Inclined lost foam filling casting process for large-thickness-difference side-pressing core castings
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUHU RUYHOO CASTING
- Filing Date
- 2026-06-17
- Publication Date
- 2026-08-04
AI Technical Summary
[0002]侧压芯是模具配套关键铸件，现有常规侧压芯产品普遍存在结构两极分化：一端铸件壁厚单薄、散热快、凝固速度快，另一端壁厚尺寸厚大，形成集中热节；常规消失模工艺采用模型水平平放、内浇口就近开设在厚大端，浇注后厚大热节区域凝固收缩量大，铁液补给不足，铸件厚壁内部频发缩孔、缩松缺陷，产品探伤合格率不足70%
[0012]本发明的有益效果：本发明针对侧压芯铸件单侧壁厚单薄、另一侧壁厚厚大、厚大热节区域极易产生缩孔、缩松缺陷的行业难题；本发明将侧压芯消失模白模整体倾斜装型、厚大壁厚端朝下、薄壁单薄端朝上布置，内浇口开设于铸件薄壁单薄侧位置，同步加大直浇道截面尺寸提升铁液补缩储备量；依靠重力作用，自上部薄壁内浇口持续向下方厚大热节区域补给凝固收缩所需铁水，构建自上而下顺序凝固体系，取消外置冒口，彻底改善厚大部位内部致密性，降低铸件废品率，简化浇注系统结构、节约铸件原材料。本工艺适配各类壁厚悬殊侧压芯铸铁件消失模批量生产，工艺稳定性强、生产成本低。
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Figure CN122500133A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lost foam casting technology, and in particular to a tilted lost foam casting process for side-pressure core castings with large thickness differences. Background Technology
[0002] Side-pressure cores are key casting components for mold assembly. Existing conventional side-pressure core products generally exhibit structural polarization: one end of the casting has a thin wall thickness, rapid heat dissipation, and fast solidification speed, while the other end has a thick wall, forming a concentrated hot spot. Conventional lost foam casting processes use a horizontally placed mold with the ingate located near the thick end. After pouring, the thick hot spot area experiences significant solidification shrinkage, resulting in insufficient molten iron replenishment. Consequently, shrinkage cavities and porosity defects frequently occur inside the thick-walled casting, and the product flaw detection pass rate is less than 70%.
[0003] Existing improvement solutions mostly involve adding large-volume external risers to the thick end for feeding, which has three drawbacks: ① The risers consume a lot of materials, resulting in low casting yield and high raw material costs; ② The riser cutting and grinding process is cumbersome, increasing machining time; ③ In lost foam negative pressure casting, the riser foam vaporization and venting are not smooth, which is prone to porosity defects; Another solution is to add chills to cool the hot spot, but the chills require high precision placement, the tooling cost is high, and the thin-walled end is prone to white iron and cold shut problems, which cannot solve the problem of insufficient feeding in the thick part from the root cause of solidification sequence.
[0004] Therefore, there is an urgent need to develop a new lost foam casting process that does not require additional risers, relies on model placement and gating system optimization to achieve directional feeding, and completely eliminates shrinkage cavities and porosity in thick side-pressure cores. Summary of the Invention
[0005] In view of this, the purpose of this invention is to propose a tilted lost foam casting process for side-pressure core castings with large thickness differences. To achieve the above objectives, the present invention provides a tilted lost foam casting process for side-pressure core castings with large thickness differences, comprising the following steps: Step 1, White mold forming: The white mold of the side pressure core is prepared by cutting and forming EPS foam board. According to the solid structure of the part, the white mold is divided into two major structural sections: thin-walled single installation section and thick and heavy pressure-bearing section. Step 2, tilting the mold: Before filling the sand box, fix the white mold of the side pressure core in an inclined position inside the sand box, with the thick and heavy sections facing down and the thin sections tilting up. The overall tilt angle of the white mold is 3° to 12°. Step 3, Gating system layout: The ingate is opened on the thin-walled section of the outer wall at the top of the white mold. The ingate is connected to the sprue. The high-temperature molten iron is stored in the enlarged sprue cross-sectional volume as the only feeding liquid reservoir. No additional metal feeding risers are set within the mold cavity. Step 4, Coating and Drying: Apply a special refractory coating for lost foam casting to the white mold and the integrated casting system, and dry it in stages at low temperature until the moisture content is ≤0.5%; Step 5, Negative Pressure Dry Sand Molding: Add dry sand to the sand box and compact it by vibration, then turn on the negative pressure system; Step 6, casting and molding: Molten iron is poured into the sprue at a uniform speed. The molten iron passes through the sprue → ingate → thin-walled section of the casting. It continuously supplies molten iron to the thick and heavy section below by gravity. The thin-walled section solidifies quickly first. The sprue and the thin-walled channel form a continuous liquid source to compensate for the volume shrinkage of the solidified part below. Step 7, heat preservation and cooling: After pouring, maintain pressure and heat for 3-8 hours. After the casting has completely solidified, release the pressure and remove the sand to obtain the finished side-pressure core casting.
