possible molding method?

[mrplastic]

Hi guys,

I am wondering, considering the method of rotational molding, can one insert plastic powder ie polypropylene into an aluminum mold and simply cook the powder until melted. The mold will then be left to cool with the plastic having taken the shape of the mold.

Does this sound possible?

thanks.

[brentb]

If you gyroscopically spin the mold to coat evenly the interior of the heated mold.
KPM
brent

[brentb]

This is called rotational or gyroscopic molding!

KOM

[mrplastic]

Thanks for the reply. Can i use pellets instead of powder?

[brentb]

Never heard of that! Wouldn't get an even coating, I imagine!

KOM
brent

[Suhas]

MrPlastic,
Thanks for being on the forum. As a caution we all have a lot of fun here. Believe me, the reason I logged on this morning was to see if Brent had commented on your post and he did! :) :)
OK, in short, what you say is not possible since you will not to able to turn the mold in all directions, not be able to heat an injection mold to those temps and even if you do will not be able to cool it down fast enough to achieve good cycle times. If you do find a way, then as Brent says that is rotational molding.
Hope this helps.
Regards,
Suhas

[brentb]

MrPlastic,
Thanks for being on the forum. As a caution we all have a lot of fun here. Believe me, the reason I logged on this morning was to see if Brent had commented on your post and he did! :) :)
OK, in short, what you say is not possible since you will not to able to turn the mold in all directions, not be able to heat an injection mold to those temps and even if you do will not be able to cool it down fast enough to achieve good cycle times. If you do find a way, then as Brent says that is rotational molding.
Hope this helps.
Regards,
Suhas

Was something I wrote comical? For once, I was trying to be serious!. I actually did a bit of rotational Molding in Mexico and Guatemala!
I like injection molding better. All the spinning made me dizzy!

KOM

brent

[mrplastic]

Thanks.

Suhas,

If nylon6 melts at about 260 - 300C is it possible to heat the nylon to melting point then pour it into a heated aluminum mold. Wont this eliminate the need for high psi since the plastic will not cool down in the mold, hence the mold can be filled slowly? So lets assume that we have a container carrying the nylon which is directly connected to the mold. Both are heated to eg 260C. The mold is then detached and left to cool.

I am new to the whole plastic molding process. I have watched youtube videos on the injection molding process. If i may ask this question:

Is a screw necessary to melt the plastic and for the plastic to bind together? I mean this does not happen in rotational molding, so i am having a bit of difficulty understanding the engineering behind infusion molding. I appreciate the three stages in the screw and the whole friction element, but why cant they just melt the plastic and push it into the mold at high psi?

Excuse my ignorance, no arrogance intended. Just curious.

Thanks again.

[Suhas]

Mr. Plastic,
Copying and Pasting your text and answering in capitals.
-----
If nylon6 melts at about 260 - 300C is it possible to heat the nylon to melting point then pour it into a heated aluminum mold. Wont this eliminate the need for high psi since the plastic will not cool down in the mold, hence the mold can be filled slowly? So lets assume that we have a container carrying the nylon which is directly connected to the mold. Both are heated to eg 260C. The mold is then detached and left to cool.
YES, THIS IS DONE AND IS CALLED CASTING. BUT YOU WILL NOT BE ABLE TO GET THE FINER DETAILS, GOOD TOLERANCES AND THE TOP THAT MAY NOT BE THE SHAPE YOU NEED. CYCLE TIMES WILL BE VERY HIGH COMPARED TO INJECTION MOLDING WHERE THE TIMES ARE IN SECONDS. THIS WILL NOT BE ECONOMICAL TO MAKE MILLIONS OF PARTS SUCH AS BOTTLE CAPS.
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Is a screw necessary to melt the plastic and for the plastic to bind together?
THE SCREW IS NOT USED TO BIND THE PLASTIC TOGETHER. IT IS USED TO CONVEY, MELT AND METER THE REQUIRED AMOUNT OF PLASTIC IN FRONT OF THE SCREW (LIKE A DOCTOR'S SYRINGE) AND THEN INJECT IT INTO THE MOLD AT HIGH PRESSURE. HIGH PRESSURE IS REQUIRED SINCE PLASTIC IS VERY VISCOUS, THE MOLD IS COLD AND STARTS TO COOL THE PLASTIC DOWN AND MAKE IT EVEN MORE VISCOUS.
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------ but why cant they just melt the plastic and push it into the mold at high psi?
YES THAT IS WHAT THEY DO.
Look at this: http://www.youtube.com/watch?v=BU5xlb_RGUs
Hope this helps,
Suhas

[mrplastic]

Thanks Guys. Much appreciated.

[sampeacock22]

hi,

According to my knowledge, it is known as rotational molding. It depends upon the plastic material which you want to mold. thanks all for sharing their views.