Designing a low energy plastic "chopper"

[robert]

I run a electronics tooling company , but I am very interested in plastic recycling . As a "hobby" I have started designing a very efficient plastic chopper that could be run off a 24-32 VDC solar electric system . After some experimenting I have decided that 15mm squares is the largest I can chop plastic and still have them "lay flat" and not have too much air due to curved squares . So I have determined the minimum amount of chopping required but everything else is still up in the air. So I have some questions 1. Will 15mm squares be processed by most injection molding machines ? 2. Any one have any idea for what is the most efficient way to cut a milk jug , bleach bottle , Etc. Into 15mm squares ? 3. any ideas in general for energy efficient plastic chopping ? I have two ideas so far 1.efficient electricals and 2.making the cutters from Stellite so they would stay sharp longer and still be tough .
Any ideas or thoughts would be appreciated.

[iautry1973]

Robert, is this something you are planning to do to recycle material for you to use in a product of yours or for public use? If this is a device you are looking to sell for the general public to use you may want to look into who would use the plastic as the end user. If the idea is for the public to cut up random plastic items and then send it somewhere you will end up with mixed streams of varying plastic. This would make it hard for someone to recycle the plastic and use it as differing materials have different properties etc. Also the material needs to be "clean" (not covered in food etc.). If you aren't using the material yourself might be good to tie in with a plastic recycler as to how they would pelletize the material for you and their requirements.

And to answer the main question....no most molding machines would have issues with a 15mm square. Most use pellets that are about 2 1/2 to 5mm in size (I would have to go measure some to be exact). Large molding machines might be able to handle it, but no guarantees as it could hang up in the screw. Also there are other things to look at like drying, loading material to the machine, etc.

[robert]

Robert, is this something you are planning to do to recycle material for you to use in a product of yours or for public use? If this is a device you are looking to sell for the general public to use you may want to look into who would use the plastic as the end user. If the idea is for the public to cut up random plastic items and then send it somewhere you will end up with mixed streams of varying plastic. This would make it hard for someone to recycle the plastic and use it as differing materials have different properties etc. Also the material needs to be "clean" (not covered in food etc.). If you aren't using the material yourself might be good to tie in with a plastic recycler as to how they would pelletize the material for you and their requirements.

And to answer the main question....no most molding machines would have issues with a 15mm square. Most use pellets that are about 2 1/2 to 5mm in size (I would have to go measure some to be exact). Large molding machines might be able to handle it, but no guarantees as it could hang up in the screw. Also there are other things to look at like drying, loading material to the machine, etc.

The machine will be for my own use and for sale if someone wants one , I understand that the plastic must be clean and dried to avoid bubbles , I'm already doing that . What do you mean by " it could hang up in the screw" ? the machines I have seen don't look to easy to "hang up".

[Platt1990]

Mainly what is meant by that would be clogging issues near the feed throat witch can cause a “bridge” problem. I would be more worried about melting problems. If the squares are to thick it could cause it to not melt as it goes from the feed to transition parts of the screw. With this as a factor it could wedge between the screw and barrel causing it to wrap or stall out, not to mention this could cause damage to the screw/barrel. I’ve worked with up to 4,000 ton machines and our regains had to be smaller than that or the above issues as well as cosmetic issues and structural issues appear from what I believe is from an uneven melt

[robert]

Mainly what is meant by that would be clogging issues near the feed throat witch can cause a “bridge” problem. I would be more worried about melting problems. If the squares are to thick it could cause it to not melt as it goes from the feed to transition parts of the screw. With this as a factor it could wedge between the screw and barrel causing it to wrap or stall out, not to mention this could cause damage to the screw/barrel. I’ve worked with up to 4,000 ton machines and our regains had to be smaller than that or the above issues as well as cosmetic issues and structural issues appear from what I believe is from an uneven melt

I have quite a bit of plastic that has been hand cut , I just looked through the wight HDPE and the thickest square I could find was 2.6mm , there may be a few thicker but not very many. does that seem too thick in your estimation ?

[iautry1973]

Robert, what I was meaning is exactly what Platt1990 mentioned. It could get hung up in the feed throat of the machine and the issues with the screw as well as there is a finite amount of space between the screw and barrel. Are you going to be molding parts with this material yourself or is this something you are trying to sell the material to others?

[robert]

Robert, what I was meaning is exactly what Platt1990 mentioned. It could get hung up in the feed throat of the machine and the issues with the screw as well as there is a finite amount of space between the screw and barrel. Are you going to be molding parts with this material yourself or is this something you are trying to sell the material to others?

