Rotopactor wins export award

Press, 19 September 1985, Page 35

Rotopactor wins export award

The Barmac Rotopactor, which recently won a 1985 Mobil Export Award for efforts in the North Amercian market, has become a success story for Tidco International. Last year, the Rotopactor, which is a New Zealand invention, had also won an inventors’ award. “The success of the Rotopactor is due to the relatively , low running costs in comparison to more conventional crushing methods,” said a marketing engineer for Tidco, Mr lan Rodger. “In many cases, it has been installed in place of those more conventional crushers.” ““As licensed manufacturers, we are competing favourably against more industrialised nations,” he said. In North America, the Rotopactor is applied to other jobs than just aggregate production, mineral industry and for agricultural lime. At Contract 85 Tidco will also have on display a new jaw crusher, which is another New Zealand invention, a conveyor system and extremely efficient screening equipment. For many years, the principle of crushing stone on stone has been accepted as an ideal, but one which is hard to put into commercially practicable terms. In the early 19705, Messrs Jim Macdonald and Bryan

Bartley put their heads together in order to develop this crushing principle into an efficient form. The machine that has resulted from this collaboration is the Barmac Rotopactor. Like most good designs, the machine is very simple with few moving parts and few points which are subject to wear and tear. Material is fed into a chute which in turn leads to the centre of a revolving rotor. Through two openings in the side walls of the rotor, material is ejected with great force on to a bed of stone formed in the crushing chamber.

After the material has impinged on the stone bed in the crushing chamber, it falls clear and is collected in two chutes and fed to the conveyor taking the product away. By varying the speed of the rotor, the material can be caused to break to form mainly chippings, or alternatively to produce a very high percentage of sand or fine sizes. The shape of the finished product is consistently excellent. Wherever possible, the designers have incorporated stone beds to minimise wear on the crusher itself. The feed hopper that passes material to the rotor has a stone-bed floor; likewise, the side walls inside the rotor cavity are profiled to induce a stone trap as

well as the crushing chamber itself. It is in the chamber that a very important difference is found between the Rotopactor and other centrifugal impact machines. Hitherto, it has been considered necessary to allow the ejected material from the rotor to impinge on a vertical metallic face. In the Rotopactor, the ejected stone impinges on a stone bed lying at an angle of about 40 degrees. This different approach eliminates the need for expensive wearing parts on which to impact the stone and a similar saving is made in using the rotor stone traps. The key unit in the crusher is the rotor, the diameter of which is either 840 mm or 990 mm; this is attachhed to the vertical shaft by means of a tapered locking bush. The bush and securing bolts are protected by a Nihard cap, which also serves to distribute the stone into the rotor flutes. Horizontal surfaces inside the rotor are equipped with four wearing plates which are specially profiled to deflect the flow; at the periphery special tip plates are fitted to the two exits from the rotor, these areas being the only ones exposed to direct wear from the feed material. The drive to the crusher is attached to the lower end of the vertical shaft. This is normally direct-coupled to an electric motor or driven by means of vee-ropes. The motor itself is carried in a vertical position and can form an integral part of the machine. It is important to use the correct rotational speed for the rotor in order to produce the required crushed product; the speed at which

the material leaves the rotor is much higher than with conventional crushers and is usually around 55m/s to make good shaped chipings and of the order of 70m/s when sand production is required. The reduction ratio for a given material is related to speed: with speed determined, capacity is directly related to the power available. The more work done on a given quantity of stone the more fines will be produced; the machine can be adjusted to produce the type of results required and can be quickly changed between one duty and another. The change is made by altering the rotational speed and here two choices are available: with vee-rope drive, rotor-tip speed can be altered by a change of pulley; with a direct drive, the same thing can be obtained by a change of rotor diameter. The present Barmac Rotopactor is essentially intended for use as a tertiary crusher, accepting a feed size up to 57mm. To obtain the greatest flexibility from the machine it is recommended that the crusher is operated in closed circuit with an efficient screen. In this way, a controlled finished product can be obtained and surplus oversize returned to the crusher for further reduction. Tramp metal can pass through the crusher without damage and the worst condition that can occur is that bridging takes place within the rotor, causing it to be out of balance; this in turn causes excessive vibration which can be sensed by a simple vibration-sensitive switch operating a warning device or stopping the machine.