Specialist polyurethane product manufacturer Urethane Moulded Products (UMP) completed the development of a new tooling system in December that has enabled the company to manufacture 600-mm-diameter polyurethane knife-gate valve sleeves, commonly used in mine slurry applications.

“To date, the company has spent about R800 000 on various tooling systems to manufacture urethane valve sleeves ranging from 18 mm to 600 mm,” UMP director Trevor Carolin tells Mining Weekly.

He notes that the company manufactures two variants of urethane sleeves for abrasion-resistant valve manufacturer Dual Products, the Dual Valve knife-gate series, which includes the dual slurry knife-gate (DSKG) valve and the narrower dual-wafer slurry knife-gate (DWSKG) valve.

“Effectively, urethane sleeves are replacing rubber sleeves in slurry-pump valves because urethane is less abrasive and the coefficient of friction between the moving steel blade and the urethane sleeve is lower,” Carolin comments.

Meanwhile, Dual Products director Stephen van Rensburg highlights that the DSKG and DWSKG valves have been tested on slurries at State-owned power utility Eskom’s Matla power station, in Mpumalanga, and on slurries in different mining applications, including gold and uranium, with positive results.

“Initial tests using urethane and rubber stroke sleeves respectively were conducted in Finland, where water was used to test the efficacy and durability of the product over other materials. The results indicated that the knife-gate valve, with a urethane sleeve, could handle 75 000 strokes, compared with only 5 000 strokes using a rubber sleeve. This is one of the main reasons why urethane was selected for the valves,” he explains.

Urethane offers improved wear life of valves, compared with rubber, Carolin explains, adding that urethane reduces friction in valves and slurry pipelines, which increases pump efficiency and, therefore, decreases energy costs.

He further asserts that UMP’s urethane valve sleeves are up to 25% cheaper than those of its international competitors, as UMP has improved the technology of its products for increased efficiency. It has also developed the tooling system to improve the cost efficiency of manufacturing the goods.

For each size of urethane sleeve manufactured, a new tooling system needs to be developed, such as when metal-pressing tooling is required. “There are several components that go into the manufacture of valves, and tooling needs to be customised for each of these parts, which were designed, developed and manufactured by UMP,” Carolin points out.

When developing the tooling system for urethane sleeves, the valve application needs to be determined, which will, in turn, determine the level of abrasion resistance required from the sleeve, he notes.

Carolin says that UMP has, therefore, designed its sleeves for worst-case scenarios, resulting in a product that has high cut-and-tear resistance.

“Another factor that needs to be considered when developing tooling systems is the range of pressures to which the valves will be exposed. “UMP’s urethane sleeves have successfully been tested at pressures of up to 25 bar, without leaking, while the valves have been designed to resist only about 16 bar.”

Carolin further notes that Dual Products conducted several pressure tests at their factory in Benoni to ensure that the sleeves can resist the same pressures as the valves, resulting in several iterations.

The testing also necessitated the development of different polyurethane formulations. UMP initially tried to replicate rubber valve sleeves using standard polyurethane systems, which did not work, and had to develop a special urethane formulation to ensure the correct blade contact pressure.

The company first launched the polyurethane sleeve in April last year and has since registered increased demand for different sizes of urethane valve sleeves.

UMP manufactures the products for Dual Products, which has received requests from companies in Russia, Australia and Chile for urethane valve sleeves with diameters of up to 1 500 mm.