Is there any one out there that has built a plastic injection press. I'm looking into building one. I have all the books about the small hand presses , But that does not cover what I have in mind. I want a press that will hold a 5" by 9" mold base. A 2oz to 3oz shoot, with a air clyinder to inject the plastic. The mold base it should open and close with a air clyinder. Ronald
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Looking to make a plastic press
- Thread starter ronaldf
- Start date
Depending what the cavity is that you are trying to fill, I am not sure you will be able to develop enough pressure with an air cylinder, unless you have a very high pressure compressor system. Even in small Arburg presses, which have similar mold capacity as you want, you need to have hydraulic pressure in the range of at least 1200 psi. You could consider an electric motor on a screw system to generate the shot pressure, but you need to be sure you can control it very closely.
I have thought about a barrel with a screw . not sure how they work. I may have to use a hydraulic system. I know the basics of mold design, but all most nothing of the machines, I looked for a older press , the ones in this area seam to have been sent to the scarp yard. I looked on ebay at some older machines, I saw some older Arburg presses but did not but was not sure what I was looking at. My goal is to be able to reproduce some of the old lighted Christmas Decorations. The parts are small in size. the molds would have 2 or 4 cavilitys. Ronald
Based on what I have found, looking on the web for used machines, I think you could buy a used small machine cheaper than you could build one and all of the mechanicals would be there. You may have to upgrade some of the controls is all. Here is a link as an example:
http://www.machinetools.com/us/listings/view/knockner-ferromatik-f20
http://www.machinetools.com/us/listings/view/knockner-ferromatik-f20
Let me restate what I'm trying to do. I have a 17 year old son who is wanting to learn maching. The schools no longer teach maching in this area. I'm putting to getter a small shop of older machines. I want all of them to be from the era were a line shaft was used. WE will restore them and bring them back to life. One of the things I want him to learn is how to make plactic molds. My dad was a master tool and die maker. My uncle Jim Owned a good size plasic injection company in Ohio. Evey time I ask him about plastic, All I hear about how it is not worth it because china . Yes In time I would like to buy some used small plastic press, But any one can plug in a machine and it will work. You learn nothing If you build one you learn how they work . Right now I looking for information about barrel and nozzle design. Ronald
I bought a small plastic injection machine for my wife's jewelry business. It came out of a school shop,and has about a 1 oz. shot. It has just an air cylinder on top,about 4" in diameter. It has a funnel at the top of the heating chamber where the plastic pellets are poured in. There is a hole 1/2" in diameter with a 1/2" dia. plunger that goes down into the hole and squirts the plastic into a mold. This heating chamber would not get hot enough(needs to be about 400 deg.. I bought 4 hearing elements from MSC. They look like dynamite caps,with 2 small wires coming out their backs,just like the caps. I drilled 4 holes 1/4" dia. into the aluminum frame next to the heating element and shoved them in. It works fine now.
I had to make a new injection nozzle because the old one was not stainless steel,and had corroded badly. I think only polystyrene pellets were ever used in the machine,but the nozzle was corroded. There is a valve inside the nozzle with a strong coil spring about 1/4" in diameter,but made of wire nearly 1/16" thick. It holds a round piece of stainless steel over the hole so plastic cannot just ooze out of the opening. The pressure of the plastic being forced down actually forces this valve upwards a little,letting the plastic shoot out of the nozzle. The whole nozzle and chamber is forced downwards by the plunger,pressing it into the opening of the mold. Things need to fit,or plastic will squirt out around the top of the mold. I made the molds out of aluminum,but attached 1/4" plates of pre hardened 4140 steel to the tops. Aluminum gets too beat up by the plunger. I made a 3/8" x 1/16" deep opening in the top of the molds that just fits the tip of the nozzle. The molds are clamped tightly by a built in vise in the machine.
The air pressure we use is 80 #. I learned to color the clear plastic pellets by this method: Take a tupperware 6" tub. put the plastic in it,about a cup or so. Add 1 teaspoon of mineral oil. Add the color powder,about 1/2 teaspoon(depending on how dark you want the tint). Use oil base color powders. Put on the lid. Shake the contents thoroughly. The mineral oil carries the powder everywhere,coating all the pellets evenly. THIS IS A TRICK THAT IS VALUABLE,and was a lot of trouble to work out!!!!!
These color powders give a transparent color to the plastic,but that is all we wanted. The oil is sort of dissipated and does no harm at all. Good for lubricating the innards of the machine,and the plastic,too.
Even buying the plastic was a PITA. They wanted to sell us 55 gallon drums of it,and 55 gallon drums of simple,signboard colors,too PER COLOR would have been over $300.00. I had to learn about plastic,and solve some knotty problems.
