EZ10 torque failure?

[DNGO]

I am working on an EZ10 adapter project. Customer requires that the EZ10 metal shell, which is adhered to the plastic base by a loctite E-60HP glue and cured, passed torque test at 1.2nM. We tested the adapters with a torque wrench at 1.4nM (we increased the requirement as a safety net) as a part of the QC process and they passed. However, when the parts got to Japan, the customer tested them and there was a lot of failure. What could have caused the failure?

 

[MintJulep]

"Plastic" in general, is difficult to bond with adhesive, and you haven't told us exactly what plastic.

Nor have you told us the nature of the failure.

Is the plastic part molded? Is mold release used? Is it cleaned? Was it cleaned for your internal test pieces, but not production?

Is there a plasticizer that is migrating with time to the bond line?

How hot does the thing get in use? Notice that E-60HP strength falls off rapidly with temperature.

 

[DNGO]

MintJulep,

Below is more details about my problem.

The plastic is molded from CoolPolymers D5110 resin, a thermally conductive PPS. The mold release was used and the part was cleaned from the agent.

Nature of failure - The EZ10 metal shell did not adhere to the plastic when re-tested at 1.2nM.

E-60HP adhesive was used and cured according to the mfg's spec. The adapters are to be attached to MR16 LED lamps so i don't think it will get really hot. Note that the adapters were never used on the field. They failed torque test at the customer's incoming inspection.

 

[MintJulep]

Nature of failure - The EZ10 metal shell did not adhere to the plastic when re-tested at 1.2nM.

Ok.

But WHERE in the joint did the failure happen?

Did the epoxy not adhere to the plastic?
Did the epoxy shear?
Did the plastic fail?
Did the epoxy not adhere to the metal part?
etc.

 

[DNGO]

It appears the epoxy did not adhere to the plastic.

 

[MintJulep]

Almost certainly a lack of proper surface preparation.

Mold release not really cleaned. Cleaning not done at all, cleaning process is not effective, cleaner is contaminated, before an after cleaning parts handled by the same people....

 

[Pud]

Have you contacted Loctite? Looking at the datasheet, it shows pretty poor performance on a range of plastics, which I would have thought it would be good on.

PPS is used in other applications for it's high operating temperature and it's chemical resistance, which would indicate it is a material very (if not impossible) to bond.

Then you have the problem of differential expansion rates of two dissimilar materials possibly causing bond failure during thermal cycling (maybe during transport?).

Mould release, especially if silicone based, will require mechanical means (abrasion) to get it off.

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[DRWeig]

I agree with both Pud and MintJulep. I've experienced this before:

Long ago, we used a Dow Corning pliable epoxy potting material in a stainless steel (SS) tube. The instructions called for cleaning the tube with solvents and applying a certain model of Dow primer in order to adhere to the SS. Neither was being done.

Without the prep, only the expansion of the epoxy at curing time made a good seal. The SS did not expand as much, so there was pressure all around the interface. Stick the tube in cold water, though, and the epoxy shrunk more than the SS. A nice gap all around, large enough to wick water, and the potting could easily be pulled out of the tube. Proper cleaning and priming of the SS eliminated the issue.

If you're shipping your part to Japan in the cold cargo bay of an airplane, your two parts may be temporarily separating during the flight. Combined with the poor adhesion to that plastic, I would expect a failure.

Best to you,

Goober Dave

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[DNGO]

Pud,

Where did you see the epoxy's poor performance on a range of plastic? I looked at Loctite E-60HP spec and did not seem to see any reference on it.

Thanks

 

[CoryPad]

On Loctite's data sheet:

http://tds.loctite.com/tds5/docs/HYSAE-60HP-EN.PDF

The strength with nylon and acrylic is lousy, but moderate for PC, ABS and PVC.

 

[SnTMan]

Epxoy can often be a poor choice for bonding thermoplastics. Contact an applications engineer at Loc-Tite, 3M or whoever. That's what they are there for.

Regards,

Mike

 

[Compositepro]

Plastic and metal have widely different CTE. Your part is designed to go through a fairly wide temperature range regularly. The shape of the parts will place the bond under high stress when temperature changes. The bond will not last long. Use a rivet, pin or other mechanical snap-fit design to resist torque. Unless, of course, you are designing it to fail after the warranty expires.

 

[DRWeig]

I vote snap-fit

Best to you,

Goober Dave

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