A special-shaped water-soluble salt core and its preparation method and application

Abstract

The present invention relates to a special-shaped water-soluble salt core and a manufacturing method and application, belonging to the technical field of internal combustion engine parts manufacturing. The salt core is annular, and the cross section of the salt core is special-shaped. The cross section of the salt core includes a top, a middle, and a bottom. The top is close to the piston top surface, and the top is semicircular; the bottom is arc-shaped, and the two sides of the middle are straight lines and arcs respectively. The arc side of the middle is closest to the combustion chamber, and the outer side surfaces of the top and the middle arc side are both provided with annular grooves. The special-shaped structure design of the salt core increases the surface area of ​​the salt core. After the salt core is dissolved in water, the surface area of ​​the inner cooling oil cavity formed near the piston head near the combustion chamber is increased, that is, the heat dissipation area is increased. After the cooling oil enters the inner cooling oil cavity, the cooling oil and the aluminum alloy of the piston head realize rapid heat exchange, and the heat exchange efficiency is increased by 5%-10% compared with the inner cooling oil cavity with equal cross-section.

Description

Technical Field

[0001] The invention relates to a special-shaped water-soluble salt core and a manufacturing method and application thereof, belonging to the technical field of internal combustion engine parts manufacturing. Background Art

[0002] The piston is the "heart" of the engine and the most demanding component under the working conditions of the engine. It transmits power in high-speed reciprocating motion and bears extremely high mechanical and thermal loads. With the development of supercharging technology, the maximum burst pressure and average effective pressure of high-power medium-speed diesel engines are constantly increasing. In particular, in terms of reducing fuel consumption, increasing the burst pressure is one of the means. In order to further meet emission requirements and pursue better economy, the development trend of the piston is to require that it can withstand higher mechanical and thermal loads while ensuring appropriate size, weight and reliability.

[0003] As the temperature of aluminum alloy materials rises, the mechanical properties of aluminum alloys will continue to decline. When the temperature rises to a certain value, the material strength of the aluminum alloy cannot meet the working requirements of the engine.

[0004] Therefore, the piston must be forced to cool to remove the heat transferred to the aluminum alloy during the combustion process. This heat is removed by the cooling oil in the cooling oil cavity inside the piston through heat exchange with the piston wall. The piston cooling oil cavity is cast into the piston through a soluble salt core, and then the salt core is dissolved with water. The cavity formed is the inner cooling oil cavity of the piston.

[0005] For aluminum alloy pistons, in order to meet the high explosion pressure requirements, improvements are needed in two aspects: one is further refinement of the aluminum alloy material, and the other is effective cooling of the aluminum alloy piston.

[0006] As the diesel engine is strengthened, the heat and mechanical loads on the piston also increase significantly, causing the temperature of the piston head to rise, which leads to ablation of the piston top surface, especially the edge of the combustion chamber throat. When the temperature of the first ring groove of the piston is too high, it will cause the lubricating oil to gel and carbonize, and the retaining ring will pull the cylinder. Under the same aluminum alloy material, the piston with good cooling performance has longer thermal fatigue resistance and service life.

[0007] At present, most aluminum alloy pistons for internal combustion engines on the market have an inner cooling oil cavity with a constant cross section. With the further increase of explosion pressure and power, the heat dissipation effect of the inner cooling oil cavity with a constant cross section is limited. The heat generated by combustion cannot be quickly taken away by the cooling oil, and the thermal impact of the piston ring groove and the combustion chamber is increased. Under the same structural strength and stress conditions, the cooling effect of the inner cooling oil cavity with a constant cross section is limited. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a special-shaped water-soluble salt core and a manufacturing method and application. The surface area of ​​the salt core is increased through the special-shaped structural design of the salt core. After the salt core is dissolved in water, the surface area of ​​the inner cooling oil cavity formed near the piston head near the combustion chamber is increased, that is, the heat dissipation area is increased. After the cooling oil enters the inner cooling oil cavity, the cooling oil and the aluminum alloy of the piston head achieve rapid heat exchange, and the heat exchange efficiency is increased by 5%-10% compared with the inner cooling oil cavity with equal cross-section.

[0009] The technical solution of the present invention is as follows:

[0010] A special-shaped water-soluble salt core, the salt core is annular, the cross section of the salt core is special-shaped, the cross section of the salt core includes a top, a middle, and a bottom, the top is close to the piston top surface, the top is semicircular; the bottom is arc-shaped, the two sides of the middle are respectively a straight line and an arc, and the arc side of the middle is closest to the combustion chamber;

[0011] There are circular grooves on the outer side of the top and the outer side of the middle arc side, and multiple circular grooves are arranged to form a wavy surface. Circular grooves are also formed in the inner cooling oil channel made of the salt core. The arrangement position of the circular groove in the inner cooling oil channel of the piston is close to the piston ring, piston top, throat, and the rounded corner of the bottom of the combustion chamber, which increases the heat dissipation area of ​​the inner cooling oil channel and improves the cooling effect.

