This article will take an in-depth look at metal shredders.
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To recycle scrap metal efficiently, it must be processed and prepared for reuse. Metal shredders are used to handle various types of metal scraps, breaking them down into standardized shapes and sizes for sorting and further processing in recycling operations. Their robust design ensures long-lasting performance, allowing both ferrous and non-ferrous metals to be crushed before being sent to steel mills for recycling. Additionally, shredders enable the destruction of metallic materials when necessary.
Scrap metals are often bulky and difficult to handle in their original form. For example, an old car is cumbersome but becomes easier to move and process once shredded. Shredding reduces the volume of scrap metal into smaller, more manageable pieces, making it easier to separate ferrous and non-ferrous metals, as well as other materials like rubber, plastics, and fabrics. Some shredders can even distinguish between magnetic and non-magnetic materials to maximize the value of recycling.
Here are some components of metal shredders and their functions:
Once shredded, metal becomes much easier to transport to a facility for further processing. The shredding process also separates non-ferrous materials such as plastics, foam, glass, aggregates, wood, rubber, textiles, and electrical components. These materials are then directed to recycling streams to prevent them from ending up in landfills.
Shredded ferrous metals are sent to a furnace where they are melted down. After melting, the metal undergoes refining to ensure its quality and remove impurities. Electrolysis is a common refining technique, using a direct electric current to induce a chemical reaction. Post-electrolysis, the metal is cooled and solidified, ready for use in producing new products.
In the crushing process, four main external forces are applied: rolling, shearing, impact, and grinding. Press rolling is effective for coarse and medium crushing, especially for hard and large materials, as it involves reducing the thickness of metal stock by passing it under one or more rollers.
Shearing is employed for fine crushing and is particularly useful for breaking down tough materials. Impact forces are used to crush brittle materials and are commonly applied in medium crushing, fine grinding, and ultra-fine grinding.
Grinding is used for breaking down small pieces and fine particles, specifically in fine and ultra-fine grinding stages. Often, the crushing process incorporates multiple external forces working together simultaneously.
The core principle of a metal crusher involves hammering. The main machine's rotor, driven by a high-speed, high-torque motor, spins as hammers strike the material, breaking it into smaller pieces within the crushing chamber. Crushers can be categorized into dry, wet, or semi-wet systems based on their operation. A dry system includes a dust removal feature and uses an air cyclone sorting system to separate metal from non-metal materials. In contrast, a wet system applies water during the crushing process to simultaneously wash and sort the materials. The semi-wet system applies a minimal amount of water only as needed to reduce dust while crushing.
Single-shaft metal shredders have a rotor and hydraulic ram used to press garbage and scrap against the rotor, which starts the cutting process. Pressure sensors allow the ram to travel backward and forwards, preventing jamming and overheating of the material. Large bulk materials can be broken down into particles as small as 10 mm using these shredders, which can be equipped with various screen sizes. All single-shaft metal shredders have a classifier screen that provide a user with variable measurement settings that output units can be sized at.
The double-shaft metal shredder is a favored choice in industrial applications due to its low-speed operation, high torque, and substantial throughput capabilities, making it effective for processing a wide range of materials. These shredders, which can be driven by either electric motors or hydraulic systems, are designed for volumetric reduction, helping to minimize the space occupied by waste materials. Despite often lacking a classifying grid, the distinctive blade design and controlled production parameters of double-shaft shredders allow for effective size control of the output material. These advanced primary shredders offer versatility and durability for heavy-duty use. Depending on the material type and desired output size, double-shaft metal shredders can be equipped with various components or used in conjunction with other shredding stages to achieve the required material size.
Three-shaft metal shredders can be used either independently or as part of specialized shredding systems. They come in three models (800-1000-1300mm) and offer capacities ranging from 1.5 to 3.5 tons per hour, equipped with a screen for separating the output material. The processed material can be reduced to sizes between 30x30mm and 50x50mm. These shredders feature a robust cutting system with durable rotor blades and a sweeper shaft. The cutter discs are individually replaceable, and the shredder includes a pivotable screen basket and protective bulkhead seals for the shaft bearing. They are available with either mechanical or hydraulic drive systems and offer automatic power-down and reverse functions.
Four-shaft metal shredders feature two drive rotors that push scrap material onto additional cutting rotors located below. These cutting rotors, powered by separate gear motors, are designed to pre-shred materials before further size reduction or processing with a granulator. Comparable in size to twin-shaft shredders, four-shaft models are often used for tougher waste, such as cars, that cannot be processed by twin-shaft shredders. They include replaceable classifying grids and are available in both electric and hydraulic versions, allowing for versatile material processing and precise output size control. Four-shaft shredders represent advanced technology aimed at creating highly efficient and adaptable equipment. With anti-wear treatments on grids and interchangeable shaft technology, these shredders significantly lower management costs and reduce maintenance requirements.
