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Whats an inexpensive potting compound solution?

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RF_Burns

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Just wondering what can be used as an inexpensive potting compound. The commercial solutions seem fairly expensive at $40.00 for 350ml. The small 12V timer will cost more for the potting than all the components together cost!

RTV seems even more expensive.

Any ideas?

thanks
 
Just wondering what can be used as an inexpensive potting compound. The commercial solutions seem fairly expensive at $40.00 for 350ml. The small 12V timer will cost more for the potting than all the components together cost!

RTV seems even more expensive.

Any ideas?

thanks

hi,
Why do you need to pot the unit. ??
There are lots of different formula's for different type of protection.
 
If you application doesn't see a high temperature, you could use paraffin wax.
 
Its just a power-off timer for 2-way radios. Prevents dead vehicle batteries if left on over the weekend, or even overnight in the winter.

Using a little 2"x1.5"x1" potting box seemed to be the easiest to install.

I never thought of wax, would have to check what temp it would soften at for hot summer days.

Thanks for the ideas
 
The melting point of paraffin wax can be as low as 120F, so that's not a good candidate for your potting requirement.

Perhaps silicone caulking sealer, which is fairly inexpensive, would work.
 
I have found the common silicones (ones that smell like vinegar while curing), corrode the board and upset the circuit's operation. I know the RTV type is safe, but is very expensive as well, some are $80.00 for a caulking gun size tube.
 
Home brewed machinable wax will work well and has a high enough melting point to be in Florida in the summer with no issues. There are several brews available but it is basically wax and a certain type of plastic melted together and poured into a cast and it hardens solid enough to machine. The plastic is the lids off of milk bottles if I am not mistaken. A quick google will get the answer or if you cant find it PM me and I will get the formula from the minilathe site I read about it on for you. Cheap to make too. Heres the link to that thread: https://groups.yahoo.com/group/7x12minilathe/message/53490
Bob
 
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Looks like you have to join that group to view messages.
I do not think they will mind if we repeat it here. Saves people with no interest in their forum joining to read this.

New website is Machinable Wax
-----------------------------------------------------------
Found this website: **broken link removed** they
have a great description on how to make machinable wax at home. All you
basically do is melt LDPE in a deep fat fryer full of paraffin wax. Basically
you raise raise 4lb of paraffin wax to 95C for LDPE or 110C for HDPE. You then
add 1 lb of LDPE or HDPE very slowly. Any amount can be made. Considering the
limitations of a Maker bot drimel toolhead, this could be a great substrait.

The store this is from looks like it's dying, so I will quote it here:

"You may be looking for a cost effective solution for machinable wax.
One basic composition of machinable wax is simply standard parrafin wax,
available at most craft stores, and polyethylene.

What is polyethylene? Its most basic description is that it is a thermoplastic
and it is derived from petroleum. The two main types are Low Density and High
Density polyethylene, commonly referred to as LDPE and HDPE respectively. The
following is a list of common LDPE/HDPE items:

* Grocery store bags
* Garbage Bags
* Paint drops (plastic sheets)
* Lawn Chairs
* Cutting Boards
* Plastic Lumber
* Milk Jugs
* Commercial Bathroom stalls

One of THE most common uses is in plastic grocery store bags. This is also
probably the best source of LDPE/HPDE for use in making homemade machinable
wax. Its readily available as most people have 50 or so stuffed away in a
pantry or cabinet. Perfect to make a little machinable wax with.

Alternate sources for use in a machinable wax recipe, would be plastic drop
clothes used in painting. They can be purchased at most home improvement
stores.

Most plastics are usually marked with LDPE or HDPE and have a number 4 or 2
(respectively) located on recyclable polyethylene.

In general its easier to melt down LDPE for use in machinable wax. LDPE has a
lower melting point, and hence mixes better with the parrafin. LDPEs melting
point for continuous heat is 203F (95C). HDPEs melting point with continuous
heat is 230F(110C). It may be helpful to note that in general Target uses LDPE
and Walmart uses HDPE.

What to use for melting??? You everyday kitchen cooker will work fine. Its
HIGHLY recommended that you dedicate a cooker to your machinable wax recipe.
Temperature control that lists numbers is better than just lo/med/high. Do not
use a double boiler, they generally only get up to 212F(97C). Thats only barely
hot enough to melt LDPE, and it would take a lot longer.

So you have your block of candle wax, a few handfulls of grocery store bags,
and a cooker. A METAL kitchen strainer will be very helpful as well. The large
ones used for pasta noodles are best. You also need a mold to poor your
machinable wax into. Use metal molds, plastic tupperware will melt or warp from
the heat.

