Wear and tear: cost is not the only factor to consider when buying auto shredder wear parts

Recycling Today, April, 2004 by Deanne Toto

Valerie Horvat of Global Partners Alliance LLC, Bettendorf; Iowa, says rotor caps arc" 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 offal 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 arc 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.