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Interactive Audio Lesson
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Understanding Cycle Time and Its Components
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Today, we will discuss the cycle time of scrapers, which is crucial for understanding their efficiency during operation. Can anyone tell me what cycle time comprises?
Does it include loading and dumping times?
Exactly! Cycle time is made up of several components such as Load Time (LT), Haul Time (HT), Dump Time (DT), Return Time (RT), Spot Time (ST), Turn Time (TT), and Acceleration, Deceleration, and Braking Time (ADBT). A way to remember this is with the acronym 'LHD RSTT ADBT'.
What’s the difference between fixed and variable time?
Good question! Fixed time stays constant regardless of how far you travel, while variable time changes based on distance and speed. Fixed aspects include loading and dumping times, whereas haul and return times are variable.
So, optimizing those fixed times is important too, right?
Exactly! Let's dive deeper into the loading time and how we can make it more efficient. Remember, the goal is to find an optimal loading strategy to avoid diminishing returns.
Optimizing Loading Time
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Loading time is essential because it’s often consistent across different scraper sizes. Can someone guess how we can improve our loading rates?
Using a pusher loader should help, right?
Correct! A pusher loader can maintain consistent loading times across sizes and improve overall productivity. However, we must also be cautious as overloading can lead to reduced production rates due to increased resistance.
What happens if we load past a certain capacity?
Great question! This situation is known as the 'law of diminishing returns.' Once the scraper bowl is too full, the loading rate decreases because the incoming material faces resistance from materials already in the bowl.
How do we find that optimal load capacity?
You can determine this through empirical testing or by studying load growth curves that indicate where loading efficiency starts to decline.
Understanding Haul and Return Times
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Now, let’s discuss haul and return times. Why do you think these times are variable?
Because they depend on how far we travel and the terrain, right?
Exactly! The haul and return times vary because they are influenced by distance and the speed, which can change due to project site conditions. How can we improve these times?
By maintaining the haul route?
Yes! Maintaining the haul route is crucial. It can reduce rolling resistance and improve overall speeds, which can significantly enhance productivity. Regular maintenance of routes saves time and cost.
Is there a special method to inspect haul routes?
Good point! Inspections help determine if additional maintenance is needed, like watering the road to manage dust or grading to ensure smooth travel. Efficient routes lead to optimized cycle times.
Dump Time and Its Influences
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Next, let’s explore dump time. What key factors influence dumping?
I think it depends on the material type and the size of the scraper.
Exactly! Bigger scrapers generally have longer dump times because they handle more material. Additionally, if the material is cohesive, it can take longer to dump. Can anyone think of an example?
Like if we’re dealing with clay instead of sand?
Correct! Clay may stick in the bowl, increasing the dump time. What's another factor we should consider when dumping?
The constraints of the dumping area?
Exactly! Congestion around the dump area can delay the dumping process. Planning the site layout to minimize these delays is crucial for operational efficiency.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section explains the components that make up the cycle time of a scraper, differentiating between fixed and variable times, and emphasizes the optimal conditions for loading to improve efficiency. Key components like loading time, haul and return time, dump time, and the significance of maintaining haul routes are highlighted.
Detailed
Detailed Summary of Loading Time
This section addresses the components of the cycle time in the operation of scrapers used in construction and excavation. The equation for cycle time is provided 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
The components divide into fixed time, which is independent of travel distance (loading, dumping, turning, acceleration, deceleration), and variable time, which is dependent on the haul and return distance. Important points include:
- Loading Time: Remains constant for scrapers regardless of size, and is affected by assistance from pusher loaders. An optimal loading capacity should be identified to avoid the law of diminishing returns, as overloading may cause production rates to decrease.
- Haul and Return Time: Variable components of the cycle time that directly depend on travel distance and the machine's speed, which can be influenced by project site conditions and haul routes. Proper haul route maintenance is crucial for reducing resistance and improving efficiency.
- Dump Time: Varies with scraper size and material being dumped, and is also influenced by site constraints. Efficient dumping techniques should be prioritized to enhance operational safety and effectiveness.
- Spotting and Turning Time: These aspects are critical for smooth operations between different phases of scraper use, and their timing can significantly impact overall cycle time. Maintaining haul routes can further enhance productivity and machine lifespan.
The insights from this section are essential for optimizing scraper operations, enhancing productivity, and reducing costs in earthmoving projects.
Audio Book
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Definition of 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 in the context of scrapers is defined as the total time it takes for the machine to complete a work cycle. It consists of multiple components: Loading Time (LT), Hauling Time (HT), Dumping Time (DT), Return Time (RT), Spotting Time (ST), Turning Time (TT), and the time needed for Acceleration, Deceleration, and Braking (ADBT). Each component reflects a different part of the machine's operation.
Examples & Analogies
Think of cycle time like the time it takes for a bus to make a round trip. The trip includes a series of stops: picking up passengers (loading), traveling to a destination (hauling), dropping off passengers (dumping), and returning to the starting point. Each segment of the trip is necessary and contributes to the overall timing.
Components of Cycle Time: Fixed vs Variable
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You can split the cycle time into 2 parts: fixed time (not dependent on travel distance) and variable time (depends on travel distance). Fixed time includes loading, dumping, turning, and ADBT. Variable time includes haul and return time, which relies on distance and speed.
