What are the characteristics of sand flushing defects in the production of gray cast iron parts using green sand? What is the difference between slag eye defects?

1、 The typical characteristic of sand flushing defects is that sand flushing, as the name suggests, is a defect caused by the metal liquid "flushing" the sand mold. You can imagine it as a turbulent river washing away the soil on its banks.

Location: It always appears in the area with the fastest flow rate and strongest impact force of the molten metal. The most common ones are directly opposite the sprue, at the turning point of the mold cavity, or on any sand mold surface or core directly facing the impact of the metal flow. Wherever the metal liquid flows like a water gun, problems are most likely to occur. Appearance: On the surface of the casting, it appears as rough, irregular grooves or pits, often in the shape of long strips, and its extension direction is consistent with the flow direction of the molten metal at that time, as if it has been plowed through. Touching the material: This is the most crucial point. In these grooves or the resulting internal holes (sand holes), you can clearly see or feel scattered, metal coated sand particles. It can be removed with tools and has a noticeable grainy texture. These sands come from the sand molds themselves that have been washed away. Simply put, to recognize sand flushing, three points should be taken: the location is in a high-speed flushing area, the appearance is rough grooves, and there is sand inside.

2、 The typical characteristic of slag eye defect is that the slag carried by the molten metal itself enters the mold cavity. You can think of it as a pot of boiling Congee, and the "Congee oil" and foam that could not be skimmed off on the surface were mixed into the bowl.

Location: Because slag is usually lighter than molten iron, it will float above. So the majority of slag holes appear on the upper surface of castings, at the root of risers, or in the corners of the mold cavity that are finally filled with molten iron. It is' floating 'up. Appearance: The slag eye can be an independent hole or a pit on the surface of the casting. Its inner wall is relatively smooth, not as rough as sandblasting, often with a glassy luster or presenting a blue black, dark gray oxidation color. Texture: In the hole, what you find is not loose sand, but a kind of glassy, brittle and hard non-metallic material. The color is usually dark (such as dark green, black), and the structure may be porous foam or dense glaze. This is the slag generated during the melting and pouring process. Simply put, there are three key points to identify slag eyes: they are located on the upper part of the casting, the inner wall is relatively smooth, and there are glass like brittle slag inside. The fundamental reason for the core difference is different: sand flushing is a physical and mechanical problem, and the root cause is that the sand mold is not solid enough or the metal flow is too "violent". Slag eye is a metallurgical chemical problem, which is rooted in insufficient melting purification or failure to pour slag blocking. 

Judgment tip: When a defect is found on a casting: 

1 First, check where it is: if the defect is on the opposite side of the gate or at the corner of the mold cavity, first suspect sand flushing; If the defect is on the top surface of the casting or under the riser, the first suspicion is slag holes. 

2. Look inside again: If it's sand inside, it must be sand flushing; If there is glass like brittle slag inside, it must be slag eyes.

Solution for sand flushing and slag hole defects in the production of gray cast iron parts using green sand. 

1、 The essence of sand flushing is that the strength of the sand mold cannot withstand the impact of liquid flow. Therefore, the solution must be a two pronged approach: strengthening sand molds and optimizing casting. Option 1: Comprehensively improving the strength of sand molds is the most fundamental measure to solve sand flushing. 1. Optimize sand properties: Increase effective bentonite content: Regularly replenish new bentonite to ensure its effective content is within the process requirements (usually 7% -10%). Accurate control of moisture: If the moisture is too high, the sand mold will become soft, and if the moisture is too low, the sand mold will become brittle. By controlling the compaction rate, find the optimal moisture point (usually fluctuating around 3-4% moisture, but subject to the compaction rate). Reduce old sand dust: Strengthen dust removal airflow, regularly eliminate some old sand and supplement new sand, and control the dust content below 12% -15%. Ensure sufficient mixing and grinding: Ensure sufficient mixing time to evenly wrap the bentonite and moisture on the surface of the sand particles, forming a strong "clay film". 

2. Improve the surface hardness and density of the sand mold: Check and increase the compaction pressure of the molding machine to ensure that the Skaller hardness of the sand mold, especially the complex parts such as grooves and holes in the mold, reaches 90 units or more. Uniform compaction: Check the sand injection port and compaction plate to ensure that all parts of the sand mold have uniform compaction and no loose areas. 

