5. Cycle Time Calculations

The swell factor is a ratio of loose dry unit weight of the material by bank dry unit weight of the material. Particularly for push loaded scrapers, the swell factor will increase by 10% due to pushing.

The swell factor describes how much a material expands from its bank state (when it's compacted) to its loose state. For example, if we apply additional pressure (like from a pusher), the material gets compacted more, causing its unit weight to increase and thus affecting the swell factor. This means that when estimating load capacities for push loaded scrapers, we must account for this increase in swell factor.

Think of packing a suitcase. When you first pack, the clothes are loosely arranged, but if you press down hard, you can fit more inside. The swell factor is like the suitcase's capacity; it's influenced by how tightly the clothes are packed.

Gross weight of the machine is the empty weight plus the weight of the load in the machine. For example, if the empty weight is given as 43,944 kg and the weight of the load is calculated to be 32,901.2 kg, the gross weight equals 43,944 kg + 32,901.2 kg = 76,845.2 kg.

Calculating the gross weight involves adding the machine's own weight (when empty) to the weight of whatever it is carrying. This is important because knowing the total weight helps in assessing how well the machine will perform and what kind of resistance it will encounter during operation.

Imagine a truck. If it weighs 5 tons when empty and can carry 3 tons of cargo, its gross weight when loaded is 8 tons. Knowing this weight allows the driver to calculate fuel efficiency and how hard the truck will have to work on inclines.

The rolling resistance across the haul route is uniform, with an average of 50 kg per ton. Different segments of the route may have different gradients, affecting the overall resistance, like +3% or -3%.

The haul route’s design includes various gradients which the scraper must travel over, influencing how much effort it will take to move the load. The resistance can vary from segment to segment, which we calculate separately. Uniform resistance simplifies this by providing a constant value across the entire route.

Consider riding a bicycle uphill versus downhill. Going uphill (positive gradient) requires more energy (or effort) than going downhill (negative gradient) where gravity assists. Similarly, scrapers must exert more effort on inclines than on declines.

Total cycle time is the sum of the loading time, dump time, turn time, and haul time. For example: haul time = 6.1 minutes, loading time = 0.8 minutes, dump time = 0.37 minutes, and turning time = 0.21 minutes, leading to a total cycle time of 7.78 minutes.

Calculating the total cycle time is essential for understanding how long it will take to complete a round trip from load to dump and back. Each activity within this cycle has a specific duration that contributes to the overall efficiency of the operation.

Think of preparing a meal. If it takes 10 minutes to chop ingredients, 15 minutes to cook, and another 5 minutes to plate, you’d need to add these times to know how long the whole meal will take. Similarly, in machinery operations, each task adds to the total time needed.

The balanced number of scrapers served by one pusher is the cycle time of the scraper divided by the cycle time of the pusher. In this example, it yields approximately 5.68 scrapers per pusher.

Balancing the number of scrapers to pushers ensures that neither piece of equipment slows the process due to waiting. Here, we find that one pusher can adequately serve nearly six scrapers, acknowledging that logistical and operational issues may necessitate rounding this number down or up.

Imagine a restaurant kitchen where one chef can serve several tables, but if he has too many customers (like too many scrapers), they might have to wait too long. Finding the right balance helps maintain a smooth and efficient workflow.

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