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Reduced Risk and Explosions – Pre-shredders can reduce risk and improve the efficiency of auto shredding operations

Brian Smith, Global Marketing Manager of Metso Outotec, a frontrunner in sustainable technologies, end-to-end solutions and services for aggregates, mining, metals refining and recycling industries, looks at the benefits of the pre-shredder and why auto shredding operations should consider its use. 


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Auto shredding plants around the world face the hidden dangers of explosions caused by unshreddable material or other unforeseen objects in their feedstocks. With safety as the primary concern, these dangers also lead to costly damage and downtime to the shredding operation.

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Brian Smith

Although many modern shredding plants are designed to meet the gruelling conditions inflicted by processing bales, logs, end-of-life vehicles (ELVs) and heavy grades of scrap, these machines are not impervious to their rigorous workloads and the potentially debilitating effects of unshreddable materials.

Faced with ongoing operational risks and coupled with increasing regulations, shredder owners around the world have become more cognizant of the impact, and are integrating pre-shredders to alleviate the risk. The allure of pre-shredders has grown far beyond mitigating risk. However, as operations managers and scrap yard owners recognise the enhanced value, this machinery provides through operational efficiencies, reduced downtime, quality throughput and lower cost per ton processed.

Safety and environmental considerations

 Pre-shredders, like the Lindemann EtaRip, can help reduce or eliminate the risk of explosions and fires inside the primary shredder from undetected gas bottles, fuel tanks or other hazardous elements in ELVs, logs or bales.

A pre-shredder can lower a yard’s risk by minimising explosions and fire propagation and the associated losses with incidents of this magnitude. This helps to create a safer working environment for the shredder operator and other scrap yard employees.   Moreover, these units can decrease noise pollution commonly associated with unshreddables and explosions. This not only provides for better community relations but also for a safer and more pleasant working environment.

The open chamber and the slow RPM on the start rotors on this machine provide an improved scenario to mitigate explosions and deal with fires in an offline configuration, lowering the risk of damages across the entire shredding line. Some units can be equipped with dry fire suppression systems.

In addition to the environmental and safety benefits of a pre-shredder, suppliers continue to develop dust control, air treatment, volatile organic compounds (VOC) and sound control solutions for auto shredder operators.

Operational perks at the primary shredder

 A pre-shredder can improve wear life on the primary shredder’s castings, protect against unshreddable or explosive materials and reduce peak power loads to the shredder.

By processing a homogeneously sized product, yards can also achieve much higher throughput from their auto shredders. In our testing of shredder throughput before and after the installation of an EtaRip pre-shredder, the average tonnes per hour processed increased by more than 17 per cent.

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Depending on a yard’s downstream processing capacity and market conditions, some yards can benefit by yielding the same tonnage of output but with fewer operating hours. This reduces operator burnout, labour costs and energy costs without sacrificing throughput. It can also allow for routine scheduled maintenance to keep the shredder operating in peak condition.

By stabilising the operating load of the shredder with preprocessed material, the primary shredder can operate in a more efficient energy range, reducing or eliminating “peak loads” as charged by utility companies. This is an especially important feature for shredder yards that are charged on an electrical power demand basis.

Additionally, the homogenous infeed to the primary shredder helps to create a full-box shredding scenario that runs on constant rpm with higher output. The reduced drop in rpm arising from high drive motor loads can also result in less stress to the driveline, which means less maintenance and longer life.

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Lower cost per tonne is an important goal for all shredder operations. More even loading of the primary shredder results in fewer surges, more consistent full-box shredding, less process time inside the primary shredder and a steadier discharge stream. In a power consumption analysis, Metso Outotec recorded nearly a 14 per cent kilowatt-per-tonne energy savings by preprocessing material with its pre-shredder.

Additionally, because the pre-shredder releases entrapped dirt and soil, this abrasive material does not enter the primary shredder’s chamber. That filtering process, coupled with the pre-shredding of high-density bales and the rejection of unshreddables, improves the life and value of shredder consumables by reducing premature damage to hammers, rotors, grates and liners. In testing, we found a 20 per cent reduction in hammer consumption when material was preprocessed with a pre-shredder—similarly, less high-impact shock results in longer life for the complete power driveline.

Pre-shredder principles

Installed upstream of the primary shredder, pre-shredders can help to reduce and defuse material before it is fed into the shredder. In addition to reducing the risks of unshreddables and explosions, pre-shredders can homogenise incoming material, allowing the shredder operator to better control the feed rate for the primary shredder. Ultimately, this can lead to a more uniform flow of material that increases production capacity and reduces the cost per tonne of material processed.

Pre-shredders can differ from one another in terms of power, chamber size, ease-of-operation through the human-machine interface (HMI), and efficiencies based on the code that controls the operational characteristics.

The EtaRip, for example, is a low-speed, high-torque pre-shredder that tears apart bundles, logs, bales or ELVs before this material is fed to the primary shredder. A set of parameters in the operation code creates hands-free operation, controlling the rpm, oil pressure and rotational direction to produce efficient operation while protecting the machine from inappropriate materials. Additionally, the operator of the crane that is feeding the pre-shredder can use a remote control to override the pre-shredder’s operation at any time.

Where a pre-shredder makes sense

Market conditions in the metals recycling industry are ever-changing. Between steel price fluctuations, competition and the ongoing effort to become more efficient, the need to reduce an operation’s cost-per-tonne Reduced Risk and Explosions p fourprocessed is growing. This competition can also extend to the acquisition of shredder feedstock. But, for many, that can also increase the risk as unknown materials that are fed into the shredder.

A pre-shredder can be an ideal solution for scrap yards that want to increase throughput, reduce wear parts costs, reduce shredder downtime, and operational risks, while increasing operational efficiencies and diversifying their feedstock options with a larger market reach.

In addition, pre-shredders can be helpful to scrap yard operations that have an existing shredder that is too small to handle high-density bales or for operations that have an ageing shredder prone to more frequent breakdowns.

Reducing explosions and downtime at the primary shredder are common reasons shredder operations consider pre-shredders. But, with increasing demand and stronger competition, the improved efficiencies and lower cost-per-tonne processed are key factors driving the integration of pre-shredders.

Note: Studies referenced in this article are based on a Lindemann EtaRip pre-shredder and a 98-inch Metso Texas Shredder. Actual results will vary based on equipment and operating conditions.

To find out more about EtaRip Pre-shredders click here or if you would like to contact Brian, please email him at or visit