Method for solving the problem of air hole in gray iron body produced by lost foam casting

Abstract

This invention relates to the field of lost foam casting technology and provides a method for solving the porosity problem in gray iron casting. A necked ceramic tube is added to the lower end of the sprue, utilizing its "liquid seal-stabilized flow" characteristics to keep the pouring cup continuously filled. When molten iron flows in, the flow velocity at the neck increases, reducing the chance of gas entrapment and maintaining a stable molten iron level in the pouring cup, preventing air from entering the mold cavity. Venting is enhanced by adding a dedicated venting pipe to the bottom of the mold: a foam sprue is connected to the bottom slag discharge channel, covered with a paper ceramic tube, and then a steel pipe is fitted over the paper ceramic tube, with sand tightly packed between the paper ceramic tube and the steel pipe. Isolated bosses are connected to the main mold using foam material, enabling continuous molten iron filling. Through the synergistic effect of these three elements, this invention effectively controls porosity defects in gray cast iron parts, significantly reducing customer complaints and demonstrating significant engineering application value.

Description

Technical Field

[0001] This invention relates to the field of lost foam casting technology, and in particular to a method for solving the problem of porosity in gray iron bodies produced by lost foam casting. Background Technology

[0002] Lost foam casting, also known as solid foam casting, is widely used in the production of gray cast iron parts due to its advantages such as no need for core making and flexible processes. However, in actual production, gray cast iron parts, especially complex body castings, often exhibit dense porosity defects, leading to customer complaints and increased rework and repair costs. Porosity in critical areas can even result in significant losses due to the scrapping of castings. The main contributing factors include: 1. Gas entrapment during the pouring stage: The surface of molten iron in the pouring cup is prone to fluctuation, and air is drawn into the mold cavity along with the flow of molten iron, forming subcutaneous pores or internal pores. 2. Poor ventilation in the mold cavity: After the mold cavity is sealed after sand embedding, the gases generated during casting, such as foam gas and molten iron gas, cannot be discharged in time and accumulate to form pores. 3. Discontinuous molten iron filling: Isolated bosses on the casting, such as flanges and small lugs, are narrowly connected to the main cavity, which obstructs the flow of molten iron and makes it easy to stagnate. After local cooling, gas is released and porosity is formed.

[0003] Existing technologies often employ single measures, such as increasing the size of the pouring cup or adding venting holes, but they do not coordinate and optimize from three aspects: "gas source control - process venting enhancement - mold filling continuity assurance", resulting in limited improvement in porosity defects. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for solving the problem of porosity in gray iron bodies produced by lost foam casting, thereby solving the problems in the background art.

[0005] To achieve the above objectives, the present invention provides a method for solving the problem of porosity in gray iron bodies produced by lost foam casting, comprising the following steps: Step 1, Assembly: Based on the size and material requirements of the model, the boxes are assembled reasonably. A corresponding box layout diagram is prepared for each box. The box layout diagram includes the box number, material, pouring temperature and time, pouring weight, sprue, runner, ingate specifications and quantity, and boiler height. Step 2, Model Structure Review and Inspection / Repair: Conduct a structural review of the assembled model, provide feedback and mark any structures that cannot be cast or are difficult to embed in sand, especially any isolated bosses on the model, and repair any openings or seals in the model and address any connections between the model and isolated bosses. Step 3, Model coating, drying, and reinforcement: After the model has passed inspection, the coating, drying, and reinforcement work are carried out. Drying requires two passes to ensure the coating thickness and dryness of the model surface. Step 4, Gating System Setup and Sand Burying: The model is transferred to the modeling platform, and the gating system is set up according to the parameters of the gating diagram. A necked ceramic tube is added to the lower end of the sprue. Before the sand burying operation, the quality of the gating system setup is reconfirmed according to the parameters in the gating diagram. After ensuring that there are no errors, the sand is spread. First, the molding surface is buried. After the molding surface sand has completely cured and reached a certain time, the model is turned over and the bottom surface is buried with sand. After burying the sand, an exhaust pipe is set on the bottom surface of the model to enhance the exhaust. Step 5, Smelting and Casting: First, melt the scrap steel in the furnace. When the molten iron reaches 60% of the required weight, add the alloy according to the composition ratio, then add more scrap steel and continue smelting until the required weight of molten iron is reached. Take a sample to test whether the composition of the molten iron meets the requirements before the furnace. If it is qualified, raise the furnace temperature to above 1520℃ and let it stand at high temperature for 6-8 minutes. During the standing process, allow the slag in the furnace to float fully to ensure the purity of the molten iron. Remove the molten iron and remove the slag. Casting is carried out in accordance with the "slow-fast-slow" method.

