Abstract:
A method for cooling foundry castings, characterized in that it comprises the steps of: forming a cooling fog by nebulizing a flow of water, exposing a substantial part of the external surface of the casting to said cooling fog, measuring the temperature of the casting, and interrupting the exposure of the casting to the cooling fog when the measured temperature drops below the predetermined threshold.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method and apparatus for cooling foundry castings.  
         [0003]     2. Description of the Related Art  
         [0004]     The invention was developed in particular for installations for the production of aluminum castings, by gravity or low pressure die-casting. However, the invention is not limited to this sector of use and can be used in all technical sectors in which there is a need to rapidly cool foundry castings.  
         [0005]     In the case of castings of aluminum or similar light alloys, the casting comes out of the mould at temperatures in the order of 500° C. To be capable of being handled for the operations subsequent to die-cast (flogging, etc.), the temperature of the casting must drop to values in the order of 120-150° C. or lower.  
         [0006]     Cooling the castings in ambient air requires an extremely long time. The cooling time depends on the weight of the casting and of the sand cores contained therein. In the case of a cylinder head, the cooling time in ambient air is in the order of hours.  
         [0007]     Installations where castings are cooled in ambient air require large accumulations areas in which the pieces are laid for cooling. This solution is not very practicable because it uses a large surface of the installation as an accumulation storage location for the pieces undergoing cooling and due to the problems that originate from the handling of the pieces in the cooling area.  
         [0008]     Cooling installations are known in which the pieces to be cooled are made to pass through a forced air tunnel. In a forced air cooling tunnel, the temperature of the pieces drops to the desired value in about 20 minutes. The problem of forced air cooling tunnels consists in that the flow of cooling air contains polluting vapors which must be abated before the air is discharged into the atmosphere and this requires highly powerful and costly air extraction and treatment facilities, also in consideration of the high flow rate of air required to cool the castings.  
         [0009]     On the other hand, the use of water to cool foundry castings would have the drawback of causing stresses and warping in the pieces. Moreover, the cooling water would wet the sand contained in the castings, making difficult the subsequent step of flogging the castings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     One object of the present invention is to provide a method and an apparatus for cooling foundry castings in a more rapid manner than is currently used which allows to overcome this drawbacks.  
         [0011]     According to the present invention, said object is achieved by a method and by an apparatus having the characteristics set out in the claims. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0012]     The characteristics and advantages of the present invention shall become readily apparent in the course of the detailed description which follows, given purely by way of non-limiting example, with reference to the attached drawings in which:  
         [0013]      FIG. 1  is a lateral schematic view of an apparatus for cooling foundry castings according to the present invention and  
         [0014]      FIG. 2  is a plan schematic view of the apparatus of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     With reference to the figures, the reference  10  designates an apparatus for cooling foundry castings. The apparatus  10  can be installed in an installation for the production of aluminum castings, by gravity or low pressure die-casting. The cooling apparatus  10  receives the foundry castings at the output of the mould and cools them down to a temperature whereat the castings can be subjected to the subsequent operations, such as flogging, etc.  
         [0016]     The apparatus comprises a cooling chamber  12  within which is provided a support base  14  able to support a foundry casting  16 . The figures show, by way of example, a casting constituted by a head for an internal combustion engine of a vehicle. Naturally, it is understood that the method and the apparatus according to the present invention can be used for cooling castings of any type and material. The foundry casting  16  which is subjected to the cooling operation is further provided with the riser and with the pouring channels  18  and contains the cores of sand agglomerated with resins which are used to form channels, seats and cavities of various types in the structure of the castings.  
         [0017]     In the example illustrated in the figures, the cooling chamber  12  has the shape of a parallelepiped with rectangular base and is provided with at least one opening for the introduction and the extraction of the casting  16 . In the illustrated example, the cooling chamber  12  lacks one of the two vertical walls with smaller sides in order to form an opening  20  contained in a vertical plane which allows the introduction and extraction of the casting along a horizontal direction indicated by the double arrow  22 . The casting  16  is preferably introduced and extracted by means of an automatic manipulator device (not shown) constituted for example by an anthropomorphic robot.  
