WO1996038246A1

WO1996038246A1 - A reciprocating piston for a liquid metal injection machine

Info

Publication number: WO1996038246A1
Application number: PCT/BR1996/000016
Authority: WO
Inventors: Wilmar Fischer
Original assignee: W. Fischer Representações Ltda.
Priority date: 1995-06-01
Filing date: 1996-04-19
Publication date: 1996-12-05
Also published as: BR9502167A

Abstract

A reciprocating piston for a liquid metal injection machine, said piston moving inside an injection cylinder (2) by actuation of the free end of an impelling rod (20) and comprising an internal chamber (17), for refrigerant fluid circulation, which is maintained in fluid communication with corresponding refrigerant fluid internal axial ducts (60, 70) in the impelling rod (20), said piston further comprising a male articulating element (30), affixed to one of the parts defined by the piston and by the free end of the articulating rod (20), and a female articulating element (40), provided at the other of said parts and receiving the male articulating element (30), in order to avoid mutual relative axial movements and to allow a relative angular movement between said parts in any direction contained in a plane orthogonal to the piston axis, sais male and female articulating elements (30, 40) being axially and internally hollow, so as to provide the fluid communication between the axial ducts of said impelling rod (20) and internal chamber (17).

Description

A RECIPROCATING PISTON FOR A LIQUID METAL INJECTION

MACHINE Field of the Invention

The present invention refers to a reciprocating piston for a liquid metal injection machine, particularly employing high viscosity liquid material, such as aluminum alloy, for casting metallic pieces. Background of the Invention The liquid metal injection machines include a reciprocating piston moving inside an injection cylinder which receives periodically, through a radial opening, a metallic alloy in liquid state and normally under high temperature which will be introduced in a mold for metallic pieces. In the case of machines for injecting aluminum or aluminum-containing alloys, the operating temperature is around 700oC (aluminum melting temperature) .

The opening for the admittance of liquid metal into the cylinder is preferably provided adjacent to a cylinder end, where the reciprocating piston is found in a resting inoperative position, therefore not actuating in the application of forces on the liquid mass which is being introduced into said cylinder. In these machines, the piston is rigidly affixed to an impelling rod which is operatively coupled to adequate piston driving means . These pistons are usually made of copper.

After introducing the aluminum into the cylinder, the piston is impelled so as to force the aluminum fluid mass towards the inside of the mold.

Several factors may cause disalignments of the impelling rod in relation to the geometrical axis of the piston axial displacement. Although being very small, such disalignments cause, due to the rigidity of the rod-piston assembly, a consequent displacement of the piston inside the cylinder. This fact is sufficient to provoke the excessive and early wear of the piston and even of the cylinder.

This wear, which impairs the fluid tightness at the cylinder portion submitted to the pressure imparted by the moving piston, occurs in function of the gaps which appear between the piston and cylinder and which are sufficient to allow the penetration of the liquid aluminum, with its corresponding viscosity, between said parts during the piston operation, increasing the wear of said parts and causing the locking of the piston and consequent destruction of the equipment. In some molding operations, the liquid mass used for injecting the metallic part comprises an aluminum composition with a certain percentage of silicon, which usually varies from 7 to 17%.

Aluminum-silicon alloys produce a fluid mass which is more abrasive as greater is the percentage of silicon in the composition of said alloy. This abrasion increases the wear between the piston and cylinder, reducing their useful life. Besides the durability of the piston and cylinder portions being directly associated to the silicon percentage, there are other factors that affect the determination of the useful life of these elements, such as the injection pressure and piston cooling.

In function of both the high injection pressure and temperature of the melted metallic alloy, during the operation of the piston, there is an increase in the piston temperature, causing its dilatation, which, due to the difference of the thermal dilatation coefficients between the cylinder and piston, will increase the wear mentioned above.

