Wear and Tear

Time is money." This is a familiar adage to processors of scrap metals, and it is particularly true when the market is sizzling as it is now. When the market is
this hot, scrap processors cannot afford to have a shredder down for an extended period of time awaiting replacement hammers or other critical wear parts. Wear part reliability and availability become imperative as the market for scrap metals improves.

Wear parts are essential to a shredder’s proper functioning, and operators have to consider more than cost when shopping for replacement wear parts.

Wear parts enable a shredder to run at its maximum processing capability, Art Borin, president of Amsco Wear Products Inc., Goshen, N.Y., says. "Wear parts should not just be designed to control cost, they should be designed to give you the best possible combination of wear life, feed rate, processing capability and, therefore, profitability."

EYEING THE BOTTOM LINE. Greg Stegmaier, product manager for Columbia Steel Casting Co. Inc., Portland, Ore., also stresses the importance of considering more than just the cost of wear parts.

"Do not over emphasize the price of the part," he says. "It’s the value obtained by using the wear part that should be the focus of your attention."

Determining the value of a wear part takes observation and calculation.

"As you process more tons, as you are able to find the magic combination in your shredder that allows you to process material at a high feed rate, obviously, your costs are going to go down because your produced tons are going to go up," Borin says. "You want to find the happy medium between cost, quality and the ability to process the material in an efficient manner."

Borin says shredder operators should strive to obtain "full-box" shredding, a concept he learned from Jim Mosebach of Metal Management, to maximize the longevity of their wear parts. "You have a burden or a load inside the machine that is not only working on the wear parts, but is also working on other pieces of scrap," he says. Such full-box shredding reduces the wear on the hammers and other parts inside the shredder box, prolonging their usefulness.

Industry estimates put the average cost of wear parts from $2 to $2.65 per ton of metal shredded. Although John Martinek, vice president of Levand Steel & Supply Corp., Birmingham, Ala., says wear parts for smaller machines could cost as much as $5 per ton of material shredded.

"The size of the shredder will make a significant difference in the cost percentage of replacement parts," Martinek says. Because wear parts have to be replaced more often in smaller auto shredders, they cost more per ton compared to wear parts for larger shredders, he says.

"The cost of wear parts is directly related to how much they shred," Rusty Manning, sales manager for Riverside Engineering, says. "Approximately two pounds of wear parts are consumed for every ton of steel shredded."

It is more difficult to determine the overall cost of wear parts as a percentage of an operation’s cost. This number varies by operation and depends on what figures the operator factors into the equation.

Randy Brace, vice president of engineering for Riverside Engineering, San Antonio, says shredder operators’ direct shredding costs can be broken down into five categories: labor, wear parts, utilities, maintenance and fuel. He adds that shredders have evolved during the years to shred at higher densities while consuming less energy and fewer wear parts and requiring less maintenance.

"All of these improvements have led to lower costs per ton," Brace says. "On average, the overall percentage of the wear parts to the total direct shredding costs should be between 20 percent and 25 percent."

Brace says that when costs such as waste disposal, depreciation, interest, property and equipment costs and other administrative and overhead costs are factored into the equation, wear parts represent from 5 percent to 15 percent of a shredding operation’s total costs.

VARYING DEGREES OF WEAR. Shredder boxes are comprised of a variety of wear parts, including hammers, anvils, rotor caps, end disk caps, pin protectors, side liners, grates and reject doors. While everything within the shredder box receives material impacts and will eventually need to be replaced, the degree of wear varies for each part.

"The expected life on a hammer is a lot shorter than everything else in the mill," Kevin Toft of Riverside Engineering says. Toft is a sales account manager located in Riverside’s Moline, Ill., office.

"Hammer cost will make up about 50 percent of total overall replacement casting costs," Martinek says.

Brace says that apart from hammers, castings showing the highest wear rates and replacement costs are bottom grates, anvils/cutter bars, rotor caps, pin protectors and upper anvils/upper breaker bars.

Toft adds that side liners historically have the longest wear. "Depending on what they shred and how much they shred, some customers will have side liners that last a year; some will have side liners that last three to four years."

Valerie Horvat of Global Partners Alliance LLC, Bettendorf, Iowa, says rotor caps are another high-wear item. "The reason that those particular products were invented was to cover a more expensive component on the rotor to protect it from impact," she says. "The theory was that you could replace these smaller parts more cheaply and keep your big capital investment protected for as long as possible."