[0006] Preferably, the overall tilt angle of the white mold in step two is 5° to 8°.
[0007] Preferably, in step three, the cross-sectional size of the sprue is increased by 15% to 40% to increase the amount of molten iron stored inside the sprue, without setting any feeding risers.
[0008] Preferably, the negative pressure value of the negative pressure system in step five is controlled between -0.03MPa and -0.06MPa.
[0009] Preferably, the molten iron poured in step six is ductile iron, and the pouring temperature is 1380-1430℃.
[0010] Preferably, the molten iron poured in step six is gray iron, and the pouring temperature is 1350-1400℃.
[0011] Preferably, the fourth step of low-temperature drying is divided into three stages: pre-drying, main drying, and slow cooling; the pre-drying temperature is 35-45℃, the main drying temperature is 50-65℃, and the heating rate throughout the drying process is ≤8℃ / h to prevent the EPS foam from bulging due to heat and the coating from peeling off.
[0012] The beneficial effects of this invention are as follows: This invention addresses the industry problem of shrinkage cavities and porosity defects easily occurring in side-pressure core castings where one side has a thin wall thickness and the other side has a thick wall thickness, particularly in the thick, hot-spot area. This invention uses an inclined white mold arrangement for the side-pressure core lost foam casting, with the thicker wall end facing downwards and the thinner wall end facing upwards. The ingate is located on the thinner wall side of the casting, and the cross-sectional size of the sprue is simultaneously increased to enhance the molten iron replenishment capacity. Relying on gravity, molten iron is continuously supplied from the upper thin-walled ingate to the lower thick, hot-spot area to meet the solidification shrinkage requirements, constructing a top-down sequential solidification system. This eliminates the need for external risers, thoroughly improves the internal density of the thicker sections, reduces the casting scrap rate, simplifies the gating system structure, and saves casting raw materials. This process is suitable for mass production of lost foam castings with side-pressure cores of varying wall thicknesses, exhibiting strong process stability and low production costs.
[0013] Solidification sequence optimization: The sloping layout with thinner upper and thicker lower sections allows the thinner upper section to solidify first and lock the gating system. The sprue acts as a long-term feeding source, and under the action of gravity, the molten iron continuously feeds the thick and hot section at the bottom from top to bottom. This eliminates shrinkage cavities and porosity in the thick section from the solidification mechanism, and increases the pass rate of internal flaw detection of castings to over 98%. Eliminating the riser structure: By eliminating the external feeding riser at the thick end, the casting process yield is increased by 12% to 18%, saving foam raw materials and molten iron consumption, and reducing production costs; Simplified post-processing steps: No riser cutting or grinding steps, shortening subsequent machining time and reducing processing losses; High process adaptability: Only the placement angle of the white mold and the size of the gating system need to be changed. No new chills or special tooling are required. The existing lost foam production line can be directly modified and put into production. The modification cost is low and it is suitable for mass production of a full range of side-pressure core castings with large thickness differences. Improved stability of negative pressure molding: Thick parts are in a low position, molten iron fills the mold smoothly, and the decomposed foam gas is smoothly discharged upward through the thin wall and gating, thus reducing the incidence of porosity defects. Attached Figure Description
[0014] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0015] Figure 1 This is a schematic diagram of the inclined assembly structure of the side-pressure core white mold of the present invention.
[0016] The diagram is marked as follows: 1-Straight runner, 2-Ingate, 3-Thin-walled single section, 4-Thick and heavy section. Detailed Implementation
[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.
