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"Recycled" Plastic - Abrasive?

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Nigel Graham 228/06/2022 22:46:44
2287 forum posts
33 photos

The stuff I mean is the chocolate-brown, rather rough-cast material that reveals lots of little vesicles (gas bubbles?) and scattered, tiny inclusions when cut. Typically used for garden furniture, it has also found a useful career as sleeper material for miniature railways.

Helping replace old, decaying wooden sleepers on our club's track, with ones made from this reconstituted plastic, I noticed my 2mm twist-drill for the securing screws' pilot holes had become blunt surprisingly rapidly.

Now, this bit is in the set packed with my 'Parkside' battery-drill / screwdriver from Aldidls so I expect and am happy with its decent household DIY, not top-notch professional, quality, but ....

- The bit itself not very wear-resistant?

- The material inherently a bit abrasive?

- Or really, just that drilling several tens of holes each perhaps an inch deep, even an A1-grade drill-bit would be blunt by now?

'

(I managed to re-sharpen it free-hand on a bench-grinder, enough to make a test hole in a thin bit of steel without too much effort, but I would not guarantee my grinding accuracy!)

DiogenesII29/06/2022 06:38:58
589 forum posts
234 photos

Could be, depending on where the source material comes from it could contain glass-filled nylon etc..

IIRC even materials like ABS will blunt drill bits on repetition.

Michael Gilligan29/06/2022 06:50:18
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20289 forum posts
1064 photos

That’s interesting, Nigel

I guess that an inevitable consequence of ‘recycling’ is that traceability gets diluted.

… Who knows what’s in it ?

It may be worth asking ‘Gator Composites’ : **LINK**

The web-page invites questions : https://gatorcomposites.com

MichaelG.

David Jupp29/06/2022 07:15:18
838 forum posts
17 photos

There is also the question of what pigment is used to give the brown colour, plus any fillers added. Some could be minerals and hence abrasive to some degree.

John Haine29/06/2022 07:20:13
4718 forum posts
273 photos

I could imagine that they don't do much pre-processing of the waste plastic before making the new material, so it could have all sorts of crud included.

Russell Eberhardt29/06/2022 08:20:33
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2752 forum posts
86 photos
Posted by John Haine on 29/06/2022 07:20:13:

I could imagine that they don't do much pre-processing of the waste plastic before making the new material, so it could have all sorts of crud included.

I somehow doubt that John. Big injection moulding machines and the necessary tooling are very expensive and unknown "crud" in the material could lead to rapid wear of the tool. When I was last involved with plastic moulding (admittedly 20 years ago) the most common filler was talc, aka French chalk, which is very soft.

Russell

Brian Baker 129/06/2022 08:30:45
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201 forum posts
36 photos

Greetings, having replaced over 8000 sleepers at Parklands Railway, and many, many more at other tracks, I can tell you that the material used is processed as little as possible, presumably to keep costs down, and mainly originates from reprocessed car bumpers and the like. It is first shreaded to produce "crumb" to which a dye is added, and it is extruded at minimum temperature into the shape required. Metal fragments, and other rubbish tend migrate to the more molten centre of the extrusion as does any gas or solvent included in the crumb, hence the bubbles and honeycomb effect.

It is important that the correct type of screws are used and other than a locating dimple, predrilling is often not required. For full details, find "Plastic Magic" in Model Engineer in 2014, although I wrote it, I think it is worth a read.

Re the drills, this sleeper replacement is hard work for a drill, so I think your drill has done well.

For all that, we finished parklands more than 5 years ago, now the track rides well, I think softer than with wooden sleepers, and we no longer have to grovel on the ground replacing rotten wooden sleepers, and can pend the time drinking tea and eating cake instead.

Regards

Brian Baker

John Haine29/06/2022 09:23:10
4718 forum posts
273 photos

So not injection moulded then!

Russell Eberhardt29/06/2022 10:33:18
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2752 forum posts
86 photos
Posted by John Haine on 29/06/2022 09:23:10:

So not injection moulded then!

I stand corrected.

Nigel Graham 229/06/2022 11:15:15
2287 forum posts
33 photos

Interesting replies - thank you.

Our track uses a mixture of welded steel-strip cross-ties and plastic chairs, both secured to the sleepers by screws. For the plastic we use self-drilling, self-tapping screws really intended for steel cladding on steel-framed buildings, but have found it necessary to pilot-drill for them - in the particular plastic we use. (That which Brian Baker uses, may be a different form.)

I have found a pilot-hole for these screws advisable too, when assembling steel to steel in my own workshop; but this was through 2-3mm thick steel.

I don't know the make of the plastic stock we use but it comes in long lengths with a slightly grained finish, some circular scars and oddly miss-shapen ends that do suggest moulded rather than extruded. Abrasion is not likely to be problem in the mould itself except over a sustained period. The graining might be to suggest wood, as it is sold for outdoor furniture-making among its main uses.

The inclusions appear as scattered white specks, difficult to identify, but they might be something harder than the surrounding poly-whatever.

The plastic is also somewhat brittle, as I found when trying to force a piece into the end of an ERW-steel tube, having not quite machined enough off to give a light drive fit. I use a manual shaping-machine for this operation, testing the thickness against an off-cut of the tube.

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