Installed in one of South Africa's deepest gold mines the Blair, multi rope, single winders are manufactured by Fuller Vecor and operate at Anglo American's Vaal Reef number 11 shaft.

Known as the "Super Winders" they are designed to raise and lower the weight of 14 family cars down a 3.1 kilometre deep mine shaft. The payload is not excessive, but add the weight of the 3 kilometre long ropes and the engineering requirements make these some of the world's largest winders.

Design parameters are indeed impressive:

• Drum diameter 5.7 metres
• Hoisting depth 3150 metres
• Payload 13500 kg
• Rope speed 19 m/sec
• Rope diameter 42 mm
• Brake pitch diameter 6.77 metres
• Winder inertia 2,780,220 kgm 2
• Required braking torque 4,315,781 Nm

Safe control of these prestigious winders is of paramount importance and to achieve this Twiflex employ a total of 12 off VMS / VR type disc brakes acting on 2 discs 6.67 metres in diameter. Each caliper weighs over 770 kg and is applied by means of powerful, direct acting springs, giving a braking force equal to 180000N for each brake. With 12 brake calipers acting on the two 6.67 metre diameter discs, a total braking torque available for an emergency stopping situation is 7,311,600 Nm.

In mine winder disc brake technology each brake module contains a number of "dish shaped" springs which apply direct mechanical force to friction pads against a disc.

The brakes are released by applying hydraulic pressure to a piston and cylinder arrangement which compresses the spring pack. Controlled braking can, therefore, be achieved by varying the hydraulic pressure to each caliper.

When considering selection for mine winder disc brakes it is necessary to design a system that will statically hold twice the weight of the cables and fully loaded skip at the bottom of the shaft.

It is also required to slow down, and stop, a fully loaded skip near the bottom, and at a predetermined retardation rate. This first criteria results in providing a braking torque far in excess of the normal requirements.

That being the case, and because of the requirement to minimise winder rope stresses, particularly in ultra deep mining, an advanced braking control is needed.

This control is designed to accurately regulate the degree of hydraulic pressure needed for optimum retardation.

Conventional winders are designed with 4 to 5 metre drum diameters and result in a contact velocity between the disc and friction liner of 15 to 18 m / sec. "Super Winders" are engineered with 5.7 metre drum diameters and result in contact velocities of 25 m / sec and therefore higher disc temperatures. This requires an advanced design of friction liner material and the Twiflex Development Team needed to work closely with their friction liner manufacturer to develop a material that could maintain its coefficient of friction up to 350oC.

Another factor is the energy absorbed by such a braking system during an emergency stopping situation. In this case it can be as much as 155 MJ, therefore, the friction liner area and disc thickness are important when considering acceptable disc temperatures. For the "Super Winders" the 12 off VMS / VR caliper brakes employed on each winder have a total friction liner area of 4.3 m2 and act on brake discs 80mm thick.