US2993400A

US2993400A - Method for comminuting solid synthetic resinous materials

Info

Publication number: US2993400A
Application number: US664262A
Authority: US
Inventors: Glenton Henry David; Phipps John Wildey
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1957-06-07
Filing date: 1957-06-07
Publication date: 1961-07-25
Anticipated expiration: 1978-07-25

Description

ly .1961 H. D. GLENTON ETAL 2,993,400

METHOD FOR COMMINUTING SOLID SYNTHETIC RESINOUS MATERIALS Filed June 7, 1957 I'll 1 mm, QM M y 1961 H. D. GLIENTON ET AL 2,993,400

METHOD FOR COMMINUTING soun SYNTHETIC RESINOUS MATERIALS Filed June 7, 1957 3 Sheets-Sheet 2 no 5 (b) HTTOR/V'KS Jon/v M4 osr PHI/"P5 ByaWWIMW HEW/7r D4 :00 Gas/V7100 y 1961 H. b. GLENTON ET AL 2,993,400

METHOD FOR COMMINUTING sour; SYNTHETIC RESINOUS MATERIALS Filed June 7, 1957 .5 Sheets-Sheet 3 FIGS by M Ma m 2,993,400 METHOD FOR COMMINUTIN G SOLID SYNTHETIC RESINOUS MATERIALS Henry David Glenton, Poulton, near Blackpool, and

John Wildey Phipps, High Welwyn, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed l'une 7, 1957, Ser. No. 664,262 4 Claims. (Cl. 83-45) This invention relates to a method and apparatus for comminuting solid synthetic resinous materials in sheet or strip form.

Many proposals have been made for converting these materials into a suitable physical form for use in moulding and like operations. For example, it has been suggested that particles of the required shape and size may conveniently be produced by cutting a sheet along a serrated line and then making a second serrated cut spaced back from the first. However, it has been found that this method is not wholly successful, particularly when the material of the sheet is soft, as there is a tendency for it to be squeezed between the cutting edges, and instead of a number of separate particles resulting these are connected together by thin threads or webs.

In order to overcome this disadvantage, a method of comminuting sheet or strip of solid synthetic resinous material (hereinafter referred to as sheet) has been proposed which comprises advancing sheet over a table (a) towards a stationary serrated knife which co-operates with at least a pair of moving serrated knives, (b) along the line of one of the sides of the serrations on the stationary knife and (c) at a rate not greater than half that required to advance it the length of said side during the interval between cuts by said moving knives, one of said moving knives cutting the sheet protruding over every alternate indentation of said stationary knife and the following moving knife cutting the sheet protruding over every other alternate indentation of said stationary knife.

The object of the present invention is to provide an improved method and apparatus for comminuting sheets of solid synthetic resinous materials to produce particles, in which (a) the cut particles do not tend to be returned to the cutting edges and therefore do not tend to prevent regularity of cutting; (b) sheets of said materials which are relatively soft, e.g. plasticised polyvinyl chloride sheets, even at temperatures above normal, e.g. 40 C., are fed steadily to the cutting edges without puckering, which may occur when they move over a table in a horizontal direction, as previously proposed; (C) out particles of any desired shape may be conveyed directly from the cutter in any direction relative to the direction from which the sheet is supplied; (d) the working parts of the apparatus are fully accessible; (2) the apparatus occupies only a small floor area; and (f) the apparatus is easily constructed.

In order that our invention shall be fully understood it is illustrated in respect of the attached drawings.

FIGURE 1 is a cross-sectional diagrammatic representation of a means for supplying plasticised polyvinyl chloride composition sheet and comminuting it by the method of our invention.

FIGURE 2(a) is a cross section of the serrated edge of a knife suitable for use in our invention.

FIGURE 2(b) shows the same serrated edge of the stationary knife and, superimposed upon it, the leading edge of a sheet which has already received a series of cuts in position ready to receive another out which will remove the portions marked X.

FIGURE 2(0) shows the same serrated edge of the rates Patent Patented July 25, 1961 stationary knife and, superimposed upon it, the leading edge of the same sheet moved into position for the next cut which will remove the portions marked Y.

FIGURES 2(d)' and 2(e) correspond to FIGURES 2(1)) and 2(c) respectively but the direction of movement of the sheet (as indicated by the arrow) is different.

FIGURES 3(a) and 3(b) show two successive positions of the leading edge of a sheet prior to cutting, superimposed on a stationary knife having teeth of a different shape from those illustrated in FIGURES 2(a) to 2(a).

FIGURES 4(a) and 4(b) show two successive positions of the leading edge of a sheet prior to cutting, superimposed on a stationary knife having teeth of yet another shape.

