[ViperTX]

We should probably refer to the two as:

Mold clamp pressure.

Injector pump pressure.

I'm assuming that is what we are arguing about. I've never see a machine...so, I'm only guessing.

Harrybaldacc....count me on the plans when you're able to get to them. Thanks!

[Scooby]

In that case reading that anyone wanting to make a moulding machine should give up unless making chocolate gave me the wrong impression.
I am sorry if i offeneded Harry, to me i thought the statement was very clear and mould pressure or injection pressure was not the point or issue and certainly not the argument, being told that im only good enough to mould chocolate and should stay away from plastic, even though hes made a machine, grated on me a bit so i spoke out, obviously im on my own with these feelings, i wont post again. Good luck with your machines.

[Kipper]

To all wannabe build a Plastic injection moulder, I have build 2 machines that will do polypropylene and up to Nylon 6 and glass filled nylon, the machine has the capacity of a 26 ton large moulder, it makes professionally made parts, and has a capacity of 500grams.I have e-mailed many plans to most guys like you all over the world for this machine, soon the owners of these plans will surely want to talk about this. As for you guys, Plastic moulding requires high pressures of 6500 tons approx and heating capacity of not less than 200degress Celsius, so unless you want to mould chocolate ,stay away from plastic

500 grammes sounds perfect! Have you any images I could have a look-see at? :cheers:

[Kevin R]

Hey guys,
Do you guys think from looking at my machine that it is capable of sustaining actual thermal injection with real plastic. I intend on testing ABS and poly Ethylene crystals. I have gotten an email saying my machine and plastic will explode. Is that true?? Either way im gunna risk it and im trying polyethelyne saturday. If you guys have any tips or advice i would love to here it. If you guys would like to check out my hobby site that would be wonderful. http://www.backyardengineer.com or email me at [email protected]

[miljnor]

How do you get plastic into your mold on your machine kevin? from the picture it looks like you pour it in from the top?

if its gravity fed there wont be and explosion.

To have and "explosion" you have to have enough pressure build up in the system to overcome one of your machines clamps or the actually machine body. If your pump cant do this then the system will just stall.

An explosion implies flying debris, if i just leaks then well....you know, no explosion.

although safety precautions should be taken for an explosion I think a more likely outcome is burnt plastic and no flow do to melt/viscosity issues.

But im not and expert...just and armchair engineer. Ignore me

[legendboy]

anybody intrested in this machine? I was going to throw it on ebay

you can see the hopper to the left of the machine

[Kevin R]

Thanks for asking Miljnor,

Plastic is inserted from the top. You are right it is poured in. It is gravity fed however, I designed the machine to run on its side, for an easier conversion to automated thermal injection at a home workshop. For those who haven't seen my machine here you go.

I would love to hear what you guys have to say feel free to shoot me an email: [email protected] or check out my site at http://www.backyardengineer.com

[plastibob]

This is an exaggeration that is chemically inaccurate. Plastic explosives are a class of compounds which contain the element nitrogen in a form of chemical bond known as a nitrate bond with oxygen atoms or as an azide bond which is between multiple nitrogen atoms; these chemicals bonds are unstable and can react explosively. Many of the thermoplastics used for injection molding do not even have nitrogen atoms in their chemical make up and those that do have the nitrogen in totally different forms of chemical bonds which are stable and non-reactive.

This is not to say that the temperatures and pressures used in injection molding are not dangerous; they are. Overheated thermoplastics can de-polymerize and form flammable and/or toxic gases which can under the correct conditions explode. But this is not any different to the explosion hazard of propane gas or natural gas. The pressures and mechanical forces used in injection molding are comparable to those in heavy duty hydraulic systems and require similar attention to correct and safe procedures.

Using exaggeration and inaccurate analogies to dramatise dangers is not helpful. Sometimes it can be counterproductive because an inexperienced person does not have sufficient knowledge to know what is an exaggeration and what is not. When they discover that part of a warning is indeed exaggerated the tendency is to discount the whole warning including the parts that are reliable. There was a fable written many generations ago about the dangers of 'crying wolf' too often.

It takes a lot of pressure to fill a mold and even greater pressure to hold the mold closed on a real injection molding machine the cavity pressure is around 5000 psi. Bench top type machines will only do some of the easy flow, lower temperature plastics effectively. What you have to watch for is is getting sprayed by molten plastic, as it will continue to burn into the skin. PVC can be dangerous to process. You never would want to mix PVC and Acetal as that can create an explosion and dangerous gas.

[Harrybaldacc]

I think that you are making a big deal out of all this, I simply meant in my reply, to an injrection machine that was not build strong enough and that if it wre going to be operated by air or hydrolic , it would simply break.As it turned out to be , that the person building this machine was HAND OPERATED, and your experience would have told you had you seen the machine, not to make such an extreme comment about plastic explosions, and if you had some 30 years of plastic like I had you would think better.
Harry

[kreutz]

Harry;

I still want to see your machine's plans, if possible.

Merry Christmas and Happy New Year!!

Kreutz.

[Khalid]

Now i see KREUTZ in injection mold business

[kreutz]

Now i see KREUTZ in injection mold business

Hi Khalid, just trying to learn something new...

Best regards,

Kreutz.

[ZipSnipe]

So what happened to Rod.M ? He starts a thread and then disappears!

[Geof]

So what happened to Rod.M ? He starts a thread and then disappears!

Threads gain a life of their own; dying and then getting resurrected.

Seeing that this one has resurrected I have a question that someone may be able to answer; what plastic is used for the balls in track balls?

[Harrybaldacc]

If this question is directed to me , I do not know what you are talking about.

[plastibob]

Threads gain a life of their own; dying and then getting resurrected.

Seeing that this one has resurrected I have a question that someone may be able to answer; what plastic is used for the balls in track balls?

If you are talking about the ones in a mouse, they are polyurethane overmolded over a steel ball.

[Geof]

If you are talking about the ones in a mouse, they are polyurethane overmolded over a steel ball.

Not the ball in a mouse the ones such as described here:

http://www.trackballworld.com/

mouses turned upside down.

I want a quick/cheap and precise way to make rigid plastic balls 2.750" diameter that are accurate to +/-0.001 for size and concentricity.

Quick/cheap means less than $20.00 including material and labor costs.

[plastibob]

The trackball that your referring to is some type of thermoset material, like a cellulosic, polyester or melamine. The print on the outside for the optics is in all likely hood is a water transfer graphic, then it has a polyurethane clear coat. Like anything the more you get the lower the cost, I'm not sure what kind of quantity your looking at.

[Geof]

The trackball.... I'm not sure what kind of quantity your looking at.

Initially a hundred or so, but I don't really expect to find anyone to supply the precision I am asking for at $20 each for this quantity. Which is why I am interested in finding out what is the material with the idea of injection molding blanks that could be machined to size and precision.

[mactec54]

Hi Geof

Do you want it to be a solid or just a thick wall I did mold some ball's at one time around 1.750 dia after molding they were tumbled & polished they came out to be with in .0001 no machining needed a lot of hour's in the tumbler to size them