How your choice of bucket steel impacts the bottom line

Buckets don’t always get the attention they deserve.

And that’s too bad, because there’s money to be saved right from the start – just by choosing the right steel.

Buckets work hard on a range of machines, from track excavators, wheel excavators and track loaders to wheel loaders, backhoe loaders and within dragline operations. There is plenty of room for improvements in all of these applications.

Naturally, all buckets are subjected to wear. Even if general-duty or heavy-duty buckets work with less abrasive materials, such as soil and clay, they will benefit from a harder abrasion-resistant steel as service life will increase while maintenance costs will decrease. Compared to using a mild steel, the positive effects can be dramatic.

When working in more abrasive materials, such as rocks and gravel, a severe-duty bucket is an ideal choice. For a severe-duty bucket, the right steel becomes even more crucial.

Using premium abrasion-resistant steel makes good business sense. A severe-duty bucket built with steel with a Brinell hardness of 400 to 500 HBW will last much longer and save operators money by minimizing downtime for maintenance and repairs.

Another advantage is that severe-duty buckets add flexibility to operators. They’re more of a multitasker than general-duty and heavy-duty buckets. A severe-duty bucket’s capacity may not be optimized to work in softer materials, but its overall versatility for all kinds of abrasive materials often makes the severe-duty bucket a cost-effective choice.

Steel’s value

The harder the abrasive material, the more important it is to select the steel in the bucket carefully.

If a bucket’s structure is made of a relatively mild steel, such as A36, grade 50, A514 or S355, and exposed to abrasive materials, the service life will be short and costs for repair and downtime are going to be high.

To increase service life, the milder steel should be “beefed up” with wear-resistant components – a wear package for protection. This kind of bucket is not optimized for its task. It has a lot of deadweight in the structure due to the combination of mild steel and additional wear parts.

It’s possible to make a bucket that is both stronger and lighter than a bucket made in milder steel. The trick is to use a hard steel that is tough enough to also work as a structural steel.

A bucket with all of its main components – floor, shell, side sheets, cutting edge, side cutters, cheek plates, wear bars and wear plates – made of a wear-resistant steel such as Hardox 450 will be both strong and light. It will also outlast buckets with lower-grade steel several times.

When the abrasion-resistant steel is both hard and tough, the bucket’s performance can be optimized for strength, lightness and high capacity. That’s the benefit of using a high-quality wear steel with structural properties.

The high wear resistance of Hardox steel, for example, often allows the use of thinner material – 3/4-in. Hardox 450, for instance, instead of 1-in. mild steel – saving 25 percent weight without jeopardizing performance and service life.

Thinner material will reduce the bucket’s weight, which, in turn, reduces the wear and tear on the hydraulic system and on the excavator boom. It also reduces fuel consumption. Or, if service life is a major concern, keeping the same thickness will make the bucket last even longer.

A lighter bucket allows for a higher-capacity bucket to be used and has the potential to cut down the number of passes when loading a truck, resulting in a substantial increase in productivity. If, for example, it takes a wheel loader three passes instead of four to load a dumper, it makes the loading 25 percent more efficient.

When steel meets rocks

By simply matching the steel grade against the most commonly handled abrasive material, producers take a major step toward a long-lasting bucket with minimal repair and maintenance costs.

Wear depends mainly on three conditions: the abrasive materials, the type of steel and the general conditions (i.e., operating technique, dry or wet material, temperature). All of these factors affect the bucket’s service life.

Rocks or other highly abrasive materials vary in hardness and shape. Every type of rock wears in its own unique way. A single rock often contains different mineral grains of varying hardness and shape.

A hard material such as granite consists of quartz, feldspars and biotite. Quartz is predominantly the most abrasive material in all ore and rock handling. The higher the content of quartz or other hard minerals, the greater the wear and the greater the need for attention to wear resistance for the steel used in the bucket.

Wear abrasive material, such as aggregate rock, is free to slide and roll. With impact wear, the rock hits the surface of the wear component at various angles. To withstand a combination of sliding and impact wear, the steel needs to be both hard and tough.

The wear drop

The steel’s hardness is usually measured in Hardness Brinell (HB). The harder the steel, the harder the minerals it can handle without excessive wear.

For many abrasive minerals, such as granite, there is a transition zone where fast wear changes to slow wear. As an approximation, fast wear will occur if the mineral is more than 1.8 times harder than the steel.

Put simply, it’s a matter of different wear mechanisms coming into play. The wear rate graph (see page 20) shows that cutting wear gives a faster wear rate than plastic wear. If the steel is hard enough, the edges of the mineral will not be able to cut into the steel’s surface, resulting in a slower wear rate.

For granite, the transition to slow wear starts at around 340 HB and then drops rapidly as the hardness increases. From a service life point of view, this makes it all the more important to choose a steel grade that is hard enough for the actual abrasive material.

The Wimmer experience

Wimmer International, a European-based manufacturer of excavator attachments, has been in the North American market for more than 20 years.

From its Maine operations, Wimmer North America provides buckets and other attachments to the United States and Canada through a dealer network. Wimmer has been producing buckets with Hardox for more than 10 years, mainly working with Hardox 450, which offers about 50 percent longer service life than a 400 HB AR material of the same thickness, according to SSAB.

“Customers who watch their cost choose our excavator buckets and attachments,” says Eric Clark, general manager at Wimmer North America. “They understand the concept of buying quality. A product that performs better and lasts longer is less expensive in the long run. They will experience fewer breakdowns and get a product worth maintaining and rebuilding. It’s just a question of doing the math.”

According to SSAB, Wimmer North America is one of the first companies in the U.S. that is both a Hardox Wearparts center and a certified Hardox In My Body member. This means Wimmer North America is dedicated to using Hardox in its products – and for good reason.

“The difference between Hardox 450 and a traditional AR steel is not only the longer service life,” Clark says. “Another important advantage is that Hardox is workable. We can build a complete bucket out of Hardox, and it doesn’t give us any production problems.”

Information for this article courtesy of SSAB.