A gating system for preventing shrinkage porosity of a high-grade vermicular graphite cast iron cylinder head

Abstract

The present invention discloses a gating system for preventing shrinkage cavities in a high-grade vermicular graphite cast iron cylinder head. The gating system is of a closed-open structure and includes a pouring cup, a sprue, a sub-sprue, a runner, a sub-runner, and an ingate. The left end of the runner is connected to the lower end of the sprue, and the right end is connected to the upper end of the sub-sprue. The lower end of the sub-sprue is connected to the right end of the sub-runner. A plurality of ingates are provided on the sub-runner. The sectional area ratio relationship of each unit of the gating system is: F 直 > F 横1 > F 阻 < F 分横 ≤ F 总内 , F 直 : F 横1 : F 阻 : F 分横 : F 总内 = 1.3 - 1.5: 1.2 - 1.4: 1.0: 1.3 - 2: 1.5 - 3. The present invention has the advantages of reasonable structure, good feeding effect, low casting rejection rate, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of cylinder head casting, and particularly to a gating system for preventing shrinkage cavities of a high-grade vermicular graphite cast iron cylinder head. Background Art

[0002] The cylinder head is an important component with the most complex structure and high technical content in an engine. In the past, the mainstream materials for cylinder heads of medium and heavy-duty engines were: ordinary gray cast iron, chromium-molybdenum-copper alloy gray cast iron, and low-grade vermicular graphite cast iron. However, with the continuous improvement of engine technology, the wall thickness of castings has become lighter and the structure has become more compact, the compression ratio and power have increased day by day, and higher requirements have been put forward for the material properties of the cylinder head. The performance of gray cast iron / low-grade vermicular iron cylinder heads can no longer meet the above requirements. Compared with gray cast iron / low-grade vermicular iron, high-grade vermicular graphite cast iron has higher physical and mechanical properties. Currently, the cylinder heads of large-displacement engines at home and abroad have basically upgraded the material to high-grade vermicular graphite cast iron.

[0003] Vermicular graphite cast iron itself has the characteristics of good casting process performance and a small tendency to produce shrinkage cavities and porosity. However, as the material grade increases, when the material grade exceeds RuT400, in order to ensure high strength, the addition amounts of alloying elements such as tin and copper are high, and the shrinkage tendency of molten iron is very large. Coupled with the typical mass production characteristics of the modern automotive industry, higher requirements are put forward for the casting processability of the cylinder head, and the process design requirements are harsh.

[0004] Currently in the domestic industry, a certain casting company accepts the 13-liter cylinder head according to the RuT420 grade and applies it in batches, but the rejection rate of shrinkage cavities and porosity is about 10%. A certain casting company accepts the 9-liter cylinder head according to the RuT450 grade, but the rejection rate of shrinkage cavities and porosity is about 30%, and production has stopped due to the high rejection rate of shrinkage cavities and porosity. Other casting companies have stopped at the development stage because the rejection rate of shrinkage cavities and porosity of high-grade vermicular graphite cast iron cylinder heads is as high as 50% - 70%. The highest grade of cylinder heads in the domestic industry is RuT420, and there is no batch application of high-grade vermicular graphite cast iron cylinder head material RuT450.

[0005] Currently, the casting process of high-grade vermicular graphite cast iron cylinder heads usually adopts the vertical casting process. According to the production line, one-piece or multi-piece layouts in one box are selected. During production, due to the presence of many hot spots such as cylinder head bolt holes, guide holes, and injector holes, the temperature field is complex. Coupled with the thinning of the wall thickness caused by the lightweight of the casting, the tendency of shrinkage cavities and porosity is aggravated. In addition, the solidification characteristics of high-grade vermicular graphite cast iron itself result in ineffective feeding of hot spots, forming isolated liquid phase regions and generating shrinkage cavity and porosity defects.

