WO2001083111A1

WO2001083111A1 - Granulator mill with composite rotor comprising offset teeth

Info

Publication number: WO2001083111A1
Application number: PCT/IB2000/001403
Authority: WO
Inventors: Luigi Molinari
Original assignee: Officina Meccanica Molinari & C. S.N.C.
Priority date: 2000-04-28
Filing date: 2000-10-02
Publication date: 2001-11-08
Also published as: ITBG20000015A1; AU7308400A

Abstract

This granular grinding mill with composite rotor for grinding plastic, wood and other materials and/or articles of similar consistency comprises a rotor equipped with a plurality of cutting teeth (17) arranged side by side in a variously helical pattern to sweep a cylindrical surface, in order to engage in small number against at least one longitudinal rectilinear skimming blade (25A, 25B) effecting a cutting action, said rotor comprising cavities (19) suitable for dragging into rotation the articles and/or materials being ground in order to enable the ground particles to pass through a base grid (29) acting as a sieve defining the size of those fragments to be utilized.

Description

GRANULATOR MILL WITH COMPOSITE ROTOR COMPRISING OFFSET TEETH

TECHNICAL FIELD This invention relates to a granulator grinding mill with offset multiple blades. BACKGROUND ART

In modern industry there is a well known requirement to salvage a multiplicity of materials for recycling to other uses. Examples of these materials include plastics, wood, tinplate from containers, etc. The essential initial step taken in this salvaging process is to convert the material into a granular homogeneous form. This is achieved using suitable grinding mills. These mills operate with a scissor action by confronting rotary cutting blades with other blades. Their size and materials of construction vary according to the material to be ground. The main defect of most grinding mills lies in the action of their rotary cutting blades. In this respect, as these have identical opposing cutting faces, they give rise to a multiplication of non- constant forces, proportional to the face area used for cutting. As these forces are of an incidental or unpredictable nature, arising suddenly and of considerable intensity, the drive units provided must be of higher power than that necessary for overcoming normal operating forces. This is already high in grinding large-dimension materials, but when crumbling material already reduced to small pieces the problem, although no longer unpredictable, is accentuated to a maximum, resulting in a constantly high energy expenditure, as each blade action involves the entire cutting face. This defect creates problems of various kinds in addition to high energy expenditure, such as low production related to the dimensions of the materials fed, their type, blade maintenance and deterioration of the drive members, and also necessitates the provision of safety devices to prevent accidental blockage of the rotary blade supports. Another negative aspect of usual grinding mills is the operating noise, which in some cases necessitates the use of acoustic protection means (ear covers, plugs etc.), so making them unsuitable for domestic use. An object of this invention is to define a grinding mill for industrial or domestic use which enables constant operating forces to be generated. A further object is to define a grinding mill, as aforedefined, in which the operating forces are less than those of current mills. A further object is to define a mill, as aforedescribed, which provides a constant yield. A further object is to define a mill, as aforedefined, into which materials of different size can be fed. A further object is to define a grinding mill, as aforedefined, in which maintenance needs are reduced and optimized. A further object is to define a grinding mill, as aforedef ined, in which blocking risks are reduced to a minimum. A further object is to define a grinding mill, as aforedefined, in which operating noise generated by impacts involving high mechanical energy is reduced. A further object is to define a grinding mill which requires lower drive power for equal productivity. DISCLOSURE OF INVENTION These and further objects will be seen to be attained on reading the ensuing detailed description of a granular grinding mill with composite rotor for grinding plastic, wood and other materials and/or articles of similar consistency, characterised by comprising a rotor equipped with a plurality of cutting teeth arranged side by side in a variously helical pattern to sweep a cylindrical surface, in order to engage in small number against at least one longitudinal rectilinear skimming blade effecting a cutting action, said rotor comprising cavities suitable for dragging into rotation the articles and/or materials being ground in order to enable the ground particles to pass through a base grid acting as a sieve defining the size of those fragments to be utilized. BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of non-limiting example on the accompanying drawings, on which:

