Hammer mills completely to impact for crushing, to be used in the building circle and in agriculture

Description

This invention covers hammer mills to be used in the building industry and, in particular, in installations for the production of cements, mortars, sands, fillers, micronized materials, etc., and in agriculture, i.e. in all those applications that require the use of equipment for crushing materials commercially advantageous.

It is known that conventional hammer mills are built with a rotor with hammers (two or more, for balancing the equipment) with the task of throwing the material being fed against the armour-plated walls of the crushing chamber, thus resulting in the breakdown of the material; the efficiency of the operation depends on the trajectories followed by the material to be ground. The first impact against the moving hammers, with a low percentage of ground material, is followed by the projection of the ground residues against the armour plates and against other material in motion; tougher parts are caught between hammers and armour. The penetration of the material, by impact against the face of the hammer, is usually rejected by the head of the hammer because of the absence of proper timing between the entering material and the hammers. It follows that the main difficulties with the present condition of the hammer mills have to do with the obsolete operating systems. Since the equipment must also ensure the crushing of very tough materials, the tendency has been to stiffen the outer casing without ever intervening on the operating principle. The severe wear of hammers and armoured walls (due to the presence of unwanted tangential effects), the low rate of production (because of a high percentage of recycle), a high, and at times excessive formation of dust, the poor polyhedric nature of the final product, particle sizes that are not homogeneous and unfit because of the presence of an excess of dust; a crushing operation not capable (and not controllable) of working on sizes of less than three millimetres in diameter (filler programmed production) are the main drawbacks of existent equipment and technologies. In addition to these problems of a technical/productive nature, there are those having to do with the safety on the

workplace and with the impact on the environment; the very large quantities of dust produced during operations is detrimental to the healthy condition of the work place and of the operators.

To ensure the crushing of inerts, the hammers, integral with the motion of the main rotor, must possess a high peripheral speed (in order to achieve the high strength for the first impact). This speed is directly proportional to the rotor rpms. For secondary mills, in order to treat crushed aggregate to a minimum size of approx. thirty millimetres in diameter, the hammers must have a peripheral speed of no less than 40 í 50 m/sec, whereas, for tertiary mills, for crushed aggregates of less than thirty millimetres in diameter, it is necessary to achieve nearly a double speed, i.e. 70 - 80 m/sec. The module of this speed, however, reaches values that are so high that an easy and complete passage of the material from the feed hopper cannot be achieved. The high speeds give rise to a phenomenon of interference. The material is rejected by the hammer and is conveyed between the max. perimetral circumference of the hammer and the wall of the armour plates until it is subjected to crushing. In addition, a high percentage of inerts, not striking the face of the hammer, bypasses the first reduction of particle sizes. The extreme accuracy required in order to achieve a head-on impact against the face of the hammer and to prevent the occurrence of tangential stresses, which also produces a wear of the hammer and an unexpected reduction in the size of the inerts, requires a very small inlet time (which can obviously be adjusted through an inlet speed).

Necessity and impossibility of reaching high speeds, high stresses involved and particle sizes not in line with project requirements result in a poor performance of the existing equipment.

Recently, a mill defined as "hammer mill with additional impact speed" has been presented on the market, with the following advantages:

- An hourly production twice that of traditional mills with new hammers

- Much reduced recycle - Particle size (material finess module) that can be programmed as a function of impact speed

- Optimal polyhedric nature of the final product

- Increased life of those parts that are subject to wear

- Reduced production of dust (significant percentage of dust abatement as compared to a traditional hammer mill).

The operating principle with additional impact speed is subject, with this invention, to substantial precautions and modifications which make it possible to avoid the restrictions also experienced with this type of mill, such as hammers wear, inadequate (and not pre-established) particle size distribution of the final product, excessive times for tooling, wear of the elements involved, and it allows the expansion of the field of application to agriculture as well.

Having produced a physical prototype of the equipment and carried out tests on a sample of inerts (representative of the type of material to be used on an industrial scale), it is possible to point out a series of achievable advantages.

In particular, it is possible to identify:

Ease of inlet flows with the use of anti-wear guide plates with variable inclination;

Introduction of an anti-wear steel tube to position the blades with dovetail joint and centrifugal clamping;

Wear compensation of accelerating blades by means of adjustable eccentrics;

Hammers wear reduction by means of adjustable eccentricity;

Increased working forces and power;

Increased service life for hammers and accelerating blades; Increased ease of maintenance and reduction of tooling times (reduction in the number of components and simplified maintenance operations);

Increased safety factor;

