2.2.3. Shuttle Loading

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, it is nothing but load time, hauling time, dumping time, return time spotting because most of the conventional scrapers have a pusher loader scraper. So, it has to spot the pusher, that spotting time is also included then turning, then ADBT that means the time needed for increasing your speed or decreasing the speed, time needed for applying the brakes.

Cycle time is the total time it takes for a scraper to perform its job, which includes several components: loading (LT), hauling (HT), dumping (DT), returning (RT), spotting (ST), turning (TT), and acceleration, deceleration, and braking time (ADBT). Each of these components is crucial in determining how long it takes for the scraper to complete one full cycle of operation, from loading to dumping back to loading again.

Think of a bakery that makes a batch of cookies. The cycle time for baking involves several steps: preparing (loading), baking (hauling), cooling (dumping), cleaning the baking trays (returning), resetting the oven (spotting), and the time it takes to make adjustments (turning and ADBT). If any step takes too long, the entire batch is delayed, just like a scraper.

So, basically you can split the cycle time into 2 parts. One is fixed time, the other one is variable time. Fixed in the sense this part of the cycle time does not depend upon your travel distance. So, that is called as fixed time, say your loading, dumping, turning, your accelerating, decelerating. All these things comes under the fixed time. So, it is not dependent upon the distance travelled. The other one is a variable time, your haul and return is a variable time because it is significantly dependent on your travel distance.

Cycle time can be categorized into fixed time and variable time. Fixed time includes components like loading, dumping, and turning, which remain constant regardless of distance traveled. In contrast, variable time depends on aspects like how far the scraper has to travel and the speed at which it moves, which can change based on different conditions on site.

Imagine a road trip. The time spent preparing the car (e.g., filling gas, packing) is the fixed time; it doesn't matter how far you drive. The driving time, however, varies based on distance and speed. If you take a scenic route (long-distance), it could take longer compared to taking the highway (short-distance) to the destination.

So, the loading time of the scraper is fairly consistent irrespective of the scraper size. So, that means whether it is going to be a smaller scraper or bigger scraper in both cases. So, commonly we can say that we are going to assist this scraper with the help of a pusher according to the size of the scraper the compatible size of the pusher you have to select.

Loading time for scrapers tends to remain constant, regardless of the size of the scraper being used. This is because, regardless of size, scrapers often rely on pushers to assist with the loading process. This compatibility between scrapers and pushers is critical in minimizing loading time and enhancing efficiency.

Consider how a large truck and a small truck might fill up at a gas station. The time it takes to fill the gas tank—loading time—remains fairly similar regardless of truck size. However, having the right size fuel pump (the pusher) can make the process smoother and quicker.

Another important concept which we need to know is about the load growth curve for scraper loading. So, we commonly believed that when we load this scraper when we fill the bowl of the scraper to the maximum capacity we are going to maximize production. So, this is what is a common belief this is what is a common assumption, but that is not true. So, people have done the studies and they proved that when we tried to load the scraper to its fullest capacity. So, the production starts reducing beyond a particular time...

The load growth curve illustrates that loading a scraper to its maximum capacity does not always yield the best production rates. As the bowl fills (around 80-85% capacity), resistance increases from the material that is already present, which can hinder the loading efficiency and actually slow down production. Therefore, it's vital to find an optimal loading capacity to maintain efficiency.

Think of a container being filled with water. Initially, water flows in quickly, but as the container gets close to full, the flow slows down because the space for additional water decreases. If you keep trying to pour more past its limit, it spills out instead of filling more efficiently.

So, the next important component of the cycle time of the scraper is your haul and return time, as I told you it is a variable time, it is going to depend upon your travel distance and the speed of your machine...

Haul and return time is a critical variable component of cycle time. This time is affected by the distance the scraper must travel and the speed at which it operates. Some conditions can speed up or slow down this process, and maintenance of the haul route is essential for reducing resistance and ensuring efficiency in travel times.

Consider a delivery driver. The time it takes for the driver to travel to deliver a package (haul) or return to the starting point (return) varies based on distance and traffic conditions. Keeping the roads well-maintained would be akin to having clear and fast routes for the driver to navigate.

So, the next important thing which we are going to see as a component of your cycle time is your dump time. So, your dump time of your scraper it depends upon your scraper size obviously, bigger the scraper your dumping time will be more...

Dump time can be influenced by several factors including the size of the scraper and the type of material being dumped. Loose materials are easier to dump compared to cohesive materials. Furthermore, dump area constraints, like congestion from other machines, can also delay the dumping process.

Imagine dumping sand from a truck into a pile. A small truck might empty easily without any issues, while a large truck might struggle if the site is crowded or if the sand is compacted. Hence, operational efficiency at the dumping location is vital for timely completion.

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