Bronze Bells Wooden Airplane Propellers Charcoal Briquettes Gas Log Fireplaces
Today on "how it's made"... Bronze bells... Wooden airplane propellers... Charcoal briquettes... And gas-log fireplaces. Throughout history, bells have played both practical and ceremonial roles. Village bells would ring to mark time and to warn of danger. Church bells would toll to summon worshipers. Bells are traditionally cast of bronze, a metal that's as durable as it is melodic. when it comes to bell making, there'd be neither swing nor ring without a mold. And only a quality mold makes a quality bell. The mold is made using a pattern. This particular bell will have decorative lines on the surface, which will require a separate mold made from this five-piece pattern. After greasing the pattern's surface with a release agent, workers lower a wooden casing around it. This casing will hold the mixture of fine silica sand and epoxy they'll use to make the mold. Workers pack the material tightly between the pattern and casing. The epoxy sets in 10 minutes, and now they have a sand mold in which to cast the bell's decorations. They still need a mold to cast the bell itself. They make it with this aluminum pattern. After spraying it inside and out with a release agent, they lower the decoration mold they just made right over it... Then on top of that, a steel casing to contain the sand mix. Workers pack the sand mix and wait for it to set. Then they flip the casing and add another section to hold even more sand mix. But before the next load of sand, they insert what's called the gate. This aluminum rod shapes the channel through which they'll pour the molten bronze into the mold cavity. They fill up the mold with more sand. Then they form a funnel around the central channel because it's virtually impossible to pour molten bronze directly into such a small hole. They poke the sand mix to make sure it's set, then pull out the gate. They separate the two casings, each of which contains a section of the mold. Then the patterns come out, leaving behind the mold cavity. Workers tidy up the mold walls and paint on a powdered graphite solution which will act as a barrier, preventing the hot metal from eroding the epoxy that holds the sand mold together. Next, they spray on a second coat of wash. The sand is so fine that without this step, the mold would reproduce the brush strokes onto the cast bell. Now they measure the size of the pour hole and custom-make a ceramic filter to glue inside. This filter will screen out the slag, oxidized particles that form when molten metal meets air. Workers stack the two mold sections back together and clamp them tightly so that the bronze won't leak out during casting. Melting enough bronze ingots for an average-size bell takes about two hours. To get a smooth enough consistency, the furnace has to heat the metal to about 2,100 degrees. For a quality casting, they must pour the bronze in one continuous flow-- no stops and starts. The funneling basin they made in the sand prevents overflowing. The bronze takes about a half-hour to solidify and up to 24 hours to cool. Workers remove the sand mold with a jackhammer, being very careful not to hit the bell inside. The extracted bell is covered in a residue of burnt epoxy, which they remove with a wire brush. Then, with one well-aimed strike of a sledgehammer, they disengage the gate. Now they mark the exact center point of the bell. That's where they'll install the hardware from which the bell will hang. They drill a small hole, then gradually drill it larger and larger. A big hole can't be bored in one shot because the friction-induced heat would crack the bell. Workers tip the bell on its side to hang the clapper-- the official name for the bronze hammer inside. Every bell this factory produces goes through six stages of polishing, starting with a coarse grinding belt and finishing with a fine-cloth buffing wheel. Two hours of polishing later, the bell looks as beautiful as it sounds. coming up... A new spin on a centuries-old invention-- the wooden propeller. The propeller dates back to 1493, when leonardo da vinci sketched out the concept for a helical screw that could propel a machine vertically into the sky. The propeller is still occasionally referred to as an airscrew-- a term that accurately reflects its basic design and function. The key to making one--  plenty of sanding. Wooden propellers start out as a laminated block of maple wood. Lamination is a process where several layers are glued together. The block has between 36 and 48 layers less than 1/16 of an inch thick. Depending on the model, workers select a master pattern that is between one and two yards long. They lay this pattern over the maple block and mark a one-inch center hole. They drill the hole... And lay in a centering pin to hold the pattern in place. A worker traces the pattern on the top of the block. He then cuts the outline with a band saw. This is the propeller's profile. Next, he traces a pattern on the side of the block. This is the propeller's pitch-- the amount of twist in the blades, which dictates the amount of propeller thrust. Using a pattern guide, he marks where the pitch blends into the center hub, then removes the bulk of the pitch with a band saw. Now he clamps the block onto a computer-guided milling machine that carves the pitch to very precise dimensions. The machine's carbide-tipped cutters shave infinitesimal amounts of wood with each pass. Precision milling just one end of the propeller can take up to 60 passes. Next, a worker shapes the airfoil with a band saw. The airfoil is the side of the propeller that is shaped like an airplane wing and produces forward thrust. The pitch side... And the airfoil side. Workers use a tool called a spokeshave to smooth the propeller even more. Then they verify the airfoil's thickness and curve with a hand gauge. A spray of dark paint helps them know where they've been as they begin smoothing the propeller's surface. They remove any remaining carving marks using