Patent Publication Number: US-7210514-B2

Title: Die casting machine

Description:
FIELD OF THE INVENTION 
   The present invention relates to a die casting machine, and more particularly, to an improvement in a lubricant oil feeding means which feeds a lubricant oil into a clearance between the inner peripheral surface of a sleeve and the outer peripheral surface of an injection piston. 
   DESCRIPTION OF THE PRIOR ART 
   A die casting machine is well known in the art which comprises at least two or a first and a second die which are disposed in abutment against each other to define a casting space therebetween, a sleeve mounted on the first die and communicating with the casting space, an injection piston slidably disposed within the sleeve for injecting molten metal fed into the sleeve into the casting space, drive means for reciprocating the injection piston, and lubricant oil feeding means for feeding a lubricant oil into a clearance between the inner peripheral surface of the sleeve and the outer peripheral surface of the injection piston. 
   An arrangement is known for a lubricant oil feeding means in which a nozzle communicating with a supply of lubricant oil has its distal end disposed above an end face of the sleeve to cause the lubricant oil to drip down from the distal end of the nozzle towards the clearance between the sleeve and the injection piston (Japanese Laid-Open Patent Application 77274/1999). 
   Another arrangement for the lubricant oil feeding means is also known in which the lubricant oil is fed as a mist from a spray nozzle (Japanese Laid-Open Patent Application 142877/1994) rather than dripping it down. 
   However, with either lubricant oil feeding means, it is difficult to cause the lubricant oil to be spread around both peripheral surfaces from the clearance between the end face of the sleeve and the end face of the injection piston, causing an early abrasion of portions which are not covered by the lubricant oil or which require time until they are covered by the lubricant oil to have an influence on the useful life of the sleeve and the injection piston. 
   To overcome above problem, it may be contemplated to increase the supply of the lubricant oil, but when the amount of lubricant oil supplied is more than is required, there results a disadvantage that an excess amount of lubricant oil reacts with molten metal to be gasified during a pouring operation and causes cavities to be generated or causes an imperfect plating. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, the present invention intends to provide a die casting machine including a lubricant oil feeding means which improves the useful life of the sleeve and the injection piston as compared with the prior art. 
   Specifically, the present invention relates to a die casting machine comprising at least two or a first and a second die disposed in abutment against each other to define a casting space therebetween, a sleeve mounted on the first die and communicating with the casting space, an injection piston slidably disposed within the sleeve for injecting molten metal supplied through the sleeve into the casting space, drive means for reciprocating the injection piston, and lubricant oil feeding means for feeding a lubricant oil into a clearance between the inner peripheral surface of the sleeve and the outer peripheral surface of the injection piston. In accordance with the present invention, the lubricant oil feeding means comprises a lubricant oil feed passage for feeding a lubricant oil into a clearance between the inner peripheral surface of the sleeve and the outer peripheral surface of the injection piston, and an air feed passage for feeding air into a clearance between the inner peripheral surface of the sleeve and the outer peripheral surface of the injection piston. The air in the air feed passage is effective to pump the lubricant oil from the lubricant oil feed passage into the clearance between the outer peripheral surface of the injection piston and the inner peripheral surface of the sleeve. 
   With the lubricant oil feeding means mentioned above, since the lubricant oil is pumped by the air, it is possible to allow a required minimum amount of lubricant oil to be spread quickly and extensively around the outer peripheral surface of the injection piston. 
   Accordingly, the useful life of the sleeve and the injection piston can be improved with an amount of lubricant oil which is reduced as compared with the prior art and the generation of gas which would result from a reaction with molten metal within the sleeve can be suppressed, thus preventing a casting cavity from occurring and improving the quality of the products. 
