EP0783373B1

EP0783373B1 - Synchroniser and accelerator system for feeding aggregates which coincides with the hammer action to be used with a hammer mill

Info

Publication number: EP0783373B1
Application number: EP95932899A
Authority: EP
Inventors: Nadia Paolini
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-09-30
Filing date: 1995-09-13
Publication date: 1999-06-02
Anticipated expiration: 2015-09-13
Also published as: ATE180690T1; IT1281944B1; DE69510072D1; ITSA940008A1; WO1996010457A1; AU3576995A; EP0783373A1; ITSA940008A0; JPH10511886A; CN1159772A; CA2201109A1

Abstract

The invention under proposal is a system for feeding aggregate to hammer mills producing sand or other granular material in general, its function being to provide a regulated acceleration of the immission of raw material for processing and the elimination of contact between the hammers and the material to be crushed during those unfavourable moments which give rise to the build-up of unprocessed material in the grinding chamber, thus preventing the optimal use of the hammer surfaces which are then particularly subject to attrition, above all, at the striking edge. This invention, consists in a steel, rectangular box-like structure containing a roller (4) driven by a toothed transmission belt (8) connected to the rotor of a two-hammer mill at a speed such that the said roller (4) executes one revolution for every two revolutions executed by the hammer mill rotor, so that the two peripheral speeds of the roller (4) and the rotor (11) are coordinated according to the ratio determined by the type of mill.

Description

Technical Field

The invention under proposal is a perfected system for feeding aggregate to hammer mills producing sand or other granular material in general, its function being to provide a regulated acceleration of the immission of raw material for processing and the elimination of contact between the hammers and the material to be crushed during those unfavourable moments which give rise to the build-up of unprocessed material in the grinding chamber, thus preventing the optimal use of the hammer surface which are then particularly subject to attrition, above all, at the striking edge.

Background Art

As things currently stand, hammer mills, and in particular those employed in sand production in the tertiary sector, quickly develop serious and costly problems. With hammer mill feedling systems currently in use, raw material for processing is not regulated in its supply rate to the hammers, with the result that the material rarely comes into direct contact with the hammers crushing face but is presented towards the hammer's edges, this tendency becoming more pronounced as the hammer's surface wears.
As a consequence, raw material is largely pushed outward towards oncoming material to be ground, which in its turn produces a considerable slowing-up of the supply rate to the hammers. What this means in practice is that the hammer is restricted to working solely at the edges and the material, in the absence of any means of controlling its rate of fall, is unable to find its way to the centre of the working face in the interval between one strike and the next, which leads to serious attrition of the striking edge and a considerable recycling of raw material. In particular aggregate sizes 1 and 2, the type normally used in the production of sand, has a low-weight mass and in order to be effectively ground to sand needs to be positioned so as to receive the full purchase of the hammer. One way of ensuring full contact is to get the hammers to turn at a minimum speed of around 70 metres per second, equal to approaching 22 revolutions per second of the rotor or 44 beats per second in the case of two-hammer mills. At such a hammer rotational speed the constant delivery of raw material to the hammers and its low rate of fall combined with the high speed of the hammers themselves, results in the aggregate meeting with the higher area of the hammer (its head), thus reducing production rate rather than increasing it.
The lightness of fine aggregate, with a very limited falling speed (gravitational speed) and the arrival after just a few hundredths of a second of the successive hammer blow is not sufficient time for the material to position itself squarely beneath the hammering face ; thus, the material literally "slips" away from contact with the hammers' optimal crushing area, to such an extent that 50-60% of raw material introduced is discarted and must be reintroduced. Furthermore, the continuos supply of new aggregate quickly saturates the milling chambers so that the hammering action is considerably attenuated by the mass of material in constant arrival. This results is an excessive consumption of the hammers with in particular the higher external area, the striking edge, becoming particularly worn. The primcipal effect of the blunting of the striking edges is that after a short period the sand produced no longer conforms to its granulometric standard and the percentage of fine sand to uncrushed or insuffienciently crushed aggregate present is so reduced as to require the urgent replacement of the hammers.
A system is known to us, US-A-3595290, that provides a six-scoop impeller in a six-hammer mill for comminuting grain. However this system has only one sense of flow of the grain toward the impact surface of the particular-shaped hammers and achieves an increased feeding speed of the grain to the hammers.

