1.3. Load Growth Curve

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.

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.

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.

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.

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.

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 of the scraper is fairly consistent, regardless of scraper size, largely due to assistance from the pusher.

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.

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.

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%.

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.

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 are variable times dependent on travel distance and machine speed, which are influenced by site conditions.

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.

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 varies based on scraper size, the material being dumped, and site constraints. Dumping techniques significantly affect efficiency.

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.

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).

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