Sarco delivers sizable trunnion cast for SAG mill breakdown

South Africa Roll Company (Sarco), South Africa’s only mill roll and ring manufacturer has manufactured and delivered what it believes to be the largest locally cast semi-autogenous grinding (SAG) mill trunnion casting to grinding mill manufacturer New Concept Projects (NCP).

Sarco says the trunnion has successfully been delivered and will be installed and commissioned once the appropriate downtime period is scheduled.

The trunnion was manufactured for a client of NCP that had experienced an operational failure of its existing 10.97 metre trunnion and, as a result, had to be replaced.

Cast weight for the trunnion casting was 75 tons and once stripped the casting weighed 55 tons before machining. Once the final machining process of the trunnion had taken place, the mill trunnion weighed approximately 45 tons, according to Sarco’s business development engineer Adelé Vorster.

Vorster also said that the trunnion was manufactured in the notable time of 12 weeks. This period included the development of the pattern, which took about six weeks, the actual casting period, which took another six weeks, all while conforming to global quality standards.

The casting was produced by Sarco at its foundry in Vanderbijlpark, Gauteng and was made using spheroidal graphite iron, which has a reputation of having a notable strength-to-weight ratio, is relatively easy to cast and has an ability to withstand high operating pressures.

South African Roll Company (Sarco) has long been recognised as one of the leading international manufacturers of castings used in the steel and non-ferrous manufacturing industries. Producing castings weighing up to 65 tons requires the foundry to have large melting capacity and the machine shop to have custom-built CNC equipment. All the processes in between pouring of the metal and final machining have to match and accommodate the size and weight of the castings – no mean feat.

The company can manufacture horizontal centrifugal cast mills for hot strip mill finishing stands, steckel mills and plate mills. They also manufacture static cast or monobloc rolls through carefully selected material specifications and heat-treatment cycles, in line with clients’ requirements.

The foundry houses six coreless induction furnaces with a total capacity of 86 tons, as well as thermal analysis systems to evaluate and optimise molten metal quality before tapping and casting. A horizontal centrifugal caster, a vertical centrifugal caster for sleeves or rings and five continuous sand mixers are available on site.

Eight natural gas-fired, heat-treatment furnaces and various casting pits range in width and depth to accommodate large-size castings.

Machine shop (heavy and light bay)
Critical to the manufacture of mill roll castings is our machine shop. The machine shop has a wide variety of equipment, custom-built for roll manufacturing. The shop is divided into a heavy bay and a light bay. The heavy bay handles castings from 10 to 85 tons in cast mass with a bed diameter up to 1 650mm and total length up to 10 metres. The light bay is for castings from 450 kilograms up to 10 tons with a bed diameter up to 1 400mm and length of 5 500mm.

Facilities include roughing lathes, CNC finishing lathes, single head milling machines, large and duplex neck milling machines, large and small finishing grinders, a rough/finish grinder, automatic ultrasonic scanning equipment and a Lismar roll inspection machine for surface defects detection.
Sarco boasts its own sand reclamation plant and sand testing station, with moulding equipment and chills for static and centrifugal casting.

Sarco also offers a fully equipped technical laboratory, a machine shop with heavy and light bays, a research and development division, as well as a fully developed quality-assurance department.