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In manufacture
a carefully controlled mix of raw materials, mainly comprising either
diabase rock or silica, is heated to high temperature until molten. In
the case of glass wool this is accomplished in a furnace, whilst
for rock wool production a cupola is used.
The resulting molten glass or rock product is then spun and formed into a flexible mat for further processing into finished products. Inorganic rock or slag are the main components (typically 98%) of stone wool.
The remaining 2% organic content is generally a thermosetting resin binder (an adhesive) and a little oil. Glass wool products usually contain 95% to 96% inorganic material.Stone wool is made from volcanic rock, typically basalt or dolomite, an increasing proportion of which is recycled material in the form of briquettes.
Slag wool is made from blast furnace slag (waste).
Glass wool is made from sand or recycled glass, limestone and soda ash; the same ingredients as for familiar glass objects such as window panes or glass bottles. In addition, glass fibre has boron added to improve its moisture tolerance.
The required amounts of material are measured and sent to a melting furnace. For stone wool this is the rock or recycled material plus energy. Manufacturers are working hard to increase the recycled content of mineral wool whilst maintaining the high quality of their product.
For glass wool the raw materials are sand, limestone and soda ash, as well as recycled off cuts from the production process. Recycled window, automotive or bottle glass is increasingly used in the manufacture of glass wool and it now accounts for 30% to 60% of the raw material input. In some plants this is as high as 80%.
The reuse of off-cuts and recycled materials has helped to steadily reduce the energy input required to produce mineral wool.
FurnaceThe raw materials are melted in a furnace at very high temperatures, typically 1300°C to 1500°C. The smoke that is created during this process is filtered and flue gases cleaned to minimise any environmental impact.
SpinningAfter the furnace droplets of the vitreous melt are spun into fibres, droplets fall onto rapidly rotating flywheels or the mixture is drawn through tiny holes in rapidly rotating spinners. This shapes it into fibres.
BindingSmall quantities of binding agents are added to the fibres. The structure and density of the product can be adapted to its precise final usage.
CuringThis is then cured at around 200°C.
CuttingThe mineral wool is sawn to the required size and shape, for example into rolls, batts, boards or it is customised for addition to other products. Off-cuts and other mineral wool scraps are recycled back into the production process.
PackagingDue to its impressive elasticity, mineral wool can be compressed to reduce its volume during packaging, making it cheaper and easier to transport and handle.
Gases and WasteWaste such as off-cuts are recycled into the production process reducing inputs and energy requirements. Gases from the production processes are cleaned in filters and after-burners to minimise impact on the environment.