Various types of medium and large ductile iron castings, resin sand process, insulation time required for the sand box after pouring

When producing resin sand for medium and large ductile iron castings, precautions for sand box insulation: During the insulation process of ductile iron castings, special attention should be paid to cooling uniformity, stress release, and sand mold stability to avoid defects. The specific precautions are as follows:

1. Control the cooling rate to avoid excessive temperature differences

During the insulation period, it is necessary to maintain a stable temperature around the sand box, avoid local exposure to cold air, rain, or direct sunlight, and prevent significant differences in cooling rates between different parts of the casting, which can cause thermal stress. For castings with complex structures (such as uneven thickness), insulation materials (such as asbestos cloth and insulation cotton) can be covered outside the sand box to slow down the overall cooling rate, especially to protect thick areas from slow heat dissipation.

2. Ensure the integrity of the sand mold and prevent premature collapse. During the insulation stage, the sand mold should be kept intact to avoid external collisions and vibrations that may cause cracking or collapse of the sand mold. Otherwise, the casting may lose support locally and deform due to its own weight or stress. -The strength of resin sand will change over time at high temperatures. It is necessary to avoid flipping the sand box too early and wait until the casting temperature drops to a safe range (usually below 200 ℃) before proceeding with the operation.

3. Monitor temperature changes and seize the opportunity to open the box. By embedding temperature measuring points or infrared thermometers, regularly monitor the temperature of the casting surface and thick parts to avoid relying solely on experience to judge the time and ensure that the temperature drops to a reasonable range (generally below 200-300 ℃) before opening the box. Large tonnage castings need to pay attention to the internal temperature to avoid rapid surface cooling but still high internal temperature, which may cause internal stress due to rapid heat dissipation after opening the box.

4. Preventing oxidation or contamination of castings: If the insulation environment is humid, attention should be paid to the permeability of the sand mold to avoid the formation of oxide scale on the surface of the castings due to water vapor condensation; When placed outdoors, it is necessary to cover it with waterproof cloth to prevent rainwater from seeping into the sand mold. Reasonable insulation control can minimize the internal stress of ductile iron castings, ensure their stable metallographic structure and mechanical properties, and is an important foundation for subsequent processing and use.

1、 The resin sand process refers to the insulation time of a 3-ton ductile iron sand box. After pouring the 3-ton ductile iron parts using the resin sand process, the insulation time of the sand box needs to be determined based on the casting structure, wall thickness, and cooling requirements. The core is to avoid defects such as cracks and deformation in the casting caused by premature opening. It is generally recommended to keep the insulation for 16-24 hours.

Specific adjustments can be made based on the following factors:

Casting wall thickness: If the casting wall thickness is large (such as exceeding 100mm), the insulation time should be appropriately extended (up to 24 hours or more) to ensure slow cooling inside; When the proportion of thin-walled parts is high, it can be shortened to about 16 hours. Cooling state: Before opening the box, the temperature of the casting can be confirmed to have dropped below 300 ℃ (not too hot to the touch or close to the ambient temperature) by measuring the temperature or observing the gaps in the sand box, and then the opening operation can be carried out.

Resin sand has good collapsibility, but ductile iron castings are sensitive to cooling rate. Reasonable insulation can reduce internal stress and ensure casting quality.

2、 The resin sand process refers to the insulation time of a 5-ton ductile iron sand box. After pouring the 5-ton ductile iron parts using the resin sand process, the insulation time of the sand box needs to be comprehensively judged based on the wall thickness, structural complexity, and cooling rate of the casting. The core is to avoid internal stress, cracks, or deformation caused by rapid cooling. It is generally recommended to maintain the insulation for 30-40 hours. Specific adjustments can be made based on the following factors: if the wall thickness of the casting is large (such as exceeding 150mm) or the structure is complex (there is a connection between thick and thin parts), the insulation time should be appropriately extended (up to 40 hours or more) to ensure slow and uniform cooling inside. Before opening the box, it is recommended to confirm through temperature measurement that the temperature of the casting has dropped below 250-300 ℃ (at this time, the resin sand has basically collapsed and the internal stress of the casting has been fully released), and then proceed with the opening operation. Although resin sand has good collapsibility, large tonnage ductile iron castings have larger volume and mass, and accumulate more heat. Slow cooling can effectively reduce tissue stress and thermal stress, ensuring stable casting performance.

3、 The resin sand process refers to the insulation time of a 7-ton ductile iron sand box. After pouring the 7-ton ductile iron parts using the resin sand process, the insulation time of the sand box needs to be comprehensively judged based on the wall thickness, structural complexity, and heat dissipation rate of the casting. The core is to reduce internal stress through slow cooling, avoid defects such as cracks and deformation, and generally recommend insulation for 40-18 hours. Specific adjustment reference: If the wall thickness of the casting is large (such as exceeding 200mm) or there is a significant uneven thickness structure, the insulation time should be extended to 35-40 hours to ensure that the internal heat of the thick part is fully released and the cooling is more uniform. Before opening the box, it is recommended to confirm through temperature measurement that the casting temperature has dropped below 200-250 ℃ (at this time, the resin sand performance is stable and the internal stress of the casting is fully released), and then proceed with the opening operation for greater reliability. Large tonnage castings accumulate more heat, and thermal and structural stresses are more likely to accumulate during the cooling process. Adequate insulation time can help slowly release stress, ensuring the structural stability and mechanical properties of ductile iron.

4、 The resin sand process refers to the insulation time of a 9-ton ductile iron sand box. After pouring the 9-ton ductile iron parts using the resin sand process, the insulation time of the sand box should focus on the volume, wall thickness, and heat dissipation characteristics of the casting. The core is to reduce internal stress through slow and uniform cooling, avoid defects such as cracks and deformation, and generally recommend insulation for 48-56 hours. Specific adjustment reference: If the wall thickness of the casting is large (such as exceeding 200-250mm) or the structure is complex (with thick protrusions, thick thin connections, etc.), the insulation time should be extended to about 48 hours to ensure that the internal heat of the thick parts is fully dissipated and the cooling rate is more uniform. Before opening the box, it is recommended to confirm through temperature measurement that the temperature of the casting has dropped below 200 ℃ (at this time, the resin sand has stable collapsibility and the internal stress of the casting is more fully released), and then proceed with the opening operation more safely. The 9-ton casting belongs to the category of large tonnage heavy parts, with high heat accumulation and slow heat dissipation. Sufficient insulation time can effectively alleviate the thermal stress and structural stress during the cooling process, ensuring the structural stability and mechanical properties of ductile iron.