Making an Extruder

Screw extruders are very close tolerance devices that must be able to handle lots of abrasion and temperature. The screw is also the "plunger" that forces the molten material through the sprue/runner system into the mold cavity.

This you will need to buy. It should be a screw extruder to help in mixing the plastic on its way to the mold. Different materials may require different length to diameter, and compression ratios. Band heaters for the barrel and cartridge heaters for the mold can be bought from molding supply houses.

The hydraulics are straight forward, but must be able to handle lots of heat and pressure. You'll need about a ton of clamp force for each square inch of mold area you have.

You might consider buying an old Arburg molder and refurbishing it. They are great, versatile molders.

Have fun. I never tried to build one, but I've used a lot of them.

Take pictures and send them if you do this.

That's very interesting, but not able to mold nylon. OK very small parts maybe. But you still need much more heat than it takes to melt a milk bottle.

I'm gonna go have another look at that.

I know very little about thermoforming. You say "much more heat" -- is that just for melting the nylon, or does the whole system require some kind of pre-heating or something?

Well, first thermoforming is a different process from injection molding.

Yes, nylon is a higher performing thermoplastic than the bottle plastics. Longer chains of polymers take more heat and mechanical energy to be processed. It also neans that they can tolerate higher service temperatures and resist more mechanical shock and chemical attack.

So, it takes more heat and pressure to injection mold nylon than the bottles.

Nylon can also be recycled, but after one or two times the material degardes too much.

More than you wanted to know.

The whole system does not require heat. From what I have researched, because there is so much heat required to process the nylon pellets the hopper has to be heated to eveporate the moisture. The mold that it is being injected in has to be heated as well. Both of those temperatures however shouldnt exceed 140F F. The heating chamber that the screw drive pushes the pellets through howver will need to be heated to ~ 500 -515 F to allow the nylon pellets to be extruded through the die or nozzle.

as far as purchasing an older model molder and refurbing, I have searched on several occasions and have yet to find a machine in the sub 10,000 range. I would think that between the insight and knowledge of an engineering community such as this :), and my unrelenting ingenuity, I should be able to construct a working machine that produces a quality product for bottom dollar, while simultaneously educating those who ( however few and far between ) wish to do so as well, but have not found the adequate literature on how to do so. I have yet to find any other forum, topic, video, or tutorial on exactly how this can be done.

That last part poses the question, IS the lack of information because the people who have done it are trying to protect their proprietary secrets, or is it just an outlandish pipe dream where the end greatly unjustifies the means?

who knows, but we have to occupy our minds with something...

Ahhh!

I like a gauntlet thrown!

And your attitude.

Alright team, lets get some requirements refined

Heat range, material forces, continuous heat or batch (you said small lots)

Even used machines are expensive. That's because of the complexity of the sensors and control system. Not to mention the cost of the barrel/screw which can easily run $6K USD, and the hydraulics. They are not simple machines. They are also not well suited to small quantity parts manufacturing.

What are you molding? Shape, size, cross section, parting line square inch area?

You have to tell us what you want to do. Pictures??

Is nylon the only choice of materials you have?

Wow. Some great replies to your questions here. You are doing very well at describing what you want to accomplish, and I think you will get some good information here (but not from me as this is not my field however, I will monitor this thread and think on it).

It sounds that you could offer a lot here on other topics, notwithstanding getting some help for your current project.

Welcome to CR4!

10-4! Give me the weekend and I will have some specifics up on Monday. It would be tomorrow but I have a Government sponsored vacation I must attend so I wont have time to until Sunday night.

I will say, this being my first day here, you ladies and gents are really starting to grow on me. I like people who love a good challenge.

We too

You sound like you are made for the place.

Welcome.

Part size, quantity, and cost should determine how to proceed.

The capital costs of setting up an injection molder are high. It is usually more cost effective to utilize the factories/resources already set up to perform this work for you.

