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A short class with Sarah and her students. The other ways are under More.
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Today, we're going to break down the cycle time of scrapers. Who can remind us what the formula is?
Isn't it Cycle time equals Load Time plus Haul Time and so on?
Exactly! The cycle time includes loading, hauling, and dumping times, among others. We can remember it with the acronym 'L-H-D-R-S-T.' What do you think LT, HT, and other components mean?
Loading Time, Haul Time, Dump Time? What do the others stand for?
Great questions! RT is Return Time, ST is Spot Time, TT is Turn Time, and ADBT is for Acceleration, Deceleration, and Braking Time. This means every part contributes to our total cycle time.
What affects the Haul and Return Time specifically?
Good point! Haul and Return Time varies based on distance and travel speed, which can depend on project conditions like rolling resistance.
So, the conditions of the haul route matter too?
Absolutely! Regular maintenance of haul routes reduces cycle time significantly. Let's keep these fixed and variable times in mind as we move forward.
Let's dive into loading time. Why do you think loading time remains consistent across different scraper sizes?
Is that because they use pushers to help load them?
Right! The assistance from pushers ensures the loading time doesn't vary much regardless of scraper size. Remember the average load time for a pusher-loaded scraper in common earth is about 0.8 minutes. Can anyone explain why trying to load too much is counterproductive?
Because it causes resistance inside the bowl which slows things down?
Exactly! This is where we encounter the law of diminishing returns. Filling beyond a certain level reduces loading efficiency. Understanding the load growth curve is critical for optimizing our operation.
Can we visualize this curve?
Yes! The curve illustrates how the percentage of payload versus loading time peaks initially and then drops. We need to aim for optimal payload to maximize efficiency.
Now let's move on to hauling times. Who can tell me what impacts the speed of hauling?
The condition of the terrain?
Exactly! And it’s also about ensuring the haul route is maintained. What maintenance methods can improve our travel speed?
Using graders and watering trucks to control dust?
Correct! Proper road conditions reduce both rolling and grade resistance. How does this relate to cycle time?
Less resistance leads to faster hauling, which reduces cycle time?
Absolutely! It improves productivity and helps control costs. Remember, the investment in haul route maintenance pays off!
Let's look at dump time next. Who knows what factors might affect it?
The size of the scraper and the material being dumped?
That's correct! Loose material is quicker to dump than sticky soil. Now what about turn times? How does congestion in dump areas impact turning?
If it's congested, it'll take longer for the scraper to dump and turn?
Exactly! And in terms of safety, it’s best to dump before turning. How does this keep the operation safe?
Yes! Safety is crucial. Remember to always weigh effectiveness against safety when planning operations.
Finally, let’s discuss the role of pushers in our cycle. Why is it important to balance the number of pushers and scrapers?
To prevent waiting times that could slow down operations.
Correct! Efficient coordination prevents increased cycle times. What other factors can impact the cycle time of a pusher?
The condition of the loading pit and the size compatibility of the pusher to scraper?
Absolutely spot on! Also, the method of loading plays a role. We need to choose the right loading technique for our equipment compatibility!
An example of fixed time could include the time taken for loading and unloading, which doesn't change regardless of how far the scraper hauls material.
An example of a variable time might be how long it takes to travel back to the loading site, which depends on the distance and the machine's speed.
When loading a scraper, take heed and beware, Too much weight will slow, so load with care.
Imagine a baker trying to fit too many loaves in the oven at once. The heat won't reach the middle loaves, much like how an overloaded scraper can't load efficiently.
Remember L-H-D-R-S-T to recall the components of cycle time: Load, Haul, Dump, Return, Spot, Turn.
ADBT: Acceleration, Deceleration, Braking Time - Keep machines in motion smoothly.
Term
Cycle Time
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Term
Load Growth Curve
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The total time taken to complete one full operation cycle in a scraper, including loading, hauling, dumping, and returning.
The portion of the cycle time that does not depend on travel distance.
The portion of the cycle time that varies based on distance traveled and speed.
A graphical representation showing the relationship between loading time and the percentage of the bowl filled with material.
The time taken to unload the material from the scraper.
A machine that assists the scraper during its loading phase.
This section discusses the components and calculation of the cycle time for scrapers, emphasizing the distinction between fixed and variable time and the significance of loading techniques.
The section explains the formula for cycle time in scrapers, breaking it down into its components - loading time, hauling time, dumping time, and more. It differentiates between fixed time elements that don't vary with distance and variable time elements that do. Additionally, concepts like the loading growth curve and factors affecting cycle time such as haul route maintenance are explored.
The cycle time of a scraper is calculated using the formula:
Cycle time = LT + HT + DT + RT + ST + TT + ADBT
Where:
In essence, cycle time encompasses all parts of the operation, with loading time noted as generally consistent across different scraper sizes when assisted by a pusher. Studies suggest that loading scrapers to maximum capacity might decrease production rates due to resistance buildup inside the bowl, emphasizing finding an optimal load capacity.
Furthermore, the section delves into the distinction between fixed time (which does not vary with distance) and variable time (which is contingent on distance and speed). It stresses the importance of maintaining haul routes to minimize resistance and increase efficiency, proposing effective practices to ensure lower cycle times. Dump time is influenced by factors like material type and site constraints. Moreover, the performance of a pusher is crucial, as it facilitates the loading of scrapers, and maintaining a balance between the number of scrapers and pushers is vital for optimizing productivity.