In the known injection machines, in order to reduce the heating effect resulting from the piston operation, the piston is provided with a cooling system which uses water as a refrigerant fluid, as described ahead. In this construction, the piston comprises in its inside an internal cooling chamber with an opening facing the wall portion of said piston, whereto is rigidly affixed an end of the impelling rod, which is axially and centrally trespassed by a hole, in order to receive, with a radial gap, a copper tube having an end which is opened towards the inside of the piston cooling chamber. The cooling is achieved, by introducing water inside the refrigerating tube towards the piston cooling chamber, where the water flow circulates before being lead to a duct defined by the radial gap between the external wall of the refrigerating tube and internal wall of the axial hole of the impelling rod, said water carrying the absorbed heat outwardly from the piston. Disclosure of the Invention

Thus, it is an object of the present invention to provide a reciprocating piston for a liquid metal injection machine for molding metallic pieces, whose operation is not affected by eventual disalignments of the impelling rod, allowing to reduce the wear of the piston and cylinder portions with a consequent increase of the useful life of the equipment. Another object of the present invention is to provide a piston such as described above, which maintains with the cylinder wall an interference relationship, maintained substantially constant during the useful life of the piston. These and other objectives are attained by a reciprocating piston for a liquid metal injection machine, said piston moving inside an injection cylinder by actuation of the free end of an impelling rod and having a head region provided with an internal chamber, for refrigerant fluid circulation, which is maintained in fluid communication with corresponding refrigerant fluid internal axial ducts in the impelling rod, said piston further comprising a male articulating element, affixed to one of the parts defined by the piston and by the free end of the articulating rod, and a female articulating element, provided at the other of said parts and receiving the male articulating element, in order to avoid mutual relative axial movements and to allow a relative angular movement between said parts in any direction contained in a plane orthogonal to the piston axis, said male and female articulating elements being axially and internally hollow, so as to provide the fluid communication between the axial ducts of said impelling rod and internal chamber. Brief Description of the Drawings The invention will be described below, with reference to the attached drawings, in which:

Fig. 1 shows, schematically and in a longitudinal view, a liquid material injection machine comprising a reciprocating piston according to the invention; Fig. 2 shows, schematically and in a longitudinal sectional view, part of the reciprocating piston mounted inside a cylinder, according to the prior art; Fig. 3 shows, schematically and in a longitudinal sectional view, a reciprocating piston obtained according to the present invention and mounted inside a cylinder;

Fig. 4 shows, an end view, of an axial tubular extension of the piston head region according to a first embodiment of the invention; Figures 4a and 4b show longitudinal sectional views of the axial tubular extension of the piston head region, said views being taken along lines A-A and B-B of figure 4, respectively;

Fig. 5 shows a perspective view of the piston head region of the piston according to the embodiment shown in figures 4, 4a and 4b; Fig. 6 shows an enlarged longitudinal sectional view of the piston head region illustrated in figure 5; Fig. 7 shows a perspective view of the piston head region according to another embodiment of the invention; and

Fig. 8 shows an end view of the axial tubular extension of the piston head region shown in figure 7.

Best Mode for Carrying Out the Invention

The present invention refers to a reciprocating piston moving inside an injection cylinder of a liquid material- injection machine, particularly employing liquid metal for casting metallic pieces, as illustrated in figure 1. According to the prior art, as illustrated in figure 2, the liquid metal injection machine comprises a reciprocating piston 1 moving inside a cylinder 2, in order to inject, in a mold for liquid metal, preferably aluminum or silicon-containing aluminum alloy, for obtaining metallic pieces. In the construction of the prior art reciprocating piston, the latter is rigidly affixed to an impelling rod 4 which is operatively coupled to piston driving means transmitting to said piston an impulse so that it may reciprocate inside cylinder 2. In this construction, the impelling rod 4 is provided with an axial hole 5, defined concentrically to its longitudinal axis and opened to an adjacent wall portion of piston 1, said wall portion being provided with an opening, communicating with the inside of an internal cooling chamber 6 defined in piston 1 and discussed ahead.

In order to reduce the temperature effect on piston 1, the latter is provided with a cooling system including a refrigerating tube 7 coaxial to both the impelling rod 4 and piston 1, occupying the whole longitudinal extension of the axial hole 5 and having a diameter smaller than the diameter of said axial hole 5, so as to form, with the radial spacing between its external lateral wall and adjacent internal lateral wall of the axial hole 5, a refrigerant fluid return annular duct 8, whose actuation will be discussed below.

The refrigerating tube 7 has an end extending beyond the end of the impelling rod 4 which is mounted to piston 1 and which occupies part of the inside of the internal chamber 6 of piston 1. In order to avoid the leakage of the refrigerant fluid to the exterior of the reciprocating piston 1 by the mounting surface of the impelling rod end affixed inside piston 1, said rod end is provided with an elastomeric sealing element V. The refrigeration of the reciprocating piston 1 in this prior art construction is achieved by injecting water into the refrigerating tube 7 towards the cooling chamber 6, until the water reaches said chamber, where it is forced to circulate due to the injection pressure to which it is subjected, absorbing the heat from the environment before returning, in a heated condition, through the return annular duct 8, outwardly from the equipment. This reciprocating piston construction has the deficiencies discussed above.

