US2737296A - Mechanical screener - Google Patents

Description

March 1956 H. R. STEPHENS ET AL 2,737,295

MECHANICAL SCREENER 4 Sheets$heet 1 Filed Aug. 25, 1954 I N VENTORS H. RICHARD STEP/{5N5 GZAHAM HAROLD TUCKJER- WILL/AM ALLAN MART/N BY f Mam}! 1955 H. R. STEPHENS ET AL 2,737,296

MECHANICAL SCREENER 4 Sheets-Sheet 2 Filed Aug. 25, 1954 INVENTOBS n RICHARD 6TPHN$ GRAHAM HAkOLD TUCKER.

WILLIAM ALLAN MART/N BY fi r AGENT Mamh 1956 H. R. STEPHENS ET AL 2,737,296

MECHANICAL SCREENER Filed Aug. 25, 1954 4 Sheets-Sheet 3 .52 5 E 1 INVENTOTZFQ M RICHARD STEP/ ENS GIAHAM HAROLD TUCKER WILL/AM ALLAN MARTIN March 6, 1956 Filed Aug. 25, 1954 H. R. STEPHENS ET AL MECHANICAL SCREENER 4 Sheets-Sheet 4 INVENTORS H. RICHARD 5TEPHEN5 GZAHAM HAROLD TUCKER WILL/AM ALLAN MART/N av 14.44! ,7 A m AGENT to Canadian Industries (1954) Limited, Montreal, Que bec, Canada, a corporation of Canada Application August 25, 1954, Serial No. 452,101

Claims priority, application Canada February 5, 1954 2 Claims. (Cl. 209-283) This invention relates to a machine for mechanically screening a cohesive explosive material such as nitrocotton.

Present methods for screening materials such as nitrocotton are entirely manual whereby an operator forces the nitrocotton through a screen using his hands. This method is obviously slow and tedious and these disadvantages make the hand method impractical in the commercial production of large quantities of screened nitrocotton.

Nitrocotton becomes rapidly more sensitive to detonation when its moisture content falls lower than 4%. A moisture content of from four to six percent renders the nitrocotton a relatively insensitive explosive. A safe moisture content of from 26 to 28% is generally present when the material is put through the screening step but should the nitrocotton be allowed to gather at any one spot in the screening apparatus it may dry out and become a dangerous explosive. This possibility must be avoided in mechanical means for screening nitrocotton in order to make the operation a completely safe one.

It is an object of this invention to provide a mechanical means for screening damp cohesive materials while preventing any drying out of the materials while undergoing this operation.

It is a further object of this invention to provide a safe mechanical screening means for damp explosive materials which become dangerously explosive when dry.

The objects of this invention are achieved through the use of a double-armed rotating member moving in fixed relationship to a stationary cone-shaped metal screen, said arms being equipped with semi-flexible scrapers to force the nitrocotton through the screen.

The construction of one modification of our invention may be illustrated by referring to the accompanying drawings in which Figure 1 is a side elevation of the screener showing a cut-away view of the apparatus along a central vertical axis. 1 represents a central vertical support and drive shaft which is normally rotated in a clockwise direction by a suitable system of pulleys and an electric motor. The hub 2 is attached to the drive shaft conveniently by means of the riveted pin 3 and the rotational motion is imparted without loss to the hub through the key 4 which looks the hub on the shaft. 5 is an extension made of brass rod running from the hub to the arms 6 and 6'. The arms are also fashioned of brass rod and carry fan-like fittings 7 set at a proper angle in order to defiect the material being screened back away from the outer circumference and towards the centre of the screen. The arms 6 also carry semi-flexible strips 8 set at an angle in order to rub against the upper surface of the screen 9 and force the. material through the perforations in the screen as the arms rotate. 10 represents a radial supporting rib which along with circular supports 11 and 12 serve to support the screen from the bottom and yet present little cross-sectional area to interfere with the screening operation. 13 is a ring-shaped member bolted to 12 in order to clamp down the edge nite States Paten r 2,737,295 Patented Mar. 6, 1956 of the screen. The periphery of ring 13 is fitted with six L-s'haped taper clamps 14 which hold down another ring 15 attached to the hopper 16. 17 represents the upper flared portion of this hopper. The conical wooden block 18 serves two purposes. It clamps down the centre of the screen and at the same time prevents any accumulation of nitrocotton in the centre where it may dry out and increase its sensitivity to detonation. The bolt 19 passes through the block and screws into the threaded portion of the hub 20 of the supporting frame 10-+-1112.

