EP2796226A1 - Kolben mit optimaler Kühlwirkung für Kaltkammerdruckgusssysteme - Google Patents

Kolben mit optimaler Kühlwirkung für Kaltkammerdruckgusssysteme Download PDF

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Publication number
EP2796226A1
EP2796226A1 EP20140468003 EP14468003A EP2796226A1 EP 2796226 A1 EP2796226 A1 EP 2796226A1 EP 20140468003 EP20140468003 EP 20140468003 EP 14468003 A EP14468003 A EP 14468003A EP 2796226 A1 EP2796226 A1 EP 2796226A1
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EP
European Patent Office
Prior art keywords
piston
fluid
cooling
passageway
piston body
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20140468003
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English (en)
French (fr)
Inventor
Bostjan Taljat
Gregor Hali
Matjaz Meglic
Ales Brili
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HTS IC D.O.O.
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HTS IC d o o
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Publication date
Application filed by HTS IC d o o filed Critical HTS IC d o o
Publication of EP2796226A1 publication Critical patent/EP2796226A1/de
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B22D17/20—Accessories: Details
    • B22D17/2015—Means for forcing the molten metal into the die
    • B22D17/203—Injection pistons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B22D17/20—Accessories: Details
    • B22D17/2015—Means for forcing the molten metal into the die
    • B22D17/2038—Heating, cooling or lubricating the injection unit

