Phosphor Bronze

Phosphor bronze is an alloy of copper with 3.5 to 10% of tin and a significant phosphorus content of up to 1%. The phosphor bronzes have superb spring qualities, high fatigue resistance, excellent formability and solderability, and high corrosion resistance.

  • PB1 is a continuously cast product used for machined components washers and bushes.
  • PB2 This has a higher tin content than PB1 this addition aids wear resistance and is used in gear applications.
  • PB102 is wrought with a high hardness mainly id bar and rod form used in the manufacture of machined parts and electrical components.
  • SAE660 – this is a leaded gunmetal used for a bearing material, good strength and , machinability and abrasion resistance.

Discovery

Historically one of the world’s oldest metal alloys, with its origins dating back almost 4,000 years.

Machining

You can get in a lot of trouble when drilling this in the lathe. Phosphor bronze has a tendency to bind and lock.

On the cutting edges of the drill grind a flat that is parallel with the centre-line of the drill.

You only need to remove a few thou: a touch on the grinding wheel or a few strokes on the oil-stone or diamond pad.

This will stop the drill digging into the phosphor bronze and then rotating the drill in the chuck or the whole chuck rotating in the spindle/tailstock.

Also, I find the best way is to use lots of cutting fluid to remove the heat and to lubricate the cutter, especially important when drilling phosphor bronze.

When machining the bearings for the traction engine I turned all of this wisdom upside down. Using very sharp carbide tips designed for aluminium and no cutting fluid with great results.

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Phosphorus

A non-metallic element. Solid at room temperature. Applied to the inner face of a cathode ray tube that when bombarded with electrons will emit light of various colours. Chemical symbol is P. Primarily used in agriculture and steel production. Discovered in 1667 by Hennig Brand who accidentally discovers the element phosphorus during an experiment with urine. But he keeps it secret and Robert Boyle later discovers and describes the element.

Uses

Phosphor bronze has many uses where resistance to fatigue, wear and chemical corrosion are required.

  • bearings
  • pistons – in steam engines

References

  1. Phosphor Bronze – a good starter page looking at the microstructure of PB from the Copper Development Association.
  2. Phosphor Bronze and Overview – a summary of a number of articles on Science Direct looking at very specific properties and applications.
  3. All About Phosphor Bronze – a brief summary of the properties, strength, and applications of phosphor bronze.

Bearings

The main bearings, the big-end and the camshaft bearings are all phosphor bronze in my Transitional Engine.

In addition the sliders are made from phosphor bronze.


glanze tools and phosphor bronze

Machining the axle bearings for the miniature Burrell traction engine. Here I used the carbide tips designed for turning aluminium to machine PB and they worked superbly.

1000rpm, no cutting fluid and the surface finish is superb.


Phosphor bronze saddle on Burrell

Phosphor Bronze Saddle

The saddle for the cylinder on the miniature traction engine is phosphor bronze.

The underside curve was machined with a flycutter. This gave a clean machined surface. However, I still had to finish the machining using an abrasive drum.

This gives me a cylinder for the Burrell machined from parts.

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