How do they make clear tubing/rod

[kq9ak]

Just wondering if anyone has seen it in person? How do they get such close tolerences? Keep it straight with out tapering? Even wall thickness? How long is the stock before they cut it down into 4ft/5ft pieces? I know large machinery has got to be involved, it just has to be such a mesmerizing process.

[S.HY.]

extrusion. molten glass is forced through an opening and formed in a process similar to making penne pasta

[J Howard]

imagine a small swimming pool of glass. pull the plug on the floor and glass flows over a cone that injects air into the flow. thickness is determined by flow rate and air pressure. it falls several feet towards the floor and twists towards horizontal. pulleys pull it down a long conveyor belt and through various annealers, first hotter then cooler, then ultimately cooled. the long continuous tube is scored broken lifted fire polished and stacked into boxes continuously, flowing around a foot per second. (the factory in corning that i saw in action was making lead glass 10mm tubing for automotive lights)