Batch Plant Sampling

You might be seeing the theme as we go along but if you don't let me fill you in.  A large amount of quality problems are due to simple errors.  Here's another one for you.

Imagine that your batch plant's 2 bin gradations are coming back with 1/2" rock in it, even though it should be screening ALL 1/2" rock into the 3 bin.  Your first reaction is that there is a hole in the screen right?  That was ours too and after shutting down the hot plant, cooling it down for an hour, and then finally inspecting the screen we found that there was no hole in the screen and had just wasted a bunch of people's time and money.  It was a mystery and we couldn't figure out how the rocks had gotten into the 2 bin sample but figured that there must have been some contamination at the lab.  The next day we had the same thing happen.  The reason?  We had a new technician pulling samples from the batch plant and he wasn't instructed on how to properly pull a sample.  At our plant we had four sample devices, one for each bin.  The technician was supposed to prop them up next to the sample openings and put them in to the batch tower one at a time.  However, to save time, the technician had thought, why not just put all of the samplers in at one time and pull them out as the bin empties to get a good sample.  The problem is that there was no divider between each of the sample rails and as the 3 bin dumped material into its sampler, rocks bounced off of it into the 2 bin sampler.  Simple mistake right?  Luckily our plant operator saw this happening the next day that we sampled and properly educated the technician on the correct way to sample and why we sample that way. 

Another thing to remember with sampling from a batch plant is that you should not leave the sampler in one place to collect the sample because the stream of material coming from the bin may be segregated with small rock on one side and large rock on the other.  When you hear the bin open you should steadily push the sampler down the rails and pull it back at the same speed once it reaches the end.  This will ensure that you sample the entire stream. It is not something that I can easily explain to you through a blog but be sure that you walk through it with someone who is experienced and practice a few times before you pull a sample you will be testing. 

Proper sampling is the first step to having good test results.  If you sample improperly it can ruin your test results and waste both your time and the time of others if they have to find a solution to fix the poor test results.