3.2 - Calculating Return Time
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Understanding Gravimetric Capacity
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today, we're focusing on gravimetric capacity. Can anyone tell me what that means?
Is it the maximum weight a machine can handle?
Exactly! It’s the safe operating load the manufacturer specifies. Overloading can lead to serious issues, including increased wear on tires. Remember, 'weight makes machines ache' — a mnemonic to remember the importance of adhering to these limits.
What if the density of the material changes? How does that affect things?
Great question! You'll need to check your load weight against this gravimetric capacity to ensure safety.
And what's the first step if I want to check?
You'll need the density of your material. Multiply that with the volumetric load to find the actual weight. Rounding out today's session, remember: always check your machinery limits!
Calculating Haul and Return Times
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now let’s calculate haul time! What are the necessary components?
The distance and speed of the truck?
Correct! You derive speed from the performance chart, considering resistances. Once you have that, you can compute haul time. Can someone explain how return time differs?
It’s calculated when the truck is unloaded, so the speed should be higher!
Precisely! The return speed generally increases since the truck is empty. Making sure you consider these variables is crucial!
What about congestion? How does that figure in?
Congestion can definitely delay both dumping and haul times. Therefore, understanding site conditions is essential.
Balancing Excavators and Trucks
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Let’s discuss balancing trucks and excavators. What key factor do we need to consider?
The bucket capacity versus truck capacity?
Yes! Ideally, your truck capacity should be 4 to 5 times the capacity of the bucket. Why do you think this balance is critical?
To avoid waiting times and keep productivity high!
Exactly! By calculating the balance number of trucks based on cycle times, we can optimize our operations. When is it more advantageous to round down?
When it ensures that the excavator doesn’t sit idle waiting for a truck!
Spot on! Rounding down keeps the loader engaged. Remember, maximizing productivity and minimizing idle time is key.
Calculating Production Rates
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now let's calculate truck production! Who knows how to estimate it based on our previous discussions?
It's truck payload divided by truck cycle time, right?
Exactly! And remember to adjust for efficiency—how many operational minutes are available?
Fifty minutes out of the hour based on job efficiency!
Great! So when you calculate truck production, adjusting for both payload and efficiency will yield your final production rate. Let’s make sure we practice this with real data.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section discusses the calculation of return time for trucks, focusing on the importance of not exceeding the gravimetric capacity of machines. It covers the factors affecting loading time, dumping time, haul time, and the optimum balancing of trucks and excavators.
Detailed
In this section, we delve into the intricacies of calculating return time for hauling trucks, focusing on several key elements. We first establish how loading time is determined by the number of bucket loads multiplied by the bucket cycle time, and proceed to examine the significant concept of gravimetric capacity—the maximum safe load given by the machine manufacturer.
Employees must ensure that the total weight of the load does not exceed this capacity, considering variations in material density. The section highlights that overloading can result in excessive wear and tear on machinery, particularly tires, leading to increased operational costs over time.
Next, we look at factors affecting dumping time, such as the type of dumper and the nature of the material, further enhanced by site congestion. The section utilizes information from author Peurifoy et al. to guide estimations for favorable and unfavorable dumping conditions. Following this, we explore haul time factors, including distance, speed derived from machine specs, and site resistances, with computations reflecting truck operations under unloaded conditions.
By breaking down these components, we gain a clearer understanding of balancing between the number of trucks and excavators to achieve optimum productivity, based on the balancing of capacities for maximum efficiency. The section concludes by prompting calculations for optimal truck numbers based on given parameters.
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Understanding Return Time Calculation
Chapter 1 of 2
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Now let us see how to balance the interdependent machines, trucks and the excavators. I hope you remember earlier we have discussed how to balance the interdependent machines your scraper and the pusher? In a similar manner we are going to discuss how to balance the number of trucks and the excavator? So, balancing is very important, just now we discussed balancing the capacity of the interdependent machines very important.
