Polishing machines improve belt quality

The Sandvik polished belt range has four austenitic stainless steel grades and two martensitic grades available in a range of belt thicknesses and widths.

The installation of in-house and purpose-designed machines for producing polished stainless steel belts is paying off for Sandvik, as demand for new types of plastic film continue to increase.

Polished steel belts have been used for several years for the manufacture of photo and packaging films using the film casting process, where raw material solidifies on a steel belt as a thin film.

Inherent benefits of this method are consistent thickness and flatness and good optical performance.

More recently, the growth in the market for electronic equipment, such as LCD displays, digital cameras and mobile phones has led to strong demand for higher technology plastic films.

Film casting on polished steel belts is still the ideal and preferred production process, but there is now a need to achieve much higher specifications on surface quality to meet particular application requirements.

In essence, the belts must have a perfect surface.

They must be defect free, since any belt defect will be passed to the manufactured film and, as in the case of an LCD screen, will affect the electrical field and impair the image quality.

Sandvik has met the needs of the market in two ways.

First, a high-grade surface finish or 'super finish' relies on the use of steel with low and controlled inclusion levels.

Sandvik employs steel making techniques involving several remeltings of the steel using ESR (electro slag remelting) and VAR (vacuum arc remelting) practices.

Second, Sandvik has designed and installed special polishing machines at its manufacturing plant at Sandvik Japan, capable of producing the highest quality, mirror finish belts.

The Sandvik polished belt range has four austenitic stainless steel grades and two martensitic grades available in a range of belt thicknesses and widths for producing different types of plastic film.

There are five different grades of polished belt available ranging from a standard surface specification for packaging films to the highest specification surface finish for LCD films.

Surface specifications are defined by the number and size of acceptable inclusions and surface roughness.

The Sandvik manufacturing process ensures that the specification limits are carefully controlled and checked, both during and after the polishing process.

Inspection of polished belts is a stringent and demanding operation involving both automated equipment and close visual inspection.

Sandvik provides extensive after sales support including full repair and servicing and operator and maintenance engineer training.

A global sales and service organisation is capable of providing support anywhere in the world.

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