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Temperature rise due to cycle test

  1. May 2, 2016 #1
    Hello all,

    I am working on a few test scripts to test the life of a hydraulic cylinder. (It is a mechanically operated cylinder and has a positive displacement)
    The testing will involve thousands of continuous pump and retraction operations, due to which the temperature of the piston seal and the oil will rise.
    I need to provide necessary idle time in between the cycles to avoid any failure of the piston seal.

    What I have considered so far is the friction pressure on the seal due to its compression (by installation) and friction pressure to the fluid pressure on the seal. From which I was able to arrive at the heat generated per second. However, the friction factors were taken from the supplier catalogue to arrive at these values.

    I need to account the heat generated due to work done on the oil and the influence of the number of cycles and time taken to perform these cycles. To build these equations I need to make some assumptions like the cylinder walls do not participate in heat transfer and also there is no loss in heat while the oil while it is pumped (the entire system is a closed loop hydraulic system).
    I need to build the equations and determine the idle time that needs to be provided in between the cycles.
    I may have not explained here very well, but if anyone is interested to help, I can provide better details.

    I have attached the excel sheet to the point I have attempted so far. Not sure if i have taken the right approach and moreover I was not able to include the effect of cycles.
    In the excel sheet, the ones in the boundary are seal details and need not be worried about.

    upload_2016-5-3_11-33-40.png
     

    Attached Files:

    Last edited: May 3, 2016
  2. jcsd
  3. May 3, 2016 #2

    Nidum

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    Please do .
     
  4. May 6, 2016 #3
    Hello Nidum,

    Thank you for the interest.

    I will start with the explanation of the system:
    It is a hydraulic cylinder, closed loop system. The reservoir is connected to the piston chamber, with the manually operated pump to suck the oil from the reservoir into the piston chamber through a couple of unidirectional check valves
    There is a return line, where the pressurized oil is pulled out of the piston chamber through another check valve which open on external load application. Its a complete mechanical system.
    upload_2016-5-6_18-1-31.png

    The above is just the brief to understand what sort of a system I am working on. Right now, we are about to perform an endurance test. The piston lifts a weight of 300 kg, when oil is pumped. Using an automatic fixture, we will program it to pump the oil 200,000 times. With each pump stroke having a small volume of oil displaced, it requires 25 strokes to achieve the full stroke. Then, the release valve is opened to let out the pumped oil to the reservoir and the cycle continues.

    To simplify, the piston travels 12.7mm*200,000pumps*(Pump + Retraction =2) = 5080 km under a load of 300 kg acting directly on the piston.
    Since this is a testing and not a real usage model, we would like to provide breaks in between the cycle test, as this is a case where there will be heat generated to an extent that piston seal would lose its intended material properties.

    What I want to simplify in my calculation is the heat loss of oil during which the oil takes the path from reservoir-to-piston area-to-reservoir by transferring heat to manifold and reservoir enclosure material.

    So, the heat generation will be in between the piston seal and the cylinder bore diameter, due to continuous rubbing.
    Also, the oil will get heated up as well, since it is taking the load.

    Well, that is as far as I have come. But if i can convert this heat generation to the raise in temperature of the seal, I should be able to provide the right duty cycle for this endurance test.
    The calculation is in excel, where I have considered the friction due to seal installation + friction due to fluid pressure acting on it as the heat generated by the seal.
    The heat generated by oil to be the work done on oil.

    But honestly I am not sure if I have my equations correct.

    Please help.
     
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