When to sample
Sampling from a melting furnace should wait until the furnace is about 2550 F or about 1400 C to allow the alloys to dissolve.
Sampling too hot
The cup thermocouple wire melts about 2540 F, so sampling very hot metal can melt the thermocouple. When this happens, the wire on one side of the cup will spring out slightly as the thermocouple melts. Normally you will lose 200 to 300 degrees transferring iron from the furnace to the cup, so a furnace at 2700-2750 F is usually not a problem. If you are melting the thermocouple, hold the iron in the spoon for a few seconds before pouring the cup. A good furnace operator will “see” the iron temperature and know when it is too hot.
Sampling too cold
The first arrest where crystals first form in the iron is the liquidus temperature. If you sample too cold, you may miss this temperature and not get a true analysis. If the iron is cold, take a larger sample in the spoon to keep the metal from losing temperature as fast, and wash out the sampling spoon to reduce heat loss.
Keeping the cup stand lower to the ground means splash from the pouring spoon doesn't fall far, and there is less danger of iron bouncing away into clothing. It is also more ergonomic and safer for the operator.
To fill the cup up, keep the stand and the cup upright and not leaning to one side or the other.
Cups that have been uncovered for a time will collect foundry dirt, which often includes carbon riser as well as other metals, so make sure they are clean. And of course, don’t use any cups that have been exposed to water or rain. The instantaneous formation of steam and resulting explosion of molten iron could cause injuries.
Cup Contact with Stand
The contact area under the cup is friable sand and the cup should not ever be removed and then replaced on the stand. The contact points would then become loose and the cup will fail once filled with molten metal.