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

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 minumum 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 hundreths 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 discarded and must be re-introduced. Furthermore, the continuous supply of new aggregate quickly saturates the milling chamber 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 principal 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.

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 hammers is in strictly regulated quantities, delivered in separate batches, and synchronised with the position of the hammers, so as to eliminate the possiblity 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 feeding rate to

coincide with the action of the hammers enables a constant, evenly 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, co-ordinated according to the type of hammer mill being used, maintain an 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 coincides 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 driven pulley (6) moved by the hammer mill rotor through an induction pulley (7) along a transmission belt (8) which is stretched by means of a tension pulley (9). The roller's rotating axle (10) protrudes from the box structure ( 1 ) to connect with the driven pulley (6) in such a avay that the end of the two pulleys, driven (6) and induction (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 actualise 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 immission of the latter into the crushing chamber is timed to coincide with the downward action of the hammers, which is to say, then, that immission is phased with hammer action.