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Interactive Audio Lesson
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Understanding Cycle Time Components
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Good afternoon, class! Today we're diving into what makes up the cycle time of a scraper and a pusher. Can anyone tell me what the cycle time includes?
I think it includes load time and dump time.
Exactly! Cycle time is made up of several components, including load time (LT), haul time (HT), dump time (DT), return time (RT), spot time (ST), turn time (TT), and ADBT, which stands for Acceleration, Deceleration, and Braking Time. Now, can someone tell me how we categorize these components?
Are they divided into fixed and variable times?
Correct! Fixed times are those that don't depend on the distance traveled, while variable times like haul and return depend on distance and speed. Remember the acronym F.V. for Fixed and Variable! Can anyone explain why it’s crucial to understand the load time?
Is it because loading time affects overall efficiency?
Exactly! Efficient loading maximizes productivity. Great job today!
Load Growth Curve
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Now, let’s talk about the load growth curve. Why do we need to consider this curve when loading a scraper?
It's important because overloading might reduce the loading rate?
Excellent point! The load growth curve illustrates that when you try to load the scraper to its maximum capacity, the rate of loading starts diminishing after a certain point. We shouldn’t try to fill the scraper bowl completely to avoid inefficiency. Can anyone guess what's the maximum payload often recommended?
Something like 85%? That’s when the loading speed decreases.
Exactly! So always aim for optimal loading. This confirms the principle of 'diminishing returns.' Well done, everyone!
Haul and Return Time
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Let's move to haul and return time. What factors do you think these times depend upon?
The distance traveled and the speed of the machine?
Correct! Additionally, it’s impacted by project site conditions. Why is maintaining haul routes crucial?
To improve travel speed and reduce costs?
Exactly! Appropriate maintenance increases productivity and decreases costs. Remember, a well-managed haul route saves time and money. Excellent insights today!
Dump Time and Turning Time
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Let's wrap up with dump and turn times. What affects the dump time?
The size of the scraper and the type of material being dumped!
Exactly! Larger scrapers and tricky materials lead to longer dump times. And what about turning time?
It varies based on whether the scraper is in a cut area or a fill area.
Great point! The congestion in each area impacts the turn time as well. Always remember this to optimize cycle efficiency. Fantastic engagement today, everyone!
Introduction & Overview
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Quick Overview
Standard
This section examines the components of cycle time associated with scrapers and their pushers, breaking down the cycle time into fixed and variable elements, explaining the significance of each, and emphasizing the importance of optimizing loading times and haul routes.
Detailed
Components of Pusher Cycle Time
Cycle time is a crucial factor in determining productivity in earthmoving operations. It is 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, Braking Time)
Key components of cycle time can be categorized into fixed and variable times. Fixed time includes all times that do not depend on the distance traveled, such as loading, dumping, turning, and ADBT. Conversely, variable time includes haul and return times, which significantly depend on distance and travel speed influenced by project conditions.
It is essential to recognize that the loading concepts include the ideal loading mechanism to optimize the scraper's capacity, including understanding the load growth curve that shows diminishing returns when overloading the scraper.
Additional components involve proper maintenance of haul routes to minimize travel-related delays and improve machine productivity. Techniques like using bulldozers to rip hard surfaces before scraper loading can enhance efficiency. This section further elaborates on the stages of dump time, turning time in different areas, and the cycle time components for pushers, emphasizing the need to balance the number of scrapers with pushers effectively.
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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 duration for completing one full cycle of work performed by a machine, in this case, a scraper assisted by a pusher. The formula includes various components: loading time (LT), which is how long it takes to load the material; haul time (HT), the duration for transporting the material; dump time (DT), the time taken to unload the material; return time (RT), which accounts for the time taken to return to the starting position; spotting time (ST), to correctly position the pusher loader for the next load; turning time (TT), to change direction; and ADBT, which encompasses the time for acceleration, deceleration, and braking during this cycle. Each component contributes to the overall efficiency and productivity of the operation.
Examples & Analogies
Think of cycle time as a recipe for baking a cake. Just as each step in the recipe contributes to the final cake—mixing ingredients, baking, cooling, and decorating—each component of the cycle time works together to determine how quickly and efficiently a scraper can operate within its task.
Fixed vs Variable Time
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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, while variable time depends on distance and speed.
Detailed Explanation
Cycle time can be divided into fixed and variable components. Fixed time includes activities that do not change regardless of how far the machine travels. For example, loading and unloading always takes a specific amount of time, irrespective of distance. In contrast, variable time relates to the haul and return journeys—these are influenced by distance and the speed of the machine, which may change based on various site conditions such as terrain and machine type.
Examples & Analogies
Imagine you're planning a road trip. Fixed time could represent the duration of pit stops—fueling, eating—always taking about the same time. Variable time, however, would change based on how far you’re driving; if you have to drive a longer route, the traveling time increases.
Loading Time and Its Consistency
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Loading time of the scraper is fairly consistent, regardless of scraper size, due to assistance from a pusher. The average load time for the pusher loaded scraper in common earth is about 0.8 minutes.
