[Robin Hewitt]

I'm having to make a quick benchtop plastic injection tool. Ram comes down into pot of molten ABS and pushes it into the mould, you know the type I mean.

Simple question, what is the melting pot made of? I think it may be brass with a stainless steel ram??

[chrbau]

I have worked with big molding machines and I remember it as being stainless. Here's a link to a place where you can buy a couple of books that gives you complete plans for smaller machines:
http://www.camdenmin.co.uk/EngPrac.htm
This page is really long, so on it, search for:

Secrets of Building a Plastic Injection Molding Machine

You will find two books that covers the subject. I'm not in any way affiliated with Camden, but I have to say they have many interesting books about constructing a lot of stuff.

[Robin Hewitt]

I have ordered the book. Not entirely sure if it will be much help though, I want full auto using hydraulics and I doubt the book goes that far

Bench top machines seem to use a fairly tall, narrow, melting pot and heat it at the bottom end. Looks like I dump cold plastic in the top and then drop the ram. The melt forces back up, hits the cold pellets, congeals and forms the seal which explains why it doesn't just extrude up around the piston, stick and gum up the entire works. Right?

I'm aiming for a max injection pressure around 2000 psi for ABS, little 990 lbf ram on to a 20mm piston with a 6" stroke. If I put die springs on top of the ram I can nudge it down, compress the springs to a switch and hold any pressure I want. Hopefully 2000 psi is way too much?

The reason I think it's brass is because Traving claim a "Nickel plated barrel", Nickel is a soft metal, but are they using it as a lube or as a rust preventer??? I could give Brian a call at Travin but he's probably miffed since I took my moulds off him and shipped them to HK, he'd probably try to sell me something

http://www.travin.co.uk/tp1.html

[DonW]

Injection molds are almost always made entirely of stainless. No brass.
(I used to work in the mold design dept of a major plastic products manufacturer...)

[kiwihoon]

I'm having to make a quick benchtop plastic injection tool. Ram comes down into pot of molten ABS and pushes it into the mould, you know the type I mean.

Simple question, what is the melting pot made of? I think it may be brass with a stainless steel ram??

Giday Robin
I am a plastic moulder and tool maker I have 2 injection moulding machines and a small cnc machine to make moulds .I have 25 years experance and it sounds like you want to make a plunger machine which just forces the material into the mould rather than a screw type .I sugest a tough barrel ie stainless as this i most important piece with a brass plunger which can more easly changed or repaired .
As for you using ABS this is a tough plastic to mould high heat is needed around the 250 plus celcius and a big runner. Sugest you start out with poly pro
Hope this helps Kiwi

PS if you want some drawing of machine barrels let me know [[email protected]]

[Robin Hewitt]

I will be guided, but I have to admit there was an ulterior motive. It is much easier to get 6 inches of 1.5" brass, durned sight easier to drill and ream it to

(Band heaters seem to start at 1.5" if you want 600 Watts).

Here's a few more details as I flesh out the design...

Using what I have, it's a single 90 bar pump mounted on a half horse motor.

I have an 80mm double acting ram to open and close the mould which gives me slightly over 10,000 lbf max.

Only having one pump I plan to put in a second 25mm ram on the same circuit closing a pair of die springs, all that does is hold the pressure when I divert the oil to the 25mm injection ram giving me up to 990 lbf via more springs.

990 lbf on a 20mm piston gives me up to 2000 psi injection pressure.

Not being much on health and safety, I want the die exposed rather than buried away inside where I can't get at it, so I'm putting it on the end of the machine with the cavity moving away from the machine on two 40mm rods (I have lots of 40mm rod) most everything else comes out of a standard 3 meter 4"x1" steel bar.

I just have to figure out how connect to the ejector plate and save having to build springs in to the mould. I'm hoping inspiration will strike sometime in the next few hours

[dmc-tech]

" Not being much on health and safety "

Dear Robin,
I implore you to reconsider your position on safety,
Molten plastic at 250 C @ 2000 psi, add a air bubble in the feed line,
and you could be wearing it on your skin or face if a coupling or seal gives away.

The only way to get "set" plastic of skin is to remove the skin.

[Robin Hewitt]

Sounds horrendous

Does that happen very often?

[DJPLAST]

Listen to DMC-TECH. He knows what he is talking about. It works the same way here in the states. This stuff does not give second chances. High heat, high pressure, semi molten material and moving machine components, NO ROOM FOR LACK OF SAFETY!!!

[Robin Hewitt]

NO ROOM FOR LACK OF SAFETY!!!

Probably true but it is my experience that once a thread moves to the topic of safety there is little hope of getting any more useful information

I like to be safe, but only to a point. If I am in no more danger than when driving my car then I think it is an acceptable risk.

Faced with a litigous society the safety "experts" have gone too far IMHO, too many warnings, rules and regulations, I have become desensitised.

Safety rules are written for morons who should not be trusted with a can opener, there is no separate list for the reasonably intelligent.

Hence my question, "How likely is it to happen?".

If likely, I'll put guards on, but as I've never noticed plastic spatter inside machine guards, I don't think it is.

Edit: PS: I have around 20 pounds of high quality sporting gunpowder in my workshop, easily enough to blow me to kingdom come because health and safety says it has to be in a stout plywood box rather than a cardboard box. They have converted a fire hazard in to a bomb. Nobody had an accident with gunpowder at home, but some safety wallah saw a potential accident and made it 1000 times more dangerous by containing it. If my house catches fire I presume the fire service will stand well back while my fireproof box burns through. Goodbye house. I shall have to take insane risks, anything to get that box out if it happens.