By minimizing—or even eliminating—carryover, effectively handling difficult material compositions, and reducing routine maintenance requirements, manufacturers will position their facility for consistently efficient processing.
By Mike Hook
When it comes to conveying recyclable metal, there are several universal—yet crucial—considerations that need to be made to ensure the conveyor will perform efficiently and reliably, including:
• How heavy will the load be?
• What volume of material will need to be conveyed?
• How far will the material have to travel?
• What will the composition of the material be?
• Is the material wet or dry?
• Is the material flowable?
Conveyors that move metal scrap are workhorses. However, metal scrap conveyors are not one size fits all. Metal scrap, which can be dry or coated in cutting fluid, comes in many types and forms: flowable chips, bushy bundles of turnings, stampings, and other large pieces of metal. This creates a dynamic set of application criteria that the conveyor must be engineered to handle.
While selecting a conveyor that will accommodate the unique properties of metal scrap is a solid first step to getting the most service life out of a conveyor, there are additional factors to consider for reducing downtime. Common causes of downtime include carryover, inability to convey a specific composition of material or payload, and preventive maintenance issues. Here is a look at some of the ways conveyor manufacturers are engineering equipment solutions to reduce downtime.
#1: Preventing Carryover
As conveyor problems go, carryover (or carryback) is both a chronic nuisance and a leading cause of unscheduled downtime. When material fails to discharge at the end of the conveyor and is pulled back into the back side of the unit, it results in unplanned maintenance. Carryover will sometimes even damage the equipment.
Some conveyor belt types for metal scrap are more predisposed to carryover than others. For instance, steel belt conveyors, which are widely considered a versatile choice for metal scrap conveyance, are more prone to carryover because of how the belt is constructed. Made up of a series of pans that have gaps between them, material sometimes becomes lodged between the pans.
A couple of conveyor belt designs are engineered specifically to eliminate carryover of metal scrap. The first is a magnetic conveyor that, as the name implies, uses magnets to make ferrous metal scrap stick to the conveyor. As the material reaches the end of the conveyor and the magnets cycle back into the unit, the metal scrap loses contact with the magnets and cleanly discharges from the conveyor. The obvious drawback is that a magnetic conveyor will not move non-magnetic metals, such as aluminum and copper.
Another type of conveyor that is engineered to eliminate carryover is a pivot belt conveyor. Each individual pan on a pivot belt conveyor is hinged on one side. As the pans move from the feed area toward the discharge chute, the surface of the pan containing the scrap faces up. When the pan reaches the discharge chute and begins to cycle back into the unit, gravity forces the pan to rotate on the hinge, which flips the pan over. This motion causes the pan to flap and flings the scrap off the pan, which prevents the scrap from sticking to the belt. This type of conveyor is ideal for thin, flat, and oily stamping scrap.
#2: Avoiding Bundles of Trouble
Inability to convey a specific payload or composition of scrap material is another common cause of conveyor-related lag or downtime. Bushy bundles of stringy metal scrap are notorious for causing delays, especially when loading onto screw/auger conveyors. Rather than following the feed of the auger, the bundles roll around in the in-feed hopper—usually until an operator manually breaks them apart and forces them along the conveyor. This process is not only slow and a waste of resources, but it is also unsafe.
Adding a step to automatically pre-condition the bundles for conveyance will result in more efficient operation. Auxiliary systems can be installed that will tear bundles into smaller pieces prior to the metal scrap being fed to the auger. This enables the conveyance system to consistently move metal scrap without operator intervention.
Heavy loads are another problem. Occasionally, loads will become heavier than the conveyor is designed to move, which can overload motors and damage the scrap-handling equipment. Some conveyor systems include safeguards such as torque-limiting protection that automatically shuts the conveyor down when a load becomes too heavy.
#3: Improving Build Quality and Streamlining Preventive Maintenance
The build quality of any equipment significantly factors into the amount of maintenance it will require. However, with conveyors, there are certain engineering features that help eliminate structural weaknesses, increase the service life of the equipment, and decrease common maintenance issues. Features that can be engineered into conveyors to reduce maintenance include:
• Large rollers cut down on friction and reduce belt pull
• Flanged rollers help keep the belt tracking straight, which reduces frame wear
• Belt reinforcing impact plates to help protect the belt
• Heavy-gauge side frames
• Track and wear bars for precise belt tracking and longer life
• Integrally die-forming side-wings and flights
• Welded seams rather than bolt together construction keeps the unit straight and strong
Routine conveyor maintenance includes lubricating bearing and rollers with an advanced lubricant and checking belts for wear and slack (the frequency of maintenance and inspections depends on run time). Some design features or system options can help decrease routine conveyor maintenance. Examples of these options include self-cleaning systems and lube systems that automatically grease bearings, as well as controls that provide maintenance-schedule alerts and remote monitoring systems that can warn the maintenance staff of a potential issue without them having to physically be at the machine.
discharged without carryover.
Efficient Processing
A conveyor that is not providing optimum performance can be a significant drain to metal scrap recycling operations. By minimizing—or even eliminating—carryover, effectively handling difficult material compositions, and reducing routine maintenance requirements, manufacturers will position their facility for consistently efficient processing. | WA
Mike Hook is the Sales and Marketing Director for PRAB and has more than 15 years of mechanical design and application experience. PRAB is a leading manufacturer of engineered conveyors and equipment for processing turnings, chips and metalworking fluids. PRAB also designs and builds industrial wastewater recycling systems. Mike can be reached at [email protected].