According to the present invention, inside the cylinder 2 moves a reciprocating piston 10, which is mounted in an articulated form, to an impelling rod 20, one of said parts carrying a male articulating element 30, actuating in a female articulating element 40 provided at the other of said parts and to which said male articulating element 30 is retained against relative axial displacements by an annular lid 41 affixed by bolts to the female articulating element 40. The articulating elements are preferably obtained from special steel alloys . According to the preferred embodiment shown in the drawings, the male articulating element 30 comprises a mounting portion 31, through which said male articulating element 30 is attached, preferably to a free end 21 of the impelling rod 20, and an engaging portion 32, preferably in the form of a spherical head, projecting axially from the mounting portion 31 of the male articulating element 30 and actuating in a bearing portion 42 of the female articulating element 40. The female articulating element 40 further comprises a respective mounting portion 43, through which it is affixed to piston 10.

In the preferred illustrated construction, the mounting of each articulating element 40, 30 to the respective piston and rod parts 10, 20 is achieved by the engagement of the mounting portion 43, 31 of said articulating elements 40, 30, which are preferably threaded into a corresponding internally threaded axial opening 19, 29 produced in said respective part. In another possible construction, at least one of the male or female articulating elements 30,40 is incorporated to the respective part of piston 10 and impelling rod 20. After threading the mounting portion 31 of the male articulating element 30 to the free end 21 of the impelling rod 20, an adjustment bolt B is disposed in a radial hole 22 made in a wall portion of said free end 21 and opened to the internally threaded portion of the latter, so as to attach the male articulating element 30 to said free end 21.

In order to receive the spherical head 32, the bearing portion 42 of the female articulating element 40 is defined in the form of a concave cavity that reproduces the diametral spherical profile of the head 32, in opposition to the portion of the latter wherefrom is projected the mounting portion 31 of the male articulating element 30.

For retaining the spherical head 32 in the bearing portion 42 of the female articulating element 40, the assembly receives, after attaching the mounting portion 31 of the male articulating element 30 to the piston 20, the annular lid 41 which is affixed to the bearing portion 42 of the female articulating element 40 through bolts. In the illustrated construction, the annular lid 41 has an end face facing the piston 10 and shaped to receive an adjacent spherical portion of the head 32 and communicating with an opposite end face, opened to the adjacent free end 21 of the impelling rod 20 and having a diameter slightly larger than the diameter of the mounting portion 31 of the male articulating element 30, so that angular movements of the head 32 result in angular movements of the impelling rod 20 in any direction contained in a plane orthogonal to the axis of the piston 10. According to another object of the invention, in order to reduce the wear of the piston head, a piston head region 12, in contact with the mass to be pressed, is shaped for maintaining, when piston 10 operates pressing the liquid metallic mass, a substantially constant contact with the adjacent lateral and internal wall portions of the cylinder 2 during the useful life of the piston.

