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Among the various factors which are used to determine the productivity of an extrusion press, the dead cycle time is one of those which can best define the level of performance of the machine and the technical expertise of its builder. This consideration, however, must be made from comparable measurements, for example, of the dead cycle time, which, usually, is considered as being the period between the end of extrusion of a billet 'n' up to the end of upsetting of the next billet 'n&l'. And, in any evaluation of the performance of a press a particular billet length and diameter must be used to define dead cycle time. G Bessey elaborates.
The length of the chosen billet can be the maximum billet length for the press, or more precisely the estimated average length according to the programmed production mix. It is true, in fact, that most presses have a dead cycle time that varies in relation to the billet length.
One second reduction in dead cycle time represents from 0.7% to 1.0% gain in productivity, according to the level of performance of the user.
The majority of presses now being used in the world have dead cycle times which are 5sec to 20sec higher than those that may be obtained by using technology developed by the author's company, technology that also allows presses to operate at normal speeds without impairing reliability.
Methods used to reduce dead cycle time
Most methods that are involved in the reduction of dead cycle time relate to the hydraulic equipment and the automatic control equipment on the press. And, as regards the former, the use of logic valves which operate at speeds higher than those of three-way types are recommended.
It is, however, useful to note that the performance of such components can change according to the circuit in which they are installed, and for each machine an initial set-up by a specialist is necessary. The best possible adjustment of communication must be obtained by changing the various parameters of each valve, such as: