WHAT TO CHECK FOR IF YOUR PLANT IS “LOOSING” CEMENT.October 26, 2016
At some point most Concrete Producers will have a inventory problem of not being able to balance the amount of cement delivered Vs. the Automatic Batch Controller inventory. The problem can be a few tons to several truck loads over a short time period.
FIRST STEP – Confirm the Automatic Batch Controller is not capturing a lighter or heavier weight then the actual batch weight. Settle time of 3-4 seconds is common for most plants. Live bottom cement scales (screw) might need to have the screw motor turned off to capture the final weight before restarting automatically by the Automatic Batch Controller.
To check this:
Start a batch in automatic mode. When the feed light on the manual panel turns off, press the HOLD button on the panel and watch the actual scale weight (not the feed amount) for about 10 seconds. The scale should settle after about 3 seconds without any change in weight. Compare the scale weight to the “Feed Weight” displayed on the screen. If the number continues to fluctuate then try the following;
1. Check the calibration of the scale with a certified scale company. Inspect the scale system, including levers, load cells, bearing points and hoppers. Correct any damaged parts or altered factory adjusted settings and re-calibrate the scale.
2. Perform a scale build-up with certified test weights. Each build up increment should be no more than 20% of full scale capacity. At each scale build up point, add a test weight equivalent to 1 grad to a scale corner. Record the added weight before checking the 1 grad weight at the next corner. Any required adjustments can be completed with a summing box. A scale build-up confirmation will confirm the accuracy of the scale in a full range of batch sizes.
3. Confirm the plant foundation is level and not settling. A batch plant scale must be level in order to be accurate. Scales can be “unloading” on one corner with a false average into the actual amount.
4. Make sure the Bag House cartridge or bags are clean. Plugged bags will pressurize the silo pushing cement past a 3 psi butterfly valve seal. Also confirm the “cleaning sequence” time for the bag house is adequate for the amount of cement being offloaded.
5. Confirm you are using Hypalon shrouds and not gum rubber boots on the inlet and outlet valves/screws to the cement weigh batcher. Gum rubber boots are more rigid and can push or hang up the cement scale.
6. Last but not least, confirm the bulk truck driver is actually offloading the complete load of cement. It is difficult to confirm a full load has been offloaded with out running the truck back across a set of truck scales. It is rare but it does happen that drivers leave the plant site with some cement still inside the bulk truck.