[0006] Preferably, the necked ceramic tube at the lower end of the straight gating system is made of high-alumina clay and can withstand high temperatures of ≥1500℃. The inner diameter of the necked ceramic tube is larger at the upper end and smaller at the lower end.

[0007] Preferably, the upper end of the necked ceramic tube is connected to the sprue, and the lower end is connected to the sprue recess. The gap is sealed with cloth tape to prevent sand from entering the gap.

[0008] Preferably, the exhaust pipe on the bottom surface of the model is a foam gating system.

[0009] Preferably, the foam sprue is connected to the slag discharge channel on the bottom of the model, a paper ceramic tube is fitted over the foam sprue, a steel pipe is fitted over the paper ceramic tube, and sand is buried between the paper ceramic tube and the steel pipe for compaction.

[0010] Preferably, the model and the isolated bosses on the model are connected by connecting ribs to achieve continuous filling of molten iron.

[0011] Preferably, the connecting rib is 1 / 2 to 2 / 3 the thickness of the isolated boss, and is made of EPS foam material of the same material as the model.

[0012] The beneficial effects of this invention are as follows: Because traditional pouring cups are prone to air intake due to fluctuations in the molten iron surface, a necked ceramic tube is added to the lower end of the sprue. Utilizing its "liquid seal-stabilized flow" characteristics, the pouring cup is kept continuously filled. When molten iron flows in, the flow velocity at the neck increases, reducing the chance of gas entrapment. Simultaneously, it maintains a stable molten iron surface within the pouring cup, preventing air from entering the mold cavity. As molten iron flows from the pouring cup along the sprue, the reduced cross-sectional area of ​​the neck accelerates the flow, forming a stable liquid seal on the upper surface of the ceramic tube, preventing air from entering the pouring cup and avoiding gas entrapment during the initial pouring stage.

[0013] This invention enhances venting by adding a dedicated vent pipe to the bottom of the mold: a foam gating system is connected to the slag discharge channel on the bottom surface, and a paper ceramic tube is wrapped around it. A steel pipe is then wrapped around the outside of the paper ceramic tube, and sand is buried between the paper ceramic tube and the steel pipe to ensure tightness. The height of the vent pipe is set at 1-1.5 meters, which should ideally be higher than the height of the pouring cup to prevent molten iron from overflowing from the top of the vent pipe at the end of the pouring. Each mold box has 2-3 vent pipes. During pouring, the gas in the mold cavity (foam vaporization gas and molten iron precipitation gas) is discharged upward along the vent pipe, preventing the gas from diffusing into the interior of the casting.

[0014] This invention connects isolated bosses to the main model using foam material to achieve continuous molten iron filling: Foam connecting body: EPS foam of the same material as the model is used, and the shape is an integrated structure of "main model-connecting rib-isolated boss". The thickness of the connecting rib is 1 / 2 to 2 / 3 of the thickness of the isolated boss, and the length covers the farthest distance between the isolated boss and the main model.

[0015] This invention achieves effective control of porosity defects in gray cast iron parts through the synergistic effect of these three factors, greatly reducing customer complaints and demonstrating significant engineering application value. Detailed Implementation

[0016] 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.

[0017] 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.

