PRESS-SHEARS FOR CUTTING AND/OR BALING SCRAP METAL
Bruno J. J. Wientzek
Shears were the first machines used to break up scrap metal. Guillotine shears with a mechanical drive were made
long before World War I and were designed to cut bars,tubes,light sections,plate crop,and other items. The small size ofthe opening between the blades precluded the use of these machines for cutting large pieces of scrap.
A new type of machine was built in the 1930s – alligator shears. These machines still had a mechanical drive,but
the opening between the blades was larger and the productivity of the machine was increased. However,there was still a riskof accidents in using these shears,since some of the scrap that had to be cut was fed manually.
After World War II,the demand for shears rose due to the large stocks of accumulated scrap metal. Alligator shears
were provided with an additional attachment to compress (press) the scrap metal. This device was located in front of theblade opening. However,it compressed tubes and other types of scrap so much that they were able to pass through the open-ing without being cut. At the same time,different sizes of alligator shears were being made in large quantities. Indeed,therewas hardly any scrap-processing floor that was not equipped with alligator shears.
Facing increasingly stringent requirements on the productivity and safety of scrap-processing equipment,machine-builders were compelled to develop a new type of shears that could process large volumes of scrap in a short time with min-imal use of manual labor. These requirements were met by hydraulic shears.
In addition to conventional hydraulic shears – which are loaded by a crane or special excavators and are designed only
to cut metal – press-shears are also now on the market. Press-shears can not only cut scrap metal up to 6 mm thick,but can alsobale lightweight scrap. One line of press-shears is the SIERRA series,made by the company SIERRA International Machinery.
We will examine the principle of operation of SIERRA model T1000 (with a cutting force of 1000 ton-f). This model
includes a charging box,a charging chamber,and two movable covers. When in the closed position,the covers compact (com-press) the charged material into a bale (Fig. 1). The cross-sectional dimensions of the bale – 700 ×900 mm – correspond tothe dimensions of the closed pressing chamber. The length of the bale is regulated within the range from 250 to 1000 mm bychanging the stroke of the cylinder of the pusher. The pusher moves the already-formed bale to guillotine shears (Fig. 2) forsubsequent cutting (Fig. 3a). The cutting force is created by a hydraulic system that acts on the vertical cylinders of the bladeswith a maximum pressure of 350 bars. Movable crossheads are secured to the rods of the cylinders,and the top blade – whichcuts the scrap at a 12°angle – is in turn secured to the crossheads. The guides of the crossheads are composed of replaceablebronze slabs that are lubricated automatically through a central lubrication system. The horizontal bottom blade is stationary.Both blades have four cutting edges,which quadruples their service life. To facilitate the blades’replacement,the press-shearsare equipped with sectional blades having three sections. The opening between the blades measures 970 ×740 mm.
The 1000-ton-f cutting force makes it possible to cut scrap having different cross sections; rectangular,95 ×900 mm;
square,165 ×165 mm; circular,185 mm in diameter. The press-shears can cut scrap with a strength of up to 45 kgf/mm2.The density of the bale depends on the material of the scrap and the fullness of the charging chamber and is within the range450–1200 kg/m3.
The charging chamber (Fig. 4) has a length of 9000 mm,width of 2450 mm,and height of 1400 mm with the cov-ers in the open position. When the covers are closed,the chamber’s width and height are 900 mm and 700 mm,respective-DOBRO GmbH. Translated from Metallurg,No. 11,pp. 58–60,November 2003.
0026-0894/03/1112-0473$25.00 ©2003 Plenum Publishing Corporation
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Fig. 1. Compression of scrap in SIERRA press-shears.
Fig. 2. Guillotine shears of the SIERRA press-shears.
Fig. 3. Diagram of operation of SIERRA press-shears in the compression and cuttingregime (a) and the compression regime alone (b).
ly. The entire interior of the chamber is lined with replaceable slabs of the high-strength steel Hardox:the bottom is madeof Hardox 500 (the units of strength are from the Brinnell scale),while the walls are made of Hardox 400. The thickness ofthe face slabs of the bottom,the side walls,and the flat cover is 25 mm,and the thickness of the curved cover is 20 mm.
The length of the charging chamber can be increased to allow the press-shears to process tubes or beams up to 15m
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Fig. 4. Charging chamber.
Fig. 5. Horizontal pusher-cylinder – compression cylinder.
The pressing operation is performed with a specially shaped curved cover and a flat straight cover brought into
motion by three cylinders with a short stroke. As a result,the covers can be moved rapidly into position while exerting a uni-form pressing force. Each cover exerts a pressing force of 310 ton-f.
The vertical clamp of the press-shears is made of Hardox 400 high-strength steel,while the guides are made of
replaceable bronze slabs. Lubricant is delivered through a central lubrication system. The pressing force exerted by theclamp is 180 ton-f.
