Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D19/00—Casting in, on, or around objects which form part of the product
  • B22D19/04—Casting in, on, or around objects which form part of the product for joining parts
  • B22D19/045—Casting in, on, or around objects which form part of the product for joining parts for joining tubes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C7/00—Patterns; Manufacture thereof so far as not provided for in other classes
  • B22C7/02—Lost patterns
  • B22C7/023—Patterns made from expanded plastic materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C7/00—Patterns; Manufacture thereof so far as not provided for in other classes
  • B22C7/02—Lost patterns
  • B22C7/023—Patterns made from expanded plastic materials
  • B22C7/026—Patterns made from expanded plastic materials by assembling preformed parts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/02—Sand moulds or like moulds for shaped castings
  • B22C9/04—Use of lost patterns
  • B22C9/046—Use of patterns which are eliminated by the liquid metal in the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D19/00—Casting in, on, or around objects which form part of the product
  • B22D19/0009—Cylinders, pistons

Definitions

• the object .of the present invention is a casting method, in particular for obtaining an engine cylinder head. More in particular, the invention relates to a casting technology known as "lost foam" .
• this technology provides for the manufacture of a 'model of the part to be obtained by casting, made of a material , such as polystyrene, adapted for dissolving, for example by evaporation, in contact with the molten metal .
• a material such as polystyrene
• the model is coated and laid with the pouring gate in a container filled with sand and adapted for receiving the molten metal , which exactly replaces the material forming the model , and solidifies as it cools down.
• Engine cylinder heads have already been manufactured using this technology.
• An example of use of the lost foam technology to manufacture a cylinder head is described, for example, in document US 5 449 033.
• valve seats are made of steel or of composite or ceramic material , during the driving they can easily undergo breakage and make the completed cylinder head mechanical processing casting to be discarded. Moreover, in order to obtain an optimum heat exchange between the valve seat and the casting body, the valve seats should have the least inner/outer diameter ratio (ring thickness) and a maximum height . However, this contradicts the object of having a high shaft/seat interference to have a good driving as the valve seat thus shaped would be fragile in said step and therefore subject to easy breakage .
• the operation for inserting the valve seats requires the casting thickness in the combustion chamber cap to be larger than what needed so as to not damage the combustion chamber in the driving step .
• the same concept applies to valve guides, where for the same reason, the containment bosses are normally oversized. In fact , this operation may cause cracking in the cylinder head casting due to the press force, which has sufficient power to overcome the interference existing between the diameter of the machined seats on the casting and the diameter of the valve seats and of the valve guides . Such increase of thickness of the casting is to the detriment of the cooling fluid flow section.
• Another typical disadvantage of the lost foam technology is that the finish of the inner surface of the intake and discharge ducts of the molten part is substantially defined by the quality of the material forming the model . Since this is usually made of a foamed material , such as polystyrene, even though it is suitably coated to oppose the inside and outside thrust of sand, the inner surface of the ducts always appears quite rough and with some flaws . Such anomalies will be reproduced on the molten part, thus interfering with the mixture flow towards the combustion chambers and the outwards flow of exhaust gases . Further flaws arise from the fact that the model has to be divided into sectors that are then glued in order to obtain the inside of the ducts . The connection of the sectors and the necessary adhesive could cause deformities and blowholes to the casting. [0009] .
• the object of the present invention is to propose a casting method, in particular for an engine cylinder head, which allows remedying the disadvantages mentioned above .
• FIG. 1 shows a section view of a model of foamed material with pouring gate of a cylinder head of an engine, immersed in the filling sand before casting the molten metal , with the valve seats incorporated and the valve guides inserted;
• FIG. 2 shows an alternative embodiment of the model of figure 1, where the intake and exhaust ducts of the cylinder head are coated with tubular inserts incorporated in the model ;
• FIG. 3 shows an enlarged detail of the model of figure 2 ;
• FIG. 4 shows a partly axial sectioned view of a valve seat; [0016] . - figure 4a shows a top plan view of the valve;
• FIG. 5 shows a section view of a die for manufacturing a first sector of foamed material of the model of figure 1 or 2 with the valve seat incorporated therein;
• FIG. 6 shows a section view of a die for manufacturing a second sector in two parts of the model of figure 1 ;
• . - figure 7 shows a section view of a die for manufacturing a third sector of the model of figure 1 ;
• . - figure 8 shows a section view of a die for manufacturing a second sector of the model with tubular inserts incorporated therein of figure 2 ;
• . - figure 9 shows a section view of a die for manufacturing a further sector for the model of figure 1 or 2 ;
• figure 10 shows a cutaway view of a second example of model of foamed material for an engine cylinder head, equivalent to figure 1 ;
• FIG. 11 shows a view similar to the previous one and equivalent to figure 2 , wherein the model incorporates tubular inserts for coating the intake and discharge ducts .