[0018] This embodiment provides a method for solving the problem of porosity in gray iron bodies produced by lost foam casting, including the following steps: S1, Box Assembly: Based on the size and material requirements of the model, boxes are reasonably assembled. A corresponding box layout diagram is prepared for each box. The box layout diagram includes the box number, material, pouring temperature and time, pouring weight, sprue, runner, ingate specifications and quantity, and boiler height. S2, Model Structure Review and Inspection / Repair: Conduct a structural review of the assembled model, provide feedback and mark any structures that cannot be cast or are difficult to embed in sand, especially marking isolated bosses on the model. Repair or seal any openings in the model, and connect isolated bosses to the model using connecting ribs to achieve continuous molten iron filling. The connecting ribs are half the thickness of the isolated bosses and are made of EPS foam material of the same material as the model, with a length covering the furthest distance between the isolated bosses and the main model. S3, Model Coating, Drying, and Reinforcement: After inspection, qualified models undergo coating, drying, and reinforcement. Drying requires two passes to ensure the coating thickness and dryness of the model surface. S4, Sprue System Setup and Sand Burying Operation: The model is transferred to the modeling platform, and the sprue is set up according to the parameters of the gating diagram. A necked ceramic tube is added to the lower end of the sprue. The necked ceramic tube is made of high-alumina clay and can withstand high temperatures ≥1500℃. The inner diameter of the necked ceramic tube is D=160mm at the upper end and D1=140mm at the lower end. The upper end of the necked ceramic tube is connected to the sprue, and the lower end is connected to the sprue socket. The gap is sealed with cloth tape to prevent sand from entering the gap. When molten iron flows from the pouring cup along the sprue, the necked section accelerates the flow of molten iron due to the reduced cross-sectional area, forming a stable liquid seal on the upper surface of the ceramic tube. The liquid level is ≥50mm, which isolates air from entering the pouring cup and avoids gas entrapment in the early stage of pouring.

[0019] S5. Before the sand burying operation, reconfirm the quality of the pouring channel according to the parameters in the box layout diagram. After ensuring that there are no errors, start spreading sand. First, bury the molding surface. After the molding surface sand has completely cured and reached a certain time, turn it over and bury the bottom surface with sand. S6. After sand molding, the mold face is facing down and the bottom face is facing up. Molten iron is quickly poured into the sand mold. EPS foam quickly vaporizes, producing a large amount of gas and impurities. The gas in the mold cavity needs to pass through the thick sand layer, which is difficult to completely expel due to high resistance. The residual gas inside the sand mold can easily cause porosity defects in the casting. To enhance venting, a special venting pipe is added to the bottom of the mold: a 40*40mm foam gating channel is connected to the bottom slag discharge channel, and a φ60mm paper ceramic tube is fitted on the outside. A φ100mm steel pipe is fitted on the outside of the paper ceramic tube. The space between the paper ceramic tube and the steel pipe is tightly sealed with sand. The height of the venting pipe is set at 1.5 meters, which should be higher than the height of the pouring cup in principle to prevent the molten iron from overflowing from the top of the venting pipe at the end of the pouring. Three venting pipes are set for each box. During pouring, the gas in the mold cavity is discharged upward along the venting pipe to avoid the gas from diffusing into the casting. S7, Smelting and Casting: The furnace first melts the scrap steel. When the molten iron reaches 60% of the required weight, alloys are added according to the composition ratio, and then scrap steel is added to continue smelting until the required weight of molten iron is reached. The molten iron flows along a continuous path from the main mold to the connecting ribs to the isolated bosses, avoiding stagnant pores at the bosses due to flow interruption. The foamed connecting ribs vaporize rapidly at high temperatures and do not remain in the casting. S8. Take a sample to test whether the composition of the molten iron meets the requirements before the furnace. If it meets the requirements, raise the furnace temperature to above 1520℃ and let it stand at high temperature for 6-8 minutes. During the standing process, allow the slag in the furnace to float to the surface to ensure the purity of the molten iron. Remove the molten iron and scrape off the slag. Then pour the iron according to the "slow-fast-slow" method.