   The above and other objects and advantages of the invention will become apparent from the following description of an embodiment thereof with reference to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation of one embodiment of the present invention; 
       FIG. 2  is an enlarged section of a rear end of a sleeve  7 ; 
       FIG. 3  is a right-hand side elevation of the sleeve  7  and an injection piston  9 ; 
       FIG. 4  is a side elevation illustrating an idling operation of the injection piston; and 
       FIG. 5  is a side elevation illustrating a pouring operation. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENT 
   An embodiment of the invention shown in the drawings will now be described. There is shown a compact size die casting machine  1 , to which lubricant oil feeding means  2  according to the invention is applied. The die casting machine  1  comprises a fixed die  3  acting as a first die which is mounted on a stationary frame, not shown, and a movable die  4  acting as a second die (see  FIG. 5 ) which is driven for reciprocating motion toward and away from the fixed die  3 , and when the movable die  4  is brought into abutment against the fixed die  3 , a closed casting space  5  (see  FIG. 5 ) is defined therebetween. 
   A sleeve  7  is disposed in the fixed die  3  and communicates with the casting space  5  and is internally formed with a sprue runner  6 . An injection piston  9  is slidably disposed within the sleeve  7  and is driven for reciprocatory motion therein by drive means, not shown. 
   At its one end, the sleeve  7  is notched in its upper portion to provide a gate  10  which allows molten metal to be poured into the sleeve. The molten metal is poured into the sleeve when the injection piston  9  assumes its retreated position as shown in  FIG. 1 . 
   It is to be noted that a clearance between the sleeve  7  and the injection piston  9  depends on the size of these members, but is generally very small on the order of 0.03 to 0.06 mm. As a consequence, with the prior art practice of dripping lubricant oil into the clearance between the end face of the sleeve and the end face of the injection piston, there may be portions around the inner peripheral surface of the sleeve or the outer peripheral surface of the injection piston where lubricant oil is not spread, or it may take a length of time until lubricant oil is spread over these portions. In these portions, abrasion proceeds in an accelerated manner, influencing the useful life of the sleeve and the injection piston. 
   However, the lubricant oil feeding means  2  of the present embodiment is designed to improve the useful life of the sleeve  7  and the injection piston  9  as compared with the lubricant oil feeding means of the prior art as mentioned above. 
   Specifically, as indicated in  FIG. 2 , the lubricant oil feeding means  2  comprises an air feed passage  16  connected to a flute  15  formed around the outer periphery of the sleeve  7  at a location toward the rear end thereof and communicating with the interior of the sleeve  7  through the flute  15 , and a lubricant oil feed passage  19  connected to a transverse slot  17  which communicates with the flute  15  to be in communication with the interior of the sleeve through the transverse slot  17  and the flute  15 . The air feed passage  16  is connected with a compressor, not shown, which serves as a air supply, and an air supply valve  18  is disposed therein to open or close the passage, as shown in  FIG. 1 . The lubricant oil feed passage  19  is connected to an air cylinder which serves as a source of lubricant oil supply, and an air switching valve which supplies air to or displaces it from the air cylinder or a lubricant oil feed valve  20  is disposed in the passage. 
   As shown in  FIGS. 2 and 3 , an annular groove  21 , which is arcuate in section and extends continuously circumferentially, is formed in the inner peripheral surface of the sleeve  7 , and the flute  15  opens into the groove  21 . Thus both the air feed passage  16  and the lubricant feed passage  19  open into the groove  21 . 
   Accordingly, when the injection piston  9  is located at its retreated position, an annular space X having a greater clearance than the above mentioned clearance (0.03 to 0.06 mm) is formed between the groove  21  and the outer peripheral surface of the injection piston  9 . 
   The circumferentially continuous groove  21  has a center O′ which is located with an offset on the order of 1 to 5 mm above the center O of the sleeve  7 , whereby the groove  21  has a depth which is shallow downward and deep upward. As a consequence, the volume of the groove  21  is reduced downward as compared with upward, and accordingly, if the quantity of the lubricant oil which is held as a reservoir in the lower portion of the groove  21  as the oil is fed from the upwardly located lubricant oil feed passage  19  is small, the liquid level rises quickly within the groove  21 , whereby the oil is quickly spread circumferentially over the entire area of the outer peripheral surface of the injection piston  9 . 
