Gallows Frame

A headframe (also known as a gallows frame,winding tower,hoist frame,pit frame,shafthead frame,headgear,headstock or poppethead) is the structural frame above an underground mine shaft.

Modern headframes are built out of steel, concrete or a combination of both. Timber headframes are no longer used in industrialized countries, but are still used in developing nations. Conventionally steel headframes are used when a drum hoist is employed, and concrete headframes are built for friction hoists; however a steel headframe can be used with a friction hoist for shafts with a smaller capacity and depth.

A steel headframe is less expensive than a concrete headframe, providing the height (defined as the vertical distance from the collar elevation to the center-line of the highest head sheave) does not exceed 50 m. Steel headframes are more adaptable to modifications (making any construction errors easier to remedy), and are considerably lighter, requiring less substantial foundations. As steel headframes are easier to design, they have the potential to utilize "off the shelf" design tools. Construction of a steel headframe can be easily interrupted and restarted if necessary for statutory holidays or bad weather, where slip forming concrete is not. Upon mine closure and mine reclamation a steel headframe is easier to demolish and may have value as scrap metal.

A recently erected steel headgear in the Zambian copper belt town of Chililabombwe at the Konkola number 4 shaft has a total height of 81 metres to the top of the maintenance crane rail, with the centre-line of the head sheaves at 71 metres above the collar, making it the highest steel headgear in Africa.

Concrete headframes require less maintenance and are less susceptible to corrosion than steel headframes. There is much less waste of concrete during construction of a concrete headframe than there is of steel in construction of a steel headframe. Concrete headframes provide an enclosure upon construction, whereas steel headframes require cladding and insulation to protect from weather. Concrete headframes are less susceptible to vibrations and sway less during high winds. Concrete is usually more readily available than steel (except in remote locations), and the price is predictable, whereas fabricated steel prices can be volatile.

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Wikipedia