• the present invention relates to a casting method of an engine cylinder head using the technology known as "lost foam" ..
• This technology provides for the manufacture of a model of the part to be obtained by casting, made of a material adapted for dissolving, for example by evaporation, in contact with the molten metal .
• the model is made of a foamed material , such as polystyrene .
• foamed material such as polystyrene
• the model with the pouring gate associated to it is coated and laid in a container adapted for being filled with sand or other material resistant to the heat generated by the molten metal .
• the sand is made - for example by vibrating the container - to fill any recess or hole in the model of foamed material .
• the molten metal is cast in the container .
• the molten metal exactly replaces the foamed material and, once cooled, it solidifies .
• the sand, along with the coat are removed from the metal casting thus obtained.
• the casting method of the present invention provides for the incorporation, in the model of foamed material , of at least one insert made of a material resistant, that is , inert, to contact with molten metal , so that said insert is embedded in proper position into the casting when the molten metal replaces the foamed material .
• incorporation into the model means both a complete burying in the foamed material forming the model, and a partial incorporation, that is, an insertion or embedding of only a part on the insert in the foamed material, while another part protrudes from the model .
• incorporation of an insert into the model means both an embedding of the insert into the model as the latter is manufactured, as for example is the case for valve seats as it will be described hereinafter, and an insertion of part or all the insert into a special seat into the model , after the manufacture of the latter, as for example is the case for valve guides .
• incorporation of an insert into the model means both an embedding of the insert into the model as the latter is manufactured, as for example is the case for valve seats as it will be described hereinafter, and an insertion of part or all the insert into a special seat into the model , after the manufacture of the latter, as for example is the case for valve guides .
• the choice of incorporating an insert into the model at the same time as or after the manufacture of the latter, may depend for example on reasons related to the manufacture technology of the model itself . For example, if the model is obtained by pressing, an insert having a certain inclination relative to the die shakeout direction, such as for example the valve guides , cannot be incorporated in the model during the pressing step and must be inserted afterwards .
• the model of foamed material also serves as support and handling element for at least one insert during the various steps of the casting method, up to the casting of the molten metal .
• the insert is arranged in the same position it must take when it is incorporated in the casting.
• Material resistant or inert to the contact with the molten metal means a material that does not substantially change in shape at the temperature of the molten material , or that does not undergo phase transitions or variations in its molecular structure at such temperature .
• the insert is made of a metallic material, such as a pure compound or an alloy, its casting temperature must be higher than that of the cast metal .
• said insert is a valve seat 2 for an intake or exhaust valve .
• said insert is a valve guide 10 for an intake or exhaust valve .
• said insert is a tubular element 7 , 8 for coating the intake 30 and/or exhaust 31 ducts .
• the model of foamed material is obtained by pressing.
• the model cannot be obtained by pressing in a single piece, but it consists of a plurality of portions , or sectors, as it will be defined in the following description, each obtained in a special die and then glued to one another to form the model .
• the model once moulded, the model exhibits a layered structure, that is, consisting of a plurality of layers, or "slices" , glued to one another .
• the cylinder head model is completed by an upper part 11 and by pouring gates 12 and 12 ' which, not being directly involved in the method of the invention, are not described in detail and are only partly shown in the drawings .
• the method provides for obtaining the foamed sectors 1 in a specific die 20 ( Figure 5) .
• Such die exhibits special references 16 to arrange, prior to the injection of the foamed material, the valve seats 2 for the intake and discharge valves . Seats 2 will then be incorporated in the foamed material and then constrained to the lower sector 1.
• the valve seats 2 and the valve guides 10 are indicated with a single reference number but, even though they are structurally identical, they usually differ from one another in their dimensions .
• valve seats 2 and die 20 must be specifically shaped.
• valve seats 2 ( Figures 3 , 4 , 4a) present an annular structure that develops around an axis x which, with valve mounted on, is inclined by a certain angle ⁇ relative to the vertical axis Y of the engine head as shown in the drawings .
• the valve seats 2 are made, for example, of metal or ceramic material or of sintered material .
• each valve seat 2 exhibits an inner side surface comprising two annular portions having taper opposed to one another. A first lower portion 14 narrows from bottom upwards; the second upper portion 15 widens upwards .
• the lower conical surface 14 is adapted for settling on a first reference boss with truncated cone shape 16 that extends from one of the parts forming die 20 ( Figure 5) .
• a second part of die 20 adapted for closing on the first one, exhibits a second boss with truncated cone shape 15 ' adapted for settling on the upper conical surface 15 of the valve seat 2 , locking it into position.
