DESCRIPTION

Field of the invention

The present invention generally relates to the technical field of industrial shredders and it particularly relates to a method for controlling the rotation speed of the shafts of double-shaft shredder for the material to be sorted and/or disposed of, as well as a computer program which allows to carry out such method and a shredder with such resident program.

State of the Art

Industrial shredders for metal and non-metal scrap, for example light metals, heavy metals and non-ferrous scrap, are known.

The object of such shredders is to reduce the size of the cumbersome scrap or of the voluminous metals so as to facilitate sorting and disposal or recycling.

Typically, the most robust shredder includes a pair of facing shafts, provided with blades between which the scrap is made to pass through for shredding.

Each shaft is connected to a pair of hydraulic motors driven by a pump and electric or diesel engine system, in a per se known manner. Therefore, the rotation speed of the shafts is directly proportional to the flow rate of the pumps.

Furthermore, in a per se known manner, each shaft is connected with a pressure transducer which detects the pressure thereof caused by the resistance of the scrap to be shredded. The transducer communicates such datum to a control system or PLC.

However, such known shredders are subject to the jamming of the material to be shredded with ensuing blocking of the shredder, as well as significant time and financial loss on the entire disposal and sorting chain.

Summary of the invention

An object of the present invention is to at least partly overcome the aforementioned drawbacks, by providing a method for controlling the rotation speed of the shafts of a shredder that is particularly reliable.

Another object of the present invention is to provide a method which allows to reduce the possibility of the material jamming in the shredder.

A further object of the present invention is to provide a method which allows to reduce the full blocking of the operation of the shredder.

Another object of the present invention is to provide a method which allows to protect the shafts of the shredder from mechanical stress, to extend their service life.

These and other objects that will be more apparent hereinafter are attained by a method for controlling the rotation speed of the shafts of a shredder and/or by a computer program and/or by a shredder as described, illustrated and/or claimed herein.

The dependent claims describe advantageous embodiments of the invention.

Brief description of the drawings

Further characteristics and advantages of the invention will be more apparent in light of the detailed description of some preferred but non-exclusive embodiments of the invention, illustrated by way of non-limiting example with reference to the attached drawings, wherein:

FIG. 1 shows a diagram of the method described;

FIG. 2 shows a diagram of the method described wherein the change of the flow rate of the pumps PO1 and PO2 occurs provided a determined criterion is met;

FIG. 3 is a schematic illustration of the shredder 1 wherein the pumps PO1 and PO2 are power-supplied by different motors;

FIG. 4 is a schematic illustration of the shredder 1 wherein the pumps PO1 and PO2 are power-supplied by a single motor.

Detailed description of some preferred embodiments

With reference to the aforementioned figures, herein described is a method for controlling the rotation speed of the shafts Al and A2 of a double shaft industrial shredder T for metal and non-metal scrap, for example light metals, heavy metals and non-ferrous scrap, so as to reduce the size of the cumbersome scrap or of the voluminous metals to facilitate disposal or recycling and sorting.

The expression sorting is used to indicate dividing the components of the scrap into separate but homogeneous groups to send them to the respective destinations.

The shredder T may include pressure sensor means, for example two or more pressure transducers Pl and P2, each connected with a respective shaft Al and A2. Although in the description hereinafter the sensor means will be in the form of two pressure transducers Pl and P2, it is however clear that different types of pressure sensors or several pressure transducers connected to each shaft may be taken into account without departing from the scope of protection of the attached claims.

Advantageously, the transducers Pl and P2 may detect a pressure value Ppi, Pp2 exerted on each shaft Al and A2 depending on the resistance to the passage of the scrap to be shredded therebetween.

The shredder 1 may also include a logic control unit UL comprising a CPU, for example a PLC.

Specifically, the transducers Pl and P2 may communicate the detected pressure value Ppi, Pp2 to the logic control unit UL.

The logic control unit UL may further be configured to compare the pressure value Ppi, Pp2 relating to each shaft Al and A2 with a threshold pressure value P_soglia pre-set or which can be pre-set in the logic unit as explained below.

In addition, the shredder 1 may include two pairs of hydraulic motors, each connected with a shaft.

