also can be beneficial with degassing. Mixed results were found while purging the furnace with nitrogen gas, while phosphorous additions to the furnace appeared to help in some instances. Gas defects were the leading causes for scrap castings both before and after machining, and additional work with mini- mizing turbulence, gating design, pouring tempera- tures, pouring practices and other practices may be needed. Pouring temperatures in the 2,100-2,275 F (1,149-1,246 C) range were needed to reduce misrun scrap, but may have contributed to higher amounts of centerline shrinkage porosity. Tese temperatures are 25-50 F higher than the current melting and pouring practices for bismuth alloy (C89833) castings. Different tech- niques of both horizontal and vertical venting were found to be effective in removing some of the gas. As experience was gained during the
trials, the use of proper mold venting addressed many of the gas issues. With proper venting techniques and minor gating changes, typical degassing meth- ods were suitable. Te C83470 material was poured
manually. No issues were found pour- ing this material, although some gating modifications may help reduce turbu- lence and gas issues. Some extra slag build-up in the ladles was noticed at times. Air monitoring did not pick up any significant levels of sulfur dioxide during melting or pouring.
both single-point tooling and gang tooling. Te chips produced from both processes were larger and longer than those from other traditional plumbing alloys. Te gang tooling could not evacuate the large chips easily, causing heat build-up and premature tooling failure.
Elevated High speed air vent valves (front) and water supply 8-in. isolation valves are shown. Castings were found to have good
surface finish when steps were taken to control gas absorption. In some instances, sawing and grinding the material was challenging due to mate- rial build-up on the wheels or blades. Additional investigation into cutting wheels and methods is needed. No major concerns were seen with grind- ing flash or trimming parting lines. Castings made from the C83470 material (Fig. 1) were machined using
Table 1. UNS C83470 in ASTM Standards Element/Property
Copper Tin
Lead Zinc Iron
Antimony
Nickel (incl. Cobalt) Sulfur
Phosphorous Aluminum
Manganese Silicon
Tensile Strength (psi) Yield Strength (psi) % Elongation
sulfur content can help break up the chips and reduce the size of the long, curly ribbons. Dye penetrant was used on
selected machined castings, and no cracking was found in these castings. Pressure tests of the C83470
material found it to be pressure tight. After successful pressure testing (up to 150 psi), many castings were fractured to examine the internal grain structure for potential defects. Defects found in these castings had minimal impact on pressure testing. Cold shuts and gas defects, where the defect did not penetrate the entire
B30-14a (Ingot) 90.0 - 96.0
3.0 - 5.0 0.09 max 1.0 - 3.0 0.50 max 0.20 max 1.0 max
0.20 - 0.60 0.03 max 0.01 max -
0.01 max - - -
B505-14 (Cont.) 90.0 - 96.0
3.0 - 5.0 0.09 max 1.0 - 3.0 0.50 max 0.20 max 1.0 max
0.20 - 0.60 1.0 max 0.01 max -
0.01 max
36,000 min 15,000 min 15 min
Table 2. Example Tensile Bar Results From Casting Trials Sample
Fig 1. Chips on the left are from the sulfide- bearing tin bronze (C83470) and on the right are from the bismuth C89833 no-lead alloy.
1 2 3 4 5 6 7 8
Average
Tensile Strength, psi 37,300
32,100 35,000 36,900 36,800 33,200 38,000 36,700 35,750
15,600 15,900 15,600 19,300 18,000 18,400 18,300 17,300
B584-14 (Sand) 90.0 - 96.0
3.0 - 5.0 0.09 max 1.0 - 3.0 0.50 max 0.20 max 1.0 max 0.20-0.60 0.10 max 0.01 max -
0.01 max
28,000 min 14,000 min 15 min
Yield Strength, psi 17,300
Elongation, % 26.0
20.0 22.0 28.0 22.0 17.0 31.0 26.0 24.0
February 2016 MODERN CASTING | 37
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