Definitions

  • a casting piston disclosed in this invention can be utilized in any die-casting or industrial application other than die-casting, including but not limited to cold-chamber pressure die-casting of aluminum or magnesium alloys. Although there are numerous possibilities for application of the piston subject to this invention, explanation in the present work is primarily based on examples in cold-chamber pressure die-casting process.
  • molten metal is poured into a shot sleeve and from there pushed by the casting piston mounted on a shot rod into a die, where molten metal is solidified to form a cast part of desired geometry.
  • Molten metal in this case refers in particular to, but it is not limited to molten aluminum or magnesium, both having relatively high processing temperatures. Further description of die-casting process and specific technical terms defining different components of casting systems shall not be provided in this exhibit, as these can be found elsewhere.
  • Components of casting system in direct contact with molten metal are subjected to extreme thermal loading.
  • the piston pushes molten metal to the die and provides sufficient pressure to molten metal to fill the die and solidify with no porosity defects.
  • the piston in particular its front surface, is exposed to both extreme thermal and mechanical loading. The first is due to direct piston contact with molten metal, whereas the later is due to high pressure exerted to the piston front surface at final stages of casting cycle.
  • Optimum cooling of the piston is critical in assuring best quality of cast part and improving production performance.
  • Cooling intensity is a parameter dependent on a series of controllable, say independent variables. It is simply determined by heat capacity rate of cooling fluid (CF) multiplied by difference in CF inflow and outflow temperature. Heat capacity rate of CF is calculated by multiplying its mass flow rate and its specific heat. The specific heat is defined by selection of CF, whereas both the mass flow rate and the inflow temperature are defined by setup of CF control unit.
  • the CF outflow temperature is directly influenced by cooling effectiveness of the piston, which can also be understood as a piston design and material parameter. This also means that cooling intensity of the piston is determined by the piston cooling effectiveness, heat capacity rate of CF and the inflow temperature. It must be, on the other hand, equal to heat energy passing from molten metal (MM) to CF in a given time.
  • Cooling effectiveness of the piston is thus its ability to transfer heat energy from MM to CF. It directly depends on the piston design and materials utilized. It may be expressed as a ratio between the actual transfer of heat energy and the maximum possible transfer of heat energy from MM to CF, both at given CF inflow temperature and flow parameters.
  • the heat transfer from MM to CF is determined by: (i) difference in temperature between the piston front surface and MM, surface area of the piston front, and the corresponding heat transfer coefficient, (ii) difference in temperature between the piston front and the surface a cooling channel inside the piston, the corresponding distance, and coefficient of thermal conductivity (CTC) of the piston material, and (iii) difference in temperature between the cooling channel wall and CF, surface area of the cooling channel, and the corresponding heat transfer coefficient (CHT).
  • the piston cooling effectiveness can be improved by finding new solutions in the piston design primarily influenced by the following independent parameters: (i) surface area of the cooling channels, (ii) distance between the piston front and the cooling channel surface, (iii) CTC, and (iv) CHT.
  • CTC directly depends on selection of the piston-front material
  • CHT depends on surface quality of the cooling channel.
  • the other two parameters, surface area of the cooling channel, and distance between the piston front and the cooling channel surface, are directly influenced by the piston design.
  • Intense cooling that can be reached by the pistons with highest cooling effectiveness assists to shorten production cycle time and improve productivity. However, it may also result in premature solidification of casting metal before entering the die, which may also result in negative impact on casting performance and the cast-part quality. Therefore, it is decisive to optimize cooling of the piston throughout the casting cycle.
  • Optimum cooling conditions of the piston normally require: (i) minimum cooling intensity in the pour and shot phase to keep MM at correct temperature and prevent its premature solidification; (ii) maximum cooling intensity in the pressurization phase to assist: (i) solidification of MM in shortest possible time, thus improve productivity, and (ii) the piston front-wall strength by lowering its temperature.
  • Die casting industry is generally using standard-type pistons that are simple single-part pistons, usually made of copper based alloys, with internal cooling (see Figure 6 ).
  • An important development in the piston cooling intensity is achieved by Allper (US 8.136.574 B2 ) by increasing the piston internal surface area in contact with coolant in their multi-part piston.
  • a step further is made by Brondolin (US 2012/0031580 A1 ) with generally the same multi-part piston. They improved cooling of the side piston walls by increasing surface area of direct coolant contact with the main piston body, which improved the piston cooling effectiveness.
  • a general idea of making a cooling circuit built into a part of piston is presented in US2012/199305 .
  • the gap between the piston and the shot sleeve can be sealed by different technical solutions. Allper presented an invention of a sealing ring and demonstrated its advantages. Design allows MM to flow and freeze in the gap between the piston and the sealing ring, thus improving sealing effectiveness (see US 5.233.913 ). There are several versions dealing with technical details on fixing the ring to the piston body, preventing its rotation relative to the piston body, and design variations of grooves that get MM to the gap between the piston and the sealing ring (see US 7.900.552 B2 and US 2012/0024149 A1 ).
  • Multi-part casting pistons present a step forward in cooling effectiveness with respect to standard-type pistons. Nevertheless, there is room for improvement in the piston performance. Important design and technical advancements are required to reach its optimum thermal and general functional performance. Following are preferred technical provisions to obtain a casting piston with optimum performance:
  • a single-element die-casting piston with integrated cooling system is presented in this invention.
  • Single-element in this invention refers to the piston body.
  • the piston may contain one or more sealing rings, which are either permanently bonded to the piston body or manufactured as replaceable parts.
  • the invention described in detail in the following text provides solution to above defined technical provisions.
  • Figure 1 to 7 show the novel piston design and explain the invention.
  • Figure 1 shows a die-casting piston and a shot rod assembly indicating an integrated system of cooling channels and the coolant path.
