By the time it arrives in your home, cast iron is one of the most durable materials you’re likely to lay your hands on. Getting it to that point, though, turns it to be an incredibly finicky process.

io9’s comment of the day comes from commenter amp0730, an engineer at an auto parts foundry. They explained just what goes in to making the cast iron so strong — plus the unlikely role that K-Y Jelly sometimes plays in the whole process:

I’m an engineer at a foundry that makes ductile cast iron automotive components. Namely suspension components, which more or less are the bits that hold the wheel onto the chassis of your car. So, as they say in our industry, “safety critical” components.

Cast iron has a very deserved reputation for being very brittle, which is why ductile iron is so useful; by adding certain elements to the melt, you can make cast iron parts that are very malleable and won’t crack over time. This ductility is crucial though.

If we were to ship a part that didn’t get enough “ductility alloy”, the part will be very brittle and could fail while someone was driving the car. Which is why we perform an ultrasonic test on 100% of the parts we ship out of our plant.

For the most part, this is done during the finishing process in large tanks filled with UT solution, but in a few spots we have to use portable testers. To use this tester, you need to smear a little gel on the part (similar to what they use for ultrasounds).

So what happens if someone in the stockroom screws up and we don’t have any UT gel and we need to ship parts that can’t be tested in a UT tank? Some poor sap has to go to the dollar store and buy all of the KY personal lube (which will do the same thing in a pinch) that they can.

And then they have to explain why they want to get reimbursed for $40 worth of KY...

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Image: sorapol / shutterstock