| 1. | 1) A method of grinding and screening wooden materials (M) using a grinder (1) comprising a container (2) in which materials to be ground (M) are received and provided near the bottom (2a) with one or more screws (3,4) having on their spirals (7,8, 9,10) peripheral cutting elements (11) cooperating with grinding blades (12) fixed inside the said container (2), characterized in that said screening operation of said material (M) occurs during the grinding process when said material (M) is passing through gaps (19) defined between said grinding blades (12) and said spirals (7,8, 9,10) of said screws (3,4). |
| 2. | The method according to claim 1) characterized in that the screening degree varies as a function of the pitch of said spirals (7, 8,9, 10). |
| 3. | The method according to claim 1) characterized in that the screening degree varies as a function of the slanting angle of said spiral (7,8, 9,10). |
| 4. | The method according to claim 1) characterized in that the screening degree varies as a function of the number of grinding blades (12). |
| 5. | The method according to any of the preceding claims characterized in that said screening operation is carried out for all the ground material (T) with only one passage through said gaps (19) before the outlet. |
| 6. | A grinder (1) adapted to carry out the method according to claim 1) comprising : a container (2) in which the materials to be ground (M) are received ; one or more screws (3,4) arranged near the bottom (2a) of said container (2), each of said screws (3,4) comprising a cylindrical element (5,6) on which at least a couple of spirals (7,8, 9,10) are wound, having opposite winding direction converging to the centre of the cylindrical element (5,6) on which they are wound; a plurality of cutting elements (11) provided on the outer edges (7a, 8a. 9a, 10a) of each of, said spirals (7, 8,9, 10); a plurality of grinding blades (12) fixed inside said container (2) adapted to cooperate with said cutting elements (11), characterized in that said container (2) at the lower part and below said screws (3,4) is provided with a free space adapted to allow said ground material (T) to fall down by gravity. |
| 7. | The grinder (1) according to claim 6) characterized in that said container (2) has an open bottom. |
| 8. | The grinder (1) according to claim 6) characterized in that said grinding blades (12) consist of a flat profile (15) arranged longitudinally to the container (2), a plurality of teeth (16) being made on said profile. |
| 9. | The grinder (1) according to claim 8) characterized in that said teeth (16) have a triangular shape. |
| 10. | The grinder (1) according to claim 8) or 9) characterized in that said grinding blades (12) are arranged at the center of said container and are supported by a holding structure (17) developed longitudinally to said container (2) and having the cross sectional shape of a triangle with the vertex turned upwards and the horizontal base turned to the bottom (2a) of the container (2) on whose slanted sides (17a, 17b) said grinding blades (12) are fixed. |
| 11. | The grinder (1) according to claim 10) characterized in that said grinding blades (12) are all parallel to each other. |
| 12. | The grinder (1) according to claim 11) characterized in that said grinding blades (12) are four for each side (17a, 17b) of said holding structure (17) with triangular shape. |
| 13. | The grinder (1) according to claim 6) characterized in that said screws (3,4) are two and are arranged juxtaposed and parallel to each other with opposite rotation directions (13,14). |
| 14. | The grinder (1) according to claim 6) characterized in that said one or more screws (3,4) are cooperating with driving means adapted to rotate them. |
| 15. | The grinder (1) according to claim 6) characterized by comprising discharging means for said ground material (T). |
| 16. | The grinder (1) according to claim 15) characterized in that said discharge means consist of a conveyor belt arranged below said screws (3,4). |
It is well known that the wooden materials such as the tailings arising from pruning or felling trees, are suitably ground and then stocked to be then used for other purposes.
To this end grinders are being used turning the wooden material into small pieces having a variable dimension according to the needs of the user.
A first type of grinders of the prior art generally consists of a container into which the material to be ground is introduced and provided with means for conveying the material to a hammer rotor.
On rotation the hammers crush the material that after grinding passes through a screen arranged before the outlet.
The portion of crushed material that does not pass through the screen is taken again into the cycle by the rotor and undergoes a further crushing in the subsequent turns.
A first drawback of this technique consists in that a portion of the material undergoes several crushing treatments before being discharged, thus decreasing the output of the grinder.
Another drawback of this technique consists in that a great power is required because the rotor to be able to carry out properly its function, must have a big mass to acquire a sufficient kinetic energy to overcome the stronger resistance to crushing opposed by the material.
A further drawback consists of the high noise during operation, due to the high number of revolutions of the rotor and the impact of the hammers against the material.
