Tips or Procedures to Mix PTFE Powder with Graphite

Why would you need to cool the powders if you are mixing by hand?

Just pour the powders into a suitably sized container and mix with a shovel. It ain't rocket science.

Or,

Electric dry powder and mortar mixer

Thanks Lyn, but is not so easy as mix mortar. The PTFE when is manipulated by hand make clogs that once sinterized makes that parts fail by shear. It could be prevented cooling the powders. But I have some remainig questions that I hope the group could help to answer

Yours,

Esteban

Ok,

Gather your thoughts and present the questions in as much detail as possible.

Blocking might be a problem alright. Have you asked the powder suppliers for suggestions?

yes, the manufacturers suggest 'purchase a machine', but for experiments with 50 gr of tpfe and 1 gr of filler, the machine is not a choice.

First it was 18 kilos, and now it's 50 grams????

Use a cup and a spoon.

"Use a cup and a spoon."

Agreed. If heat is a problem, store the mixing utensils in the freezer before use.

I'd go for "cup and fork" if there's a tendency for the ingredients to "lump". Or even a small balloon whisk:

I'd buy one of these:

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Tumbler - Lortone 3lb Rotary - Professional and...$85

Etsy

A bit OTT IMHO.

Yes, but it's only $85.00.

Good point. Can't buy a decent balloon whisk for less than €150.00 around here - then there's the wear-and-tear on the wrist and elbow joints to consider.

PTFE is perfectly stable below 200 deg.C, starts to decompose a bit at >250 deg.C and doesn't melt till about 327 deg. C. As for graphite, the M.Pt. is around 3,600 deg.C.

So I repeat the question posed by Lyn, "why do you need to cool it."

P.S. Like all polymers PTFE isn't a pure substance, but a mixture of different molecular weight chains of polytetrafluoroethylene. There will therefore be some variation in properties from one manufacturer to another.

This is a simple design that you could build yourself and power it with a hand crank. Later, if you go into higher production, add a motor/belt drive.

fine!, where did you find that picture?, there is a manufacturer website?

I searched images for Pharmaceutical mixers. If you are near New York May 1 - 3, there is a Pharma trade show at the Javitt Center, search "INTERPHEX". Dozens of equipment manufactures. But you could weld together two trash cans or oil drums and make something that works depending on the cleanliness you require. If you need stainless, you can get cook pots at a restaurant supply cheap enough and have a local welding shop cobble it up.

Mixing PTFE is a very challenging application. It can be done both batch and continuous, however you must be careful to keep the heat down. Mixers impart energy that is quickly converted to heat. The only successful method I know is to add dry ice to the mix.

You can start your mixer search here

http://www.powderandbulk.com/process/blenders_mixers.htm

Did you read the part where the OP will be mixing 51 gram batches?

not?, where?

Post #5:

"yes, the manufacturers suggest 'purchase a machine', but for experiments with 50 gr of tpfe and 1 gr of filler, the machine is not a choice."

So, approximately a single serve packet of snack nuts. Not?

I wrote that, the machine is not a choice because are designed to amounts of powder.

that is the reason why I am asking for manual procedures of mixing because the trials are with small samples and then if all goes fine, to scale to machines

I interpreted the production batch was 18 Kg and the test was 50 grams.

it is right.

50 grams is roughly equivalent to 18 small packs of sugar, in volume.

I believe that stirring it with a spatula while the container is placed on a small vibrating table will give satisfactory results for small batches and heat will not be an issue.

Powder coat manufactures use cryogenic mills to mix and grind their products to the final desired particle size. Since you say buying a machine isn't going to work, ask a powder coat lab to do it for you (check with this guy @ www.powdercoatingresearch.com.)

The other option is to fluidize the materials together using dry air (assuming you already have the particle size you want.) If you were to disperse the material from a fluidized container that may give you the uniform distribution you need.