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, oxidation, 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. Inspection and Monitoring

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.