[0012] Preferably, the arc on one side of the middle part is concave toward the center of the salt core, so that the arc of the inner cooling oil channel and the combustion chamber formed by the salt core casting follows the shape, and compared with the inner cooling oil channel without rounded corners, the effective cooling area of ​​the inner cooling oil channel and the combustion chamber is larger, and the cooling effect is better.

[0013] Further preferably, the radius of the middle arc is R1, and the value of R1 is equal to the sum of the R angle at the bottom of the combustion chamber and the distance L, wherein the L value should be greater than or equal to 6% of the piston diameter.

[0014] Preferably, a protrusion is formed between two adjacent annular grooves, the bottom fillet of the annular groove is r1, the outer fillet of the protrusion is r2, the opening angle of the annular groove is θ1, the spacing between adjacent annular grooves is L2, and the height of the annular groove is H; the r1 value range is determined according to the size of the piston and the salt core, the r1 fillet radius is greater than or equal to 0.5, that is, the surface area of ​​the internal cooling oil channel is maximized to enhance the cooling effect; the r2 fillet radius value is greater than or equal to 0.2, that is, a rounded transition, and no sharp transition is allowed to prevent stress concentration; the θ1 value is greater than or equal to 45°, which is easy to process and shape; the L2 value is greater than 2 times of r1+r2 to prevent sharp corners; the H value is less than or equal to r1, which is easy to process and shape. The default unit of fillet r and R is mm.

[0015] In summary, the values ​​within this range, when the piston structural strength permits, fully increase the surface area of ​​the salt core, that is, increase the heat dissipation area of ​​the piston inner cooling oil channel, and increase the surface area of ​​the inner cooling oil channel by 5%-10%, thereby achieving the best heat dissipation effect, that is, the heat dissipation effect of the inner cooling oil channel can be improved by 5%-10%.

[0016] Further preferably, the straight line on one side of the middle portion is an oblique line, which forms a certain angle with the vertical plane, the angle being θ2, and the value of θ2 needs to meet the structural strength requirement of the distance between the piston inner cooling oil channel and the piston ring groove.

[0017] A method for making a special-shaped water-soluble salt core comprises the following steps:

[0018] (1) Raw material ratio

[0019] The salt for making the salt core and water glass are stirred and mixed in a ratio of 97% salt + 3% water glass; after the salt and water glass are stirred and evenly mixed, they are sieved (40-100 meshes) to prevent uneven salt particles, which is not conducive to the pressing and forming of the salt core;

[0020] (2) Suppression

[0021] Salt core pressing specific pressure (pressure per unit area): 125-160MPa;

[0022] System pressure calculation formula: P 系统 A 系统 =P 盐 A 盐

[0023] Where: P 系统 is the system pressure, which is adjusted according to different varieties. 系统 is the top cylinder area, the equipment fixes this parameter to a fixed value, P 盐 The specific pressure of the salt core is 125-160MPa, A 盐 It is the projection area of ​​the salt core, and the value varies for different models;

[0024] (3) Demolding to check whether the salt core blank has cracks or delamination;

[0025] Visual inspection: the salt core blank should not have cracks or falling pieces, and the arc should be smooth and round. It is easier to see whether the salt core has cracks or delamination under sunlight, or use a metal rod to gently tap the salt core to judge whether there is crack by the sound;

[0026] (4) Sintering

[0027] Place the pressed salt cores on a special tool rack and put them into a box-type roasting furnace. Leave gaps between the stacks to ensure uniform heating.

[0028] The calcination temperature is 600℃~800℃. The calcination time should be determined according to the size of the salt core, generally 2~5 hours. The sintered salt core is slowly cooled with the furnace, and the cooling time is 2~5 hours. It is taken out when it cools below 200℃.

[0029] (5) Machining

[0030] Use special tools to process the arc-shaped central part of the salt core and the circular groove on the outer side;

[0031] Special tools are used to trim the salt core fillets, flash burrs, and all parts of the salt core must be smoothly transitioned after trimming. No cut marks, protrusions, or pits larger than 0.2mm are allowed. Forming tools are used to process circular grooves, which results in a high yield rate and high production efficiency for the salt core.

