What's new
What's new

A plastic molding reality check...how crude can it be and still work?

implmex

Titanium
Joined
Jun 23, 2002
Location
Vancouver BC Canada
Hi All:
Here's a link to a Youtube video I just watched, that is a nice reminder just how crude a plastic injection mold and plastic injection molding can be and still make some sort of usable part.
Production of Pipe Elbow || Incredible Technique of Making Elbow || Pipe Fitting - YouTube

For all of us who've been moldmakers it's pretty cringe worthy because it's incredibly rough and violates most of the rules we learned about our trade.

For those who are Prima Donnas about how special they are, it's a nice reminder to the rest of us that the tenths they pretend to split are not always necessary tenths.

For those who really do build high end tooling, it's a nice affirmation of the vast gap between a "mold" and a mold.

I especially liked the process control around deflashing the parts and trimming the sprues...high end and OSHA approved if I do say so myself!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 

BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
Another priceless moment: when he carefully lays out his clean white sheet to cover the grungy floor, and then immediately walks on it to grab raw material for mixing.
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
I got some Enco cheap Metal stamps from India 35 years ago that were in boxes
that appeared to be simply melted on a stove and poured into a mold.

"Casting" plastic.
 
Last edited:

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
Interesting the resin comes as a powder rather than pellets. I wonder what he other powder he adds. The bag seems to say, "polyester", not the PVC I expected..

I am impressed by how easily the parts come out of the mold.

It could be there is an excess of draft on those cores, so much so, that in usage, the fitting is loose on the pipe at the mouth end.
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
With all the energy being used to heat the extruder barrel, you would think
they would have (2) people, using (2) molds, to keep the utilization up.

They could even be different pieces molded, IE a Tee fitting along with the Elbow fitting shown, as they are putting the mold in place for each part.
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
The first thing that caught my eye is their use of a third member from a differential as a right angle gear reducer.

The second is that this back alley operation shares one thing in common with the most 1st Class USA operation....you need plastic feedstock. Those bags of plastic look pretty crude, but they're still a workable plastic. The evil oil companies produced them out of evil oil, and without that basic material about 75% of our world would cease to exist.
 

implmex

Titanium
Joined
Jun 23, 2002
Location
Vancouver BC Canada
Hi magneticanomaly:
You asked in post#6:
"Interesting the resin comes as a powder rather than pellets. I wonder what he other powder he adds. The bag seems to say, "polyester", not the PVC I expected.."

I'll bet the resin is regrind of everything under the sun including the kitchen sweepings and the residual crusty feces from the last known use of the plastic.
There's probably another hole in the wall shop just around the corner with an old beater grinder that gets its feedstock from the ship breaking operation just down the road.
The additive is titanium dioxide to make the mud coloured grot they're using look a bit more acceptable so it'll sell.
The label on the bag likely means nothing; in fact I'll bet when that bag gets a big enough hole in it, they'll just throw the bag into the hopper and make "parts" out of it too.

There's probably less than 1000 PSI injection pressure, judging by the frail looking clamp mechanism and the large projected area.
Obviously all the dents provide excellent venting, and flash at the parting line is not objectionable to them.

I'll bet too, that any piping system that uses these elbows is going to leak like a bastard...I doubt you can glue it reliably and as digger doug points out in post #8, there looks to be a lot of draft on those cores to make them release so easily; dents dings and all, so good luck getting a leak proof joint.

But the ingenuity and "get 'er done" of this operation is pretty impressive in a bizzarre way too...I doubt you see many whiners looking for "safe spaces" in their operation, and I didn't get a sense of a robust HR or safety department meddling anywhere.
I wouldn't ever want to go back to an environment like that, but give them a decent workspace and I'll bet they could compete pretty effectively...even if they had to leave a bloody trail of dismembered employees in their wake to do it.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
I'm not sure it will leak....that size pipe is almost for sure drain pipe and therefore has no PSI in it.

Then, you factor in that in Pakistan, no infrastructure has a life expectancy of more than a couple years....and it's the right product at the right price for the job.
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
I'm not sure it will leak....that size pipe is almost for sure drain pipe and therefore has no PSI in it.

Then, you factor in that in Pakistan, no infrastructure has a life expectancy of more than a couple years....and it's the right product at the right price for the job.