Detailed Explanation
Cycle time is divided into fixed and variable components. Fixed time remains constant regardless of how far the scraper travels; it encompasses actions like loading and dumping. Variable time varies based on the distance and speed of the scraper. Hence, the overall cycle time can be affected by how far the scraper must travel for hauling and returning.
Examples & Analogies
Imagine a trip to a grocery store. The time spent in the store (fixed time) remains the same no matter where you live, while the driving time varies based on how far you live from the store (variable time).
Loading Time Consistency
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The loading time of the scraper is fairly consistent irrespective of its size, as it is assisted by a pusher. For typical earth, the average load time for a pusher-loaded scraper is around 0.8 minutes.
Detailed Explanation
Loading time for scrapers does not significantly vary between different sizes due to assistance from a pusher. Regardless of the scraper's size, the loading process remains stable, with an average time of about 0.8 minutes for common earth materials. This consistency allows for better planning and estimation in projects.
Examples & Analogies
Consider a shop where larger customers and small customers take the same time to load their purchases into their vehicles because they both receive the same level of assistance. It showcases that assistance can normalize process times.
Load Growth Curve
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Loading scrapers to maximum capacity reduces production rates due to the law of diminishing returns: as the bowl fills, resistance from material inside the bowl hinders the loading process.
Detailed Explanation
The load growth curve illustrates that beyond a certain point, increasing the load makes it harder to add more material due to existing material creating resistive forces. This resistance is why scraping to full capacity can actually slow down the loading rate, violating the typical assumption that fuller buckets mean more productivity.
Examples & Analogies
Imagine trying to cram too many clothes into a suitcase. Initially, it’s easy, but as you pack more, it’s harder to add clothes, and you actually end up with less space. Thus, rather than maximizing capacity, it’s better to optimize how much you pack efficiently.
Importance of Maintaining Haul Route
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The haul and return time depend on the travel distance and speed. Maintaining the haul route is essential to reduce cycle time, improve productivity, and decrease operational costs.
Detailed Explanation
Travel efficiency is directly related to the state of the haul route. A well-maintained haul route can enhance speed, reduce cycle times, and subsequently lower costs. Careful management of the haul route through maintenance ensures smoother operations, directly impacting productivity.
Examples & Analogies
Think of a road trip; a well-paved road allows for faster driving, while rough roads slow you down, increasing travel time and fuel costs. Similarly, maintaining a haul route is key to ensuring that the scraper operates at peak efficiency.
Dump Time Factors
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Dump time depends on scraper size and material handled. Loose materials are easier to dump, while cohesive materials require more time. Dumping area constraints also play a role.
Detailed Explanation
The time it takes to dump can vary based on how large the scraper is, the type of material being dumped, and specific conditions at the dumping site. Larger scrapers or sticky materials increase dump times because of their characteristics or site congestion. Understanding these factors helps in effective planning.
Examples & Analogies
Similar to unloading a moving truck, the ease of unloading boxes varies with size and weight. If boxes are heavy or if the unloading area is cramped, it becomes significantly slower, highlighting how dump conditions impact efficiency.
Turning Time and Its Variability
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Turn time is typically not affected by the scraper type but varies between turning in fill vs. cut areas due to congestion and assistance requirements.
Detailed Explanation
While the type of scraper doesn’t alter the turning time, the environment does. Turning in a more congested cut area takes longer than in a fill area because of the potential for needing assistance from other machines and the process of turning while still loaded.
Examples & Analogies
In a busy parking lot, turning your car around takes more time due to how many cars are around. In contrast, turning in an empty lot is quick and easy. Similar situations occur with scrapers, where environmental factors influence turn times.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Cycle Time: Encompasses all operational phases of a scraper.
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Loading Time: Consistent irrespective of scraper size, crucial for efficiency.
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Diminishing Returns: Overloading scrapers can reduce overall productivity.
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Haul and Return Time: Critical variable costs affected by travel distance and speed.
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Dump Time: Influenced by the type of material and site constraints.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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A scraper loading 20 cubic meters of dirt takes roughly 0.8 minutes, irrespective of its size, due to pusher assistance.
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When loaders exceed 80% capacity, material resistance causes decreased loading rates, demonstrating the law of diminishing returns.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Time to load, time to go, speed up the haul we know.
📖 Fascinating Stories
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Once upon a time, a scraper named Loady learned that overfilling led to slow loading. After finding balance, his productivity bloomed.
🧠 Other Memory Gems
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Remember 'LHD RSTT ADBT' to recall all parts of the cycle time.
🎯 Super Acronyms
Cycle time components
- LT
- HT
- DT
- RT
- ST
- TT
- ADBT — like a race where speed wins!
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 loading, hauling, dumping, and returning in scraper operations.
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Term: Load Time (LT)
Definition:
The time taken to fill the scraper bowl with material.
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Term: Haul Time (HT)
Definition:
The time spent moving the loaded scraper to the dump site.
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Term: Dump Time (DT)
Definition:
The time required to empty the scraper bowl at the dump site.
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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: Spot Time (ST)
Definition:
The time needed to position the scraper for loading.
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Term: Turn Time (TT)
Definition:
The time consumed when the scraper changes direction.
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Term: Acceleration, Deceleration, and Braking Time (ADBT)
Definition:
Time spent in accelerating to speed, slowing down, and stopping the vehicle.