losing strength over time - any suggestions to improve?
losing strength over time - any suggestions to improve?
(OP)
Hi, I'm using a polymide (nylon) 6 (Akulon K-222, http:// www.matweb .com/searc h/Specific Material.a sp?bassnum =PDSMEU048) and having a problem with the part losing 20% strength over time when exposed to air/sun/humidity.
We make a product that joins rebar at their junctions prior to pouring concrete. When pouring, the clips need to withstand the load. We've created a pull test and the product can hold 100 pounds when first opened from a sealed box (it's been sitting for at least a month sealed). If the part is left out of the box in our warehouse for a few weeks, it drops to 80 pounds. I have a few questions:
Does anyone know how much time Nylon 6 takes to fully set?
Is there an alternative material for the same price or lower that would be an alternative? FYI, we've tested Polypropylene with 10% glass and it's relactively close to holding 100 pounds. Will this have any loss in strength over time?
Thanks in advance for any help.
We make a product that joins rebar at their junctions prior to pouring concrete. When pouring, the clips need to withstand the load. We've created a pull test and the product can hold 100 pounds when first opened from a sealed box (it's been sitting for at least a month sealed). If the part is left out of the box in our warehouse for a few weeks, it drops to 80 pounds. I have a few questions:
Does anyone know how much time Nylon 6 takes to fully set?
Is there an alternative material for the same price or lower that would be an alternative? FYI, we've tested Polypropylene with 10% glass and it's relactively close to holding 100 pounds. Will this have any loss in strength over time?
Thanks in advance for any help.






RE: losing strength over time - any suggestions to improve?
Perhaps the nylon is absorbing water and losing strength? Are you in a humid environment? If in the warehouse, UV degradation is probably not a factor.
Only a guess. ..
Jeff Mowry
www.industrialdesignhaus.com
Reason trumps all. And awe transcends reason.
RE: losing strength over time - any suggestions to improve?
Akulon K222D is a very good quality unfilled nylon 6.
Like all unfilled nylon 6, it will absorb water from the atmosphere and lose rigidity, but gain impact strength.
The difference in some properties can be as much as 300% change between dry as moulded and fully conditioned.
Adding glass fibre will give a substantial increase and result in a lesser change due to conditioning.
Acetal might be a good substitute.
Glass coupled polypropylene at 20 to 30% glass might work.
PBT might work but might be brittle. ABS might work.
Regards
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RE: losing strength over time - any suggestions to improve?
I'm in Oregon with a little humidity, so that's probably the culprit. Would wrapping the product in plastic be beneficial?
Adding glass is a great idea, but there are two problems; the costs are higher and more importantly, it becomes too brittle.
Oh yeah, I remember the 300% difference in K222, thanks for the reminder. Our molder also told us about this and it could be major factor.
Acetal was our next option and I'll test this.
Thanks for all your help!
bill
RE: losing strength over time - any suggestions to improve?
Regards
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RE: losing strength over time - any suggestions to improve?
The trick in any application is usually not to find a material that works but to find the cheapest one that will work. For you that is probably glass fibre filled PP homopolymer.
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell
RE: losing strength over time - any suggestions to improve?
We had problems with the clips breaking, being brittle. We're finding out the nylon was not conditioned properly. We're conditioning the Nylon now, but my concern is they keep absorbing water and losing strength. We've changed other Nylon products to Acetal (Celcon M-90) material and have been very happy with the results.
Our molder is going to try Delrin 500p and Celcon M-90.
I enjoyed your last statement about using 'cable ties or old coat hangers.' The benefit to our product is the use of an applicator (gun) that eliminates bending over and discharging 30 ties per minute (time savings of 1/4 to traditional wire). Zip ties? That's a good question but our main competition is wire ties.
Truly appreciate all your help!
bill
RE: losing strength over time - any suggestions to improve?
We have tried PP w/10% glass and it seemed to work well, just not as strong. We'll test w/25% and see what happens.
Thanks,
bill
RE: losing strength over time - any suggestions to improve?
For nylon 6 that is about 3% water content in a typical atmosphere and about 9% if permanently submerged or in an atmosphere of 100% RH.
It is only the nylon content of a compound that absorbs water, so the weight gain will be proportionally less for glass filled grades.
I agree with Demon3 that 25% Glass filled PP is probably the best value. It will mould a bit slower, but will be lighter (giving more parts per Kg of resin) and will be cheaper per Kg.
Coupling agents substantially improve the performance of glass filled PP. Homopolymer will be best.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: losing strength over time - any suggestions to improve?
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell