Milestones

Today, on the way home after running some errands, my beastmobile (1995 Dodge Caravan) turned 140,000 and now sits at 140,009.5. Every mile I drive in the beastmobile sets a record for most mileage I've ever had on any car I've owned. Ever since I was a kid, I've been fascinated by the odometer in my parents' or my cars. Something about five or more digits all rolling over at the same time. Daft, I know but hey, whatcha gonna do, eh??

When I get a new car I don't want one of those newfangled digital odometers. It just wouldn't be the same...

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Something happened at work yesterday that was a first time experience for me. Something baaaaad, which I could not prevent, yet happened on my watch.

If you don't already know, I work for a plastics manufacturing company that makes medical implant devices through injection molding. We use these relatively complicated machines to make tiny plastic parts that dissolve over time inside the body. They do this due to body temperature and moisture so that a second surgery is not needed to remove the devices. The whole concept is really state of the art and very cool.

However, it's not so cool when the key component of the machine breaks inside the machine, while it is running. This is precisely what happened yesterday. Bear with me (for dramatic effect...)

I was sitting at the machine when I noticed the problem beginning. Little did I know at the time what would be the result of the problem. The material enters the barrel of the machine through a feed throat, where it goes through four stages of heating before being injected into the mould cavity. The temperature profile I was using was approximately 170 C, 197 C, 212 C, and 225 C. (Pretty hot, eh?) The material is forced through the barrel by way of a very large metal screw, which is itself heated similarly to the barrel temperatures. The screw turns one way and the material turns the other way, at tremendous force, generating even more heat and shear pressure.

I first noticed the cushion of material filling unusually slowly in the screw cavity. Ok, sometimes the material gets clogged, so I wasn't worried. On the third shot since I noticed this, the dosage time ran out, so I had to take the machine off-cycle and manually feed the material in the barrel by turning the screw myself. This also happens occasionally so again I was not overly concerned, but I was keping an eye on it. On the fourth shot, the cushion only filled to .2 ccm (this part usually requires 5.6 ccm of material plus approximately 1.20 ccm cushion) and stopped. Cold. The dosage time ran out again. So I took the machine off cycle again to fill the cushion when I heard a very loud and unusual sound.

SNAP!!!

Stop. Don't read any further, yet. Can you guess what broke??




Exactly.


The screw snapped.

Clean in two.

Right inside the barrel.

Fan- [&!!%@@&%$!!%@@&%$*##!!%@@&%^&%%$*#] -tastic.

This screw is custom fitted to fit precisely inside the barrel with no extra wiggle room.

Brilliant.


Wanna see the damage??




Of course you do....

Without having measured the screws we use, I'd say each one is about 30 inches long and weighs three or four pounds. This particular screw is known as a powder metal screw. It was only six months old, and used to make about 13,000 parts. It cost in the neighborhood of $5000.00.

Screws like this should last much longer than this one did. Much longer.

So instead of making parts yesterday, my partner and I had to replace the barrel and screw assembly setup from the broken one to a brand new (clean) setup for running today.