A variety of complex factors are involved in the production of hot asphalt mixes, which makes the process vulnerable to sudden equipment stops. The consequences of such unplanned maintenances to the business are dire, since the cost of having a stopped plant is high. In order to minimize production disruptions, new technologies applied to wear components and electronic monitoring of asphalt plant motors during production bring predictability to maintenance, replacing corrective maintenance with preventive and predictive maintenance.
Preventive maintenance is a widespread concept applied to equipment that has the goal of scheduling machine stops according to the expected amount of wear, based on average statistics of generic applications. Predictive maintenance on the other hand is much more complex because it considers the current conditions and the dynamics of the components, according to a specific application, in order to schedule maintenance at the correct time. According to Marcelo Zubaran, application engineer and product specialist at CIBER Equipamentos Rodoviários, “obtaining the correct information at the right moment regarding a component wear or a tendency of failure of a motor is a major advantage to asphalt mix production”. Predictive maintenance can only be implemented with devices continuously monitoring the equipment components, be it mechanical or electronic devices.
Components with an abrasive wear profile developed over the life time of the tool could use a predictive maintenance plan. The plant’s mixer vanes exhibit wear proportional to the time used and thus, through physical markings on the vanes, it is possible to have a visual response on the wear level and predict when to replace the component. The conditions of the plant’s bag filters are monitored indirectly during production through pressure meters installed in the filter box, which indicates if the filters are likely to saturate. This prevents further damage to the filter elements and even wear of the plant hood.
On the other hand, state-of-the-art technologies such as constant monitoring of the power consumption of motors during production, known as the fault diagnosis system, also provide valuable information to the operator in real time on the operating conditions of the motors. “If any of the plant’s motors are not operating at its optimum condition, the plant immediately triggers an alarm. The operator may choose to conclude a particular asphalt mix demand and then check the conditions of such motor or stop the plant. In this way, predictive maintenance technology allows us to perform preventive maintenance”, according to Marcelo Zubaran.
To enable this technology, it is necessary for the motors to be connected to an electrical current measuring device and for such device to be connected to some data transmission network. Frequency inverters coupled to motors, which allow varying their rotational speed, are capable of measuring the current of a motor. In addition, technologies such as Soft Starter, which smooths the start of “big” motors without frequency inverters can measure the electric current, and integral starter systems, like Tesys U, can also measure the current of motors. Such devices must have a network interface in order to enable digital communication with the plant’s computer, which will manage this information through a software.
These technologies tend to minimize unplanned stops and enable assertive maintenance planning. As a consequence, productivity is increased, production and logistics costs are reduced, which is the only possible way of achieving just-in-time logistics.