Keeping Nylon Conditioned? 3

[DragonForge]

Hello Chaps

Great forum you have here.

We are currently injection moulding training swords for the martial arts industry. At present we are using an impact modified barium filled pp and it certainly does the job.

However, the market is demanding a stiffer product so we have been experimenting with different materials (adding glass to the pp did not work).

We have found that Nylon 6 if conditioned by immersing in water for a week has the exact properties that we are looking for. However, as the nylon starts to equalise with the atmosphere it becomes too brittle.

Does anybody know of a way to make the nylon retain the water - would lacquering or applying a coat of wax work for instance?

Any help or suggestions would be appreiated.

Thanks

 

[Demon3]

Water plasticizes nylon (makes it softer) but is volatile so it evaporates over time. Your question translated to "please suggest a non-volatile plasticizer for nylon". A Google search may turn up something or someone here may have suggestions. I know that for example EMS sells plasticized nylon.

PP has the same stiffness as conditioned nylon, i.e. around 1.5 GPa and is cheaper. What properties are you looking for? I am pretty sure you can make this work using PP and the right additives and be cheaper than using nylon.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[DragonForge]

Hi Chris

Thanks for the reply and translating my question.

The PP we are using at the moment has a 40% Barium fill. We use this to get the weight up as unfilled PP is far too light.

However, the Barium seems to act as an elastomer(?) and makes the PP too flexible. We have tried adding glass but this reduced the impact strength and this product needs as much impact strength as possible.

The Nylon came in at the same weight as the filled PP which was one of the main advantages.

 

[Demon3]

Hi DragonForge (cool Nick),

Any filler should make your PP stiffer so something odd is happening (believe me, fillers are my specialist area). Barium sulfate is good as it's dense and white. Perhaps there's some additive in the BaSO4 like a wax to help disperse it and that's what's making the PP softer. My guess is that you're adding the filler via a masterbatch in wax.

So, some solutions. Try adding the BaSO4 as the neat powder, it should stiffen the PP as any filler will.

Another idea is to try another dense filler. I would try magnetite available from Minelco

http://www.minelco.com

it has a higher density than barium sulfate (5.0 compared to 4.5 g/cm3). It's black so it could look nice for a sword.



Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[DragonForge]

Hi Chris

Thanks for the information.

The Barium is compounded with the PP at the factory so I am not sure if any wax is involved (as you may have gathered this is not s specialist area for me!).

So from what you have said, increasing the percentage of Barium should, in theory, make the product stiffer? The resulting weight increase would not be a bad thing. Do you think the increased Barium precentage will adversley affect the impact properties?

The magnetite looks interesting. I think we will have to sample it.

 

[Demon3]

Adding filler increases stiffness and generally reduces impact resistance although there are exceptions to the latter.

Adding fine, well dispersed calcium carbonate to PP homopolymer can double the unnotched impact resistance for example.

How heavy / dense does the material have to be? How much BaSO4 are you adding?

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Compositepro]

I'm guessing that the barium sulfate does indeed make the material stiffer but that the added mass increases the inertia of the sword so that it is perceived as being "floppy" or less stiff. Is the nylon sword the correct weight?
If you have to increase its weight you will probably run into the same problem. You can increase the stiffness of the part by changing geometry (thickness) or by increasing the stiffness to weight ration of the material. You could even injection mold around a thin-walled steel tube.

 

[Demon3]

Adding ribs along the length would help keep stiffness up at constant weight. Also, it would give a cool look to the sword.

Blending in a more reinforcing filler like Mica could help keep the stiffness up too.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Pud]

Why not use a toughened nylon? There are even glass filled versions of the stuff. No break Izod.

Google long fibre filled materials - if your feed point is down the handle end you should get a real stiff sword (no innuendos, gentlemen thank you!)

Want heavier? Try acetal.

Cheers

Harry

http://www.tynevalleyplastics.co.uk

 

[Pud]

Forgot to add - by soaking in water for week you are saturating the nylon - it will always "dry" out to a nominal level.

