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Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to Cycle Time Components
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Today, we're going to learn about the cycle time of a scraper. Can anyone tell me what cycle time includes?
Doesn't it include load time and haul time?
Yes, exactly! Cycle time is defined by several components: Load Time (LT), Haul Time (HT), Dump Time (DT), Return Time (RT), Spotting Time (ST), Turning Time (TT), and ADBT, which stands for Acceleration, Deceleration, and Braking Time.
How do we categorize these times?
Great question! We can divide them into fixed and variable times. Fixed times do not depend on travel distance, while variable times depend on both distance and speed.
What are examples of fixed time?
Examples of fixed time include loading and dumping times, as they do not change with distance. Let's summarize: fixed time includes loading, dumping, and turning, while haul and return are variable.
Understanding Variable and Fixed Times
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Now that we've covered the components, how can we differentiate between fixed and variable times?
Fixed time is not affected by how far we travel, right?
Exactly! The loading, dumping, and turning times are fixed because they remain constant regardless of the distance. Now, can anyone tell me what makes haul and return times variable?
That's because it depends on the distance traveled and the speed of the machine.
Right! The speed can be affected by different project conditions, which is why we need to consider these factors when assessing cycle time.
Load Growth Curve and Diminishing Returns
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Let's now explore the concept of the load growth curve. Why do we need to be cautious about loading scrapers to full capacity?
Because overloading can reduce the loading rate?
Absolutely! As the bowl gets fuller, the material inside starts resisting incoming earth, which leads to what we call the law of diminishing returns. Can anyone think of a practical implication of this?
Regularly checking the optimal loading time to avoid wasting time?
Yes! Aiming for the optimum loading practices enhances efficiency and reduces unnecessary delays.
Haul and Return Time Maintenance
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Now, let's talk about haul and return times. What can we do to optimize these times?
We need to maintain the haul route well to make it easier for the machine to travel.
Exactly! Maintaining the haul route reduces rolling resistance, which, in turn, increases the travel speed and productivity of the machine. Can anyone suggest methods to maintain the haul route?
Using water trucks and graders!
Correct! Those practices will significantly help in reducing cycle time and enhance productivity.
Cycle Time of Pusher Tractors
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Let's transition to discussing pusher tractors. How do they assist scrapers in cycle time?
They help reduce the loading time of scrapers!
Correct! They can even serve multiple scrapers. But why is it important to balance the number of pushers with scrapers?
To prevent either from waiting on the other, which would increase the cycle time and reduce efficiency.
Exactly! Balance is key to optimizing production. Now, can anyone list what parts make up the cycle time of a pusher?
Loading time, boost time, maneuver time, and positioning time!
Well done, everyone! Let’s wrap up with a quick recap.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
Cycle time is crucial for understanding the efficiency of a scraper. It can be divided into fixed time (loading, dumping, turning, acceleration, deceleration) and variable time (haul and return), which reflect the impact of distance and speed on productivity. Insight into optimum loading practices also helps maximize operational efficiency.
Detailed
The cycle time of a scraper is defined mathematically as the sum of various time components: Load Time (LT), Haul Time (HT), Dump Time (DT), Return Time (RT), Spotting Time (ST), Turning Time (TT), and Acceleration/Deceleration and Braking Time (ADBT). The important takeaway is that cycle time can be categorized into fixed and variable elements. Fixed times are consistent regardless of distance, including loading, dumping, and turning, while variable times, such as haul and return times, depend significantly on the travel distance and speed of the machine, which, in turn, is influenced by project site conditions. The significance of load growth curves reveals that overfilling a scraper leads to diminishing returns on loading rates. By managing cycle time effectively, especially through proper haul route maintenance, operators can enhance productivity and reduce costs. Furthermore, pusher tractors are utilized for loading scrapers effectively, emphasizing the balance needed between pushers and scrapers for optimal operation.
Audio Book
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Understanding Cycle Time
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Cycle time = LT + HT + DT + RT + ST + TT + ADBT
(Where, LT-Load, HT-Haul, DT-dump, RT-Return, ST-Spot, TT-Turn, ADBT- Acceleration, Deceleration and braking)
Detailed Explanation
Cycle time is the total time taken to complete one full operation cycle of a machine. It includes several components: load time (LT), haul time (HT), dump time (DT), return time (RT), spotting time (ST), turn time (TT), and the time for acceleration, deceleration, and braking (ADBT). Each of these components contributes to the overall time taken in operating machines like scrapers in construction or mining projects.
Examples & Analogies
Think of cycle time like cooking a meal. Each step in the cooking process—like preparing ingredients, cooking, serving, and cleaning up—represents a component of your cycle time. Just like a meal takes time to prepare and serve, machinery in construction has specific tasks that take time to complete.
Fixed and Variable Time Components
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You can split the cycle time into 2 parts: fixed time and variable time. Fixed time does not depend on travel distance and includes loading, dumping, turning, acceleration, deceleration, and braking. Variable time is dependent on haul and return distances.
Detailed Explanation
Cycle time can be divided into fixed and variable components. Fixed time remains constant regardless of the distance traveled and encompasses tasks like loading, dumping, and the mechanical operations of the scraper. On the other hand, variable time is influenced by the distance traveled during the haul (moving material from one location to another) and return trips. This means that the more distance covered, the more time it takes.
Examples & Analogies
Imagine a car trip. The time spent getting in the car, buckling your seatbelt, and starting the journey is fixed—it doesn’t change based on how far you’re going. However, the driving time does depend on the distance you travel. If you have a long way to go, it will take longer, just like how a scraper takes longer for variable times based on how far it needs to haul material.
