Making an Electret, or several actually.

[conradelektro]

It might be interesting to mix some 19th century electrets, but nowadays one can use plastic materials. I often use Plexiglass (Polymethylmethacrylat, PMMA) https://en.wikipedia.org/wiki/Poly(methyl_methacrylate)

The best is to rub the surface (e.g. only one surface of a disk) with real fur. I bought an old fur hat, be careful, it has to be real fur. Cat fur or fox fur works best. You want fur with very fine hair. The fur has to be dry.

The best surface is a disk. If you use other shapes, you could get several areas with opposite charge. Good shapes are also spheres (hard to get from Plexiglass) or tubes (one can use PVC tubes).

Many plastic materials work, but one has to find out which ones are best. Also many plastic foils work, but are hard to handle. I prefer thin plastic sheets which are stiff and can be cut with scissors.

https://www.youtube.com/watch?v=notE4ugcgvk

https://www.youtube.com/watch?v=_TmoQFEk8d0

https://www.youtube.com/watch?v=PzoUiZnR5QA

Greetings, Conrad

[Grumage]

Thanks Guys.

I'm off to the workshop to mill the " sprue " hoping that 5mm depth will be sufficient " head " to allow for material shrinkage into the mould cavity.

Many thanks Conrad for the additional information about Electrets from plastics.

Cheers Graham.

[Void]

I have 500 grams of  Carnauba flakes, 500 grams of Rosin crystals and 200 grams of Beeswax. The recipe states a 45%, 45%, and 10% Beeswax by weight.
Am I correct that 100 grams of Beeswax added to the Kilogram of the other ingredients is right?

Hi Grum. If you use 500g of carnauba and 500g of rosin and 100g of beeswax, you would calculate
the percentages like this:

First calculate the total weight:
500g + 500g + 100g = 1100g.

Then, to calculate the percentages by weight of the carauba and rosin:
(500 / 1100) x 100 = 45.45% for each

The percentage by weight of the beeswax is:
(100 /1100) x 100 = 9.09%

So, that is close to 45%/45%/10%.

P.S. It probably wouldn't matter much, but 500g + 500g + 111g would be even closer to 45%/45%/10%.


All the best...

[Grumage]

Update.

Well, I didn't manage to finish the mould because number 3 son who's had a little time off work recently finished a project he'd started some nine years ago.

https://www.youtube.com/watch?v=-kNKswjpc20

This was one of many different  casting kits that I used to market a decade back.

I did however carefully measure the ingredients and cook up a batch of wax. The smell wasn't too bad, almost organic.

I used clean Stainless Steel utensils got all the air out and allowed the mixture to cool and set. Upon touching the top surface a loud crack was heard, I assume the wax had adhered to the edges of the bowl I had used and then suddenly released. It promptly shattered into many smaller pieces.

From this exercise I noticed that there was little to no " slump " in the material so a deep " sprue " won't be needed on the mould. A good polished surface however, is a must!

More to come, cheers Graham.

[Grumage]

Hello Everyone.

How ( NOT ) to make an Electret. Take 1.

https://youtu.be/QEYXeuAxIqQ

                       

Cheers Graham.