The first disintegrator was made by Carr and consisted of two concentric cylinders or baskets of steel bars, rotating in opposite directions at a very high speed. The material was fed between these and was dashed to pieces by being thrown against the bars and the outer casing.
Fig. 70.—Disintegrator.
A simpler form was soon introduced by Carter, in which only one axis was employed, carrying radial beaters which dashed the material against the serrated outer casing, a portion of the circumference of which was fitted with gratings, through which the ground material was thrown as soon as it was sufficiently reduced in size, the fineness of the grinding being regulated by changing the grates as required. This type of disintegrator is, with slight variations, made by all the leading makers of tanners’ machinery; and one form is shown in [Fig. 70], and a similar but smaller machine, opened to show construction, in [Fig. 71].
In the more modern machines the sides as well as the circumference of the casing are frequently corrugated in order to increase the action on the material.
Mills running at such high rates of speed as 3000 revolutions per minute will grind most hard substances, such as stone or brick, without injury, but pieces of iron among the tanning material are apt to cause damage, and various magnetic devices have been employed for separating this metal, but with only partial success. In the best mills, therefore, the beaters and inner casings are constructed so that they can be easily replaced, and the damage is then rarely serious.
Fig. 71.—Disintegrator opened, showing construction.
In order to avoid vibration, the discs and beaters of all these high-speed mills must be balanced with great accuracy. This is best accomplished by removing the spindle from the mill, and allowing it to roll on two levelled straight-edges, and then filing or chipping the beaters on the heavy side until it will remain indifferently in any position.
A new form of disintegrator has been recently brought out in America by the Williams’ Patent Crusher and Pulveriser Company, in which a series of discs are keyed to the main shaft, to the circumference of which a number of sets of “hammers” are suspended by means of hinge-bolts. Each of these steel bars, or hammers, has a free arc movement of 120°, and when the machine is in motion take a position divergent from the centre on account of the centrifugal force. After striking a blow against any material fed on to a plate serving as an “anvil,” the hammers recoil, and, after passing any material which is not shattered by the blow, again resume their normal position, leaving the next set of hammers to beat against the unground material. The hinged suspension of the hammers imparts a degree of flexibility to the mill which is not found in any other machine of this character, and lessens the risk of serious damage to the machine by the introduction of pieces of metal along with the bark. The makers claim that this machine can be repaired more rapidly and with less expense than any other disintegrator of equal power on the market. Considerable improvements have recently been made in the details of its construction. [Fig. 72] shows a section of this mill. Of course only the end hammers of each set can be seen in the figure.