Ultrasonic welding Nylon 33% glass 2

[PLCRookie]

Does anyone have experience ultrasonic welding Nylon with 33% glass? Specifically, what effect will humidity of the environment have on weld integrity? I know that the material is extremely hydroscopic, but can the material absorb enough moisture as to degrade the weldability? Any comments welcome. Also any references or links to sites with info really appreciated!

 

[patprimmer]

Moisture uptake will degrade the weld.

Best results will be obtained if you can weld within a few hours of moulding.

the parts can be stored longer in plastic bags, or in a dry environment.

If the nylon is wet you will nee to dry it in an oven.

You can do a real rough test by rattling the parts together. A clinky rattle means dry, a dull thud means wet Once you have heard wet and dry mouldings, it is quite easy to tell.

Regards

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[patprimmer]

Also, if you weld wet, you will see froth and bubbles at the joint.

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Demon3]

As an aside, the reason for the sound difference Pat mentioned is that as molded unfilled nylon had double the modulus (stiffness) compared to the same part that has adsorbed water from the atmosphere. This means you have to be careful when looking at literature value for nylon properties. As molded the modulus is good but impact resistance is poor, whereas under real condistions, it adsorbs water so the modulus is fair but the impact resistance is very good.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[PLCRookie]

Thanks for the rely. I am having a problem maintaining proper burst pressure on a nylon (33%glass)part. I have been told that you "can't" weld it unless it is totally dry. We are not an air conditioned plant, and it has been quite humid here lately. I am drying some of the parts now in a dessicant chamber to see what difference I can observe. I have also noticed a different "look" to some of these parts, and I have been told by the molder that the glass is coming to the surface of the parts at the weld area due to the way he must run the mold. What could happen to the glass to make it come to the surface? My knowledge of injection molding is small. Any help appreciated. Thanks for the replies so far.

 

[Demon3]

Hello,

If you could weld the parts right after they are made that would be best because they would still be dry. To dry a "wet" part will take a long time.

The weld line will always be far weaker than the rest of the part because of the way the polymer and glass flows. Basically at the weld line there will be an area with more or less zero glass and areas with too much glass. In addition, the orientation of the glass will be poor and will not give much strength. This effect can not be avoided.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[PLCRookie]

Thanks Demon3. We had problems welding this part recently, and I consulted with a leading ultrasonics manufacturer (maker of my welding equipment). They recommended a joint design change, which, when implemented, eliminated leaks and drove the burst pressure high and consistent. We ran along like this for about 2 months..then, low burst pressure. I am concerned that the glass is being sent to the outer layer of the part during the molding process. I have dried some parts, and the burst is more consistent, but it is still low by about 200 psi....significant drop.

Is consistent welding of this high glass content nylon even possible.

Thanks for the help.

 

[patprimmer]

The glass does not normally come to the surface, it actually sucks back from the surface and leaves a tiny bubble behind which gives a silvery surface appearance.

This is caused by any of or a combination of the following.

Insufficient melt temperature.
Insufficient hold up pressure.
Insufficient hold up time.
Insufficient injection speed.
Insufficient mould temperature.
To small gate size.
Insufficient cushion.
Worn check valve.
Wet material.

Basically, for glass filled nylon, you need quite hot material (generally about 300 deg C).

You need maximum fill speed, dropping down just short of full.

You need to hold up with pressure just short of flash.

You need to hold up until the gate freezes.

The smallest dimension on the gate should be at least 1/2 and ideally 2/3 maximum section thickness of the part.

You need a mould temperature of at least 90 deg C.

You need the machine to hold a stable but small cushion for the entire hold up time.

You need the material to be dry before moulding. If material bubbles and spits from the nozzle between shots, it is probably to wet.

If your moulder does not appreciate all the above, you probably need a new moulder.

What type of nylon is it.



Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[PLCRookie]

Thanks patprimmer. The material is ENTEC.

 

[PLCRookie]

Sorry, ENTEC N1033HL BK.

 

[patprimmer]

Entec appear to be a custom compounder. They may vary their source of base resin and even the glass fibre. This might cause variations.

If in doubt try someone like Ticona, BASF, Solutia, DuPont, DSM, UBE or Emserwerk to test their prime grade materials and see if the standard improves. Some compounder's do a very good job at high quality consistent materials, but some do to much horse trading.

It still sounds like poor control of moulding conditions to me. Also Both myself and demon3 have recommended welding very soon after moulding. You should try that to see if it improves things.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

The nylon you mention is type 66.

While it has excellent properties in prime condition when properly moulded, it is more sensitive to degradation and is harder to mould and weld than is type 6.

35 to 40% GF type 6 might do better for you.

Are they failing at the weld or elsewhere.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[PLCRookie]

Thanks pat for the response. They are all failing at the weld joint. I have been able to burst the body of the part when the weld is optimal. I do have more info. now. The welding guys say not to go over 20% glass fill for welding this kind of part, however, I have had very good luck with this material previously. Also, I have new drying parameters (which I am currently carrying out)to eliminate the moisture prior to welding. Apparently, I have not been drying them well enough. I also have a larger booster for the welder as recommended by the weld guys. I should know more at the end of the day.
Again, thanks pat and demon3. for all of your information.

 

[patprimmer]

I have seen 45% glass filled and 50% carbon fibre filled nylon 6 successfully welded. It was done on line after moulding. It required quite a lot of energy and required a good joint design where the area of the wld was large and the load was in shear, not tension.

Regards

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[patprimmer]

The part I refer to is the "Titan" winch handle for yacht winch handles. You should be able to see their range at major ships chandlers.

They have quite a few handles with varying levels of glass, depending on design.

The weld is to hold the bottom side in so the beam is fully boxed in. They use small bolts on some models to reinforce the joint at the highest loaded point.

They also have a step in the fit so as to give some mechanical assistance to shear.

When tested to destruction, it is normally the bronze drive dog that fails, not the plastic.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[PLCRookie]

This particular part has a shear joint also. I have dried parts prior to welding,according to my molders suggestions, and the average burst pressure actually dropped compared to parts dried by another process. We definitely have some problems filling the mold the way we would like, and we are working on both right now. My next test will be to use a larger booster.

Thanks for the reply.