         [0018]     Alternatively, the cooling chamber  12  could be constructed in the form of a tunnel with a motorized conveyor which extends through the cooling chamber and which transports the castings through the chamber. Said conveyor could be capable of being operated in steps to maintain the casting in stationary position during the cooling time and to carry the cooled casting outside the cooling chamber at the completion of the cooling step.  
         [0019]     The cooling chamber  12  contains means able to create a cooling fog formed by a suspension of very fine water droplets. Preferably, the means for generating the cooling fog comprise a plurality of nebulizer guns  24  fed by a jet of water under pressure produced by a pump  26 , preferably electrically or pneumatically operated. When the nebulizer guns  24  are fed by a flow of water under pressure, produce a fog formed by very fine water droplets in suspension in the air which fills the internal volume of the cooling chamber  12  surround the foundry casting  16  and its riser  18 . The cooling fog is not projected onto the external surface of the casting but forms a substantially static cloud which surrounds the casting to be cooled. In contact with the casting at high temperature, the cooling fog vaporizes, removing the heat of vaporization of the water from the piece. The fog comes in contact with the surface of the piece in uniform fashion, without producing sudden local cooling which could generate stresses or warping in the structure of the piece.  
         [0020]     The cooling chamber  12  is provided with a temperature measuring device  28  able to measure the temperature of the casting  16  housed within the cooling chamber  12 . The temperature measuring device  28  comprises a sensitive element  30  ( FIG. 1 ) which is placed in contact with a point of the casting  16  and is maintained in contact with the piece  16  throughout the cooling step.  
         [0021]     The sensitive element  30  of the temperature measuring device  28  can be a thermocouple. To enhance the accuracy of the temperature measurement, the sensitive element  30  is placed in contact with a wall of a cavity of the casting  16  open inferiorly. In this way, the sensitive element  30  is substantially sheltered from the action of the cooling fog. The sensitive element  30  must remain in contact with the casting  16 . To obtain this, the sensitive element can be positioned at the end of a lever  32  articulated to the base  14  and provided with a counterweight  34  which tends to maintain the sensitive element  30  in contact with the wall of the lower cavity of the casting  16 .  
         [0022]     The temperature measuring device  28  provides an electric signal, indicative of the temperature of the casting  16 . This signal is received by a control unit  36  which compares the measured temperature with a predetermined threshold temperature. The control unit  36  is provided to interrupt the feeding of the pump  26  when the measured temperature drops below the reference threshold. For example, the feeding of the pump  26 , and hence the generation of fog in the cooling chamber  12 , can be interrupted when the measured temperature drops below about 130-140° C.  
         [0023]     When a hot casting  16  is introduced into the cooling chamber  12 , the temperature measuring device  28  measures its temperature by means of the sensitive element  30 . When the measured temperature exceeds a reference chamber, the pump  26 , which generates the cooling fog, is started. The production of the fog continues until the measured temperature drops below the reference threshold. Interrupting the production of fog according to the measured temperature of the casting  16  allows to prevent the fog from being deposited on the piece, wetting the sand. Assurance is thereby provided that the castings exiting the cooling chamber  12  are perfectly dry. Therefore, even if the cooling operation is performed in the presence of water, the subsequent step of flogging the pieces is not compromised in any way.  
         [0024]     The cooling system according to the present invention is extremely efficient. Within a few minutes (4-6 minutes) the temperature of a casting with a weight, including the cores, in the order of 40-50 kg is reduced from about 500° C. to about 130-140° C.  
         [0025]     As an alternative to the illustrated solution which entails the activation and deactivation of the pump which generates the cooling fog, a solution can be obtained in which the fog is produced in continuous fashion and the casting is moved outside the operating range of the cooling fog when the temperature measured of the casting drops below the predetermined threshold.