[0006] In the existing technical solutions, the gating system follows the gating system of the previous gray cast iron / low-grade vermicular iron cylinder heads. The position of the ingate is selected away from the hot spots, and a large number of chill blocks are used at the hot spots to achieve the effect of reducing the tendency of shrinkage cavities and porosity in the hot spot areas; the gating system only serves as a channel for the molten iron to fill the mold during pouring. The design of the ingate size, feeding ingate size, sub-runner size, minimum choke area, and the sectional ratio of each unit of the gating system only requires smooth filling and good slag collection effect, and does not have an effective feeding function; due to the fact that the design standard of the gating system has not been improved with the upgrade of the material, the rejection rate of shrinkage cavities and porosity is high.

[0007] The disclosure of the above background technical content is only used to assist in understanding the concept and technical solution of the present invention, and it does not necessarily belong to the prior art of this patent application. Without clear evidence indicating that the above content was publicly available on the filing date of this patent application, the above background technology should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0008] The purpose of the present invention is to propose a closed-open gating system to solve the technical problem of high rejection rate caused by shrinkage cavities in the casting of high-grade vermicular graphite cast iron cylinder heads in the above existing technologies.

[0009] Therefore, the present invention proposes a gating system for preventing shrinkage cavities in high-grade vermicular graphite cast iron cylinder heads.

[0010] Preferably, the present invention may further have the following technical features:

[0011] A gating system for preventing shrinkage cavities in high-grade vermicular graphite cast iron cylinder heads, the gating system is of a closed-open structure, and it includes a pouring cup, a sprue, a sub-sprue, a runner, a sub-runner, and an ingate. The left end of the runner is connected to the lower end of the sprue, and the right end is connected to the upper end of the sub-sprue; the lower end of the sub-sprue is connected to the right end of the sub-runner; several ingates are provided on the sub-runner; the cross-sectional area of the sprue is F 直 , the cross-sectional area of the runner is F 横1 , the minimum choke area is F 阻 , the cross-sectional area of the sub-runner is F 分横 , the total area of the ingates is F 总内 , and the sectional ratio relationship of each unit of the gating system is: F 直 >F 横1 >F 阻 <F 分横 ≤F 总内 , F 直 : F 横1 : F 阻 : F 分横 : F 总内 = 1.3 - 1.5:1.2 - 1.4:1.0:1.3 - 2:1.5 - 3.

[0012] Further, the cross-riser from left to right is respectively a main body section, a flow-slowing section, and a slag trap. The height h2 of the slag trap is ≥ the height h1 of the flow-slowing section, and the cross-sectional area F of the flow-slowing section 横2 is greater than the cross-sectional area F of the sprue 直 .

[0013] Further, the cross-sectional area F of the flow-slowing section 横2 = 2F 直 ~3F 直 ; The sub-sprue is of a Y-shaped structure, and its upper bifurcations are respectively connected to the flow-slowing section and the slag trap of the cross-riser; The minimum choke area is provided at the lower part of the sub-sprue

[0014] Further, the inner gates are horizontally arranged on both sides of the sub-cross-riser, and a number of positioning holes or positioning protrusions are respectively provided on both sides of the sub-cross-riser; The distance O in the vertical direction from the center of the inner gate of the gating system to the center of the cylinder head bolt hole L = D / 4~D / 2, where D represents the diameter of the cylinder head bolt hole boss, and the center of the inner gate is located above the center of the bolt hole

[0015] Further, it is determined that the inner gate size value A = D / 3~2D / 3, and the draft value is 3°~10°;

[0016] The inner gate boss diameter value B = 3D / 2~2D;

[0017] The distance c from the inner gate boss surface to the inner gate is D / 3~2D / 3

[0018] Further, the range of values of the width a and height b of the sub-cross-riser: a≤b. The distance from the center of the inner gate to the top of the sub-cross-riser is b1, and the distance from the center of the inner gate to the bottom of the sub-cross-riser is b2, b1≥b2; The distance d from the sub-cross-riser to the inner gate surface is 2c≤d≤2D

[0019] Further, the distance in the vertical direction from the center of the inner gate at the front end and the rear end of the gating system to the center of the bolt hole takes a value close to the upper limit; The inner gate size value A at the front end and the rear end of the gating system takes a value close to the lower limit; The distance c from the inner gate boss surface to the inner gate at the front end and the rear end of the gating system takes a value close to the upper limit

[0020] Further, the minimum choke area F 阻 is greater than the theoretical minimum choke area A C .