I will be molding parts my self AND if some one wants one I will sell a copy of the machine to them . If you look on Youtube there are probably 20 plastic choppers that people have made for their own use and the issue of energy efficiency of the choppers is a issue that is discussed , Since I work with power electronics I feel that I have something to contribute , but to maximize the efficiency I need to start with reducing the amount of chopping . Also I don't think you are getting the scale of this , if there are even a few machines that can handle say a 15x15x4 chip then that is adequate to start with , because , over time as home plastic recycling grows , manufactures will respond by making machines for this market. But if I try to chop the plastic to 2.5x5 I will increase energy consumption 18 TIMES OR MORE ! That is not the way of the future I am sure ! just look at cars we have electric cars that use under 175 Watts a mile now , "The future belongs to the efficient".

[iautry1973]

Robert, I understand you are passionate about this, but just trying to help. I appreciate that you are trying to help recycle material, but I am also trying to answer the question you asked. Most machines will have an issue with a 15mm x 15mm x 4mm chip without further reducing the size. To give you an example smaller machines can require "micro pellets" because the normal pellets are physically to large to fit through the space between the barrel and the inner diameter of the screw. You can literally seize it up ($$$). Molding products is not just a simple thing and the science behind it has been developed over a long time. Molding machine manufacturers are not likely to change the design of the machines to accommodate your specific chip as there is a ready supply of pellets out there and existing technologies to use recycled materials (in pellet form). Redesigning the machine itself to use it isn't something easy. Adding a piece of equipment upstream might help to process the material. If you are adamant at keeping the chip the same size I suggest finding a local molder and asking them to even try to purge the material through a barrel. If you can't get it to do that then you won't be able to mold parts at all. Good luck and I hope you are able to get something to work for you.

[robert]

I don't mean any disrespect but "Molding products is not just a simple thing and the science behind it has been developed over a long time. Molding machine manufacturers are not likely to change the design of the machines to accommodate your specific chip as there is a ready supply of pellets out there and existing technologies to use recycled materials (in pellet form). Redesigning the machine itself to use it isn't something easy." sounds like the argument against electric cars .
But I appreciate your point , So let me rephrase my question . Is there ONE machine made on planet earth that is most likely to handle a 15x15x4 Chip ? I'm talking about the AK-47 of injection molding machines .

[iautry1973]

Robert,

There might be some very large tonnage machines that can possibly "handle" it, but nothing that I know of that was designed to take something like that. May I pose this a different way. When you are looking at molding something you look at the part & mold design first before you pick out what machine it is going to go into. In other words you don't take a single cavity part that is 1"x1"x1" and throw it in a 1000 ton press....bad stuff happens. So if you are going to try and mold with this size chip are you going to be molding small parts or large parts? Is it going to be a high use product where it may be small parts, but large cavitation? If it is a small part and low cavitation I don't see it working on any machine.

Also besides the earlier points in the discussion (from me and another person) even if it makes it into the screw the material may not process correctly. The material melts in the barrel mostly from frictional heat. The frictional heat comes from the pellets rubbing against each other and the screw and barrel. I am not sure how in the barrel the large chips would react. It may not melt enough to be able to inject the material.

As for your statement that it sounds like the argument against electric cars, I don't think you understand the molding industry already uses recycled materials. You are not really introducing something new to the industry. Why would a molder use your material over a material that is already recycled and comes in a useable form? It would be like asking someone to use your specific battery for a car that requires a battery swap on the road to use. Why would they do that when their current electric car can be plugged in and is more useable? At this point I don't think you understand molding and need to do some more investigation. Figure out what the end use for these chips are (what parts you are going to make), talk to a local molder to see if they can run some material through a barrel for you to see if it will even work, talk to several machine manufacturers and see what they say, and maybe look at uses other than injection molding.

[robert]

Your not getting my argument , you continue to say nothing will change because what we already have works and there has been a lot invested in it . I am sure that some one said something like that when jet engines were introduced for aircraft , how much was invested in piston aircraft engines at the time ? a hundred times the investment you are talking about ? , a thousand ? , what about the piston Steam engine industry ? , or a thousand industries that were huge and are now gone or just minor players . Currently the industry is either spending 18 ? times as much energy as I propose on cutting , or shredding and melting the plastic twice ? , Going from piston engines to turbines increased efficiency about 40% ( from very roughly about 25% to about 40%) and a huge industry was demolished to do it ! I think you are so close to the industry that you can't see what I see , I see a lot of low hanging fruit , easy BIG efficiency gains , when you go shopping for a new injection molder does the sales man tell you about how much energy you will save with the new machine ? is there a government testing program for efficiency , a "EPA estimated mileage" ? does the the total life cycle efficiency get talked about ? I will bet you any amount you want to name that in 100 years injection molding will be so different that it will be hard to recognize . If a screw cannot be made to work then go to a piston system the sugar industry uses big rollers , a simple robust system , but there are designs that use pistons that are more efficient and at some point using 30,000 HP rollers won't make sense if there are 10,000 HP pistons. Even if a reciprocating system is more complex and will require retooling , the energy savings will make it worth it. What I am saying is sooner or later someone will "make it work" the efficiency gains are too large for there to be any other outcome . To answer your question a molder will use the 15x15x4 chips because they will be cheaper , and since energy is the main continuing expense in home recycling because the plastic if often free the cost savings could be very big , Would you want to find a way to use 15x15x4 chips if you could get them at 1/3rd the per pound price ? and over time the more expensive 5x2.5 chips started becoming unavailable ?