Loading Time Characteristics
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The loading time of the scraper is fairly consistent irrespective of the scraper size due to assistance from a pusher. The average load time for a pusher loaded scraper in common earth is about 0.8 minutes.
Detailed Explanation
Loading time for scrapers is generally uniform, regardless of their size, primarily because they are assisted by a pusher. This support means that varying sizes of scrapers will have similar loading times due to the additional force provided by the pusher. For common earth material, the average loading time is approximately 0.8 minutes.
Examples & Analogies
Think of loading a suitcase. It doesn’t take significantly longer to pack a larger suitcase if you have someone helping you. The assistance speeds up the process, just like a pusher helps the scraper load material faster. Even if the suitcase is larger, the loading time can still be quite similar when help is involved.
Load Growth Curve and Optimal Loading
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Loading scrapers to maximum capacity will reduce rather than increase the rate of production due to the resistance encountered by existing material in the bowl. This is called the law of diminishing returns.
Detailed Explanation
There is a common misconception that loading a scraper to its fullest capacity will always yield the best production results. However, past studies have shown that after reaching a certain fill level (around 80-85%), the loading rate decreases because the material already in the bowl starts to resist the addition of new material. This is an example of the law of diminishing returns; loading beyond a certain point is counterproductive.
Examples & Analogies
Consider trying to fit too many groceries into a shopping cart. Initially, you can add items easily, but once the cart gets full, adding more makes it difficult, and it might even spill over or make it harder to push. This is similar to scrapers—overloading leads to inefficiency.
Haul and Return Time Details
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Haul and return time depend on travel distance and machine speed. Maintaining the haul route is essential to reduce cycle time and improve productivity.
Detailed Explanation
Haul and return times are essential components of cycle time and vary based on how far material needs to be moved and the speed of the machinery involved. To ensure efficiency, it is crucial to maintain the haul route, as this minimizes resistance and allows machines to operate more quickly, which reduces overall cycle time.
Examples & Analogies
Think of it as a bicycle ride. If the road is smooth and well-maintained, you can cycle quickly and efficiently. However, if the road is rough with potholes, it will take much longer to get to your destination. Just like smoothing out a road for bicycles, maintaining a haul route for scrapers helps improve their travel efficiency.
Dumping Time Dynamics
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Dump time depends on scraper size, material type, and constraints in the dumping area. Larger scrapers generally need more time to dump, especially if the site is congested.
Detailed Explanation
Dump time varies significantly based on several factors: the size of the scraper, the material being dumped, and the conditions of the dumping site. Bigger scrapers naturally require longer to unload, and if the dumping area is crowded or has obstacles, it may take even longer due to waiting and maneuvering.
Examples & Analogies
Imagine trying to unload a large moving truck in a tight garage versus an open parking lot. If it’s crowded, you’ll take more time getting everything out. The same applies to scrapers and their dumping times.
Effects of Turn Time
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Turn time is generally independent of scraper type. However, turning in the cut area takes longer than in the fill area due to congestion.
Detailed Explanation
Turn times do not typically vary with the scraper itself. However, a scraper turning in a congested cut area often takes longer than in a less crowded fill area because there are more obstacles and equipment in the cut zone that may impede movement.
Examples & Analogies
Consider turning a car in a busy parking lot filled with people and other cars versus a wide-open road. It’s much easier and faster to turn in the open space, while in the crowded lot, you may need to stop and adjust your angle, adding time. This is similar for scrapers when turning in different work areas.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Cycle Time: The overall time taken by a scraper to perform its operations.
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Load Growth Curve: Understanding the optimal load for efficiency.
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Fixed Time vs Variable Time: Distinguishing between components that are constant and those that change based on distance.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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For instance, if the haul distance is doubled, the haul time will also double, thereby affecting the overall cycle time.
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An example of the load growth curve can be seen when a scraper is consistently filled to only about 80-85% of its capacity for optimal loading.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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In the cycle time race, Load, Haul, Dump in their place; Fixed times firm, variable can sway, Keep them balanced for work and play.
📖 Fascinating Stories
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Once upon a time, in a land of earthmovers, a brave scraper learned the importance of not overloading. It found joy in speeding down well-kept haul routes while keeping its partners, the pusher tractors, balanced for maximum productivity!
🧠 Other Memory Gems
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To remember the components of cycle time, think 'LHD 2 STT AD,' standing for Load, Haul, Dump, Spotting, Turning, Accelerate, Decelerate.
🎯 Super Acronyms
Remember 'LHTDSTTAD' to recall Load, Haul, Turn, Dump, Spot, Turn, Acceleration, Deceleration - the key components of cycle time!
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Cycle Time
Definition:
The total time required for a scraper to complete a loading, hauling, dumping, and returning operation.
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Term: Load Time (LT)
Definition:
The time taken to load material onto the scraper.
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Term: Haul Time (HT)
Definition:
The time taken to transport the loaded scraper to the dump site.
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Term: Dump Time (DT)
Definition:
The time taken to unload the material from the scraper.
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Term: Return Time (RT)
Definition:
The time taken for the empty scraper to return to the loading site.
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Term: Spotting Time (ST)
Definition:
The time taken to position the scraper at the loading site.
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Term: Turning Time (TT)
Definition:
The time taken for the scraper to turn during operations.
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Term: Acceleration, Deceleration and Braking Time (ADBT)
Definition:
The time taken for the scraper to increase/decrease speed and to come to a stop.
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Term: Fixed Time
Definition:
Components of cycle time that do not depend on travel distance.
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Term: Variable Time
Definition:
Components of cycle time that depend on travel distance.