The general machinable wax recipe is a 4:1 ratio of parrafin wax to LDPE/HDPE.
Your machinable wax recipe could vary depending on how hard or soft you want
the wax to be. Obviously, the more plastic you add the harder it will get. But
like sugar in a glass of tea, eventually the polyethylene will stop disolving
and you will get large clumps of polyethylene form in the pot. If you poor it
in a pan without straining it, it will look like goo in your wax and will not
carve very well.
We will use a 4lb wax to 1lb LDPE in this machinable wax recipe example. So you
will end up with about 5 lbs of machinable wax.

Start out by melting the wax in the pot. Get it good and hot, about 250-275F,
max 275F.

Once youve reached temp, start feeding in small pieces of the plastic. If you
can, cut up the plastic into small strips before feeding it in. It will melt
better and more consistently than just dumping whole bags in. Stir constantly
and use good ventilation.

You will know youve added enough because the plastic will stop melting as well.
It will start balling up into clumps.

Now you can use the kitchen strainer, poor your wax through the strainer into
your mold. This will remove any unwanted clumps from the mix.
For cooling, try to slow down the cooling as much as possible. You can wrap the
mold with an old blanket, or use a small space heater to keep the area around
the mold warm. Some warping is unavoidable. You can either plane the finished
product, or use a CNC router to shave down the top.
You will be left with a good quality machinable wax. Refine your machinable wax
recipe. You may try different types of wax, or different types of polyethylene
in your recipe.

We also offer kits of shaved LDPE and HDPE. Our kits are sold by weight and use
LDPE/HDPE shavings that will melt better than most types of plastic you may
find."
 
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Many Asian made potted devices use an inert filler, usually powdered talc. You can use about 80-85% filler and 15-20% resin, it brings the cost right down but is a little harder to mix and pour. They use the same stuff in those really cheap figureines you buy in the gift shops.
 
Thanks 3Vo, I didnt test the link last night before I went to bed, but that is the same as the link. The stuff apparently works very good and is very stable at higher temps.
Bob
 
Just for giggles I checked out paraffin prices on the web.

In 5lb quantities prices are $3 to $5 a lb.

Candlewic: Paraffin Candle Wax sells 50lb for $66. That is a lot of wax unless you are doing a production run or sharing an order.

It seems all paraffin has some oil content. Paraffin Candle Wax from Candlewic shows 1.5% down to .3%, The lower the oil content the higher the price and melting point.

The oil leads me to think that maybe an oil proof conformal coating should be used first.
 
Paraffin wax is often sold in grocery stores with the canning supplies.
 
That machinable wax sounds really interesting, but I wonder about the effects on components of 100C + slow cooling substance.
 
Anyone have any advice on the effects of pouring 100C wax onto the electronic components such as electrolytic caps etc?

I'd like to give this a try.. but i'm kinda worried about this.

In the past I have used Bondo auto body filler for some circuits were just a simple point to point wiring (no circuit board) but I think its too thick to pour or press into a small potting box.

thanks for all the ideas.
 
I think wax is a bad idea. Wax and pitch were the kind of hot melt fillers they used in the bad old days.

What was wrong with my idea of using a 2-part resin and cheap filler powder?
 
After looking at the data sheets for the max temps for most components, I too tend to think that it could be a bad idea to expose the components to that high of a temp for whatever time it takes to cool below a critical point. The Model airplane epoxy that I use is very inexpensive and as RB suggested there is an additive called micro balloon filler that extends the amount of space that the epoxy fills. The epoxy kit is 9 USD and the filler (which is essentially glass beads) is an additional 4-5 dollars and will end up filling about 12 Fl Ounces. I would look into the exothermic/endothermic temps of epoxy also since it does generate heat but not as high or for as long if I remember corrsctly. I would hate to see you build a circuit and damage it beyond repair due to overheating before you even get to use it.
Bob
 
Thanks for all the input. I think I'll go for the 2-part and filler.

Now to find a Canadian distributor.
The stuff is available through Tower Hobbies on the web and they ship North of the Border. I would use the finishing grade since it dries clear so you can see if the components are outgassing or discoloring. Just a thought
Bob
 
Inert fillers like talc powder can be bought from art supply stores (for sculptors) and cost only a couple of dollars a pound.

Exothermic reaction won't be a problem when using a lot of filler, there is such a small % of resin:volume that you have the opposite problem, you probably need to incubate it to get it warm to get a good hard cure.

The main problem with wax is that is fills the void but doesn't bond, so over time as it expands and contracts it separates from the box and all the components leaving a tiny airgap around everything, and moisture will seep in through capillary action. Resins sold for "topcoat" use bond well and have some flexibility and elasticity designed in so it won't separate from the components.
 
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