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Hello, I am considering making these screws by collaborating with a local makerspace who have a metal-capable CNC machine
My plan is to upgrade the CNC machine with a 4th axis
Can any of you offer any advice?
when my team were making the compression moulds, we found that the shredded plastic took up much more volume compared to when they were molten and moulded
so this leads to another advantage of using the screw to ‘pre-compress’ the plastic in the heated pipe:
in the original injector, the shredded plastic is poured straight into the heated pipe, in the form of irregular and poorly packed solids, and the piston has to compress the plastic as it melts to squeeze out all the air between the shredded plastic before actually extruding it outwards, and as such the actual volume of plastic is a fraction of the working volume of the injector (area of pipe hole x stroke length = volume)…
but if the plastic is already compressed by the screw and it is already in a liquid state before it is injected, then 100% of the working volume of the injection action is filled with plastic, and although my design has a shorter stroke length , it may actually deliver more plastic and be able to make bigger injection moulds
its better to ask a local engineering workshop directly to design something like this for you, because they would know if they are able to make it using their capabilities
they might also give you suggestions for improving the strength , usability and accuracy of the part you are making
in the scenario of a precious plastic injector immediately following an injection operation, some plastic would likely have flowed back up along the gap between the solid rod and the pipe wall, and if the rod is then pulled back up for the next injection operation, it will carry this plasic to an unheated part of the pipe
but in the case of using the screw as in my design, there is no need for the screw to egress as its fully ingressed position is the same as it would be in an extruder
the mechanical advantage of the motor gearbox will keep it in control of the rotation of the screw
the lever at the back can be extended to give more leverage, the cantilever converts the vertical force to horizontal force while adding even more leverage due to the shorter stroke length
so it should easily equal or exceed what is possible with the original injection machine
the function of the non return valve is simply to stop backflow during the high pressure injection, a cursory search online shows that not every plastic injection machine is equipped with it anyway, the viscosity of molten plastic should not allow it to easily flow back along the helix of the screw, especially with the thin depth at the ‘metering zone’ in the front of the screw , and the fact that the plastic will have to travel a much further distance back along the screw helix instead of simply exiting into the mould
furthermore if you are comparing the quality of the machined screw to the apparently loose-fitting solid rod used in Dave Hakken’s video , its likely that the screw would give a better seal, depending on the quality of the rods you can source
This is a cutaway view of the ‘plunger’ , showing how the pointed end of the shaft meets the cap of the pipe, thus allowing the pipe to apply longitudinal force upon the shaft without causing excessive friction for rotation
The shaft is supported by the 6000 bearing
This is a view of the rear part where the horizontal ‘plunger’ is
It is constructed of 4 parts, a 6000 bearing holding the shaft, a 26mmx30mm pipe which holds the bearing, a 30mm square bar which holds the pipe , and a pair of metal plates which connects to the cantilever at the rear.
The 30mm square bar of the plunger sits on a longer 30mm square bar, which acts as a rail for the plunger
This is a view of the arrangement of the sprocket, bearing, and hex shaft
On the other hand, the stepper reduction gears are not intented to be used on high torque applications such as an extruder (not even titanium gear steppers). If the extruder gets clogged, your stepper gear teeth will most likely break instantly
my understanding is that a stepper motor will skip when it is overloaded, long before any mechanical damage will occur to it?
does anyone have any data on just how much torque does the precious plastic extruder will require?
the reason I am looking at a stepper motor is because I would like to have more control over the RPM
Using a regular motor would mean purchasing a variable frequency drive which costs as much as the motor itself
i would suggest using 4 carjacks , one in each corner, to limit the instability of the platform, and their cranks should be connected to each other so that one single crank can be used to lift and lower them simultaneously
Can an improved extrusion screw (compared to a wood drill) put more pressure and force on the extruded plastic, to the point that it can be used as an injection machine?
Hello everyone, do you think its a good idea to make the screw out of a soft and easily machined metal, such as aluminum?
https://www.mnn.com/earth-matters/wilderness-resources/blogs/ocean-plastic-rivers “10 rivers may deliver bulk of ocean plastic” with links to the original research paper
But somehow it worked better with high speed (450rpm) than with 80rpm – with 80rpm pieces would get stuck and block the knives…?
How is the RPM adjusted? If the machine runs at 80rpm by reducing its power, that might be why the plastic pieces get stuck
Ideally you will get 80rpm by gear ratios, so you have full power and multiplied torque
Hello everyone, are the holes on your cut pieces very tight as well? Just checking before we start going ahead with the building process and possibly do something irreversible