According to the Health and Safety Executive's guidance for the safe operation and use of mobile jaw crushers, equipment operators may be subject to multiple risks including exposure to dust, noise, whole-body vibration and being struck by objects ejected from the crusher. Technidrive developed an energy-efficient, Automatic Jaw Crusher Unblock System using WEG products entirely.

Commonly used in the quarrying, mining, recycling of demolition waste and chemical industries, jaw crushers are a reasonably complex application for systems integrators, due to the flywheel's large inertia, cyclic loading and differences in materials fed through the system.

Technidrive were approached by a customer eager to implement a new motor in their jaw crusher machine. With over 20 years of industrial drives experience, Technidrive used their expertise to meet the project criteria and exceed the initial requirements. Using a combination of quality WEG products, efficiency and reliability of the motor and the efficiency and safety of the entire jaw crusher system were improved. WEG was chosen to supply the motor, control and alternator for the project due to the quality, versatility and energy efficiency of its product line and its technical expertise.

Crushing is an essential process required to turn rock into a useable product. Rock enters the jaw crusher from the top of the machine and gets compressed between two surfaces — the fixed and moveable jaw. The rock is crushed until it is small enough to fall through the opening. Ensuring the size of raw material is appropriately matched to the jaw opening can alleviate blockage incidents. Technidrive achieved this by removing oversize product before processing and careful control of the crusher feeder. However, blockages can still occur, unblocking a crusher requires plant shut down and system isolation. Despite these precautions, a crusher continues to pose a serious risk to personnel due to the amount of stored kinetic energy released during unblocking. Technidrive wanted to develop a highly energy-efficient system, and crucially eliminated operators from the dangerous job of manually removing blocked material from jaw crusher machines.

Technidrive commenced this project by carrying out power, torque and speed calculations to decide upon a suitable selection of WEG electric motor and gear units. The electric motor selection was based on power and speed; further mechanical calculations were carried out to ensure the motor shaft could cater to the high radial loads the application can impose. The WEG W22 Premium Efficiency IE3 motor was eventually selected for its superior cast iron frame, inverter rated windings and insulated non drive end flange.

The next vital part of the system is the motor's control, which can incorporate a soft start or variable speed drive (VSD) to control the motor starting speed or torque. The VSD model selected was a CFW11 WEG inverter with built-in soft programmable logic control (PLC) functions. 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, minimise output current, and reduce electrical noise.

Electrical disturbances are not the only consideration; crusher blockages can be a real problem for operators, resulting in prolonged downtime. One of this project's main advantages was the level of control achieved through an innovative piece of software developed by Technidrive.

On a normal start from empty, the VSD ramps the crusher up on a slow ramp time, restricting the absorbed current due to the high inertia of the application. This method keeps the power supply requirements low for a more efficient system and reduces the mechanical system's stress. Over time this can lead to significant maintenance cost savings and extend the life of the machine. It is estimated that a ten-degree reduction in operating temperature typically doubles the motor's lifetime.

The innovative software allowed for a special start-up function when starting the jaw crusher from full. If the crusher is stopped full, the VSD can be remotely activated in an unblock mode, with a high-speed ramp time in forward or reverse depending on the crusher's position. It will continue to automatically control the direction, current, ramp times, DC bus voltage, torque, position, and speed until the product in the chamber has been cleared and the crusher has run empty for a set period. This innovative system removes the dangerous and laborious job operators have had to do for years, by manually unblocking jaw crushers using rock breakers or winches to remove the product.

Another essential part of the system is the alternator, which is vital to achieving an efficient and reliable design. According to the International Energy Agency (IEA), 16 per cent of motor failures are due to external conditions, such as contamination, so ensuring application suitability was essential. The alternator selected was from the WEG G-line range with some unique features such as a dust filtering system, to allow it to operate in a dusty quarry atmosphere, without the risk of foreign particles entering the system. The alternator also included a digital input AVR to allow remote voltage adjustment, standard I-PMG auxiliary winding system feature to let a dynamic response to load change and short envelope compared to traditional external PMG alternators.