A hydraulic shear is an excavator-mounted attachment used to cut steel beams, reinforcing bar, pipe, and structural steel sections during demolition and dismantling work. It replaces or complements the bucket on a hydraulic excavator and derives its cutting force from the carrier's hydraulic system via a dedicated cylinder acting on one or two moving jaws.
Working Principle
A hydraulic cylinder drives a moving blade against a fixed counter-blade, generating a shearing action rather than a crushing or impact force. The jaw geometry concentrates force at the blade tip, allowing material to be severed progressively from the point of contact toward the pivot. Most units offer continuous 360° hydraulic rotation, allowing the operator to reposition the jaw without repositioning the carrier.
Design and Components
Core components include the housing, the hydraulic cylinder, the fixed and moving jaw with replaceable blades, the rotation motor and gearing, and the mounting bracket or quick-coupler interface. Blades are bolted or pinned to the jaw body so they can be replaced or indexed as cutting edges wear or chip. Jaw shapes vary: straight blades for flat steel sections, and profiled or notched jaws for round bar and pipe.
Classification by Carrier Weight Class
Shears are sized to match excavator operating weight. Compact units are typically designed for carriers in the 5–15 t class, with jaw openings in the range of 300–600 mm. Mid-size shears are matched to 20–40 t carriers, with jaw openings up to roughly 900 mm. Heavy demolition shears for carriers above 40 t, used on high-reach demolition machines, can reach jaw openings above 1,000 mm.
Technical Parameters
Cutting force at the blade tip rises with jaw size and hydraulic pressure, ranging from several hundred kN on compact models to several thousand kN on heavy-duty units. Attachment weight ranges from roughly 500 kg for small units to more than 10,000 kg for the largest demolition shears. Required hydraulic flow and pressure are specified by the manufacturer and must match the carrier's auxiliary circuit for correct cylinder speed and force output.
Blade Material and Maintenance
Blades are manufactured from hardened, wear-resistant steel, commonly in a Brinell hardness range of roughly 400–500 HB, to withstand repeated contact with structural steel and rebar. Blade edges are indexable or reversible on many models to extend service life before replacement. Pivot pins, bushings, and the rotation gearbox require scheduled lubrication and inspection for wear.
Application Areas
Hydraulic shears are used in building demolition for cutting structural steel framing, in scrap processing for sizing steel sections, and in reinforced concrete demolition in combination with other attachments to separate rebar from concrete debris after breaking. Dedicated scrap and demolition variants differ mainly in jaw geometry and blade profile rather than in basic working principle.
Mounting and Carrier Compatibility
Attachment to the carrier is via a pin-on bracket or a hydraulic quick-coupler, with the rotation drive and cutting cylinder connected to the excavator's auxiliary hydraulic circuit. Correct matching of carrier operating weight, hydraulic flow, and attachment weight is required to maintain stability and achieve rated cutting force.