[0021] Further, the minimum choke area value F 阻 = 2A C ~3A C .

[0022] Furthermore, the cross-sections of the ingate and the runner are circular.

[0023] The beneficial effects of the present invention compared with the prior art include: designing the minimum choke area F 阻 to be larger than the theoretical minimum choke area A C , which can not only play a role in choking flow, but also provide feeding pressure for the runner; when using this gating system to cast high-grade vermicular graphite cast iron cylinder heads, the rejection rate of shrinkage cavities and porosity is controlled below 2%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the gating effect diagram of the present invention.

[0025] Figure 2 is the schematic diagram of the position of the ingate corresponding to the casting of the present invention.

[0026] Figure 3 is the schematic diagram of the feeding dimensions of the gating system of the present invention.

[0027] Figure 4 is the front view of the gating system of the present invention.

[0028] Figure 5 is the three-dimensional view of the gating system of the present invention.

[0029] Figure 6 is the schematic diagram of the analysis of the hot spot characteristics of the cylinder head casting itself. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be further described in detail below in conjunction with the specific embodiments and with reference to the accompanying drawings. It should be emphasized that the following description is merely exemplary and not intended to limit the scope of the present invention and its applications.

[0031] Referring to the following drawings, non-limiting and non-exclusive embodiments will be described, where the same reference numerals represent the same components, unless otherwise specifically stated.

[0032] As Figures 1 to 5 shown, a gating system for preventing shrinkage cavities of a high-grade vermicular graphite cast iron cylinder head, the gating system 3 is of a closed-open structure, which includes a pouring cup 31, a sprue 32, a sub-sprue 34, a cross gate 37, a sub-cross gate 36, and a runner. The left end of the cross gate 37 is connected to the lower end of the sprue 32, and the right end is connected to the upper end of the sub-sprue 34; the lower end of the sub-sprue 34 is connected to the right end of the sub-cross gate 36; several runners are provided on the sub-cross gate 36. The cross-sectional area of the sprue is F 直 , the cross-sectional area of the cross gate is F 横1 , the minimum choke area is F 阻 , the cross-sectional area of the sub-cross gate is F 分横 , the total area of the ingates is F总内 The sectional area ratio of each unit of the gating system is: F 直 > F 横1 > F 阻 < F 分横 ≤ F 总内 F 直 : F 横1 : F 阻 : F 分横 : F 总内 = 1.3 - 1.5: 1.2 - 1.4: 1.0: 1.3 - 2: 1.5 - 3. Other ratios include: F 直 : F 横1 : F 阻 : F 分横 : F 总内 = 1.3 - 1.5: 1.2 - 1.4: 1.0: 1.3 - 2: 1.9 - 3.

[0033] The cross - runner 37 from left to right is respectively the main body section, the flow - slowing section, and the slag - collecting pocket 33. In specific implementation, the height h2 of the slag - collecting pocket 33 ≥ the height h1 of the flow - slowing section (h1 ≥ 100 mm), and the cross - sectional area F of the flow - slowing section 横2 = 2F 直 ~3F 直 . A filter screen 39 is provided at the connection of the sub - sprue 34 and the cross - runner 37, preferably a foam ceramic filter screen. The sub - sprue 34 is of a Y - shaped structure, and its upper bifurcations are respectively connected to the flow - slowing section and the slag - collecting pocket 33 of the cross - runner 37. The minimum choke area is located at the lower part of the sub - sprue 34.

