Drying of nylon 66 parts

[PLCRookie]

Hi all. I am interested in drying parts made of Nylon 66 (33%glass)prior to ultrasonic welding. I have a problem with moiture uptake in these parts, as they tend to sit around a while before welding. They are shipped from our molder in ziploc bags with desicant bags, but they still seem to take up moisture before we can weld them. I am thinking of a large oven (with dessicant) to store or dry prior to welding, but I am having trouble finding a supplier of this type of equipment. I also would like to purchase equipment to test these parts that will give me a reliable reading of the exact moisture content of a given batch of parts, so that I can determine the point at which my welding suffers. The idea is to be able to control the moisture content right before the welding process.
Any help would be appreciated.

 

[Demon3]

As you suggested, one way is to measure water content directly. Methods would include Karl Fischer (

http://www.readycult.com/analytics/literature/KF_Titration_Basics.pdf),

possibly FTIR spectrosopy or weight loss in TGA at 120 C for example.

An indirect method would be to measure the modulus or impact resistance. As molded nylon has high modulus (eg 3 GPa) and low impact resistance. Once it has taken up water from the air the modulus is approximately halved and the impact resistance is much higher as the water plasticizes the polymer. Even dropping the part on a hard surface and listening to the noise will give you some idea of the modulus and therefore the water content.

Having said all of that. When I did some limited ultrasonic and vibrational welding of nylon we had no problems with weld strength even for samples that had been left out exposed for months. Someone with more experience than me may know why you are having problems.

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- James Branch Cabell

 

[patprimmer]

You can normally weld wet nylon, but it is better done dry.

Nylon takes up moisture rapidly on the surface, but it migrates through the nylon very very slowly. This is effected by concentration gradient and temperature.

The best time to weld is in line with moulding while the parts are still slightly warm.

A quick drying process will dry the surface only, but this is enough.

A quick test is to rattle the parts. Dry parts klink or tinkle, wet parts make a dull thud.

4 hours in a plain oven at 120 deg C will dry wet nylon good enough for welding. Something like an old bakers oven will do. A bank of domestic ovens will also do.

Dehumidified ovens do a better faster job, but are not really necessary for this.

Dehumidified dryers are readily available from moulding machinery suppliers and I cannot believe that anyone who put in one ounce of effort could not be inundated with suppliers. It is almost as easy as buying a new car or life insurance. Try google. I got 270,000 hits in 0.27 seconds



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[PLCRookie]

Thanks guys.
I will be purchasing a moisture analyzer to test these parts prior to welding. We have not had any trouble thru the winter month, however, now that it is 100F + degrees, and high humidity, our problems are huge. The sound of the parts is definitely "dull". I would like to have a quantative valve for this, so that I can eliminate it from the process. Pat, I agree that welding right after molding is best, this is where I see greatest increase in the weld process.we do not mold the parts here, they are molded about 3 hours away form us. The only thing that has changed so far is the parts themselves. All of the welder settings are as they were when results were good.
Again thanks for the info. guys.