   A connecting rod  22  which connects between the injection piston  9  and drive means has an external diameter which is chosen to be suitably less than the external diameter of the injection piston  9 , whereby when the connecting rod  22  is inserted into the sleeve  7 , a clearance between the inner peripheral surface of the sleeve  7  and the outer peripheral surface of the connecting rod  22  is greater than the clearance between the sleeve  7  and the injection piston  9  while an annular space Y (refer  FIGS. 4 and 5 ) which is greater than this clearance is formed between the groove  21  and the outer peripheral surface of the connecting rod  22 . 
   The air feed valve  18  and the lubricant oil feed valve  20  are adapted to be controlled to open and close by a controller  25  which controls the entire die casting machine  1 . A first and a second touch sensor  26  and  27 , which are a pair of detectors disposed on the locus of movement of the connecting rod  22  which operatively associates the injection piston  9  with the drive means, provide inputs indicating that the injection piston  9  is located at either a retreated position or an advanced position. 
   The first touch sensor  26  is disposed close to the drive means while the second touch sensor  27  is disposed close to the fixed die  3 . An abutment member  28  which projects radially outward from the outer periphery of the connecting rod  22  abuts against either touch sensor  26  or  27 . Specifically, the first touch sensor  26  detects that the injection piston  9  is located at the retreated position shown in  FIG. 1  and the second touch sensor  27  detects that the injection piston  9  is located at the advanced position shown in  FIG. 4 . 
   The controller  25  will now be described. In response to an input from the first touch sensor  26  indicating that the injection piston  9  is located at the retreated position as shown in  FIG. 1 , the controller  25  opens the lubricant oil feed valve  20  of the lubricant oil feeding means  2  for a given time interval to feed the lubricant oil, then closes it, then opens the air feed valve  18  for a given time interval to feed air, and then closes it prior to the pouring operation. 
   When the lubricant oil feeding means  2  has fed the lubricant oil and the air, an idling operation takes place by causing the drive means to advance the injection piston  9  to its advanced position while there is no molten metal in the sleeve  7  and this condition is maintained for a while. At this point, the air feed valve  18  is opened for a given time to feed the air and is then closed. 
   The drive means then causes the injection piston  9  to retreat from the advanced position to the retreated position, a molten metal which may comprise aluminum alloy, for example, is poured into the sleeve  7  subsequently by pouring means and then the drive means drives the injection piston  9  forward to inject the molten metal in the sleeve  7  into the casting space  5  for the purpose of a casting operation. Under this condition, the drive means is maintained still momentarily while the pouring means is returned to prepare for the next pouring operation. At this time, the injection piston  9  still remains intermediate the advanced position and the retreated position while applying a pressure to the molten metal in the casting space  5  (see  FIG. 5 ). 
   When the aluminum alloy in the casting space  5  is solidified, the movable die  4  is retreated while the injection piston is advanced to the advanced position to take out a casting. At this time, the abutment member  28  abuts against the second touch sensor  27  to provide an input indicating that the injection piston  9  is located at the advanced position, whereupon the air feed valve  18  of the lubricant oil feeding means  2  is opened to feed only the air into the groove  21 , thus removing metal residues (burrs) and metal powders by blowing them away and the machine is left in a standby condition for a while until the forward end of the injection piston  9  is cooled down. This is to prevent the inner surface of the sleeve  7  and the outer peripheral surface of the injection piston  9  from being damaged by a retreating movement of the injection piston  9  under the condition that the forward end of the injection piston  9  is expanded to a degree exceeding a clearance with respect to the sleeve  7  as a result of a direct contact with the molten metal. 
   When the forward end of the injection piston  9  has cooled down, the drive means is used to retreat the injection piston  9  to its retreated position (see  FIG. 1 ). At this time, when the first touch sensor  26  provides an input indicating that the injection piston  9  is located at its retreated position, the lubricant oil feed valve  20  is opened for a given time interval to feed the lubricant oil as before, followed by opening the air feed valve for a given time interval to feed the air. Subsequently, the controller  25  repeats the described control operation. 
