Ferrous Shears: A Look Inside

When shopping for a hydraulic ferrous shear, one manufacturer suggest taking a look at the the basic components common to all systems. 

When purchasing or replacing a hydraulic shear, the scrap processor faces a much more difficult task today than in earlier years. The first hydraulic shears were introduced to the scrap processing market in the mid-1950s. At that time, there were only three or four manufacturers, each with a very limited variety of models and few features other than the ability to cut iron and steel scrap. These earlier models usually consisted of a fixed box -- usually 20 feet long -- a feed cylinder to push the material under the knife, and some type of lid to keep the material from slipping out of the box.

Early designers and manufacturers had the most difficulties with the shape of the bed in the feed box and the cutter head or blade slide. Some offered the feed box in a V shape, with a flat or straight knife, while others elected to go with a flat feeding bed, with the cutter head in the shape of an inverted V. Over the years, these cumbersome design flaws have been corrected by the dozens of manufacturers now flooding the shear market. Processors can now choose from among numerous "special features," and are faced with almost as many models and styles as those made available to consumers by the automotive industry.

There are many specialized applications where the material to be processed requires a shear with special features. Examples include rail cars, ship scrap (even submarines), heavy plate and pipe structures. In addition, the requirements of scrap consumers will dictate the blade width of some special shears -- such as 24-inch wide for foundry material, 60-inch wide for export material, etc.

However, the majority of shear operators in the industry today need a machine that offers maximum efficiency, as well as the flexibility to process the widest possible range of incoming material.

When a processor gets serious about replacing or purchasing a new hydraulic shear, he should avoid being overwhelmed by the forest of shear manufacturers, and instead focus on some of the trees -- the actual features that these manufacturers have to offer.

The best way to evaluate some of these features is to break them down into their three basic components: the shear frame, or cutter head; the feed box; and the power pack.

When considering the shear frame, some questions to keep in mind are as follows:

• How many cylinders are required to provide the cutting and clamping force? Fewer is usually better because of reduced maintenance and downtime over the life of the shear.

• How are cylinders attached to the top of the shear? The old method of using bolts to attach the cylinders to the frame can weaken the top plate over the life of the shear. This causes the bolts to break and the frames to crack. More recent engineering allows for machining of the cylinder and threading of the front portions. The cylinder is then inserted into a machined opening in the frame and a threaded ring is screwed on to the front part against the frame to hold the cylinder in place.

• What is the height of the cutter head relative to the width of the knife? A short head generally means a high concentration of forces in small areas of the frame. This can lead to problems over the life of the machine. Some manufacturers are so concerned about this that they mount huge brackets or gussets on the outside of the frame to add additional support to the frame. A tall cutter head in relation to knife width will spread the force over a much larger area and eliminate these problems.

How the cutter head is guided in the frame is also very critical. Both the shape of the guide area and the material that is used to line, or protect, the guide surface are very important. The shape of the guide area can determine if the force used in cutting will force the frame to open or if it is dissipated or distributed into the columns. Material that is used to line the guide areas can be steel-on-steel or steel-on-bronze. However, neither of these allow much protection if they are not properly lubricated. Modern plastics have been used against steel in some machines to provide that emergency protection.

The knife angle is an important feature of the shear. On most shears, knives are angled at 7 to 10 degrees. One model has a 12-degree angle on the top knife. The angle, or rake, of the blade will force the material to the high side of the knife, which places an overload in that side of the frame. Most manufcatures stay in the 7- to 10-degree angle range in an effort to eliminate, or at least reduce, this load.

One manufacturer uses a device called a breaker bar, located in front of and just below the top knife. This bar comes in contact with the material to be sheared before the knife does. The initial contact of the bar stresses the material over the bottom knife and positions the material to be sheared in an optimal position. This feature can increase shearing efficiency by as much as 20 percent, and can reduce wear on the knife.

How the blades are held in place in the blade holder and how the blade holder protects the base metal is also very important. Poor design and/or weak material in the blade holder or seat area can cause a cold flow or deformation of the base metals. This can make proper cutting clearance impossible. Thru bolts are a necessity to maintain control of the blades during shearing.

It is important to maintain proper running clearance between the top blade and the bottom blade. This should be done from the outside of the shear frame, usually with a wedge moved against the blade slide to force it closer to the bottom blade. Shims should not be used, because they usually require a great deal of labor and preparation during the turning or changing of blades. If used improperly, shims may cause serious damage.

There are too many types of boxes on the market for us to address in this space. However, two of the most successful types are the so-called baler shear compression box and the three-dimensional side-compression box.

