Belt scale accuracy

[jms1387]

I am curious if others have had material disappear from the inventory? As of now we are contracting out our crushing at a recycle yard and we had roughly 11,000 tons of 1-1/2 roadstone crushed. The entire pile was crushed for 2 projects i had left myself a 1,000 ton cushion in the event one of the projects went over on tonnage. towards the tail end my inventory was showing 6,000 tons on the ground i shipped out 4,000 of that and the pile was gone. I know theft and un ticketed trucks is not the factor as i am the only one at the site. so my question is are belt scales on a radial stacking conveyor accurate at all? i always hear how accurate they are but my inventory tells me otherwise. any insight would be great as I need to explain a 20k write off this week.

Thanks
JMS

 

[JDOFMEMI]

How often do you check the calibration on the scale?

On a radial stacker, any time you move it the calibration will change. The best place for the scaleison a transfer conveyor that does not need to be moved.

 

[ol'stonebreaker]

A radial stacker is also usually quite steep which can have an effect on accuracy. If your output is fairly consistent, do an emergency stop and using a piece of thin plate cut to fit the contour of the belt wedge it into the rock on the belt as a stop. Start cleaning everything off the belt for a weight sample. Once you've cleaned enough back from the stop then move it back 3 ft, 5 ft or whatever you want, insert the stop at the measured point and clean everything everything off the belt between the two points. Weigh it and calculate ACCURATELY the belt speed and with the weight per foot of sample you can arrive at TPH at that time. Doing this several times these you can calculate a fairly close TPH output to compare against the belt scale. As already said, move the scale to a flatter more stationary conveyor.
Mike

 

[lantraxco]

Never thought of that, if it's steep enough for material to be rolling back, you're constantly weighing the same material more than once?

 

[ol'stonebreaker]

I'll add that w/ a 33% error something is seriously wrong w/ the scale. Either location and or calibration.
Mike

 

[Shimmy1]

Have had gravel crushed numerous times. Even have had piles GPS-mapped to determine yardage. Was done the day after crushing finished to prevent inaccuracy due to settling. We never came out on those piles, either. I have wasted hours running across a scale checking weights. I load 20 yd³ loads with a 4 yd³ loader. Of all the loads checked, I can honestly say I believe I could figure losses due to inaccuracies in loading at 500 lbs per load. If I figured 1000 lbs MORE than accounted for every load on a 20,000 pile, and used 2500 lbs/yd³ (which is a ridiculous number) I would only end up about 450 yds short. I have never even been within 1000 yds³ of what the crusher said, or the engineer using GPS. My response to this problem is if you aren't the crusher, and you're not paying for material off the truck scale, you need to be figuring at LEAST a 10% loss into the pile. Just my opinion.

 

[ol'stonebreaker]

Safest way for everyone is every outgoing truck weighed on platform scales w/ tare weight AM and lunchtime if hauling a full shift. If platform scales aren't available then it's a crapshoot for everybody.
Mike

 

[Jonas302]

How are you scaling your loaded trucks could be a calibration issue in that scale also should put the stacker over your dump truck for a least a few loads during crushing to run across a scale