Plastic injection molding and extruding

Plastic Injection molding is simple with the right equipment. All that you need is a heater and some plastic.

Recycled plastics will yield the best results if kept to their respective groupings. Refer to the recycle symbols and do not mix types.

ABS is my plastic of choice, I used an old HP inkjet printer as the raw materials for this example.

I used a commercially available temperature control for this project but I have posted an accurate precision temperature controller in another Instructable.

All told this project took me about 2 hours and about $50 to assemble and test...

shown below is a 3mm ABS extrusion being done


NOTE: I have added a section with an example of a crude press lever.

Step 1 Important Notice!!!!

SAFETY….

Hot plastics are NASTY and EVIL!!!!… USE gloves and a face shield at minimum. For example… Hot ABS is at minimum 110 Degrees Celsius or 230 Degree Fahrenheit and will stick to you plus will continue to burn you after it burns your skin off… Use extreme caution!!!!

Materials required will be shown as used. This as a free-form Instructable. Be sure to read through entirely before deciding if you should build. I built and documented this on the fly as I built it for myself…

I recommend using this in an extremely well ventilated area like outside. The initial set up will produce smoke if the plastic is overheated...

Comments

[Dokholliday]

I'm understanding that everyone is concerned with the constant feeding of raw stock into the extruder so as to have the ability to extrude in an endless cycle so one might put his stock on a reel. If one were to install multiple batch bins and of of course for such an upgrade one might also have to invest in more heaters etc so as to be feeding one while the other is being refilled and brought up to a predetermined preheated temp and then to the final preferred heat to make you final plastic temp (+ 10 or 20 degrees F) as uniform and consistent heat where on might install with valves and or a simple valve system one could alternate between 2, 3, 4 or more. In the commercial world I know there are also insulated heated flexible lines that maintain the heat of the material to keep it fluid till the material reaches the extrusion head 9The ones I was familiar with was for hot glue applications). If a person had a way to use copper line and maybe some sort of DC current to heat a predetermined length or maybe an element that would heat the tubing one could fix an array of hoppers and extrude indefinitely or until such time as the equipment need cleaning. BTW if one had access to a porcelain tube of knew how to coat tubing with a non conductive agent then one would be able to transmit and transition you plastic in a fluid state from point a to b by using this method and or wrapping the tube with and element. ( http://www.instructables.com/id/DIY-Hot-Air-Soldering-Iron-using-12-18volts-DC-at-/step4/Heating-element/ )

[pfred2]

So what you've made here is essentially a big homemade hot glue gun?

Checking out your article I couldn't escape the thought that most everything you used in it looks like stuff found in an electric hot water heater. I've ripped a few of those apart for stock and materials so I have a bunch of the heating elements and thermostats that come out of them now. I didn't think to save any of the insulation though. The insulation is usually pretty nasty by the time a hot water heater is shot.

I think if I did this I might want to use a wooden dowel for the plunger. Seems like such a shame to waste a perfectly good socket and extension. Run properly this thing should never get hot enough to char wood should it?

[baslisks]

the normal plastic I would use gets to 240 degrees Celsius. So a wet rod wouldn't char but a dry one would. Would rather use a metal plunger and avoid that possibility.

[lordl9999]

I have a VERY similar project going on, can you help me with my wiring or show me how you've done it?

would be VERY appreciated!

http://www.instructables.com/answers/basic-wiring-for-a-home-made-benhtop-injection-m/

[escher7]

Your how-to is excellent and very clear. Forgive my "dumb" but the extruding plastic itself is used how?

[jongscx]

I've seen this done with wood auger attached to an electric motor, essentially making it an auto-feed using the pellets.

[hmuringa]

HI!!! Do you use this plastic filament for 3D printing?

Instead of using recycled plastic Ii put the raw material (ABS) as little plastic marbles (ABS is sold like in small balls, very cheap), do you think I can get a filament good enough for using on a reprap???

Thanks

[palmeida2]

Hi Hmuringa,

could you tell me on the internet where I could find ABS raw material to buy it?