Horizontal and vertical hammer mill metal shredders operate by repeatedly striking feed material with heavy hammers, which can weigh between 250 and 1,000 pounds and rotate at speeds of 500 to 700 revolutions per minute (rpm). These hammers are driven by motors ranging from 2,000 to 10,000 horsepower. In a hammer mill shredder, material is introduced into a rapidly rotating steel drum, where it is struck by hammers on a shaft, breaking it into smaller pieces. Horizontal models feature hammers that strike horizontally, whereas vertical models have hammers striking vertically.
Despite their design differences, all hammer mill metal shredders operate on the same principle: large hammers attached to a rotor shred vehicles and other heavy metal items. These shredders are equipped with multiple outboard flywheels and either electric or diesel motors that power the spinning hammers. Large hammer mill shredders also include features like rejecting doors and manganese liners for expelling uncrushable materials. At peak performance, they can process up to 350 tons of material, or 450 automobiles, per hour, and annually produce 2.5 million tons of high-density, uniformly fragmented metal scrap.
While it might not be immediately obvious, industrial metal shredders, especially those used in scrap metal recycling, play a crucial role in environmental protection. Without metal shredders, processing large volumes of scrap metal efficiently would be challenging. Their absence would mean longer processing times to meet the rising global demand for scrap metal and a slower reduction of scrap metal accumulation worldwide.
To safeguard the Earth's natural resources, it is essential to minimize the use of new metal as raw material and instead increase the recycling of metal. The shredding process also allows for the effective separation of scrap metal from non-metal and non-ferrous materials, helping to prevent these materials from ending up in landfills.
Capacity: The effectiveness of a metal-shredding facility hinges on choosing an industrial shredder with adequate capacity. Factors such as the volume of material, its physical dimensions, weight, and bulk density all impact a shredder's capacity. The size of the cutting chamber may limit a facility's overall capacity. It is crucial to review a shredder’s capacity rating carefully and consider having some additional capacity beyond estimates. Operating a shredder too close to its maximum capacity can shorten its lifespan, while an oversized shredder might consume excessive power and occupy more floor space than necessary.
Output Specification: Before purchasing a shredder, operators need to clearly understand its intended use and capabilities. For some, the primary goal is not to process metal but to reduce the size of bulky items that are difficult to store. In these cases, the shredder’s output might be less critical. However, for others, particularly those facing strict compliance regulations, output performance is crucial. Additionally, some organizations have specific requirements for their shredders. Therefore, it is essential to choose a shredder that meets the desired output specifications. Ideally, a metal shredder should be versatile enough to adapt to changing needs.
Environmental Consciousness: There are considerable differences in attitudes toward recycling and trash management in the US. Operators must therefore prioritize their performance standards when purchasing shredders that are appropriate for the job required. Due to their reduced carbon footprint, electric motors, rather than diesel hydraulic drives, are used to power several contemporary types of metal shredders because this technology uses less energy. If the expense of the manufacturing process is detrimental to the environment, there is little value in turning rubbish into raw materials for new products. Investing in more "green" machinery also makes financial sense because fuel-guzzling shredders can be expensive due to their high energy requirements. These energy requirements may reduce the potential ROI (return on investment) of a metal shredder and metal-shredding operation.
Types of Material to be Processed: Different shredder designs are optimized for various materials. For instance, high-speed chippers are ideal for shredding tree branches, while plastics are typically processed in granulators (rotary knife cutters), though bulky plastic items may first go through a shredder. When shredding vehicles, a hammer mill metal shredder is often used after initial shredding. While four-shaft shredders can handle specific tasks more quickly, twin-shaft shredders might be preferred for their adaptability and quieter, less dusty operation across diverse waste materials.
Maintenance: Metal shredders endure significant stress and require regular maintenance to ensure proper operation. Components such as cutters, blades, or hammers will become dull and need sharpening, adjustment, or replacement. When choosing a shredder, consider factors like ease of upkeep, repair requirements, and the availability of replacement parts. Maintenance accessibility should be a key consideration in equipment selection.
Safety: Industrial shredding can be hazardous, prompting manufacturers to design safer equipment. Modern shredders incorporate safety features such as protective mechanisms to prevent exposure to moving parts and proactive diagnostic controls that reduce the need for manual intervention. Enhanced safety includes auto-stop functions for foreign objects, low-noise operation to minimize noise exposure, and advanced detection systems (UV, infrared, heat, and spark) to prevent fires. Ergonomic designs also ensure that maintenance can be performed safely and comfortably, reducing the risk of injury.
Metal shredders typically employ grease or oil lubrication techniques. The area around metal shredders can be reasonably simplified using grease lubrication. Grease lubrication makes the motion of all moving components smooth on the metal shredder. Oil provides the best lubricant for metal shredders. Still, regardless of the type of lubrication used, it is important to pay attention to the quantity and consistency of the lubricant to maximize a shredder’s performance.
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