As you know from Part 1 of this series, aerosols are a very popular way of dispensing beauty products such as hairsprays, deodorants, and shaving creams.
In Part 2 we explained how aerosol packaging consists of metal cans and some valve hardware that looks simple but is really only slightly less complicated than the Space Shuttle. And in Part 3 we explained how a complicated mixture of chemical goodies (like hairspray polymers, for example) and a potentially explosive gas work together to create your hair style.
But there are still some unanswered questions: How do the liquid and the gas get inside the can? How is the can sealed so the gas doesn’t just evaporate? And once it’s all put together, how do we keep the whole thing from exploding? In this fourth and final installment of Adorable Aerosols, we’ll answer those questions as we explain how aerosols are made.
Aerosols require a special, highly automated manufacturing process. In fact, entire factories are built that specialize in making these products. These factories use long conveyor lines to move the products from station to station where different operations are performed.
Step 1: Preparing the Cans
At the start, the inside of the cans are cleaned with a blast of compressed air to get rid of any dust or dirt that might cause the valve to clog. A clogged valve = an aerosol that won’t spray = a return trip to Walmart for you. So it’s important that the cans are clean before they travel to the next station where they’re filled with liquid concentrate (the goodies in the formula that make it work).
Step 2: Filling
The liquid concentrate is blended in large stainless steel tanks and pumped to a filling station on the conveyor line. At this station, a filling nozzle injects a metered amount of the concentrate into the can. The exact proportions are critical: too much or too little liquid in the can will screw up the spray properties of the finished product. After the concentrate is squirted into the cans, they travel to another station that loosely inserts the valve assembly into the hole on top of the can.
Step 3: Gassing
The cans then travel to the next station where they get gassed. No, that doesn’t mean they have too much to drink. It means the cans are charged with the propellant gas that makes them spray. As you can imagine, this is a very tricky process: the gas is under extreme pressure and evaporates in seconds. So this takes two steps that require split second timing. First, a nozzle shoots a high pressure stream of gas around the valve cup, into the can. Second, a fraction of a second later, the valve cup is pushed down and locked into place. This process involves a device called a crimper that uses little metal fingers to push down onto the valve cup and spread it outwards. This force causes the metal cup to fit tightly against the opening of the can. If the pressure applied during this process is even slightly off, the can won’t seal tightly. And a can that isn’t sealed = a leaky can = a defective product = another return trip to Walmart for you.
This process is also called “under-the-cup-filling” because the propellant is filled before the valve cup is crimped on. There’s another process known as “pressure filling,” where the propellant is filled into the can through the valve stem opening after the valve is crimped into place.
Step 4: Testing
After they’re gassed, the cans take a nice, hot bath. Literally. The conveyor belt runs the cans through a long trough filled with very hot water. As the cans pass through the water bath, people watch for escaping bubbles. Bubbles = gas is escaping = a defect in the can or valve = another trip…ah, never mind, you get the picture.
Step 5: Final Packaging
After their trip to the spa, the cans are dried off by jets of air sort of like those dryers in restrooms except you don’t get to wipe your hands on your pants. Finally, the cans pass through a capping station that places the over cap on top of the package. Then they’re packed into boxes and palletized for shipping.
Whew! That’s much more complicated than just filling a bottle of shampoo! And much more dangerous too. The entire process must be done under special ventilation to avoid buildup of explosive propellant.
So there you have it. Now you should have a pretty good appreciation of how hairsprays and other beauty care aerosols are made.