White metal
{{Short description|Type of decorative bright metal alloy}}
{{about|metallic alloys|the musical genre|Christian metal}}
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The white metals are a series of often decorative bright metal alloys used as a base for plated silverware, ornaments or novelties, as well as any of several lead-based or tin-based alloys used for things like bearings, jewellery, miniature figures, fusible plugs, some medals and metal type.{{cite web |url=https://www.belmontmetals.com/product-category/white-metals/ |title=White Metals |access-date=April 18, 2021 |last= |first= |date= 17 April 2019|publisher=Belmont Metals |location= |language= |quote= }} The term is also used in the antiques trade for an item suspected of being silver, but not hallmarked.
A white metal alloy may include antimony, tin, lead, cadmium, bismuth, and zinc (some of which are quite toxic). Not all of these metals are found in all white metal alloys. Metals are mixed to achieve a desired goal or need. As an example, a base metal for jewellery needs to be castable, polishable, have good flow characteristics, have the ability to cast fine detail without an excessive amount of porosity and cast at between {{convert|230 and 300|°C|°F|0|lk=on}}.
Silver
In compliance with British law, the British fine art trade uses the term "white metal" in auction catalogues to describe foreign silver items which do not carry British Assay Office hallmarks, but which are nonetheless understood to be silver and are priced accordingly.
Tin-lead and tin-copper alloys
File:Pigs and Bars of Babbitt.jpg
Tin-lead and tin-copper alloys such as Babbitt metal{{US patent reference |number=1252 |issue-date=17 Jul 1839 |inventor=Isaac Babbitt |title=Mode of making boxes for axles and gudgeons}}. have a low melting point, which is ideal for use as solder, but these alloys also have ideal characteristics for plain bearings. Most importantly for bearings, the material should be hard and wear-resistant and have a low coefficient of friction. It must also be shock-resistant, tough and sufficiently ductile to allow for slight misalignment prior to running-in.
Pure metals are soft, tough and ductile, with a high coefficient of friction. Intermetallic compounds are hard and wear-resistant but brittle. By themselves, they do not make ideal bearing materials.
Alloys consist of small particles of a hard compound embedded in the tough, ductile background of a solid solution. In service, the latter can wear away slightly, leaving the hard compound to carry the load. That wear also provides channels to allow in lubricant (oils). All bearing metals contain antimony (Sb), which forms hard cubic crystals.
| class="wikitable" style="text-align:center" | ||||
| % Sn
! % Sb ! % Cu ! % Pb ! Applications | ||||
|---|---|---|---|---|
| 93 | 3.5 | 3.5 | – | style="text-align:left"| Light and medium internal combustion engine big-end bearings |
| 86 | 10.5 | 3.5 | – | style="text-align:left"| Light and medium internal combustion engine main bearings |
| 80 | 11 | 3.0 | 6.0 | style="text-align:left"| General-purpose heavy bearings (lead increases plasticity) |
| 60 | 10 | 28.5 | 1.5 | style="text-align:left"| Heavy-duty marine engine bearings, electrical machines |
| 40 | 10 | 1.5 | 48.5 | style="text-align:left"| Low-cost, general-purpose, medium-duty bearings |
Applications
White metals are commonly used in bearings and bushings because of their high load-bearing capacity and self-lubricating properties, which reduce friction and extend the lifespan of these components.{{cite journal |last1=Dean |first1=R.R. |last2=Evans |first2=C.J. |year=1976 |title=Plain bearing materials: The role of tin |journal=Tribology International |volume=9 |issue=3 |pages=101-108 |doi=10.1016/0301-679X(76)90032-3}}{{cite book |last1=Freeman, Jr |first1=John R. |last2=Woodward |first2=R.W. |year=1921 |series=Technologic Papers of the Bureau of Standards |number=188 |title=Some Properties of White Metal Bearing Alloys at Elevated Temperatures |publisher=Bureau of Standards |page=4 |ol=OL7756898W |url=https://archive.org/details/somepropertiesof02ree/page/n1/ }} In the automotive industry, they are found in engine components like crankshaft and connecting rod bearings.{{cite book |author=Doug Woodyard |year=2009 |title=Pounder's Marine Diesel Engines and Gas Turbines |publisher=Butterworth-Heinemann |edition=9th |chapter=Chapter Fourteen – Doxford Low-Speed Engines |isbn=978-0-7506-8984-7}} Additionally, white metal is popular in jewellery and decorative items due to its cost-effectiveness and ability to mimic more expensive metals like silver.{{cite web |url=https://www.sputtertargets.net/blog/an-introduction-to-white-metals.html |title=An Introduction to White Metals |last=Green |first=Julissa |website=Sputter Targets |access-date=Aug 11, 2024}} In the printing industry, white metal alloys were historically used to cast typefaces.{{cite book |author=Vincent Rich |year=1994 |title=The International Lead Trade |publisher=Woodhead Publishing |edition=1st |page=115 |isbn=1855731037}}
See also
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References
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