Why Use PREDICT

Obviously, if a foundry chooses to use PREDICT, it's going to add a step to the process, and there are costs associated with any change in operations.  The question becomes, why should a foundry want to use it? PREDICT was written initially to prevent failing tensile tests in an iron foundry.  The failures didn't occur frequently but were of great concern when they did.  There were additional testing costs when failures happened, but they were insignificant in the foundry's mind compared to having to notify customers of tests failures for castings that had already been shipped. They could have moved the testing in-house to reduce the turn around time for results, but a more economical and logical answer was to eliminate tests failures. 

The simplest way of eliminating failures would have been to raise the target tensile strengths, but that would adversely affect the machinability of the iron.  It appeared the best solution to the problem was to reduce the variability of the tensile test results.  Of course, deciding that was the best solution and accomplishing it were two different things.  A number of ideas were tried and the knowledge of the process improved with each attempt.  PREDICT was the culmination of all of those attempts. 

Illustration 1 - Class 40 Monthly Standard Deviation 


Illustration 2 – 80-55-06 Yield Strength Monthly Standard Deviation

Illustration 3 – 100-70-03 Yield Strength Monthly Standard Deviation

Illustrations 1 through 3 show the improvement in the standard deviation of the tensile results from three different grade of iron achieved from using PREDICT. In each case, the first two-thirds of the chart shows the results prior to using the program. 

Once the improvement in control had been achieved, the other more directly measur­able benefits from using PREDICT became noticeable. 

Lower Alloy Costs 

Some customers will specify a minimum amount of a particular element must be maintained for certain grades of iron.  Usually those specified elements are expensive.  It's easy to see that PREDICT, by improving control of the element, allows targeting them closer to the minimum; thereby, reducing the amount that needs to be added.  

One of the first steps in improving control is reducing the test results that are abnor­mally high. As the higher tensile strengths are frequently caused by having more strengthening elements than needed, the answer is to lower the content of them.   The easiest way of reducing them is simply not adding as much alloy. 

Finally improved control allows the reduction of targets. I recommend targeting the tensile strength at two standard deviations above the minimum. If the standard devia­tion of the tests are 3.0 ksi on a class 40 gray iron, that means targeting 46 ksi. If improved control takes the standard deviation down to 2.0 ksi, the target becomes 44. How much alloy does it take to get the additional strength? I'll depend on the foundry and what they're using to obtain their strength, but it will be a worthwhile figure. 

To give an idea of magnitude of these potential savings, let's assume that copper may be purchased for $1.40 per pound and ferro-molybdenum is $2.40 per pound.  (These are fairly realistic in-plant costs for these alloys.) If the copper and molybdenum could both be reduced by .05 percent, for every 1000 pound ladle treated there would be a savings of $2.70. Since yield is about 50%, that means a saving of over 1/2 cents per pound of casting. 

Improved Machinability 

Machinability is important to the people who buy castings but is very difficult to apply a dollar value to it.  In fact, most smaller foundries' customers can't even provide a good measure of it.  A more quantifiable definition of the effect PREDICT has is being sought.  Until that definition is obtained, only anecdotal proof of its effectiveness can be supplied.  That comes in the form of a quote from a machinist who has machined a ductile iron 80-55-06 part before and after PREDICT.  "Using a scale of 1 through 10, the parts used to be a 6.  Now they're a 9." 

Certainly, it's a topic that's hard to sell with strict dollars and cents, but it's something to think about. 

Charge Costs 

It doesn't take long working around foundries to learn the significance of charge costs.  Money saved on the charges effects everything.  PREDICT provides a number of ways to save money on charge costs. 

One of the limiting factors for induction melting of ductile iron is the manganese in steel.  If you're trying to make 65-45-12 and your manganese is too high, you'll fail elongation requirements.  By controlling the chemistry with PREDICT, one foundry has found that it has been able to reduce pig and increase steel in their ductile charge when making 65-45-12.  (PREDICT pointed out that they were keeping the manganese so low they were struggling to meet the yield requirements.) 

Similarly, a foundry making 80-55-06 found from using PREDICT that they could increase their steel (manganese) and reduce their copper additions while making a more controlled iron.  They achieved cost reduction through charge costs and alloy reduction. 

There is also the opportunity available, at times, to obtain charge materials at lower cost that may have more variable residual elements.  Those varying residual ele­ments may have been avoided in the past, but with PREDICT compensating for the changes the material can be used. 

There are many ways that PREDICT can achieve savings and improve operations.  The trial period we offer with PREDICT allows the foundry to see if it will work for them at no risk.