Pirotecnia Posted March 14, 2012 Posted March 14, 2012 How can we calculate the jar ideal speed? Thanks!
marks265 Posted March 14, 2012 Posted March 14, 2012 I turn my speed adjustment knob to the right until the centrifugal force takes over, Then turn the knob to the left until it starts to mill again. Then repeat in fifteen minutes Mark
oldguy Posted March 14, 2012 Posted March 14, 2012 How can we calculate the jar ideal speed? Thanks! Depends on the diameter of the jar? If you can get around 68 to 72 RPM, you are usually in the ball park
dan999ification Posted March 14, 2012 Posted March 14, 2012 can you adjust the speed of the mill? to find the current speed, find the centre of the jar and draw a line to the outer edge from the centre [the radius] run the mill for a few minutes while filming it, now watch the footage and count the rotations for one minute using the line as referance, evrytime it passes 12 o clock count one, there you have the rpm.if you cant adjust the speed a bigger or smaller jar will change things not only because the smaller jars spin faster [ do more revs] but they also weigh less and unless you have a motor with high torque the speed will change with the weight difference.mine runs at about 68-75 rpm.if you can adjust the speed, as said spin it as fast as it will go without floating the contents/letting centrifugal force take over. dan.
dagabu Posted March 14, 2012 Posted March 14, 2012 I turn my speed adjustment knob to the right until the centrifugal force takes over, Then turn the knob to the left until it starts to mill again. Mark That's about the perfect speed guys, just shy of to tumbling. @ Mark, I bet the milling is pretty darn fast in that jar huh? -dag
oldguy Posted March 14, 2012 Posted March 14, 2012 That's about the perfect speed guys, just shy of to tumbling. @ Mark, I bet the milling is pretty darn fast in that jar huh? -dag What kind of jar?Is there something special about it?Just curious.
dagabu Posted March 14, 2012 Posted March 14, 2012 What kind of jar?Is there something special about it?Just curious. Probably not, it is the speed at which the jar turns. Mark was saying that he turns the speed up until the media stops cascading and starts to take the rid all the way around the jar. Once it does that, he turns the speed down until the cascading is at its fullest potential. It's really easy to hear with a jar 1/2 full of media with no comp, the racket it makes is almost unbearable. The greater the noise, the great number of hits the media makes as it is cascading down the heap, therefore the better the grind. After 15 minutes, the dynamics of the comp change enough so that the media starts to make the round trip again and you have to turn the speed down slightly. -dag
marks265 Posted March 14, 2012 Posted March 14, 2012 After 15 minutes, the dynamics of the comp change enough so that the media starts to make the round trip again and you have to turn the speed down slightly. -dag Actually I learned it to be the other way around. When bigger particles are milled it piles up faster and hangs on faster like a ride at the fair such as a "Tilt O Whirl" where you get pegged to the outside wall by gravity. The smaller the particles are the easier it is for the media to get through the material. After 15 minutes the particle size is reduced considerably. If tougher material is being used I would suggest check more than once. By turning up the speed a little more, you move the mill towards a "Ninja Blender" with material flying everywhere in the jar until the centrifugal effect takes over again. Your right about the sound IMO. You know how optimized your run speed is by listening. The jar can get quite noisy but it sure reduces the milling time. If you look at my latest mill in my blog you will see a small green drive belt. What it does is drive the second roller. Not doing so allows a high probability for slippage to occur and actual mill speed will change while running. A passive roller only supports and slows the jar because of friction losses. That's it, the cat's out of the bag, now you know all my deep dark secrets Mark
marks265 Posted March 14, 2012 Posted March 14, 2012 can you adjust the speed of the mill? dan. In regard to my mill: I have an industrial based drive system. I have a 3 phase 220VAC motor that is controlled by a frequency inverter drive. The little knob I turn adjusts the amount of analog input(voltage) that tells the drive how fast I want the motor to turn. In small horsepower motor configurations the freq. drive can be input (plugged into) 120VAC single phase which is a normal wall outlet in your house if you live in the USA. As long as the load does not exceed the ampacity of the drive you could use a larger motor if one was available at reduced cost. Buying a 3/4 hp motor to do the work of a 1/4 hp motor is just a waste of money and adds weight to the mill. In a mechanical sense you would have to change pulleys and or belts. There are adjustable sheaves but they are expensive. Another tidbit is that with a freq drive I can overspeed the motor. A basic plain Jane motor has an RPM of about 1765 RPM at 60 hertz. A freq drive can take it out to 120 hertz. However there is a formula that shows horsepower loss. As the frequency rises over 60 hertz efficiency is lost. I think there is a square root formula for hp or torque for this condition. With my pulley configuration I normally run my mill at about 45 hertz. For you foreign gents and others that don't know, 1 hp is about 764 watts IIRC. I am not going to look up the exact numbers on some of these things and I am getting older ya know. Mark
oldguy Posted March 14, 2012 Posted March 14, 2012 It depends on your mill design, how hard pulleys are to switch over. I could change mine in 10 minutes.
pyrogeorge Posted March 15, 2012 Posted March 15, 2012 Critical speed=265,45/sqrt(jar i.d - Media O.D) Opitmal speed is 65% of the critical speed.
dagabu Posted March 15, 2012 Posted March 15, 2012 Critical speed=265,45/sqrt(jar i.d - Media O.D) Opitmal speed is 65% of the critical speed. Looks good on paper but is not accurate in practice, I run at an optimal speed of 70 RPM in an empty jar (media only) and 68 with a loaded jar (1/2 chem load) which is 5% above optimal speed. It's all just a place to start, everyone needs to tweak their own jars. -dag
pyrogeorge Posted March 16, 2012 Posted March 16, 2012 I agree dagabu.In my jar i made a lot ot test speeds to find the ideal speed.
Mumbles Posted March 16, 2012 Posted March 16, 2012 The true optimum speed can vary quite a bit. According to Lloyd Sponnenburgh's book (which is where that formula probably was originally sourced), the optimum can vary from 45 to 110% of the critical speed. Things like viscosity and hardness of material will affect this. It would seem that particle size would probably also play a factor. He does say that for dry powders that 65% is about right. Note that is not meant to be an absolute. I'd think if you have to go significantly more than 65%, it would sound like there is a bit of slippage though.
dagabu Posted March 16, 2012 Posted March 16, 2012 The true optimum speed can vary quite a bit. According to Lloyd Sponnenburgh's book (which is where that formula probably was originally sourced), the optimum can vary from 45 to 110% of the critical speed. Things like viscosity and hardness of material will affect this. It would seem that particle size would probably also play a factor. He does say that for dry powders that 65% is about right. Note that is not meant to be an absolute. I'd think if you have to go significantly more than 65%, it would sound like there is a bit of slippage though. And the shape of the media as well. I use cylinders and they seem to take more "oomph" to get them to cascade but are really close to the critical speed. -dag
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