Balers have a steel frame that supports a hydraulic ram powered by an electric motor-driven pump. Hydraulic oil is then pumped under pressure to the cylinder and moves the plunger (ram) against the material that is being baled. The material is packed into a dense block (bale) in the bale chamber. Once it is made, it is tied by hand or mechanically and ejected from the baler.
http://www.visionbaler.com/hyd....raulic-shearing-mach
