DIGGING FOR GOLD

Wanganui Chronicle, Volume 75, Issue 118, 21 May 1932, Page 10

DIGGING FOR GOLD

UNIQUE MACHINERY MANUFACTURE IN AUCKLAND LARGEST OF ITS TYPE MADE, [ . INGENUITY IN CONSTRUCTION. What is claimed to be the largest and most powerful dragline excavate i of its type ever made is now in course of construction at the works of the Vulcan Steel Construction Company, Limited, Auckland, states the New Zealand Herald. The machine incorporates many striking and. ingenious features never before adapted to a dragline unit, and which have been specially evolved to meet the require ments of this plant, which will be used on the excavation work of the Nokomai Gold-mining Company. The area to be worked on the Nokomai Crock, a tributary of the Mataura River, Central Otago. The machine has been designed by Mr. J. S. Whitaker, an English engineer residing in Auckland, who has had a life-time of experience in the design and manufacture of excavating machinery. Mr. Whitaker was responsible, when in England, for the design of what arc believed to bo two of the first mechanical revolving shovels to come to New Zealand. They were used on the construction of the WellingtonAuckland main trunk railway. Electric Welding Processes. In the construction of this unique drag-line excavator, cast iron castings arc almost entirely eliminated and replaced by parts made of electricallywelded steel construction. Ponderous members also have been built up by the electrical-welding process and now lie upon massive timber cushions in the yard of the Vulcan Steel Construction Company, in process of assembly. They bear striking testimony to the resource of New Zealand’s engineering industry.

The ingenuity with which castings have been eliminated and welded construction substituted is exemplified in the case of the searings for the various bearings. The bearings for the main winch are almost entirely of the roller and ball type, and on this unit of the machine alone they amount to several hundreds of pounds in value. Each of the bearings is mounted on a spherical seating which in a number of instances are so large that they are not listed by overseas manufacturers and are being made at the works of the company. Special equipment has been constructed for this work, and some remarkably fine workmanship has resulted. The fitting and 4 poise,” as demonstrated by the ease with which the huge searings can be swung by hand pressure, are particularly striking.

Huge Travelling Tower. When erected the plant will appeal to the lay observer as something in the nature of a steel tower, about 60 feet high and travelling on rails. A cable, stretching from the head of the tower and across the area of gold-bearing shingle to be worked, will carry a bucket for scooping up the shingle. The main operating motor will be of 310 horse-power, an impressive feature. The main hoisting drum of the winch is four feet in diameter and 6ft. 9in. wide between the flanges, being carried on a nickel chrome steel shaft Olin, in diameter and capable therefore of bearing an enormous strain. A considerable number of men has been busily engaged for nealy two months on the construction of the plant and a night shift of electrical welders is being worked. On the machinery side, many ingenious devices have been brought into play in co-ordinating existing machinery with the unusual demands upon it. The machining of the huge forged steel bolts, horseshoe in shape, which secure the main winch bearings, provided a problem of their own. Although the plant being made is unique, dragline excavators as such are by no means a new type of equipment. Some of the most important earth removal works of recent times have been carried out by this class of machinery, as, for instance, the Sukkur Barrage, in India, the Assuan Dam extension, levee work on the Mississippi River and the Chicago Drainage Canal. It has also been largely used in other countries in “open” mining, usually for the stripping of overburden. This method is now being adopted for the first rime in New Zealand by the Nokomai Gold Mining Company. Use of Automatic Control. The dragline excavator consists in general of two main groups, the revolving type, where the line is attached to the end of a crane jib, and the slackline-dragline type, which is operated by means of an aerial cable. The latter type is again divided into two main classes, one in which the bucket always remains upon the ground and scrapes the material forward, and the <»ther in which the bucket digs the material and is lifted from the ground, with its contents, which are tipped in the air above a hopper or other receptacle. The machine being constructed by the Vulcan Construction Company is of the last-named class. The bucket- capacity of the new machine is such that eight tons of riiingle is removed at a single “bite.” A leading feature is the great extent to which automatic control of the machinery has been carried out. An electrical working model showed that the operator was able to control the machine without looking at the operating ground. It is stated that, while the dredge has its proper application, the dragline possesses features which make for improved performance. By its use, it is claimed, the bottom of the mine can be worked dry, ensuring complete recovery of the gold which lies in the formation crevices; the first cost ot the equipment, considering the quantity of material treated, is very low; a greater depth of faro can be worked; there is a much reduced cost of wear nnd tear; and greater digging power is available, compared with other types of excavators. Method of Operation. When the now machine is operating the bucket is allowed to run down the cable way by force of gravity until the desired spot for digging is reached. Thereupon the tension control is released and the bucket drops to the ground. The top carriage presses on

to the bucket and automatically closes the catch. The hauling control is then placed into “digging” position and the rope drags the bucket, nose down, along the ground. As soon as the bucket is filled, the carrying rope is set to maximum tension, thus pulling the nose out of the ground and preventing further digging. The control is placed into “hauling” position. Thd bucket leaves the ground and carries the material toward the hopper. On reaching the tipping point, the tipping arm comes into contact with the catch and automatically releases it. The bucket, opens and discharges the material, while the hauling control automatically shifts into il neutral;” the bucket runs out again, and the next cycle begins. Tt is claimed that the operator’s task is in no way strenuous or nerve-wracking, the operations being enacted anlomal n aily.