1.7. Estimation of Cycle Time

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 are pusher loader scrapers. 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. So, all this manure comes under this ADBT acceleration deceleration and the braking.

Cycle time refers to the total time taken for one complete operation of a scraper, which includes various components: Load time (LT), Haul time (HT), Dump time (DT), Return time (RT), Spotting time (ST), Turn time (TT), and Acceleration, Deceleration, and Braking time (ADBT). Each of these processes contributes to the overall cycle time and needs to be measured for effective project management and productivity analysis.

Imagine a bus that has to pick up passengers (Load time), drive to a destination (Haul time), drop off the passengers (Dump time), return to the starting point (Return time), park (Spotting), and maneuver at the pick-up point (Turn time). Just like each step takes time for the bus, each component of cycle time is crucial for a scraper's operation.

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 come 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 divided into two categories: fixed time and variable time. Fixed time is constant and includes tasks like loading, dumping, turning, and maneuvering, regardless of how far the machine travels. On the other hand, variable time, such as hauling and returning, changes based on the distance travelled, which means it can vary depending on factors such as machine speed and project conditions.

Think of fixed time like a standard delivery fee for a pizza, which remains the same no matter where you live. Variable time is like the distance fee for the pizza; if you live far away, you pay more, just like hauling and return times depend on how far the scraper needs to go.

So, the loading time of the scraper is fairly consistent irrespective of the scraper size. 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 and we are going to supplement the loading power. The average load time for the pusher-loaded scraper in common earth is 0.8 minutes.

The loading time for scrapers is largely consistent regardless of the scraper size, largely due to the assistance provided by a pusher. This means whether you're using a large or small scraper, the average loading time remains near 0.8 minutes when handling common earth. It's important to choose a pusher that is compatible with the scraper size to optimize productivity.

It’s like using a smaller or bigger grocery cart to carry groceries. Regardless of the cart size, it takes about the same time to fill it up because you have someone helping you get the items from the shelf to the cart, similar to how a pusher helps load the scraper.

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 a production. So, this is what is a common belief... So, do not try to load the scraper to its maximum capacity. The incoming earth encounters greater resistance as the quantity of earth in the bowl increases resulting in a reduction in rate of loading.

The load growth curve illustrates that while many believe that fully loading a scraper maximizes production, this is not necessarily true. Studies show that once a scraper reaches about 85% capacity, resistance from already loaded material slows the rate at which new material can enter, leading to diminishing returns in loading efficiency. Thus, optimal loading should be below maximum capacity.

Imagine trying to stuff too many clothes into a suitcase. Initially, it’s easy to put in clothes, but as the suitcase fills, it becomes harder to add more. Eventually, you can only fit a little more, wasting your time and effort - just like a scraper that reaches full capacity and struggles to load 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. So, haul and return time depends upon the distance and the travel speed.

The haul and return time is a variable component of cycle time, influenced by the distance the scraper must travel and the speed it can achieve given the project's conditions. Because the speed often varies considerably between loaded and unloaded conditions, it is essential to efficiently maintain the haul route to optimize travel speed and consequently reduce overall cycle time.

Consider a truck driving to deliver goods. If the route is bumpy and long, the driver will take longer to reach the destination. However, if the road is smooth and well-maintained, the truck can travel faster, demonstrating how maintaining a clear path significantly affects the delivery time.

It is economical to maintain the haul route. So, whatever efforts, whatever money you spend for maintaining your haul road, it is going to give you good return by saving your cycle time, by increasing your productivity and thereby reduce your unit production cost.

Investing in the maintenance of the haul route is cost-effective because it reduces cycle time, enhances productivity, and lowers overall production costs. Efforts might include using graders, sprinkling water to control dust, and ensuring the route is clear of obstructions. Proper maintenance leads to smoother operations, which contributes to better productivity for machines like scrapers.

Think of it like taking care of your driveway. If you regularly maintain it, you can drive your car quickly and smoothly. If it’s filled with potholes, it will take much longer to traverse, and you may even damage your vehicle. Similarly, a well-maintained haul route helps scrapers work more efficiently.

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