plasic problem

What material did you specificity for use in molding the part?

What evidence can the molder show you that what he used was what you specified (empty bags, supplier invoices, etc)

Have you any prior examples where that material was used successfully?

Who manufactured the material.

The last design project I had where parts were to be subjected to high voltage tests, the standards for things like dielectric ratings and moisture were established by IEEE.

Whose criteria did you use when selecting the material.

The mold designer and mold maker had to be aware of the material to be used in molding so that the cavities and inserts could be properly compensated for shrinkage.

If the mold shop substitute a material other than what you or the mold designer called for, evidence of that switch may be present in the molded parts. Have you had a knowledgeable third party inspect the molded parts for deformities? Have you tested the parts for evidence of unauthorized substitution?

You haven't given us much to go on.

L. J.

It has nothing to do good or bad plastic. It is type of the plastic which is important. If you have hydrophobic type plastic or hydrophillic type will tell you which will be effected by humidity conditions.

Electrical conductivity in plastic parts comes from two side as below

1. Side one is ionic contamination like sodium, potassium, chlorine and flourine etc. and is quality of starting materials

2. Is the mositure absorption ability of the organic. If starting material does not absorb moisture then it does not become conductive.

During my work with organic adhesive for electronic products did worked with one of the Indian supplier call Global Applied Materials in chennai, India and they guided me with this and provided product which will not chnage dielectric properties from 40 to 85 percent humididty test conditions.

If you select correct starting material and your process of manufacturing is clean then yes you can have part which will work good

Masyood

Thank you for the response.

Material is Nylon from a very reputed supplier - MNC.

This material was being used regularly without any problem for long period as housing of switches. Product made with this materail also had passed in type tests, including all dielectric tests.

This problem would have occured only in few batches. The problem got highlighted only when customer complaint was received, forcing the company to recall some batches from market.

The product from defective batches passes all dielectric tests in dry condition. ( HV test, Insulation Resistance). Hence products went through QC checks on production line.

But product fails to meet these requirements under humid conditions!!

No evidence in the form of raw material is available. Evidence of defective products are available. But supplier blames it on processing problems & refuses to own the responsibility of material.

The point for arguments sake is - even if we assume that some parameters during molding were not in limits specified, can the effect of it be so hard that insulator started to work as conductor in humid conditions?

Supplier's safety data sheet do not warn of the extreme change in properties. It is actually is safety related serious issue.

How to force supplier to take responsibility of the defect ? Which safety laws would be applible? (like product liability etc)

what was the end application of the now conducting plastic you refer to e.g.

cabling to be put in metallic conduit, we can use plastic

romex type wire 2or 3 conductor + ground that can go to b-x

power cord material e.g. bosch hammer drill power cord we can check for self insulates working

BUT

residential application e.g. toaster or God forbid the coffee maker yaaaah, is there the possiblity that the shops' new coffee maker has another hazard? will the h&s tyrant have something new available to give us **** for drinking?

HELP we can't have that taken away to!

'da ber

Nylon is probably the worst polymer you could have chosen for the application. Nylon is NOTORIOUS for moisture absorption. There are also multiple flavors of nylon on the market and every polymer manufacturer makes several.

Add to the fact that not a single polymer supplier will supply minimum and maximum ranges for any of the standard specifications. ALL are "typical" which is specific to one particular batch on one particular day measured with one particular machine or process.

If moisture absorption is an issue (which apparently it is.) the parts should be made from Polyphenelynesulfide instead of Nylon. It and Teflon have the lowest moisture absorption of any polymer group out there. Tefon has a higher dielectric strength, but it is not structurally sound and will creep. Some "typical" data to chew on:

http://www.aipdaytona.com/pdfs/nylons.pdf

http://www.aipdaytona.com/pdfs/extreme.pdf

http://www.aipdaytona.com/pdfs/amorphous_new.pdf

http://www.aipdaytona.com/pdfs/chemical.pdf

http://www.aipdaytona.com/pdfs/peeks.pdf

Check out the Techtron PPS in the last column in the last .pdf file compared to the others for moisture absorption and strength.

One other point, the issue could be on the molder's side. the injection molding machine may have been running hotter than normal that day and could have charred the shot a bit, or the machine might have been contaminated with a carbon filled nylon from an earlier setup. This is why polymer manufacturers won't supply min and max limits to their product, processing can alter the properties quite a bit.

Thank you for the response.

The Nylon used was electrical grade, & was used for this applications as per supplier's recommendations & published literature.

The supplier has been changed after this incident & Nylon from other supplier is giving excellent results for same application (similar to the excellent results from the earlier supplier before this problem occured)

Yes, it is well known that Nylon absorbs more moisture than any of the currently known engineering plastic. But certainly a healthy Nylon insulating material does not result in acting as conductor even if it absorbs maximum moisture!!

There is no possibility of contamination as volumes are so high that one mold continuously run on one machine & the molding plant is equipped with modern machines / techniques!!

The point is - even if we consider the possibility of running of mold hotter than specification, could the insulator turn into conductor & pose a serious safety hazards, inviting legal complications & worst possibility of somebody getting electrocuted?.

In such situation what are the avenues available for forcing the supplier to accept the responsibility? (supplier's safety data sheet do not warn of any such consequenses - all it say about hotter mold is it may cause some problems to molding opertaor due to evolved gases & hence adequate ventilation must be provided !!)

This problem surely is not limited to technical issue alone, but legal issue related to safety / inadequate caution to customer during use etc. Any suggestions on how to proceed on this? What are the agencies who can help in this matter?

I cannot recommend any agencies because I don't know what part of the world you are in. Underwriters Labs or CSA would be the premier certifying agencies in North America. TUV would be in Europe. But even if you were here in the US, more than likely, the liability will fall on you unless you can prove that your supplier was not providing product per your specifications. You can suspect it all day long, but unless you can produce documentation that proves malfeasance or negligence on the part of your supplier, you will be the one holding the bag. You have the legal responsibility in most jurisdictions to test your incoming product adequately. And in this case that would mean megaohm/HIPOT checks after soaking a representative sample of the incoming batch in water for say 24 hours or so. More often than not this sort of thing is ultimately traced to poor or non-existent incoming quality control procedures and poorly worded specifications given to the supplier as being contributing factors. Additionally, while there may have been a breakdown in your specifications or testing procedures, it is engineering's responsibility to engineer out as many potential points of failure as possible as well. Selecting a polymer with a well known propensity to absorb water is setting the product up for potential failure and is one issue that can be addressed by engineering. Maybe not every nylon will absorb enough to arc over, maybe your supplier accidentally mixed up pallets of plastic during that batch, but I'd be willing to bet that the megger will show a definite change in resistance as water is absorbed even by properly performing parts. You have to decide if the added cost of a different polymer and the associated changes in tooling required are offset by the potential liability. I can tell you now that if this were a US court, your company would be on the hook for all of the liability. You need to keep that in mind.