   Describing the operation of the lubricant oil feeding means  2  of the die casting machine  1  mentioned above, under the condition shown in  FIG. 1  where the movable die  4  is separate from the fixed die  3  and the injection piston  9  is located at its retreated position or the condition which prevails before the pouring operation, the controller  25  initially opens the lubricant oil feed valve  20  for a given time interval to deliver the lubricant oil through an air cylinder. This lubricant oil of a given quantity is fed through the lubricant oil feed passage  19 , the transverse slot  17  and the flute  15  into the groove  21 , or more specifically, into an extensive annular space X formed between the groove  21  in the sleeve  7  and the outer peripheral surface of the injection piston  9 . 
   Since the center O′ of the groove  21  is offset upwardly from the center O of the sleeve  7 , if the quantity of the lubricant oil fed from the lubricant oil feed passage  19  is small, the lubricant oil can quickly spread circumferentially over the entire outer peripheral surface of the injection piston  9 . 
   When a given quantity of lubricant oil has been introduced into the annular space X, the air feed valve  18  is then opened for a given time interval to feed the air into the annular space X through the air feed passage  16  and the flute  15 , whereby the internal pressure of the annular space X rises to cause the air in the annular space X to find its way out through a clearance between the inner peripheral surface of the sleeve  7  (toward the rear end) and the outer peripheral surface of the injection piston  9 . This allows the lubricant oil which has been introduced into the annular space X to be pumped quickly and extensively throughout the clearance between both members. 
   When the air feed valve  18  is closed, an idle reciprocating motion of the injection piston  9  which is applied with the lubricant oil takes place under the condition that the molten metal is not yet poured in order to spread the lubricant oil around the entire inner peripheral surface of the sleeve  7 . Specifically, at this stage, the lubricant oil is spread only around the inner peripheral surface located toward the rear end of the sleeve  7  and it is necessary that the oil be spread around the entire surface. When the second touch sensor  27  detects that the injection piston  9  is located at the advanced end, the controller  25  opens the air feed valve  18  to feed the air into the groove  21 , or more specifically, into an annular space Y located between the groove  21  and the outer peripheral surface of the connecting rod  22  which is inserted into the sleeve  7  and having a greater clearance therebetween than in the remainder, thus removing metal residues (burrs) and metal powders which are left within the groove  21  by blowing them away. 
   The injection piston  9  is then retreated to move away from the second touch sensor  27 , whereupon the air feed valve  18  is closed. Subsequently, the movable die  4  is brought into abutment against the fixed die  3  to define the casting space  5 , and the molten metal is poured into the sleeve  7  through the gate  10  by pouring means, not shown. Upon completion of the pouring operation, the injection piston  9  which is now located at the retreated position is driven forward to the advanced position, injecting the molten metal of aluminum alloy into the casting space  5 . 
   When removing a casting, in response to an input from the second touch sensor  27  indicating that the injection piston  9  is located at the advanced position, the air feed valve  18  is opened to feed the air into the annular space Y formed between the groove  21  in the sleeve  7  and the outer peripheral surface of the connecting rod  22 , thereby removing metal residues (burrs) and metal powders by blowing them away. 
   Subsequently, the lubricant oil feeding means  2  repeats the described operation. 
   It will be understood from above description that the use of the lubricant oil feeding means  2  allows the lubricant oil to be spread more quickly and more extensively as compared with the prior art, thus enabling the useful life of the sleeve  7  and the injection piston  9  to be improved as compared with the prior art. 
   In the above description, the air feed valve  18  is opened in following relationship with the lubricant oil feed valve  20 , but this is not an essential requirement, and both valves may be opened simultaneously, thus spraying the lubricant oil into the annular space X. 
   Also in the embodiment, the air feed valve  18  is opened during the idling operation and during the pouring operation, but this is not an essential requirement and this valve may be opened during only one of these operations. 
   In addition, the first and second touch sensors used in the embodiment may be replaced by other sensors. 
   While the invention has been described above in connection with the embodiment, it should be understood that a number of changes, modifications and substitutions therein are possible without departing from the spirit and the scope of the invention, which is solely limited by the appended claims.