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Cycle Time Calculation
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Now, let’s talk about cycle time. Can someone tell me what components make up the cycle time?
I think it’s loading, mixing, and discharging times?
Correct! The total cycle time is the sum of all these factors. Why do you think we can’t overlook the discharging time?
If it takes too long to discharge, then the next batch can’t start quickly, which affects productivity.
Exactly! Productivity directly correlates with cycle time. Remember this formula: Cycle Time = Loading Time + Mixing Time + Discharging Time. Let’s see how we can calculate productivity next.
Introduction & Overview
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Quick Overview
Standard
This section elaborates on various types of concrete mixers, such as free fall and power mixers. It highlights their mechanisms, including the specifics of pan and trough mixers, while detailing how loading, mixing, and discharging times contribute to the overall cycle time and productivity of concrete mixing.
Detailed
In this section, we delve into the different types of concrete mixers, primarily focusing on free fall non-tilting reversible mixers and power mixers. Free fall mixers operate based on the gravitational flow of materials with a unique drum rotation mechanism to mix and discharge concrete. In contrast, power mixers utilize high-speed paddles to achieve rapid and homogeneous mixing, accommodating stiffer mixes. The section further explains the pan mixer and trough mixer configurations, emphasizing their efficiency and productivity in concrete mixing. It discusses cycle time calculation, which encompasses loading, mixing, and discharging durations, and their influence on mixer productivity. The necessity of adhering to established minimum mixing times per IS 4925 is highlighted to ensure optimal mix quality.
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Understanding Cycle Time Components
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Now, how to calculate the cycle time of the concrete mixer machines? In the earlier lectures, we have determined the cycle time of different equipment. Now, similarly, we have to find the cycle time of the concrete mixer machine also. So, what are the components of the cycle time of a concrete mixer machine? So, it is nothing but your loading time, mixing time and discharging time.
Detailed Explanation
Cycle time refers to the total time taken to perform a complete mixing cycle in a concrete mixer machine. It includes three main components: loading time, mixing time, and discharging time. Loading time depends on how the materials are introduced into the mixer (manually or using hoppers or conveyors) and can vary based on the loading method. Mixing time is influenced by the type of mixer used (power mixer, free fall mixer) and its capacity. Discharging time depends on whether the mixer is tilting or non-tilting.
Examples & Analogies
Imagine making a smoothie in a blender. First, you need to prepare the fruits and load them into the blender (loading time). Then, you turn on the blender to mix everything together (mixing time). Finally, you pour the smoothie into a cup (discharging time). The total time from preparation to pouring is your cycle time for making a smoothie.
Factors Influencing Loading and Mixing Times
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So, loading time depends whether you are going to manually feed in the material or you are going to use the tilting hopper for feeding the material or you are going to use a belt conveyor for feeding the material. So, it depends upon what arrangement you have for loading the mixer machine. Accordingly, your loading time will vary. Similarly, mixing time, it depends upon the type of your mixer machine whether you are going for power mixer or you are going for free fall mixer or what is the capacity of a mixer machine.
Detailed Explanation
The loading time varies based on how materials are loaded into the mixer—by hand, using a tilting hopper, or a belt conveyor. These methods affect the speed and efficiency of getting materials into the mixer. The mixing time is also affected by the type of mixer machine, as power mixers generally mix faster than free fall mixers. The capacity of the machine can also determine how long it takes to mix the materials effectively.
Examples & Analogies
Think of loading a car for a trip. If you pack your suitcase by hand, it might take longer compared to having a helper (like a conveyor) do it for you. Once loaded, if your car has a powerful engine (like a power mixer), it can accelerate quickly, just as a power mixer can mix concrete faster than others.
Understanding Discharging Time
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then the discharging time; so, that also depends upon the type of mixer machine whether it is going to be tilting type or it is going to be a non-tilting reversible type. So, all these things will affect your discharging time.
Detailed Explanation
Discharging time is the duration it takes to release the mixed concrete from the mixer. This time can vary depending on whether the mixer is a tilting type, which allows easy pouring, or a non-tilting reversible type, which may take longer to discharge. Knowing the discharging method is important for accurate cycle time calculations.
Examples & Analogies
Imagine a bucket being tilted to pour water versus a bucket that has a spout at the bottom. Tilting the bucket is quicker than waiting for the water to flow out of the spout. Similarly, tilting mixers can easily discharge concrete compared to non-tilting mixers.
Calculating Productivity of Concrete Mixer
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Now, how to calculate the productivity of your batch? Generally, we know that concrete is producing batches. Batch by batch, we produce it. So, how do you know the batch production in meter cube per hour? So, it depends upon your batch size and it depends upon your batch cycle time.
Detailed Explanation
To calculate the productivity of a concrete production batch in cubic meters per hour, consider the batch size (the amount of concrete produced in one cycle) and the cycle time (how long it takes to complete one batch). The formula for productivity is: Productivity = (Batch Size) × (60 / Cycle Time) × (Efficiency). Here, efficiency is the operational effectiveness of the mixer over time, often expressed in percentage.
Examples & Analogies
Think of baking cookies. If one batch of cookies takes 30 minutes to bake and you can fit 12 cookies in the oven at once, your productivity would be how many cookies you can make in an hour. If you only have the oven for an hour (two baking cycles), you could make 24 cookies per hour, assuming the oven is running effectively the entire time.
Understanding Optimal Mixing Duration
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Another important thing, we have to note here is the mixing duration. The mixing duration is very critical. We have to make sure we meet at least a minimum mixing duration as stipulated by the guidelines of the manufacturer.
Detailed Explanation
The mixing duration is crucial for achieving a homogeneous concrete mixture. Each type of mixer has recommended minimum mixing times provided by the manufacturer. Not following these guidelines can lead to inadequate mixing; too short of a duration can result in lumps of aggregates, while too long can lead to problems like evaporation of water and initial setting of the mixture.
Examples & Analogies
It's like cooking a stew. If you don't let it simmer long enough, the vegetables may not be cooked properly, affecting the flavor. Conversely, if you let it simmer too long, it might dry out. Finding the right cooking time is essential for the best outcome, just as it is for mixing concrete.