Plastic Material Selection

[SaturnVI]

Greetings:

I have a project I'm working on that involves some plastic supports about 2 feet long, 2 to 3 inches thick and about 3 to 4 inches high. This component has to be relatively tough, dimensionally stable, relatively stiff (low or no vibration), highly resistant to creep and as inexpensive as possible. The environment for this part is that found in a home so relatively low humidity, room temperatures and no direct exposure to sunlight.

My initial idea is for a glass reinforced nylon, but I'd like some pointers incase there are better materials out there. Also, this part will most likely be injection molded. Will adding glass fiber significantly add to the cost of the molded units? Does fiber reinforcement require a relatively continuous part (no holes)?

Thanks

 

[patprimmer]

From the very subjective information you supply, GF Nylon sounds the most likely prospect.

Long fibre might be better, but it's more expensive.

A lot more detailed info is required, including required numbers and load details. Far to much to be provided free on a forum like this.

You need to employ someone qualified to design the part, or at least consult material suppliers, moulders and toolmakers before and as you design it yourself.

Regards

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[dwightdixon]

What you propose is a pretty beefy part. It would take a relatively long cycle time and would cost major money to make the tool. Glass reinforced nylon is not cheap. You do not sound very knowledgeable about plastics design. Are you working for a company with more experienced plastics designers available to help you or are you an inventor with an idea and do not know how to proceed? What is the proposed number of products you intend to make per year? If over 10,000 then injection molding may be possible. If you just going to make a few, fiberglas layup may be your best way or fabricate them out of metal or plastic stock. How is this function being accomplished by other suppliers of this product?

 

[SaturnVI]

Greetings:

This part was origionally built out of aluminum, and it is my opinion that that was the best solution. Unfortunately, the boss thinks differently and would like to crank out large quantities of this device as cheap as possible. All of my plastic design experience has been with smaller components made of ABS. I've not had to deal with a part where creep could be a major problem, nor where plastic is a major load bearing component.

The part in question has to support a series of solenoids which need to stay properly aligned over time. I don't have any specs on the mechanical forces that the solenoids will produce, so I'm looking at beefing up the design as well as sellecting a strong plastic to compensate for the unknowns.

As far as quantity, my guess is about 1,000/year up to about 10,000 or so. Thanks.

 

[plastx]

If you core it right you could extrude the part but that depends on what design features you need. If the solenoids can slide into a channel then it's possible. Solid wall of 2 inches and plastics don't go well together. GF Nylon sounds like a good place to start. The glass will in some cases lower the cost of a material but in nylon 6 or 6/6 it's not a major factor. Careful of changing humidity and temps. If as you state that the unit will be in consistent room conditions that may be OK but nylon will move if the humidity shifts. You may need UL rated materials so factor that in for a household fixture. Any chemicals need to be considered too such as cleaners. I used to have checklist for plastics that defined what environmental factors like heat, light, humidity, chemical / mechanical factors like impact, loads, flexure / agency like UL/CSA, building codes / cost .

As always, Pat and Dwight give sound advice about working with competent suppliers to get the most out of your product.

Mike

 

[nbucska]

Don't forget that solenoids generate heat, too, and they may rely on the thermal conduction of the mounting when specifying the duty cycle.

I would check the cost of cast aluminum or zink, too.


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