Casting Call

Operators of automobile shredders have numerous ongoing expenses, including the cost to purchase hammers and other castings used within the plant.

With automobile shredding continuing to grow as a scrap processing technique in the past 20 years, the supplier base of companies offering castings also has grown.

Plant operators now have several choices not only in suppliers but also in the types of products (with competing shapes and chemistries).

Recycling Today Editor-in-Chief Brian Taylor recently asked one of these suppliers, Barry Sheppard, vice president of aftermarket sales with U.S. Shredder & Castings Group, based in Trussville, Ala., to provide an update on some of the newer options available to shredding plant operators.

Recycling Today (RT): For shredder operators who have been buying the same castings for more than a decade, what are some innovations that may be worth investigating?

Barry Sheppard: There have been several new designs in grates introduced. For example, there are staggered grates for spider rotors; progressive “no grow” grates; and double-beam grates for larger mills with high-horsepower, low-rpm configurations.

People are looking at staggered grates because I think they discovered that if you’re running a disc or spider rotor, what you want to do is place that grate opening under the hammer to improve the discharge time, even if you have to stagger the hammers somewhat. So operators want as many hammers as possible to be located in proximity to the grate openings to increase production.

The progressive “no-grow” grate is designed to address the problem of grate openings tending to flare out as they wear. This provides an unintended larger opening for material to move through as grates age. The new “no-growth” castings tend to hold their true initial form and retain openings with a uniform size.

Double-beam grates are for larger mills, usually the 98-inch mills and larger, that have high-horsepower and low-rpm motors. What can happen is that the rotors in this configuration have so much torque and power that the grates in these mills can bow downward before they even have a chance to wear out. Once the grate is bowed, material can fall through the gap that is created or it can cause material to settle outside the diameter of the hammer swing. A double-beam grate can prevent that bow shape from happening and get more life out of the grate.

RT: In what ways should shredder operators consider the make-up of their feedstock (i.e. percentage of auto bodies versus loose tin) when they are purchasing hammers?

Sheppard: What we have found in our conservations with customers is that if they are running more than 40 percent autos as feedstock the rule of thumb is to go with manganese hammers—but this is not always an easy answer.

For example, if you’re in the Midwest running obsolete farm equipment and auto hulks, manganese can make sense. If you are scheduling to run only heavy plate for several days, in the 98-inch mills the differential heat treated (DHT) alloy castings seem to perform well.

I’d recommend working with your supplier and be willing to try manganese, uniform alloy and DHT-alloy hammers as well as new designs.

It’s good to have an open dialog with suppliers. No one mill is quite the same as the others, and everybody has different feedstock. Beyond that, shredding plant owners can have different requirements from the steel mills, foundries or brokers to whom they are selling. What works for one operator may not work for another; there is no collective answer for decisions like this, and a lot of trial and error can be involved.

RT: To what extent should the rotor speed or motor horsepower be considered when shopping for hammers?

Sheppard: In general, in slower rotor speed mills with higher horsepower, you will obtain longer hammer wear life. But the downside is that a larger hammer may leave the operator with more “throw-away weight” (the weight of the hammer at the end of its useful life).

The general design of a hammer is in a “bell shape,” but the real key is designing a hammer that will provide maximum productivity and with less throw-away weight around the pin hole.

With hammers, the rule of thumb is that you don’t want the throw-away weight to be north of 50 percent of the weight at purchase. You’re paying for all 349 pounds (as an example), but if the hammer is not designed right or it’s wearing incorrectly and you’re left with 200 pounds of throw-away weight, it can be disconcerting because you paid for the whole darn thing.

The good news is that I think life spans are getting longer. There have been advancements in both design and chemistry. People demand a quality product and they’re not putting up with substandard suppliers.

RT: How does the heat treating process affect the durability or other properties of hammers?

Sheppard: It’s very important—it’s as important if not more important than the chemistry. Many of the casting failures operators experience are not because of chemistry problems but because of heat treatment shortcomings.

When there was something wrong with the heat treatment of a casting, it’s usually pretty evident to the operator by the presence of wormholes or fractures in the part. A castings supplier should spend the money to get an analysis done by someone who is qualified to do so. Make sure you’ve identified the problem. This involves good communication between the plant owner and the supplier.

Considerations including feedstock composition, rotor speed and horsepower can factor into the decision when auto shredder plant operators buy castings.

RT: What are some situations or unique or emerging shredder applications that may prompt a recycler and castings supplier to consult with a metallurgist to develop castings with new chemistry?

Sheppard: It usually has to do with the life span or wear patterns of the castings. Operators may feel that the wear life of their castings is diminishing. Or, a good time to work with new suppliers may be if they want to look at a redesign of their overall shredding plant.

Another situation is when they are dealing with suppliers who are not serving them well—either falling short on quality or missing their promised delivery times. If they are switching casting vendors, it just as often seems to be service-related as it is from casting failures. A lot of plant operators run lean inventories and they are depending on the supplier to deliver on time.

We recommend that a recycling company work with its casting supplier to design hammers, grates, etc. to meet their exact needs. This can include identifying to what extent they want to focus on production output required versus an ideal density required.

My suggestion is that operators or managers should work with their suppliers and be open in the dialogue. As suppliers, we should take the time to visit the shredder and sit down with operations people and know exactly what their needs are. Are they looking for higher density, more production or some combination?

Another important factor is whether the recycling company is open to trying a new product. If the recycling company’s leaders understand that they’re the first ones trying something new, and that we may need to work through the good, the bad and the ugly, then that provides a needed framework.

Plant operators who can keep good records of their production numbers and are willing to share them can provide the needed feedback that helps bring a new product to market.

Barry Sheppard works for Trussville, Ala.-based U.S. Shredder & Castings Group from an office in Belmont, N.C. He can be contacted at barry@usshredder.com.