Figure 2 represents a cross-sectional view of the end of one of the rotating members. As in Figure l, 6 is the brass rod, 7 is the deflector shown set at an angle and 8 is the semi-flexible strip, here shown held in place by set-screws 21 running through the rod 6 at right angles to the strip 8.

Figure 3 illustrates a top view of the screen itself showing how it is preferably made up of 3 segments 9, 9a and 912 so that the slots in the sections of the screen, which are of greater length than width, run in a substantially radial fashion. It is preferable that the screen be made of expanded metal, fashioned by cutting alternate slits in a sheet of metal and then spreading the sheet until these slits open to form tapering slots as shown in Figure 4.

Figure 5 serves to illustrate the construction of the supporting frame showing the radial supports 10, the inner circular support 11 and the circumferential support 12 and the threaded hub 20.

In operating our invention, the two arms 6 and 6' of Figure 1 are set in rotary motion and the damp nitrocotton is placed by hand or other means within the hopper l617. The action of the flexible strips 8 against the screen 9 forces the nitrocotton through the screen. The end pieces 7 keep moving the excess away from the outside towards the centre where the screening action is taking place and the block 18 prevents any build up near the centre where linear motion is relatively small. After passing through the screen, the nitrocotton may be collected conveniently in any sort of container or receptacle.

The screening rate using the old manual method was pounds per man-hour. Using our invention a screening rate averaging 330 pounds per man-hour may easily be attained.

It is to be understood that the scope of the present invention is not limited to the details specifically set forth in this disclosure, wide variations therein being possible without departing from the spirit of the invention.

Having thus described our invention What we claim 1. Apparatus for screening damp cohesive materials comprising in combination a supported conical screen consisting of sections of standard expanded metal screen material, said conical screen being clamped down at its periphery and at its central point to a supporting framework, a rotating member consisting of a central vertical drive shaft, a hub attached to the lower end of said drive shaft, said hub supporting two opposed radial arms, said arms being set to rotate at a fixed distance above and parallel to the surface of said conical screen, each of said arms supporting a semi-flexible strip along its bottom edge, said semi-flexible strip being adjusted to rub along the upper surface of said screen, and fan-like elements attached to the end of each of said arms and fixed at an angle whereby said fan-like elements deflect said damp cohesive materials toward the central portion of said conical screen as the said arms are rotated and a circular hopper atiixed to the periphery of said conical screen and surrounding said rotating arms.

2. Apparatus for screening damp cohesive explosive materials comprising in combination a suppoited conical screen consisting of three sections of standard expanded metal screen material, each section being oriented with the elongated perforations in the screen running in a substantially radial direction, said conical screen being clamped down at its periphery by a ring and at its central point by a conical wooden block, said ring and said block clamping said conical screen to a supporting framework, a rotating member consisting of a central vertical drive shaft, a hub attached to said shaft at its lower end, said hub supporting two opposed radial arms, said arms being set to rotate at a fixed distance above and parallel to the surface of said conical screen, each of said arms supporting a semi-flexible strip along its bottom edge, said semi-flexible strip being adjusted to rub along the upper surface of said screen, and fan-like elements attached to the end of each of said arms and fixed at an angle whereby said fan-like elements deflect said damp cohesive explosive materials toward the central portion of said conical screen as the said arms are rotated and a circular hopper having a flared upper portion afiixed to the periphery of said conical screen and surrounding said rotating arms.

References Cited in the file of this patent UNITED STATES PATENTS 101,423 Boon Apr. 5, 1870 462,111 Cooper Oct. 27, 1891 1,704,525 Andrews Mar. 5, 1929

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