Lubricated head and piston

Abstract

The present invention refers to a head for making a piston (2) of a press for a die-casting machine. The head comprises at least one ring seat (14) suitable for receiving a respective sealing ring (16) and wherefrom at least one ring locking protrusion (4) suitable for engaging a respective through opening (6) obtained in the sealing ring (16) extends. A lubrication circuit (20) is formed inside the head. The lubrication circuit comprises at least one lubrication end duct (22) leading into the base of said ring locking protrusion (4), whereby, when the ring is mounted on the head, the lubricant escapes from the piston head through the gap (23) between the ring locking protrusion (4) and the respective through opening (6).

Description

LUBRICATED HEAD AND PISTON

[0001] The present invention relates to a piston head and a piston for a press of a die-casting machine, for example of the cold chamber type. In particular, the present invention is aimed at a piston with a lubrication circuit suitable for promoting the sliding of the piston into a container of molten metal of a press for the die-casting machine.

[0002] In WO2021144722A1, in the name of the same Applicant, a piston for a die-casting machine was proposed comprising a piston head having a side wall wherein a ring seat is obtained wherein a sealing ring is housed that is suitable for forming a seal on the wall of the container of the press wherein the piston slides. The ring seat is delimited at the rear by an annular shoulder. A lubrication circuit is obtained in the head, which lubrication circuit is suitable for facilitating the sliding of the piston in the container of the diecasting machine.

[0003] The lubrication circuit comprises at least one lubrication end duct leading into a surface channel which runs through the bottom wall of the ring seat such as convey the lubricant towards the gap between the annular shoulder and the sealing ring.

[0004] Such an embodiment of the piston allows the lubricant to at least partially solve the problem of the complete occlusion of the openings of the end ducts under the ring and / or of the gaps wherefrom the lubricant should escape, particularly in the case of high axial and radial loads to which the sealing ring is subjected.

[0005] However, the Applicant has found that the lubricant escaping from the gap between the rear annular shoulder and the sealing ring is not always able to ensure the desired lubrication of the front part of the container wherein the piston slides, especially in the case of presses with limited strokes or special designs, or extremely stressful molding cycles with high temperatures and rhythms.

[0006] The problem that is generated with limited machine strokes, or in projects wherein the design of the container and the shaft does not allow the head and sealing ring to partially or completely escape from the container on the mold side is indeed linked to the poor lubrication of this final container part.

[0007] Furthermore, insofar as in some embodiments, channels or passages are obtained in the piston head that connect the front wall of the head with the ring seat such as to facilitate an inflow of metal under the sealing ring in order to progressively compensate for thewear thereof, in some cases the metal flowing under the sealing ring may reach the end duct openings under the ring and / or the gaps wherefrom the lubricant should escape, causing the occlusion thereof.

[0008] The object of the present invention is to propose a piston head provided with a lubrication circuit but capable of overcoming the limitations and drawbacks of lubricated piston heads according to the prior art.

[0009] This object is achieved with a piston head according to claim 1, with a piston according to claim 12, and with a sealing ring according to claim 13.

[0010] The features and advantages of the piston head, the piston, and the ring according to the present invention will be apparent from the description provided below, given by way of non-limiting example of preferred embodiments thereof, according to the accompanying drawings. In said drawings:

[0011] - Figure 1 is a perspective view of a piston head according to the invention, in one embodiment;

[0012] - Figure 2 is a side view of the piston head in Figure 1;

[0013] - Figure 3 is a side view in partial section of the piston head;

[0014] - Figure 3a is an enlarged view of the detail A which is circled in Figure 3;

[0015] - Figure 4 and 4a are a perspective view and a side view of a piston head of the preceding figures and provided with a sealing ring mounted on the front portion of the piston head;

[0016] - Figure 5 is a side view of the head of Figures 4 and 4a, with the sealing ring shown in axial section;

[0017] - Figure 6 is an exploded perspective view of the head;

[0018] - Figures 7, 7a, 7b, and 7c are a perspective view, an end view, an elevation view, and an axial sectional view of only the sealing ring of the head;

[0019] - Figure 8 is a side view of an example of a piston provided with a head according to the invention;

[0020] - Figure 9 is a sectional view of the piston in Figure 8; and

[0021] - Figure 10 is an enlarged view of the detail G in Figure 9.

[0022] With reference to the attached figures, 1 denotes a piston head for making a piston 2, an example of which is shown in Figures 8-10, of a press of a die-casting machine, for example of the cold chamber type.

[0023] The press comprises a container wherein the piston 2, or at least one of the end parts thereof for pressing the molten metal, is slidably housed.

[0024] The piston head 1 comprises a head body 10 having a side wall 12 extending about a head axis X. The head body 10 ends at the front with a front wall 13 for pressing the molten metal.