[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly. Example 1
[0019] The side pressure core is made of ductile iron, with a single thin-walled section thickness of 12mm and a thick end wall thickness of 65mm. The manufacturing process is as follows. S1. A white mold for lost foam casting with side pressure core is prepared by cutting and molding EPS foam board, with a thin wall of 12mm at one end and a thick wall of 65mm at the other end. S2. Select a standard sand box with a diameter of 1200mm×1000mm×800mm. The inside of the sand box is pre-installed with adjustable angle nylon support pads. The polished side pressure core white mold is bound to the pads with high temperature resistant fiberglass straps. Adjust the inclination angle of the pads to control the overall axis of the white mold to be tilted at an angle of 6° with the horizontal plane. S3. All ingates are integrally bonded to the top surface of the thin-walled single-segment outer wall using EPS foam. Each casting has two flat ingates with a cross-sectional size of 25mm × 12mm and a length of 35mm, laterally connected to the vertical sprue. The original standard sprue cross-section was Φ50mm; this has been optimized by increasing it by 25% to Φ58mm, increasing the volume by 25.2% to meet the feeding fluid storage requirements of the thicker sections. No external metal risers or concealed risers are installed on the sides or top of the mold cavity, thicker pressure-bearing sections, or other surfaces; no chills are pre-embedded. The enlarged sprues serve as the sole feeding fluid reservoir. The gating system is spot-bonded to the white mold using the same EPS foam adhesive, with the adhesive usage controlled at 0.2g / cm² to avoid generating additional fumes during excessive adhesive pouring. S4. A two-coat process is adopted: the first coat has a dry film thickness of 0.8mm and is allowed to level naturally for 15 minutes; the second coat has a dry film thickness of 1.0mm, with the total dry film thickness controlled at 1.8±0.2mm. The Baume degree of the coating is adjusted to 38-40°Be to ensure the coating's breathability and resistance to molten iron erosion. The coating is then transferred to a closed, constant-temperature drying chamber for three-stage drying, with continuous fresh air circulation and a constant air humidity of 22% throughout the process: ① Pre-drying stage: temperature 40℃, drying time 14h, heating rate 6℃ / h; ② Main drying stage: temperature 58℃, drying time 22h, heating rate 5℃ / h; ③ Slow cooling stage: uniformly cooling from 58℃ to 32℃ at a cooling rate of 4℃ / h for 8h. After drying, the moisture content of the white mold coating was sampled and tested with a moisture meter. The actual measured moisture content was 0.42% ≤ 0.5%, which is qualified. The heating rate throughout the process did not exceed 8℃ / h, and there were no defects such as EPS foam bulging, coating peeling, or edge cracking. S5. Select 40-70 mesh round dry quartz sand with a silica content ≥96%. Control the sand temperature at 25℃±3℃. Fill the sand uniformly from the top of the sand box. Simultaneously, turn on the variable frequency vibration table with a vibration frequency of 50Hz, an amplitude of 0.3mm, and a compaction time of 180s to ensure a dry sand bulk density of 1.62g / cm³, eliminating voids inside the sand mold. After compaction, seal the top surface of the sand box with a film, turn on the negative pressure pump station, and stabilize the negative pressure value at -0.045MPa. Maintain the pressure and keep it ready. Control the negative pressure fluctuation within ±0.002MPa to prevent the sand mold from collapsing during the filling process. S6 uses a medium-frequency furnace to melt QT550-7 ductile iron. After the molten iron is tapped from the furnace, it undergoes spheroidizing inoculation and secondary in-flow inoculation treatment, and the final pouring temperature is stably controlled at 1405℃. A uniform bottom pouring method is adopted, with a pouring time of 72s and a constant pouring flow rate of 2.3kg / s. The filling flow direction strictly follows: high-temperature molten iron is stored in the sprue → two ingates → upper thin-walled mounting section → the lower thick pressure-bearing section is filled from top to bottom by gravity. During the filling process, the thin-walled section has a small wall thickness and a fast heat dissipation rate. It solidifies first within 11 minutes after pouring, directly locking the inner gating channel. At this time, 12.6 kg of high-temperature molten iron remains inside the enlarged sprue. Under the continuous action of gravity negative pressure coupling, it feeds back to the thick hot section at the bottom through the intergranular gaps of the solidified thin-walled section, compensating for the 2.7% solidification volume shrinkage of the thick section. During the filling process, the styrene gas decomposed from EPS gathers upward and is quickly extracted by the negative pressure system through the sand mold pores of the thin-walled section and the sprue, with no gas retention.