The force created by the horizontal cylinder of the pusher – the pressing cylinder (Fig. 5) – reaches 165 ton-f. The
head of the pusher is also made of Hardox 400. The piston rod is shielded from damage by a protective front plate. Thepressing force and the length of the pusher’s stroke are regulated.
Bales with a density of up to 1200 kg/m3can be made in the processing of scrap up to 6 mm thick. In this case,the
vertical clamp is moved to its lowest point and the pusher is used to compress the scrap into a bale (Fig. 3b).
With the pusher travelling a distance of 600 mm and the clamp and blades raised to their normal heights,the
press-shears can make at least 4–5 cuts a minute. A short stroke (raising and lowering) can also be chosen for the clamp andthe blade,which significantly increases the number of cuts per minute. These figures are accurate for materials with astrength of up to 45 kgf/mm2.
The press-shears have a productivity of 15–35 tons/h when processing pieces of steel scrap of moderate size. The
productivity of the equipment depends on the material,the density of the charge,and the skill of both the operator of the exca-475
vator that charges the scrap and the operator of the press-shears. Many years of practical experience have shown that theiraverage productivity is 22 tons/hr. Here,with allowance for obligatory downtime (waiting,interruptions,maintenance,andadjustments),productivity ranges from 20 to 27 tons/h and depends on the time of year. Thus,over the course of a year,thepress-shears can process 137,000–152,000 tons of scrap.
The standard model of the press-shears is equipped with three 90-kW electric motors made by the company ABB.
The motors are directly connected to Rexroth axial-piston pumps and Denison vane pumps. Taking into account the machin-ery built into the system,the press-shears can develop a total power of 320 kW.
The press-shears are equipped with a hydraulic system made by Rexroth. The optimization of the design of the com-ponents and their operating regimes ensures that the system will deliver a large amount of power while keeping energy con-sumption low. The system is provided with protection from high pressure and has 100% filtration capability,thanks to theinclusion of four magnetic filters with 10-µm cells. Standard equipment is used to heat (and cool) the hydraulic oil. If nec-essary,additional measures can be implemented in order to be able to operate the press-shears at extremely low temperatures.The hydraulic oil should have a viscosity of 22 for outside operation of the machine and 36 for inside operation.
The supply voltage of the press-shears is 380 V at 50 Hz,while the input is 320 kW. The system is controlled by
means of programmable controllers made by the Allen Bradley company. These controllers operate on direct current at 24 V.The above-described system operates reliably under extreme conditions in different scrap-processing facilities. The controlcircuits of the valves are also supplied with 24 V dc. All of the tasks involved in the operation of the press-shears are depict-ed visually on a control panel located in a control room. The tasks can be managed in both the manual and automatic regimes.
The lubrication system automatically delivers the necessary amount of lubricant to the guides of the guillotine shears
and the vertical clamp during each stroke. The operation of the system is monitored visually and regulated both manuallyand automatically. If necessary,a central lubrication system can be used to lubricate the cylinders of the covers.
The total weight of the SIERRA T1000 press-shears is 155 tons. Its installation requires a 22.0 ×8.5 m foundation
slab 300–400 mm thick. The slab is constructed as a steel framework (channels or I-beams) that is then filled with concrete.
The optimum configuration of the components of the press-shears is determined at the proposed site of installation.
The charging box can be installed to the left or the right,depending on the location of the machine proper. As a variant,twocharging boxes can be used (one on each side). The locations of the control room and the hydraulic system are also deter-mined at the site. If the press-shears are located outside,a lightweight enclosure – such as one composed of panels – can beerected to house the hydraulic system.
The company SIERRA International Machinery has been making scrap-processing machinery since 1962. SIERRA
is also itself a large scrap processor,in addition to being involved with the disassembly of large metal structures and provid-ing environmental services. Most of the work the company does in this area involves the use of SIERRA-made equipment.The advantages of the latter have been demonstrated through practical experience. Among them are the following:
• the use of a unique charging system;
• the possibility of using the press-shears not only for cutting,but also (if necessary) as a highly productive baling press;• execution of the required operations at high speeds;• the use of an efficient Rexroth hydraulic system;
• the use of different materials for the guides of the blades and the clamp (Hardox steels and bronzes),which pre-vents scratches and major equipment breakages during heavy-duty operation;• ease of control of the covers;
• the safe operation of the press-shears,thanks to the presence of a self-diagnostic system;• low energy consumption;• low cost.
The subsidiary SIERRA Europe Recyling Ltd. was created in 2001 and operates in the European market. In the
Russian market,SIERRA has been exclusively represented by the company DOBRO GmbH since October 2002. The firstmachines have already been shipped by this firm. Among the important services the company offers clients are profession-al consulting on equipment selection and quick and professional servicing of installed machinery on site.
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