Patent Publication Number: US-2021162492-A1

Title: Back-spray system and injection piston

Description:
TECHNICAL FIELD 
     The present invention relates to a back spray system for an injection piston used in a die casting machine. More particularly, the present invention comprises a system to sufficiently lubricate the interior of the die casting sleeve and plunger tip from the die mold to a pouring port. 
     BACKGROUND ART 
     In die casting, molten metal, such as aluminum, is poured into a shot sleeve through a pouring port in the shot sleeve. A predetermined amount of the molten metal is transferred into a shot sleeve for insertion by an injection piston into a die cavity forming a casting, the metal is cooled and the casting removed from the die. The injection piston, consisting of a shot rod and a plunger tip, is axially moved or extended into the shot sleeve to “shoot” the molten metal into the die cavity. It is necessary to both lubricate and cool the plunger tip and the shot rod due to the high temperatures, the presence of molten metal on the plunger tip and the plunger rod, and the friction between the plunger tip and the shot sleeve. 
     A shot system is prone to many different problems. Excessive wear and poor lubrication frequently occur between the enlarged plunger tip and the shot sleeve, as well as dripping and wasting of lubricant used to minimize wear. Lubrication of these contiguous surfaces has heretofore suffered from inefficiency and plugging of the lubricating lines and the lubricating holes causing excessive wear and parts fatigue. The cleaning of these lubricating holes or ports has been difficult and time consuming, while excess emission lubrication and improper lubrication creates a smoke emission problem during die casting operation. 
     In attempting to overcome lubrication problems, various lubricating systems have been developed. However, it is difficult to cause the lubricant to spread around the peripheral surfaces from the clearance between the end face of the shot sleeve and the end face of the injection piston, causing an early abrasion or fouling of portions that are not covered by the lubricant. 
     SUMMARY OF INVENTION 
     Technical Problem 
     It is an object of an aspect of the present invention to provide, for example, a system that allows lubricant to get a proper place in a shot sleeve. 
     Solution to Problem 
     A back spray system in accordance with an aspect of the present invention is a back spray system for lubricating a shot sleeve of a die casting machine, including: a shot sleeve; an injection piston having a plunger tip and a shot rod connected to the plunger tip; a groove surrounding the shot rod; and a collar surrounding the groove; the shot rod having a shot rod hole through the length of the shot rod; the groove having at least one groove hole connected to the shot rod hole; the collar having a predetermined number of collar holes in communication with the groove and positioned circumferentially about the collar, and lubricant, having been supplied to the shot rod hole, flowing through the at least one groove hole into the groove, and then being released from the groove through the collar holes to a space between the plunger tip and the shot sleeve. 
     An injection piston in accordance with an aspect of the present invention is an injection piston used in combination with a shot sleeve, including: a plunger tip; a shot rod connected to the plunger tip; a groove surrounding the shot rod; and a collar surrounding the groove; the shot rod having a shot rod hole through the length of the shot rod; the groove having at least one groove hole connected to the shot rod hole; the collar having a predetermined number of collar holes in communication with the groove and positioned circumferentially about the collar, and lubricant, having been supplied to the shot rod hole, flowing through the at least one groove hole into the groove, and then being released from the groove through the collar holes to a space between the plunger tip and the shot sleeve. 
     Advantageous Effects of Invention 
     An aspect of the present invention allows lubricant to get to a proper place in a shot sleeve. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a general description of a die casting machine; 
         FIG. 2  is a side view of a conventional shot sleeve showing the injection plunger at a withdrawn position; 
         FIG. 3  is a side view of an injection piston of one embodiment of the present invention showing the plunger tip and the shot rod; 
         FIG. 4  is a side view of the injection piston showing the collar disposed over the groove; and 
         FIG. 5  is a cross section view of the injection piston taken along line A-A of  FIG. 4 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Having described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale. 
     The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be through and complete and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to the elements throughout. 
     SUMMARY 
     It is therefore the general object of one or more embodiments of the present invention to provide a lubricating system to apply lubricant as far forward in the shot sleeve as possible. Another object is to sufficiently atomize lubricant to cover all the interior of the shot sleeve from die mold to pouring port. 
     There is provided back spray system comprising an injection piston having a plunger tip and a shot rod with a gun drilled hole through the length of the rod connecting a lubricant supply to a collar located behind the plunger tip. 
     The collar has a predetermined number of holes or ports positioned circumferentially about the collar sized and positioned to dispense a precise and uniform amount of lubricant and air to the space between the plunger tip and the shot sleeve. The number of holes depends on the circumference of the shot rod. Under the collar is a channel with two drilled holes connected to the shot rod hole that extends the length of the shot rod. 
     When the injection piston is in use a lubricant and air mixture travels through the shot rod holes to the collar where the mixture is released or sprayed out to thoroughly cover the shot sleeve and plunger tip and apply lubricant to the far forward portion of the shot sleeve. 