[0032] The salt core is made by pressing and sintering, with smooth transition of fillets at various locations. The cross-sectional shape of the salt core is easy to form and process. The presence of the circular groove does not increase the difficulty of making the salt core. Verification through actual production has shown that the strength of the salt core meets the technical requirements.

[0033] Preferably, in step (1), the sieve is 40-100 mesh.

[0034] An application of the above-mentioned special-shaped water-soluble salt core in a piston includes a piston, a combustion chamber is provided on the top of the piston, the bottom of the combustion chamber is arc-shaped, a ring is provided on the side of the piston near the top of the piston, and a cooling oil channel is provided in the piston on the side of the combustion chamber. The cross-section of the cooling oil channel is the same as the cross-section shape of the special-shaped water-soluble salt core.

[0035] Further preferably, the distance between the section of the cooling oil channel on the combustion chamber side and the section of the combustion chamber is L, and the value of L should be greater than or equal to 6% of the piston diameter.

[0036] When the special-shaped water-soluble salt core is used to cast a piston blank, the presence of the annular groove can gather the gas generated during the casting process into the annular groove and discharge it outside the piston blank through the salt core fixing hole, thereby effectively reducing the casting scrap rate.

[0037] The main material for making the salt core is salt. Experiments have shown that the salt core can quickly dissolve under the action of a certain pressure of water and can form an effective special-shaped cooling oil cavity. The wall of the cooling oil cavity in the piston is smooth and the annular groove has a good filling effect.

[0038] Through actual casting of blanks, it is verified that when the inner cooling oil cavity of the piston made of special-shaped water-soluble salt core is used with the inner cooling oil cavity of the piston made of conventional salt core, the cooling efficiency of the inner cooling oil cavity made of special-shaped water-soluble salt core is greatly improved.

[0039] The beneficial effects of the present invention are:

[0040] (1) The salt core is designed with an R-arc that is in the same shape or similar to the arc of the combustion chamber on the side close to the combustion chamber, which fully ensures that the inner cooling oil channel and the combustion chamber are equidistant or approximately equidistant, and has a better heat dissipation effect than the inner cooling oil channel with a beveled edge shape;

[0041] (2) Several concentric circular grooves are processed on the surface of the salt core, such as the top (near the piston top surface), the inner side of the salt core (near the piston combustion chamber and throat), and the outer side of the salt core (near the first ring groove and the fire land of the piston) to increase the surface area of ​​the salt core, that is, to increase the heat dissipation area of ​​the cold oil cavity in the piston, further improving the heat exchange efficiency;

[0042] (3) When casting the piston blank, a small amount of gas will be precipitated from the salt core after being heated. After adding a circular groove on the salt core, the circular groove can collect the gas generated by the salt core after being exposed to high temperature. This part of the gas will be discharged from the casting through the channel of the circular groove and the salt core mounting hole, thereby reducing the scrap rate of the casting and ensuring the process yield rate of the casting;

[0043] (4) The production method and specific technical parameters of the special-shaped salt core are described in detail. The salt core is simple to produce and is formed using a forming tool, which has high production efficiency.

[0044] (5) The piston made of the salt core has passed the high-strength engine bench performance verification, and the cooling effect is improved by 5%-10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the structure of the heteromorphic water-soluble salt core

[0046] Figure 2 for Figure 1 A partial enlarged view of point Ⅰ in the middle;

[0047] Figure 3 It is a schematic diagram of the cross section of a special-shaped water-soluble salt core;

[0048] Figure 3 Middle: R1 combustion chamber side fillet, R2 piston top side fillet, R3 piston center side fillet, R4 piston outer circle side fillet, r1 annular groove bottom fillet, r2 annular outer chamfer, θ1 annular groove opening angle, θ2 salt core outer side bevel, L2 annular groove spacing, H annular groove height, a is the distance of the salt core bottom fillet, a value greater than or equal to 0, non-important dimensions, other values ​​do not have a specific range, depending on the specific product;

[0049] Figure 4 It is a schematic diagram of a tool for machining special-shaped water-soluble salt cores;

[0050] Figure 5 is a cross-sectional view of the piston;

[0051] Figure 5Middle: 1 piston, 2 piston inner cooling oil channel, 3 ring insert, 4 piston top, 5 throat, 6 combustion chamber bottom, 7 combustion chamber, L1 salt core inner arc drop, L distance between combustion chamber and oil channel, R combustion chamber bottom fillet.

