Stationary scrap shear with sidecompactor and column guiding - efficient and long lasting

Depending on the manufacturer and the specific application, various types of scrap shears are available on the market; here is a brief overview:

Alligator shears

Small hydraulic shears into which material is fed by hand and then cut, i.e. by operating a foot pedal. They are used for processing cables, catalytic converters, wheel rims, and other manually manageable parts.

Excavator shears

Attachments for material-handling excavators used to shear through structural beams, typically during demolition work.

Horizontal shears (container shears)

Mobile shears featuring a blade slider that moves horizontally along the floor of the press box, the slider, equipped with blades on its upper front edge, shears scrap lying on the floor against front wall fitted counter-blades as it advances, discharging the material through an opening at the front. A pre-compactor moves above the blade carriage, ensuring the scrap is pre-compressed and forced down to the floor level. Scrap is loaded from above.

Lid shears

Lightweight scrap shears that use interlocking lids to compress scrap within an elongated compression box before a feed mechanism moves it into the shear head. There, it is vertically compressed by a down-holder device and sheared by a vertical blade slider (guillotine). Due to their lightweight design, most models are mobile and can be transported on heavy-duty trailers or their own chassis.

Inclined-bed shears

Shears that use an inclined loading box and side "flippers" to feed scrap into a shear head positioned relative to the vertical box floor; the shear head then pre-compresses and shears the material.

Side-compression shears

These are classic, stationary scrap shears that compress heavy scrap using a side-compression unit moving horizontally across the compression box and a folding lid. Once the scrap has been compressed to the shear width and maximum shear height, a pusher moves it into the shear head; there, it undergoes further vertical compression by a down-holder (stamper) before being sheared off by a vertically guided blade slider (guillotine). These shears differ primarily in the design of the blade slider guide, lid, and side-compression unit, as well as the use of a pre-fill hopper. They are the most effective and powerful scrap shears on the market.

In addition to these main types of scrap shears, there are specialized shears adapted for specific types of scrap. Examples include:

• Long material scrap shears for pipes, profiles, and bars
• flame-cutting plate shears for cutting up steel mats (e.g., 10 x 3 m)
• Press shears for crushing/cutting aluminum die-cast scrap
• Bulky waste shears for incineration plants

Alligator shears

Advantages:

• low acquisition costs
• fast and effective for processing small quantities
• targeted separation of specialized scrap, such as catalytic converters and cables
• no special operating permit required

Disadvantages:

• low productivity combined with high labor costs
• risk of injury due to manual scrap feeding
• low shearing forces

Excavator shears

Advantages:

• low acquisition costs
• easy to use for demolition work on steel structures
• targeted application for beam scrap
• no special operating permit required

Disadvantages:

• low productivity; ties up personnel and material handling excavators
• requires the use of heavy material handling excavators
• time-consuming alignment of the shear attachment before a cut can be made

Horizontal shears (container shears)

Advantages:

• moderate acquisition costs
• continuous automatic operation
• easy loading and removal of cut scrap
• small footprint
• mobile application possible

Disadvantages:

• limited shearing force
• limited pre-compaction
• limited adjustability of cutting length

Lid shears

Advantages:

• moderate acquisition costs
• mobile application possible (for mobile versions)
• narrow installation width due to folding wings

Disadvantages:

• lightweight design; overhaul is complex because wear plates are largely welded on and form part of the basic structure or structural integrity
• many moving parts; high wear and tear
• short service life due to lightweight construction; dents in the press box can cause the feed mechanism to jam
• cut material must be removed regularly to prevent damage to the guillotine or the machine being torn from its foundation
• suitable only for light to medium-weight scrap due to the limited pre-compression forces of the wings

Inclined-bed shears

Advantages:

• high throughput capacity, with long material
• can process long scrap

Disadvantages:

• low compaction of the cut scrap
• not suitable for all materials (no feed mechanism); e.g., bulky material, as containers, are difficult to capture
• requires a plate conveyor for discharge (scrap is discharged downwards); additional equipment increases the risk of downtime
• requires a large, massive foundation

Side-compression shears

Advantages:

• high throughput capacity
• suitable for heavy structures that are compressed before cutting
• high compaction, resulting in high bulk density of the cut scrap
• long service life (depending on the specific design)

Disadvantages:

• high investment cost
• requires a large foundation

Blade slide guidance system

The guidance of the blade slide is crucial for the operation of a scrap shear. If the blade gap between the upper and lower blades cannot be precisely adjusted (< 0.5 mm) across the entire shearing width, the scrap will be torn rather than cut, even when high shearing forces are applied. Not only does this render the shearing force ineffective, but it also significantly reduces the shear's productivity, as the hydraulic system is forced to constantly operate at high force levels, thereby limiting speed.

This effect is comparable to cutting paper with scissors: if the pivot is loose, even the sharpest blades are useless.

