TABLE OF CONTENTS Revolving shovels were the first important power excavators. Part-swing, steam-powered dipper models mounted on railroad cars or barges were in use over 150 years ago.
Other models clamshell, dragline, and backhoe were gradually developed. In the first 20 years of the 1900s, steam power was largely replaced by internal-combustion engines and electric motors.
Also, full-swing replaced part-swing, and crawler self-propelled mountings became standard. More recently, rubber-tire carriers have become common.
Until around 1950 practically all these machines manipulated their buckets by means of cables (wire ropes), winding onto mechanically or electrically driven drums. Swing and travel depended on gear arrangements. Controls were mechanical, air, hand or foot pressure hydraulic, or combinations of these systems.
By 1975, production of cable and mechanical drives in backhoes had been largely replaced by hydraulics in all but large mining excavators. Hydraulic-operated cranes and booms are standard among smaller machines, and the hydraulic clamshell has gained acceptance. Also, the hydraulic excavator has replaced the dipper shovel in most kinds of work.
As a result, the importance of the cable-operated excavators has declined greatly, particularly among small machines. However, they are dominant as draglines, clamshells, and big cranes and dipper models.
Structure. A shovel has three structural divisions. Anatomically, the top or revolving unit is the head and torso, the mounting or travel unit is the legs, and the various attachments are the arms and hands. A revolving unit and a travel unit together make up a basic shovel.
There are five attachments (also...