     Other objects features and advantages of the invention will be apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings. 
     [Configuration of Die Casting Machine] 
     Turning now to  FIG. 1  there is shown a simplified diagram of a die casting machine  10 . The die casting machine  10  comprises a frame  12  which includes a fixed die  14  mounted to the frame  12  and a movable die  16  acting as a second die which is driven by reciprocating motion (not shown) toward and away from the fixed die  14  and when the movable die  16  is brought into abutment against the fixed die  14  a cavity  18  is formed there between. A shot sleeve  20  passed through the fixed die  12  and communicates with the cavity  18 . In shot sleeve  20  there is an injection piston  23 , comprised of a plunger tip  26  and a shot rod  24 . The shot rod  24  is slideably disposed within shot sleeve  20  and is driven back and forth through the shot sleeve  20 . The shot sleeve  20  is a symmetrical round metal sleeve through which the shot rod  24  slides. The shot rod  24  pushes the molten metal into the cavity  18  of the die after the molten metal is poured into the pour hole—opening  22 . The pour hole  22  is located at the end position of the shot sleeve  20  away from the dies. The pour hole  22  is located at an upper portion of the shot sleeve  20 , so as to allow molten metal to be poured into the shot sleeve  20 . The molten metal is poured into the shot sleeve  20  when the injection piston  23  assumes its retrenched position. 
     In  FIG. 2  there is shown a conventional shot sleeve  20  showing the injection piston  23  having a plunger tip  26  and a shot rod  24  at a withdrawn position. In  FIG. 2  the injection piston  23  is awaiting input of a molten metal, such as aluminum, to be placed into the shot sleeve  20  through pour hole  22 . As the injection piston  23  is pushed toward the die there is a tight space  25  between the periphery of the plunger tip  26  and the inside of the shot sleeve  20 . This space  25  varies depending upon the inside diameter of the shot sleeve  20  and the outside diameter of the plunger tip  26  but is generally on the order of 0.03 to 0.06 mm. This tight clearance causes excessive wear due to poor lubrication. 
     [Description of Back Spray System] 
     The lubrication problem has been overcome by the back spray system of the present invention one embodiment of which is shown in  FIGS. 3 and 4  and comprises an injection piston  23 . The injection piston  23  of the back spray system comprises a shot rod  24  having a collar  30  at the forward end. Note that the back spray system is similar in configuration to such conventional die casting machines as illustrated in  FIGS. 1 and 2 , except for the configuration of the injection piston  23 . 
     Inside shot sleeve  20  the back spray system will apply lubricant to the inner periphery of the shot sleeve  20  so that as the plunger tip  26  is pushed into and out of the shot sleeve  20  the lubricant coats the entire area. Any of the conventional lubricating oils may be used as the lubricant. To get the lubricant to the proper place a shot rod hole  32  is drilled the length of the shot rod  24  to right behind the forward end of the shot rod  24 . The size of the shot rod hole  32  will vary depending upon the size of the shot sleeve  20  and injection piston  23  and to an extent the lubricant used. Typically the shot rod hole  32  is from approximately 6.5 mm to about 19.05 mm (about ¼ to ¾ inch) in diameter. The lubricant is supplied under pressure to the rear end of the shot rod  24  through equipment known to those skilled in the art. 
     The plunger tip  26  is connected, such as a screw connection, by threads  34  to the end of shot rod  24 . Behind the plunger tip  26  is a recessed groove  36 . In the examples of  FIGS. 3 and 4 , the shot rod  24  has a tip having a reduced diameter, and such a reduced diameter part is provided with a groove  36 . Note, however, that the shot rod  24  does not necessarily need to have the reduced diameter part and the groove  36  also does not necessarily need to be provided in the reduced diameter part. The collar  30  covers the groove  36 , as shown in  FIGS. 3 and 4 . Then, the groove  36  and an inner wall surface of the collar  30  constitute a channel. As shown in the embodiment of  FIG. 5 , which is a cross-sectional view taken along line A-A of  FIG. 4 , in the groove  36  there are two groove holes  38  spaced 180° apart that connect to the shot rod hole  32 . The groove holes  38  are through holes connecting the surface of the shot rod  24  and the shot rod hole  32 . These groove holes  38  pass lubricant from the shot rod hole  32  to collar holes  40 . It should be understood that the number of groove holes  38  may vary but typically these groove holes  38  can be from approximately 6.5 mm to about 19.05 mm (¼ to ¾ inch) in diameter but do not have to be the same size as the shot rod hole  32  and typically each is smaller in diameter so that the amount of lubricant/air mixture in the shot rod hole  32  is equal to the amount of lubricant/air mixture in groove holes  38 . 
