Unblocking jaw crushers often involves employing rock breakers, hammers or winches to dislodge material – a hazardous manual task for the operators involved. Here’s how Technidrive helped RJ Mitten & Sons, a Northern Ireland-based quarrying specialist, with a significant upgrade to enhance the safety and efficiency of its jaw crusher machines.
Teaming up with Technidrive, renowned for its expertise in industrial drive systems, RJ Mitten & Sons installed two new jaw crusher unblock systems at its Rockfield quarry site. The crusher unblock systems were retrofitted onto RJ Mitten’s existing Kue-Ken primary jaw crusher and secondary jaw crusher, powered by 75 kW and 55 kW motors respectively. As these machines were over 40 years old, the new unblock system has given the crushers a new lease of life both increasing energy efficiency and safety.
Crushing plays a crucial role in the transformation of rock into a usable product. At the onset, product enters the jaw crusher through the machine’s top and undergoes compression between two surfaces — the fixed and movable jaw. This process continues until the rock attains a size small enough to pass through the opening. Properly matching the size of the raw material to the jaw opening can help reduce blockage incidents.
Strategies such as removing oversized products before processing and meticulously controlling the crusher feeder can aid in this endeavour. However, despite these measures, blockages still occur. In fact, before the upgrade, RJ Mitten was experiencing blockages a couple of times a month. Clearing a blocked crusher necessitates shutting down the plant and isolating the system.
Even with these precautions, crushers pose a significant risk to personnel due to the release of kinetic energy during unblocking. It was necessary to physically hang upside down in the crusher and use straps and a rock hammer to release blocked product.
Recognising this risk, Technidrive aimed to develop a system that not only prioritised energy efficiency but also eliminated the need for operators to manually remove blocked material from crusher machines.
Technidrive’s approach focused on developing an energy-efficient and automatic unblocking system for the jaw crushers. The selection of electric motors and gear units for the system is essential. This choice was complemented by integrating a CFW500 WEG inverter with built in soft programmable logic control (PLC) functions, to control the motor.
There were several advantages to this selection, including the standard DC bus chokes to reduce harmonics. The inverter was selected with an output sinusoidal filter to create a nice sine wave, reduce output current and importantly reduce electrical noise.
The installation, conducted by RJ Mitten’s in-house team, was swift, taking just half a day to complete. The jaw crusher unblock systems have been in operation for 18 months now, showcasing remarkable improvements in safety and productivity.
“Previously, it would take two to three hours to clear a blockage in the jaw crusher,” explained Noel Mitten, partner at RJ Mitten & Sons. “Thanks to the upgrade, this task now only requires ten minutes, showcasing the significant efficiency gains we’ve achieved. Crucially, we no longer have to perform this manually.”
One of the groundbreaking features of the upgrade is the innovative software developed by Technidrive. During a standard start-up procedure from a standstill, the variable speed drive (VSD) gradually accelerates the crusher with a slow ramp time, limiting the absorbed current due to the considerable inertia of the application. This not only minimises the power supply demands, enhancing system efficiency, but also alleviates strain on the mechanical components.
Consequently, this approach can result in substantial savings in maintenance costs and prolong the machine’s lifespan.
Moreover, the advanced software facilitates a specialised start-up function for situations where the jaw crusher is fully blocked. If the crusher is halted while full, the VSD can be activated in an unblock mode, swiftly initiating a rapid ramp time either in forward or reverse, contingent upon the crusher’s position. It automatically regulates various parameters including direction, current, ramp times, DC bus voltage, torque, position and speed until the chamber is cleared of product and the crusher operates empty for a predetermined duration.
“This system eliminates the hazardous and labour-intensive task operators traditionally face when manually unblocking crushers,” explained David Strain technical director at Technidrive. “Crucial to the system’s reliability is the VSD, carefully programmed to ensure efficient, reliable and safe operation for the motor and mechanical equipment, equipped with specialised Unblock program. Since we first developed this system in 2016, we’ve installed over 80 crusher unblock systems and continue to increase crusher safety and efficiency across the globe for both end users and OEM’s.”