• Truncated cone boss means a circular-section projection that extends on a bottom surface and that preferably exhibits a mean diameter considerably larger than its height .
• the upper conical surface 15 is also adapted for receiving the lower end 7" and 8" of the tubular elements 7 and 8 coating the intake 30 and exhaust 31 ducts , when provided ( Figures 2 , 8 , 11) .
• said surface 15 will exhibit a smaller diameter, and therefore adjacent to the lower conical surface 14 , thus forming mechanical machining allowance of the valve seat 2.
• each of the two conical portions 14 , 15 extends by half the height of the valve seat 2.
• the taper of the upper annular portion 15 is equal too or larger than angle ⁇ between axis X of the engine valves and vertical axis Y.
• each valve seat 2 exhibits a substantially cylindrical outer side surface 17.
• At least one annular projection 18 extends from said outer surface 17, defining an undercut adapted for serving as axial locking means of the valve seat 2 to the foamed material , when the latter has polymerised and afterwards, to the casting metal when the latter has solidified.
• At least one longitudinal groove 19 serving as anti-rotation means for seat 2 is obtained in said annular projection 18.
• the two sectors 3 and 4 that define the bottom part of the intake and exhaust ducts are obtained with a single die 21 which forms the two parts (figure 6) .
• the sector 5 that defines the top part of the ducts is obtained with a die 22 (figure 7) .
• said die 22 is provided with mobile pins 23 , each adapted for obtaining a lower seat 10 ' in sector 5 , wherein the lower end of a valve guide 10 is afterwards introduced.
• the upper sector 9 is obtained with a special die 25. According to the invention, also this die is provided with mobile pins 26 , each adapted for obtaining an upper seat 10" , coaxial to the lower seat 10 ' , in sector 9 , wherein the lower end of a valve guide 10 is afterwards introduced.
• valve guides 10 are introduced, for example prior to the model coating, in the special seats 10 ' and 10" .
• the cylinder head model is complete and ready for the optional coating.
• valve guides 10 exhibit a plurality of circular grooves 35 and of longitudinal slots 36 adapted for ensuring higher stability in the casting, preventing any rotations or vertical movements of the valve guides when the molten metal of the cylinder head fully incorporates them on the diameter and when the contraction of said molten metal caused by the shrinkage after the solidification is complete .
• the casting method according to the invention provides for the incorporation of tubular elements 7 and 8 coating the intake 30 and exhaust 31 ducts in the cylinder head model . [0063] .
• the method relating to this alternative embodiment differs from what described above with reference to a cylinder head without tubular elements 7 and 8 only in that a single sector 6 obtained in a die 24 may be used in place of the foamed material sectors 3 , 4 and 5 and of the relevant dies 21 and 22 (figure 8) .
• the presence of the tubular elements 7 and 8 allows joining sectors 3 , 4 and 5 in a single sector 6 enclosing said tubular elements 7 and 8.
• tubular elements 7 and 8 are laid in die 24.
• die 24 exhibits side seats 7' , 8 ' and lower conical seats 7a, 8a suitable for serving as guiding means for proper positioning of elements 7 and 8.
• die 24 is provided with mobile pins 23 ' adapted for obtaining the lower seats 10 ' in sector 6 for the passage of the valve guides 10.
• the tubular elements 7 and 8 have respective holes 32 , 33 obtained in the upper side surface for allowing the passage and positioning of the lower ends of the intake and exhaust valve guides 10.
• the mobile pins 23 ' partly enter into the tubular elements 7 and 8 passing through said holes 32 , 33 , so as to prevent the foamed material from entering into elements 7 and 8 while concurring to their centring in die 24.
• valve seat 2 in the presence of at least one of the tubular elements 7, 8 , the corresponding valve seat 2 will have an upper conical annular portion 15 with larger diameter than the lower one, substantially by an amount equal to twice the thickness of said tubular elements, for defining a support step for the lower end of said elements .
• the valve seats 2 also serve as guiding means cooperating with the tubular elements 7, 8 for proper centring of sector 6 on sector 1.
• the foamed material model fitted with the inserts is coated by dipping. After drying, the model is fully coated with a compact coating film having suitable thickness for standing the vibrations for the settling of the filling sand 13 and afterwards, the metallostatic pressure .
• the coating also covers the visible (exposed) portions of the valve seats 2 , of the ends of the valve guides 10 and also the ends and the inner portion of the tubular elements 7 and 8 , if provided. Since the coating is compact, along with the packed sand, it has the further function of keeping valve seats, valve guides and tubular elements for the intake and exhaust ducts into position, preventing any collapsing of said parts during the casting step .

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Cylinder Crankcases Of Internal Combustion Engines (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Compressor (AREA)
• Reciprocating, Oscillating Or Vibrating Motors (AREA)

Applications Claiming Priority (1)

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• 2005
  • 2005-01-14 WO PCT/IT2005/000017 patent/WO2006075344A2/en not_active Ceased
  • 2005-01-14 DE DE602005014571T patent/DE602005014571D1/de not_active Expired - Fee Related
  • 2005-01-14 EP EP05709181A patent/EP1836014B1/de not_active Expired - Lifetime
  • 2005-01-14 AT AT05709181T patent/ATE431766T1/de not_active IP Right Cessation

Non-Patent Citations (1)

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