Another drawback consists of the high dustiness caused in the environment where the grinder is located, due to the ventilation generated by the drum and the hammers during rotation.
Another grinder of the prior art generally consists of a container on whose bottom two juxtaposed screws are arranged, provided with spirals rotating in opposite directions in operation.
In this way the material loaded on the screws, is ground by the two spirals in
proximity of the central zone between the two screws where the two spirals are cooperating.
A grating arranged at the zone under the screws carries out screening of the crushed pieces before the discharge.
The material of bigger size that does not pass through the grating, undergoes a further crushing treatment in the zone between the spirals and the underlying grating.
A first drawback of such technique as in the preceding case, consists in that a portion of the material undergoes several crushing treatments before being discharged, thus decreasing the hourly output of the grinder.
Another drawback of this technique consists in using a high power to allow crushing of the material by the screw spirals.
A further drawback consists in that the product to be crushed is easily jammed, getting stuck between the two spirals or between the spirals and the underlying grating.
The present invention aims at overcoming said drawbacks.
A first object of the invention is to provide a method of grinding and screening wooden materials and a grinder to carry out said method, allowing to obtain higher hourly outputs relative to the grinders of the prior art with equivalent loading capacity using the known grinding and screening methods.
Another object of the invention is to provide a grinder requiring lower powers relative to equivalent grinders of known type.
A further object of the invention is to provide a grinder having a more reliable operation relative to the grinders of known type.
A last but not least object of the invention is to reduce the dust emissions in comparison with the machines of the prior art.
The foregoing objects are attained by a method to carry out grinding and screening of wooden materials using a grinder comprising a container receiving the materials to be ground provided near its bottom with one or more screws having on the spirals peripheral cutting elements cooperating with grinding blades fixed inside said container, said method according to the contents of the first claim, being characterized in that said screening operation of said materials occurs during the grinding process when said material is passing through the gaps defined between said grinding blades and said spirals of said screws.
The grinder to carry out said method, being also object of the present invention, is of the type comprising: - a container in which the materials to be ground are received; - one or more screws arranged in proximity of the container bottom, each of said screws comprising a cylindrical element on which at least a couple of spirals are wound with opposite winding directions and converging to the center of the cylindrical element on which they are wound; - a plurality of cutting elements arranged on the outer edge of each spiral ; - a plurality of grinding blades fixed inside said container and adapted to cooperate with said cutting elements, and is characterized in that said container in the lower part and below said screws has a free space adapted to allow said ground material to fall down by gravity.
According to a preferred embodiment the grinder of the invention has a container with open bottom and a plurality of grinding blades centrally arranged in said container.
These grinding blades are supported by a holding structure developed longitudinally to the container and has the cross sectional shape of a triangle with the vertex turned upwards, the base turned downwards and the slanted sides supporting two rows of grinding blades.
These grinding blades cooperate with the cutting elements of the spirals of two parallel and juxtaposed screws near the container bottom.
Advantageously the opening of the container bottom allows a discharge of the ground material that in this way is not put again in the cycle so that it is not ground again passing through the same grinding blades.
Still advantageously the coaxial and opposite winding directions of the spirals of the same screw cause the material to be ground to flow to the center of the container along the longitudinal direction of said container.
The material which was not ground and reaches the central zone of the screw and the container, at this point undergoes a mixing up avoiding stay of the material and the consequent possible jams.
The foregoing objects and advantages will be better understood by the following description of a preferred embodiment of the invention which is being given as an illustrative but not limiting example in the accompanying sheets of drawings in which: - Fig. 1 is an isometric view of the grinder of the invention;
- Fig. 2 is a side view of the grinder of fig. 1 without the side wall ; - Fig. 3 is a front view of the grinder of fig. 1 without the end wall ; - Fig. 4 is an isometric view of the grinder inside without the screws; - Fig. 5 is an enlarged detail of fig. 4; - Fig. 6 is an isometric view of an enlarged detail of fig. 3; and - Fig. 7 shows the grinder of fig. 3 in operation.
The grinder of the invention is shown in fig. 1 where it is generally indicated with numeral 1.
The grinder is preferably constructed and shown in the figures as a towed cart, but it is obvious that in other embodiments the grinder could be an independent fixed unit.
The grinder 1 of the invention comprises a container 2 at whose bottom 2a two screws 3,4 are arranged, each comprising a cylindrical element 5,6 on which a couple of spirals 7,8 and 9,10 are wound with coaxial and opposite winding directions, converging to the center of the cylindrical element 5,6.
