Shear power: learning how scrap shears work is the best first step in the shopping process.

When shopping for a hydraulic ferrous shear, one helpful technique is to take a look at 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.

Throughout the years, these design flaws have been corrected by the manufacturers who serve the shear market. Processors are faced with almost as many models and styles as those made available to consumers by the automotive industry.

MATCHING UP. Many specialized applications require require a shear with special features for the material to be processed, such as 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 inches for foundry material, 60 inches 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 range of 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 the trees--the actual features 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 flame, or cutter head; the feed box; and the power pack.

SHEAR FRAME. 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 during 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 during the shear's lifetime. 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 during 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 flame is also very critical. The shape of the guide area and the material used to line the guide surface are very important. The shape of the guide area can determine if the cutting force 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 emergency protection.

The knife angle is an important feature of the shear. On most shears, knives are angled at seven 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, overload that side of the frame. Most manufacturers stay in the seven- to 10-degree range in an effort to eliminate, or to 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 optimizes the position of the material to be sheared. This feature can increase shearing efficiency by as much as 20 percent and 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 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, sometimes making proper cutting clearance impossible. Thru bolts are needed 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.

POWER PACK. The power pack is the heart of the shearing system. It is by far the most important element, as it determines cuts per minute and thereby 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 they only offer an average of three to four cuts per minute.

Other systems use a combination of high-pressure piston pumps and low-pressure vane 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.

Other points should be considered 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 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 scrap shearing system.

INVESTMENT. 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 shearing equipment can be a vital, efficient component in a scrap processing operation for 20 years at least. Those can be 20 productive years for a company, 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 to justify the company's initial investment.

A scrap processing operation's manager should take a serious look at the three main components of a hydraulic ferrous shear and thoroughly review them with the other members of his or her organization. Before putting the money down on a new shear system, a scrap processing company should have full knowledge of the strengths and weaknesses of not only the product, but also the company that manufactures it and the people at that company who will have to stand behind and to support that product once it's a part of the scrap processor's operation.

The author owns Gunn Phillips Associates LLC, a Dade City, Fla.-based independent vendor of new and used scrap processing equipment and operations consulting services. He can be contacted at [phone].