The following are hypothetical examples of energy-saving metrics estimates, which illustrate the use of the data spreadsheet and the estimating principles described above.  There is one example for each of the energy savings categories:  1) Furnace melt energy saved per pound of metal in castings poured; 2) Casting melt energy saved per pound of metal in castings shipped; 3) Non-melting energy saved.  

Example 1: R&D Project for Increased Melting Furnace Efficiency

Example 2:  R&D Project for Decreased Scrap/Increased Yield; Aluminum & Magnesium Diecastings

Example 3: R&D Project for Increased Finishing Efficiency for Steel Castings

Example 1: R&D PROJECT FOR INCREASED MELTING FURNACE EFFICIENCY
Category 1:  Furnace melt energy saved per pound of metal in castings poured

Suppose a new technology will improve the efficiency of a gas reverberatory furnace by 10%.   Estimate the year-to-year, average, and steady-state energy savings.
Using the “Energy Consumed” chart on the top half of the data spreadsheet, Page 1, gas reverberatory furnaces would be involved in the following process segments of the industry:

•  Aluminum Die Casting

•  Aluminum Permanent Mold

• Aluminum Lost Foam

• Aluminum Sand

• Zinc Die Casting

To supplement the spreadsheet data, an investigation is needed to determine the share of gas reverberatory furnaces in each process segment.  For purposes of this example, assume that investigation determines:

o        Aluminum Die Casting               40% of melting is done in gas reverb furnaces

o        Aluminum Permanent Mold       45%

o        Aluminum Lost Foam                35%

o        Aluminum Sand                         25%

o        Zinc Die Casting                        20%

Example 2: R&D PROJECT FOR DECREASED SCRAP/INCREASED YIELD; ALUMINUM & MAGNESIUM DIECASTINGS
Category 2:  Casting melt energy saved per pound of metal in castings shipped

This is powerful category of energy savings potential in the metalcasting industry.  Another aluminum example has been chosen to illustrate this potential through comparison with Example 1.  The subtlety here is the fact that “revert reduction” (see footnote 5) covers an entire alloy/process segment of the industry; whereas, a melting furnace efficiency improvement covers only the sub-segment of industry which uses that melting furnace type.  The metalcasting industry uses all of the major melting methods, and each alloy/process family has more than one, sometimes several, melting furnace types.  Example 2 compared to Example 1 illustrates this well.

Research for revert reduction in ferrous alloys has even more potential for energy savings because of the melting energy content of the ferrous alloys.  A ferrous example was not chosen so that the comparison to Example 1 would not be distorted.

Suppose a new technology is proposed for die casting aluminum and magnesium that affects the shot delivery, gating geometry, gating size, and “biscuit” size.  Suppose that technology has the potential to increase the average yield of aluminum and magnesium diecastings from typically 70% (footnote 5 and the table in the lower half of the data spreadsheet) to typically 75%.  It is also estimated that the efficiency of the metal delivery will reduce scrap in the molding process from 4% typically for aluminum die castings to 3% and from 5% to 4% for magnesium die castings.

Note how the data in the lower half of data spreadsheet is developed.  Tons Shipped by alloy/process family is the base parameter.  Tons Produced is created by adding back scrap castings.  This is done by this ratio:  (Tons Shipped) x (1+Scrap Percent/100).   For example, magnesium diecastings typically have 5% scrap, and 2003 estimated tons shipped are 106,600.  Therefore,

Tons Produced =  (106,600 tons) x (1+5/100) = 111,930 Tons

Similarly Tons Melted must include not only those scrap castings but also the risering and/or gating necessary to fill the mold cavity and feed solidification shrinkage.  That “extra” metal is removed from the casting and remelted.  So, any reduction in scrap and increase in yield reduces the energy necessary to ship the same amount of castings.  Continuing with magnesium in the data spreadsheet,

