The Project:
This project started with the following conversation:
Client: Hey Tom, we’ve got a problem with water sampling and we were hoping you could help us out.
Captain Meticulous: What’s the problem?
Client: We sell equipment that allows municipalities and private developers to sample water quality from the bottom of a well, and the extreme water pressure at the bottom of deep wells is damaging the bellows we use to draw in the water sample. We need a part that can withstand 100 psi (pounds per square inch).
Client exits stage left, leaving Tom and the engineering team to ponder the task.
The Cliff Notes:
The Cliff Notes:Keeping well water safe – that’s a worthwhile goal. While you can sample the water at the top of a well with a rope and bucket, it’s the stuff at the bottom that represents the “leading edge” of water quality. If contaminants from groundwater and aquifers find their way into the well, it’s probably a good thing to catch them with a test as soon as they show up, rather than wait until they bubble into the water that people wash with, cook with, and drink.
The Challenge:
The bellows had to be virtually indestructible, yet flexible enough to bend easily. The wall thickness had to be consistent all the way around – too thin and it would break, too thick and it wouldn’t function properly. The seams had to withstand pulling and stretching without splitting or becoming deformed. No contaminants could get into the bellows (that would defeat the purpose).
To get an idea of what 100 psi feels like, imagine an African elephant standing on its hind legs. That’s what our bellows had to withstand on a daily basis.
The Result:
We’re very proud of this bellows. If you were in the room with us (or if you contact us to request a sample), you could feel for yourself how flexible and utterly indestructible it is. We’ve given it to kids with the instruction, “See if you can destroy this thing without using a blade.” Weeks later, they’re still tugging, twisting, gouging, even biting (don’t try this at home). No matter how horrible it looks after all this abuse, it still can be restored to its original shape, and it still accordionates like it did right off the production line.
Ongoing Quality Control:
The QC on this bellows is kind of fun. First, we weigh them with really expensive scales (the kind that can register an errant eyebrow hair), making sure the same amount of plastic is used in each one.
Then, we stretch the bellows to make sure the walls don’t collapse. We look for weak seams and look for contamination or parting line flash (thicker plastic that builds up where the mold halves meet when they are beginning to need maintenance.
And five times an hour, we test a bellows for its ability to withstand pressure far greater than it will ever meet at the bottom of a well. We insert a bellows into a pumping case and increase the pressure 10 psi at a time until 125 psi is reached. (Think of the trash compactor scene in the original Star Wars movie.) If the part fails, we hear air escaping.
When a part fails any of these tests, we stop production, scrap the faulty units and troubleshoot the problem until we can get back the original level of precision. Unlike injection molding, where once you’ve got the mold perfect, you’re done, with blow molding you need to continually fine tune the process with each run.
