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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 going to discuss the efficiency of scrapers in relation to pushers and how various configurations affect our productivity. To start, who can define what we mean by productivity in this context?
Isn't it about how much material we can move in a certain period of time?
Exactly! And when we discuss scrapers and pushers, it's crucial to understand their operational dynamics. Can anyone tell me what factors might affect a scraper's productivity?
The number of scrapers we have compared to pushers?
Right! If scrapers outnumber pushers significantly, we often run into inefficiencies. For example, while one scraper might be limited, a pusher could be waiting idly.
So, if we have five scrapers, how do we know if that’s the right number?
Great question! We can estimate production using a specific formula. The efficiency of the scrapers at five leads to a production of 636.89 bank cubic meter per hour.
What about if we increase the number of scrapers to six?
Good observation! Increasing it provides a higher output—723.36 bank cubic meters per hour, which is what we aim for in tight deadlines!
In summary, the number of scrapers is essential for productivity. We will dive deeper into how to actually calculate the required rimpull next.
Next, let’s explore how to calculate rimpull. Who remembers the formula for maximum usable rimpull?
Is it related to the weight on the powered running gear and the coefficient of traction?
Exactly! The formula is: . Can anyone tell me our example's weight on the powered running gear?
I think it was half of the gross weight.
Correct! Using a gross weight of 76,000 kg leads us to 38,000 kg on the drive wheels. If we apply the 0.7 coefficient of traction, what rimpull do we get?
That would be 26,600 kg.
Perfect! Now, let’s compare that with the power generated based on the engine. How do we estimate that?
We use the formula involving horsepower and the speed of the gear.
Absolutely! If we calculate for first gear, we find a supplied rimpull of 18,240 kg. Since that's below our maximum usable rimpull, there won't be any slippage.
In summary, calculating rimpull helps us understand the machine’s potential and ensure that our operations run smoothly.
Now, let's factor in altitude, which influences our rimpull calculations. Who can remind me how altitude affects machine performance?
It decreases the power output due to reduced air density, right?
Correct! For altitudes above 300 meters, we face a performance drop. What’s the reduction per 300 meters?
Three percent each time!
Exactly! In our case, at 600 meters, we adjust the supplied rimpull by reducing it by 3%. What does that give us from the first gear?
It brings the rimpull down to 17,692.8 kg.
Excellent! So now we determine the rimpull available for towing by subtracting the required rolling and grade resistance. What was the total required to overcome resistance?
It was 4,560 kg.
Correct! So, this leaves us with what for the first gear?
We still have 13,132.8 kg for towing!
Great job! Summarizing, altitude can dramatically affect rimpull, and understanding this ensures operational efficiency.
Let’s wrap up by discussing how we use these calculations for operational planning. Why do you think these concepts are vital for project completion?
They help us know if we can actually use the machines efficiently, right?
Exactly! Knowing the rimpull ensures we select the right gear and avoid slippage, particularly in challenging conditions. Can anyone recap how we determined when not to use the top gear?
We found it wouldn't provide enough rimpull to counter the rolling and grade resistance.
Correct! Knowing when to switch gears can be crucial in maintaining productivity and avoiding stall-outs.
In summary, balancing scrapers and pushers according to these calculations helps us maximize productivity and control costs.
Well said! Always remember the dynamic relationship between machines aids in optimal project execution.
The effective force at the wheels that enables the scraper to move efficiently.
Key metric for understanding how traction varies with surface conditions.
The expected output of scrapers depending on their configuration.
Essential calculations that dictate operational efficiency in earthmoving projects.
Rimpull to pull, don't be late, traction and weight decide your fate.
Imagine a construction site where scrapers with their powerful rimpull glide smoothly over clay, freed from the weight of asphalt and empowered by perfect traction beneath their wheels.
R-T-C-G: Rimpull, Traction, Cycle, Grade - remember this to ensure smooth operations.
P.E.R.F.E.C.T for productivity: Pusher, Efficiency, Rimpull, Frequency, Effective load, Calculate time.
Term
Rimpull
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Term
Coefficient of Traction
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Term
Scraper Cycle Time
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The tractive effort available at the wheel contact, essential for pulling loads.
A measure of the friction between the wheels and the ground surface.
The total weight of a machine including its payload.
The total time taken for a scraper to complete one loading cycle.
A machine used to assist scrapers in earthmoving operations.
Adjustments made to engine power outputs due to elevation changes.
The frictional force that opposes the motion of a vehicle on land.
The resistance incurred while moving on an incline.
This section discusses how to calculate the required rimpull for scrapers and their impact on productivity depending on their numbers relative to pusher equipment.
The section elaborates on the dynamics between the number of scrapers versus pushers in an earthmoving operation, specifically analyzing how varying numbers of scrapers affect overall productivity and how to calculate the required rimpull, taking into account specific conditions such as weight, traction, rolling resistance, and alteration due to altitude. It concludes that optimal combinations hinge on productivity and cost considerations.
This section explores the economics and calculations involved in determining the required rimpull for a scraper operation, particularly considering the number of scrapers relative to pushers. The primary focus is on estimating production rates based on the configurations selected. With five scrapers, the load cycle efficiency results in a production rate of 636.89 bank cubic meters per hour. With six scrapers, the rate increases to 723.36 bank cubic meters per hour, showing that more scrapers lead to higher productivity.
The section dives deeper into the efficiency formula:
Additionally, it delves into the scrapers and pushers relationships, outlining scenarios where scrapers might be limited by their numbers or where excess scrapers would stall production due to pushers' limitations.
A significant part of the section discusses the necessary calculations to determine the usable rimpull of the scraper based on factors like coefficient of traction, rolling resistance percentages, and altitude corrections. It includes formulas to ascertain if the implemented rimpull for various gears meets the project demands. The conclusion reflects that in this specific case, the first and third gears are efficient for operation while the second and top gears might pose challenges under given conditions, due to insufficient available rimpull. Overall, the assessment of rimpull's adequacy is crucial for effective scraper operation.