Tons Melted = (111,939 Tons Produced) / (70% Yield/100) = 159,900 Tons

Example 2

Using this logic and the Tons Shipped data from the spreadsheet, the scrap reduction and yield increase can be used to determine a lower value for BTU’s per ton produced in melting.  A reduction in Tons Melted in the lower table can be applied via ratio to the Melting BTU’s per Ton Produced in the upper table.  Here’s how the calculation lays out:

New technology would enable reductions in scrap

•  For aluminum, from 4% to 3%, on average

• For magnesium, from 5% to 4% on average

New technology would enable in increase in yield for both alloy families from 70% to 75% on average

Example 3: R&D PROJECT FOR INCREASED FINISHING EFFICIENCY FOR STEEL CASTINGS
Category 3:  Non-melting energy saved

Suppose a new technology can be developed which would inhibit the formation of oxide macroinclusions during the pouring of carbon, low alloy, and high alloy steel castings.  Based on DoE sponsored “Clean Steel” R&D, the causes of oxide macroinclusions have been discovered, and reoxidation of steel as it is poured is a primary and difficult to resolve cause.  This new technology would inhibit the reoxidation phenomenon during pouring.

The benefits to the steel casting industry would be the following:

• The technology would apply to all alloy and process subsets of cast steel, except investment casting.  (In this hypothetical example, we know the new technology would not work in a pre-heated mold)

• The major cause of cosmetic weld repair (oxide macroinclusions on the casting surface) would be reduced along with the following consequences of cosmetic weld repair:

  • Surface visual inspections  

  • Arc-air excavation of surface inclusions and subsequent weld repair

  •  Grinding of those weld repairs

  •  Post-weld heat treatment

  •  Post-heat treatment shot blasting and re-inspection  

    • In a small subset of cases, post-heat treatment magnaflux of weld areas

    • In a smaller subset of cases, post-heat treatment radiography of weld areas

  •   Post-heat treatment discovery of additional oxide macro inclusions that had been covered by a thin skin of initial solidification

  •  Repeat of arc-air, weld, weld-grind, and post-weld heat treatment for a subset of the original inspection group.

  •  Repeat of the shot blasting and re-inspection

  •  Inventory, storage, and material handling consequences of the above rework cycle(s) 

•  A reduction in scrap castings; since steel castings are readily weld-repairable, the typical steel foundry scrap rate would not be reduced dramatically.  The scrap rate would decrease from about 4% (total internal and external scrap; footnote 8) to about 3.25 % to 3.5%, depending on C&LA or High Alloy.  

This example illustrates some of the techniques for estimating when data is thin, as described on Pages 3 and 4 under “Estimating Techniques.”

From pie chart on Page 2 of the Metalcasting Metrics Data Spreadsheet, the following table of process energy content was derived.  This, as Examples 1 and 2, is hypothetical, and it is assumed that the investigator making the estimate would have investigated available sources for reasonable breakdowns of Carbon and Low Alloy and High Alloy process elements.  The sample breakdown in the table below is based on the author’s steel casting industry experience, but may not be representative of a broader and/or more in-depth evaluation.  As part of the example’s assumptions, high alloy steel castings made in the investment casting process have been excluded.  All of the Carbon and Low Alloy segment (assuming any investment cast C&LA tonnage is low) and the sand cast High Alloy segments are included.

Establish the baseline for finishing energy consumption in C&LA and HA steel castings due to oxide macroinclusions.  Refer to “Other Processing” in the table in the top half of the Metalcasting Metrics Data Spreadsheet and Metalcasting Industry Energy Content in the table above.

After gathering data and opinions from steel casting experts the following are elements of energy consumption in “Other Processing” that are affected by oxide macroinclusions:

Energy content is steel castings scrapped is another savings component; however, cosmetic weld repair of oxide macroinclusions avoids much of the scrap.  The cost of that repair and rework is accounted for above.  Reduction in scrap for Carbon & Low Alloy is expected to be from 4% typically down to 3.25%.  For High Alloy, it is expected to be from 4% down to 3.5%.  (See Example 2 for detailed methodology for scrap reduction.)

Naranjo/Gwyn; BCS/ATI                                                                                                                                                    
July 21, 2003