For example, a pair of hydraulic motors Ml, M4 may be connected with the shaft Al, while a pair of hydraulic motors M2, M3 may be connected with the shaft A2.

However, it is clear that each shaft Al, A2 may be connected with only one hydraulic motor or three or more without departing from the scope of protection of the attached claims.

Furthermore, the motors Ml and M4 may be connected with a pump PO1 whose flow rate is regulated by a solenoid valve El connected with the control unit UL mentioned above.

On the other hand, the motors M2 and M3 may be connected with a pump PO2 whose flow rate is regulated by a solenoid valve E2 also connected with the control unit UL mentioned above.

The pumps PO1 and PO2 may have a respective characteristic maximum flow rate Porl_max or Por2_max and they may be power-supplied by drive means, for example a single motor MM1, for example as shown in FIG. 4, or a respective motor MM1, MM2, for example as shown in FIG. 3. The motors MM1 and MM2 may for example be electric or diesel motors, sized in a per se known manner.

Advantageously, the control method according to the invention may include some steps which may occur sequentially or iteratively in subsequent work periods.

Therefore, as regards the pump PO1 there may be defined a flow rate value at the beginning of the work period Porl_l and a flow rate value at the end of the work period Porl_F.

Similarly, as regards the pump PO2 there may be defined a flow rate value at the beginning of the work period Por2_l and a flow rate value at the end of the work period Por2_F.

In a time instant pre-defined in the control unit UL within a work period, there may be defined a detection by the transducers Pl and P2 of the pressure value Ppi and Pp2 of the shafts Al and A2.

It is clear that in such instant, the pumps PO1 and PO2 may have a flow rate value equal to the initial one Porl_l and Por2_l.

Subsequently, the control unit UL may compare the detected value Ppi and Pp2 with the pressure value P_soglia.

It is clear that the value P_soglia may be lower than the pressure value for blocking the rotation of the shafts Al and A2, as well as of the shredder T, so as to act before the shredder is fully blocked due to scrap that is difficult to shred.

For example, the value P_soglia may be equal to 220 bars, while the blocking pressure value may be equal to 260 bars.

The values P_soglia and blocking pressure may be variable and they may be determined depending on the type and amount of material to be sorted and/or disposed of.

For example, as regards the type of material there may be considered characteristics such as the inherent nature of the material - for example if metal or non-metal - density and hardness.

It is therefore clear that such values may be set or are suitable to be set in the control unit UL before the step of detecting the pressure values Ppi and Pp2 of the shafts Al and A2.

From the aforementioned comparison, should even only one of the detected values be greater than or equal to the pressure value P_soglia, or the scrap creates a determined resistance to the passage through the shafts Al and A2, causing an increase in the pressure value Ppi and Pp2 on one of them, the final flow rate value Porl_F or Por2_F - obtained by reducing the initial flow rate Porl_l or Por2_l of one of the two pumps PO1, PO2 by a respective value R1 or R2 - may be set by the control unit UL by acting on the respective solenoid valve El or E2.

It is clear that the final flow rate value may correspond to the initial flow rate value of the pump in a subsequent work period subsequent to the first work period.

Furthermore, it is clear that also the values R1 and R2 may be pre-set or suitable to be set in the control unit UL prior to the detection step of the transducers Pl and P2.

On the other hand, during the detection step, for example in a subsequent work period, should the detected pressure value Ppi and Pp2 of both shafts Al and A2 be lower than the threshold pressure value P_soglia, the logic unit UL may set the final flow rate value Porl_F or Por2_F equal to the maximum flow rate value Porl_max or Por2_max of the pump PO1, PO2 whose flow rate had been reduced.

Such values shall therefore be the initial flow rate values Porl_l and Por2_l in a subsequent work period.

In any case, the logic unit UL may set the final flow rate value Porl_F and/or Por2_F equal to the maximum flow rate value Porl_max and/or Por2_max when - in a work period - the detected pressure value Ppi and Pp2 of both shafts Al and A2 is lower than the threshold pressure value P_soglia, therefore without the flow rate of at least one of the pumps PO1, PO2 having been necessarily reduced previously.

Advantageously, the reduction of the flow rate of one of the pumps, will cause the reduction in rotation speed of the respective shaft Al or A2, facilitating the shredding of the scrap.