Global Partners distributes SWB castings, which are manufactured in Germany.

Manning says that anvils typically can withstand between 30,000 and 50,000 tons of shredded material before they need to be replaced, while grates can withstand from 35,000 tons in smaller shredders to 150,000 tons in some larger shredders.

Borin says secondary wear parts would be roof plates, reject doors and top grates.

Denny Jennerjohn, a shredder engineer at Metso Lindemann, Cedar Rapids, Iowa, cautions against overextending the running time on some parts, which could cause excessive wear in other areas. "An example would be if they overextend the running time on a set of hammers, they are going to cause excessive wear on the rotor in certain areas. The result of this is that they exchange the lower cost of hammer material for the higher cost of rotor wear material," he says. "Another example would be running your side liners too long, which could also cause excessive wear on rotor end discs."

Operators have two primary material categories to choose from when purchasing wear parts for their shredders: manganese steel and alloy steel. These materials have different characteristics as far as impact resistance and abrasion are concerned.

SELECTING WEAR MATERIAL. "Alloy steel is a through-hardened material, which means that when you receive it, it is as hard as it is going to get," Borin says.

"Manganese steel is a work-hardening material, which means it starts off at 250 Brinell and the harder you hit it, or the more you subject it to impact, the harder the material becomes. It develops a work-hardened exterior, but retains a ductile core," he says.

Jennerjohn says, "If they are running alloy wear parts and they are trying to shred plate and structural steel, they are probably going to have breakage issues. If they are running alloys, they should stick to cars and light iron. If they are trying to run plate and structural to produce a foundry grade, they should consider manganese materials."

For an operation that often encounters unshreddables in its feed stream, Brace recommends manganese hammers.

"Manganese hammers are extremely tough and break resistant with the ability to work harden at the impact surface," he says. "This unique characteristic of manganese, along with its lower cost, has proven to provide many shredders with trouble-free shredding."

Martinek says most rotor caps are made from alloy steel, which is not suitable for grates, liners and breaker bars.

Brace adds, "Alloy hammers are an excellent choice for shredders that have a consistent feed of ‘regular’ shredder scrap, i.e. autos, loose tin, white goods and a little plate and structural." He says alloy hammers can provide a lower cost per shredded ton.

Stegmaier says, "There are still shredder operators who use solely manganese and those that solely use alloy steel. Other operators use a mix depending on the material being shredded or to give an even wear across the rotor."

Alloy steel wear parts can also be differentially hardened. Pat Comparin of Global Partners describes the SWB differentially hardened hammers as being softer near the pinhole. However, the bottom of the hammer, which is through-hardened, is nearly twice as hard in comparison, he says.

Global Partners’ Horvat says a differentially hardened hammer provides two advantages. "It is going to give the operator longer wear life on his hammer pin because that pin area is softer and is not going to gouge into the hammer pin like traditional hammers have done. But the impact surface of the hammer is harder, not only than the pin area, but harder than other hammers," she says.

In addition to choosing the correct wear part material based on their operations, shredder operators can do a number of things to increase the longevity of their wear parts.

INCREASING LONGEVITY. Horvat suggests buying the most high-end, longest-life product available. She says she believes that once the operators do the calculations, their cost per ton will be lower, and they will have spent less time replacing hammers.

Riverside’s Manning suggests modifying the layout of older shredders, positioning the wear parts for maximum wear, while Toft recommends proper maintenance of the shredder itself. "A properly maintained shredder and rotor are going to run through fewer stationary wear parts, fewer liners and grates."

Martinek says operators should look for improvements in wear part design. He also suggests looking for unshreddables. "Operators can save labor and production costs of unscheduled downtime by carefully examining their scrap and raw material for unshreddables."

Brace offers processing tips for increasing the longevity of a shredder’s wear parts. He suggests mixing heavier and lighter scrap metals together to generate optimum production while reducing wear. Decreasing the amount of dirt processed with the scrap metal also reduces wear. Brace also suggests shredding only to the density that you need. "Wear in the shredder goes up exponentially with an increase in density."

Borin says, "The best thing an operator can do is very carefully use scientific testing procedures to establish baseline performance data. After doing that, they can experiment to see if they can obtain better wear life and better performance using different designs, different materials, etc."

While this type of scientific comparison may cost shredder operators some time, it may save them considerable money in the future.

The author is associate editor of Recycling Today and can be contacted via e-mail at dtoto@RecyclingToday.com.