[0034] The cross - runner 37 is the main unit for slag - blocking in the gating system. Therefore, it is necessary to reduce the flow rate of the molten iron in the cross - runner 37. Tests on the quality of cast iron metallurgy show that a flow rate of the molten iron below 30 cm / s is appropriate. The F in front of the slag - collecting pocket 33 横2 The cross - runner is both the flow - slowing section and provides feeding pressure for the choke and the ingates. Flow velocity V 流 = W / t (kg / s), where W = total weight of the casting (kg); t = pouring time (s).

[0035] More specific description of the ingate 35. Refer to Figure 2 , The ingates are horizontally arranged on both sides of the sub - cross - runner 36, and a number of positioning holes or positioning protrusions 38 are respectively provided on both sides of the sub - cross - runner 36 to improve the efficiency of assembling the gating system on the molding sand. The distance O in the vertical direction between the center 4 of the ingate and the center 5 of the cylinder head bolt hole L= D / 4 to D / 2, where D represents the diameter of the boss of the cylinder head bolt hole, and the center of the ingate is located above the center of the bolt hole. In the casting process of high-grade vermicular graphite cast iron (RuT450) in this embodiment, there are a total of 7 ingate positions for each casting. Since the hot spots at the bolt holes at the front and rear ends of the casting are larger than those at the middle bolt holes, the larger the hot spot, the farther the corresponding ingate position is from the center of the hot spot to avoid the formation of contact hot spots at the junction of the ingate and the casting. Therefore, the distance in the vertical direction from the center of the ingate at the front and rear ends of the casting to the center of the bolt hole takes a value closer to the upper limit.

[0036] Determine the dimensions of the ingate in the gating system and the risering ingate runner. Select circular ingates and risering ingate runners, and determine the size of the ingate based on factors such as the size of the internal hot spot and the structural dimensions, so that the solidification time of the ingate is the same as or slightly later than the hot spot of the bolt hole of the casting. Calculate the following dimensions based on the modulus to be compensated at the hot spot part of the casting, and refer to Figure 3 to determine the dimensional parameters, including:

[0037] Determine that the value of the ingate size A is D / 3 to 2D / 3, the draft angle is 3° to 10°. The hot spots at the bolt holes at the front and rear ends of the casting are larger than those at the middle bolt holes. The larger the hot spot, the smaller the corresponding ingate size to avoid the formation of contact hot spots at the junction of the ingate and the casting. The value of the ingate size A at the front and rear ends of the casting takes a value closer to the lower limit. (D is the diameter of the boss of the cylinder head bolt hole);

[0038] Determine that the value of the diameter of the boss of the risering ingate runner is B = 3D / 2 to 2D. (D is the diameter of the boss of the cylinder head bolt hole);

[0039] Determine that the distance c from the boss surface of the risering ingate runner to the ingate is D / 3 to 2D / 3. The hot spots at the bolt holes at the front and rear ends of the casting are larger than those at the middle bolt holes. The larger the hot spot, the larger the corresponding distance between the ingates to avoid the formation of contact hot spots at the junction of the ingate and the casting. The value of the distance c from the boss surface of the ingate runner to the ingate at the front and rear ends of the casting takes a value closer to the upper limit. (D is the diameter of the boss of the cylinder head bolt hole).

[0040] The value range of the width a and height b of the sub - runner: a ≤ b. The distance from the center of the ingate to the top of the sub - runner is b1, and the distance from the center of the ingate to the bottom of the sub - runner is b2, b1 + b2 = b, b1 ≥ b2; The distance d from the sub - runner to the ingate surface takes a value of 2c ≤ d ≤ 2D.

