Thermal Analysis

1.  Liquid Iron Sampling - uniformity & consistency are mandatory

1. Make sure the sample ladle is free of iron and slag and is as hot as practical.
2. Don't use graphite or clay-graphite ladles for sampling since they tend to produce some inoculating effect.
3. Make sure the iron being sampled is as close to the same temperature as possible from sample to sample.  (Note that this temperature will vary depending on whether it is a furnace or ladle sample.)
4. For electric furnace samples, best results are usually obtained once a temperature of ~2700^oF has been reached in the furnace.
5. If sample ladle is filled from another ladle, we recommend filling the sample ladle, emptying it and refilling before pouring your sample.
6. Make sure the cup stand is kept as clean as possible, free from resin build-up and spilled iron, out of any cold drafts and at as constant a temperature as possible.
7. Make sure the cup and stand are level, not tipped, and that the cup is poured completely full.
8. If frequent samples are poured (more than ~4-5/hr.), use a second stand and alternate between stands to prevent overheating of the stand.
9. Good sampling practice will result in consistent maximum temperature at least 50^oF to 100^oF above the liquidus temperature.
10. When pouring final iron samples, allow at least two minutes after inoculant addition before pouring your sample.
11. Remove the sample from the cup stand as soon as analysis is completed to minimize resin build-up and to permit the stand to cool prior to the next test.
12. Regularly clean the cup stand and contacts with a wire brush or other means.

2.  Equipment Calibration

• from the cup all the way back to the instrument - extremely important!! (Be aware of variations between IPTS thermocouple standards.  Cups for the N. American foundry industry are 1948 IPTS.  Do you know whether your instrument is being calibrated per 1948, 1968, or 1990 IPTS?)

Table showing errors between IPTS 68 and IPTS 48 and also the temperature differences which exist if IPTS 48 thermocouples are used with IPTS 68 instruments.

(From 9/23/81 memo from L.R. Jones/E-N to W.F. Shaw)

3.  Cup purchasing, storage & monitoring

1. Purchase cups in large quantities (obviously based on your usage) with the specification that all cups in each order be from the same manufacturing lot.
2. Store cups in as warn and dry an atmosphere as possible.  If stored in a cold warehouse, make sure cups are brought up to room temperature well in advance of their usage.
3. Before using a new lot number, compare TA curves from current vs. new lot of cups to ensure that no significant differences occur.
4. Include the supplier's lot number on your melt records & note when a change in lot number occurs.