Best regards,
Pedro

[hmuringa]

Hello!!!

The raw material I was talking about is called pellet... Just google ABS pellet and you'll find tons of places... Most are for industrial use, but you can also find on ebay:

http://www.ebay.com/sch/i.html?_from=R40&_trksid=p5197.m570.l1313&_nkw=abs+pellet&_sacat=See-All-Categories

=]

[palmeida2]

Thanks for your reply! i already have look and found it.

Best regards and good construtions

[codesuidae]

Are there any entrained air bubbles in the extruded rod?

At the rate you are extruding, how much distance is required for the rod to be cool enough to coil onto a roll?

[Random_Canadian]

some bubbles and brittleness do occur if the heat is to high..

[kill-a-watt]

Since this appears to be a batch extruder, how long of a filament can you produce?

Have you tried spicing lengths together?

How does the recycled plastic print compared to virgin plastic?

[Random_Canadian]

Constant feed is possible and I haven't tried splicing. A single plunger stroke will give about a 26 inch length and continuous feed is kind of possible since the plastic is quite sticky. virgin is definitely better but that may be due to heating irregularities in the rig.

[Random_Canadian]

I was getting about a 2 foot length. At the bottom of the stroke I was able to lift the plunger and insert more plastic to continue the length, The is a little knob formed where the plastic pieces join. So far I have been able to get a 6 foot length.

I mainly use the 2 foot rods for plastic welding without any problems. I have as of yet to do more testing on the differences between the plastics. One note is that overheating will produce a brittle plastic. The recycled plastics that I have now seem to have similar flex properties as the new plastics.

I hope that this helps...

[dex drako]

have you thought about using a drill bit big enough to fit in the tube as an auger in the pipe instead of the plunger? that way you could keep feeding in more platic without stopping.

[Random_Canadian]

I did try a wood auger bit inside of the 1/2 inch black pipe , It was an excellent fit but it would not create enough pressure to extrude, the plastic just sort of milled around but would not come out of the extrusion port. I think that there was not enough friction between the surfaces to work but I am not certain.

[dcassina]

Hey Random_Canadian,

Thanks for the instructable... I'm about 60-70% done with this project. Can you let me know what temperature control you purchased online for this one? Or at least what type I should look for... I looked at your other instructable but am not too familiar with circuits so am choosing to buy one.

Thanks in advance,
Diego

[Random_Canadian]

I purchased several years ago from eBay. Try doing a search for a kiln controller. Be sure to look for one that includes a thermocouple. The search that I did shows that they have come down dramatically in price.

Good luck with your build. I will be posting extra instruction to this which is a simple manual lever type plunger.

[Random_Canadian]

Sorry and a power relay if the controller does not have an internal one.

[dcassina]

Thanks for the quick replies... I'm looking for a kiln controller, but I'm still a little unfamiliar... so the heating cartridges (two of them) connect to the temperature controller? I searched the internet quite a bit but am having trouble finding information on this.

[Random_Canadian]

The controller will activate a power relay. This is used to isolate the controller from main power. The relay is just a switch that interrupts power to the heaters. The power relay will typically have 2 power inputs, 2 power outputs and 2 controller inputs. Main power is connected to the inputs and the two heaters are connected in series(high wattage heaters) or parallel(low wattage heaters) to the outputs. The controller should come with a manual which will contain the circuit diagrams.

I hope that this helps

[fcjamesihug]

Like the article.

Cheap PID controller with k-type thermocouple:
http://www.dealextreme.com/p/digital-temperature-controller-66334
About $17 with free shipping

[pyrosniperfreak]

Hey, is there any way to use this technique to mold rubbers? maybe silicone, or maybe some other harder rubbers?

[dmwright]

There are band heaters made specificly to wrap around pipe made by the same outfits that make the cartridge heaters you are using but a lot easier to get good even heat transfer.  Take a peak at mcmaster.com to see what they are then scroung e-bay for them.

BTW if you run the heaters at 120vac they work fine but make half the heat, 400w becomes 200w.
Really neat hack!!!!

