PICKING THE RIGHT BUCKETS IS CRITICAL FOR AGGREGATE OPERATIONS
Editorial focus by Harold Hough
Horsepower, hydraulics, computer controls and tires are all important to the efficient operation of heavy equipment at an aggregate operation. But all that equipment and technology must rely on buckets, blades, and ground engaging tools (GET) that actually move the material. Consequently, any attempt to save money on these parts can actually negate hundreds of thousands of dollars spent on high tech heavy equipment. “It’s surprising,” noted one heavy equipment salesman, “companies will spend thousands on new heavy equipment and then try to save a few dollars on the part that actually moves the earth.”
Ironically, the amount of money that goes into buying buckets and GET is immense. An aggregate operation will probably spend two to three times as much on earth moving parts for heavy equipment working in abrasive material over a 60,000 hour life than the original cost of the equipment. That doesn’t include the additional cost of installation, down time, or inefficiencies caused by running with worn parts. Nor, does it include the hidden cost of over-stressing the equipment because parts were worn or improperly used. Consequently, understanding the factors that determine the design of buckets, blades, and GET is important to making the right choice.
UNDERSTANDING BUCKET DESIGN
Choosing a proper bucket isn’t easy and requires balancing several factors. Unfortunately, there is no simple formula that will guarantee that you will pick the right equipment for the job. And, even if you do, there is a good possibility that the criteria will change during the life of the equipment. Therefore, it is important to understand the tradeoffs involved in designing buckets.
The key factor is making your equipment move gravel, aggregate, earth, or ore at the lowest price. That means getting the most amount of dirt in the bucket, getting the equipment to penetrate the earth, and making it durable.
The actual dimensions of the bucket are critical and determine how well an earth mover can use hydraulic power to dig. Bucket loadability is a function of the width of the bucket, the curvature, and the type of teeth on the bucket. Unfortunately, there are several tradeoffs involved and the bucket that can best penetrate the ground will not be the most durable bucket. In addition, different materials require different height to curvature relationships. Consequently, the only way to pick the best arrangement for your heavy equipment is to look at the various tradeoffs and pick a combination that gives you the lowest cost per yard of material moved.
One important factor is bucket width. A wide, shallow bucket will load loose material more quickly than a deep, narrow bucket with the same capacity. However, when digging in a material that is tougher to penetrate, a wide bucket may have more trouble penetrating the mass because as the width of the bucket increases, the force per inch of cutting edge decreases. In that case, a narrow, deep bucket that can focus the force onto a narrow edge is better. But the selection isn’t that cut and dried. If the material is also sticky, a shallow bucket is better for unloading. In that case, some compromise between deep and narrow and wide and shallow has to be reached.
Engineers who work for heavy equipment manufacturers have investigated the science of digging because it determines bucket performance and how aggressively the heavy equipment can dig. The engineers have discovered that the key factors include bucket design, the amount of hydraulic power available and the boom/stick geometry.
The amount of force that goes into digging is determined by the tip radius, which is the distance from the bucket tips to the bucket pin (which connects the bucket to the main boom). The shorter the distance between the pin and tip, the greater the breakout forces and the less capacity in the bucket. However, the capacity can be increased by making the bucket wider or deeper, but as mentioned earlier, wider buckets don’t have the same penetration ability and deep buckets can’t handle sticky material.
The edge of the cutting edge can also improve the digging forces. A thin edge penetrates better, but does not wear as well as a thicker edge. A V-type edge also penetrates better than a straight edge because the amount of force per inch is greater than with a straight edge.
By now it’s obvious that there could be an infinite number of bucket designs. Consequently equipment manufacturers have designed several generic bucket designs for a variety of uses. There are general purpose buckets with more capacity for a given width, and lighter, higher-strength structures to decrease load time and increase payloads. On the other end of the spectrum, there are heavy duty rock ripping buckets with special tooth designs that applies the entire machine force to one or two teeth for maximum penetration in hard rock. In between are designs for abrasive or heavy materials that require special handling.
However, the most important tool in picking a bucket is the mind of the buyer. Don’t necessarily look for the cheapest bucket with the biggest payload. Look at the various designs and the needs of your operation to make the best choice.