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Problem during moulding

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Arthur.Clarke, Jun 30, 2011.

  1. Arthur.Clarke

    Arthur.Clarke Active Member


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    Hi, I am having problems vacuum pressing copoly polypropylene.

    For some odd reason, it is not resulting in a smooth press, the always seems to be a lumpy ridge in the arch of the orthotic and the colour isn't as shiny, it just a poor press and I can't seem to understand why.

    I am using the following,

    Vacuum press from algeos with a compressor,
    membrane is 2mm thick of the vacuum press
    The plastic is heated using the correct heating temp.

    Where am I going wrong? I don't want to waste anymore plastic (I am a student)!

    Regards,

    Arthur
     
  2. is the plaster cast wet ? if so it needs to be dry

    are you using something to allow the air to escape? - stocking over the cast

    is the membrane not pulling hard enough? - add an EVA sheet under the plaster cast

    are you getting a complete vacuum? check
     
  3. Make sure plastic not too hot, cast too damp. Add thin layer of neoprene between cast and poly when vacuuming. Dont worry about it not being shiny you need key it for top cover anyway.
     
  4. RobinP

    RobinP Well-Known Member

    Raise cast with EVA block 10-12 mm.

    EDIT: Sorry Mike, didn't read you had already suggested that
     
    Last edited: Jun 30, 2011
  5. Arthur.Clarke

    Arthur.Clarke Active Member

    No the plaster cast is dry.

    I have tried with and wothout a stocking net.

    Yes the membrane is pulling enough.

    Yes it is a complete vacuum, what I mean by that is there is no part of the membrane being open.
     
  6. Arthur.Clarke

    Arthur.Clarke Active Member

    I am using an infra-red oven not a convection oven, I have tried it cooling it down with a cool hair dryer then pressing it.

    I'm loosing the shine on the extrinsic side of the shell.

    I have also sprayed silicone to the membrane, no luck.

    I used a thin layer of poron 1.6mm between the cast and poly. Again bamboozled why this is happening!
     
  7. Arthur.Clarke

    Arthur.Clarke Active Member

    Yes I raised the whole cast by 15mm, then took the raise away and raised the posterior part of the cast.

    This is googly, and I cannot solve the problem!!!
     
  8. get the infra-red oven checked out
     
  9. I'd say there's your problem. If the plastic is hotter on one side than the other, or hotter on the surface than the core, it will not mould properly.

    Or you could try a different material. I've found Mandrillian (high molecular weight poly) to be both easier to work with and more durable.
     
  10. RobinP

    RobinP Well-Known Member

    You're taking the Michael there aren't you Robert? Mandrilian is a made up name from Superman 1 isn't it?;)
     
  11. What I do now ?
     
  12. Nothing. You've been taken. :empathy:

    Mandrillian does sound like a supervillian. "mandrillian's lair" has a nice ring to it. I think more orthotic materials should have cooler names.
     
  13. Spinklesponk 262, man that stuff is the dog's...

    Isn't Bobba Fett supposed to be wearing Mandrillian battle armour in the Star Wars film? Just checked geeks-ville and its Mandalorian armour- close, i think they've missed an opportunity there.
     
  14. Not shiny on the B side? Not sure that's going to make any difference to the function of the device, but hey-ho. The shiniest devices I ever saw were made by the late, great Paul Rasmussen of Precision Intricast. If memory serves, he once told me he used a stone tumbler to finish the devices. Which ever way he did it they had a beautiful finish. Kevin will be able to confirm the method (unless is a trade secret).
     
  15. Call yourself a star wars fan? Its Mandalorian armour but not actual beskar'gam (PROPER mandalorian armour made of beskar) until you reach about 40 years after the battle of Yavin (yes, he survives the sarlacc on account of being so badass).

    One day Simon, you and I will sit down to a game of star wars trivial pursuits. In this one area, and one area alone, I'm pretty sure I can take you.

    Starflex sounds a bit like a B movie baddie...
     
