Static, Nipples and Terrifying Molten Plastic Processes

Hey All! 

THERMOFORMED CUPS!!

It's been a long time since I last posted! Life is crazy but mostly I am lazy.

Today I thought I would skip the math and teach you all some relaxing applied engineering theory to enjoy with a cuppa on your friday night. Nothing too long or too difficult. I'm going to talk about extruders, injection molders and static. And I'm going to be using my personal experience at my internship as a narrative technique to tie it all together. But first, a public service announcement. Prepare for capital letters...

ROBIN HOOD - THE PANTOMIME IS ON AT MAIRANGI PLAYERS (birkenhead) SATURDAY (11th) AND SUNDAY (12th) AT 4PM. 

The show is seriously hilarious so if you're looking for a fun afternoon with friends, tickets are $10-$15 dollars. I've seen it twice now and I'm looking forward to seeing it again on sunday. Alrightie, back to the engineering stuff that you clicked the link for...

My internship - you use their products though you may not know it...

I work for a place called Huhtamaki. It's in Henderson. It's a really big company with its headquarters in finland. They used to make candy but now they have naturally evolved into a packaging company. Obviously. The factory in henderson makes cups and cartons. Recognise any of these?

Huhtamaki makes these products and so, so much more. Heaps more. They seriously make a lot of products. I once spent a whole two days organising their database of product drawings. Because they make so many products they have a huge variety of machines. I'm going to tell you a little bit some types of machines so that you can learn to appreciate your plastic possessions even more. 

Extruders - Thermoformers COMBO

Extruders are one of the more terrifying machines at the factory if you personify them. Pellets of plastic are thrown into a freaking huge cylinder where a massive screw (yes a screw and it's about the diameter of your head) double teams with some heaters and twists the pellets against each other so hard that they eventually give up, melt and are submissively forced out the cylinder into whatever shape the extruder wants. They are then rolled into giant balls of static death (unless treated. Static is a thing I'm going to be talking about later).Huhtamaki makes rectangular sheets of plastic which sit around the factory like giant inedible roll ups. Its easy to see how logical the transition between candy and packaging is.

So now you have a sheet of plastic. Great. Unfortunately not many people want to buy massive rolled sheets of plastic. This is why extruding normally has to be combined with thermoforming (or some other process). This is a fancy way of saying you are going to heat something up before shaping it. 

Engineers have got pretty creative with different ways to shape plastic after they've warmed it up (aka increased the temperature past its glass transition point for all you polymer savvy people out there). The most obvious way to shape something is to give it a really hard punch with the inverse of the shape you want. Can you think of some other ways? Cover up the next line and take a guess.,,

((Using a vacuum to force it onto a mould, blowing a bubble onto a mould (basically just positive and negative air pressure)))  

Injection Moulders

This is a pretty big generalisation but injection moulders are how you make anything complex. For instance the greek economy. To the right of the diagram you can see that most of an injection moulder is very similar to an extruder. This is because the plastic has to be liquidised before it can be injected. Imagine trying to inject beads of plastic into something - its a stupid idea and it just wouldn't work. The left side of the image looks like a giant syringe. It literally "injects" the mould with plastic with a needle half the diameter of your pinky or less. The moulds are very very precise and complex. They're expensive and difficult to make and design. You could spend your whole life learning to make really really good injection moulds if that's what floats your boat.

The fact that they are injected should give you a big clue of how to spot something that has been injection moulded. It will have a nipple. Yes, that is the technical word for it. This, of course conjures all sorts of amazing images of humans being injection moulded. If you ever want to write some engineering fan fic that is a great starting point. Your homework if you choose to accept it, is to check for nipples on plastic things - toys, cups, cartons. Let me know what you find.

Evil, Evil but Useful, Useful Static 

If static was a person it would be a rotten crook who committed horrible crimes but when you got to know them you find out it have a kid and are actually a really great parent. It is both a horrible safety risk and very good and useful.

Static is created when something rubs against something else and leaves behind a charge. However the charge has no way of escaping because the charged material is either not grounded or not conductive. As soon as a pathway becomes available, the charge will move through it to become grounded. 

Unless they are wearing rubber boots, humans can easily become this pathway.You may have experienced the power of static before when you touch the external of the car (which is not grounded as it sits on pesky rubber wheels) or perhaps you have recently been hit by lightning. 

As you can imagine, static is a big issue for anyone dealing with large amount of plastic (a non conductive substance). The extruded rolls of plastic I talked about before are packed with static which mostly forms during rolling. You might think that discharging them would be as simple as touching the roll with a metal pole but no! The plot thickens! Because plastic is not conductive, the static electricity in the material cannot travel very far in order to get to the metal pole in the first place. So even if you discharge one location, there is still plenty of static where that came from. 

So yes, it's a HUGE issue. At Huhtamaki we're looking at purchasing some more neutralisers which basically emmett an air flow with the opposite charge so that people don't have to get "hit by lightning" every time they clean a plastic pipe on the ceiling. I talked to an operator today at work who had been zapped a few times. On one of those occasions he was sent home because he couldn't move his hands and his fingers had changed colour.

Static can also be really useful. I am currently working on a project that makes use of "static pins". They basically allow the plastic label of a product such as an icecream container to stick to a plastic mandrel so that it can be inserted without damage into a mould in preparation for thermoforming. BAM full circle!

Goodbye!

I hope you learned something or were at least a little bit entertained by my lame jokes. Remember to always check for nipples!