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Hydraulic Cylinders in Walking Beam Furnaces

Hydraulic cylinders or actuators provide the lifting and traveling functions that are characteristic to walking beam furnaces. The walking beam function moves the steel slab or stock from the charged to the discharge sides of continuous, reheat furnaces. Walking beam furnaces have several advantages over pusher-type furnaces. The walking beam furnace allows the heating of the bottom side of the steel slab, which gives greater flexibility in slab size and reduces heating times as well as furnace sizes. Walking beam furnaces provide better control of heating and give more consistent discharge temperatures. Walking beam furnaces reduce the skids marks and abrasive damage to the bottom side of the steel slab. In addition, slab pile-ups and the sticking together of steel slabs is eliminated. Walking beam furnaces are also bi-directional, which is another advantage of over other types of furnaces.

System Operation

Walking beam furnaces use an electro-hydraulic positioning system and cyclical operating cycle that repeatedly moves the steel slabs or stock through the furnace in an oscillating, lift-move-lower-lift sequence. At the beginning of this operating cycle, steel slabs rest on stationary ridges of the charge side of the furnace. The steel slabs move through the furnace in an apparent “walking” movement by first enabling the hydraulic lift actuators that pivot bell cranks to lift the steel slab above the stationary ridges of the walking beam furnace. Once lifted, a hydraulic travel cylinder pushes the walking beams with the steel slabs for the distance of the hydraulic travel cylinder’s stroke. Then, the lifting cylinder retracts and lowers the steel slab to rest on the stationary ridges again. The travel cylinder then returns to its home position where the lifting cylinder pivots the bell cranks to lift the steel slab again thereby repeating the operating cycle.

Hydraulic Cylinders

While the lifting and traveling hydraulic cylinders of walking beam furnaces are for the most part custom-made, as a general category of mechanical actuators, they do possess a number of standard features. The most common features are single- or double- acting, telescopic, servo-positioning (with servo motor), zero-leakage, high temperature, standard speed (0.5 meters per second), high frequency, high pressure (up to 3000 psi) and capable of operating for a long time in hazardous (chemical) environments due to the application of anti-corrosion coatings. The cylinders are constructed for small, medium, large, extra-large and heavy-duty applications. NFPA-type cylinders are readily available. They are made of honed steel, medium hardened steel or cast iron with treatments such as, black oxide, nitrided, or phosphated. The materials generally meet the standards according to ASTM, ISO, CSA, SAE, API, BSI, CEN, as well as others. In addition, the piston rod end attachment style is customer-specified and can range from threaded rod end, single male clevis, bearing with swivel, among others. The mounting style is variable, including welded cap, bolted cap and tie rods. The piston rods are typically coated with chrome, nickel-chrome or sulfamate nickel. The inside of the barrel is usually is chrome plated. Prior to placing the cylinder into operation, they are tested hydrostatically and undergo non-destructive testing