3. Strengthen the surface protection of the mold: use high-quality coatings: spray or brush a layer of refractory coating (such as zircon powder coating) on areas prone to sand flushing (such as the corresponding area of the sprue). This is equivalent to putting a layer of "armor" on the sand mold. Ensure the paint is dry: The paint must be thoroughly dried or ignited to form a strong fire-resistant layer. Underdried paint is actually more likely to be washed away. 

Option 2: Optimize the design of the pouring system to quell the "violent" metal flow Adopting an open pouring system: making the cross-sectional area ratio of the sprue, runner, and inner runner reasonable (such as 1.5:1.2:1.0), ensuring smooth filling of the molten metal and avoiding spraying. 2. Increase the cross-sectional area of the sprue: This is the most effective method to reduce the flow rate of molten metal into the mold cavity. As the speed decreases, the scouring force naturally weakens significantly. 3. Change the direction of the sprue: Do not direct the sprue directly towards the mold wall or sand core. You can change its direction to follow the tangent direction of the mold wall and use "wall flow" instead of "impact flow" to fill the mold. 4. Set up a "dam" or "buffer" structure: set up a slag collection bag in the transverse pouring channel, or set up a sand mold protrusion (sacrificial block) on the front of the metal flow impact to actively bear and consume the impact force, protecting the main cavity behind. 

Plan 3: Standardize operation and control pouring temperature: While ensuring filling and flowability, avoid excessively high pouring temperature to reduce the thermal erosion effect on the sand mold. Smooth pouring: During pouring, align the pouring cup and keep the pouring nozzle as close as possible to the pouring cup to form a "steady flow" and avoid splashing and impact of the metal liquid. 

2、 The solution to the "slag eye" defect is that the essence of the slag eye is that "the slag has entered the mold cavity". Therefore, the core of the solution is "blocking" and "arranging". 

Plan 1: Strengthen slag blocking before melting and pouring Thoroughly remove slag: After tapping iron in an electric furnace or blast furnace, thoroughly and carefully remove slag in a ladle. After slag removal, a layer of insulation covering agent (such as perlite) can be sprinkled on the surface of the molten iron to prevent secondary oxidation and isolate the air, thus preventing the generation of new slag.

 2. Using a teapot bag: This is the most effective measure. The unique design of the teapot bag allows the metal liquid to flow out from the bottom, while the slag floats on the surface and is blocked by the partition wall, thus achieving automatic slag blocking. 

Option 2: Optimize the pouring system and set up a "slag trap". An excellent pouring system itself is an efficient slag filter. 

1. Use a sprue cup with slag blocking function: Plug out sprue cup: Before pouring, the floating slag floats to the top of the sprue cup. After removing the plug, clean metal liquid enters the sprue from the bottom. Filter plate: Placing a ceramic filter at the bottom of the sprue cup or in the runner can physically intercept most of the slag. 

2. Fully utilize the slag blocking effect of the transverse runner: adopt a "slow flow, full filling" transverse runner: ensure that the transverse runner has sufficient cross-sectional area to be completely filled with molten metal, so that the slag will be trapped at the top of the transverse runner due to the upward floating effect and will not enter the inner runner. Set up a slag collection bag: Design a protruding "slag collection bag" on the runner. Due to the low density of slag, they will float up and be collected in this' trap 'instead of entering the mold cavity.

 Ensure that the slag collection bag is located at the rear end of the inner runner. Plan 3: Standardize pouring operations 1 Continuous pouring: During the pouring process, the flow cannot be interrupted. Once the flow is interrupted, air will enter the ladle and form new oxide slag. 

2. Keep the sprue cup full: Fill the sprue cup with molten metal from beginning to end to create static pressure and allow occasional slag to float on the sprue cup surface without entering the sprue. When a defect occurs, please first accurately determine whether it is sand flushing or slag hole based on its characteristics, and then prescribe the right medicine: to deal with sand flushing, the core is "strong sand mold, slow flow rate". Check the strength and compactness of your sand, and then examine whether your pouring system is too 'violent'. Dealing with scumbags: The core is to 'clean up the scum and set up a good card'. Check if your slag removal is thorough, if the pouring ladle is a teapot ladle, and if your pouring system has efficient slag blocking structures (such as filters and slag collectors). Through this systematic approach, these two types of problems can be effectively solved, significantly improving the quality of castings.