[0025] In the remainder of the description, the terms "front" and "rear", or equivalent terms, refer to the advancement direction of the piston 2 during the step of pressing the molten metal.

[0026] A ring seat 14 is obtained in the side wall 12, which ring seat is suitable for receiving a respective sealing ring 16. The ring seat 14 forms a bottom wall 18.

[0027] At least one ring locking protrusion 4 suitable for being engaged by a respective through opening 6 obtained in the sealing ring 16 extends from the bottom wall 18.

[0028] In some embodiments, the piston head 10 is provided with two ring locking protrusions 4 diametrically opposite each other.

[0029] In other embodiments, the piston head 10 is provided with three or more ring locking protrusions 4, uniformly distributed along the circumference of the piston head 10.

[0030] The at least one ring locking protrusion 4 constrains, or helps to constrain in combination with other ring locking elements - as will be described below - the sealing ring 16 both axially and angularly.

[0031] For example, the ring locking protrusion 4 extends from a cylindrical portion 18a of the bottom wall 18.

[0032] In one embodiment, each ring locking protrusion 4 extends radially with respect to the head axis X. In an embodiment shown in the figures, each ring locking protrusion 4 is in the form of a right prism, i.e., it has walls perpendicular to the bottom wall 18.

[0033] In one embodiment, the ring locking protrusion 4 in the form of a right prism has a base having two larger sides 4' parallel therebetween and orthogonal to the head axis X, i.e., having a predominant extension along the circumference of the bottom wall 18 of the ring seat 14. In one embodiment, the two larger sides 4' are only connected by semicircular sides 4". In other words, the ring locking protrusion 4 has a substantially rectangular cross section, with the smaller sides 4" rounded.

[0034] A lubrication circuit 20 is obtained inside the head body 10, which lubrication circuit is suitable for facilitating the sliding of the piston 2 into the container of the die-casting machine.

[0035] According to one embodiment, the lubrication circuit 20 comprises at least one lubrication end duct 22 leading into the bottom wall 18 at the base of a ring locking protrusion 4, whereby, when the sealing ring 16 is mounted on the head, the lubricant escapes from thepiston head through the gap 23 between the ring locking protrusion 4 and the respective through opening 6.

[0036] In one embodiment, the at least one lubrication end duct 22 leads into a surface channel 24 which runs through the bottom wall 18 and ends at the base of the ring locking protrusion 4.

[0037] In the example shown in the drawings, two lubrication end ducts 22, which extend parallel to each other and orthogonally to the head axis X, lead into the surface channel 24.

[0038] For example, the surface channel 24 extends axially, i.e. parallel to the head axis X.

[0039] In one embodiment, the ring seat 14 is delimited at the rear by an annular shoulder 26. The ring locking protrusion is axially spaced apart from said annular shoulder. In other words, the ring locking protrusion is obtained at the front with respect to the annular shoulder 26.

[0040] In one embodiment, the at least one lubrication end duct 22 leads into a point of the bottom wall 18 between the annular shoulder 26 and the ring locking protrusion 4. The surface channel 24 thus extends between the opening of the lubrication end duct 22 obtained in the bottom wall 18 (i.e., from the rearmost opening in the case of multiple lubrication end ducts 22) and the baseof the ring locking protrusion 44.

[0041] In one embodiment, the ring locking protrusion 4 forms, at the surface channel 24, an axial recess 28 suitable for locally increasing the passage section of the lubricant in the gap 23 between the ring locking protrusion 4 and the sealing ring 16.

[0042] In other words, a concave region, i.e., a trench, is formed in the rear vertical wall of the ring locking protrusion 4, which extends from the front end of the surface channel 24. This axial recess 28 therefore forms a privileged passage for the lubricant to escape. This passage may not be occluded by the sealing ring 16 even when it is subjected to axial loads.

[0043] More specifically, the surface channel 24 ends at one of the larger sides 4' of the ring locking protrusion. In one embodiment, the end portion of the surface channel 22 and the ring locking protrusion 4 jointly form a lowered area 29 extending predominantly along said longer side 4'. In other words, if seen in plan view, the surface channel 24 assumes a "T" shape.

[0044] In one embodiment, in the ring seat 14 there is obtained, at the front with respect to the at least one ring locking protrusion 4, an annular groove 30 suitable for being engaged by a complementary annular rib 32 formed in the sealing ring 16.

[0045] Furthermore, in one embodiment, a plurality of metal inflow channels 34 which connect an annular portion 13' of the front wall 13 of the piston head 10 to the ring seat 14 for storing metal below the sealing ring 16 leads into a front distal portion 18b of the bottom wall 18 of the ring seat 14. This accumulation of metal below the sealing ring 16, when it solidifies, creates a thickness that progressively compensates for the thinning of the sealing ring 16 due to wear.

