Everyone’s opened a screw top drinks carton. You unscrew the top, take it off and it’s open. Right? Well yes, but what’s been going on during that operation? Here’s what.
When you buy the carton, it’s sealed. The liquid’s completely separated from the surrounding air. But how do you break the seal? By opening it. But how does that work?
The photo on the right show the INSIDE of the opening with the foil seal broken but only just. There’s a cunning mechanism in the screw top that cuts the foil when you unscrew the top, and then forces it down into the carton to clear the way for pouring the liquid.
The screw top has a projection which points down into the spout and catches on the spigot of a secondary screw insert inside the spout. The cunning secret ingredient is that the screw insert (pale blue in the photograph) is threaded into the spout with a screw thread of the OPPOSITE sense!
So when you UNSCREW the red top, the spigot catches on the projections of the blue insert and SCREWS IT DOWN !!
The points on the blue insert enter the foil seal, cut it and push it DOWN into the carton.
Here the blue insert is partly screwed into the spout.
And here it is screwed further into the spout and protrudes below the opening.
You can see it protruding here.
And here it’s fully open ready for pouring. So simply by unscrewing the red top, you’ve not only opened the spout but broken the seal and pushed the foil out of the way, ready for pouring.