just for testing purposes. The
house will never get above 87 F during the hottest summer days, but will
soon dip to 47 in another six weeks or so. So, those being the extremes
of storage, I think the device will do well.

I may pick up a block of one of the other wax types you recommended and
try cycling it throughout the next year, throwing in built up summer car
heat as an extra challenge. One block isn't going to kill the budget.

 

[Chris Jones]

On 02/11/2019 12:01, Rick C wrote:

On Friday, November 1, 2019 at 8:32:39 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 11:16:01 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:56:30 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 1:34:44 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated?

Because that was the way it was done at places I've seen doing it.

All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

Getting the dissolved air out of the potting compound before it goes into the mold lets you do it when there's a lot more exposed surface for the bubbles to come out of, and can speed up the process a lot.

This is not a production run, no one cares if it takes a while. The process you describe is overly complex for a one-off.

It was a prototyping set-up. It was just complex enough to avoid inconvenient and time-consuming problems. People want prototypes as soon as possible, and they don't like hanging around when they don't have to.

To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

You are imagining that the encapsulant has a high vapour pressure component that boils at a specific pressure. Dissolved air doesn't work that way. Any water in the encapsulant will boil at about 20 torr if the encapsulant is at room temperature, but there shouldn't be any.

I never mentioned any numbers.

Surprise, surprise.

I'm not talking about foam from the air. I'm talking about the encapsulant forming enough vapor that the entire stinking mess expands out of the container and spills into the vacuum chamber making a huge mess that then has to be cleaned up so you can start over. This isn't imagination. This is experience.

You've had experience of doing it wrong, and you want to reject the experience of people who had done it often enough to do it better.

I didn't invent that set-up - I got to see it in use and more or less understood why it was set up the way it was, which you seem to be having a problem with.

The only problem is that you insist on making it many steps when those extra steps add nothing of benefit. Now that we have gotten to the root of the issue you stop talking about the issue and attack the person.

Bottom line is there is no need to pump the epoxy first and then again when adding it to the mold.

You can't achieve a very good vacuum at the bottom of a deep mould that
is already filled with a liquid potting compound. Gravity acts on the
liquid, causing the pressure at the bottom of the liquid to be higher
than that at the top of the liquid.

Surface tension might also hinder the escape of gas from crevices in a
device that is already submerged.

Depending on the purpose of the potting process you may or may not care
about small bubbles remaining, but some people do need to care.

I have never needed to be extremely careful about eliminating bubbles so
I have never built anything to pour encapsulant under vacuum, but I do
degas the encapsulant in a separate beaker before pouring, simply
because it does tend to froth and overflow unless that step is carried
out in a beaker able to contain many times the volume of the liquid
encapsulant.

 

[Rick C]

On Sunday, November 3, 2019 at 9:09:08 PM UTC-5, Chris Jones wrote:

On 02/11/2019 12:01, Rick C wrote:
On Friday, November 1, 2019 at 8:32:39 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 11:16:01 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:56:30 PM UTC-4, Bill Sloman wrote:
On Saturday, November 2, 2019 at 1:34:44 AM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated?

Because that was the way it was done at places I've seen doing it.

All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

Getting the dissolved air out of the potting compound before it goes into the mold lets you do it when there's a lot more exposed surface for the bubbles to come out of, and can speed up the process a lot.

This is not a production run, no one cares if it takes a while. The process you describe is overly complex for a one-off.

It was a prototyping set-up. It was just complex enough to avoid inconvenient and time-consuming problems. People want prototypes as soon as possible, and they don't like hanging around when they don't have to.

To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

You are imagining that the encapsulant has a high vapour pressure component that boils at a specific pressure. Dissolved air doesn't work that way. Any water in the encapsulant will boil at about 20 torr if the encapsulant is at room temperature, but there shouldn't be any.

I never mentioned any numbers.

Surprise, surprise.

I'm not talking about foam from the air. I'm talking about the encapsulant forming enough vapor that the entire stinking mess expands out of the container and spills into the vacuum chamber making a huge mess that then has to be cleaned up so you can start over. This isn't imagination. This is experience.

You've had experience of doing it wrong, and you want to reject the experience of people who had done it often enough to do it better.

I didn't invent that set-up - I got to see it in use and more or less understood why it was set up the way it was, which you seem to be having a problem with.

The only problem is that you insist on making it many steps when those extra steps add nothing of benefit. Now that we have gotten to the root of the issue you stop talking about the issue and attack the person.

Bottom line is there is no need to pump the epoxy first and then again when adding it to the mold.

You can't achieve a very good vacuum at the bottom of a deep mould that
is already filled with a liquid potting compound. Gravity acts on the
liquid, causing the pressure at the bottom of the liquid to be higher
than that at the top of the liquid.

That is true for various values of "deep". In this case you will never notice the delta from the top to the bottom of a less than 1 foot deep mold. Materials like this are the same density as water to a first approximation. Water is 32 feet to 1 atm. So 1 foot of mold will only cause 1/32 of an atm difference in pressure.

Surface tension might also hinder the escape of gas from crevices in a
device that is already submerged.

When the volume of trapped air expands my multiple factors, it will help get the air out. Any remaining bubbles will be very tiny when the vacuum is released. Since these air bubbles will exist whether or not you pre-vacuate the epoxy, it has no impact on the result.

Depending on the purpose of the potting process you may or may not care
about small bubbles remaining, but some people do need to care.

How can you do better in getting rid of them?

I have never needed to be extremely careful about eliminating bubbles so
I have never built anything to pour encapsulant under vacuum, but I do
degas the encapsulant in a separate beaker before pouring, simply
because it does tend to froth and overflow unless that step is carried
out in a beaker able to contain many times the volume of the liquid
encapsulant.

It won't froth if you don't draw too much vacuum.

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209