We had many small precision plastic parts custom molded in 5000 to 500,000 parts/year quantities. Per-part cost ranged from $0.03 up to $1.00. We typically purchased/owned the custom tooling (molds ranged from $2000-$20,000) and contracted with specialized factories do the actual injection molding, trim, inspection(QC), packaging, and shipping.

If you only need a few dozen small parts/year, the DIY approach might work. Good luck!

Our friend really wants an injection molder, not an extruder.

And extruding thermoplastic rubber isn't even close to molding nylon.

No offense meant. That's just my take on it.

No offense. I was only trying to present leads. But these extrusion processes can be adapted to castings as well as films. I never worked with nylon but some materials used demanded higher heat. I usually get into trouble when I enter a discussion into a field I am not well versed. I usually just change feet but my mouth is still full. Thanks for removing one foot. Dupont is more interested today in making resins for others to extrude. They still would be good contacts.

Yes, in my haste I seemed to have mislabeled this thread. I am looking more for an injection molding application than I am an extruder. I need to force molten resin, not pull it. Might need to find an admin to see if we can label it correctly so that other people will not be mislead in the future.

the substance I will be using is DuPont Zytel 80G. It is a very strong an durable nylon that resists a large amount of chemical and environment degradation. I have procured a data sheet over my lunch break, but it must wait until I have time to study it. Plus these darn smart phones just don't have a big enough screen to read on.

There.

Desclaimer: I am not an admin.

I think from reading your post and the replies to same, you should really look for someone to produce the parts for you. The cost to make an injection mold unit prohibits your application. Engineering cost alone for making a one of a kind unit, really is prohibitive as well. I have spent many years designing these types of processes and would highly suggest the route I have outlined above.

How many pieces?

How quickly a turnaround?

A small number done slowly can be done quite cheaply using a shop press, a return spring, a barrel with a band heater and an egg cup to measure the beads. The downside is that 1. it takes time to melt the beads, 2. it can get too hot and catch fire, 3. it is slow.

I used one like this 30+ yrs ago. It was all down to timing.

Retract ram, remove mould and separate out piece, put mould back, put in measured amount of beads, count to 10, lower ram, retract ram etc.

Of course you can use an electrically driven hydraulic ram, temperature cutout/cutin, computer weighing and dispensing system and keep yourself busy for years.

Have fun

Jim

I see new member lihuiqian is having a tough time making friends at CR4.

Nine posts to date, and only four remain on record. All four of those comments are

CR4 ADMIN: Deleted Post SPAM

Is this a desirable member? Ten strikes and you're out?

I've got one for her, too

Just kidding.

Those spammers are pretty quick and often fire off a bunch of posts before we can catch up.

You should see the stuff that you don't see.

I think that once you really do your research on this one you will find that building your own IM machine from scratch to make the parts is not your best option. If you decide that injection molding them is the best/most economical route, I would suggest that refurbishing a machine will be a better value. Or, alternately, you could rent machine time from a molding shop. This is frequently done for prototypes, mold try outs, etc. Otherwise it is really hard to even know where to begin telling you how to build a machine, build a mold, set up a proper IM molding process, etc. when you seem not to have any IM experience.

Next, if you give some details on what you are trying to make, how many, and over what period of time. The economics of IM are well suited to large quanties of parts, made from particular materials, and having a complex geometry. Other processes are better suited in other cases.

Finally, on your choice of materials. Nylon (polyamide) materials are good in a number of applications. However, there are certain things that you need to be aware of. I will list a few here. The moisture content needs to be well controlled during the molding process to prevent material degredation. Mositure in the end use environment will affect the material properties. Nylons absorb water from the atmosphere and the absorbed water will plasticize (soften) the material. Conversely, in a dry environment, the nylon release moisture and will be brittle. The datasheet may list some properties of this "dry" material to reflect this behavior. Also, heat plus moisture will cause hydrolysis which will permanently degrade the material. While nylons are resistant to many chemicals, it is also attacked by certain chemicals. DuPont should be able to provide you with details on these and other propertis and you can do application specific testing.

I will watch for futher details of you project and see what details I can help fill in.