The baler shear type box usually has two compression sides, or wings, which are mounted on the bed by either bolted or welded hinges. Some of these types of boxes have smaller wings mounted to the primary side or wing. This type of design offers strengths as well as weaknesses.

On the positive side, this box will usually have a wider opening. When ready for charging, it can compress a wide range of mixed material. The roll of the wings is to tuck the material into the box. The top wing is generally effective in keeping the material from climbing out of the box during compression.

However, because of the two hinged primary sides and the two wings mounted on the top, this design requires a line of hinges four times the length of the box. For example, a 20-foot-long feed box would require 40 feet of hinges per side, or a total of 80 feet of hinges to be maintained.

The main hinges that are located at the bed level are exposed to all of the fine material and liquids that find their way into the box. To avoid damage from this long-term exposure, this design requires a good preventive maintenance program.

Natural physics also pose an obstacle here. The forces at work during compression are not only a result of the force created by the cylinders, but also additional force created by the lever action, achieved by the way the cylinders are mounted. The problem here is that the maximum force applied is not always directed at the proper point in the compression cycle or stroke. Also, the compression sides and wings can cause damage to each other if the force generated by each is not controlled.

This can become such a problem in some designs that mechanical stops have had to be added to protect the components at risk. Also, in this type of box, when the charge is completely compressed and ready to be sheared, the hinged sides have to be completely closed. This applies pressure against the material. The effort of the feed ram to overcome this pressure causes shock to the overall system, as well as a considerable amount of abrasion and wear on the liners.

The baler shear box type design can also be more difficult for the operator, especially if both the primary side and the additional wing are mounted on top. The operator may have to use one hand to move both pieces of one side while using the other hand to move both pieces of the other side. This can lead to inefficiency in operation.

The side compression box also has strengths and weaknesses. Its primary weakness is that it is usually narrow in width when opened to accept a charge. This side compression ram is difficult to guide during its movement. Most types use the box frame to try to keep the ram from cocking.

While this may be successful, it creates a loss of compression force caused by the friction of the ram against the box frame. When compressing, the lid and the side ram are used against each other, which could cause damage to the system over the long-term. Shearing tall materials can also be difficult using the side compression box design.

There are advantages to this design, however. The height and shape of the side compression ram makes for very effective use of the available force through this point-loading action. The height problem can also be overcome by using the over travel of the side ram to continually force the material close to the lid hinges. This gives the lid maximum effectiveness.

When the lid is allowed to travel below the top of the box, it can position the material to allow the side ram to use its maximum force. The lid hinges are mounted above the bed and out of the way of the material that causes so much damage. Some boxes on the market use a tube to guide the side ram during its travel. This allows for use of the maximum force with no loss due friction.

Once the charge is completely compressed and ready for shearing, the side ram can be moved away from the charge. This reduces wear and eliminates shock and vibrations. The closed box with lid and side ram completely forward leave an open area that can be used for a charging area, thereby eliminating the need for a dumb hopper.

The power pack is the heart of the shearing system. It is by far the most important element, as it determines the tons-per-hour of output.

Some manufacturers offer low horsepower and low operating pressure systems. These systems are designed to consume electric power efficiently, but these systems only offer an average of three to four cuts per minute.

Other systems use a combination of high-pressure piston pumps and low-pressure valve pumps. These systems offset their higher horsepower requirements by offering an average of five to seven cuts per minute. Until the scrap is cut, there is no production. Cuts per minute determine the tons produced at the end of the shift.

There are other points to consider when comparing high-pressure and low-pressure pumps. Low-pressure pumps are usually vane type pumps. These pumps generally cost less to purchase but require extensive maintenance. The high-pressure pump is usually a piston pump. This pump is more expensive to purchase but it is relatively maintenance-free and more dependable over a longer period of time.

The system that is designed with less shock is usually the system that performs with less downtime and maintenance. The design of the hydraulic systems generally determines the overall efficiency of the system.

A new shear is a major investment. For many operations, it may be the largest investment the company will ever make. With this in mind, the capital cost of the equipment itself should not be the overriding consideration in the buying decision.

The proper piece of equipment can be a vital, efficient component in a scrap processing operation for 20 years at least. Those can be 20 productive years, requiring little more than the usual preventive maintenance and wear-and-tear servicing, or they can be years plagued by frequent downtime, costly servicing and other nightmares just to keep the shear in operation and justify the investment.

Take a serious look at the three main components of a hydraulic ferrous shear, and thoroughly review them with the other members of your organization. Before putting your money down, have full knowledge of the strengths and weaknesses of not only the product, but the company that manufactures it and people at that company who will have to stand behind and support that product once it’s a part of your operaton.