[0052] Figure 6 for Figure 5 An enlarged view of the inner cooling oil channel and the bottom of the combustion chamber. DETAILED DESCRIPTION

[0053] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0054] Embodiment 1:

[0055] A special-shaped water-soluble salt core, the salt core is in a circular ring shape, the salt core cross-section is special-shaped, the salt core cross-section includes a top, a middle part, and a bottom part, the top part is close to the piston top surface, the top part is semicircular; the bottom part is arc-shaped, the two sides of the middle part are a straight line and an arc respectively, and the arc side of the middle part is closest to the combustion chamber.

[0056] There are circular grooves on the outer side of the top and the outer side of the middle arc side, and multiple circular grooves are arranged to form a wavy surface. Circular grooves are also formed in the inner cooling oil channel made of the salt core. The arrangement position of the circular groove in the inner cooling oil channel of the piston is close to the piston ring, piston top, throat, and the rounded corner of the bottom of the combustion chamber, which increases the heat dissipation area of ​​the inner cooling oil channel and improves the cooling effect.

[0057] The arc on one side of the middle part is concave toward the center of the salt core, so that the curvature of the inner cooling oil channel and the combustion chamber formed by the salt core casting follows the shape. Compared with the inner cooling oil channel without rounded corners, the inner cooling oil channel and the combustion chamber have a larger effective cooling area and a better cooling effect.

[0058] The arc radius in the middle is R1. The straight line on one side of the middle is an oblique line, and the angle between it and the vertical plane is θ2.

[0059] A bulge is formed between two adjacent annular grooves, the bottom fillet of the annular groove is r1, the outer fillet of the bulge is r2, the opening angle of the annular groove is θ1, the spacing between adjacent annular grooves is L2, and the height of the annular groove is H. The surface area of ​​the inner cooling oil channel is increased by 5%-10%, that is, the heat dissipation effect of the inner cooling oil channel can be improved by 5%-10%.

[0060] Embodiment 2:

[0061] A method for making a special-shaped water-soluble salt core comprises the following steps:

[0062] (1) Raw material ratio

[0063] The salt for making the salt core and water glass are stirred and mixed in a ratio of 97% salt + 3% water glass; after the salt and water glass are stirred and evenly mixed, they are sieved (40-100 meshes) to prevent uneven salt particles, which is not conducive to the pressing and forming of the salt core;

[0064] (2) Suppression

[0065] Salt core pressing specific pressure (pressure per unit area): 125-160MPa;

[0066] System pressure calculation formula: P 系统 A 系统 =P 盐 A 盐

[0067] Where: P 系统 is the system pressure, which is adjusted according to different varieties. 系统 is the top cylinder area, the equipment fixes this parameter to a fixed value, P 盐 The specific pressure of the salt core is 125-160MPa, A 盐 It is the projection area of ​​the salt core, and the value varies for different models;

[0068] (3) Demolding to check whether the salt core blank has cracks or delamination;

[0069] Visual inspection: the salt core blank should not have cracks or falling pieces, and the arc should be smooth and round. It is easier to see whether the salt core has cracks or delamination under sunlight, or use a metal rod to gently tap the salt core to judge whether there is crack by the sound;

[0070] (4) Sintering

[0071] Place the pressed salt cores on a special tool rack and put them into a box-type roasting furnace. Each stack of salt cores should not exceed 12 layers according to size, and there should be gaps between the stacks to ensure uniform heating.

[0072] The calcination temperature is 600-800℃. The calcination time should be determined according to the size of the salt core, generally 2-5 hours. The sintered salt core is slowly cooled with the furnace, and the cooling time is 2-5 hours. It is taken out when it cools below 200℃.

[0073] (5) Machining

[0074] Use special tools to process the arc-shaped central part of the salt core and the circular groove on the outer side;

[0075] Special tools are used to trim the salt core fillets, flash burrs, and all parts of the salt core must be smoothly transitioned after trimming. No cut marks, protrusions, or pits larger than 0.2mm are allowed. Forming tools are used to process circular grooves, which results in a high yield rate and high production efficiency for the salt core.

[0076] The salt core is made by pressing and sintering, with smooth transition of fillets at various locations. The cross-sectional shape of the salt core is easy to form and process. The presence of the circular groove does not increase the difficulty of making the salt core. Verification through actual production has shown that the strength of the salt core meets the technical requirements.

[0077] Through the testing of the finished salt core, the special-shaped water-soluble salt core of this application meets the following technical indicators:

[0078] a) Strength

[0079] Salt core outer diameter D(mm) Withstand pressure (N) D≤80 ≥50 80﹤D≤110 ≥50 110﹤D≤130 ≥90 ＞130 ≥95

[0080] b) High temperature resistance, able to withstand heating at 600℃ for more than 30 minutes without damage.