[0020] The castings produced in this way systematically solve the problem of porosity defects in the casting body by optimizing the gating system structure, strengthening cavity venting, and improving the fluidity of molten iron filling.

[0021] 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 method for solving the problem of porosity in gray iron bodies produced by lost foam casting, characterized in that, It includes the following steps: Step 1, Assembly: Based on the size and material requirements of the model, the boxes are assembled reasonably. A corresponding box layout diagram is prepared for each box. The box layout diagram includes the box number, material, pouring temperature and time, pouring weight, sprue, runner, ingate specifications and quantity, and boiler height. Step 2, Model Structure Review and Inspection / Repair: Conduct a structural review of the assembled model, provide feedback and mark any structures that cannot be cast or are difficult to embed in sand, especially any isolated bosses on the model, and repair any openings or seals in the model and address any connections between the model and isolated bosses. Step 3, Model coating, drying, and reinforcement: After the model has passed inspection, the coating, drying, and reinforcement work are carried out. Drying requires two passes to ensure the coating thickness and dryness of the model surface. Step 4, Gating System Setup and Sand Burying: The model is transferred to the modeling platform, and the gating system is set up according to the parameters of the gating diagram. A necked ceramic tube is added to the lower end of the sprue. Before the sand burying operation, the quality of the gating system setup is reconfirmed according to the parameters in the gating diagram. After ensuring that there are no errors, the sand is spread. First, the molding surface is buried. After the molding surface sand has completely cured and reached a certain time, the model is turned over and the bottom surface is buried with sand. After burying the sand, an exhaust pipe is set on the bottom surface of the model to enhance the exhaust. Step 5, Smelting and Casting: First, melt the scrap steel in the furnace. When the molten iron reaches 60% of the required weight, add the alloy according to the composition ratio, then add more scrap steel and continue smelting until the required weight of molten iron is reached. Take a sample to test whether the composition of the molten iron meets the requirements before the furnace. If it is qualified, raise the furnace temperature to above 1520℃ and let it stand at high temperature for 6-8 minutes. During the standing process, allow the slag in the furnace to float fully to ensure the purity of the molten iron. Remove the molten iron and remove the slag. Casting is carried out in accordance with the "slow-fast-slow" method.

2. The method for solving the problem of porosity in gray iron body during lost foam casting according to claim 1, characterized in that, The necked ceramic tube at the lower end of the straight gating system is made of high-alumina clay and can withstand high temperatures of ≥1500℃. The inner diameter of the necked ceramic tube is larger at the upper end and smaller at the lower end.

3. The method for solving the problem of porosity in gray iron body during lost foam casting according to claim 2, characterized in that, The upper end of the necked ceramic tube is connected to the sprue, and the lower end is connected to the sprue socket. The gap is sealed with cloth tape to prevent sand from entering the gap.

4. The method for solving the problem of porosity in gray iron body during lost foam casting according to claim 1, characterized in that, The exhaust pipe on the bottom of the model is made of foam gating.

5. The method for solving the problem of porosity in gray iron body during lost foam casting according to claim 4, characterized in that, The foam sprue is connected to the slag discharge channel on the bottom of the model. A paper ceramic tube is fitted over the foam sprue, and a steel pipe is fitted over the outside of the paper ceramic tube. Sand is buried between the paper ceramic tube and the steel pipe to ensure compaction.

6. The method for solving the problem of porosity in gray iron body during lost foam casting according to claim 1, characterized in that, The model and the isolated bosses on the model are connected by connecting ribs to achieve continuous filling of molten iron.

7. The method for solving the problem of porosity in gray iron body during lost foam casting according to claim 6, characterized in that, The connecting ribs are 1 / 2 to 2 / 3 the thickness of the isolated bosses, and are made of EPS foam material, the same material as the model.