Due to the availability of different sampling locations and equipment, there are several methods of taking total samples. The uniformity of the sample obtained cannot be stressed enough, as it eliminates a variable in the test results. The technician must remember that safety comes first.
1. production sampling
Sampling the top of the bin is extremely dangerous as well as a difficult, if not impossible, method to obtain a representative sample. For this reason, this method of sampling is undesirable. Discharge of the sample to the compartment or belt bin can be taken on the sample discharge slope. In these cases several small samples should be taken at short intervals and combined to form a total sample. Each of these samples should include the full cross section of the material flow from the slope or belt. Continuity of operation will normally not allow the technician to control the flow rate from the discharge chute so that these samples can be taken easily. A mechanical turning or slide chute system is the fastest, safest and most accurate system for taking a belt sample; Unfortunately very few mechanical systems exist.
Belt sampling involves taking material samples directly from the conveyor belt. The proper procedure is:
1) Make sure the belt is carrying a normal load of material that has not been disassembled;
2) Have the plant operator stop the belt, and use proper lock out procedures;
3) Take a complete cross section of the material, being careful to include all the material on the belt and only the material in the section. A template is recommended, especially on a vertically inclined belt. Remove most of the sample with a scoop or shovel and the rest with a brush; And
4) Take as many complete cross sections as necessary to obtain a sample that meets the minimum sample size.
2. stockpile sampling
coarse aggregate reserves
It is recommended to sample coarse aggregates using the following procedure.
1) Locate the area of the store from where transportation will start.
2) Using a front-end loader, dig into the stockpile and set aside a small pile of 10 to 15 tons of material. This should be done in the same way as a truck being loaded for shipment (Fig. 2.1 and 2.2). When building small piles, the loader bucket should be as low as possible, and the operator should roll the material out of the bucket instead of dumping the material. Reducing the distance that allows the material to free-fall will reduce the amount of separation that can occur in smaller piles (Figure 2.3). Each additional bucket load of material should be taken and dumped in the same manner as described above, and placed evenly on top of the previous one. (Fig. 2.4).
3) Mix the small lumps well. Using a loader bucket, go to the end of the rectangular pile and roll the material over. Keeping the loader bucket as low as possible, push the bucket into the material until the front of the bucket passes through the midpoint of the original pile. Then the loader bucket should be slowly raised and rolled forward to create a smooth mixing of the ingredients. (fig. 2.5, 2.6 and 2.7). Move to the opposite end of the pile, and repeat this mixing process. If the pile does not seem to be reasonably uniform, additional mixing should be done.
4) The stack is now ready for sampling. Do not hit the top (Fig. 2.8). The sample will be taken at the center of the volume which is approximately one third of the height of the pile. The sample shall consist of at least 6 complete shovels of material taken at equal increments around the pile (Fig. 2.9, 2.10 and 2.11). The shovel will be inserted horizontally to the full depth of the material and raised vertically. Care should be taken to keep as much material as possible on the blade of the shovel (Fig. 2.12).
fine aggregate stockpiles
Fine aggregate samples are normally obtained in the same manner as coarse aggregate samples, using a fire shovel or sample tube to collect the material.