Fire Extinguishers Doughnuts Shock Absorbers Banjos
Today on "how it's made"... Fire extinguishers... Doughnuts... Shock absorbers... And banjos. The first fire extinguisher on record was built in europe in the middle ages. It worked like a giant syringe that squirted water at a fire. The modern extinguisher uses compressed air as a propellant and douses the fire with flame-retardant liquid, powder, or foam. Squeezing the lever opens a valve that releases compressed air. The pressure then propels the chemical through the hose and out the nozzle. Production of the release valve starts with cylindrical pieces of aluminum called blanks. A carousel runs each one through 16 different machining stations. At each stop, under a shower of lubricant, tools shape the blank for 6 1/2 seconds. As each blank completes the circuit, it comes off the carousel. From blank to valve in a minute and a quarter. Now the fire extinguisher's aluminum handle is riveted onto the valve. It pivots on a pin. Next, an aluminum lever is riveted onto the handle. This is the lever you squeeze to use the fire extinguisher. Then comes the valve stem--  the valve's inner workings. Workers simply place it inside, and an automated assembly machine does the rest. It positions a spring over the stem to create resistance when you squeeze the lever. Then comes a retainer to hold both the stem and spring in position. Now workers slip on a plastic thimble to position the rubber "o" ring that goes on next. The "o" ring acts as a seal between the valve and cylinder so nothing leaks out. The siphon tube runs from the valve down into the cylinder. The firefighting chemical goes up this tube, then out the nozzle. The compressed air inside the cylinder is what propels the chemical. This gauge shows if there's sufficient pressure for that to happen. After coating the gauge's threaded stem with sealant to prevent leaks, a worker screws it onto the valve. The valve unit is now fully assembled, tested, and ready for installation on top of the cylinder. To attach it, the cylinder needs a threaded collar. With the help of a press, a worker positions it. The cylinder also needs a bottom. The technique this factory uses to fuse the bottom and collar is called brazing. It's similar to soldering but with a copper ring as a bonding metal. After positioning a brazing ring at the base of the open cylinder, a steel bottom is pressed into place. Then workers position a brazing ring over the collar. Now into a brazing furnace for an hour and 45 minutes. The 2,000-degree heat melts the two copper rings, boding the parts they connect. Next stop, the static-paint booth, where workers apply a positive electrical charge to the paint particles and a negative charge to the cylinders. This draws the paint onto the surface evenly. Then it's into an oven for 45 minutes to bake the paint. Once the cylinders cool, automated machinery fills them with a fire-extinguishing powder. The main ingredient is a form of ammonia. When it's sprayed on a fire, the heat melts the particles of powder, fusing them into an oxygen-blocking blanket that smothers the flames. After the cylinders are filled, an automated machine screws a valve onto the collar of each one. Now it's time to pressurize the cylinder. The lever is squeezed to open the valve, enabling a compressor to fill the cylinder with air. They keep filling until the air pressure reaches 13 bars, about six times the pressure in a car tire. Next, workers screw on the nozzle and install a locking pin. This immobilizes the lever so the extinguisher can't discharge accidentally. As the instruction sticker says, in case of fire, you just pull the pin, aim, and spray. This mounting bracket lets you hang the fire extinguisher in an accessible spot so it's close at hand if you need it. When we return, frying up one of america's favorite treats. Doughnuts used to be called oily cakes because they were deep fried in pork fat. When dutch pilgrims first brought them to america, they were ball-shaped. But then someone found that removing a nut of dough from the center helped them cook far more evenly. And so the doughnut was born. In the world of doughnuts, there are two basic types-- yeast doughnuts and cake doughnuts. The batter for cake doughnuts drops from the mixer right into boiling vegetable oil. The nozzles shape the dough as it passes. The doughnuts fry for about a minute and a half. Then a conveyor carries them out of the vat to cool. Yeast doughnuts require more time to make. A high-speed mixer works the yeast dough, then workers pull it off the machine into bins. From there, it goes into a hopper that extrudes the dough as a sheet. Then it's on to another conveyor belt where a series of rollers flatten the dough sheet to just 3/4 of an inch thick. The sheet passes under a shower of cinnamon... Then hits a rotating cylinder that rolls it into a log. A small metal rod sprinkles the dough with water. This keeps it sticky enough to hold its shape while going under another flattening roller. A dusting of cornstarch keeps the dough from sticking to the blade that now cuts it into pieces. A retractable arm drops the blocks of dough four at a time onto wire-mesh trays. Then it's off to the proofer, a machine much like a large bread box in which heat and humidity help the yeast dough rise. This leavening process takes about 20 minutes, during which time the trays--  over 300 of them-- go up and down and then out to the fryer. A gate slows the doughnuts down just before the drop so they slide in without splashing hot oil. Gas burners keep the oil at a constant boil. Anything less and the doughnuts would come out partly raw. Halfway through, they get a flip so they'll cook evenly throughout. After two minutes, the doughnuts leave the fryer and move through a curtain of sweet glaze. A strong air current blows off the excess. And these fry cakes are ready to eat. They gradually cool as they spiral through the production area on their way to packaging. Now let's see how they make doughnuts with filling. A machine separates the yeast dough into little blobs, then sends them rolling down plastic tunnels. This shapes them first into pucks, then into round dough balls. Rollers then flatten the balls before they enter the proofer to rise. There's cornstarch everywhere to prevent the dough from sticking to the machinery or to the conveyor belt. Row after row of doughnuts fry in hot oil... Then slide into a large drum that tumbles them around, covering them with a sugary coating. Now it's time for the doughnuts to get filled. These nozzles inject just the right amount of jelly. Each worker fills 