There is a common misconception that higher digging arm crowd force equates to better digging performance.
Using digging arm crowd as the main means of filling a bucket in hard ground can actually result in higher fuel consumption, slower bucket filling time and more stress on the excavator.
The most efficient way to fill the bucket is to use bucket curl to break through the soil and then use the boom to raise the bucket out of the ground.
The angle of the bucket teeth is part of this: the cutting angle should allow the bucket to penetrate the ground with the least amount of resistance, while the bucket curl fills the bucket as quickly as possible and lifting the bucket out of the ground as soon as it is full decreases resistance and improves cycle times.
Despite this I still see plenty of operators trying to pull the bucket through the ground using arm force.
By using arm force, the operator is effectively trying to push hundreds of tonnes of dirt horizontally. This slows the cycle times and increases fuel consumption dramatically.
When pushing against that amount of resistance, it also increases stresses on the excavator and can lead to higher maintenance costs and more downtime.
A simple way to look at this is to consider how you dig in your backyard at home. Grab your shovel and break out soil the conventional way by driving the shovel into the ground and then pulling back to fill it.
Then try filling it by pushing it horizontally in the ground, and see how much extra energy you need to apply and how much longer it takes you to fill a shovel. An excavator is no different, and the things that you noticed in the backyard equate to extra fuel and a longer cycle time in an excavator.
If you don’t mind getting your hands dirty, and even better example would be to use your hand to dig, because excavator arm geometry is similar to the human arm. Compare digging by using your wrist to close your fist on some dirt with dragging a semi-open hand through the soil using elbow action.
The difference in time taken to fill the fist and the force required for this should be readily apparent.
Contractors measure productivity by calculating how many cubic metres of soil can be shifted per litre of fuel burnt. It’s all about completing the maximum amount of work while using the least amount of effort.
Kobelco keeps this to the forefront when developing its excavators. This has led to Kobelco being widely regarded as a market leader for production and fuel economy across successive generations of excavator.