roxtech
Member
Hi Dears,
we have hopper with 8" openning and under hopper 1.5ft inclind bed with load cell of 50 kg. material drop over loadcell bed and then drop into other tank. we want to calculate ton/hr. As we know for flow ton/hr = speed of flow*weight/length of bed.
But here we have not speed of material.
Any body help me how to calculate flow of material?
Regards,
widelto
Member
When you open the hopper your load cell starts weighing when weighs is steady an before load drop into next tank take the weigh measurement.
Start your hour anytime it can be at 00 minutes if you desire it.
Start weigh measurement from zero, when fisrt batch is on the load cell you add actual weigh to old weigh that is zero, next batch do the same add actual batch to old weigh but this time old weigh is not zero, continue until the end of the hour.
Next hour you need move actual hour to past hour and start everything from zero. You can use a fifo with 24 places in order to see how is your production hour by hour.
roxtech
Member
OP
Lancie1
Lifetime Supporting Member
Roxtech,
I don't think you can calculate speed of material without some more information. The speed of your material will be based on gravity, and mass of material, and co-oeficient of friction of the material, and friction of the inclined chute, and size of the hopper opening, and depth of material in the hopper, and how round the material is, and how viscous or sticky it is. There are just too many factors to calculate it, but you may find some rough rules-of-thumb for specific materials.
I think what Widelto meant is that you don't really need speed to calculate the tons per hour.
It can also be calculated by taking a weight reading per some time period, then adding them all together for 1 hour.
For example, if you read the weight (in kg) every 1 second, for 3600 seconds, then your
Tons per hour flow rate = (Weight 1 + Weight 2 .....+ Weight 3599 + Weight 3600) divided by 1000 kilograms per metric ton.
For this method to be accurate, your time interval needs to be set so that you are measuring a new batch of product each weight reading. What you will get is an average Tons/Hour for the past hour. If you want an instantenous Tons/Hour reading, then multiply the weight in kg/second x 3.6 metric tons/hour.
1 kg/sec = 3.6 metric tons/hour
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It sounds like an impact flow meter. Here is an extract from isa.org See the link for pictures.
"The flowmeter measures only the horizontal component of the force of the material flow striking the plate. It is critical these following factors remain constant for reliable and repeatable measurement. The horizontal force is dependent on particle mass, velocity of the particle, angle of impact of the particle against the plate, and the energy absorbing characteristics of the particle. Thus, with these factors held constant, the flowmeter responds to the mass or weight of the material striking the plate. Because the flowmeter measures only the horizontal force, it is unaffected by vertical force changes caused by material buildup on the nonimpingement area of the sensing plate. Consequently, there is no zero drift, which in turn eliminates the need for frequent recalibration."
So as long as velocity, angle of impact, and the energy absorbing characteristics of the particle remain constant, then the force on the load cell will be proportional to the mass flow rate. The easiest way to find the proper multiplication factor would be to catch a test sample and compare it to the integrated value of the load cell during the test sample.
Brownhat,
Okay, I will take your word for it! So the load cell will measure the weight. I think he said that.
What Roxtech wants now is a way to calculate the flow rate of the product, given only the weight from the load cell.
Clay B.
Lifetime Supporting Member
I may be missing something here but I do not think you can figure thruput with the setup you have. Just weighing what is on the conveyor is going to tell you what is on the conveyor not how much it is passing.
Think of it this way: You have the conveyor running at 100 RPM's and the scale reads 60 lbs. Next you have the conveyor at 200 RPM's and the scale reads 60 lbs. zSo you weight did not change but your speed went up.
Better yet: Lets say you kept the speed at 100 RPM and the weight stayed 60 lbs. You ran a test and at this speed you measured you dumpped 2 tons in an hour. Well now your running at your contant speed but for some reason the scale is going heavier and lighter, what does this mean?
Is the material falling off the end of the conveyor faster now or is the material lumping up in the hopper?
You have no way of knowing. With this setup density becomes an issue real fast and accuracy goes right out the window.
As Brownhat suggest for Flow weight Measurement a specialized scale is needed.
widelto
Member
Hi Dears,
we want to calculate ton/hr.
That´s what i told you, but now you say, you want to calculate drop material speed.
The only thing I can think of is like this:
when your hopper is loaded take weigh measurement, when material start dropping start a timer, when material finish dropping and hopper is empty stop timer an take interval. Now you have time and weigh, so you have weigh/time, that´s speed of falling material.
You need to be have some mechanism to know excatly when the hopper output is open and close.
I may be missing something here but I do not think you can figure through-put with the setup you have. Just weighing what is on the conveyor is going to tell you what is on the conveyor, not how much it is passing.
...material drops over loadcell bed, and then drops into another tank.
I don't think there is anything as fancy as a conveyor here. The material gravity-flows out of hopper onto an inclined load cell, then falls into a tank. I think the load cell is under the inclined bed, not under the hopper. I don't think I have seen such an arrangement in my life time.
I think the flow rate will vary proportionaly to the height of material in the hopper, just as water in a barrel will flow faster out a hole in the bottom when the barrel is full.
I suppose if one knew all the flow characteristics of the material, such as viscosity and coefficient of friction, then an equation could be derived based on height of material in hopper, shape of bottom of hopper (flat or cone), size of hopper opening (8" round or rectangular?), and resistance to flow. Those mechanical engineers in the audience probably have some books with such formulas already worked out.
Still, this will not help unless Roxtech has a hopper level sensor to feed the material height into the equation.
So that takes us back to Widelto's method. Take a weight reading each second while the hopper is emptying, find the total for one hour, to get Average Tons per Hour flow rate.
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If this is an impact flow meter, then the basic equation for flow rate is something like flow (ton/hr) = weight / v . The v is held constant, because the powder is dropped from a consistant height. You can figure about what the v will be if you look at how far the material drops. Remember you only need to consider the horizontal component of v. The easiest thing to do is to catch a test weight, and see how close your guess at v was.
Remember you only need to consider the horizontal component of v. The easiest thing to do is to catch a test weight, and see how close your guess at v was.
Good point about it being the velocity needed by this impact flowmeter to determine the flow rate, and I think you have figured out what device Roxtech is using, and what he needs to do to find the velocity of the material (not the "flow of material" that he asked for). Excellent!
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