We found a little Industrial Arts supply place in Chicago that sold plastic pellets by the pound,finally. DO NOT try melting down plastic bottles. They are made of PETA plastic,which is a higher melting point plastic. I got into trouble trying to do that before we found a small plastic source.
I see small plastic injection machines on Ebay,but they are usually pretty expensive.
I had to make a new injection nozzle because the old one was not stainless steel,and had corroded badly. I think only polystyrene pellets were ever used in the machine,but the nozzle was corroded. There is a valve inside the nozzle with a strong coil spring about 1/4" in diameter,but made of wire nearly 1/16" thick. It holds a round piece of stainless steel over the hole so plastic cannot just ooze out of the opening. The pressure of the plastic being forced down actually forces this valve upwards a little,letting the plastic shoot out of the nozzle. The whole nozzle and chamber is forced downwards by the plunger,pressing it into the opening of the mold. Things need to fit,or plastic will squirt out around the top of the mold. I made the molds out of aluminum,but attached 1/4" plates of pre hardened 4140 steel to the tops. Aluminum gets too beat up by the plunger. I made a 3/8" x 1/16" deep opening in the top of the molds that just fits the tip of the nozzle. The molds are clamped tightly by a built in vise in the machine.
The air pressure we use is 80 #. I learned to color the clear plastic pellets by this method: Take a tupperware 6" tub. put the plastic in it,about a cup or so. Add 1 teaspoon of mineral oil. Add the color powder,about 1/2 teaspoon(depending on how dark you want the tint). Use oil base color powders. Put on the lid. Shake the contents thoroughly. The mineral oil carries the powder everywhere,coating all the pellets evenly. THIS IS A TRICK THAT IS VALUABLE,and was a lot of trouble to work out!!!!!
These color powders give a transparent color to the plastic,but that is all we wanted. The oil is sort of dissipated and does no harm at all. Good for lubricating the innards of the machine,and the plastic,too.
Even buying the plastic was a PITA. They wanted to sell us 55 gallon drums of it,and 55 gallon drums of simple,signboard colors,too PER COLOR would have been over $300.00. I had to learn about plastic,and solve some knotty problems.
We found a little Industrial Arts supply place in Chicago that sold plastic pellets by the pound,finally. DO NOT try melting down plastic bottles. They are made of PETA plastic,which is a higher melting point plastic. I got into trouble trying to do that before we found a small plastic source.
I see small plastic injection machines on Ebay,but they are usually pretty expensive.
I have seen these machines on the web. Was wondering how they worked. So the nozzle has a check valve built in to it. That helps a lot. What we are making are molds for lighted decorations for Christmas C6 light strings. We want to reproduce some bubble lights. and other decorations. The finished product has to be able to with sand the heat produced by a light bulb. They were made of celcote acetate[ spelling may not be right] when they were made in the 1940'tys. Looking for a modern plastic that will work. Ronald
Make sure if you decide to make steel molds that you use (I think) M1 or M2 tool steel. Regular tool steel can't take the temperture shock from going 2000 degrees to a couple hundred degrees when the water cycle hits the inter cooling chambers. I was taught how to make molds but never had the chance to make one. Sounds like a nice project, Best of Luck.
Plastic was only 400º if they want to make the plastic bases and buy the glass tubes. If I HAD to make the tubes,I'd buy laboratory glass tubing and use a torch to melt one end shut,and draw the other end out to a tip,etc..
Cellulose acetate is not at all a high temp.plastic. Polystyrene would work as well. You aren't going to get the bases of your lights to 400º. I made our molds out of aluminum. You actually POSSIBLY could make a model,and cast it in J.B.Weld. JB will stand 600º. If you can impart a decent polish to the JB,and use a 1/4" thick steel top for the mold,I think it would work quite well. Easier than cutting the mold out of solid metal,unless you have CNC.
Cellulose acetate is not at all a high temp.plastic. Polystyrene would work as well. You aren't going to get the bases of your lights to 400º. I made our molds out of aluminum. You actually POSSIBLY could make a model,and cast it in J.B.Weld. JB will stand 600º. If you can impart a decent polish to the JB,and use a 1/4" thick steel top for the mold,I think it would work quite well. Easier than cutting the mold out of solid metal,unless you have CNC.
the tubes are going to be the hard part. I have been looking into glass moulding. I'm still studing on that. I believe I can make a mold out of plaster put in crushed glas then put in in the kilm. The molds for the bases will take some work to make. not sure what route I will go I have been looking into epoxy. you can use rtv to make the part and cast the mould in it. Ronald