Detailed Explanation
In this section, we focus on how to calculate the return time for trucks in a construction setting. Understanding return time is crucial because it helps us determine how efficient our hauling operations are. To do this, we need to consider key aspects like the truck's condition (loaded vs. empty) and the various resistances it faces during operation. Calculating return time involves using the truck's speed, which can be gathered from manufacturer performance charts that provide information on how different loads affect the speed and efficiency of equipment.
Examples & Analogies
Imagine you are driving a car loaded with groceries. While your car is heavy with groceries, it moves slowly to the grocery store. Once you unload the groceries and drive back home, your car returns quickly since it’s light. Similarly, in truck operations, when the truck is loaded with materials (like rocks or dirt), it takes longer to reach its destination than when it is empty, which is why calculating return time is so important.
Key Factors Affecting Return Time
Chapter 2 of 2
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
So, returning time depends upon the distance and the truck speed in an unloaded condition when we use the performance chart. Here, the truck will be in the unloaded condition, empty weight, and consider the resistances also. So you know the distance and speed I can calculate the return time, obviously the return speed will be more, so the return time will be less as the truck is in the empty condition.
Detailed Explanation
The return time for a truck is primarily influenced by the distance it needs to travel back to the loading point and the speed of the truck when it is empty. Empty trucks can travel faster compared to loaded trucks because they face less weight-induced resistance. When calculating return time, it is essential to get the speed from manufacturer charts, taking into account the specific conditions like terrain and any other resistances (like rolling resistance due to the truck’s tires on the road). Hence, knowing both the distance and the speed gives us the capability to calculate how long it will take for the truck to return.
Examples & Analogies
Think of a delivery truck that unloads packages at a mall. When it's loaded, it moves slowly because it’s carrying heavy boxes. Once the truck is empty, it speeds back to the warehouse much faster. This illustrates how the load affects travel time, emphasizing the importance of considering the truck being empty while calculating return time.
Key Concepts
-
Gravimetric Capacity: The specified maximum loading weight a machine can safely handle.
-
Loading Time: Calculated from the number of loads multiplied by the loading cycle time.
-
Dumping Time: Influenced by the truck type and site conditions.
-
Haul Time: Determined by the driving distance and the performance specifications.
-
Return Time: Typically less than haul time since trucks are empty.
-
Balancing Equipment: Finding the right number of trucks per excavator to maintain productivity.
Examples & Applications
If a truck's gravimetric capacity is 10 tons, and it carries a material of density 2 tons per cubic meter, the maximum volume it can carry is 5 cubic meters.
For a loader with a bucket cycle time of 1 minute, and needing to fill a truck that takes 30 minutes to dump and return, the loading time is 5 times the cycle time, leading to a total truck cycle time of 35 minutes.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
If you load too much, you'd be in a clutch, machines won't budge, instead of the rush!
Stories
Imagine a giant machine at work, it can only lift so much. Load it too high, and it breaks down—just like our friend who ate too much pizza and couldn't move!
Memory Tools
Remember LDR—Loading, Dumping, Return for the order of operations in truck cycles.
Acronyms
BITE for balancing
Bucket size
Ideal truck number
Timing cycles
Efficiency management.
Flash Cards
Glossary
- Gravimetric Capacity
The maximum safe load weight that a machine can handle as specified by its manufacturer.
- Loading Time
The duration needed to load materials onto a truck, calculated based on bucket loads and cycle time.
- Dumping Time
The time taken to unload materials from the truck, influenced by the type of dumping mechanism and site congestion.
- Haul Time
The duration it takes to transport a load from one location to another, determined by distance and truck speed.
- Return Time
Time taken for a truck to return empty after unloading, generally calculated similarly to haul time.
- Balancing
The process of optimizing the number of trucks and excavators to maximize productivity and reduce idle time.
Reference links
Supplementary resources to enhance your learning experience.