Q Can we use existing gating and casting methods to cast lead-free copper alloys?Background: Most lead free alloys contain bismuth bismuth (bĭz`məth) [Ger. Weisse Masse=white mass], metallic chemical element; symbol Bi; at. no. 83; at. wt. 208.9804; m.p. 271.3°C;; b.p. about 1,560°C;; sp. gr. 9.75 at 20°C;; valence +3 or +5. (Bi) as the major alloying element. Bismuth replaces lead in the copper alloys and contributes to the machinability and pressure tightness of the alloys. Some of the lead-free alloys also contain selenium selenium (səlē`nēəm), nonmetallic chemical element; symbol Se; at. no. 34; at. wt. 78.96; m.p. 217°C;; b.p. about 685°C;; sp. gr. 4.81 at 20°C;; valence −2, +4, or +6. (Se) as an alloying element for machinability. The available literature on these lead-free Bi/Se modified alloys (known as EnviroBrasses) is extensive, and includes information on melting, pouring and casting properties. The lead-free alloys were developed to have foundry characteristics (melting and casting) as well as properties (physical and mechanical) similar to existing leaded alloys. In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke" put differently , there should be no differences in the foundry practices currently being used for leaded alloys. In addition, the design of the existing components need not be modified to satisfy property considerations. However, because most of the data in the literature comes from laboratory or pilot scale trials, it should be interpreted with caution. In large-scale production, some problems may lead to lower production rates and increased costs. Recommendations: The following provides an overview of some common concerns when changing from leaded alloys to the lead4ree alloys. Gating--Earlier studies on gating and risering of these alloys have revealed that conventional systems employed for leaded alloys could be successfully used. In addition, bismuth containing alloys perform better in respect to hot tearing. Machining--Even though lead-free alloys possess similar physical and mechanical properties to leaded alloys, they suffer from low ductility. As a result, care should be exercised while machining these alloys to minimize the potential for cracking. It may be possible the loads applied during un-lubricated machining are too high for these alloys. Moderate loading and some lubrication lubrication, introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid, semisolid, or solid—that permits free action of could mitigate this problem. Recycling--These alloys look similar to the leaded alloys. Clearly marked bins should be used to segregate seg·re·gate v. seg·re·gat·ed, seg·re·gat·ing, seg·re·gates v.tr. 1. To separate or isolate from others or from a main body or group. See Synonyms at isolate. 2. the scrap to avoid mixing with other alloys. Bismuth contamination in some alloys, such as aluminum bronzes and pure copper, is serious and causes embrittlement Embrittlement A general set of phenomena whereby materials suffer a marked decrease in their ability to deform (loss of ductility) or in their ability to absorb energy during fracture (loss of toughness), with little change in other mechanical properties, such . In addition, selenium contamination in the leaded counterparts to the lead-free alloys (C83600 and C84400) can have a deleterious effect on ductility of both the alloys and should be controlled below 0.1%. Information was supplied by the AFS A distributed file system for large, widely dispersed Unix and Windows networks from Transarc Corporation, now part of IBM. It is noted for its ease of administration and expandability and stems from Carnegie-Mellon's Andrew File System. AFS - Andrew File System Copper Alloy Div. (Div. 3). Recommendations are the opinion of the AFS Technical Dept. based on referenced literature and experience. If You need assistance with a technical issue, fax or email your question to: Casting Answers & Advice, c/o MODERN CASTING, at 847/824/7848 or moderncasting@afsinc.org. Mileta Tomovic Purdue Univ., West Lafayette, Indiana West Lafayette (IPA: [wɛst ˈlɑ.fəˌjɛt]) is a city in Tippecanoe County, Indiana, United States, 65 miles (105km) northwest of Indianapolis. The population was 28,778 at the 2000 census. The author thanks Igor Sokolchik, Purdue Univ., for the CAD drawings accompanying this column. |
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