[0020] S7: After pouring, without depressurizing or moving the sand box, maintain a negative pressure of -0.045MPa for 5.5 hours to ensure complete sequential solidification of the casting from thin-walled to thick sections. After heat preservation, slowly depressurize at a rate of 0.005MPa / min to avoid surface deformation caused by rapid depressurization. After depressurization, allow natural cooling for 2 hours, then perform mechanical vibration to remove the refractory coating and residual dry sand, finally obtaining the finished side-pressure core casting. The thick sections of the finished product show no shrinkage cavities or porosity after UT ultrasonic testing, and the mechanical properties meet the standards with no porosity defects. Example 2
[0021] The side-pressure core is made of HT250 gray cast iron of the same model, with a single thin-walled section thickness of 8mm and a thick end wall thickness of 52mm. The different parameters compared to Example 1 are adjusted as follows: The white mold of S2 has a tilt angle of 5°. The cross-section of the S3 straight sprue is enlarged by 15%, with a cross-section size of Φ57mm; S4 drying parameters: pre-drying 35℃, main drying 50℃, total heating rate 7℃ / h, total drying time 39h, final moisture content 0.47%; S5 negative pressure value -0.04MPa; S6 pouring temperature 1370℃, pouring time 68s; 6. S7 pressure and heat preservation for 4 hours. The remaining white mold forming, coating, sand filling and compaction processes are completely consistent with those in Example 1.
[0022] The resulting castings have a thick cross-section with a dense metallographic structure and no internal porosity defects.
[0023] The comparison is the traditional horizontal placement + internal gating + riser process at the thick end; castings of the same specification are placed horizontally, with the internal gating set at the thick end, and a cylindrical feeding riser added to the outside of the thick wall; the shrinkage porosity scrap rate of the thick end of the casting is 29%, the riser loss of molten iron is 16%, and the post-processing cutting process time is increased by 30%.
[0024] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and many other variations of different aspects of the invention as described above exist, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.
Claims
1. A tilted lost foam casting process for side-pressure core castings with large thickness differences, characterized in that, It includes the following steps: Step 1, White mold forming: The white mold of the side pressure core is prepared by cutting and forming EPS foam board. According to the solid structure of the part, the white mold is divided into two major structural sections: thin-walled single installation section and thick and heavy pressure-bearing section. Step 2, tilting the mold: Before filling the sand box, fix the white mold of the side pressure core in an inclined position inside the sand box, with the thick and heavy sections facing down and the thin sections tilting up. The overall tilt angle of the white mold is 3° to 12°. Step 3, Gating system layout: The ingate is opened on the thin-walled section of the outer wall at the top of the white mold. The ingate is connected to the sprue. The high-temperature molten iron is stored in the enlarged sprue cross-sectional volume as the only feeding liquid reservoir. No additional metal feeding risers are set within the mold cavity. Step 4, Coating and Drying: Apply a special refractory coating for lost foam casting to the white mold and the integrated casting system, and dry it in stages at low temperature until the moisture content is ≤0.5%; Step 5, Negative Pressure Dry Sand Molding: Add dry sand to the sand box and compact it by vibration, then turn on the negative pressure system; Step 6, casting and molding: Molten iron is poured into the sprue at a uniform speed. The molten iron passes through the sprue → ingate → thin-walled section of the casting, and is continuously supplied to the thick and heavy section below by gravity. The thin-walled section solidifies rapidly first, and the straight gating and thin-walled channel form a continuous liquid source to compensate for the volume shrinkage of the solidified thick section below; Step 7, heat preservation and cooling: After pouring, maintain pressure and heat for 3-8 hours. After the casting has completely solidified, release the pressure and remove the sand to obtain the finished side-pressure core casting.
2. The inclined lost foam casting process for side-pressure core castings with large thickness differences according to claim 1, characterized in that, In step two, the overall tilt angle of the white mold is 5° to 8°.
3. The inclined lost foam casting process for side-pressure core castings with large thickness differences according to claim 1, characterized in that, In step three, the cross-sectional size of the sprue is increased by 15% to 40% to increase the amount of molten iron stored inside the sprue, without setting any feeding risers.
4. The inclined lost foam casting process for side-pressure core castings with large thickness differences according to claim 1, characterized in that, In step five, the negative pressure value of the negative pressure system is controlled between -0.03MPa and -0.06MPa.
5. The inclined lost foam casting process for side-pressure core castings with large thickness differences according to claim 1, characterized in that, The molten iron poured in step six is ductile iron, and the pouring temperature is 1380-1430℃.
6. The inclined lost foam casting process for side-pressure core castings with large thickness differences according to claim 1, characterized in that, The molten iron poured in step six is gray iron, and the pouring temperature is 1350-1400℃.
7. The inclined lost foam casting process for side-pressure core castings with large thickness differences according to claim 1, characterized in that, The fourth step of the low-temperature drying process is divided into three stages: pre-drying, main drying, and slow cooling. The pre-drying temperature is 35-45℃, the main drying temperature is 50-65℃, and the heating rate throughout the drying process is ≤8℃ / h to prevent EPS foam from bulging and the coating from peeling off due to heat.