Forum Replies Created
It depends on the plastic you are using…pvc yes. It also depends on where u r are in the operating range for the plastic you are using. Let’s say your range is 450-550 degrees F. If your part dictates a lower viscosity and you are running 550 degrees then a few degrees can make a difference. If you are using a screw for injection or a screw for extrusion then yes as the screw in parts shear heat to the plastic. If you are plungering for injection then pid is probably not necessary.
I would recommend that you just build it! Every mold, part and machine will be unique and require tweaks to make good parts. Those tweaks will be unique to each batch of plastic as well. Making plastic parts is not like cutting metal. It will be quite challenging. Please allow yourself a lot of time to get good parts.
THis is the original injection molding machine built in the 1950 in Ohio. It kinda looks like the top one above.
Analog oven controls can only do 100% on or 0% off. This leads to overshooting of the desired temperatures and no control of the band around your desired temperature. Typical oven controllers hold +-5 degrees. PID Controllers can hold +-1 to +-2 degrees with no overshoot for many reasons you can look up on Wikipedia. One main reason is PID Controllers can apply a percentage of power any where from 0-100%. This is important when you get close to your desired temperature that is when you want to apply 10-20% power to “glide” right to your temperature set point.
Yup it takes lots of strength to resist the forces required. Lots of precision as well. Actually the controls are the easy part if you take out all of the safeties that are required by OSHA. Morgan industries makes a semi-automatic unit as you mentioned. $26000 new. Approximately $12500 new. https://www.morganindustriesinc.com/medical-applications/
Also the amount of force that is required is 3-5 tons per square inch. So 9-15 tons of clamping force would be required for your application listed above of the 50mm diameter cap.
@emmsclaire. Some real technical data would be great for this topic. Most polymer companies act like the big cigarette companies and don’t want to admit to the lethality of polymers. In the meantime, just go get one of these dust extraction systems, some more fittings from your local hardware store for venting your clothes dryer and vent the fumes out of your workshop thru the roof or propped door. Central Machinery® 31810 13 Gallon Industrial Portable Dust Collector13 gal. 1 HP Heavy Duty High Flow Dust Collector https://www.harborfreight.com/13-gallon-industrial-portable-dust-collector-31810.html
@btmetz I saw the ManyMaker in 2016 as well and was quite disappointed. Maybe others are as well? These machines will be challenging to set-up and tweak to get acceptable parts. They likely will not be able to produce medium to highly complex parts. Tianyuan Testing makes a machine very similar to these but with greater precision. Honestly it is a quite simple injection machine. Their cost was $8000 plus $3000 to be delivered to the USA.
Hello All. This is quite an interesting topic and body of work. Congrats to all for your hard work. I myself also built a semi-automatic injection molder in 2016 with compressed air. I tried to use lower cost components. I have built many machines in the past and this is quite a difficult task…one that a person will be hard pressed to share freely. Here is my version.
The precision required to make this work is way beyond anything one could create in their garage and machine building knowledge and experience of many many years.
I have not built one of these compression machines but have worked with plastic for 25 years. The basics are more pressure and hotter temperatures will make a thin part. Typically 1mm will be the thinnest that you can do with a press like this.
@calebmadden. Only steel is strong enough for shedding plastic. You could try other materials but I am certain you will be disappointed. Epoxy or fiberglass could be used to strengthen the materials you suggested but in the end the time, effort and money would still allow steel to win in the end. Sputtering or conductive paint are for conductivity, reflection or cosmetic applications their strengthening values are almost nil.
The problem with staggered blades is they tend to move the product but not cut it. A well known shredder manufacturer had staggered blades in a complete spiral or helix and it created a lot of wear at the end where the plastic was pushed to. Attached here is a pic of an industrial low speed shredding machine.
Many different materials can be used to make molds. It really depends on the complexity of the part to be made, quantity of parts required and the final part finish required. Aluminum, steel, copper, brass are all good traditional materials. Other alternative materials include: wood, epoxy, some plastics, urethanes, and even 3D printed molds can all produce molds of reasonable quality and strength for certain quantities of parts.
With over 20 years working with polymers of thousands of different types, PET is by far the hardest to work with. Everyone will want to read this link about PET
“Why (and What) You Need to Dry”
You need to desiccate dry PET before extruding!
@yustina. Mixing these polymers should be just fine. Basically you are making a new type of MDPE. medium density. There are quite a few other polymers mixed together that we don’t even know about. The challenge you will have is that you probably will not get a good mixture unless you grind them up then run them thru the extruder and then grind it again and then mold your product. This should produce a good mixture.
The final properties will depend on the start properties and the only way to really know that will be to build test samples and do the tensile, flexural and impact testing to understand. UV resistance will only be there if the original polymers has it or you add the UV additive.
Please be careful when using the terminology “composite”. That refers to any resin with glass, carbon or other fiber added. Two polymers together are “alloys” or co-polymers.
Also, polypropylene can be a homopolymer or a copolymer. Homo means only polypropylene, Co- means polypropylene alloyed typically with polyethylene.
I hope this helps!
@carmatic. A few questions…how do you keep the screw from rotating during injection? How much force do you think you can exert horizontally? Most manual presses are quite small. Typically one needs at least 5000-6000psi injection pressure for plastic. I think you should read more on why the non-return valve is located at the end of an injection screw before you delete it from your design. Also, your design will take quite a bit of time to build so I hate for you to spend a lot of time to build a boat anchor. Again not trying to be negative here but possibly help,you avoid a lot of heart ache. I like your ideas. They just need a little physics refinement.