In the illustrated constructions, the head region 12 of piston 10 is provided with an axial tubular extension 80 of metallic material, having an external cylindrical surface 81, axially aligned with the external cylindrical surface of the piston 10, and an internal frusto-conical surface 82, which opens towards the liquid metal mass to be compressed. The tubular extension is also provided with axial through slots 83 (see figures 4, 4a, 4b, 5), extending from a front peripheral edge 84 of the axial tubular extension 80, occupying at least part of the axial length of said tubular extension 80 and giving a certain level of elasticity to this region, which is required to maintain the contact between the piston and cylinder walls. These axial through slots 83 must have the smallest possible width, for example about 0.01 mm, to make difficult the liquid metal mass to pass radially outwardly through said slots . According to the embodiment which is more clearly illustrated in figures 4 and 5, the axial through slots 83 are arranged in pairs on at least two planes parallel and symmetrical in relation to one diameter of the axial tubular extension 80, the axial through slots of each plane being also parallel to said diameter. Said construction of parallel through slots 83 is more adequate to pistons of the type discussed herein and having a relative small diameter. According to the embodiment ilustrated in figures 7 and 8, which is more appropriate to pistons having relative large diameter, the axial through slots 83a are readially arranged and equally and angularly spaced from each other. The provision of the axial through slots 83, 83a, divides the lateral wall of the axial tubular extension 80 into circumferential sectors, allowing the split piston head region 12 to increase its diameter when submitted to radial expansion forces. Since it allows a larger number of slots, the radial arrangement of the axial through slots 83a illustrated in figures 7 and 8 allows a certain degree of diametral expansion of the axial tubular extension 80 with an increase of the width of the axial through slots which is smaller than that width increase resulting from a parallel arrangement of said slots when the diameter of the piston is relatively large. Thus, upon the compressing operation of piston 10, the ^"liquid metallic mass which is being compressed exerts a certain axial reaction force F against the internal frusto-conical surface 82, producing a radial component Fr sufficient to provoke a diametral expansion of the split region of the axial tubular extension 80 and the consequent and necessary contact of the circumferential sectors of the latter with the adjacent cylinder wall portion. In the constructive forms illustrated in the figures, the axial tubular extension 80 takes the form of a sleeve, usually in special steel alloy, which has a threaded internal rear region 85, with a diameter larger than that of the rear peripheral edge of the internal frusto-conical surface 82. The threaded internal rear egion 85 is mounted onto a corresponding threaded region 18 (see figures 1-4), with a reduced diameter, of the head region 12 of piston 10, allowing the axial locking of the axial tubular extension 80 of piston 10.

The head region 12 further comprises a front end face 12a which, in the embodiment of figures 1-4, is coplanar with the front peripheral edge 84 of the axial tubular extension 80 and which is also provided with a conical peripheral cut, in order to increase the area of penetration of the liquid metallic material inside the axial tubular extension 80.

The external cylindrical surface of piston 10 is provided with a circumferential groove 11, which is adjacent to the axial tubular extension 80 and which serves to lodge the material which, by any chance, may pass through the slots 83 towards the external lateral space of the tubular extension 80, thus protecting the pieces which are moving relatively to each other. Due to the high piston operating temperature, resulting from the temperature in which the liquid metal is being compressed (about 700oC) , the reciprocating piston has a cooling system which usually uses water and which conducts the refrigerant fluid through internal axial ducts aligned to each other and defined at the parts of the impelling rod 20 and male and female articulating elements 30, 40 towards an internal cooling chamber 17 defined by the space between the piston 10 and the external wall of the mounting portion 43 of the female articulating element 40. Said internal chamber 17 of piston 10 is defined by end radial slots and lateral longitudinal slots, which are preferably provided at the mounting portion 43 of the female articulating element 40 orthogonally to each other. A refrigerating tube 60 is disposed along the inside of aligned axial bores 26,36,46 provided along the impelling rod 20 and male and female articulating elements 30,40, centrally and coaxially in relation to the axes of said parts, the refrigerating tube 60 having a diameter which is reduced relatively to the axial bores ^"cited above, in order to define, externally and concentrically, a refrigerant fluid return annular duct 70, carrying heat from the inside of piston 10 to the outside of the equipment. To prevent the refrigerant fluid from reaching the inside of cylinder 2, the system is provided with sealing rings V between the joining parts of the female articulating element 40 and piston 10, annular lid 41 and said female articulating element 40 and between the male articulating element 30 and piston rod 20.

The refrigerating tube 60 has a free end 61 that is mounted, with a small radial gap, adjacently to an end of the mounting portion 43 of the female articulating element 40, said free end being opened to the cooling chamber 17, so as to send refrigerant fluid to the latter. The refrigerant fluid that reaches the internal chamber 17 is conducted to a region of the return annular duct 70 that is axially spaced from the free end 61 of the refrigerating tube 60, through radial openings 45, preferably angularly disposed in relation to the piston axis and provided at the mounting portion 43 of the female articulating element 40.

Though not illustrated, other forms of articulated coupling between the impelling rod and piston head are possible, such as providing the male articulating element in a single piece with one of said parts and the retention thereof to the other part being achieved by fitting a lateral pin, acting in an axial slot defined at the lateral wall of the other part, in case said male articulating element is not spherical.