Figure 1 is a side section through a modular rotor inserted into a grinding mill ; Figure 2 is a partial section through a grinding mill showing the formation of its modular rotor;

Figure 3 shows a constituent module of the rotor;

Figure 4 shows a peripheral cutting region of the modular rotor, in which the cutting attachments have been omitted for greater clarity. BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the aforesaid figures, a base structure 1 carries bearings 2 and 12 on two of its sides for supporting a horizontal shaft 3. Plate-like modules 5 with parallel faces 7 are keyed onto said shaft by usual means. Said plate-like modules are shaped to form radial arms 6. Cutting attachments 17 formed of hard material (indicatively, tool steel) are fixed by known methods on the end of these radial arms. In the figures the attachments 17 are shown fixed by two usual bolts 8, indicated as 8A, 8B. The plate-like modules 5 are keyed onto the shaft 3 side by side with their parallel flat faces 7 in mutual contact. This can be seen from the modules 5A, 5B, 5C, 5D... shown in Figure 2. In this figure it can be seen that said modules rest axially against a circumferential shoulder 9 and are clamped together by a threaded ring 10. Said ring acts by way of a profiled sleeve 11 formed in different sections to also carry on it the end bearing 12. On one end of the shaft 3 there is mounted a flywheel 13, comprising usual trapezoidal grooves in order to be rotated by drive belts 14 driven by a usual small pulley 16 keyed onto a usual electric motor 15. All the plate-like modules 5, 5A, 5B, 5C... are substantially identical, the only difference being the angular position of the individual splines housing the keying means 4 (or the like). In this respect, said plate-like modules are arranged side by side and clamped together angularly offset by a few degrees. In Figure 4 the extent of this angular offset can be seen from the perspective view of a peripheral region of one of the rotor cutting lines, defined by the ends of the plurality of constituent radial arms 6 of said plate-like modules. For greater simplicity said ends are shown without their cutting attachment 17, so that the recess 18 for housing the rear end of the cutting attachments can be more easily seen. The rear surface 17A of the cutting attachments rests on the base of these recesses to directly discharge onto the body of the plate-like modules the grinding forces generated during operation. This prevents these forces passing through the bolts 8, so that these can properly fix the cutting attachments 17 to the plate-like modules 5 without being subjected to greater than the small force reaction involved in this. The angular offset between the plate-like modules must be limited to values which still enable some lateral contact to remain between the ends of the radial arms in order to produce a "stepped" continuity 18A, 18B, 18C... at the cutting periphery of the resultant composite rotor 28. This prevents the material present for grinding in any one of the substantially helical cavities 19A, 19B, 19C, 19D from passing to another adjacent cavity, and instead enables it to be dragged into circulation by the continuity of the stepped helical cutting profile of the rotor. It also advantageously enables each axial component generated by the grinding force acting on an individual cutting attachment to be distributed in optimum manner to all the plate- like modules "downstream" of that force. The cutting attachments 17 have a particular profile shown in Figure 3. The cutting angle to the rotor radial direction 22 is indicated as α. This enables the upper cutting surface 23 to assume various levels without altering said optimum cutting angle α. The said possible difference in level of the surface 23 is that deriving from periodic sharpening of the cutting attachments 17. In this manner, this sharpening does not cause the distance or clearance to the rectilinear edge of the counteracting blade 25 to vary substantially. The counteracting blade 25 can be provided in various numbers. In Figure 1, for example, two blades 25A and 25B are provided in opposite positions. Said blades 25 are rectilinear and are subjected to considerable cutting forces, so that they must be fixed to particularly solid structural parts of the machine. As these blades are constructed of extremely hard material, they are preferably formed as a plurality of side-by- side pieces which are hence shorter than the total blade length. This enables, for example, the typical geometrical distortion resulting from hardening treatment to be reduced. The articles to be ground are fed into the mill through a large mouth 26 in a direction 27. They therefore fall into the cavity 19A above the composite rotor 28, and are dragged into rotation. As a result of this and the fact that they are subjected to centrifugal force, these articles tend to be halted by that part of the blades 25 which projects beyond the cylindrical base surface 29 on which they rest and slide. When the radial arms 6 with their cutting attachments 17 arrive, they thus create a cutting or fracturing action on the article. The multiplicity of these actions which arise as the plurality of cutting attachments reach the counteracting blades 25 results in progressive reduction of the article into a large number of pieces of its constituent material. The base surface 29 is perforated or gridded, to enable those fragments of ground material smaller than its holes to pass through it. Said base surface 29 therefore acts as a sieve, through which only fragments or granules not greater than a certain predetermined size can pass into the lower collection chamber 30. Until said fragments reach this minimum size, they are rotated by the composite roller 28, to undergo further size reduction by the cooperation between the blades 25 and cutting attachment 17. From this, it is apparent that by making the blades 25 and cutting attachments 17 of adequate hardness, the mill is made suitable for grinding a wide range of articles and materials. It is however important to establish the required fragment size, based on the type of ground material to be collected in the chamber 30 for its subsequent reuse. In this respect, the fragments must have a size suitable for the type of subsequent use for which they are intended. It would in fact be anti-economical to finely grind a product which could actually be used in larger fragments. The present invention enables this requirement to be satisfied by providing a base 29 interchangeable with other similar bases having sieving holes of a different size. The base 29 is constructed by known methods, the provision of a collection drawer for the fragments falling into the chamber 30 to enable them to be extracted from the mill interior being also known. Because of the considerable amount of energy involved in the grinding, the top or cover 31 of the mill must be constructed of metal plate of sufficiently large thickness. As said upper mill cover 31 must allow access to the interior for sharpening or replacing the cutting attachments 17 and the counteracting blades 25, the mill must be equipped with means to raise said cover 31, which is particularly heavy because of the considerable thickness of its constituent plate, by a sufficient amount. This raising must be achieved both under conditions of safety for the operator and by using economical means. An optimal solution to this problem is the use of a pneumatic motor 32 fixed to the structure 1 and associated with a step-down gear to operate a screw 33 engaged in a lead nut 34 hinged to a bracket 35 rigid with said cover 31. Said cover is provided with a hinge 36 in that region of the structure 1 in which the motor 32 operates. Hence on rotating the screw 33, the lead nut 34 is moved away from the motor 32, to raise the bracket 35 a sufficient extent to provide the required access.