Basic scrap shears often use welded-on guides that cannot be reconditioned, or at least not uniformly. Adjustment mechanisms are of little use because guide wear is uneven. Wear is usually greater in the actual cutting zone than in the rest of the blade slide's travel path, making parallel adjustment ineffective.

Blade slide guides that do not come into contact with scrap or intruding "shear sand" (fine particles in the feed material) offer the best resistance to wear. This is only the case with column-guided blade sliders.

Robustness of the compression box

Lightweight shears dent easily, leading to jams in the compression box during the feeding and side-compression phases, as material gets pushed under the compactors within the dents. The most vulnerable component of a conventional scrap shear is the feed cylinder, as it has the longest stroke and thus extends the piston rod the furthest. If material adheres to the rod or severe wear occurs in the feed area, the piston rod can easily become scored, leading to oil loss and—in the worst-case scenario—bending and shear failure. A feed ram rod is very long, entails long lead times, and—given lengths of 8–10 meters—cannot be shipped by air freight for larger shears.

Torsional Rigidity

The more rigid the scrap shear's design, the lower the forces the foundation must absorb. Some shear manufacturers require a massive steel base frame to be cast into the foundation to contain the forces generated during operation; this is an expensive and complex process—a fact manufacturers often omit from their quotations.

Pre-fill Hoppers

Optional equipment can enhance the productivity and availability of the shears. This includes, for example, pre-fill hoppers that allow the next load of scrap to be staged and inspected for contaminants while shearing operations are still underway; this can result in up to 20% higher productivity.

Control Cabins

Control cabins are essential—especially for large shears—to ensure safe operation and rapid pre-compression. Operating the shear via a material handler’s remote control may seem cost-effective at first glance, but it ties up both the operator and the machine; the handler must remain stationary to operate the shear and lacks the necessary vantage point to monitor the compression box or pre-fill hopper, identify hazards or contaminants, and control the shearing sequence. Poorly equipped control cabins featuring only a standing console lead to operator fatigue, whereas comfortable control seats ensure attentive operation and a clear view of the process.

Necessary Additional Equipment (Not Always Included)

• this includes complex steel structures that must be embedded in the foundation—onto which the shear is welded—to compensate for any lack of inherent rigidity in the shear’s design.
• necessary plate conveyors to ensure cut material is immediately removed and cannot damage the shear.
• control cabins are sometimes omitted in favor of remote controls, which distract the material handler operator from their primary tasks.

Hydraulic System Configuration

The design of the hydraulic system is a major cost factor for scrap shears. A shear's effectiveness depends on the number and type of pumps, pipe cross-sections, cooling capacity, and the configuration of the control valve blocks.

For example:

• power-regulated pumps increase energy efficiency.
• the number of pumps (and their pumping capacity) increases the shear's operating speed and, consequently, productivity.
• swiveling pumps can be reduced to minimum output when not in use, saving electricity and reducing heat generation.
• large-diameter pipes are expensive but reduce pressure drop and heat generation—factors that otherwise lead to cooling issues during high summer temperatures.
• large control valves within the valve blocks are costly but also reduce pressure drop and heat generation within the system.
• intelligent hydraulic control systems are expensive but enable oil recirculation and simultaneous cylinder movements, thereby increasing the shear's productivity.
• high system cooling capacity ensures operational readiness even on hot summer days or under challenging climatic conditions.
• large tank volumes indicate an inefficient hydraulic system design, as they are often employed as a low-cost solution for cooling the hydraulic oil.

In addition to shear force, the shear width is a crucial factor when selecting larger scrap shears. The two parameters are interdependent.

A narrower shear width ensures that the edge length of the cut scrap does not become excessive, even with short cut lengths. This is important for producing cupola scrap for foundries, where the maximum edge length must remain below 500 mm to allow for easy charging into smaller furnace openings. For such shears, the shear width typically ranges from 500 to 700 mm; a shear force of less than 800 tonnes is sufficient to cut scrap of this width using the shear slide. Due to the shear width, the throughput capacity of such shears is relatively low.

Larger foundries and steelworks can handle cut scrap with greater edge lengths, allowing for the use of wider shears. Since a scrap shear's productivity depends on its shear width, the width is matched to the shear force. Shears with forces up to approx. 1,000 tonnes are used for widths up to 1 m, while the next size categories—1,250 mm and 1,500 mm—require shear forces of approx. 1,400 tonnes and 1,700 tonnes, respectively. The required shear force also depends on the height of the scrap pre-compacted in the compression box; this height is usually selected in conjunction with the shear width and shear force. Compression box heights range from 600 to 1,200 mm.

When operating a scrap shear, the time required to pre-compress the scrap within the compression box is crucial, as this enables the material to be fed into the shear head.

