I need a mould to resize/reduce a plastic bottle's neck?

[shawnreit]

Hi, I'm trying to understand the viability of making or having made - a hot -mould that can resize the neck of a standard cooldrink bottle. I want to reduce the neck of a 500ml bottle so that it fits loosely into another bottle's neck. So(ie) - to heat and compress the neck( threaded apperture) to reduce and compact it to form a new neck(without thread) that can slide easily into another standard, original apperture. I'm in Cape Town, South Africa, I don't know who to contact re designing or buying such a thing. Can you help?

 

[shawnreit]

Hi, I'm replying to my own thread:
I decided not to wait for help and tried a few experiments in the workshop. I ground and sanded flatish the flanges and external thread of a bottle. Then, what finally worked , I tightened a stainless-steel hose clamp around the neck and rotated that over a candle flame.Then tightened the clamp (having inserted an appropriately sized dowel and reheated and tightened and voila - it's almost right! Then I trimmed the excess with a blade. I wasn't able to achieve the length of neck I want. I still want an efficient tool to be able to produce these en- mass. I imagine an adjustable, small, flute shaped mould with a central sizing pin - into which the bottle neck is inserted and the mould, hot from flame or element (internal?) is then tightenable to pinch the softened neck to a new size around the central pin(18mm+/- int. diam.)
What might work is a large hose clamp - not in diameter - in the width of the metal band - to produce a uniformly flat compression of greater length. If it were self-heating - that's the thing!... I'll keep experimenting, - pls feel free to suggest some professional advice.

 

[Danger]

Welcome to PF, Shawn.
I'm afraid that professional advice is one thing that I can't offer (having no profession). I was going to make a suggestion after reading your first post, but then saw the second and realized that you have a handle on the situation already. In fact, I was going to ask whether or not the particular sizing was critical. That was because it seems to me that it would be easier to expand the neck of the "receiving" bottle than to shrink the neck of the interloper.
Given the success of your initial trials, my recommendation for a commercial-quantity version would be to insert a heated and lubricated sizing mandrel into the neck, then have two semi-cylindrical outer dies, also heated, clamp down on the thing until it settles. (By "semi-cylindrical", I mean like if you take a proper size of pipe and saw it in half length-wise.)

 

[shawnreit]

Thanks, that seems like a reasonable handle too. How to heat, how to clamp? So far the pipe is do-able, how to easily rig a jig to make for a clean , easy (one levered?) operation?... - a lever armed spring mechanism - like a bottle capper. (you know?) Like a drill press, one side with half pipe - fixed, the other moveable - with other half pipe - might have the pressure and action to pop them out easily... where's the heat?... The idea is to create from a 500ml bottle - a funnel that can be used to fill a similar necked bottle. So to widen the receptor is not an option. I was considering having bottle caps manufactured by injection moulding... then I thought I'd try consider a 100% recycle product - it seems more and more feasable. - Thanks

 

[Danger]

If you do use an internal mandrel to prevent excessive collapse, I would recommend against having one fixed and one moveable "pipe" die. The reasoning is that the bottle would not remain centred on the mandrel as it shrinks. Better, I believe, to have both halves of the mould approach at the same time from opposite directions, as if mounted on calipers.
As for heating, there are a lot of options available. The mandrel and dies can have internal resistance coils, or retreat into a propane flame between bottles, or be subjected to an induction coil, etc.. The bottles themselves could be presoftened by hot air blasts or infrared lamps.
I'll keep thinking on it, but that's all that I've got for now.

 

[shawnreit]

Internal mandrel! that's a must ...and if that were NOT fixed, then the two half-pipe system can work. I mention the drill press lever arm 'cause that's something I've got. I'm trying to consider the viability of a home build for the apparatus. To have such a thing made by professional tool-makers would cost $1000's. I think a gas flame is viable, it can be angled at the mould no matter the shape of the contraption. A flat base - and the mould can sit on a hot plate, clothes-iron, gas range...For electrics and electronics I'd need to follow some instructions- I like the idea of a built-in heat source - like an "internal resistance coil"? I have to research your tech terms - thanks again