Heather Caliendo
The recycling industry is shifting towards integrated engineered systems rather than individual components pieced together throughout the size reduction process. We talked in our last article about how manufacturers and recyclers are becoming more sophisticated with size reduction equipment while also more aware of the value of reclaiming off-spec parts and other product waste.
After all, a systems-based approach supports a more efficient, resilient and sustainable recycling ecosystem. And the success of any recycling operation is high production rates with minimal interruptions.
But still day-to-day operational headaches can occur even in well-designed systems. Overlooked integration details will result in inefficiencies, production bottlenecks, and increased maintenance downtime. It’s important to identify and address the weak links in order to keep production running smoothly and the money rolling in.
Feed Problems
The conveyor is usually the first piece of equipment in the integrated recycling system. Robust design is necessary from gearbox/motor choices, bearing and roller design, quality belts with true guide belt tracking as all Rotogran conveyors have.
Granulators work at their highest production efficiency when meter fed at a constant rate within the granulators’ production capacity. Integration of the conveyor controls with feedback of the granulator motor load and running status improve production efficiency by reducing downtime from material overload and preventing shock loading of the granulator.
Shock loading is the condition where a large amount of material is introduced into the granulator in a short period of time. For example, when a granulator rated for 1000 lbs/hr is fed 100 lbs in 2 minutes, then that calculates to 3000 lbs/hr. Shock loading as per this example leads to premature granulator drive component failure including drive belts, bearings, classifying screens, broken blades, and possible damage to the granulator cutting chamber. When the granulator is fed by a shredder the chances of shock loading occurring are much higher. These can be costly repairs in terms of money and downtime.
Metal detection systems designed into the conveyor prevent tramp metal from entering the granulator. Tramp metal compromises the quality of the regrind and often damages blades, which can cascade into additional failures
Another conveyor feature that Rotogran offers when supplying conveyors as part of an integrated recycling solution is to offer a “sound tunnel” on our conveyors to further absorb sound coming out of the granulator hopper opening. The sound tunnel is exactly that, a tunnel lined with sound-absorbing material to reduce overall sound levels generated from the granulating process. While this does not directly increase production, it improves the plant environment and overall personnel efficiency.
Evacuation Systems Challenges
The role of the evacuation system is to pull processed material out of the granulator and move it to a collection or storage bin. While the process seems simple, there are problems that can occur which need safeguards. In an integrated system, the evacuation system must be running before the granulator and conveyor can be started. Airflow is monitored to ensure there is not a blower failure or blockage in the line.
Additionally, there can be sufficient airflow but perhaps a buildup of material in the collection/evacuation bin of the granulator prevents material flow resulting in material backup into the granulator chamber. This can cause a material meltdown and even a fire. Integration monitors the system and prevents such occurrences, and the downtime and financial costs relating to them.
Bearing Selection and Design
Granulating materials can create excessive dust and fine particles that lead to premature bearing failure from plastic contamination. Rotogran has a unique flange-mounted bearing assembly that spaces the main rotor bearings away from the cutting chamber allowing a gap for fines and dust particles to fall through, exiting the granulator away from the bearings.
This extends the life of the bearings, thus reducing downtime and cost associated with bearing replacement.
Selecting the Right Machine
Plastic processors focus on repurposing in-house scrap, so their granulation system requirement may be 2,000 lbs/hr capacity (required for their complete reject part size) which only runs at 20% most of the time for normal trim etc. Some size reduction manufacturers started building lighter duty granulators for this reduced capacity application.
However, recyclers are all about production. So, it’s vital to have a well-built heavy-duty granulator as part of the complete integrated granulation system in which Rotogran excels.
Some Rotogran features include solid A36/44W steel flywheels instead of open-spoke cast iron designs and an additional second non-driven solid steel flywheel is added to increase the inertial effect of the rotor assembly.
Solid steel rotor blade mounting blocks supporting the rotor blades across the width of the granulator chamber not only offer superior blade support but adds to the rigidity and inertial effect of the rotor assembly. The added inertial effect carries stored energy into every cut resulting in efficient use of the granulator’s drive motor and reduces operating cost. This also allows the granulator to slice through thicker wall parts without slowing down the rotor (also reducing power consumption).
Built Strong
Build quality matters, and you must know your process requirements. Rotogran is a manufacturer who does real front-end application engineering, evaluates your specific scrap type, volume, and production goals, and most important, stands behind it with a performance guarantee.