Depending on the type of scrap, this pre-compression process is usually monitored by an operator, as it directly determines the shear's productivity and rate of wear. The duties of the operator—who, in the case of large shears, is stationed in a control cabin with a view of the compression box—include:

• Inspecting the scrap for contaminants and hazardous materials (gas cylinders, gearboxes, springs, etc.).
• Managing the charge quantity and distribution to ensure fast and productive shear operation.
• Selecting the pre-compression strategy using the side compactor (or "wing") and the compression lid.

Scrap shears designed for heavy scrap are equipped with a side compactor to break apart structural components; the pressing forces required for this are critical. The selection of side compactor forces depends on the height of the side compactor and the length of the compression box, as well as the design of the box walls and the side compactor's guide system. Basic compression box designs lacking stiffeners or ribbing cannot withstand high pressing forces and are therefore limited to operating with lower side compactor forces. In the past, "flipper-style" side compactors were also used, allowing the compactor to operate in a staggered manner; however, it should be noted that this utilizes only half the pressing force from a given hydraulic cylinder, significantly reducing overall pressing power. Furthermore, the mechanical and hydraulic design of these "flippers" leads to high levels of wear on the side compactor.

In the past, pits were frequently used at the shear discharge point; scrap would fall into these pits, allowing for temporary buffering. The shears were installed at ground level so that the material handler operator retained a clear view of the material being fed into the shear.

This design approach has been abandoned for the following reasons:

• Modern material handlers feature elevating cabs, allowing shears to be installed at a higher elevation.
• A variety of scrap types are cut and sold today; since these must be stored separately, emptying and cleaning the pit each time would be a laborious process.
• Depending on the installation site's location, groundwater could seep into the pit.

A simpler solution is to mount the shear on a raised foundation (approx. 1 m high) and let the scrap slide onto a steel-plated concrete floor. From there, it can be easily picked up by a material handler, and the area can be cleaned at any time.

For shears with higher throughput capacities, a pivoting plate conveyor is a sensible choice; this can be supplemented with a screening system to separate out "shear fines" (small debris) before the material is stockpiled. It is crucial that such a system be robustly constructed; a flawed design could lead not only to system failure but also render the shear itself inoperable. There are also specific design details that only specialists are familiar with.

A distinction can be made between three types of feed material that should not be cut in a scrap shear:

Hazardous materials

They pose a danger to the shear and the operator:

• ammunition
• batteries, especially lithium-ion batteries
• gas cylinders
• closed containers
• radioactive material

Contaminants

They impair the operation of the shear:

• railway rails (generate pressure surges and damage the hydraulics, as they fracture rather than shear cleanly)
• saw blades (they easily become lodged in the compactor guides; due to their hardness, they are not crushed, potentially causing the compactors to seize)
• hardened wires (they can become lodged in the guides as described above, or—if blade edges are worn—get caught between the blades, potentially tearing the blades out when they retract)

Highly abrasive materials

They cause excessive wear on the blades:

• gearboxes, drive shafts, pinions
• coil springs, leaf springs
• piston rods, cylinders, shock absorbers
• wear-resistant hardened steel, blades, ploughshares

The operating costs of a scrap shear depend heavily on the material being processed. They are primarily determined by wear-related costs; for instance, wear costs for aluminum scrap are only 20% of those for steel scrap when calculated based on throughput in tonnes.

Key factors influencing wear include regular maintenance of the shear, pre-sorting of the feed material, and proper operation.

For conventional mixed scrap, the operating costs of a scrap shear can be estimated as follows:

Operating labour costs

For larger scrap shears and inhomogeneous material, an operator stationed in a control cabin with a view of the compression box should be employed. While this increases personnel costs at first glance, it ensures better utilization and reduced wear on the shear, as the operator controls and monitors loading and pre-compression processes while preventing the inclusion of contaminants.

Energy costs

For electric drives, energy costs are determined by the installed drive power, which primarily supplies the hydraulic pumps. The average power demand can be estimated at approximately 40–60% of the installed power. For example, an installed power of 400 kW corresponds to a consumption of 160 to 240 kWh per operating hour.

Consumable costs

Consumables include lubricating oils, greases, and filter elements; these costs are negligible compared to other expenses.

Maintenance costs

Maintenance costs include:

• Regular inspections (approx. ½ hour per shift).
• blade replacement or turning.
• minor repairs and weld-on repairs (hardfacing).

Maintenance and repair costs

Due to the extreme wear and tear to which a scrap shear is subjected from day one, it requires periodic overhauling. The service interval and the necessary work depend on the shear's design and type, the material being processed, and the level of maintenance provided.

Key maintenance and repair tasks include:

• replacing wear plates in the compression box and shear head (where designed to be replaceable) or applying weld overlay (hardfacing).
• replacing hold-down devices and blade slide guides (where replaceable).
• extensive weld overlay work on compactors, the lid, and other components.
• resealing hydraulic cylinder.
• changing hydraulic oil and cleaning the tank.