Detailed Explanation
The loading time for a scraper tends to remain stable because it is often assisted by a pusher. Whether the scraper is small or large, the loading time does not vary significantly because the pusher aids in the efficiency of the loading process. This consistency allows project managers to predict loading times accurately based on machinery rather than dispositional differences in the scrapers.
Examples & Analogies
Think of loading a truck: smaller and larger trucks might have different capacities, but if a fork-lift is consistently available to help load both, you can clock the loading time reliably. Like packing a backpack for school, it may take consistent time regardless of size when there's a helping hand involved.
The Load Growth Curve
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Loading scrapers to maximum capacity will reduce rather than increase the rate of production due to incoming earth encountering resistance from material already in the bowl.
Detailed Explanation
The load growth curve reveals an important insight: as you fill the scraper's bowl, the efficiency of loading decreases after reaching a certain capacity (around 85%). Beyond this threshold, the material inside the bowl becomes a barrier to the incoming loads, creating resistance that slows down the loading process. This diminishing return means you’re better off filling to an optimal level rather than maxing out the bowl.
Examples & Analogies
Picture trying to pour more cereal into a full bowl of milk. The cereal simply cannot enter fast enough because the milk is already full. You’d be pouring slower and making a mess, illustrating how too much load decreases efficiency instead of increasing it.
Haul and Return Time
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Haul and return time are variable; they depend on both travel distance and machine speed, which is affected by site conditions and machine type.
Detailed Explanation
Haul and return times differ based on how far the scraper needs to go to deliver its load and the speed it can achieve on the way. For instance, when the scraper is hauling a load, it travels more slowly compared to the return trip when it is empty. Maintaining good conditions on the haul route (like having a smooth road) is crucial as it influences the machine's speed and therefore affects cycle time. Regular maintenance of these routes leads to higher productivity and lower operational costs.
Examples & Analogies
Consider how quickly you can walk on a paved sidewalk versus uneven gravel. The distance remains the same, but the smoother the surface, the faster you can go. Similarly, maintaining the haul route allows scrapers to work more efficiently, saving both time and resources.
Understanding Dump Time
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Dump time depends on scraper size, material type, and constraints in the dump area as well as operating conditions.
Detailed Explanation
The time it takes to dump the scraper’s load varies largely based on the size of the scraper and the type of material being dumped. Larger scrapers will naturally take a bit longer for dumping due to more volume, and handling cohesive materials (like clay) may require more time compared to loose materials. Moreover, if there are space constraints at the dump area—like nearby machinery congestion—the dump time can also increase.
Examples & Analogies
Think of a waste collection truck. If it arrives at a site where the dumpster is easily accessible, it can unload quickly. However, if there are obstacles, like other vehicles or a narrow alley, unloading takes much longer. Similarly, the conditions dictate how quickly or slowly a scraper can unload.
Turn Time Variations
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Turn time is influenced by the type and size of the scraper and may vary between the fill area and cut area.
Detailed Explanation
The time it takes for a scraper to turn varies depending on its current load and the specific area within the project site. Turns made in the fill area tend to take less time compared to the cut area due to less congestion and fewer obstacles. In the cut area, more machines often compete for space, making turning more complex and time-consuming.
Examples & Analogies
Imagine driving a car in a parking lot versus a busy intersection. In the parking lot (fill area), you can make quick turns without interference, but at an intersection filled with cars (cut area), you must navigate carefully and wait for safe openings, thereby taking longer to complete the turn.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Cycle Time: Sum of times for loading, hauling, dumping, and other operations.
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Fixed Time: Components like loading and dumping that don’t vary with distance.
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Variable Time: Time taken for hauling and return trips that depend on distance.
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Load Growth Curve: An analytical tool demonstrating diminishing returns when overloading.
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Haul Route: The path that needs to be maintained for efficient transport of materials.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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An example of fixed cycle time would be the consistent loading and dumping times regardless of the distance to the dump site.
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Haul time can drastically change based on terrain; for instance, a smooth haul route allows faster travel, whereas rough terrain increases load time.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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When loading's done but goes beyond, the speed does slow, it won't respond.
📖 Fascinating Stories
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Imagine a farmer trying to fill a basket; overfilling makes the lid pop, thus slowing down the harvest!
🧠 Other Memory Gems
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Remember ADBT: Always Drive Brakes Tightly when calculating slowing down times!
🎯 Super Acronyms
F.V. = Fixed time and Variable time
- Useful for remembering the categories of time in cycle.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Cycle Time
Definition:
Total time taken to complete a cycle of operations in earth-moving equipment including loading, hauling, dumping, turning, and returning.
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Term: Fixed Time
Definition:
Time components of cycle time not dependent on travel distance, such as loading and dumping.
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Term: Variable Time
Definition:
Time components of cycle time that depend on distance traveled and speed during hauling and returning operations.
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Term: Load Growth Curve
Definition:
Graphical representation showing the diminishing returns when trying to achieve maximum payload in scraping operations.
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Term: Haul Route
Definition:
The path or roadway taken for transporting materials away from the excavation site.