our weighing system has the following material flow sequence:

Storage Hopper → Vibrofeeder → Fixed Weighing Hopper → Vibrofeeder → Conveyor Belt → Discharge Pipes → Furnace

Whenever we perform a drop test, and measure the actual discharge it always comes almost accurate

However, during actual production, when material is discharged into the furnace bin:

• The chemical analysis shows higher alloy addition than what the weighing hopper indicates.
• The chemistry suggests that ~20 kg more material must have been added than the weighing hopper measured.
• This level of chemical change is not theoretically possible with the weight recorded by the weighing hopper.
• So now the productions guys are behind us that the weighing hopper is under‑reporting the actual discharged quantity during real operation.

We have checked the load cells, cable shielding , healthiness of the weighing system, load cell mounting vibrofeerders also not touching the weighing hopper.

What could be the reason for this issue. I am puzzled.
Looking fi

 

Since the drop test is accurate, first suspect the process mass balance rather than static calibration.

Possible causes include material retained in the downstream vibrofeeder, conveyor or discharge pipes and released with the next batch; material already present in the furnace/bin; feeder operation continuing while the weighing value is captured; or PLC timing/filtering that records the weight before the hopper fully stabilizes. Mechanical vibration during production may also affect the zero or final reading even when static tests pass.

I would perform a production-condition test by collecting material after the entire conveyor and pipe system, logging raw load-cell values and PLC commands at high resolution, and checking the downstream equipment before and after the batch for retained material. Also verify the alloy chemistry calculation using independent furnace-weight and representative sampling data .... poor mixing, sampling location, residual metal or incorrect initial chemistry can easily appear as an extra 20 kg addition.

 

20Kg is what percentage of the discharge load? 0.01% 0.1%? 1%? 5%?

 

20Kg is what percentage of the discharge load? 0.01% 0.1%? 1%? 5%?

This material is Niobium which is very costly material ( 55 USD ) So 20 kg is huge difference and addition to production cost. The problem here is no vendor will improvise the purity which will impact him. The normal purity comes around 66 percent per kg of material. But to directly answer your question David, 110 kgs material discharge required for process. so 20 kg comes somewhere around 18 percent.

 

Since the drop test is accurate, first suspect the process mass balance rather than static calibration.

Possible causes include material retained in the downstream vibrofeeder, conveyor or discharge pipes and released with the next batch; material already present in the furnace/bin; feeder operation continuing while the weighing value is captured; or PLC timing/filtering that records the weight before the hopper fully stabilizes. Mechanical vibration during production may also affect the zero or final reading even when static tests pass.

I would perform a production-condition test by collecting material after the entire conveyor and pipe system, logging raw load-cell values and PLC commands at high resolution, and checking the downstream equipment before and after the batch for retained material. Also verify the alloy chemistry calculation using independent furnace-weight and representative sampling data .... poor mixing, sampling location, residual metal or incorrect initial chemistry can easily appear as an extra 20 kg addition.

Thanks for your reply. Here the problem in not extra 20 kg addition. The normal recovery requires around 110 kg of material to achieve the required chemical analysis. Now from weighing system its only 90 kgs being discharged and analysis is getting achieved which is theoretically not possible considering the highest recovery and purity of the material.