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Stone crushers have played a pivotal role in the history of America since its creation in the mid-1800s. Since then millions of tons of stone have been crushed to make everything from houses to roads and everything in between.
The first stone crusher was invented by Eli Whitney Blake, the nephew of Eli Whitney, the creator of the cotton gin. After five years, Blake鈥檚 stone crusher roared to life, thanks in part to a challenge laid before him by the town of Westville, Conn. The purpose was to put down a rock surface on the roads so wagons wouldn鈥檛 get stuck in the mud. Blake went further with the design and developed it for the railroads to create ballast.
In the 19th听century, rock crushers proved valuable in laying roads to a growing nation. On top of that, they also were used to extract precious metals out of giant blocks of stone.
鈥淩ock crushing is driven from a population standpoint because it鈥檚 the population that鈥檚 demanding the aggregate. Every type of aggregate that鈥檚 consumed, people consume it every day of the week. Whether you鈥檙e building a house or a church, a school building, or laying down highway 鈥 90 percent of the asphalt they put down on the road is stone, the rest is sand and听liquid asphalt. You know, 60 to 70 percent of concrete is made up of stone; the other is sand and the rest cement. You look at these needs and no one has been able to come up with a type of artificial resource that could be developed to take the place of stone. Every mile of highway requires 38,000 tons of stone.鈥
~ Rich Blake, president and CEO of Mellott
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According to the industry,听for every person in the area, you have to supply 10 to 12 tons of rock per year.
It鈥檚 no easy feat turning giant walls of stone into small, uniform rocks. Take the Metso Minerals 4265 Superior Gyratory Crusher, for example. It鈥檚 total weight of 264,000 pounds is housed in a 10-story high reinforced steal tower. The powerhouse is pushed by a 500-horsepower electric motor. Because of that, the gyratory crusher is capable of handling 2,557 tons of stone per hour.
In 1881, Philetus W. Gates was granted a patent on the gyratory crusher. It鈥檚 given that name because of the motion that actual does the crushing. A relentless back and forth gyration compresses the stone against the chamber walls.
Think of it as a Giant Mechanical Nutcracker
You have two hard surfaces closing together with a soft surface in the center 鈥 in this case, the rock is the soft surface. So, the two metal parts come together and compress the rock into a smaller size.
The crushers are designed to work in the choke-fed position because the rocks on top of the crusher help push down the rocks through the crushing chamber. The rocks will actually crush against themselves. That鈥檚 called rock-on-rock crushing. Larger crushers can handle rocks up to 3 feet in diameter. Anything bigger gets broken up by a hydraulic hammer.
鈥淭he overall principle of crushing is twofold. One is what they call compression crushing, and the other is what we refer to as impact crushing. Compression crushing is taking some type of stationary anvil, adding some type of eccentric anvil, and have rock enter a chamber. The rock would enter the chamber and gravity would pull the rock through. As it鈥檚 going through, the eccentric motion would crush that piece of rock.鈥
~ Rich Blake, president and CEO of Mellott
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The main shaft of the Metso 42X65 crusher weighs 52,000 pounds. As the main shaft rotates, it moves in an eccentric pattern, which crushes the rocks. It rotates 170 times a minute against the chamber walls which are solid, reinforced steel.
According to Blake, there are probably听upwards to 30,000 active stone crushers working in the United States today. Some can be as small as 2 feet in size and some could go as large as 10 feet.
Depending on the desired product, the stones can travel听through three or four different types of stone crushers.
As with all heavy machinery, safety comes to the forefront.
鈥淔irst thing, with anything safety, is awareness. The difficulty you had 50, 75, 100 years ago was people weren鈥檛 aware that things were unsafe. It was the same reason people would repel off of cliffs听of rock when they were building dams, or they wouldn鈥檛 use safety nets when they were building bridges. People weren鈥檛 aware of the force of crushing rock could be upwards to thousands of pounds. Some rock are 50,000 PSI rock that you鈥檙e crushing.鈥
~ Rich Blake, president and CEO of Mellott
Blake said he wouldn鈥檛 classify the stone crushers as being unsafe or hazardous, thanks in large part to safety procedures and new technology.
鈥淭oday, some of the technology that鈥檚 available is quite amazing,鈥 said Blake. 鈥淭he technology today checks the temperature of bearings and measures the overall force of the crusher. One dangerous event is when uncrushable materials – such as a piece of wood, rubber, or steel – enters the crusher. When that happens, today’s crushers have a built-in safety mechanism as to not damage a shaft or bearing.”
The size of the crusher machines have changed, but the general principle has not changed since the late 1800s.