As a matter of fact, should even only one shaft slow down, the pressure caused on it may be reduced, thus facilitating the operation of the shredder 1.

For example, an initial flow rate value of the pump PO1 or PO2 equal to 100% may be reduced by a value R1 or R2 for example by 60% so that the final flow rate Porl_F or Por2_F of the pump PO1 or PO2 is equal to 40%.

In a preferred but non-exclusive embodiment, the control unit UL may be configured to reduce the initial flow rate value Porl_l and Por2_l of both pumps PO1 and PO2 by acting on the respective solenoid valve El and E2 following the aforementioned comparison between the detected pressure values Ppi, Pp2 and the threshold pressure value P_soglia.

This will allow to reduce the rotation speed of both shafts Al and A2, facilitating not only the shredding of the scrap, but also preventing the full blocking of the shredder 1.

Specifically, the initial flow rate Porl_l and Por2_l of the pumps PO1 and PO2 may be reduced respectively by the values R1 and R2 so as to obtain the final flow rate value Porl_F and Por2_F.

Even in this case, at a successive detection, should the detected pressure value Ppi and Pp2 of both shafts Al and A2 be lower than the threshold pressure value P_soglia, the logic unit UL will bring the pumps PO1 and PO2 to the maximum flow rate value Porl_max and Por2_max.

Therefore, these values will not only be the final flow rate values Porl_F and Por2_F of the current period but also the initial flow rate values Porl_l and Por2_l in a subsequent work period.

It is clear that also in this case the values R1 and R2 may be pre-set or suitable to be set in the control unit UL prior to the detection step of the transducers Pl and P2.

For example, the flow rate of the pump PO1 may be reduced by a value R1 equal to 20% to obtain a final 80% flow rate Porl_F, while the flow rate of the pump PO2 may be reduced by a value equal to 40% to obtain a final 60% flow rate Por2_F.

It is clear that also the opposite may occur, that is the flow rate of the pump PO1 may be reduced by a value R1 equal to 40% to obtain a final 60% flow rate Porl_F, while the flow rate of the pump PO2 may be reduced by a value equal to 20% to obtain a final 80% flow rate Por2_F.

It is clear that these values are purely for exemplifying purposes and they may vary depending on the type and amount of material, as described above.

Furthermore, it is clear that the first and second value R1 and R2 may be equal, for example equal to 50%, or one may be greater than the other, like in the example mentioned above or even, specifically, one may be twice larger than the other.

In a further embodiment, shown in FIG.2, the values R1 and R2 may be alternatively one larger than the other, so that the flow rate of the pump PO1 and of the pump PO2 may be reduced alternatively by the larger value depending on a pre-established criterion.

For example, considering 20% and 60% reduction values to obtain respective 80% and 40% flow rates, in the even days of the week (criterio A) the flow rate of the pump PO1 may be reduced by 20% (Rl) and the flow rate of the pump PO2 by 60% (R2), while in the odd days (criterio B) the flow rate of the pump PO1 may be reduced by 60% (Rl) and that of the pump PO2 by 20% (R2).

This will allow the homogeneous consumption of the blades of both shafts Al and A2 so as to delay the maintenance operation with relative machine shut down as much as possible.

According to a further aspect of the invention, there may be provided for a computer program which can be installed in the CPU of the control unit UL which comprises instructions to command the control unit to run several steps of the method described above.

This means that such program may be installed in the CPU of any existing shredder T so as to allow the operation thereof based on the method described above.

According to a further aspect of the invention, there may be provided for a shredder T as described above, whose logic unit UL has installed a resident computer program which comprises instructions to command the logic unit to sequentially carry out the steps of the method described above.

In the light of the above, it is clear that the aforementioned method allows to reduce the possibility of the material jamming in the shredder and prevent the full blocking of the operation thereof.

Furthermore, the control logic will allow to protect the components of the shredder from the mechanical stress, to extend the service life thereof.

In the light of the above, it is clear that the invention attains the pre-set objectives.

The invention is susceptible to numerous modifications and variants. All details may be replaced by other technically equivalent elements, and the materials can be different depending on the technical needs, without departing from the scope of protection of the invention defined by the attached claims.