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Interactive Audio Lesson
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Introduction to Cycle Time Components
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Today we're going to dive into the cycle time components of a scraper. Can anyone tell me what some of these components might be?
Maybe loading time? I think there's also dumping time?
Great! Yes, loading time and dumping time are part of it. We also include haul time, return time and the time spent turning. These can be divided into fixed and variable time components. What's the difference between fixed and variable time?
Fixed time doesn’t change with the distance traveled, right?
Exactly! Fixed time includes loading, dumping, and turning. Variable time, on the other hand, is influenced by the distance traveled and it includes haul and return time. Can anyone explain why that’s important?
Because it helps us optimize our operations and reduce costs by understanding what affects the cycle time?
Exactly right! It’s all about maximizing efficiency. Let's move on to how we can visualize this with the load growth curve.
The Load Growth Curve
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Let’s talk about the load growth curve. What do you think happens when we load the scraper to maximum capacity?
I think it should increase production, right?
That's a common belief! However, studies show that it reduces production after a certain point. Why do you think that might be?
Is it because the material being added bumps against the loaded material?
Exactly! After the bowl is about 85% full, the incoming material faces resistance, leading to diminishing returns. We need to understand this to find the optimal loading time.
How do we find that optimal point?
We can draw the load growth curve and analyze the data to see how loading efficiency changes. In summary, loading beyond optimal levels wastes time and effort.
Importance of Haul Route Maintenance
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Next, let’s examine how maintaining the haul route impacts cycle time. Why is this an important aspect?
If the haul route is not maintained well, it might increase resistance, right?
Absolutely! Poor conditions can slow down the scraper’s speed and increase cycle time. What could we do to improve the haul route?
We could use graders or bulldozers to maintain the route and sprinkle water to control dust!
Exactly! Those actions reduce drag, increase speed, and ultimately improve productivity. Let’s remember that maintaining the haul route is an economical way to optimize output.
Introduction & Overview
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Quick Overview
Standard
The load growth curve section explains cycle time components such as load time, haul time, dump time, and return time, highlighting the fixed and variable time aspects. It introduces the load growth curve's significance in determining the optimal loading time for scrapers and cautions against overloading, which leads to diminishing returns on productivity.
Detailed
Load Growth Curve
The load growth curve conceptually illustrates the relationship between loading time and payload percentage in operation. It provides insights into how scrapers function and their cycle times, broken down into components such as load time, haul time, dump time, and return time. The total cycle time consists of fixed and variable components, where fixed time encompasses loading, dumping, and turning, while variable time refers to haul and return based on distance traveled.
An important principle is identified in the load growth curve, challenging the belief that filling the scraper to maximum capacity increases production. Research shows diminishing returns occur once the scraper bowl exceeds around 85% full, as the incoming material encounters resistance from pre-existing material. Understanding this can help optimize loading strategies and avoid wasted effort. The subsequent parts of the section also discuss haul routes, their maintenance, and the significance of optimizing cycle times of scrapers and pushers in light of project conditions.
Audio Book
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Cycle Time Components
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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)
So, cycle time of a scraper is nothing but load time, hauling time, dumping time, return time, spotting time, turning time, and ADBT.
Detailed Explanation
The cycle time of a scraper is the total time taken for it to complete one full operation cycle, which includes several components:
- LT (Load Time): Time taken to load material into the scraper.
- HT (Haul Time): Time taken to transport the material to the dump site.
- DT (Dump Time): Time taken to unload the materials.
- RT (Return Time): Time taken to return to the loading site.
- ST (Spot Time): Time needed to position the scraper before loading.
- TT (Turn Time): Time spent turning at the loading or dumping sites.
- ADBT (Acceleration, Deceleration and Braking Time): Time taken to speed up, slow down, or stop the scraper.
Understanding these components helps in optimizing the operation and efficiency of the scraper.
Examples & Analogies
Imagine driving a car. The different components of the car's journey (like starting, speeding up, driving at a constant speed, slowing down when approaching a stop, and stopping) resemble the cycle time components of the scraper. Just like a driver needs to manage these stages for efficient driving, a scraper operator needs to manage cycle time components for effective material handling.
Fixed and Variable Times
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Cycle time can be divided into fixed time and variable time. Fixed time does not depend on travel distance, while variable time (haul and return) depends on distance and speed.
Detailed Explanation
Cycle time can be categorized into two types:
1. Fixed Time: This includes tasks that are not influenced by how far the scraper travels. Examples include loading time, dumping time, turning, and ADBT (acceleration, deceleration, and braking).
2. Variable Time: This includes haul and return times, which vary based on distance traveled and the speed of the scraper. The speed can be influenced by factors such as terrain conditions and the type of machine used. Hence, understanding this distinction is crucial for managing and reducing the overall cycle time.
Examples & Analogies
Think of a train journey. The time it takes for the train to board passengers (fixed time) does not change whether the train travels 1 mile or 100 miles. However, the time it takes to travel those miles (variable time) will change based on the speed at which the train is going and the distance covered.