  • the die casting piston (1) is a single-element cylindrical object with the front surface (2) in contact with molten cast metal (MM), the cylindrical side surface (3) in contact with the shot sleeve (4), and the central hole used to attach the piston to the shot rod (5).
  • the piston has the coolant inlet (6), the integrated cooling system (7) and the coolant outlet (8).
  • the piston may also have a sealing ring (9) that assist sliding contact between the piston and the shot sleeve and effectively seals the gap between the piston and the shot sleeve from entering MM.
  • the piston is attached to the shot rod by thread or other type of known fixture (10) (a possible example is a bayonet type fixture).
  • the piston and the shot rod assembly described in Figure 1 is generally a well-known setup widely used in casting industry.
  • the shot rod has an internal passage or central hole (11) used to transfer coolant to and from the piston.
  • the coolant transfer can be accomplished in different ways.
  • One example is installation of two separate tubes built into this central passage, one for coolant inflow to the piston and the other for coolant outflow.
  • Figure 1 shows a widely used system of a single tube (12) built-in into the central passage. This central tube is of smaller diameter than the central passage and used for coolant inflow (13), which is in communication with the coolant inlet in the piston centerline (6), whereas the passage between the shot-rod inner and the central tube serves for coolant outflow (14), and is in communication with the coolant outlet from the piston (8).
  • Coolant inflow from the shot rod inflow-tube to the integrated cooling system can be positioned as shown in Figure 1 . Position of the coolant inlet to ICS is not particularly limited by this invention. ICS can be of any feasible geometry. Some examples are presented in Figure 2; (a) spiral, (b) series of connected concentric circles, (c) radial, or (d) any other cooling system geometry down to a random design cooling network. Cooling of the piston front surface may continue to the piston side surface in similar patterns.
  • Figure 3 shows some possibilities of cooling system built into the side wall: (a) helical, (b) series of connected circles, (c) linear channels distributed around the circumference, or (d) any other cooling system geometry down to a random design cooling network.
  • the coolant outlet is positioned depending on geometric features of ICS in communication with coolant outflow passage in shot rod.
  • ICS design allows any feasible cooling channel cross-section geometry, which directly influences surface area of the cooling system.
  • Figure 4 shows some possibilities, from (a) circle, (b) square, (c) rectangular, and (d) an example of particular geometry cross-section. For example, same characteristic dimension of the cooling channel gives in case (d) for about 35% more surface area compared to case (c).
  • FIG. 5 shows two parts with the pre-machined cooling system.
  • the cooling system is machined by standard machining techniques to either surface of the piston inner part (15) or the piston outer part (16), or possibly to the both surfaces. These two parts are then assembled and fused into the single-part piston with ICS. Side where machining of the cooling channels is performed is selected solely based on machining preferences, as it does not influence the piston thermal behavior, as long as the material for inner and outer part have same thermal properties.
  • the claimed invention is not limited to this particular manufacturing technology. Other manufacturing technologies, such as casting, metal printing, certain welding technologies or other technology may be used to obtain the results subject to this invention.
  • the cooling system subject to this invention can be made of any chosen pattern, cross-section geometry, and at any chosen distance from the piston front surface or the piston side surface, as long as stresses in the piston induced by thermal and mechanical loading throughout the transient are not compromising its structural integrity.
  • ICS can be characterized by three main parameters (see Figure 1 ): A c represents the surface area of cooling system, h represents distance from the piston front and/or the piston side to the cooling channel, and ⁇ represents heat conductivity coefficient of the piston front and/or the piston side material.
  • Parameter A f represents surface area of the piston front that is in contact with MM, thus heated surface subject to cooling.
  • the piston may also be receiving heat from the side surface in contact with the shot sleeve, which generally depends on temperature of the shot sleeve inner surface.
  • Figure 6 shows two pistons representing limiting thermal-behavior cases.
  • the piston with highest feasible cooling effectiveness, MCD can be manufactured by bringing the cooling channels as close as possible to its front surface, h 1 , for the piston-front utilize material with highest possible thermal conductivity, ⁇ 1 , and design the cooling channels with largest surface area possible, A c1 >> A f1 (see Fig.6(a) ).
  • the two limiting cases: (i) the new ICS piston and high cooling effectiveness, and (ii) the standard type piston, have significantly different thermal behavior with important influence to function of casting system.
  • Figure 7 shows temperature at the centerline underneath the piston front surface, T, normalized by temperature of MM, T MM , presented as a function of time, t, throughout one casting cycle, t c , for: (a) standard-type piston made of material with higher thermal conductivity, such as copper; (b) standard-type piston made of material with lower thermal conductivity, such as steel; (c) an ICS piston with a moderate surface area of cooling system, A c , and front surface made of copper, and (d) the same piston as in case (c) with front surface made of steel.
  • Significance of this invention is that selection of particular combination of the three parameters directly determines thermal response as spatial and/or transient function, and thus consents to directly perform piston thermal optimization.
  • the three parameters are independent, with particular influence to system thermal response: A c directly influences cooling intensity, whereas h and ⁇ influence both cooling intensity and the temperature response time. The later depends on heat capacity (mass and specific heat) of the piston material between ICS and MM. Therefore h and ⁇ can be utilized for optimization of cooling effectiveness as function of time. Design of the cooling channels can also be made so that spatial optimization of cooling is achieved.
  • Significance of this invention is also in highest flexibility of ICS design and thus ability for optimization of the cooling system for any casting application with minimum or no influence to manufacturing costs.
  • the ICS piston shall be designed and manufactured by principles of optimum thermal regulation.
  • the design for optimum ICS setup is based on performed computational modeling analysis considering main casting parameters.
  • the piston shall be considered a heat exchanger that exports the heat from MM to CF.
  • Term "cooling” used in this disclosure means that MM is cooled by CF.
  • thermal regulation and “fluid”, respectively, generalizes the relevance of this disclosure.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Pistons, Piston Rings, And Cylinders (AREA)
EP20140468003 2013-04-24 2014-04-24 Kolben mit optimaler Kühlwirkung für Kaltkammerdruckgusssysteme Withdrawn EP2796226A1 (de)

