Rotational Moulding--Granules Or Powder As Starting Material??

I think it depends on the design of the machine....most rotational molding that I know of uses powder....

http://en.wikipedia.org/wiki/Rotational_molding

http://www.plastictechnologiesaward.it/eng/subjects.pdf

http://www.engin.umich.edu/labs/EAST/me589/gallery/bioplastics_f01/599Website/pmf.htm#_Rotational_Molding

OMG ! So many known links are of no use, just plz answer the question if you can.

They are of use if you can read...

you already answered your own question...viz ''most rotational molding that I know of uses powder.... ''. My question is simple: whether granules could be used instead of powder?

This is a quote from the second link...Like I said, it depends on the design...

"4. Rotational moulding

Rotational moulding is used to produce large hollow objects. This process consists in filling the mould with the right amount of polymer in powder, granules or liquid form. The rotation and heating of the mould melts the polymer which sticks to its sides; the subsequent cooling takes place while the mould continues to rotate, until it has completely cooled, and then the object is extracted. Different variations of rotational moulding allow, among other things, to mould other materials onto an object."

A picture is worth a thousand words, goes the saying. here's the animation..

Click here to see an animation of this stage of the rotational moulding process.

http://www.tecni-form.com/moulding-animation.php

The link you provided indicates powder should be used...

WHY ARE WE HAVING THIS DISCUSSION?

The question is about apples and you are talking about oranges. The question is whether granules can be used instead of powder?? I know powder is used conventionally but do you have any evidence of granules being used for rotomolding??

You already said ''it depends on the design...''Which design, if you are for granule use as starting material??

mazhur,

You've mixed up a word, I fear.

You say, "HDPE in particular" then you say, "factory for making polyurethane water tanks".

You mean polyethylene tanks, right?

Powder.

sorry, it is polyethylene.

Mazhur,

In principle it is possible to use granules as the load material in rotational molding ... provided the melt viscosity of the load is low enough to permit the majority of the air in the spaces between the granules to be expelled from the melt by (a) centrifugally developed pressure and/or (b) cohesive forces of the melt mass.

The molecular weight distribution of the HDPE load material will be very critical in your process.

Mark Bingham
Relativity PL

But how?? Can you cite any evidence to that??

mazhur,

Have you been drinking microwaved water again?

come on, j0in me friend

the weather is fine

and it's just nine

let me drink to your health

may the microwave bring you

prosperity happiness and wealth!!

Mazhur asks: "But how?? Can you cite any evidence to that??"

My response: Yes, I can: my own evidence of using such products in manufacture. But your demanding and impolite attitude makes it unlikely that I will expand my response.

yours is just a supposition....read Roto's comment.

FYI rotomolding powders come ready-made for manufacturing PE cylindrical water tanks....and thei molecular weight is constant for the stated purposes. Regulated heat treatment is required to melt and spread them evenly inside the mold

Hi I have experimented with granules and they do not work as they take too long to melt. You can use micropelets but they are not much bigger than powder. You are welcome to visit us if you want to see a rotational moulding factory. www.jscrotational.co.uk. Regards Mark

Hi

thanks for your to the point reply which i deeply appreciate. Also thanks for your kind gesture of goodwill in offering me to visit a roto moulding factory but regret I cannot avail your offer for being located far far away!!

I too believe it is not possible to rotomold with granules as they would not melt evenly nor stick to the interior of the mold uniformly. I believe the person who told me roto molding was done by granules was only trying to hide the truth from me or just trying to mislead me in my pursuit.

thanks again

No problem where are you based

You Guys are all driving me crazy.

I am a rotational molding engineer, and have been for many years. I work for one of the largest custom rotational molders in the U.S., And have worked for the largest in the World.

Here's the deal. a large percent (like 98%) of rotational molding uses Polyethylene powder.

Granules is a general term and can be of any size. I think you may be referring to what we call pellets, and are some where around 2-3 mm dia.

Granules or pellets are used all the time. Typically in combination with powder. They can be used in multiple colors to create granite or concrete type effects. They are also used to delay melt when used with a standard powder with foaming agents ("one step foams"). People are also attempting multi-layer materials by varying the melt time by increasing the pellet size.

So here is the deal: Stuff this size (pellets) is used regularly but for specialty applications. I am not going to get into the applications, as this is long winded as is.

Powder (very small "granules") are measured by "mesh" which is the size "mesh" screen they will fall through. So what is powder and what is granules?

The (by far) majority of Rotational molding uses Polyethylene powder. Different manufactures prefer different mesh.

Somewhere in here someone mentioned a liquid. Most likely that would be plastisol, or liquid PVC which is also fairly common, but makes up a small percentage.

There is a product called "Micro spheres" also for specialty applications.

O.K. now drop it and quite firing off my google alert for roto-molding

granules are bigger in size -5mm or so and com in various colors but here we are talking about the blue ones used in making blue cylindrical water tanks.

Granules may be used for Specialty roto molding purposes but here we are referring to normal or standard rotomolded products of 500 mesh or so.