Reduced environmental impact by particle-size distribution programming and reduced use of power and sound noise. More particularly, the above-mentioned advantages are the result of: a) the presence of plates (guide plates) with variable and adjustable inclination which favours an optimal feed to the secondary rotor (full-load feed); b) secondary rotor provided with accelerating blades and integral with the motion of the main rotor through a cog belt; c) replacement of the cylinder with bolted blades for conveying the material being fed (as in the case of added impact speed equipment) with the use of an anti-wear steel tube, integral with the secondary rotor shaft by means of fastening bushings

outside the mill housing, and provided with slots for the dovetail application of the inserts; d) the inserts are locked only by the action of the centrifugal force; e) the large reduction in weight and vibrations with a resulting reduction of noise pollution, because of the replacement of the cylinder and of the locking systems of the blades in the mills of the previous system with the tube provided with slots for attaching the dovetail blades and centrifugal clamping, allow for a notable increase in the ergonomics of the work place as well as notable maintenance advantages (reduction of the number of components), spare parts assembly (elimination of the time for fastening). f) the introduction of the anti-wear tube, onto which the blades are secured, offers an additional advantage: it protects the secondary rotor shaft from wear; the tube, in fact, assembled with a play of a few millimetres (preferably 2-3 mm.) on the secondary rotor, protects the aforesaid element. g) to prevent the excessive wear of the blades on the secondary rotor and of the hammers integral with the main rotor, which force frequent maintenance interventions (re-tooling and/or blades/hammers replacement and/or reversal of the main rotor motion), blades wear compensation eccentrics have been introduced which allow for the gradual adjustment of the operating point in relation to an optimal kinematics. h) by adjusting (on the outside) the clearance angle and the clearance between the accelerating blades and the eccentrics that compensate the wear of the blades, it is possible to regulate the effect of inside stresses. I) the position of the eccentrics may be adjusted to ensure the best direction of the inert materials against the face of the hammer; the position of the registers may be adjusted so as to ensure an almost normal impact between the inerts and the surface of the hammers, thus reducing their wear (minimization of tangential stresses and wear). I) The adjustment of the angle of incidence of the flow of inerts on the surface of the hammer, by the insertion of the eccentrics for blades wear compensation, makes it possible to increase the forces involved and to work also with particle sizes a few millimetres in diameter, lengthens the operating life of the accelerating blades (the wear of the blades is adjusted acting on the module and direction of the eccentricity to ensure a constant spacing between registers and accelerating

blades) and of the hammers (the phase adjustment of the equipment, as defined in the project, makes it possible to achieve an almost normal impact between hammers and inerts and to avoid an excessive presence of tangential stresses that result in an excessive wear of the hammers). m) the possibility of extending the working life of the elements subject to wear, together with the reversibility of the motion (capable of exploiting double impact surfaces) requires fewer interventions. Adjustment using eccentrics makes it possible to use accelerating blades under conditions of wear up to 2 cm. Such a configuration would not be acceptable with devices without adjustment. n) The adoption of dovetailed accelerating blades integral with the motion of the secondary rotor and secured to it (by means of a dovetail coupling) by the sole effect of centrifugal force, makes for their quick replacement; the procedure does not require halting the machine for tightening and retightening the accelerating blades (an operation needed if the blades were secured by means of bolts and/or other devices). o) The reduction of maintenance interventions is the basic requirement toward a higher level of safety. In addition, the technical solutions assumed in this configuration require fewer components as compared to added impact speed configurations and the intervention procedures prove to be safer (due to the absence of restraining cylinders and/or clamping devices); p) Grading the particle size distribution of the inerts and the adjustment of the inserts, in order to reduce slippage effects, makes it possible to obtain a finished product in less time, a lower production of dust and a much improved environmental impact (lower energy consumption, less recycle, etc.) q) the possibility of producing micronized materials commercially advantageous, operation which, nowadays, no mill is capable of achieving.

As the attached drawings show: Fig 1 presents a front view of the inside; Fig 2 an inside front view of motor drives side; Fig. 3 the flow of materials to be crushed from the feed hopper; Fig. 4 the material as thrown by an accelerating blade onto the face of the hammer; and Fig.5 the material between the hammer and the armour plates of the mill. The hammer mill, for inert materials and additional crushing materials, reversible and not, with total impact and inclined launch, with

added impact speed, accelerating blades, secured by means of dovetail connection and timed with the main hammers, with adjustable eccentrics for blade wear compensation, basically includes the following main parts:

- Bearing structure, lined with plates made of anti-wear materials; - Feed hopper (1), complete with a charge feeder;

- Guide plates (2) to convey the input material toward the launch area, devices and support for the shafts of moving members (pulleys and V belt (8) to drive the secondary rotor);

- Main rotor, (meaning the rotor powered by the pulley and V belt from the input system), such a rotor being built with the following parts: , a) anti-wear safety devices (flywheel housings); b) the two hammers (5) integral with the motion of the rotor;

- Secondary rotor, (meaning the rotor which is put into motion through the pulley and the V belt from the primary rotor) placed above the main rotor, provided with a peripheral unit with tapered blades (4) (tapering facilitates feeding the material) equal in number to the hammers.

