Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is my power calculation correct?

  1. Mar 14, 2012 #1
    I am currently working on designing a conveyor for feeding 1t material to a furnace. Not going into detail of how it works, I would just like to confirm my approach.

    Goal: To move 1000 kilograms of mass using steel rope/pulley system. Determining power requirement

    It would be a bucket mounted on two wheels running at a very low speed (0.3 m/s) over a mild steel I-beam. From literature around the internet, friciton values are:

    mild steel on mild steel (0.74 static, 0.6 dynamic)
    rail wheel on steel rail rolling resistance 0.0020

    I am calculating power as follows:

    Speed desired: 0.3 m/s
    Time to achieve the speed: Not important but taking it to be 1s
    Mass to be moved: 950 kg + bucket assembly (~50 kg) = 1000 kg

    Friction to be overcome while driving: 1000 x 9.8 x 0.002 = 19.6N (2 wheels so 39.2N)
    Force to move the mass from rest: F=ma > F=1000 x (0.3-0/1s) = 300N

    Total force= 340N

    Power required: F x v = 340 x 0.3 = 102 W or 0.13 hp

    Am I missing something ? I am a bit skeptical about finding force required to move the mass from rest as it uses the static friction value of 0.72 which makes the required power go up by a large amount.

    Regards
     
  2. jcsd
  3. Mar 15, 2012 #2

    OldEngr63

    User Avatar
    Gold Member

    Stiction is a bear! That is the problem that you are facing here. If you want a realistic solution, you dare not use anything but the static coefficient of friction, and then give yourself a wide margin of extra power to overcome difficulties. Friction is extremely hard to prediction, and when it works against you, it can kill you!
     
  4. Mar 15, 2012 #3
    I went to market and found a winch with 5hp that according to the shopkeeper, people purchase for holding 1000 kg vertically. In my case, the load is moving horizontally. So the 5hp is surely more than my requirement I guess.
     
  5. Mar 16, 2012 #4

    OldEngr63

    User Avatar
    Gold Member

    It really depends. Can you tell yourself with certainty that μstatic ≤ 1? If not, then the frictional resistance could exceed the weight, and this winch may not be enough. A great deal depends upon the surfaces that are in contact - the material being moved and the stationary support surface - and you have not given much information about them. You are the design engineer. Just do what you have to do, and move ahead.
     
  6. Mar 16, 2012 #5
    Thanks for the advice. I will surely do some experimentation to determine the band of values in which the u(static) and u(rolling) falls. Rest I hope my approach is ok ? Just for counter-check
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Is my power calculation correct?
  1. Calculating the power (Replies: 5)

  2. Power calculations (Replies: 2)

Loading...