FIGURE 5 is an elevational view of a cutter of our invention with its hood on the stationary knife side removed;

FIGURES 6 and 7 are elevation section views taken in the region adjacent the stationary knives and the moving knives; and,

FIGURE 8 is an enlarged fragmentary view of the rotor in FIGURE 5.

In FIGURE 1, 1 and 1 are counter rotating rollers upon which plasticized polyvinyl chloride composition 2, is sheeted. 3 is a knife for cutting a narrow sheet 4, therefrom. This sheet is passed through a cooling water bath 5, and is moved by rollers 6, 7, 7' and 8, vertically downwards past stationary knife S, to rotor 19, which rotates and carries four moving knives 11, which cooperate with stationary knife 9, comminuting the sheet, and throwing the particles formed into hood 12, by means of which they are conveyed to drum 13. It will be appreciated that the hood 12, may lead to a duct which conveys the particles to drum 13, which may be in the line in which the sheet is fed or on either side of this line without any costly modification of the installation. It will also be appreciated that space occupied by the cutting device may be minimized by placing the stationary knife on the side of the sheet from which it has been supplied and operating the moving knives so as to throw the particles in the direction from which the sheet has been supplied. Furthermore, the cutting equipment is readily accessible on all sides for cleaning by detaching its hood, and also the means for moving the sheet to the knives is simple.

In FIGURES 2(b) and 2(c), the sheet is moved in the direction of one of the sides of the teeth of a station ary knife, and its leading edge is represented by 20 and 21 in the two positions prior to successive cuts.

In FIGURES 2(d) and 2(e), the sheet is moved at an angle to the same sides of the teeth with the result that the tips of the teeth are exposed at every cut in order to avoid the possibility of forming protuberances on the particles cut. The leading edge of the sheet is represented by 22 and 23 in the two positions prior to successive cuts.

In FIGURES 3(a) and 3(b), the sheet is again moved at an angle to one of the sides of the teeth of a different stationary knife and its leading edge is represented by 30 and 31 in the two positions prior to successive cuts. In these figures, it will be noted the sides of the teeth are of unequal length.

In FIGURES 4(a) and 4(b) one of the sides of the teeth of the stationary knife makes an angle to the normal to the general line of cutting and the sheet is fed along this normal. The leading edge of the sheet is represented by 40 and 41 in the two positions prior to successive cuts. Particles having a diamond-shaped cross-section are produced in this way.

In FIGURE 5, 4 is the sheet of solid synthetic resinous material moved vertically downwards by rollers 7 and 8,

3 past stationary knife 9, to rotor 10, carrying four moving knives ll. 12 is the hood for the cutter which has been partially removed for the purpose of this illustration. 13 is a drum in which the particles produced are collected and 14 is the motor driving the rotor 10.

FIGURES 6 and 7 show the manner in which successive teeth of the moving knives cooperate with the stationary knife. In these figures, 9 represents the stationary knife, 11 represents one moving knife at the instant of meshing with stationary knife 9, and 11 represents the following moving knife at the instant of its meshing with stationary knife 9.

FIGURE 8 is an enlarged fragmentary view of rotor 10 in FIGURE 5, wherein 11 and 11' have the same significance as above and 11 represents a third moving knife which cooperates with the stationary knife 9 after knife 11. As shown, the teeth of knife 11 are staggered with respect to those of knife 11 and the teeth of knife 11" are staggered with respect to those of knife 11. The tips of the teeth of knife 11 are indicated in FIGURE 8 by the letters T, T.

In accordance with the present invention, we prefer to feed the sheet to the serrated cutting line in a substantially vertical direction in order to minimize frictional drag between the sheet and the stationary knife and to obtain the optimum removal of cut particles. We also prefer to feed the sheet to the serrated cutting line at a rate less than half that required to advance the sheet, between successive cuts, along the length of the projection of said side of the teeth of the stationary knife in the direction of movement of the sheet. We also prefer to feed the sheet to the serrated cutting line in a direction which subtends a smaller angle to a line joining the tips of the teeth of the stationary knife than is subtended by the said side of the teeth of the stationary knife. In these ways, we avoid a tendency for the softer synthetic resinous materials to be squeezed during cutting over the tips of the teeth of the stationary knife and appearing as thin protuberances on the cut particles produced. It is desirable to avoid these protuberances in order to obtain free-flowing particles. Optimum free-flowing characteristics are obtained when the particles cut are substantially cubes. Best conditions to obtain these are those of (a) right angled tips to the teeth of the cutting knives, (b) a rate of feed of one third of the projection of said sides on the direction of movement of the sheet, (6) the use of sheets having a thickness of two thirds of the length of said sides and (d) a direction of movement of the sheet of 2634 with the line of the tips of the teeth of the stationary knife. As there is ditficulty in practice in grinding right angled tips to the cutting knives, an approximation to these conditions is best used.