The object and important characteristics of the invention

This invention, therefore, consists of ensuring that hammer mills operate in such a way that raw material supply to the hammeers is in strictly regulated quantities, delivered in separate batches, and synchronised with the position of the hammers, so as to eliminate the possibility of raw material being processed positioning itself overwhelmingly at the most distant areas of the hammer face at the moment of impact. Thus, at the moment of the hammer's interception there is a suspension in the supply of raw material allowing the material to be worked evenly across the crushing face and not prevalently at the edges.
More specifically, the invention consists of ensuring that the material reaches the centre of the hammer and given that it is not possible to increase hammer speed beyond a certain limit, the system under proposal accelerates the falling rate of the raw material within the milling chamber in such a way as to allow it to reach the centre of the working face where it is crushed, thereby reducing the workload of the external surface areas.
This system brings with it the enormous advantage of minimizing wear to the hammers, with an extension of their operative life five times that of a normal hammer, thereby representing a saving in replacement costs and an elimination of the numerous halts in production which often result. With the proposed system it is also possible to lower the 50-60% raw material recycling rate typical of previous systems to a bare 5-10%, which in practice means higher production for an identical processing time.
A further advantage of the invention under proposal is that its facility for synchronising and accelerating the feedling rate to coincide with the action of the hammers enables a constant , even spread impact over much longer production periods, as hammer surface wear affects areas immediately adjacent and parallel to each other ; with milling systems lacking this feeder system, however, wear takes place only at the upper striking edge. A constantly rectilinear surface area ensures the product always conforms to grain dimension standards and that fine sand is at its correct percentage.
These facilities and advantages are provided by a steel rectangular box structure containing a roller turned by the rotor of a hammer mill, with transmission supplied by a toothed chain ; the two peripheral speeds of roller and rotor, coordinated according to the type of hammer mill being used, maintain am average ratio of close to 1 :10 ; the roller, with scoops evenly spaced over its surface, picks up at fixed intervals the required amount of aggregate ; the rate of immission of this material into the milling chamber coincide with a given position of the hammers, more specifically, it is phased with the hammer action in such a way as to ensure that at each strike the area of impact is always situated between the outer edge and the centre of the hammer surface.

Description of the drawings

A better understanding may be gained from the illustrations attached, these being intended as an indication of the system's principles, while further characteristics will become evident when an optimal use of the system for any specific circumstance is considered.
Figure 1 gives an overall view of the raw material feeding system, the invention under proposal, mounted on a hammer mill.
Figure 2 shows a cross-section of the device and its internal mechanisms.
The invention under proposal illustrated in these drawings is composed of a steel box structure forming a rectangular parallelepiped (1) equipped with lid (2) and a window (3) through which the inert material is introduced ; within the box structure (1) is located a roller (4) on the surface of which, placed at regular intervals, four scoops (5) collect the raw material in the correct proportions and deliver it, in acceleration, to the crushing chamber (11) of a two-hammer mill ; the roller (4) is rotated by means of a driver pulley (6) moved by the hammer mill rotor through a driving pulley (7) by a transmission belt (8) which is tensioned by means of a tension pulley (9). The roller's rotating axle (10) protrudes from the box structure (1) to connect the driven pulley (6) in such a way that the two pulleys, driven (6) and driving (7), are perfectly aligned vertically. The play of the roller's rotating axle protruding from the box structure (1) is reduced by a cushioned support which diminishes flexion stress.

Mode for carrying out the invention

The feeding system, the invention under proposal, is simple to realise as it requires no materials, processes or any particular operating rules. Moreover, it can be adapted to the majority of hammer mills employed at a tertiary level, being simply mounted by means of bolt fixings at the uppermost point of the hammer mill, and calibrated, with the machinery idle, for a correct setting of the angle of inclination of the scoops situated on the roller (4). This is effected by having the latter rotate first in one direction, then in the other, with the hammers in a given position, and specifically, when they are about to enter into contact with the raw material, so that introduction of the latter into the crushing chamber is timed to coincide with the downward action of the hammers, that is to say, introduction is phased with hammer action.

Claims

A raw material feeding system for two-hammer mills used in the production of sand and granular material in general, made up by a steel rectangular box-like structure containing a roller (4) driven by a toothed transmission belt (8) connected to the rotor (11) of a two-hammer mill at a speed such that the said roller (4) is characterized in that it executes one revolution for every two revolutions executed by the hammer mill rotor so that the peripheral speeds of the roller (4) and the rotor (11) are coordinated according to the type of mill being employed, this ratio remaining close to an average of 1 :10 ; the system further characterised in that aforesaid roller has four equidistant scoops (5) acting to collect at intervals a regulated quantity of primary phase material and in that supply to the crushing chamber of this quantity of material occurs to coincide with a predeterminated position of the hammers, in such a way as to regularly ensure a full purchase of the hammer with the material at a location between the upper striking edge and the centre of the hammer surface.
A raw material feeding system according to claim 1, characterized in that the steel box structure is in the form of a rectangular parallelepipede (1) with a lid (2) and a window (3) through wich the raw material for processing is introduced, and in that the driven pulley (6) of the roller (4) is driven by a driving pulley (7) on the rotor axle by means of a toothed transmission belt (8) whose tension is imparted by a tensioning pulley (9) which acts on the belt internally or externally, depending on the size of the belt employed and the distance between the motor axles, the structure being capable of being mounted on all two-hammer mill equipment for crushing processs, including those already in use.
Method used to regulate the inflow timing of raw material into two-hammer mills serving in the production of sand and granular material in general, characterized by mounting the feeding system of claims 1 or 2 on the two-hammer mill, coupling the rotation of the roller (4) with the rotation of the rotor (11) by said toothed transmission belt (8) and subsequently by initial calibration, with the machinery idle, of the angle of contact of the scoops by rotation of the roller (4) first one way and then in reverse with the hammers in a given position, such that, when the latter are positioned for impact with the raw material at a location between the upper striking edge and the centre of the hammer surface, the introduction of this material to the crushing chamber coincides with the hammer strike, the introduction being in phase with strike readiness of the hammer.