How is this made? 1

[ziptron]

Hello Everyone,

Does anyone have an idea how these are made?

http://www.freshwatersystems.com/popup.aspx?src=images/Product/large/2615.jpg

This is made from polypropylene. I had the top part (the hexagonal nut) shaped part right in the middle separate from the rest of the filter head. Would this whole thing be injection molded or would these top pieces be added in later with some sort of plastic weld?

Thanks in advance!

 

[btrueblood]

Hexagonal nut?

 

[ziptron]

Yeah,

Sorry perhaps I was not clear. I uploaded a picture of what my filter head looked like. I never used tools on it so it was not over tightened, it did not freeze and when I look closely at the fracture surface it does not seem to be a brittle fracture, I see lots of little fibers within the crack...

As if it got pulled apart over time?

 

[mcgyvr]

Looks like the whole thing (round cap/threads/hex portion)is molded then the quick connect o-rings/bushings,etc.. are just pressed in.
If the hex part is cracked at the base where it meets the large round cap it's a manufacturing defect (or under engineered section)

 

[ziptron]

You're right it does seem under engineered. The only thing that boggles my mind is that this thing was in service for quite a while and its not failing in any other water cooler systems. I would assume that if it was under engineered then a large amount of them would be failing.

It is under constant water pressure, perhaps over time the pressure simply forced it to let go at the weakest parts? I kept thinking that perhaps the plastic degraded over time, but I have no idea how to check for that.

 

[IRstuff]

The inserts, I think, are nylon, and the construction is similar to other RO water filtering components I've seen. However, the only component that's ever failed in my RO systems is the reservoir bladder assembly, i.e., it could maintain the compensation pressure in the tank anymore from rust. Other than that, I've never at a part fail in 18 yrs.

TTFN

FAQ731-376
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[DesignerGuy16]

Probably blown out from too much pressure or a pressure spike. I'd agree with the under engineering comment even without seeing the back side of the cap.

If you're just trying to make it better for yourself I'd say just reverse engineer it and have it machined from a piece of round stock and buy some tube fittings. (Look to SMC, Festo, Parker, etc) Shouldn't be a difficult task, and probably wouldn't cost a ton to do.

James Spisich
Design Engineer, CSWP

 

[patprimmer]

It is cracking on the edges of the notches created by hard and flexible areas in the moulding.

These may also be weld or fold lines as the mould fills.

It may well be fibre reinforced PP which may explain fibrous surface at the break.

If it is straight PP if you cut off a chunk so as not to include the fittings, then drop it into a pot of water, if it floats it is straight PP. If it sinks it is reinforced (that is presuming the base resin is PP).

It is a one piece moulding.

It may have been subjected to abnormal water pressure or more likely excessive water hammer that has caused fatigue cracks.

Some chemicals can cause solvent stress cracks in the stressed areas. Cleaning or sterilisation with antibacterial chemicals might just do that.

Regards
Pat
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[Compositepro]

Could the filter have frozen at some time?

 

[ziptron]

Thank you everyone for your input.

A friend of mine has a lab and I brought it to a lab and played with my filter under a stereo microscope. I attached the picture of the fibers within the fracture surface.

This is the fracture between the hexagonal piece up top and the round top part. Does that look like a fibrous surface from reinforcement? It think it looks like some sort of environmental stress cracking? Any ideas?

 

[ziptron]

I've been reading a polymer failure book and started learning about thermo-oxidative degradation.

I am starting to wonder if contact with the brass fittings caused some thermo-oxidative degradation which then spread radially around the fitting due to the water pressure.

 

[IRstuff]

That style of connection has been around for decades, without any problems. Be a bit difficult to explain why it would attack an area nearly an inch away, wouldn't it?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[ziptron]

My guess would be that it was a combination of several things. A higher then normal temperature and a higher then normal water pressure .. perhaps both environmental stress cracking and thermo-oxidation contributed to the degradation of the plastic at those edges and were sped up by abnormal water temp/pressure.

 

[Compositepro]

My comment about freezing above was to say if the filter or the piping to the filter even some distance away had frozen, then the water pressure could have easily risen to the breaking point. Even steel pipes will burst and I'm sure this filter has a much lower rating. If this occurred then there may not be anything wrong with the filter at all.

 

[patprimmer]

Compositepro makes a good point that seems to have been disregarded. Was it exposed to temperatures where ice might form.

Dezincification of brass can be a serious problem in chlorinated water and the zinc chloride can attack some polymers, especially acetal, but also nylon. It is not normally a problem for PP. Thermal oxidation is also not a problem for PP at temperatures water is used at without pressure. Electric kettles are very often PP.

Have you confirmed it is PP.

Have you confirmed it is unfilled or filled. SG being more or less than 1 (ie does it sink or float is by far the easiest test. It requires nothing more than a water supply and a container to hold water, ie a bucket or tub.

Why do complicated tests before the dead simple ones?

I personally cannot get a clear enough image to positively tell if there are fibres present or if the polymer is fibrillating at the break. PP is quite prone to fibrillation due to its very linear molecule.

Regards
Pat
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[Pud]

I would guess (from my WAG chart) it is a creep stress failure.

The (supposed) material of GFPP may have been glass filled rather than glass coupled.

Hoescht (aka Ticona these days) have had many water devices on continuous test (sustained pressure) for over 20 years to determine failure modes.

Imho, if I had to design parts for sustained pressure, GFPP would be way down the list...

Then as Pat implied, it may be just cr*p moulding!

H

http://www.tynevalleyplastics.co.uk

 

[MikeHalloran]

The object in the image just doesn't look like PP to me.
Okay, maybe PP with a lot of clay filler, but the color is wrong for either neat PP or GFPP.




Mike Halloran
Pembroke Pines, FL, USA