รูขุมขนใต้ผิวหนังในการหล่อ: สาเหตุ, การป้องกัน, และโซลูชั่น

รูขุมขนใต้ผิวหนังในการหล่อถือเป็นข้อบกพร่องทั่วไป, requiring a series of preventive and corrective measures. Below are specific methods and suggestions for addressing this issue.

I. Preventive Measures

1. Control of Raw Materials

• Avoid raw materials with high titanium (Ti), อลูมิเนียม (Al), and high-alloy steel content, including stainless steel.
• Thoroughly clean raw materials with severe rust, ออกซิเดชัน, น้ำมัน, or waste sand before use.
• Dry wet materials before use to prevent gas absorption.
• Control the size of raw materials to about 300-400mm. When loading the furnace, arrange them tightly to minimize space and reduce oxidation and gas absorption in molten iron.

2. Optimizing the Smelting Process

• Clean slag thoroughly 2-3 times during the melting process, and cover molten iron with slag and insulation materials after cleaning to prevent oxidation.
• The high-temperature holding time for molten iron should not exceed 10-15 minutes to avoid quality deterioration.
• Keep tapping temperatures above 1540±10°C, removing slag promptly and covering with slag insulation to prevent cooling and oxidation.
• Avoid using carbon enhancers that don’t meet standards.

3. Control of Pouring Process

• Thoroughly dry all pouring tools, especially large and small ladles. Never use wet tools or rely on molten iron to heat-dry the equipment.
• Increase the pouring temperature and adopt a fast, high-temperature pouring method, following the “slow-fast-slow” principle. Increasing the temperature by 30-50°C can significantly reduce pore formation.
• Ensure proper slag blocking and shielding, and remove oxide scale before pouring.

4. Sand Treatment

• Keep sand moisture content below 3.5%. Maintain sand permeability at 130-180, wet compressive strength at 120-140 KPa, compaction rate at 35-38%, and surface hardness over 90.
• Use high-quality bentonite and coal powder, and add new sand according to regulations.
• After sand mixing, reclaim excess molding sand and thoroughly clean the sand mixer.

5. Mold Design

• Incorporate exhaust grooves, ducts, and dark air chambers in the parting surfaces to reduce gas pressure in the mold.
• Additional dark air chambers can further minimize gas pressure.

6. Use of Additives

• เพิ่ม 4%-6% coal powder, 2% hematite powder, หรือ 2%-2.5% ammonium difluoride to sand molds to prevent subcutaneous pores.
• Bake the inoculant to remove moisture before use. The inoculant particle size should be 5-10mm, and the aluminum content below 1%.

II. Repair Measures

If subcutaneous pores have already appeared, the following repair methods can be employed:

1. Welding Repair

• Suitable for repairing cast iron or cast steel by filling the pores through welding.

2. Brazing Repair

• Best for low-melting-point metals such as aluminum alloys.

3. Reheat Treatment

• Reheat the casting to recrystallize the pores, followed by machining to repair the surface.

4. Filling Repair

• Use high-strength metal fillers to fill the pores, then recast or machine the casting.

5. Grinding Repair

• Grind the surface to expose the pores, then weld or braze to repair the casting.

III. การตรวจสอบและการตรวจสอบ

• Regularly inspect castings using visual, ultrasonic, X-ray, or magnetic particle methods to detect subcutaneous pores early.
• Continuously monitor raw materials, ถลุง, pouring processes, sand treatment, and mold design to prevent pore formation.

บทสรุป: Addressing subcutaneous pores in castings requires a holistic approach, including controlling raw materials, เพิ่มประสิทธิภาพกระบวนการถลุง, managing pouring techniques, and improving mold design. By implementing comprehensive measures, this defect can be effectively minimized or prevented.