As the price of raw materials continues to rise and energy costs remain unpredictable, recycling in all areas of industry is becoming more important. Mike Redmond of Bosch Rexroth discusses the machines and hydraulic systems that are providing a fast and energy efficient way to make the most of the materials that are available now.
In the last few years, the price of raw materials and the cost of energy has risen significantly due to the continued imbalance of supply and demand. The rapid development of technology and the standard of living in Asia, Eastern Europe and South America has also undoubtedly contributed to this situation and is not expected to change. We must therefore use the resources we do have more efficiently, not only reusing raw materials but avoiding waste. Recycling technology is already becoming a more readily accepted way of cutting costs and making processes more efficient. The demand for machines, such as Fragmentizers, scrap shears and presses continues. The need to keep improving the efficiency and the performance of this technology is where hydraulic systems offer such powerful and attractive solutions.
There are many applications in metal recycling that take advantage of the shear force and flexibility of hydraulics to handle the moving, cutting, squashing and lifting needed. From simple shears that cut metal into shorter lengths to massive shears and presses.
There are numerous hydraulic products on the market and each one differs in terms of performance, quality and function. One such piece of technology is a scrap press, which is used to compress scrap into the smallest possible volume, forming a single block for ease of transport. In order to compress the scrap as uniformly as possible it is pressed from the side, from each end and from above. After pressing, the gate is opened and the compressed scrap is pushed out. Typically four hydraulic cylinder axes are used. In order to reduce the total cycle time these machine are often fitted with a ‘skip’. During compression of the material, a crane fills the skip with the next charge of scrap. At the beginning of the next cycle the previously prepared charge is simply tipped into the press. The skip also functions as a measuring device so that the press is always filled with the optimum amount of scrap. By employing this process, transport, storage and disposal are made easier and more efficient.
Another option is a scrap shear. This is where the scrap is first compressed as in a scrap press, but rather than being formed into a block, the material is pushed out in small steps by means of an end pusher and cut into sections. In order for this cutting process to be as efficient as possible, the scrap is pre-compressed directly at the shear blade and firmly held by a ‘hold down cylinder’. Cutting scrap into small equally sized pieces makes it suitable for further recycling processes.
The need for high forces, robustness, reliability and short cycle times means that scrap shears must use hydraulics. The hydraulic system is key to the overall efficiency of the shear and it is the hydraulics that makes the difference in performance.. A high performance scrap shear requires hydraulics that allows shock-free switching of large flows and shock-free decompression. Cutting shocks must be avoided with low energy consumption and first procurement costs ensured.
Hydraulic systems are also used in pre-shredder Fragmentiser technology which further improves productivity, efficiency and safety.. A pre-shredder uses low power and speed to pull pressed materials to pieces, effectively ‘unbaling’ them to produce a lighter material that is ready for fragmentation. This makes the hammermill more productive and reliable, not just in the shredding operation but also in the feeding process stream where the conveyor can be fully loaded. Also, further down the process line, it enables better sorting efficiency due to the better fragmentation. The hammers and other parts will also have less wear providing longer life savings on maintenance costs. By using a pre-shredder, capacity can be increased, allowing transport journeys of feedstock to be reduced to ultimately save fuel costs and reduce emissions.
A pre-shredder works by simply dropping the material, whether a car or bale, into the top where two rotorspull them in and then pull them apart. The loose material that has been created then drops out at the bottom ready for the fragmentation process. The two horizontal rotors with direct hydraulic drive can be geared together or independently driven and the speed is controlled and if necessary reversed. A hydraulic push plate is added to press the material against the rotors, preventing slippage. The direct hydraulic drives produce full driving force (torque) in forward and reverse and no gearboxes are needed to keep the drive arrangement simple and effective. Although it’s a low speed process, the force needed for this type of operation is incredibly high, making a direct hydraulic drive system an advantage.
The use of a pre-shredder can also be useful in exposing fraudulent attempts to increase the weight of feedstock bales. Should there be any fuel in a flattened car, the slow process of a pre-shredder will expose the problem and by tearing the tanks apart carefully, will virtually eliminate the threat of explosions.
The fragmentiser where all our cars, light scrap and white goods end up usually has an inclined steel belt conveyor driven hydraulically which is fully loaded with scrap metal. The scrap drops down a chute to the roll feeder, also driven hydraulically, which feeds the scrap into the hammermill at the optimum rate, holding it so as not to get pulled in too quickly to ensure the best production in relation to the power of the mill.
Other functions of the mill are also hydraulically operated such as the raise/lower of the feed rolls, the reject door and maintenance functions like hood lift, pin puller etc. The main rotor lubrication system is also hydraulic.
Whilst all hydraulic systems need to be designed properly with reference to pressures, temperatures, filtration and oil grade issues, environmental concerns are an increasing concern. The larger the plant and hydraulic components, the more consideration is needed in regards to the massive forces involved and the power of the fluid forces and how to control them. Most products are designed for a specific application and it also needs to be remembered that using it outside these areas might not be appropriate. This is true for instance, in the case of mobile equipment as opposed to industrial equipment. The best way to ensure the products used are well matched and fit for purpose is to order the complete system from a well-respected manufacturer which can provide a complete system design, including controls. This will give you an efficient, workable solution which meets the appropriate standards.
The larger hydraulic companies have been addressing these issues for many years. Rexroth, the market leader in hydraulics has the knowledge and experience to draw on when supplying hydraulic systems as well as rules and procedures to control inherent risks. My advice is that all customers need to be able to satisfy themselves as to the reliability and security of the technology including its efficiency. All round performance is required short term, but the reassurance of quality service and ongoing support will be needed in the long run.