I disagree with "no pressure" look at a 2 story house, and that drops down to the basement, makes that 90, thru a trap, and thence out to the sewer.
And then it gets plugged.....24'-30' of head pressure.

Also, the product might not be limited to Pakeystain, as Home Depot always wants the lowest price, might start importing them.
 
Last edited:

ViktorS

Aluminum
Joined
Apr 26, 2021
GregSY, you are so correct about "right product at the right price for the right job".

And honestly I sometimes wish we had a bit more of that mentality here in the "developed" world too.
I mean, yeah, german precision. That's nice and all.. But every freaking part one buys here in europe is sooo precise, so smart, so good, and unfortunatly so expensive. Sometimes I don't care. Like a parting line in a sewer pipe.

As Dan Gelbart (look him up on youtube) said:
There is no point in spending time making a part beautiful, there is enough beauty in function.

I also believe this might be one of the reasons we buy so much from china. Good enough is enough, no point shooting over the goal.
 

surplusjohn

Diamond
Joined
Apr 11, 2002
Location
Syracuse, NY USA
There used to be alot of functionality acceptable but funky things made here
I used to say that cheapness has a quality all its own.
But does it matter if a sewer pipe looks funky?
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
There used to be alot of functionality acceptable but funky things made here
I used to say that cheapness has a quality all its own.
But does it matter if a sewer pipe looks funky?

You can go back to using lead & oakum*....I'll stick with solvent welding thank you.

*Because with sloppy "it don't matter what it looks like" tolerancing in the bore, that's how you will have to use these fittings.
 

sfriedberg

Diamond
Joined
Oct 14, 2010
Location
Oregon, USA
Obviously we don't know from watching the video how accurate the molding bore is, but I would expect the repeatability to be pretty decent. As long as the mold fills (flashes out), the fitting ID is going to be determined pretty much entirely by the core. And unlike the outside of the mold and all the machinery, the cores and mold recesses were polished. Since the "operator" was watercooling the parts both before and after core removal (and I am willing to assume a level of dexterity and proficiency in pulling the core), out-of-round is probably acceptable.

So, assuming they polished the cores until the resulting parts got the right "solvent fit" for the pipe, I don't see any reason why these would fit any worse than the pipe fittings I can get at Home Depot or Lowes.

I don't know enough about injection molding to know if that crude mixer/injector is likely to leave cold shuts or other weak faults in the molded parts.
 

implmex

Titanium
Joined
Jun 23, 2002
Location
Vancouver BC Canada
Hi sfriedberg:
Normally a cooling plastic part will shrink onto the core, and if there is no draft and the core is dinged up, it will be the Devil's very own to pull the core without a mechanical stripper of some kind.
These parts just popped off the cores, leading to digger doug's observation that the reason might well be lots of draft on the cores.
If the socket for the sections of PVC or ABS pipe are tapered (lots of draft on the cores) they won't mate well with the pipe and the gap will be too big at the open end of the bore to be decently glued or solvent welded.
So that's where all the negative commentary about leaking pipes came from.

Touching on the repeatability of the part dimensions...much depends on the process control and the differences in the dimensions of two different parts out of the same mold cavity can be astounding if the parts were shot at opposite ends of the processing window for the plastic.
As you can see from the video...there IS no process control...sometimes the extruder is sitting there for minutes degrading the plastic in the barrel, other times it's run in relatively quick succession.
The core dunk duration is all over the map, and we won't even talk about the consistency of the feedstock.
The cores aren't loaded with any care, the clamp pressure is all over the map and he runs the extruder until he thinks it's done.

These are not going to be consistent parts...I'll bet they vary by 0.030" or worse.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 

Antarctica

Hot Rolled
Joined
Jan 16, 2007
Location
Annapolis, Maryland
I thought it was pretty impressive, but I don't know shit.

I will, however, be looking at every piece of plastic pipe elbow I find to see it it has the same medallion/imprint on it....
 

DavidScott

Titanium
Joined
Jul 11, 2012
Location
Washington
Lead and oakum? I always used oakum and tar. The only things that scare me in that video are the powdery regrind and how well the melt is controlled. Both will lead to severly degrading the plastic. As for solvent welding, hope they don't use too much of the wrong plastic.

It doesn't look like there is much injection pressure due to extruder only with no plunger. How much clearance do you think there is between the screw and barrel?
 








 
Top