[iautry1973]

Robert,

You asked three questions. One of them was "1. Will 15mm squares be processed by most injection molding machines ?" I have tried to answer this question for you to the best of my ability and you are upset that we as an industry are not changing to use your idea that has yet to be realized in production form. I appreciate that you are trying to help out and have an idea, however I feel that I am unable to help you anymore as you are asking the industry to change for your idea and are asking for more than the question of can a machine run that material. I will below however give you some parting advice and responses. Good luck with your project and I hope you are able to find the answers you desire.


Some more food for thought:

The molding industry has changed drastically since the beginning. We still continue to evolve and yes it will change more. Will in the future some of the machines be replaced by 3D printing? I think some yes, but not all applications. We do look at energy efficiency on new machines. A lot of companies replace older machine based off of energy efficiency and other aspects. While looking to replace a machine we started looking at what data the vendor could provide us on energy usage of their machine based on our cycle times, material used, etc. So yes there is an "EPA estimated mileage", but not like you are thinking. Your material of recycled jugs etc is NOT a material that is used in all of molding. As an example I do not have a job on the floor currently today that would use that material. We mold products based on customer requirements and that material was not chosen by our customers. The packaging material you are looking to recycle does not meet the physical requirements the end user needs for our customers (most medical sproducts etc we are molding require an engineering grade plastic not a commodity grade plastic like the original base material for your recycled jugs etc).


Suggestions for you:

If you are really wanting the machine manufacturers to change their design to accommodate the small percentage of recycled material you are going to introduce to the market, approach one of them and talk to them about could they modify a screw design etc. Also do some market research, while saving that material is a great idea what uses do you have for it? What industries could it be used for? Is injection molding the correct end user for the material? I wish you well sir.

[robert]

Robert,

You asked three questions. One of them was "1. Will 15mm squares be processed by most injection molding machines ?" I have tried to answer this question for you to the best of my ability and you are upset that we as an industry are not changing to use your idea that has yet to be realized in production form. I appreciate that you are trying to help out and have an idea, however I feel that I am unable to help you anymore as you are asking the industry to change for your idea and are asking for more than the question of can a machine run that material. I will below however give you some parting advice and responses. Good luck with your project and I hope you are able to find the answers you desire.


Some more food for thought:

The molding industry has changed drastically since the beginning. We still continue to evolve and yes it will change more. Will in the future some of the machines be replaced by 3D printing? I think some yes, but not all applications. We do look at energy efficiency on new machines. A lot of companies replace older machine based off of energy efficiency and other aspects. While looking to replace a machine we started looking at what data the vendor could provide us on energy usage of their machine based on our cycle times, material used, etc. So yes there is an "EPA estimated mileage", but not like you are thinking. Your material of recycled jugs etc is NOT a material that is used in all of molding. As an example I do not have a job on the floor currently today that would use that material. We mold products based on customer requirements and that material was not chosen by our customers. The packaging material you are looking to recycle does not meet the physical requirements the end user needs for our customers (most medical sproducts etc we are molding require an engineering grade plastic not a commodity grade plastic like the original base material for your recycled jugs etc).


Suggestions for you:

If you are really wanting the machine manufacturers to change their design to accommodate the small percentage of recycled material you are going to introduce to the market, approach one of them and talk to them about could they modify a screw design etc. Also do some market research, while saving that material is a great idea what uses do you have for it? What industries could it be used for? Is injection molding the correct end user for the material? I wish you well sir.

You are crediting me with saying things I have not said , I feel like you skimmed what I have written and assumed you know what I wrote . I have never said this "you are really wanting the machine manufacturers to change their design" . by what right do you miss read what I have wrote and invite me to leave based on it ? I have asked "Is there ONE machine made on planet earth that is most likely to handle a 15x15x4 Chip ?" If you don't know of one fine , but what is wrong with someone else answering , that does know of one ?

[Platt1990]

There probably is but none that I’m aware of that wouldn’t bridge the feed throat. Maybe something in blow molding or extrusion can use it.

[iautry1973]

Robert,

I am not dismissing you from the group, I just said I can not help you. I am not the whole group. What I am saying is I can not help you anymore as I don't know of a single molding machine that will do it. I have tried to give you alternatives. I am not going to be petty and go back and requote what you have said as if you reread your own messages you will see that you have been very argumentative about this. This forum is here for those in the molding industry to help others. If you chose not to listen to what members have to say that is your choice. All I am saying is I wish you good luck and I hope someone else can help with your idea.