[0081] c) Resistant to high temperature aluminum water erosion, it will not melt, crack, deform or fall off when immersed in 750℃-810℃ aluminum alloy.

[0082] d) Water-soluble: it can be cleaned within 2 minutes under the action of water flow at a pressure of 2MPa, or within 20 minutes under ordinary tap water.

[0083] Embodiment 3:

[0084] An application of the special-shaped water-soluble salt core described in Example 1 in a piston includes a piston, as shown in the figure, a combustion chamber is provided on the top of the piston, the bottom of the combustion chamber is arc-shaped, an insert is provided on the side of the piston, and a cooling oil channel is provided in the piston on the side of the combustion chamber. The cross-section of the cooling oil channel is the same as the cross-section shape of the special-shaped water-soluble salt core.

[0085] The distance between the cross section of the cooling oil passage on the combustion chamber side and the cross section of the combustion chamber is L.

Claims

1. A special-shaped water-soluble salt core, characterized in that: The salt core is in a circular shape, and the cross section of the salt core is a special shape. The cross section of the salt core includes a top, a middle, and a bottom. The top is close to the piston top surface and is semicircular; the bottom is in an arc shape, and the two sides of the middle are a straight line and an arc respectively, and the arc side of the middle is closest to the combustion chamber; The radius of the middle arc is R1. The value of R1 is equal to the sum of the R angle at the bottom of the combustion chamber and the distance L. L is the distance between the section of the cooling oil channel on the combustion chamber side and the section of the combustion chamber. The L value should be greater than or equal to 6% of the piston diameter. There are circular grooves on the outer side of the top and the outer side of the middle arc side; A bulge is formed between two adjacent circular grooves, the bottom fillet of the circular groove is r1, the outer fillet of the bulge is r2, the opening angle of the circular groove is θ1, the spacing between adjacent circular grooves is L2, and the height of the circular groove is H; the value range of r1 is determined according to the size of the piston and the salt core, the radius of the r1 fillet is greater than or equal to 0.5; the value of the r2 fillet radius is greater than or equal to 0.2; the value of θ1 is greater than or equal to 45°; the value of L2 is greater than twice of r1+r2; the value of H is less than or equal to r1.

2. The special-shaped water-soluble salt core according to claim 1, characterized in that: The arc on one side of the middle is concave toward the center of the salt core.

3. The special-shaped water-soluble salt core according to claim 1, characterized in that: The straight line on one side of the middle is an oblique line, which forms a certain angle with the vertical plane.

4. A method for preparing the irregularly shaped water-soluble salt core according to claim 1, characterized in that: The steps include: (1) Raw material ratio The salt core is made by stirring and mixing salt and water glass in a ratio of 97% salt + 3% water glass; after the salt and water glass are stirred and evenly mixed, sieving is performed; (2) Suppression Salt core pressing specific pressure: 125-160MPa; System pressure calculation formula: P 系统 A 系统 =P 盐 A 盐 Where: P 系统 is the system pressure, which is adjusted according to different varieties. 系统 is the top cylinder area, the equipment fixes this parameter to a fixed value, P 盐 The specific pressure of the salt core is 125-160MPa, A 盐 is the projected area of ​​the salt core; (3) Demolding to check whether the salt core blank has cracks or delamination; (4) Sintering Place the pressed salt core on a tool rack and put it into a box-type roasting furnace; The calcination temperature is 600-800°C, and the calcination time is 2-5 hours. The sintered salt core is slowly cooled with the furnace, and the cooling time is 2-5 hours. It is taken out when it is cooled to below 200°C. (5) Machining Use cutting tools to machine the arc-shaped central part of the salt core and the circular groove on the outer side; Use tools to trim the salt core fillets, burrs and flashes. After trimming, no cutting marks, protrusions or pits larger than 0.2mm are allowed.

5. The method for making a special-shaped water-soluble salt core according to claim 4, characterized in that: In step (1), sieve through 40-100 mesh.

6. Use of the special-shaped water-soluble salt core according to any one of claims 1 to 3 in a piston, characterized in that: The piston comprises a combustion chamber on the top of the piston, an arc-shaped bottom of the combustion chamber, an inlay ring on the side of the piston near the top of the piston, a cooling oil channel in the piston on the side of the combustion chamber, and a cross section of the cooling oil channel having the same cross section shape as that of the special-shaped water-soluble salt core.

7. The use of the special-shaped water-soluble salt core in a piston according to claim 6, characterized in that: The distance between the section of the cooling oil channel on the combustion chamber side and the section of the combustion chamber is L, and the value of L should be greater than or equal to 6% of the piston diameter.

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