Loading Time Consistency
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Loading time of the scraper is fairly consistent, regardless of scraper size, largely due to assistance from the pusher.
Detailed Explanation
Loading time for scrapers remains relatively constant, meaning that whether you use a large or small scraper, the time to load it doesn't change much. This consistency is primarily due to the assistance provided by a pusher tractor, which helps the scraper to load more efficiently. The loading times can be obtained from the manufacturers and are typically around 0.8 minutes for common earth material, regardless of the scraper's size.
Examples & Analogies
This is similar to using a blender to mix a smoothie. Whether you're making a small smoothie for one person or a large batch for a party, the time it takes to blend (loading time in the analogy) remains about the same because the blender does the work regardless of the quantity.
Concept of Load Growth Curve
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The load growth curve illustrates that loading a scraper to its maximum capacity can reduce production, as it encounters resistance as it fills beyond 85%.
Detailed Explanation
The load growth curve shows that although one might assume loading a scraper to its maximum capacity results in maximum productivity, this is a misconception. Studies reveal that as the scraper's bowl reaches about 85% full, the rate at which additional material can be loaded decreases due to the resistance offered by the already loaded material. This leads to a decrease in production rate, known as the law of diminishing returns. Therefore, it is more efficient to load the scraper optimally, rather than to its maximum capacity.
Examples & Analogies
Consider packing a suitcase. Initially, you can easily add clothes, but as the bag fills up, it becomes harder to add more items. Eventually, you may end up cramming things in, which doesn't help you pack efficiently - instead, it can reduce how much you can fit in effectively.
Haul and Return Time
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Haul and return time are variable times dependent on travel distance and machine speed, which are influenced by site conditions.
Detailed Explanation
Haul and return times are critical components of cycle time, as they depend on how far the material needs to be transported and the speed of the scraper. While hauling to the dump site, the scraper is loaded, and its speed will differ from the return journey when it's unloaded and can typically go faster. Maintaining the haul route is essential to minimize these times. Proper upkeep can reduce rolling resistance, thus improving travel speed and overall efficiency.
Examples & Analogies
Imagine driving a delivery truck on two different roads - one is smooth and well-maintained, and the other is full of potholes. The time taken to make a delivery will be quicker on the smooth road, just as proper maintenance of the haul route ensures maximum efficiency for the scraper.
Dump Time Considerations
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Dump time varies based on scraper size, the material being dumped, and site constraints. Dumping techniques significantly affect efficiency.
Detailed Explanation
Dump time for a scraper is influenced by several factors:
- Scraper Size: Larger scrapers generally take more time to dump.
- Material Type: Loose materials are easier to dump and take less time compared to sticky or cohesive materials that are more challenging.
- Site Constraints: If the dump area is congested with other machinery or has limited space, it can lead to increased wait times for the scraper to unload its material. Understanding these factors helps in planning effective dumping operations.
Examples & Analogies
Consider a busy restaurant where a waiter must serve food to customers. If the restaurant is crowded (congested dump site), it might take longer for the waiter to reach each table (dump time). However, if the dishes are light and easy to carry (loose material), the wait will be quicker compared to heavier, more cumbersome dishes (sticky material).
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Cycle Time: Total operational time for scrapers, covering loading, dumping, and return.
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Load Growth Curve: Demonstrates diminishing returns on loading efficiency when scrapers are overloaded.
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Fixed vs. Variable Time: Components of cycle time that either remain constant or change with distance.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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When a scraper is loaded beyond 85% capacity, the loading efficiency decreases significantly due to resistance from the material already in the bowl.
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Maintaining the haul route with water trucks reduces dust, thereby enhancing visibility and increasing the machine's speed.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Scrape it right, load it right, keep it light to avoid the fight.
📖 Fascinating Stories
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Imagine a busy construction site where a scraper is trying to carry too much dirt. Every time it overloads, it struggles and slows down, while the operator realizes they are wasting time. The lesson is learned: less is more at the load's core.
🧠 Other Memory Gems
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FLIGHT: F for Fixed time, including Loading, Dumping, Turning; while L for Variable time includes Haul and Return.
🎯 Super Acronyms
LOAD
- L: for Loading time
- O: for Overloading issues
- A: for Analysis of cycle time
- D: for Dumping efficiency.
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 taken for one complete loading and unloading operation of a scraper.
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Term: Loading Time
Definition:
The time taken to load materials into the scraper.
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Term: Haul Time
Definition:
The time taken to transport materials from a loading site to the dump site.
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Term: Dump Time
Definition:
The time taken to unload materials from the scraper.
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Term: Return Time
Definition:
The time taken for the scraper to return to the loading site after unloading.
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Term: Load Growth Curve
Definition:
A graph showing the relationship between loading time and the percentage of payload, illustrating diminishing returns on loading efficiency.
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Term: Fixed Time
Definition:
Cycle time components that remain constant, independent of travel distance.
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Term: Variable Time
Definition:
Cycle time components that depend on distance traveled.