Hard lead
Hard lead or antimony lead is the name for a group of lead - antimony - alloys which are mechanically much more resilient compared to lead. The reasons for the additions are greater hardness with acceptable brittleness, better casting behavior (less contraction when solidifying) and better rollability.
Appearance
Compared to pure lead, hard lead has a bright luster and breaks in a crystalline manner, especially with higher antimony contents. The alloys with higher antimony contents are also characterized by the fact that they keep their shiny appearance in air longer than soft lead.
composition
Hard lead usually contains between 2% and 13% antimony and traces of other metals, e.g. B. copper (usually about 0.05%), arsenic (up to 0.15%), tin or bismuth. According to Raynor, the eutectic of lead and antimony is 252 ° C and 11.1% antimony. The addition of further traces and the tendency of the melts to undercool can shift the determined position of the eutectic, so other sources provide further information in this concentration range.
application
- Elevator technology : balancing and counterweights
- until 2003: balance weights on wheels
- Molded parts, including for accumulators
- Ingots as a raw material for other alloys
- Drain pipes , drinking water pipes
- Shot (Sb 2–3.8% As 1.2–1.7%)
- Corrosion protection
- Ammunition production
Manufacturing
The most economical way to produce the alloys is to melt a master alloy (e.g. PbSb12 with an approximately eutectic composition) in lead. This can be done in the vicinity of the relatively low melting temperature of lead. It is also possible to dissolve the antimony itself in the lead melt, or even to dissolve lead in the antimony melt. However, this requires longer melting times or higher temperatures.
Related alloys
Related alloys are the letter metal alloys , which usually have an even higher antimony content and also contain tin.
literature
- DIN 17640-1: 2004
- DIN 17641 (old, but still widely used)