EAT309 €“ DESIGN
Hydraulic Cutting Equipment for the Electra-Hydraulic Power Pack
MW
PLEASE READ ALL OF THE FOLLOWING VERY CAREFULLY
In 2010 our company designed and manufactured a very successful product in the form of
an easily transportable power pack, capable of providing electrical and hydraulic power for
use by aid agencies at disaster sites around the world. The main application of unit was to
provide electrical power for lighting and medical support systems and hydraulic power to
drive essential lifting equipment and cutting gear.
in subsequent years the unit has undergone successful upgrades, the most recent of which
has produced an increase in the hydraulic power available from the unit. Feedback from
oW customers has indicated that as a consequence the performance of the currently supplied,
he: vii proprietary hydraulic cutting equipment falls significantly short of the hydraulic capability of
miré the unit.
The Technical Director and Finance Director have since decided that we have no choice but
to explore the possibility of designing and supplying our own cutting equipment. A market
survey of some of the proprietary equipment available has informed some initial details. The
general design is to follow a conventional shears’ type arrangement employing two blades
which are to be powered by two identical hydraulic cylinders. A schematic of the
arrangement with principal dimensions is shown in figure 1 below. In the closed position i
there needs to be a 4° overlap of the blades in the closed position and the angle between 3
the blades when the shears are in the fully position is 120°. To reduce costs’and I l
minimise the variation in spare parts needed to support the design it has been decided that I
exactiy the same sized hydraulic cylinder is to be used for each blade. This means that each
blade will travel through an arc of 62° from the fully to the fully closed position.
Based upon information received from customers and after initial tests in the development
laboratory it has been found that the shears should be capable of exerting a force of 7.5 kN
at the mid-point of the blades when the shears are in the fully position.
To avoid the risk of accidental damage to any personnel or equipment it has been
determined that the angular velocity of the blades as they close must not be any more than 2
revolutions per minute about the pivot point. Similarly, when ing the blade velocity must
not exceed 15 revolutions per minute. Flow control devices will need to be incorporated into i
the unit to accommodate this. 1
To prevent over pressuring the hydraulic shears it will also be necessary to include within the
unit a valve which limits the working pressure to 85bar.