a belt sander. Then they check the propeller for balance. Using a pneumatic sanding drum, they perform an overall sanding and punch in propeller specifications-- diameter, pitch, flight direction symbols, and manufacturer i.d. workers hand-inspect the propeller, then perform a final sanding and balance. A coat of clear enamel seals the wood. And a safety color sprayed on the tips makes the propeller visible while it's spinning. Two final protective coats of clear enamel, 24 hours of drying time, and these propellers are ready for takeoff. When we return, fire up the grill. It's time to make some charcoal briquettes. The charcoal briquette was invented in 1897, but interest in it was slow-burning, so to speak, until the 1920s. That's when automaker henry ford decided to recycle wood scraps from car making into barbecue briquettes, and these little nuggets became a smoking sensation. Barbecuing with charcoal has become immensely popular since ford's time, and every year, several million tons of wood scraps are converted into high-quality charcoal briquettes. Today, briquette production starts with sawdust and wood chips from lumber mills. A truck unloads it all into a pit. Bulldozers blend the material called fuel to obtain a uniform end product. As the mix travels up a conveyer, an electromagnet removes any metal contaminates. The mix falls onto a vibratory screener, which sifts out the larger pieces of wood. At this point, the fuel is still very moist. To dry it, a worm screw draws the mix up into a long, rotating dryer. The dryer heats the wood mix to a searing 1,400 degrees. The dryer is sealed to prevent oxygen from leaking in. This allows the wood to dry without catching fire. After four minutes in the dryer, the moisture has been cooked out of the mix. Workers add anthracite coal to the hopper, and it mixes in with the fuel. Anthracite coal is known for burning at high temperature. Then they mix in lime. Lime makes the briquettes turn white after they're ignited-- a visual indication that the barbecue is ready to rock 'n' roll. The mix, now blackened, passes under a second electromagnet to remove any metal that could damage the equipment downstream. Finally, workers blend in cornstarch, which binds the ingredients together. A worm screw supplies the mixture to a press roll, where a constant spray of water keeps the mixture from sticking. The press rolls compact the mixture into briquettes. The process takes just a fraction of a second. At this point, the briquettes contain 35% moisture and are very soft. A screener shakes out fine material from the briquettes, which is recycled back into the process. A sweep belt transports and distributes the briquettes in a 250-foot drying tunnel. They are heated to 280 degrees for 2 1/2 hours. This will reduce their moisture level from 35% to just 5%. The lower the moisture level, the better it burns. A conveyer transports the briquettes to automated scales that weigh them for packaging. Every portion is the same, plus or minus one briquette. As the scales release the briquettes, robots below move bags into position to capture them. A sealing machine glue-seals the bags, then prints a production date and shipped code on each one. Open the bag, and a backyard barbecue is just one match stroke away. And who can resist the smokey flavor of charcoal-grilled food? When we return... Turning up a different kind of flame with gas-log fireplaces. Gas-log fireplaces are clean-burning, fully contained units that are growing in popularity. They provide instant warmth at the flick of a switch. And you'll never have to head out on a cold winter night to get more logs or clean up the ashes. To make a gas-log fireplace, workers first screw fittings to a gas-control valve. Then they attach the valve and gas pilot to the frame. The gas pilot is a small flame that burns continuously, enabling you to ignite the gas instantly. They cap the control valve with knob extensions that allow the user to control the flame's intensity from outside the fireplace. Next, they install burners and orifices. The orifice controls the gas flow in each of the burners. They attach an electrical connection from the gas pilot to the control valve... Adjust the length of the gas-pilot supply line... And screw the line to the control valve. Finally, the line is attached to the gas pilot. The fireplace's ignition system is now complete. Next, workers attach a safety device called a thermocouple to the control valve. If the flame ever goes out, the thermocouple cuts the gas supply. The unit now undergoes testing to ensure that there are no leaks. What's a fireplace without logs, even if they're replicas of the real thing? This factory makes artificial logs from a mixture of fire-resistant ceramic fibers and a liquid resin that binds the fibers together. Workers attach a log-forming mold to a pumping arm... Then immerse the arm in the mixture. The mixture fills the mold cavity. The mixture is soft when it comes out of the mold and is held together by the dense, interwoven layers of fibers. The excess fiber is trimmed off, and the log is placed on a baking rack. Then it's into an oven at 450 degrees for 5 hours. When it comes out, it's as hard as a log. Workers remove the sharp edges with a rasp, then dip the log in a mixture of binder and heat-resistant paint. Over that, they hand-paint details replicating the look of charred wood. The paint is baked on, making this decoration permanent. And it'll have no problem taking the heat. The paint can withstand temperatures up to 2,300 degrees. Back in the testing department, workers calibrate the mechanism that adjusts the fireplace flame. They use a flowmeter to verify the rate at which the gas flows. The back burner produces a yellow flame, while the front burner gives off a reddish glow. Combined, they look more realistic. Workers package the individual components and include some lava rock to simulate a bed of ashes underneath the logs. It all adds up to a beautiful, cozy fire... At the flick of a switch.