@xxxolivierxxx. Yes VFDs are quite versatile for regulating speed easily and braking a motor from 3200rpm to zero rpm in 2 seconds etc. I don’t think you really need a VFD for shredding. Just reversing capabilities and even that is not needed. Just unplug the unit and rotate it by hand backwards. Shredding is a complete science. There are several companies that only focus on that. To think the shredder will never jam is not realistic. Vecoplan, Rapid granulator and others only focus on shredding. Neither of their websites guarantees no jamming. I really suggest everyone focus on the capabilities to shred not the speed of completing the activity. You still need to make something and shredded plastic is not really a thing.
Hello All. Here is the most clearly defined way of describing phase converters.
Static phase converters are a startup device for three phase motors on single phase power.
Static phase converters operate the three phase motor they are connected to on single phase. The static phase converter does not actually generate three phase power continuously as a does a rotary phase converter, but only long enough for the motor to start up. Once the three phase motor has started up the static phase converter circuitry disconnects itself and the motor continues to run on single-phase power but because only two of three windings receive power during running, horsepower output is reduced down to between two-thirds and one-half the rated motor horse power. A 15 HP motor will start with the power of a 15 but run as a 7.5 for example.
The high starting torque with reduced running power is an important factor when considering the use of a static phase converter. In some situations this can work out very well but the static converter does have limitations. Static phase converters are not well suited for machines that operate continuously close to the maximum rated horsepower of the motor that operates them. This type of continuous full power loading can be seen in equipment such as water pumps. The pump is sized to use all of the motor’s power while pumping. Lathes are another good example of this need for full power. Although the static phase converter appears to work well on lathes in the slower speeds, in the higher speeds the converter is able to start the lathe turning but the lack of rated horsepower makes these higher speed settings useless. A TEMCO Rotary Phase Converter is best suited for this application.
Taken from http://www.phaseconverter.com/what-is-static.html
Now study up and then move forward!
Guys. This is not correct regarding capacitors and motor sizing. Go to Grizzly.com and other websites. They sell static phase converters up to 10hp and rotary phase converters up to 75 hp. The reason you don’t see/use capacitors over 5hp is because rotary is more economical using smaller capacitors to create the third phase. I used a 15hp rotary for 5 years for a yag laser engraving machine. No problems. A VFD is basically a bunch of electronic controlled capacitors. You can “create” your own phase converter” as long as all output phases are within 5% (exact same is best but nearly impossible) of one another and 10% of nominal voltage it should work just fine. Please educate yourselves. There is a lot of info on the internet regarding rotary phase converters. Best of luck to all.
PS. Currently I’m using 220v single phase 15.3 amp input VFD and getting 220v 3 phase 7.0 amp output. it’s still just capacitors only!
You are looking for this thread for what size and how to design an extrusion screw. Keep in mind that typical screws are hardened and made with very tough abrasion resistant metals. Typically that means high chromium metals.
The quest for the ultimate extrusion screw.
– Nirwan Shubhan (@nirwansub) 20/05/2018
Best of luck in your machining!
its always good to see people thinking such that your are.
thats really cool to have your mini lathe and mills working in CNC.
that being said…
I’m not trying to sound like negative NANCY here but
aluminum will not work. It has too much thermal expansion,
galls really badly when it rubs on all other metals and
is not strong enough for the amount of torque and torsion
that will be required to convey, melt and build pressure
in your screw and barrel.
Also, there are several topics here that talk about the clearance required between the screw and barrel. It’s best to check those threads.
best of luck!
My recommendations would be to start small. There is a lot to learn with these 4 machines. I would get a fulltime paying job and do this on the side until you build this up. Find you 1 product to produce and build that machine along with the shredder. Start in as cheap and small of space as possible. Best of luck! Building all of these machines yourself will take a lot of time and money.
The tech kits machines have been around a while and are very simple therefore I would expect very few problems.
typical cycle times for this machines will be in the 3-5 minute range as there will be a lot of extra work opening the mold and removing the part and letting it cool in the mold before removal.
I wouldn’t mess with these Chinese machines as they will be severely limited.
Wow. That is really cool! You will need to close all 6 sides or else you will never melt the plastic enough or just burn it. Good Luck! How many watts are those heaters?
Hi janvankelst. Can you provide some more details on what you are asking or looking for? Your question is quite open ended. Thank you
Hi Keva. The simple short answer would be no. Cloth would be like plastic bags. It will just wrap around the shredder shaft and blades. You need a simple flat bladed cutting system that is super sharp to cut both materials.
Plastic processing factories buy virgin material in pellets because they know the quality they will receive and expect. They typically only buy recycled materials in truckload quantities because it is cheap and they know it will be a pain to work with. Pellets is the defacto standard around the world how virgin plastics are created. Almost all machines are built to handle plastic in this manner.
Plastic prices in different forms are available on the internet. Some pricing can be regional or even based upon area (European, Asia-Pacific, Americas).
Also, plastic prices do not necessarily fluctuate with oil prices.
There are many other compounds, modifiers and plasticizers in plastics.
These are the items that cause price fluctuations.
Hello Door- This is a 3 phase motor which most homes in the USA do not have. You will need an inverter and an electrician to wire it properly. You will also need a gearbox to slow the speed down to around 50-150 rpm depending on the materials and part configuration you will be shredding. Best of luck!