[0041] Determine the minimum choke area of the gating system. The runner is a channel that guides the molten metal from the sprue to the ingate. A slag - collecting riser is set on the runner, and a choke is designed after the slag - collecting riser and before the ingate. The choke in the design of this risering gating system is different from that of a common gating system. Its function is not only to choke but also to provide a risering head for the ingate. The choke section is designed at the front end of the sub - runner (see Figure 4) Before the casting solidifies, the slag trap provides feeding power to the ingate for feeding, and its solidification time is later than that of the ingate. The theoretical calculation formula for the choke is as follows:

[0042] When all the castings are in the lower mold, the cross-sectional size of the choke:

[0043] (1) Select an appropriate filling friction coefficient f according to the product structure, parting surface position, ingate position, casting wall thickness, etc. r ;

[0044] (2) Determine the total volume V of the molten iron for pouring;

[0045] (3) V D includes the volume of the casting, the volume of the riser, and the volume of the gating system after the choke;

[0046] (4) V D = weight / density. For molten iron, density = 0.0072 kg / cm 3 ;

[0047] (5) Determine the height H of the static head of the sprue, H = H0 - P / C (P: the height of the casting above the ingate on the parting surface; H0: the height of the mold above the ingate on the parting surface, C: the height of the casting);

[0048] (6) Determine the height b of the upper mold of the casting;

[0049] (7) The flow velocity of the molten iron at the choke section: g = acceleration due to gravity = 981 cm / s 2 ;

[0050] (8) t is the pouring time.

[0051] When the choke is normally taken as A C and the cross-sectional area is too small, the solidification time of the smallest cross-section is earlier than that of the feeding ingate, and it cannot provide sufficient feeding power to the ingate, resulting in shrinkage cavity and porosity defects in the hot spot area; if the choke value is too large, the flow velocity of the ingate increases, the mold and core are easily eroded, the molten iron filling is not stable and is easily oxidized, the casting has a tendency to produce pores and oxidation inclusions, and the thin-walled casting has low sealing performance and poor quality. The two are contradictory. Combining F 阻 : F 总内 = 1.0: 1.5 - 3 ratio, determine the minimum choke area value F 阻 = 2A C - 3A C , the actual minimum choke area F 阻 is greater than the theoretical minimum choke area A C . On the one hand, it realizes the choke function, and on the other hand, it can also provide feeding pressure to the ingate.

[0052] The application of this gating system in the casting process of high-grade vermicular graphite cast iron cylinder heads adopts a vertical casting process with two castings in one box, including the following steps:

[0053] S1. Determine that the gating system is a middle gating type. The gating system is designed between the left combined core 1 and the right combined core 2, fully covering the sand core. The inside of the combined core forms the cylinder head cavity. The combined core includes a chassis core and a cover plate core;

[0054] S2. Determine the position of the ingates. The position of the ingates is set near the hot spots of the bolt holes of the casting. Analyze the hot spot characteristics of the cylinder head casting itself (see Figure 6 ). It can be seen that the bolt holes, guide holes, and injector holes of the cylinder head are hot spot parts. The bolt hole pointed by the arrow is the largest hot spot. The selection of the ingate position is the most crucial, directly related to the final feeding effect. If it is too far from the center of the hot spot, it cannot achieve the feeding effect and shrinkage cavity defects will occur; if it is too close to the center of the hot spot, contact hot spots will instead form at the junction of the ingate and the casting, resulting in shrinkage cavity and shrinkage porosity defects. Design an ingate near each hot spot of the bolt hole, and an ingate feeding channel, so that the feeding molten metal can reach those parts that need to be fed, and each hot spot part is fully fed without shrinkage cavity and shrinkage porosity. Design the gating system on the bottom surface of the chassis core. Each bottom surface of the 2 chassis cores forms half of the gating system, and after core combination, the bottom surfaces of the 2 chassis cores form a complete gating system 3.

[0055] S3. Determine the formation method of the exhaust system;

[0056] S4. Determine that the hot spot parts of the bolt holes, guide holes, and injector holes on the bottom and top surfaces of the cylinder head adopt the process without chill;

[0057] S5. Assemble and combine all the sand cores of the cylinder head, lock them with locking core screws, then lower the cores, close the mold, and wait for pouring;

[0058] S6. Pour the casting.

