Posted April 22nd 2016

There are two main methods involved in the production of glass – the float glass process that produces sheet glass, and glassblowing that produces bottles and other containers.

Here, we are primarily interested in the float glass process. Float glass is a sheet of glass which is made by floating molten glass on top of molten metal – usually tin, although it is possible to use lead and other alloys with a low melting point. Modern windows are made using this process as is almost all flat glass we use today.

Between 1953 and 1957, Sir Alastair Pilkington and Kenneth Bickerstaff developed the float glass process, which is often still referred to as the Pilkington process. Before this flat glass was made by either cutting large discs of crown glass or blowing large glass cylinders which were then cut open and flattened. During the process, molten glass is fed into a ‘tin bath’, a bath containing molten tin. A continuous ribbon of molten glass is fed from the melting furnace onto the surface of the tin bath where it literally floats along the surface, forming a ribbon of uniform thickness. Tin is used for this process because it is cohesive, immiscible with molten glass and has a high specific gravity. To prevent oxidisation the tin bath needs to have a positive pressure protective atmosphere of nitrogen and hydrogen.

The other main use of metal in glass manufacture is the colouring process. Glass may be given different colours by the addition of colouring ions, striking glass (precipitation of nanometer sized colloides) and coloured inclusions. Below are some of the main additives and the colours they produce:

· Iron oxide – produces a blueish-green colour and is frequently used in the manufacture of beer bottles. When combined with Chromium, the two produce a richer green which is used in the manufacture of wine bottles.

· Manganese – if used in small amounts manganese will remove the green tint given by iron. In larger amounts it produces an amethyst colour. Manganese is one of the oldest glass additives with a history dating back to the Egyptian period.

· Nickel – the colour produced by nickel depends on the concentration used and it can vary from blue to violet to black. Nickel and cobalt together can be used to decolourise lead glass.

· Gold – in small concentrations gold produces a rich, ruby red colour – ‘Ruby Gold’, or a more cranberry hue in even smaller concentrations. The colour is dependent on the size and dispersion of the gold particles. Sometimes copper can be used in place of gold to produce a similar colour.

· Silver – silver compounds, such as silver nitrate and silver halides can produce a range of colours from orange to red to yellow. The way the glass is treated can affect the end colour, particularly during the heating and cooling process.



Posted April 15th 2016

Antimony is a chemical element with the symbol Sb and atomic number 51. Its name comes from the Greek words ‘anti’ and ‘monos’, which when put together mean ‘not alone’. Its chemical symbol comes from its historic name Stibium.

Antimony is a silvery-grey, lustrous metalloid. It is found in nature mainly as the sulfide mineral stibnite. Antimony compounds have been used for many years – in ancient time it was a popular addition to cosmetics. In this setting you might be more familiar with its Arabic name, kohl – a popular addition to eye shadows. Today Antimony is primarily used as alloying material for lead and tin. This improves the properties of the alloys and enables them to be used in solders, bullets and plain bearings. Antimony alloys are also commonly used in batteries and cable sheathings. Antimony compounds are often used to make flame-proof materials, paints, ceramic enamels, glass and pottery.

Antinomy is in the nitrogen group (15) and is more electronegative than tin or bismuth, but less than tellurium or arsenic. It reacts with oxygen if heated and becomes antimony trioxide, however, it is stable at room temperature. It has a ranking of 3 on the Mohs scale which makes it too soft to make hard objects. In 1931 coins made of antimony were put into use in the Guizhou province of China, however, because of their rapid wear their use was quickly discontinued. Antimony is found occurring naturally in the Earth’s crust and is estimated at 0.2 to 0.5 parts per million. Even though the element is not abundant it can be found in over 100 mineral species.

Around 60% of all antimony produced is used in flame retardants with it being used mainly as a trioxide in making flame proofing compounds. The applications for this include children’s clothing, toys, aircraft and automobile seat covers. Antimony also forms a very useful alloy with lead, increasing its hardness and mechanical strength.

In 2005, the British Geological Survey reported that the People’s Republic of China was the top producer of antimony in the world. They had a staggeringly large 84% share, followed by South Africa, Bolivia and Tajikistan. In 2010 this figure rose to 88.9% according to the US Geological Survey. Due to its lack of supply outside China, antimony was identified as 1 of 12 critical raw materials for the EU in 2011. Since 2010 the reported production of antimony in China has fallen with no significant antimony deposits developed for the past 10 years. This means the remaining reserves are being rapidly depleted.



Posted April 5th 2016

An alloy is a mixture of metals, or a mixture of metal and another element. White metal alloys are those which are light-coloured and generally have a lead or tin base. These alloys are also known as Babbitt metal, or bearing metal, a term which is generally preferred over ‘white metals’. Babbitt metal can be one of several alloys used as a bearing surface in a plain bearing.

Babbitt metal was first created by Isaac Babbitt, from whom it takes its name, in 1839. The original formula for his bearing metal was 89.3% tin, 7.1% antimony and 3.6% copper. This formula is still used by some manufacturers today and marketed as ‘Genuine Babbitt’, or ASTM B-23 Grade 2 Babbitt. It is a soft, white non-ferrous alloy which is used to provide a bearing surface. Bearings are used in engines to support moving mechanical parts and protect them from frictional degradation. Babbitt metal also has properties that help it reduce friction which makes it a good material for use in a plain bearing.

Babbitt metal is soft and can be easily damaged if not treated correctly. This would make it seem unsuitable for use as a bearing surface, however, the structure of the alloy is made up of small, hard crystals which are dispersed in a matrix of softer alloy. This means that as the bearing wears down, the harder crystal is exposed and a path for the lubricant is provided.

Babbitt bearings work by providing a low coefficient of friction, principally achieved by 2 means. First, there is the fact that the bearing itself has a low coefficient of friction so even without lubrication, a Babbitt bearing will have much less friction than another metal such as steel or cast iron. However, by adding lubrication Babbitt bearings can have a significantly low coefficient of friction – even lower than ball bearings.

Until the mid-1950s poured Babbitt bearings were a common feature of automotive appliances. Tin based Babbitts were commonly used as they could stand up to the impact of the connecting rods and crankshaft. Babbitt bearings were also commonly used in factories, before the invention of low cost electrical motors, to distribute power throughout via a central engine. Today, Babbitt is more commonly used as a thin layer covering bearings made of replaceable steel so that it still acts as a bearing surface.

Will Rowland_005