H

http://www.tynevalleyplastics.co.uk

 

[DragonForge]

How heavy / dense does the material have to be? How much BaSO4 are you adding?.

Unfilled product comes in at approx. 500g, filled at 760g so approx. 260g of Barium

 

[DragonForge]

Compositepro wrote "I'm guessing that the barium sulfate does indeed make the material stiffer but that the added mass increases the inertia of the sword so that it is perceived as being "floppy" or less stiff. Is the nylon sword the correct weight?If you have to increase its weight you will probably run into the same problem. You can increase the stiffness of the part by changing geometry (thickness) or by increasing the stiffness to weight ration of the material. You could even injection mold around a thin-walled steel tube."

Hi Compositepro - Thanks for the input.

I think you have gone a long way to explaining the "floppy perception" there. The added weight does sound like the culprit.

I have considered re-cutting the mould to add more stiffness to the blade - however, playing with materials is a much cheaper process at this stage.

The problem with adding steel is that this product also needs to flex - like a fencing foil does only not too the same degree. As such we would have to add spring steel and this cretes a lot of problems in itself.

 

[Demon3]

Unfilled product comes in at approx. 500g, filled at 760g so approx. 260g of Barium

Is that for the PP or the nylon material? I'll have to back calculate the weight% of filler.

In any case, assuming a polymer density of around 1 g/cm3 you are increasing the density to 1.5 g/cm3.

By chance I just spoke to Mats Drugge, President of Minelco who sell the magnetite filler and he said they sell magnetite into Japanese swords. It's used in the handle as a counterweight. You learn something new every day. If you need contact info to Mats Drugge just e-mail me.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[DragonForge]

Thanks for the suggestions so far chaps - they are of great help indeed.

This project has been an uphill struggle from the start. We are trying to create a sword that handles as closely as possible to its steel counterpart. The steel counterpart in question is called a "Federschwert" (feathersword) and is designed to flex when thrust at somebody (like a fencing sword does) making it safe for use.

The barium fill gets us the required weight but makes the blade too flexible (wobbly). Making the blade stiffer made it too brittle (this product takes a pounding!)- but solved the wobbly problem.

The saturated nylon has the required stiffness, weight and impact properties but becomes too brittle as it equalises.

 

[DragonForge]

Harry wrote "Why not use a toughened nylon? There are even glass filled versions of the stuff. No break Izod.Google long fibre filled materials - if your feed point is down the handle end you should get a real stiff sword (no innuendos, gentlemen thank you!)Want heavier? Try acetal.Cheers Harry"

Hi Harry

Thanks for the input.

Problem is that this product needs to flex and return to true (as much as possible - it can't replicate steel in this respect).

Tried acetal but it was too brittle.

 

[Pud]

Where are you located - Demon has assumed you are in the USA?

h

http://www.tynevalleyplastics.co.uk

 

[btrueblood]

Sell it (nylon sword) with a water-filled trough to store it in?

 

[patprimmer]

Acetal should do the job if it is the correct grade moulded correctly.

Unfilled PP has an SG of just over 0.9, and unfilled acetal is 1.41, so it is about 50% heavier.

Nylon is about 1.14 and to get to 1.4 it needs about 40% glass.

Caprolactum is a plasticiser for nylon 6, but it needs to left there during manufacture or even added later by compounding in.

Glass filled PC might work for this one.

Presuming it is at least 3mm thick at the back edge and gated at the handle, an extrusion grade acetal homopolymer moulded in a hot mould and fully packed should be OK.

Adding long glass to PP should be OK but it will be pricey. In PP for good results, the glass needs to be what they call chemically coupled to the PP.

I like the store it in a box of water. A real out of the box solution. ;-)


Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[DragonForge]

Pud wrote "Where are you located - Demon has assumed you are in the USA?"

We are based in the U.K. - North Wales.

 

[DragonForge]

Hi Pat

Thanks for all the suggestions. We will certainly try some of them.

I'll have a chat with the materials supplier and see what's viable based on price and availability.