Share and Enjoy,
Dave

[Random_Canadian]

Thanks, sadly the only band type heater that I could find was 4 inches in diameter.


I have 240V wired to my workspace but I thought that the conversion on the heaters was half the current and about 1/4 of the power.

[dmwright]

Random,
Just checked to make sure  Watts = Volts x Amps per Ohm's law so 1/2 the voltage means half the power.  See the link below
http://www.watlow.com/reference/equations/0103.cfm

Here is a link to a lot of calculations that are really handy for figuring out how much umph one needs to heat up or melt stuff.
http://www.watlow.com/reference/files/powercalculations.pdf

All the major suppliers have these handbooks on their websites.  Some names... Hotwatt, Tempco, Dalton, Vulcan,   Watlow was the first that came to mind.

Share and Enjoy
Dave

[Random_Canadian]

I took the heater resistance as a constant in this case 144 ohms, with this scenario both voltage and current are varriable.
Try P=(V*V)/R... 240 V gives 400W while 120V gives 100W.

[dmwright]

You are absolutely right. A closer reading yeilded "Watts vary directly as ratio of voltage sguared" W1 = W2 (E2/E1)^2 down in the lower left corner of the Ohm's Law chart

[rimar2000]

This is very interesting.

do you know if is PET suitable for extruding?

[Random_Canadian]

Yes it is. You can use most thermo-plastics for this. Thermo-set plastics cannot be used. You will need to research the melting and burning points for proper machine set-up.

I have not had the need to try most others as of yet.

[rimar2000]

PET is thermo-shrinkable, that is a very good thing!

[dmwright]

PET is the stuff of soda bottles, which are stretch blow molded; first a parison is injection molded to provide the finish where the top threads on and the right distribution of material for the sides of the final bottle. The parison looks a bit like a test tube with a thread at the top and rather thick walls. The parison is heated at the blowmolder to almost it's melting temperature and clamped in a mold the shape of the finished bottle plus at bit of shrinkage. A stretch rod enters the mouth of the parison and stretches the softened PET to almost the final length of the bottle then a blast of air inflates the parison forcing it against the cool walls of the mold where the plastic solidifies. This leaves the molded bottle with a lot of molded in stress. The stress is the source of the "thermo-shrinkability you mention. One can also think of it as the plastic having a memory of its original shape and a strong desire to return to that shape if heated to near its softening point.

Share and Enjoy,
Dave

[rimar2000]

Thanks for your explanation. But I think that this is valid only for some plastic. Example, PVC has not that strong desire to return to its original shape.

[dmwright]

PVC is a odd ball, also goes by the name vinyl, there are a broad range of materials in the class from the soft flexible film to the ridgid stuff of hot water pipe. It's plastisized with oils to make a soft product or filled with mineral powders to make a strong stiff product. Heat shrink tubing for the electrical markets is made from PVC.
The reason I say it's a odd ball is that there are a limited number of processors that are willing to make products from PVC. Poly Vinyl Chloride breaks down into some nasty things if it is heated too much, chlorine and vinyl ester are a couple of the nasties.
The folks who know how to process it make some wonderful things from it, the folks who don't have actually killed some folks.
All thermo-plastic materials will try to relieve the stress that has been locked into their shape when they cooled.  That is the reason they take on such interesting shapes as one heats them to almost melting.

Share and Enjoy,
Dave

[rimar2000]

Thanks Dave. I notice that you know the subject. For me it was a surprise to learn that the shrink tubing is made of PVC.

[Euphy]

This is a good instructable - I like your simplified injection process, especially the idea that it's used to recycle plastic back into filament to use in a more subtle-duty FDM machine, brilliant idea.

[Biggsy]

A very interesting I'ble... welldone :)

Might have a go at this at some point.

[dr.knowitall]

Some very good ideas here thanks for posting up. I look forward to your future instructables regarding this subject and any for that matter.

Are you going to post ideas regarding automation? I'm sure this could be done with a simple DC motor and PWM controller.