Tin Ingot Purity Grades: The Basis of Every Application
Tin ingots are a soft, corrosion resistant non-ferrous metal with excellent plasticity, which is why they are used across so many branches of industry and manufacturing. The first question in any application is purity, because residual elements such as lead, antimony, bismuth and arsenic decide whether a grade suits soldering, packaging, chemicals or alloys. GB/T 728 defines the familiar grades Sn99.90, Sn99.95 and Sn99.99, and the impurity ceilings rise as the tin content falls.
| Tin content (%) | As | Fe | Cu | Pb | Bi | Sb | Cd | Zn | Al | Total impurities |
|---|---|---|---|---|---|---|---|---|---|---|
| 99.99 | 0.0005 | 0.0025 | 0.0005 | 0.0035 | 0.0025 | 0.002 | 0.0003 | 0.0005 | 0.0005 | 0.01 |
| 99.95 | 0.003 | 0.004 | 0.004 | 0.01 | 0.006 | 0.014 | 0.0005 | 0.0008 | 0.0008 | 0.05 |
| 99.90 | 0.008 | 0.0025 | 0.008 | 0.04 | 0.015 | 0.02 | 0.0008 | 0.001 | 0.001 | 0.1 |
Electronics and Soldering
The largest single use of tin is solder. Tin ingots are melted into solder alloys for printed circuit board assembly, component tinning, semiconductor packaging and connector manufacture, where the metal must wet copper and copper alloys reliably and form a joint that survives thermal cycling.
Lead-free solder alloys such as Sn96.5Ag3.0Cu0.5, commonly called SAC305, are formulated from high purity tin to control melting range and joint strength.
Tin is also used in tin oxide coatings for display and touch panel glass, where indium tin oxide provides a transparent conductive layer.
Purity matters most here: lead and antimony residues degrade wetting and can push an alloy outside the limits of the relevant solder specification.
Tinplate, Packaging and Food Contact
Tin is non-toxic and resists corrosion, so it is electrodeposited onto steel strip to make tinplate, the classic material for food cans, beverage cans and general packaging. Tin ingots are the feedstock for the tin anodes and chemicals used in that coating process. The same properties support food packaging boxes and closures, where a stable, food-safe surface extends shelf life and keeps the contents isolated from the steel beneath.
Chemical Processing, Catalysts and Float Glass
Tin resists attack by many acids and alkalis under normal service conditions, so it is used in chemical plant equipment, pipework and components handling aggressive media. Tin compounds serve as catalysts and stabilisers in polymer and coating production, and tin based systems are used in glass and ceramic finishing. One of the most important industrial uses is the float glass process, where a continuous ribbon of molten glass is floated on a bath of molten tin to produce flat, distortion free glass for windows and architectural glazing.
Alloys: Bronze, Bearing Metals and Pewter
Tin bronzes: copper-tin alloys, including phosphor bronze, deliver strength, wear resistance and corrosion resistance in bearings, bushes, springs and marine hardware.
Bearing alloys: high tin babbitt metals provide the soft, conformable surface layer used in plain bearings for engines, turbines and heavy machinery.
Pewter and decorative alloys: tin alloyed with small additions of antimony and copper is cast and spun into tableware, trophies and architectural fittings.
Fusible and low melting alloys: tin-lead and tin-bismuth systems are used for safety devices, tooling and thermal fuses.
Construction, Medical and Specialty Uses
In construction, tin bearing alloys and coatings are used for roofing and waterproofing detail, where the metal keeps its properties in harsh weather and over long service lives. In medical equipment, tin appears mainly through the electronics inside imaging, monitoring and diagnostic systems, where lead-free tin based solder is required, and where the low toxicity of tin is an advantage in devices that may contact patients. Further uses include ceramic glazes and pigments, glass decoration, and organotin-free stabiliser systems where regulation restricts older formulations.
Frequently Asked Questions
Q: What is the main use of tin ingots?
Solder manufacture is the largest use, followed by tinplate for packaging, chemical applications and tin bearing alloys.
Q: Which tin grade should be used for lead-free solder?
Sn99.95 or Sn99.99 is normally selected, because low lead and antimony content is needed to keep the alloy within specification.
Q: Can tin ingots be used directly for food cans?
The tin is first used to produce tinplate or tin chemicals; the coating, not the ingot, forms the food contact surface.
Q: Why is tin used in the float glass process?
Molten tin provides a perfectly level, chemically stable bath on which molten glass floats, giving flat glass a uniform thickness and a smooth surface.
Q: What are tin bronzes used for?
Copper-tin and phosphor bronze alloys are used for bearings, bushes, springs, pumps and marine components that need wear and corrosion resistance.
Q: Does tin ingot purity affect price?
Yes. Higher tin content leaves less room for residual elements, needs more refining and therefore commands a higher price.