45 doughnuts a minute. After filling, these doughnuts, known as bismarcks, are ready to go on to packaging. They're just one of the many delicious varieties that this factory turns out on a daily basis. Next, the shocking truth behind one of your car's most critical parts. Shock absorbers do more than just smooth your ride. They counteract the bounce when you hit a bump, holding your tires to the road. Without that traction, you could lose control. So by affecting steering, stopping, and stability, shocks are actually a vital safety component. Wheel vibrations cause a piston inside the shock absorber to force oil through a valve. This absorbs energy, reducing the vehicle's bounce. All this happens within the shock's two tubes-- the reserve tube and, inside it, the pressure tube, housing the piston rod and compression valve. Both of these tubes are made from a steel sheet sliced into strips. Inside this tube mill, coolant prevents the passing strip from overheating as one forming roller after another gradually rounds it into a tube. Then, a copper welding wheel fuses the tube closed. As the 6-yard-long tube comes off the mill, a cutting tool chops it into shock-absorber lengths. The tube-making process is the same for the reserve and pressure tubes, except that the reserve tubes undergo one extra step-- compressing the ends. This enables the shock to house a larger reserve tube that can hold more oil. The reserve tube's final stop is a press. A die inside stamps the part number, the manufacturing date, and the brand name. Many components are made of powdered metal-- mostly iron powder mixed with some graphite and copper. After a press compacts the powder in a die, a furnace fuses the particles. This powdered-metal part is the valve through which the piston forces the oil. Steel discs and a spring help control the speed with which the valve operates for varying driving conditions. A stamping tool crimps the end of the tube, holding the spring in position. The valve, now fully assembled, seals the bottom of the pressure tube. Meanwhile, a press punches round steel discs into other components. These loops mount the shock absorber to the vehicle. A worker positions a cup on each one, then a robot welds them together. They insert a cup-and-mount unit on one end of the reserve tube, then weld it on. This unit is called the base assembly. The base assemblies now go on a conveyor, open end up so that workers can drop a pressure tube inside each one. Automated injectors now fill the tubes with oil that's specially designed to maintain its consistency despite changes in temperature. Next comes the head assembly, which includes the steel piston rod and the mount on the other end of the shock absorber. Two copper welding wheels fuse the head assembly to the base assembly with a cap. This closes the unit, sealing the oil inside. Next, workers weld on a dirt shield-- a steel casing that prevents dirt from hindering the movement of the piston rod. A piece called a bushing is pressed into each mount. This helps tone down the vibrations coming from the vehicle. Now it's on to an automated carousel. Robots pierce a hole in each shock and inject nitrogen gas to prevent the oil inside from foaming. After injection, the robot seals the hole by welding on a tiny steel ball. And now for the finishing touch-- an electrostatic paint job. A machine runs a positive electrical current through the shocks and a negative one through the paint particles. Like a magnet, the static electricity draws the paint onto the shocks in a flawless coat. In the factory's quality-control lab, technicians use sophisticated equipment to evaluate how well a shock dampens movement at different speeds. The tube-and-valve configuration inside varies by vehicle, so the shocks on a ground-hugging sports car are quite different from those on a luxury sedan or on a light truck. Coming up, a production line that comes with strings attached. The twang of the banjo resonates in american country music and bluegrass, but this down-home sound actually has its roots in africa. Slaves brought to america wanted something that sounded like the instruments from home, so they devised the banjo. And the rest is music history. to make a banjo, a lip is carved into wood that's been steamed and bent into a circular rim. The rim is carefully measured. It must be a perfect fit for this metal tone ring. The wooden back of the banjo acts as a sound resonator, and some plastic trim gives it a more stylish look. A chemical accelerator helps the glue dry so the plastic trim adheres almost instantly. The surface is then sanded until the plastic is flush to the wood. This long piece of wood will become the banjo's neck. Using a table saw, an artisan cuts a long slot into the neck so that a metal adjusting rod can be installed later. He widens the end of the neck with two pieces of wood to form the instrument's peg head. Next comes some very delicate work, as tiny mother-of-pearl decorations are embedded in a piece of ebony. That inlaid piece of ebony is then glued onto the banjo's peg head and clamped to dry. Now it's over to a saw with 22 blades. A long piece of ebony is passed over those blades to make the banjo's fret slots. This is the banjo's fingerboard. Once it's been adorned with more inlaid decorations, the fingerboard is glued onto the banjo neck. Next, the edges of the banjo neck and peg head are trimmed down to size. Using this router, artisans give the back and sides of the banjo neck smoother contours. The rounded edges will make the instrument easier to hold and play. They finalize the shape of the neck with a rasp, then give it a thorough sanding. Here, metal frets are tapped into the slots on the fingerboard, and the overlap is trimmed. Now it's time for a little color. Stain is rubbed onto the banjo parts. When the stain dries, it's followed by 12 coats of lacquer... And finally, a thorough buffing. Now all the pieces come together, beginning with the pre-fitted tone ring and wooden rim. The plastic head through which the banjo's sound will radiate fits on the tone ring. The head is secured with a tension hoop and a series of hooks. Tightening these hooks will stretch the plastic head to adjust the instrument's tone. The banjo neck and its peg head are attached and secured with metal rods. The tuning pegs are screwed into the peg head. Then the banjo's strings are attached and tightened. This little wooden bridge sits on the plastic head and is only held in place by the tension of the strings. Finally, the back of the banjo goes into place. And now this finely crafted instrument is ready to strum away.