Enerpac Lifting Systems reduce shovel downtime
Large shovels used in the open cast mining of limestone for cement manufacture require regular maintenance. Reducing the time needed to lift and service the shovel is made possible using synchronised lifting systems developed by hydraulic systems specialist, Enerpac.
Typically, mining shovels need routine maintenance after 30,000 hours of operation. This requires the upper shovel section to be lifted off the car body to machine bearing surfaces and inspect and repair structural components. Weighing approximately 1,000 tons, lifting the upper car body requires a significant amount of force and control, it’s also time consuming and hazardous.
Enerpac has developed a shovel lift system that undecks a shovel in approximately one hour and can be readily transported on the highway. The system comprises four 500 ton cylinders with 72 inches of stroke, an Enerpac EVO synchronous control unit and four custom 8000 series hydraulic pumps. Each pump is built to operate in extremely cold or hot environments. The EVO synchronous control unit enables a single operator to control the entire lift and ensure each lifting point remains within 3/8 of an inch; with all lift points constantly monitored and automatically controlled, concerns about overstressing the structure due to uneven lifting are eliminated.
Accurate synchronised lifting using a hydraulic pump and hydraulic cylinders (single- or double-acting cylinders) is critical to the success of the shovel lift system. To achieve high precision movement, a method to efficiently control and simultaneously synchronise movements of multiple lifting points is required. The Enerpac EVO system manages this using by a PLC (Programmable Logic Controller).
The PLC monitors each cylinders’ stroke movement and load. It constantly reads stroke sensors, measuring cylinder stroke and detects deviations between the leading and lagging cylinder positions. The PLC receives these signals and interprets which corresponding electro-valves to operate, by switching to the open or closed valve position; oil flow to the cylinders is allowed or blocked. Thus, the faster cylinders stop and wait for the slower cylinders, until all cylinders are within the defined synchronous working tolerance.
The synchronisation of cylinder movements mitigates the risk of undesired load shifts and unbalanced load distribution, which could potentially cause a structure to bend tilt or twist undermining its structural integrity. The PLC-controlled hydraulic movement increases safety by eliminating, and not depending on - manual intervention to manage load-shift or other issues. Comprehensive understanding and management of a lifting operation from a central control system also improves safety and operational productivity.
The EVO-system offers fail-safe control and monitoring using fixed and project specific programmable operating parameters, including hydraulic conditions for; oil level and temperature and operational safety alarms for permissible load (individual and accumulative) and synchronous stroke tolerance parameters. Programmable data recording and “differential-lift” options reduce maintenance times by allowing a load to be manipulated into a pre- set position. Differential lift options means that various cylinders have a different starting position (different heights), for example when the object to lift has an irregular shape. Synchronisation is achieved by controlling the pump’s volumetric oil flow to each cylinder, consequently determining each cylinders’ stroke position.
In addition to lifting systems, Enerpac also supplies skidding systems for moving heavy plant equipment. These too are powered by hydraulic cylinders connect to a split flow pump, enabling single operator control of skidding loads up to 400 tons. For shovel maintenance Enerpac also supplies a wide range of bolting tools including torque wrenches and pumps, as well as portable milling machines.
Communication from the management of the company