Claims

1. A reciprocating piston for a liquid metal injection machine, said piston moving inside an injection cylinder (2) by actuation of the free end (21) of an impelling rod (20) and comprising an internal chamber (17), for refrigerant fluid circulation, which is maintained in fluid communication with corresponding refrigerant fluid internal axial ducts (60,70) in the impelling rod (20), characterized in that said piston further comprises a male articulating element (30), affixed to one of the parts defined by the piston (10) and by the free end (21) of the articulating rod (20), and a female articulating element (40), provided at the other of said parts and receiving the male articulating element (30), in order to avoid mutual relative axial movements and to allow a relative angular movement between said parts in any direction contained in a plane orthogonal to the piston axis, said male and female articulating elements (30,40) being axially and internally hollow, so as to provide the fluid communication between the axial ducts (60,70) of said impelling rod (20) and internal chamber (17).

2. Piston, according to claim 1, characterized in that the male articulating element (30) comprises a mounting portion (31) affixed to one of said parts of piston (10) and free end (21) of the impelling rod (20), and an engaging portion (32) projecting axially from the mounting portion (31), the female articulating element (40) being formed by a mounting portion (43) affixed to the other of said parts and by a bearing portion (42) projecting from the mounting portion (43) of said element, which receives and retains the engaging portion (32) of the male articulating element (30).

3. Piston, according to claim 2, characterized in that the internal axial ducts of the impelling rod (20) are defined by a central axial bore (26), lodging a refrigerating tube (60) of reduced diameter and defining externally and coaxially a refrigerant fluid return annular duct (70), the central axial bore (26) of the impelling rod (20) being axially aligned relatively to respective axial bores (36,46) provided in the male and female articulating elements (30, 40), in order to receive the corresponding part of the refrigerating tube (60) and define, coaxially, respective portions of the return annular duct (70), said refrigerating tube (60) having a free end (61) which is mounted, with a small radial gap, to the mouting portion (43) of the articulating element mounted to the piston (10), said free end (61) being opened to the internal cooling chamber (17).

4. Piston, according to claim 3, characterized in that the articulating element mounted to piston (10) has its mounting portion introduced and affixed in an axial opening (19) provided in piston (10) .

5. Piston, according to claim 4, characterized in that the internal cooling chamber (17) is defined by a space formed between the piston (10) and the adjacent external wall of the mounting portion of the articulating element affixed to the piston, said internal chamber (17) conducting the refrigerant fluid to a region of the return annular duct (70) that is axially spaced from the free end (21) of the refrigerant tube (20), through radial openings (45) provided in said mounting portion.

6. Piston, according to claim 5, characterized in that the internal chamber (17) is defined by end radial slots and longitudinal lateral slots, provided in the mounting portion of the articulating element affixed to the piston (10) .

7. Piston, according to claim 6, characterized in that the mounting of each articulating element (30,40) to the respective portion of the impelling rod (20) and piston (10) is achieved by threading the corresponding mounting portion (31,43) in a respective internally threaded axial opening (29,19) of said part.

8. Piston, according to claim 7, characterized in that the engaging portion (31) of the male articulating element (30) is in the form of a spherical head which is affixed, through the respective mounting portion, to the free end (21) of the impelling rod (20).

9. Piston, according to claim 8, characterized in that the bearing portion (42) of the female articulating element (40) includes an annular lid (41) affixed to said bearing portion (42), in order to retain therein the engaging portion (31) of the male articulating element (30) .

10. Piston, according to claim 1, characterized in that the head region (12) of piston (10) is provided with an axial tubular extension 80, which is internally frusto- conical, which opens towards the liquid metal mass to be compressed and whose lateral wall is provided with axial through slots (83, 83a) extending from the front edge of said tubular extension (80) and occupying at least part of the length of the latter.

11. Piston, according to claim 10, characterized in that the axial through slots (83) are disposed in pairs on at least two planes parallel and symmetrical in relation to one diameter, the axial through slots (83) of each plane being also parallel to said diameter.

12. Piston, according to claim 10, characterized in that the axial through slots (83a) are radially arranged.

13. Piston, according to claim 10, characterized in that the tubular extension (80) takes the form of a metallic sleeve having a threaded internal rear region (85) mounted onto a corresponding threaded region (18), with reduced diameter, of the head region (12) of piston (10) .

14. Piston, according to claim 10, characterized in that the diameter of the threaded internal rear region (85) is larger than that of the rear peripheral edge of the internal frusto-conical surface (82).

15. Piston, according to claim 10, characterized in that the axial tubular extension (80) has an external

• cylindrical surface (81) aligned with the external cylindrical surface of piston (10).

16. Piston, according to claim 15, characterized in that the external cylindrical surface of piston (10) is provided with a circumferential groove (11) adjacent to the axial tubular extension (80).