Adjustment Factors for Height of Cut and Angle of Swing

Today, we're going to discuss the importance of truck positioning in relation to the excavator. Can anyone tell me why it's better to have the truck positioned close to the excavator?

Well, I think it's about making it easier to load the truck quickly?

Exactly! When the truck is close, the cycle time decreases because the angle of swing is minimized. In fact, when a truck is positioned at a 90-degree angle to the bucket, it’s in an ideal spot. Can anyone guess what happens to productivity if the truck is further away?

The productivity decreases because the excavator has to swing more, right?

Correct! Greater swing angles lead to longer cycle times and reduced productivity. Think of it this way: 'Closer is faster'! They both start with 'C' - a simple mnemonic to remember! Now, why do we want to minimize physical effort in heavy machinery?

To maximize efficiency, I guess.

Exactly! Great job! Remember, less effort equals more efficiency.

Let's delve into correction factors next. Why do you think we need to apply correction factors when the actual height of cut differs from the optimum?

Because it affects how effectively we can move the material?

Exactly! If the actual height of cut is the same as the optimum, the correction factor is 1, meaning no adjustment is necessary. When the cut is less than optimum, we apply a correction factor to account for reduced productivity. Can anyone help me remember the relationship between height of cut and productivity?

Higher cut means more effort, so we need to reduce productivity in our calculations?

Right! Conversely, the angle of swing works similarly. More than 90 degrees means we decrease productivity, while less than 90 degrees means we increase it. A useful rhyme is: 'Swing wide, productivity slides; swing tight, productivity's bright.'

That's a fun way to remember!

I'm glad you like it! Remember, adjustment factors are critical for accurate productivity forecasting!

Now, let's cover operational constraints like truck spotting clearance. Can anyone explain why it's necessary to have space for tail swing?

To prevent collisions when the excavator is turning?

Correct! We need enough clearance to avoid accidents, which can halt productivity. Speaking of productivity, what’s haul unit exchange time?

It’s the time taken for one truck to leave and another to enter for loading?

Exactly! We want to minimize this time to streamline operations. A good way to remember this is: 'Quick turnaround equals quick work.'

That’s catchy! I’ll remember it!

Great! Always keep these operational constraints in mind, as they directly affect your productivity estimates.

Let’s learn how to estimate shovel productivity! What do we need to consider in our calculation?

The heaped volume of the bucket and the cycle time, right?

Exactly! The formula also includes applying the correction factors for height of cut and swing angle. Can someone recall how job efficiency fits into this?

It’s how much time the machine spends working in an hour?

Spot on! If a shovel works for 45 minutes in an hour, you must multiply the productivity by that efficiency. A memory aid I have is: 'Work smart, not long!'

I like that saying!

Great! Keep that in mind when calculating productivity at your work sites.

Now, I have a practical problem for us to solve. A crawler mounted shovel with a bucket capacity of 3.44 cubic meters is loading rock, working at 3.18 meters high. How do we begin?

First, we need the optimum height of cut for this excavator.

Correct! If the maximum digging height is 10.6 meters, and we're working with blasted rock, we use 50% for optimum height. So what's that?

That would be 5.3 meters, so our actual height is 60% of the optimum.

Exactly! We then look for correction factors based on our conditions. What correction should we apply?

We will use the correction factor of 0.91.

Well done! So, how do we finish our productivity estimate?

Calculating based on the cycle time and fill factor and then applying that correction factor!

Perfect! Applying these principles in real scenarios is vital for accurate estimates. Keep practicing!