[0059] Those skilled in the art will recognize that numerous variations to the above description are possible, so the embodiments and the drawings are only used to describe one or more specific embodiments.

[0060] Although the exemplary embodiments that are regarded as the present invention have been described and recited, those skilled in the art will understand that various changes and substitutions can be made thereto without departing from the spirit of the present invention. Additionally, many modifications can be made to adapt a particular situation to the teachings of the present invention without departing from the central concept described herein. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but the present invention may also include all embodiments and their equivalents falling within the scope of the present invention.

Claims

1. A gating system for preventing shrinkage cavities of a RuT450 vermicular graphite cast iron cylinder head, characterized in that: The gating system is of a closed-open structure, which includes a pouring cup, a sprue, a sub-sprue, a runner, a sub-runner and ingates. The left end of the runner is communicated with the lower end of the sprue, and the right end of the runner is communicated with the upper end of the sub-sprue; the lower end of the sub-sprue is communicated with the right end of the sub-runner; several ingates are arranged on the sub-runner; the cross-sectional area of the sprue is F 直 , the cross-sectional area of the runner is F 横1 , the minimum choke area is F 阻 , the cross-sectional area of the sub-runner is F 分横 , the total area of the ingates is F 总内 . The sectional proportion relationship of each unit of the gating system is: F 直 > F 横1 > F 阻 < F 分横 ≤ F 总内 , F 直 : F 横1 : F 阻 : F 分横 : F 总内 = 1.3 - 1.5 : 1.2 - 1.4 : 1.0 : 1.3 - 2 : 1.5 - 3; The ingates are horizontally arranged on both sides of the sub-horizontal runner, and a number of positioning holes or positioning protrusions are respectively arranged on both sides of the sub-horizontal runner; the distance O in the vertical direction from the center of the ingate of the gating system to the center of the cylinder head bolt hole L = D / 4 to D / 2, where D represents the diameter of the cylinder head bolt hole boss, and the center of the ingate is located above the center of the bolt hole; Minimum flow resistance area F 阻 Greater than the theoretical minimum flow resistance area A C； The horizontal runner from left to right is respectively a main body section, a flow slowing section, and a slag collecting pocket, and the height h2 of the slag collecting pocket ≥ the height h1 of the flow slowing section; The cross-sectional area F of the flow-slowing section 横2 = 2F 直 ~3F 直 ; The branched sprue is of a Y-shaped structure. The bifurcations at the upper part of the branched sprue are respectively connected to the flow-slowing section of the cross sprue and the slag trap. The minimum choke area is arranged at the lower part of the branched sprue.

2. The gating system for preventing shrinkage cavities of a RuT450 vermicular graphite cast iron cylinder head according to claim 1, characterized in that: The cross-section of the ingate is circular, the ingate is determined to be circular, the value of the ingate diameter A = D / 3 to 2D / 3, and the draft angle is 3° to 10°; the ingate is provided with a boss; The value of the diameter B of the ingate boss is B = 3D / 2 to 2D; The distance c from the boss surface of the ingate to the ingate is c = D / 3 to 2D / 3.

3. The gating system for preventing shrinkage porosity of a RuT450 vermicular graphite cast iron cylinder head according to claim 2, characterized in that: The value ranges of the width a and height b of the sub-horizontal runner are: a ≤ b, the distance from the center of the ingate to the top of the sub-horizontal runner is b1, the distance from the center of the ingate to the bottom of the sub-horizontal runner is b2, and b1 ≥ b2; the distance d from the sub-horizontal runner to the ingate surface is 2c ≤ d ≤ 2D.

4. A gating system for preventing shrinkage porosity of a RuT450 vermicular graphite cast iron cylinder head according to claim 1, characterized in that: Minimum value of the flow-blocking area F 阻 = 2A C ~ 3A C .

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