[0046] Therefore, in one embodiment, it is possible to identify in the bottom wall 18: a rear portion 18a, for example cylindrical in shape, delimited at the rear by the annular shoulder 26e wherein the at least one ring locking protrusion 4 is obtained, an intermediate portion 18c, which forms the annular groove 30, for example, cylindrical in shape, and a front portion 18b, into which the metal inflow channels or passages 34 lead. For example, the front portion 18b is delimited at the front by a front annular shoulder 36.

[0047] In one embodiment, the at least one ring locking protrusion 4 is obtained near the rear edge delimiting the annular groove 30.

[0048] The present invention also relates to a piston head 10 as described above and provided with at least one sealing ring 16 suitable for being housed in the ringseat 14.

[0049] The sealing ring 16 is in the form of a band, i.e. it has an axial extension that is much greater than its thickness. For example, the sealing ring 16 is made of a copper alloy.

[0050] At least one ring locking opening 6, suitable for being engaged, with shape coupling, by a respective ring locking protrusion 4, is formed in the sealing ring so that a gap 23 is formed between at least one portion of the edge - at least the rear portion - that delimits the ring locking opening and a respective wall of the ring locking protrusion for the lubricant to escape.

[0051] In one embodiment, the sealing ring 16 has a substantially cylindrical outer wall 16'. The at least one ring locking opening 6 is obtained in an intermediate annular portion 16a of the sealing ring 16 having an outer wall lowered with respect to adjacent front 16b and rear 16c portions of said outer wall 16'.

[0052] For example, the intermediate annular portion 16a has a width between 5% and 40% of the overall width of the sealing ring 16 and a depth between 2% and 40% of the thickness of the sealing ring 16.

[0053] Due to this lowered area of the sealing ring 16, the lubricant escaping from the ring locking opening 6 is partly retained within this lowered zone and thereforeguided to lubricate the entire cylindrical wall 16' of the sealing ring 16.

[0054] As mentioned above, an annular rib 32 extends from the inner wall of the sealing ring 16 that is suitable for engaging the annular groove 30 obtained in the ring seat 14.

[0055] The interaction between the annular groove 30 and the annular rib 32 helps to axially lock the sealing ring 16 and to prevent the molten metal flowing into the front portion 18b of the bottom wall 18 of the ring seat 14 from also passing into the rear portion 18a of this bottom wall 18, causing the openings of the lubrication end ducts 22 to close.

[0056] In one embodiment, the sealing ring 16 is interrupted by a longitudinal gap - not shown - which allows the ring to be opened and then fitted onto the piston head 1 for the positioning thereof in the ring seat 14.

[0057] In one embodiment, the lubrication circuit 20 obtained in the head body 10 comprises at least one proximal duct 40, for example parallel to the head axis X, which originates from or is connected to respective lubrication ducts 42 obtained in the shaft. From such proximal duct 40, two end ducts 22 parallel therebetween extend radially, both leading into the surface channel24.

[0058] Figures 8-10 show an example of a piston 2 for a press of a die-casting machine. The piston 2 comprises a head 100 as described above and a shaft 50 extending between a rear, or proximal, end 50', and a front, or distal, end 50" for connecting with the head 100.

[0059] In one embodiment, the head 100 is mounted on a support pin - not shown - which is in turn attached to the front end 50" of the shaft 50.

[0060] One or more lubricant supply ducts 42, fluidically connected to the lubrication end ducts 22, for example by means of connection bushings 44, are obtained in the shaft 50.

[0061] In one embodiment, the die-casting machine is provided with anti-rotation devices configured to keep the piston in an angular position such that the ring locking opening 6, wherefrom the lubricant escapes, faces upwards. In this way, when the lubricant reaches the upper outer surface of the sealing ring, it runs along the entire outer wall by gravity thereby obtaining a uniform lubricating effect.

[0062] With respect to the lubricated pistons of the prior art, the piston head described above allows the lubrication, which was previously constrained to exit at the rear of the band, to be conveyed to a more advancedposition. With this technical measure it was therefore possible, under the same conditions, to move the outlet point of the lubricant forward.

[0063] This allows the last part of the container, which usually remains drier, to be lubricated, especially when there are presses with limited strokes or molds with a third plate or with special designs or extremely stressful molding cycles with high temperatures and rhythms.

[0064] Due to the presence of the ring locking protrusion, the outlet holes of the lubricant are protected from molten metal even in the event that it succeeds in passing beyond the inner rib of the band.