The shaft 3a, 4a of each screw 3,4 defines the longitudinal rotation axes 3b, 4b of said screws 3,4 and is connected to driving means, not shown in the drawings for sake of illustrative simplicity, adapted to put them in rotation along the directions indicated by arrows 13,14 as shown in fig. 3.
Said driving means could for instance consist of an electric motor or in case the grinder is self propelled, could consist of the same engine driving the grinder.
On the outer edge 7a, 8a, 9a, 1 Oa of the spirals 7,8, 9,10 there is a plurality of cutting elements generally indicated with 11.
A plurality of grinding blades generally indicated with 12, are fixed inside the container 2 and are adapted to cooperate with the cutting elements 11 of the screws 3,4 to carry out the starting phase of the grinding operation.
According to the invention the container 2 at its lower part and below the screws 3,4 there is a free space adapted to allow the ground material T to fall down by gravity.
More particularly as shown in fig. 4, the free space is obtained by making the container 2 open at the bottom.
Below the container 2 there are discharging means not shown in the drawings, for the ground material T that for instance could consist of conveyor belts, screws or other discharging means of a known type.
As to the grinding blades 12, as shown more particularly in fig. 5, they have a flat profile 15 arranged longitudinally to the container 2 on which a plurality of teeth 16 having a generally triangular shape are provided.
It is clear that in other embodiments such a profile may have different shapes, in any case adapted to give to said flat profile 15 a generally comb-like shape.
According to the described embodiment, the grinding blades 12 are arranged at the center of the container 2 and are supported by a holding structure generally indicated with 17, also developed longitudinally to the container 2 and having a cross sectional general shape of a triangle with the vertex turned upwards and the base turned to the bottom 2a of the container 2.
On each slanted side 17a, 17b four grinding blades 12 are fixed and parallel to each other with the teeth 16 turned to the corresponding screws 3,4.
The number of the grinding blades is preferably four but it is clear that in different embodiments it could be a different number and as described below, it will have different effects on the grinding operation.
The grinding blades 12 and more particularly the triangular teeth 16, cooperate and graze the cutting elements 11 arranged on the spirals 7,8 and 9,10 of the screws 3,4 as shown in fig. 6, to carry out the cutting operation of the material M when contacted thereby.
On the lateral walls of the container 2 openings 18 are preferably provided, making easier the internal inspection of the container in case of malfunctioning or maintenance.
When the material to be ground M is loaded inside the container 2 as shown in fig. 7, the opposite motion of the screws 3,4 along the directions 13,14, convey the material to the central zone defined between the two screws 3,4 where the grinding blades 12 are provided.
In this zone the cooperation between the cutting elements 11 and the teeth 16 of the grinding blades 12 causes passage of the material through the gaps 19 defined between the grinding blades 12 and the spirals 7,8 and 9,10 of the screws 3, 4.
When the material M passes through said gaps 19 and reaches the lower zone of the screws 3,4, it results in small pieces and falls down by gravity as in this zone there are no elements preventing its fall.
It is clear that the screening operation of the material to be ground M occurs during said grinding process, where the wanted size of the ground material T is
defined by the same geometry defined by the gaps 19 and the rotation speed of the screws 3,4.
The geometry of the gaps 19 is particularly defined by the profile and number of the grinding blades 12, the pitch and the angle of the spirals 7,8, 9,10 of the screws 3,4.
It is also to be noted that the opening at the bottom of the container causes all the ground material T to be immediately discharged thus avoiding the possibility that the material is again put in the cycle and undergoes further grinding stages.
This involves an increase of the grinding performance and therefore a greater hourly output relative to the grinders of the prior art.
The arrangement of the spirals 7,8 and 9,10 with opposite directions to the center of the screws 3,4, causes the material to be ground M to follow a path going from the lateral walls to the centre of the container 2.
When the material M that was not ground reaches the centre of the screws 3, 4, it undergoes a whirling mixing up with the overlying material thus preventing its stay and jamming.
From the foregoing it is clear that the grinder of the invention attains the intended objects.
In the constructional stage executive variations may be made to the grinder of the invention, which were neither described nor shown in the appended drawings.
Such variations may for instance consist of a different number of screws, a different number of spirals for each screw, a different number and arrangement of the grinding blades, or even a different shape of the teeth of the grinding blades.
It is however to be understood that said and further variations or modifications, when falling within the scope of the inventive conception indicated in the appended claims, are to be considered all covered by the present patent.