     In the embodiment shown in  FIG. 4 , the collar  30  is seated over recessed groove  36 . The collar  30  has a tubular structure and has an outside diameter that is smaller than a diameter of the plunger tip  26  and larger than a diameter of the shot rod  24  around the groove  36 . In order to allow lubricant to get to an inner deep part of the shot sleeve  20 , the collar  30  is preferably provided as close as possible to the plunger tip  26  (for example, at a location behind the plunger tip  26  and as close as possible to the plunger tip  26 ). The collar  30  may be fixed in place, such as by inserting the collar  30  over the portions forming recessed groove  36  to form a tight fit. The collar  30  may be removable from the groove  36 . The collar  30  that has been removed from the groove  36  as shown in  FIG. 3  facilitates cleaning of the inside of the groove  36  and the groove holes  38 . The groove  36  may be formed in a variety of ways. For example, it may be formed by providing two ring-shaped members on the surface of the shot rod  24  or it may be formed as part of the shot rod  24  (for example, formed by shaving the surface of the shot rod  24 ). Collar  30  has a plurality of holes (collar holes)  40  drilled symmetrically around the collar  30 . The collar holes  40  are through holes connecting the outer periphery and the inner periphery of the collar  30 . The number of collar holes  40  depends on the circumference of the shot rod  24 . These holes are preferably from about 1.81 mm to about 6.5 mm ( 1/14 inch to ¼ inch) in diameter. The collar holes  40  are typically smaller than the groove holes  38  so that the amount of lubricant/air mixture in the groove holes  38  is equal to the amount of lubricant to air in collar holes  40 . The collar holes  40  are preferably countersunk to help the radial effect of the lubricant when being supplied to the shot sleeve  20 . 
     As is clear from  FIGS. 4 and 5 , lubricant supplied from an end (an end to which no plunger tip  26  is connected) of the shot rod hole  32  is passed through shot rod hole  32  into groove holes  38  under the collar  30 , then the lubricant (which is mixed with air) travels into groove  36 , finally coming out of the collar holes  40 . This design allows maximum coverage with minimum volume of the lubricant. The back spray system also allows the lubricant to get to the furthest point in shot sleeve  20  and have the lubricant be right behind the plunger tip  26 . When the plunger tip  26  is pulled backward in the shot sleeve  20  for the length of the shot sleeve  20  uniform lubricant coverage is provided from the dies to the shot pour location with the ability to add extra lubricant at any location as needed. While the shot rod  24  retracts the lubricant/air mixture will be pushed down from the shot rod hole  32  in the shot rod  24  to the groove holes  38  in the channel behind the collar  30 , then the lubricant/air mixture is pushed out the collar holes  40  in an atomized fashion to make a radial spray to cover the shot sleeve  20  with the lubricant as the shot rod  24  fully retracts. 
     EXAMPLES 
     In an example of practicing this invention, a shot rod  24  was drilled with one 7.94 mm ( 5/16 inch) diameter shot rod hole  32  the length of the shot rod  24  to push a lubricant/air mixture to a channel with two 7.94 mm ( 5/16 inch) gun drilled groove holes  38  in a channel covered by the collar  30  that has eight (8) collar holes  40  drilled to disperse the lubricant/air mixture. The lubricant/air mixture was pressurized in the shot rod  24  inside the shot rod hole  32  then pushed into the groove  36  behind the collar  30 , then pushed out of the eight collar holes  40  under pressure as the shot rod  24  retracts the length of the shot sleeve  20 . The lubricant/air mixture was pressurized through the shot rod hole  32  to efficiently atomize lubricant, while the shot rod  24  was pulled back, the atomized spray delivered the lubricant the length of the shot sleeve  20  and draw. 
     In a conventional example the amount of lubricant/air mixture spraying down the porthole was 2 to 2.5 ml per shot. After the back spray system of this invention was installed the usage dropped to 0.75-1.0 ml per shot. During a two month time period there were 11 plunger tip  26  changes with the conventional method of spraying down the porthole and 4 plunger tip  26  changes with the back spray system. Shot sleeve  20  life was also improved. Decreased consumption of lubricant was obtained as well as extended plunger tip  26  and shot sleeve  20  life. Decreased porosity of die cast parts was also observed. 
     Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 
     CROSS REFERENCE TO RELATED APPLICATION 
     The contents of Provisional Application U.S. Ser. No. 62/703,564 filed Jul. 26, 2018, on which the present application is based and benefit claimed under 35 U.S.C. § 119(e), in incorporated by reference. 
     REFERENCE SIGNS LIST 
     
         
           20  Shot sleeve 
           23  Injection piston 
           24  Shot rod 
           26  Plunger tip 
           30  Collar 
           32  Shot rod hole 
           36  Groove 
           38  Groove hole 
           40  Collar hole