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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 discussing the cycle time of a scraper. Can anyone tell me what components make up this cycle?
Is it just loading and dumping time?
Good start! The full equation is Cycle time = LT + HT + DT + RT + ST + TT + ADBT, where each letter stands for a specific type of time. Can anyone break down what LT stands for?
LT is Load Time, right?
Correct! LT represents how long it takes to load the scraper. Now, why is this time fairly consistent across different scraper sizes?
Because they often use a pusher, so the load time doesn’t change much?
Exactly! The pusher helps optimize this process. One helpful way to remember the components is through the acronym ADBT - Acceleration, Deceleration, Braking Time. Let's keep this in mind as we go on.
Okay, can anyone summarize what we just discussed?
We learned that the cycle time includes various components and that LT is influenced by using a pusher.
Great summary! It’s important to understand how each part plays into the whole cycle time.
Let's delve deeper into fixed vs. variable time components. Who can explain what fixed time includes?
Things like loading, dumping, and turning time?
That's right! And can someone tell me what defines variable time?
Variable time depends on travel distance and machine speed?
Exactly! Haul and return times fall under this category. What factors can affect machine speed?
Project conditions like rolling resistance and grade resistance.
Perfect! Let’s remember that maintaining the haul route is key to reducing cycle time. Can anyone think of why?
Because a well-maintained route helps with speed and reduces wear on the machine.
Great observation! This sum up how both components impact our overall cycle time.
Now, let’s talk about loading time and the load growth curve. What happens if we try to overfill a scraper?
It actually reduces the loading rate because of resistance?
Exactly! This principle is called the law of diminishing returns. Can someone explain the optimal loading time concept?
It’s the best loading time to maximize efficiency, not just filling it to the max capacity.
Right! We want to optimize our loading strategy. Closing this session, how can we gather this data?
From either the load growth curve or directly from manufacturers.
Exactly! Very well summarized.
A complete range of time actions involved in the scraper's operation.
Time impacts that do not depend on travel distance.
Time impacts that are dependent on travel distance and machine speed.
How long it takes to fill the scraper.
A concept highlighting efficiency drop when overloading.
Cycle time has seven parts, each plays a role from the start. Loading, hauling, dumping are a must, to keep the scraper's work a trust.
Imagine a scraper on a journey, every step it takes matters! Each part of its travel—from loading to dumping—contributes to how long it takes to finish its job well.
Remember ADBT for Acceleration, Deceleration, and Braking Time!
CYCLE helps to remember: C – Components, Y – Yield time, C – Conditions, L – Load impact, E – Efficient use.
Term
Cycle Time
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Term
Load Growth Curve
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The total time taken for one complete working cycle of the scraper, including all phases from loading to returning.
The time required to load materials into the scraper.
The time spent transporting the load from the source to the dump site.
The time taken to dump the load of materials at the designated site.
The time spent returning the scraper to the loading area after the dump.
The time taken to position the scraper properly for loading.
The duration required for the scraper to turn around during its operation.
The time required for the scraper to accelerate, decelerate, and apply brakes.
A graphical representation that shows the relationship between loading time and the percentage of payload in the scraper's bowl.
This section explains the calculation and components that make up the cycle time of a scraper, emphasizing the importance of load, haul, dump, return, spot, turn, and acceleration/deceleration times.
The cycle time of a scraper is the total time taken for a complete working cycle and is composed of both fixed and variable time components. Fixed times include loading, dumping, and turning times, while variable times are heavily influenced by the travel distance and the machine’s speed. Optimizing these times is crucial for enhancing productivity.
The cycle time of a scraper can be expressed as:
Cycle time = LT + HT + DT + RT + ST + TT + ADBT
(Where: LT - Load Time, HT - Haul Time, DT - Dump Time, RT - Return Time, ST - Spot Time, TT - Turn Time, ADBT - Acceleration, Deceleration, and Braking Time)
This section thoroughly explores each component contributing to the scraper's cycle time, which can be categorized into fixed and variable times. Fixed times, such as loading, dumping, turning, acceleration, deceleration, and braking, do not depend on the travel distance. In contrast, haul and return times vary based on travel distance and the speed of the machine, which is influenced by site conditions, such as rolling resistance and grade resistance.
Loading time for scrapers is consistently efficient across different sizes, largely due to the assistance of a pusher. Manufacturing data indicates that an average load time for a pusher-loaded scraper in common earth is around 0.8 minutes.
However, it’s important to consider the load growth curve which shows that excessively loading the scraper beyond 85% of its capacity can decrease productivity due to material resistance during loading, an effect referred to as the law of diminishing returns. The optimal loading time should be derived from the load growth curve or manufacturer specifications.
This component depends on the speed and distance traveled. Proper maintenance of the haul route can lead to improved productivity by reducing cycle time and unit production costs, highlighting the importance of effective route management.
Dump time is influenced by the scraper size and the type of material being handled. Effective loading techniques can ensure maximum efficiency, particularly when dealing with cohesive materials.
The average turn time varies between the filling area and the cutting area. The increase in congestion in the cut area can lead to higher turn times compared to the fill area.
Understanding and optimizing the cycle time of both scrapers and pushers are essential for enhancing performance in earthmoving projects.