This article was originally published in Electrochemical and Metallurgical Industry Publication of March 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.
The great need of a slime concentrator that would save the maximum amount of slimes in a concentrating plant, and at the same time be simple in construction and easy of operation, has always been recognized by mill operators, wherever the practice of concentration of ores is carried on. The adjoining illustration shows such a machine and one that is entirely new in the field of slimers. In its design and construction are embodied features differing widely from anything heretofore introduced in concentrators of this class. It is the joint invention of Messrs. Randall P. Akins and James P. Evans, both of whom have been for a long time connected with the Colorado Iron Works Co. and are well known as experienced mill builders. For nearly a year past, since the slime concentrator assumed its present form, it has been subjected to almost continuous work on all classes of concentrating ores, demonstrating daily its efficiency and superiority beyond per-adventure of doubt under varied and actual service conditions.
As will be seen by the illustration, the Akins & Evans slime concentrator is of the traveling belt type, with a longitudinal or endwise shake. It is provided with a roller or drum at each end, also a wash roller and a take-up roller below the deck. These rollers serve the purpose in their respective places of carrying, imparting the travel to, washing, taking up and adjusting the true travel of the belt. These operating features are in a measure; similar to those of a frue vanner, but there the similarity with that and other machines ends. The great advantage of the machine lies in the form or contour of its deck, which will readily be understood from an examination of the illustration with the following brief description:
The triangle shown is the pan or depression and the feed and settling space, the forward lines of which are substantially level; the central line extending from the settling space to the discharge end of the machine is the apex, and is the high line or portion of the deck from which and from the forward lines of feed and settling space the deck slopes forwardly and sidewise to the waste launders on each side. The belt is preferably of canvas or duck surface and of sufficient flexibility that in passing or being "drawn' over the deck it conforms to the contour thereof, maintaining perfectly the form of the pan or depression into which the slime pulp is distributed from the feed box. The water in the pan becomes comparatively quiet and the mineral constantly has an opportunity to settle, aided by the gentle reciprocal end-shake, and is thus caused to adhere firmly to the surface of the belt.
The pan or depression is so shaped that as the heavy mineral settles, the lighter material is thrown by the motion of the table and gradually drawn by the travel of the belt toward the discharge point of triangular feed and settling space so that the tendency is for the lighter material to come on the deck proper at the beginning of the apex, where it is gradually washed toward the sides by a series of jets of water from a longitudinal and horizontal perforated pipe about 20 inches long, placed immediately above the deck at the beginning of the apex.
Following this pipe along the apex there is a similar one extending to the discharge end which supplies wash "Water to the deck. Two independent wash-water pipes are placed near the two corners at the discharge end, which have an adjustable sweep for further cleaning the concentrates when necessary.
The overflow from the feed and settling space over its level forward edges is uniform and thin, as is also the flow over the sloping sides of the machine with the added wash water, which gives the maximum opportunity to settle any agitated mineral that may be traveling with the gangue toward the waste launders.
The concentrates, as will be premised, are carried over the end of the machine with the travel of the belt, which, passing under the wash roller below the deck in water in the concentrates box, are washed off by the reciprocal motion of the table, aided, if necessary, by jets of water supplied through a perforated pipe playing on the belt as it comes out of the water.
In this way a clean belt is constantly presented as it continuously enters the feed and settling space at the head of the deck.
The mechanical features of the machine are simple, easily assembled and cared for when in operation. The deck or top is supported by six flat oak or hickory legs, 4 inches wide and 4 inches thick at thinnest part. These legs are amply strong, and while supporting the top and preventing any side sway, are sufficiently flexible to allow of an easy reciprocal motion to the top.
The main drive shaft is located at the head or feed end, and is fitted with cranks on each side, from which lead two side rods, which in turn are attached to the deck near supports under the head end and which impart 'the reciprocal motion or end shake. On the drive shaft are tight and loose pulleys to receive the drive from the mill shaft. The tight pulley is cast heavy and also serves as a balance wheel, giving steadiness to the motion of the table. A four-step cone pulley on this shaft is belted to a similar one on a counter shaft on the supporting frame.
A pair of bevel gears engages and transmits the power from the counter-shaft through the long side shaft to the discharge end of the table, where, by means of cut gears which allow for the motion of the table, it is communicated to the roller at the discharge end by a worm and worm wheel, which in its turn imparts the travel to the concentrator belt, the speed being adjusted by shifting the belt on the cone pulleys. The travel of the belt is approximately 26, 33, 43 and 56 inches, respectively, per minute, as governed by these step-cone pulleys, at a speed of 225 revolutions per minute of the drive shaft.
The drive shaft can be run up to 250 revolutions per minute, however, without disadvantage, and on some ores to advantage.
Ample means are provided for adjusting the belt so that it will run true and also for taking up the stretch.
The wearing parts are few and the belt will last a long time, and with ordinary care the machine cannot get out of order.
The floor space occupied is 7 x 16 feet, or about the same as any standard concentrator, and less than 1hp is required for operation.
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