# Rotomolding kayaks



## DGax65 (Jun 7, 2006)

I just ran across a rather interesting post on another forum. The VP of Sales for Malibu Kayaks posted some photos of kayaks being rotomolded. 
http://www.texaskayakfisherman.com/forum/viewtopic.php?t=55155
I've read about the process, but I've never actually seen it being done with kayaks. I think you can appreciate how difficult it is to get a good product out of the mold. I'm sure that there is much trial and error that goes into getting it right. Not every kayak that comes out of the mold is going to be perfect; something that I've had personal experience with.

















OK replaced my kayak with no questions asked. That's great customer service....too bad their QC wasn't up to the same standard. I've heard that OK and Malibu are doing more QC checks now. Rotomolding a kayak is something of an art and it is difficult to consistently turn out a flawless product. Seeing these pictures just reinforces my conviction that you should thoroughly leak check any new kayak.


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## ArWeTherYet (Mar 25, 2007)

Well ya learn a new thing every day. 

Thanks for the link doug.......but I still dont fully understand how simply rotating the mold makes the plastic evenly distributes to the out side of the mold :?


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## justcrusin (Oct 1, 2006)

very cool Doug,

I was asking questions about doing this myself at home. Now that aint gonna happen  (sorry Davey G no mess this time :lol: )
Back to the fibreglass

Cheers Dave


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## Redro (Sep 5, 2005)

That's an interesting link, and sequence of pictures, Douglas.

Even wall thickness? Powder distribution in the mould depends on how the rock and roll parameters are set up. Time for some "cut and paste"........

Ever wondered how your poly kayak was manufactured? Think of it as much like making an Easter egg. The raw material is Linear Low Density Polyethylene. Colourless PE pellets are compounded with the desired colour Master Batch via an extrusion process. The coloured pellets are then ground into a fine powder on a mill (you can't rotomould pellets).
Rotomoulding is a low pressure, high temperature process for moulding large, hollow, one piece, plastic parts â€" such as big water tanks. It is very cost effective for short run/large parts in comparison with injection and blow moulding, where the mould costs (and run sizes) are relatively much higher. Both of the latter are high-pressure processes. Moulds for rotomoulding are fabricated from sheet metal or cast in aluminium and are manufactured in two halves.
The metal inserts are fixed to the mould surface before the powder is loaded â€" the PE will form around the insert during the moulding process. The graphics are also transferred onto the mould surface before loading the powder.
Once all of this is done, one half of the mould is charged, at room temperature, with a predetermined quantity of powder. The other half of the mould is then clamped on tightly.
The mould then begins to rotate in a heated environment (oven). This can either be bi-axially or, as usually in the case of kayaks, via a "rock and roll" action. The mould rolls a full 360Â° around the perpendicular axis and rocks about the other axis. The rotational speed is low â€" around 3 rev/min. The rocking angle is typically 35Â°. This is not a centrifugal process, i.e. the powder is not thrown against the mould wall. The powder lies in a pool at the bottom of the mould (bi-axial machine) and as the mould (which is steadily getting hotter) rotates it picks up the melting PE powder depositing it evenly on the inside surface of the mould.
Once the PE has been completely distributed on the mould wall the temperature in the mould (and the oven) continues to rise to around 200Â°C when the part will be cured. The hot mould is then removed from the oven and the cooling cycle begins. Finally the mould is opened again and the now solid part is removed from the cooled mould. Final trimming can now take place. Hey presto, finished kayak (without fittings) â€" with inserts and graphics permanently integrated into the kayak!


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## Dodge (Oct 12, 2005)

Doug and Nick really interesting info thanks to both of you


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## WayneD (Jul 11, 2006)

Very interesting. My work is in the process of setting up for making our own PE water tanks, I wonder if I can swing them into making a yak.......

Did you see that Night Wing guy on that website has made over 15500 posts. Holy crap!!!


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