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SI201300101A SI24339A (sl) 2013-04-24 2013-04-24 Bat z optimalno hladilno efektivnostjo za hladno-komorne tlačno-livne sisteme

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3170580A1 (de) * 2015-11-23 2017-05-24 United Technologies Corporation Stark gekühlter druckgiesskolben
US10166601B2 (en) 2015-11-17 2019-01-01 United Technologies Corporation Die cast tip cover and method of managing radial deflection of die cast tip

Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3323328C1 (de) * 1983-06-29 1984-05-03 Mahle Gmbh, 7000 Stuttgart Einteiliger flüssigkeitsgekühlter Gießkolben
US4886107A (en) * 1986-02-28 1989-12-12 Zecman Kenneth P Piston for cold chamber
DE3934778A1 (de) * 1988-12-28 1990-07-05 Allper Ag Kolben, insbesondere fuer eine druckgusspresse
US5233913A (en) 1992-08-31 1993-08-10 General Motors Corporation Swash plate compressor with spring thrust bearing assembly
DE4230080A1 (de) * 1992-09-09 1994-03-10 Hugo Kunz Druckgießkolben, insbesondere für Kaltkammer-Druckgießmaschinen
DE202010008596U1 (de) * 2010-09-21 2010-12-02 Schmelzmetall (Deutschland) Gmbh Druckgusskolben
US7900552B2 (en) 2006-04-12 2011-03-08 Copromec S.R.L. Piston for cold chamber die-casting machine
WO2011035765A1 (de) * 2009-09-22 2011-03-31 Ksm Casting Gmbh Vakuumdruckgussanlage und verfahren zum betrieb einer vakuumdruckgussanlage
US20120024149A1 (en) 2009-01-21 2012-02-02 Brondolin S.P.A. Die casting piston and ring assembly
US20120031580A1 (en) 2009-01-21 2012-02-09 Brondolin S.P.A. Die casting cooled pistons
US8136574B2 (en) 2005-10-12 2012-03-20 Allper Ag Multi-piece piston for a cold chamber casting machine
EP2468994A2 (de) * 2010-12-22 2012-06-27 Sommer Antriebs- und Funktechnik GmbH Kipptor
US20120199305A1 (en) 2011-02-09 2012-08-09 Bochiechio Mario P Shot tube plunger for a die casting system

Patent Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3323328C1 (de) * 1983-06-29 1984-05-03 Mahle Gmbh, 7000 Stuttgart Einteiliger flüssigkeitsgekühlter Gießkolben
US4886107A (en) * 1986-02-28 1989-12-12 Zecman Kenneth P Piston for cold chamber
DE3934778A1 (de) * 1988-12-28 1990-07-05 Allper Ag Kolben, insbesondere fuer eine druckgusspresse
US5233913A (en) 1992-08-31 1993-08-10 General Motors Corporation Swash plate compressor with spring thrust bearing assembly
DE4230080A1 (de) * 1992-09-09 1994-03-10 Hugo Kunz Druckgießkolben, insbesondere für Kaltkammer-Druckgießmaschinen
US8136574B2 (en) 2005-10-12 2012-03-20 Allper Ag Multi-piece piston for a cold chamber casting machine
US7900552B2 (en) 2006-04-12 2011-03-08 Copromec S.R.L. Piston for cold chamber die-casting machine
US20120024149A1 (en) 2009-01-21 2012-02-02 Brondolin S.P.A. Die casting piston and ring assembly
US20120031580A1 (en) 2009-01-21 2012-02-09 Brondolin S.P.A. Die casting cooled pistons
WO2011035765A1 (de) * 2009-09-22 2011-03-31 Ksm Casting Gmbh Vakuumdruckgussanlage und verfahren zum betrieb einer vakuumdruckgussanlage
DE202010008596U1 (de) * 2010-09-21 2010-12-02 Schmelzmetall (Deutschland) Gmbh Druckgusskolben
EP2468994A2 (de) * 2010-12-22 2012-06-27 Sommer Antriebs- und Funktechnik GmbH Kipptor
US20120199305A1 (en) 2011-02-09 2012-08-09 Bochiechio Mario P Shot tube plunger for a die casting system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10166601B2 (en) 2015-11-17 2019-01-01 United Technologies Corporation Die cast tip cover and method of managing radial deflection of die cast tip
EP3170580A1 (de) * 2015-11-23 2017-05-24 United Technologies Corporation Stark gekühlter druckgiesskolben

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