Taking Control

A dozen or so years ago, there were few sophisticated control systems in the scrap metal recycling industry. However, as the complexity of the systems has increased over the years, improved control and more information have become essential parts of the shredding operation. The use of a control console loaded with push buttons has become impractical.

The programmable logic controller (PLC) has played a major role in the world of process control for a variety of industries for more than 30 years, though it is relatively new to the scrap industry. Engineers have utilized the power of the PLC in the baking, food, beverage, chemical and a host of other industries to control the processes required to produce quality products as efficiently as possible.

The recycling industry has changed considerably during the last decade. It is no longer just selling scrap. Recyclers have truly become processors of recyclable materials, producing a variety of products, much like a plant making cereal, bread, soft drinks or even cars. It really has become quite a process.


The Role of the PLC
Downstream of the auto shredder, ferrous and nonferrous recovery systems are becoming more complex, utilizing a variety of separation and sorting equipment. As this complexity increases, a need for a better control system arises—a method that is straight forward, easy to troubleshoot and maintain and transparent to the operators.

The basic function of a PLC is to replace hardware components, such as relays, timers, counters and so on, with software. Panels loaded with relays have been replaced by a compact computer and a software program. The first big advantage is the elimination of the inevitable mechanical failures, not to mention the nightmares sometimes associated with troubleshooting problems with the older systems.

Contrary to what some may think, the PLC-based system can greatly reduce the complexity of the control system. A maintenance electrician will typically only have to deal with the field devices themselves, not with the logic behind their operation. In addition, the wiring and subsequently the drawings have become less complicated thanks to the PLC and networking.

Once the PLC program is written and tested—thoroughly debugged, if you will—that program does not change unless a technician makes changes. If it worked yesterday, it will work today. The PLC may have an occasional bad input/output and things like that, but it is designed so that you can count on the code being the same day after day. When the electrician starts to troubleshoot a problem, he does not have to sort through a hundred relays to see what has failed. All those relays are now software, they can’t fail mechanically. As a result, the number of items a maintenance person has to sort through has been greatly reduced.

Having your systems provider connected to your process via the Internet can be beneficial as well. Your supplier can help you troubleshoot using the ladder logic in the program. It can quickly point to the input that is missing or the device that may be an issue.

The trend throughout the last few years has been the move toward remote motor control panels connected on an Ethernet backbone. This greatly reduces the length of 480-volt motor leads in the field and all but eliminates control wiring in the field. Electrical control panels for new installations and retrofit plants are generally shipped completely wired and tested. The electrical contractor basically sets the panels and provides power, motor leads, emergency stops and an Ethernet cable. Even field controls for maintenance functions are now self-contained RF (radio frequency) units, completely eliminating field wiring for those devices.

The PLC has given us a lower cost system from the design phase through fabrication, installation, maintenance and future modifications.


Systems Integration
Part of the modern control system is the aspect of “systems integration.” Basically, that simply means tying all of the various pieces of equipment together under one control system, including control, operator interface and information flow. Instead of a dozen vendor-supplied subsystems, the operator sees the system as one process. Everything that happens in the system can be seen from one central SCADA (supervisory control and data acquisition) system.

Along with a few other features we will discuss, this integrated system helps to make the operators more a part of the process. They are spending less time making things happen and more time monitoring the process. The operator is no longer just another component in the process. Instead, the operator becomes the process monitor, the master sensor, if you will. The operator in the tower becomes the orchestrator of the process, watching for un-shreddables, helping the crane operator keep the feed consistent and watching for potential problems in the downstream.

You would be surprised what process improvement ideas they come up with when their focus is on the process and not on the feed shoot for eight hours.

Additional valuable tools in this whole process are the automated shredder controls, or the software and associated hardware devices that provide for automatic control of the shredder itself. Typically these modules control the in-feed conveyor speed and direction along with the feed-roll speed, direction and position. Auto pilot is a term loosely used by every integrator that has ever put a bit in a PLC to stop the infeed conveyor. Not all automatic shredder controls are the same, however. Some work, some don’t.

Having the shredder controlled automatically is an important part in having operators become more in-tune with the whole process.

A properly designed and well-tuned co-pilot type system should generally out-perform an operator over the course of a daily production shift. It has been proven time and time again that these systems can increase shredder throughput by providing a consistent load on the mill and can produce a higher quality shred by keeping the box full. However, it is still important for the crane operator and shredder operator to work together to provide a consistent flow of material on the in-feed conveyor.

Other advantages include reduced risk of complications in light of work stress on the wrists, lower operator fatigue, a reduction in mill plugging and a shorter learning curve for training new operators.

Quality automatic pilot systems can be integrated into any existing shredder system. When considering one of these systems, shredder operators should look for one with a proven track record and definitely should get some references. Look for one that integrates smoothly into your system. It should provide automatic control but also allow for quick transitioning back to full manual control. You should not lose your ability to run manually. Also, the controls should be operator adjustable to allow for variations in the types of scrap you may run at different times. They are available for new and existing installations on both DC and AC applications.


Information
Information is important as it contributes to continual process improvement. The operator and operations facilitators need feedback from the process to maximize throughput, minimize downtime and develop effective preventive maintenance routines. A proper SCADA system combined with a comprehensive reporting and downtime analysis software package can be a valuable resource, providing current and historical data. The more sophisticated packages utilize a SQL (structured query language) database platform and provide for data manipulation and reporting from a friendly Excel type environment.

Downtime tracking software can eliminate the need for manually recording, submitting and analyzing reports. A downtime package can show the plant layout and allow for quick icon selection of where the downtime occurred and which of the common causes created the event. A daily report can provide details on each day’s listing of downtime events and also detail how much of the total downtime was caused by any single piece of equipment.

Power monitoring and, more importantly, power management are becoming significant parts of an integrated system. Not only can users create energy usage and billing reports; but, when coupled with an intelligent automatic pilot system, the demand-limiting technology can make it possible to maximize shredder throughput while limiting energy peaks and demand charges.

Typically, system monitoring and reporting are available via the Internet. Users can monitor the shredding process live or can generate reports based on current or historical data anywhere they can access the Internet.

As you can see, it all ties together. It’s that systems integration thing. It’s called Plant Floor to Top Floor, giving the operators the tools to efficiently run the process, monitor and report information from the process, analyze it and use the results to improve the process.

An independent process control provider, with experience in the shredding industry, can provide you with quality, proven solutions for your company’s shredding operation.

Joe Jindrich is president and CEO of Pinnacle Engineering Inc., Cedar Rapids, Iowa. Pinnacle has provided process control solutions to a variety of industries for more than 16 years and has more than 130 ferrous and nonferrous systems in operation around the world.