In a recent exchange with sqrlz4ever about the appallingly hot weather here in South Australia, I mentioned a few things about my work as a glassmaker, and the temperatures that I deal with on a daily basis. I shared this video with him, and he suggested it would make an interesting post, with notes from an insider’s perspective.
So, How it’s made – glass.
As a glassmaker, my job is to operate and maintain forming machinery similar to what is in this video. My suggestion would be too watch the video first, and then, if interested, go through my further notes (which seem long, but this is the condensed version….it’s a complicated process, lol)
I could make this just the first post in a series; it’s a subject that I find fascinating. But such detailed breakdowns are pretty time consuming, so if you want more, say so! If there’s enough interest, I’ll continue. Cheers.
55 seconds: cullet not only comes from purchased recycled glass, but also from any glass that has been manufactured and rejected, weather it's rejected at the forming machine, by the inspection machinery, or has been quarantined during quality inspection.
1 min 9 seconds: 2730 f = 1500 c.
1 min 17 seconds: The glass actually passes from the furnace to the fore hearth, and then flows into what is referred to as the sleeve. The sleeve is essentially a drum, I'm not sure if the actual capacity, but approximately at a guess, 100 L. Beneath that is an orifice ring with a number of holes in it corresponding the amount of gobs required for each section. Normally it is two or three. My machine runs three gobs per section.
1 min 45 seconds: The preliminary mould is also referred to as the blank mould. Commonly, it's just referred to as the blank. The glass is formed into the parison, either by compressed air, in the process known as blow and blow, or by a plunger pushing up from the underside, which displaces the glass, forcing it into the blank cavity, in a process known as press and blow.
2 min 17 seconds: As the formed bottle exits the mould, it is cool enough to be able to maintain its own shape, and yet so hot that it is still in a state of plasticity. If, at this point, you removed a bottle from the conveyor, and dropped it to the ground, it will bounce. I haven't taken specific temperature readings, however the temperature somewhere in the region of 500-600 degrees Celsius.
2 minutes 56 seconds. The type of mould shown at this point can be particularly problematic. When the mould opens the glass needs to smoothly release from the surface of the mould, and as such, the mould itself needs to be lubricated at points of highest resistance. Engraved or embossed logos, such as in this example mould, require special to ensure that the glass releases from the surface cleanly.
3 minutes 37 seconds. In the annealing lehr, the glass is actually reheated initially, and then cooled at a controlled rate. If you consider the sidewall off the glass, the external surface will cool at a quicker rate than the internal surface, and as such, it will attempt to warp. Obviously, due to its nature, soda glass is unable to do so without breaking. The purpose of the annealing lehr is to enable cooling of both the inside and outside surfaces evenly. This Is why glass that has not been correctly annealed, or tempered, is not only prone to breakages, but the release of the internal stresses can be quite violent. It won’t just crack, it will shatter, and the release of the energies involved is so sudden and violent, it is more akin to an explosion.
3 min 54 seconds onwards: The packaging line shown in this video appears to be much more automated then the processes we use. Whilst we have similar automatic inspection machines, the need for quality in the finished product is such that human intervention and action cannot be fully removed. The machines need constant monitoring to ensure that the inspection process is doing what it is intended to do, and there are many flaws and quality aspects that cannot be picked up by these sorts of machines on a practical basis.
Manual gauging buy a cold and operator is done to ensure the integrity and accuracy of the automatic inspection units, and further, more detailed, digital sampling is done a few times per shift
4 minutes and 50 seconds. Not only does an increase culler ratio reduce manufacturing costs, if the cullet is of high quality, the glass produced in the furnace is much more stable and consistent, which allows the forming machines to produce ware of a higher and more consistent quality. One of the main issues we face is obtaining cullet of sufficient quality in the quantity that we would desire.