Claims

1. A granular grinding mill with composite rotor for grinding plastic, wood and other materials and/or articles of similar consistency, characterised by comprising a rotor (28) equipped with attachments (17) forming a plurality of cutting teeth arranged side by side in a variously helical pattern and angularly offset from each other to sweep a cylindrical surface, in order to engage in small number against at least one longitudinal rectilinear skimming blade (25) effecting a cutting action.

2. A grinding mill as claimed in the preceding claim, characterised in that the rotor comprises cavities (19) suitable for dragging into rotation the articles and/or materials to be ground, in order to enable the ground particles to pass through a base grid (29) acting as a sieve defining the size of those fragments which are to be utilized, and which fall into a collection drawer (30) located below said grid.

3. A grinding mill as claimed in the preceding claims, characterised in that the attachments (17) are positioned on the periphery of radial arms of plate-like modules (5).

4. A grinding mill as claimed in the preceding claims, characterised in that the plate-like modules (5) are all identical .

5. A grinding mill as claimed in the preceding claims, characterised in that the plate-like modules (5) are keyed (4) onto a drive shaft (3) in positions angularly offset one to another.

6. A grinding mill as claimed in the preceding claims, characterised in that the attachments (17) interact in their cutting action with composite counteracting blades (25A, 25B), said blades having a length in the axial direction which results from positioning side-by-side a plurality of smaller pieces.