The two rotors are connected and forced to rotate at the same rpms (in phase), by means of special drive members, pulleys and V belt;

- Anti-wear steel tube (7), integral with the motion of the secondary rotor which it protects against wear and locked on the outside of the housing by means of bushings, provided with grooves for securing by dovetail the accelerating blades

- accelerating blades (4) integral with the secondary rotor by means of anti-wear tube (7) dovetail-connected merely by centrifugal force;

- Rotary motions drive members (pulleys and cog and V belts); - Armoured plates (6) and all other mechanical parts now present in every mill and which are not mentioned here. It is to be kept in mind that, not being subjected to crushing, the approach registers of the armoured walls, that are essential for traditional mills, have no longer reason to exist: such walls will be fixed, at a distance of approx. 50 mm from the hammer, for the secondary, the tertiary mill as well as for the one suited for the treatment of small-size materials (which will be defined as quaternary). The housing of the mill holds all that has been mentioned above.

To simplify the presentation which follows the subject, we will only refer to the tertiary mill, in as much as the secondary mills, and possibly the quaternary mills, are produced similarly and all make use of the same principles that apply to the tertiary mills. The mill is fed by gravity fall into the upper part, open, by means of a feed hopper and a normal feeding device. The material (10), from the point of feed reaches the accelerating blades, integral with the secondary rotor. The height of fall and the inclination of the guide plates are calculated keeping in mind that in the time that elapses between one strike and the next, the inerts, as they fall, must cover a path equal to the depth of the blades in a radial direction, so as to avoid waste of energy and to allow operations under maximum output.

The guide plates direct the inerts inside the maximum peripheral boundary of the accelerating blades. It is the task of the accelerating blades to increase considerably the speed with which the inerts enter the crushing chamber avoiding the rejection of the material because of the high rotational speeds involved. Once the inerts are caught by the accelerating blades, they are forced to undergo a circular trajectory (as defined by the diameter of the blades) which, due to the high speeds and to the centrifugal force, is placed along the outer periphery to be then thrown along the face of the hammer. One of the features of this second rotor and of the blades, is that the inerts are received from the top, are guided along a circular trajectory and thrown against the face of the hammers of the mill, not vertically, but in a direction almost normal to the face of the hammer (avoiding the rise of tangential stresses which produce wear). In such a way, the inerts are accelerated and acquire a speed equal to the peripheral speed of the blades. At this point the two eccentrics for wear compensation adjustment of the accelerating blades come into play. These wear compensation registers (manually adjusted by means of the clamping system) divert and direct the inerts coming from the accelerating blades against the hammers which rotate along a direction opposite that of the blades they are integral with. This deviation causes the inerts to hit the hammer under almost normal conditions.

For the crushing principle to work properly, a timing operation has to be carried out between the motion of the accelerating blades and the rotation of the hammers. Such a timing operation is carried out by setting the position of the hammers with

respect to the accelerating blades by defining the phase of the toothed pulleys. By phasing the system, and most of all by the wear compensation of the accelerating blades, the impact is ensured under almost normal conditions. An initial impact/conveyance against the accelerating blades and then against the hammers, is followed by a last and final impact against the armours of the structure.

Reference notches for positioning the compensation registers will be produced to allow an appropriate setting of the system and an adequate compensation of the wear of the accelerating blades. As for the percentage of the recycle of the inerts, on this type of technology, it can be said that a very low amount of recycled inerts is obtained. The reversibility of the system (clockwise and counter-clockwise direction of the feed), capable of taking advantage of a double direction of the feed and the double impact surface, is ensured by the symmetry of the equipment.

The prototype of the equipment, according to this invention, turns out to be capable of treating micronized materials (and, hence, particle sizes defined as quaternary) reaching a peripheral speed in excess of 110 m/sec. The transmissions of the motion between main and secondary axes occur through pulleys and drive toothed belts capable of taking care of the huge loads involved and to limit the acoustic impact of the device. Each one of the eccentrics (3) provided with two holes in the shape of buttonholes for adjustments, is bolted to the housing of the structure by means of two bolts (9) with a clamping system. The entire structure is built with materials with high wear resistance. The dimensions mentioned above refer to tertiary mills and are slightly modified in the case of secondary mills or of those defined as quaternary. The industrial application that distinguishes this invention is represented by the installations for the production of cements, mortars, sands, fillers, micronized materials, etc....i.e. all those applications that require the use of material crushing equipment.