Particularly suitable synthetic resinous materials for use in the present invention are both the plasticized and unplasticized thermoplastic materials, for example, those based on polymers and copolymers of vinyl chloride, polyvinylidene chloride, cellulose acetate, polyamides, polythene, polystyrene, polymethyl methacrylate and the resinous copolymers of butadiene with styrene and methyl methacrylate. For polymeric materials which are brittle at normal temperatures it is desirable that the process of this invention is operated at an elevated temperature.

Synthetic resinous materials are frequently obtained in sheet form by the process of their manufacture or after they have been compounded with plasticizers, stabilizers, pigments, etc. For example, a polyamide such as polyhexamethylene adipamide is normally extruded in the molten state through a slot at the bottom of the autoclave in which it has been polymerized and quenched in contact with a metal drum, thus forming a thin sheet of narrow width. Various other polymers such as polyvinyl chloride are normally mixed with plasticizers etc., in internal mixers of the Banbury type, and the mixing is completed on heated rolls from which narrow sheets are removed by means of suitably placed knives. Before such sheets can be comminuted they should be cooled to the solid state, e.g. by passing them through a bath of cooling liquid. We have found that the sheets used in the present invention may be in a heat-softened condition and that intensive cooling after their preparation is seldom necessary. This results in an appreciable saving in capital and operating costs.

We claim:

1. Method of forming diced particles of solid synthetic resinous material comprising the steps of: passing heated synthetic solid resinous material between a first pair of mating rollers to form the material into a continuous sheet; passing the sheet through a cooling zone to lower the temperature thereof to a predetermined value; thence feeding the sheet of material while still in a heat softened condition past cooperating guide rollers in a vertically downward direction to a position adjacent a downwardly facing stationary serrated cutting edge, the direction of feed being substantially coincident with one set of corresponding sides of the serrations of said cutting edge, maintaining the sheet substantially free from crosssectional irregularities wholly by the action of the weight of the downwardly fed material; rotating a cutter having first and second knives extending therefrom in cooperative engagement with said serrated cutting edge in a manner to successively cut the sheet protruding over every alternate indentation of said cutting edge by the intermeshing teeth of said moving first knife and then cutting the sheet protruding over every other indentation of said cutting edge by the intermeshing action of said second moving knife, while feeding the sheet relative to said cutting edge at a rate not exceeding that required to advance the sheet one-half the length of said serration sides between successive cuts, whereby the sheet is cut into diced particles.

2. Method of forming diced particles of solid synthetic resinous material comprising the steps of: passing heated synthetic solid resinous material between a first pair of mating rollers to form the material into a continuous sheet; passing the sheet through a cooling Zone to lower the temperature thereof to a predetermined value; thence feeding the sheet of material while still in a heat softened condition past cooperating guide rollers in a vertically downward direction to a position adjacent a downwardly facing stationary serrated cutting edge, the direction of feed subtending a slightly smaller angle to a line joining the tips of the serrated cutting edge, than is subtended by one set of corresponding sides of the serrated cutting edge to the line joining the tips of the serrated cutting edge, maintaining the sheet substantially free from crosssectional irregularities wholly by the action of the weight of the downwardly fed material; rotating a cutter having first and second knives therefrom in cooperative engagement with said serrated cutting edge in a manner to successively cut the sheet protruding over every alternate indentation of said cutting edge by the intermeshing teeth of said moving first knife and then cutting the sheet protruding over every other indentation of said cutting edge by the intermeshing action of said second moving knife, while feeding the sheet relative to said cutting edge at a rate not exceeding that required to advance the sheet onehalf the length of said serration sides between successive cuts, whereby the sheet is cut into diced particles.

3. A method according to claim 1, in which the sides of said serrations define teeth having right angled tips, the rate of feed of said sheet relative to said cutting edge is about one third that required to advance the sheet the length of said one set of serration sides between successive cuts, and the thickness of said material sheet is about two thirds the length of said one set of serration sides.

4. A method according to claim 1, in which the sheet comprises a plasticised polyvinyl chloride composition.

(References on following page) References Cited in the file 01 this patent UNITED STATES PATENTS Bristol Dec. 9, 1899 Gangloff July 28, 1931 5 Matthews Nov. 11, 1941 Jehle Nov. 30, 1943 6 Gibby Apr. 21, 1953 Kubodera July 9, 1957 Quinsey Nov. 12, 1957 FOREIGN PATENTS Great Britain Dec. 31, 1952 France Jan. 21, 1957