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Metal Forming
Published in Sherif D. El Wakil, Processes and Design for Manufacturing, 2019
In drop forging, a type of closed-die forging, the force generated by the hammer is caused by gravitational attraction resulting from the freefall of the ram. The ram may be lifted by a single-acting steam (or air) cylinder or by friction rollers that engage a board tightly fastened to the ram. In this latter type, called a board hammer, once the ram reaches a predetermined desired height, a lever is actuated, the rollers retract, and the board and ram fall freely to strike the workpiece. Figure 5.42 illustrates the working principles. Whether a board hammer or single-acting steam hammer is used, accurate matching of the two halves of the die (i.e., the impressions) must be ensured. Therefore, the hammers employed in drop forging are usually of the double-housing (or arch) type and are provided with adequate ram guidance. The desired alignment of the two halves of the die is then achieved by wedging the upper half of the die onto the ram and securing the lower half onto a bolster plate that is, in turn, tightly mounted on the anvil. Also, the ratio of the weights of the anvil and the moving parts can go as high as 30 to 1 to ensure maximum efficiency and trouble-free impact.
Developing Early Iron Armour: The Development of Rolling as the Preferred Method of Manufacture Between 1854 and 1863
Published in The International Journal for the History of Engineering & Technology, 2022
The main methods of manufacture could be divided into forging the final plate from slabs under a steam hammer or welding layered plates together in a rolling mill. The advantage of forged armour plates was that the hammer exerted sufficient force to weld the slab of iron together; it was, however very difficult for even a skilled hammerman to work the plate evenly and the quality of the plates was inconsistent. The Committee on Iron interviewed James Nasmyth who, not surprisingly in view of his role in the development of steam hammers, took the view that hammered plates would produce ‘a better kind of iron’ and that although rolling could be used in the early stages of the process ‘… to make the blooms necessary for plates of the usual thickness […] they would need to be put together under the hammer.’22