Internal pressure on a cylindrical mould

[jetdob]

Hello,

Can anyone explain the way this system works. Thanks

 

[berkshire]

It looks like a tapered wedge on a screw pushing against a link.
B.E.

 

[MikeHalloran]

I think I see a hinge pin at each end of the radial elements, which suggests that they are toggles.



Mike Halloran
Pembroke Pines, FL, USA

 

[jetdob]

Thanks for the replies. Is there a chance you could describe the set up. I've been trying to build a set up like this and could use all the help I can get.

 

[MikeHalloran]

Could you possibly meet us halfway, and tell us:
- where you got the image.
- what you are actually trying to do.



Mike Halloran
Pembroke Pines, FL, USA

 

[jetdob]

Hey Mike,

The image is from a drum company. I build drum shells (musical instruments) I have a 13.75 id steel mould .Basically it is a pipe 13.75 ID by 18" depth. You place veneers in usually 2-3 plies,glue between them to form the shell. So the part in the picture is the internal pressure system.What I need to do is put pressure on the inside of the shell as it dries.I have 4 equal plates and need the best way to press out the inner plates.

Thanks Brian

 

[jetdob]

Here is a finished drum

 

[MikeHalloran]

The simplest way is to inflate a truck inner tube inside the laminated shell and pressure plates. It will try to ooze out the end faces, so you would need substantial bulkheads to trap it at each end of the assembly.

The mechanical expansion mechanism shown in your first image is probably a little safer. The radial links between the core 'star' and the shoes appear to be toggle links. I.e., they are just a little too long to fit nicely in the space, and the screw bears against something to move the 'star' axially and push the links into more nearly radial positions.

Google 'toggle linkage' for help with that.

Note: I'm not completely sure that the image actually does depict a quad toggle mechanism; that's just my best guess from what I can see.

Rather than trying to analyze the linkage, which is possible if your geometry is well known and consistent, it might be advisable to make the toggle links of adjustable length.

The quick and dirty way is a bucket of vise-grips, which also contain a toggle lock mechanism.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

The other, high-waste way to laminate the shell is to build a toroidal vacuum bag around it and let the atmosphere do the work. However, the toggle lock mechanism is capable of larger forces, and may give a tighter lamination, if you can figure out how to build it right.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

I can't rule out the possibility that you are doing it completely backwards.

The extended shank on the central screw suggests that it is used to support the assembly in v-blocks while it is rotated. There is no need for such a feature if the shell is built from the outside in.

Which further suggests that the assembly comprising four sector shoes and a centralizer linkage is not a clamp, but a collapsible mandrel, upon which the drum shell is built from the inside out. The penultimate step would include wrapping the shell exterior with a band of thin metal, retained by a bunch of big hose clamps, and baking the adhesive, e.g. in a pot furnace as appears to be taking place in your first image.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

OR, perhaps you are trying to duplicate this process:

http://www.tamadrum.co.jp/eu/Inside_TAMA/factory_002.html

It's much easier to build a laminated shell from inside out over a mandrel than to build it outside-in within a tube, but if that's what you want to do, it's clearly possible.



Mike Halloran
Pembroke Pines, FL, USA

 

[jetdob]

I understand it is easier to make the shell from inward out around a mandrel, but the reason they don't normally construct them that way is a drum has a standard OD say for a 14" shell actually they are 1/8" undersized.When you layup the plies from inward it is harder to keep your OD correct do to ply thickness. The inner method you always have the correct OD regardless of plies.Thanks for your thoughts on this subject.I have used the airbag method.I'm not real comfortable with it. It can be dangerous with the pressure and also I use heat to cure the shell so the rubber bag is not the best system for me.Thanks again for taking your time to help me on this I really appreciate your help.

 

[chicopee]

Per the original post, as the screw is turned either CW or CCW, the inner threaded hub either moves up or down thereby drawing in or pushing out, via the links, the outside four circular segments. No taper would be required in this case.