  16. And my Mrs. worries about me....

    I'm assuming 40 years after the battle of Yavin, he's well into his 70's... Lets apply some logic: In episode 2 he's what 12ish years of age? In episode 3, when Luke is born this is several years later than episode 2, jeez gestation takes 9 months. In episode 6, Luke must be in his late 20's early 30's, Leia is looking fine and in her prime, so Bobba is pushing his early 40's here minimum. 40 years on he's badass and in his late seventies early 80's? Yeah, I'm ****ting myself, rather he probably is, complete with colostomy bag, hearing aid, glasses, zimmer frame, dementia and reflexes of a house brick. Viz. I'm going to fart on him and he'll fall over in that armour. Or did I miss the bit when he stopped ageing?

    You know Robert, you can be too geeky. The sad thing is I'm off to age Carrie Fisher (Still a pin-up in THAT bikini) and Mark Hamill when Return of the Jedi was made, take their mean age and work all of this out.
     
  17. efuller

    efuller MVP

    Check the heating time. When you put the plastic in the oven, it's room temp. Depending on how how the oven is, It will take variable amounts of time to reach the perfect temp to press it. There is a too hot and a too cold. It might be that you are heating it too long and when it cools it shrinks at different rates causing the lumpiness.

    Eric
     
  18. RobinP

    RobinP Well-Known Member

    My wife opened my sealed collectors edition star wars and lord of the rings monopolies. Can you adam and eve that? The worst thing is that she opened them for the kids to play with and they subsequently trashed them. Nice
     
  19. Which is why I prefer to use natural coloured poly-copolymer as you can more easily tell by the translucency as to when it's ready for the press. I don't go specifically on time nor temperature, I go on when it's ready... I guess you'd call that experience. Neither do I worry about it being shiny. In twenty odd year, I've never had patient yet tell me it wasn't shiny enough.
     
  20. That's why you buy two copies of everything you hold dear. One for the kids, so they can get into you obsessions, and one for you so you can give it to them as an heir loom when they are at an age to realise the significance and value.

    So, here we go, probably the most important question ever posed on the Arena....


    Pick your favourite Star Wars episode...

    Me? I'm old school, I swing between all three of them. At the moment I'm an Empire man.. I know it'a an in-betweener (great series BTW), but it's cool (hence all the snow and ice at the start)

    If anyone can be arsed then put it up as a poll. You're wrong anyway, 'cause at the moment it's "Empire". We'll do the Alien films another day...
     
  21. Yep.:D Very vigourous 70 year old though. Its sci fi.:rolleyes: He's a clone. His "brothers" were engineered to mature at 2* the speed. They were ALL developed with a genetic trigger to die early. A few of them found a way to reverse it. That being the case, why should they age the same as us? You'd have to read the books, which story line wise are at least 200 times better than the films. People die in the EU books. Han and Leia have NO luck with their kids.

    I know. My wife despairs. No excuse.

    See? You're as bad. Fight it all you like, but you know what you are. It is... inevitable.

    Oh and I'm with you. Empire. Although comparing the original 3 to the prequels doesn't really work so I'd also register a strong affection for ROTS. But it has no millennium falcon and no Han solo so it can't compare.
     
  22. gaittec

    gaittec Active Member

    Your problem is most likely related to uneven heating of the plastic as stated above.

    1. If possible try a convection oven.
    2. If you have to continue with the present oven, put a rectangular flat stoneware plate in the bottom and sides if possible to even out the heat. Like bricks in a big pizza oven.
    3. Preheat the oven to the desired temp.
    4. Cut your plastic closer to the eventual size you will trim.
    5. Bring the plastic out as soon as you think the heel will shape without a wrinkle.
    6. Only use enough vacuum pressure to shape the plastic. Then shut the pump off as long as it will hold the vacuum. If not, open the valve enough to let air escape and reduce pressure.
     
  23. CraigT

    CraigT Well-Known Member

    Agree with all above.
    I used to use a cheap toaster oven and managed to get it to work by shielding the orthotic plate from the heating element and sitting it on a ceramic tile so that it had some heat from the bottom.
    You could also simply flip the orthotic plate over half way through for more even heating.
     
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