1978

Bagger 288

When digging for coal there are two kinds of mines: underground and surface. When working a surface mine, the mindset is pretty simple: scoop the coal up and ship it to a customer by rail or barge.

What if engineers want to create the biggest, fastest digging machine possible? That would be the Bagger 288, also known as a bucket wheel excavator, built by the German company Krupp beginning in 1978.

This machine is so immense that it nearly defies imagination. The digging end of it is a wheel 70 feet (21 meters) in diameter with 20 excavator scoops lining the wheel. To dig, this wheel spins. The buckets on the forward end of the wheel scoop up coal. When a scoop rotates to the top of the wheel, the coal falls out the open back of the scoop onto a conveyor. Since each scoop holds something like 15 cubic meters of material, and a scoop dumps its load every few seconds, the machine can easily move 100,000 cubic meters or more of coal in a day.

The machine has three parts. The top part consists of the bucket wheel, its motor, part of the conveyor, the operator’s cab, and the crane-like superstructure that supports it. The superstructure can move the bucket wheel up and down, and it sits on a turntable so it can rotate left and right. This structure is 310 feet (95 meters) tall and resembles a cable-stayed bridge like the Golden Gate Bridge. The second part is the rear conveyor belt and the truss structure that supports it. Together with the bucket-wheel extension, this creates a vehicle over 700 feet (210 meters) long. The third part is a set of 12 very wide caterpillar treads so the machine can move around.

This machine needs somewhat more than 20,000 horsepower (16 megawatts) to operate. It gets that power from electric motors, so it uses the world’s biggest extension cord to operate.

Could engineers make something bigger? That is difficult to imagine, because if they did it could no longer move. And the nature of the mine is that the machine has to move forward as it digs. This is about as big as moving land machines can get.

SEE ALSO Transcontinental Railroad (1869), Golden Gate Bridge (1937), Light Water Reactor (1946), Seawise Giant Supertanker (1979).

Bucket-wheel excavators 288 and 258 in Garzweiler surface mine.