[0065] The lowered area of the sealing ring, wherein the ring locking opening is obtained, allows the lubricant to slide more easily towards the lower part of the chamber and thus to better lubricate the entire surface thereof.

[0066] A person skilled in the art may make several changes, adjustments, adaptations, and replacements of elements with others that are functionally equivalent to the embodiments of the piston head, the piston, and the sealing ring according to the invention in order to meet incidental needs, without departing from the scope of the following claims. Each of the features described as belonging to a possible embodiment may be obtainedindependently of the other described embodiments.

Claims

Claims1. A piston head for making a piston (2) of a press for a die-casting machine, comprising:- a head body (10) having a side wall (12) extending about a head axis (X),- a sealing ring (16) wherein at least one ring locking through opening (6) is obtained;- a ring seat (14) obtained in the side wall and suitable for receiving the sealing ring (16), the ring seat forming a bottom wall (18), wherein from said bottom wall at least one ring locking protrusion (4) extends suitable for engaging a respective locking through opening (6) obtained in the sealing ring (16) in such a way that a gap (23) is obtained between at least a portion of the edge delimiting said ring locking through opening (6) and a respective wall of the ring locking protrusion (4);- a lubrication circuit (20) obtained inside the head body and suitable for promoting the sliding of the piston within a respective container of the die-casting machine, wherein the lubrication circuit comprises at least one lubrication end duct (22) leading into said bottom wall (18) at the base of said ring locking protrusion (4) such that when the ring is mounted on the head, the lubricant escapes from the piston head through the gap (23),the piston head being characterized in that the sealing ring has a substantially cylindrical outer wall, and wherein the at least one ring locking opening (6) is obtained in an intermediate annular portion (16a) of the sealing ring having a lowered outer wall with respect to adjacent front and rear portions of said outer wall.

2. The head according to claim 1, wherein the at least one lubrication end duct (22) leads into a surface channel (24) which runs through the bottom wall (18) and ends at the base of the ring locking protrusion.

3. The piston head according to any one of the preceding claims, wherein the ring seat (14) is delimited at the rear by an annular shoulder (26), and wherein the ring locking protrusion is axially spaced apart from said annular shoulder.

4. The piston head according to claims 2 and 3, wherein the at least one lubrication end duct (22) leads into a point on the bottom wall (18) between the annular shoulder (26) and the ring locking protrusion (4).

5. The piston head according to any one of claims 2 to 4, wherein the surface channel (24) extends parallel to the head axis (X).

6. The piston head according to any one of the preceding claims, wherein each ring locking protrusion (4) has a prismatic shape the base of which has longersides being mutually parallel and orthogonal to the head axis (X).

7. The piston head according to any one of claims from 2 to 6, wherein the ring locking protrusion forms, at the surface channel, an axial recess (28) suitable for locally increasing the passage section of the lubricant in the gap (23) between the ring locking protrusion and the sealing ring.

8. The piston head according to claims 6 and 7, wherein the surface channel (24) ends at one of the longer sides of the ring locking protrusion (4), and wherein the end portion of the surface channel and the ring locking protrusion jointly form a lowered area (29) mainly extending along said longer side.

9. The piston head according to any one of the preceding claims, wherein an annular groove (30) suitable for being engaged by a complementary annular rib (32) obtained in the sealing ring (16) is obtained in the ring seat (14), at the front with respect to the at least one ring locking protrusion (4).

10. The piston head according to any one of the preceding claims, wherein a plurality of metal inflow channels (34), which connect an annular portion (13') of the front wall (13) of the piston head to the ring seat (14) for storing metal below the sealing ring (16), leadsinto a front distal portion (18b) of the bottom wall (18) of the ring seat (14).

11. The piston head according to any one of the preceding claims, wherein the sealing ring is interrupted by a longitudinal gap.

12. A piston for a die-casting machine, comprising a head according to any one of the preceding claims and a shaft (50) extending between a rear end and a front end of connection to the head assembly, there being obtained in the shaft one or more lubricant supply ducts (42) fluidically connected to the lubrication end ducts (22).

13. A sealing ring positionable in a ring seat obtained in a piston of a press for a die-casting machine, comprising a substantially cylindrical side wall interrupted by a longitudinal gap, wherein in the cylindrical wall the at least one through opening (6) is obtained suitable for being engaged, with shape coupling, by a respective ring locking protrusion (4) obtained in the ring seat, and wherein the at least one through opening (6) is obtained in an intermediate annular portion (16a) of the sealing ring having an outer wall lowered with respect to adjacent front and rear portions of said outer wall.

14. The sealing ring according to claim 13, wherein the intermediate annular portion (16a) has a length in anaxial direction of between 5% and 40% of the overall width of the sealing ring (16) and a depth of between 2% and 40% of the thickness of the sealing ring (16).

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