Occurs in the upper thin-wall part (about 5.5mm thick) of the casting. It is a non-penetrating or penetrating gap or cavity at the joint of the molten metal after filling, with a smooth surface and the shape of the initial flow of molten iron
Gas Porosity
Caused by gas from the sand core and molding sand, remaining in the casting as bubbles. Usually, it is an invasive gas porosity
Damage
Includes damage caused by human operations (such as cleaning the gas outlet riser and removing the runner) and mechanical operations (such as collision and cracking during the process of removing the runner and vibration sand falling)
1.2 Causes of Defects
Defect Type
Causes
Cold Shut
Unreasonable pouring system design. The inner runner is too far from the upper plane, the gas outlet distribution on the upper plane is disordered, and there is no inner runner at the corresponding position of the three-five bearing shell. The thin-wall part of the casting has a fast heat loss and a rapid decrease in molten iron temperature, and there is a lack of sufficient molten iron supplement at the position of the fourth and fifth cylinders
Gas Porosity
Sand core and molding sand gas generation. The main measures to control gas porosity are to control the residual moisture of the sand core, increase the pouring temperature, control the moisture of the molding sand, ensure the quality and combination clearance of the sand core, and optimize the layout and size of the riser and gas eye needle on the upper side of the casting
Damage
The gantry cylinder block has a high integration degree and a large upper and lower plane. The increase in the number of risers and the contact area with equipment and rollers in the casting cleaning line is more likely to cause damage. Human operation damage is mainly caused by improper cleaning, and mechanical damage is mainly caused by collision and cracking of the boss during the process of removing the runner and vibration sand falling
2. Solutions to Casting Defects
2.1 Improvement Measures for Cold Shut
Improvement Measure
Details
Pouring System Optimization
Increase the inner runner (section 5mm×25mm) and change the inner runner design at other bearing shell positions to 7mm×20mm to ensure the total cross-sectional area of the inner runner remains unchanged. This improves the rationality of molten iron filling, enhances the fluidity of molten iron, and reduces the confluence of molten iron from different inner runners on the large plane
2.2 Improvement Measures for Gas Porosity
Improvement Measure
Details
Sand Core and Molding Sand Control
Control the residual moisture of the sand core to be less than 0.6% after coming out of the drying kiln, control the moisture of the molding sand to be less than 2.9%, and reduce the addition of bentonite under the premise of ensuring strength to improve the air permeability of the molding sand
Pouring Temperature Adjustment
Increase the pouring temperature from 1390 – 1400℃ to 1410 – 1420℃
Sand Core Quality and Clearance Assurance
Ensure the quality of the sand core and the combination clearance to prevent the gas passage from being blocked
Exhaust System Optimization
Re-arrange and optimize the size of the riser and gas eye needle on the upper side of the casting, add exhaust sheets at the corresponding cylinder hole positions on the upper plane of the casting, and connect the inclined oil hole boss with the adjacent boss to discharge the gas from the sand core
2.3 Improvement Measures for Damage
Improvement Measure
Details
Human Operation Damage Prevention
Increase the diameter difference between the boss and the gas eye needle, and set a stepped structure between them to ensure the processing allowance of the boss after fracture. Change the position of the inner runner from the bearing shell to the side wall above the bearing shell to avoid damage to the bearing shell during cleaning
Mechanical Operation Damage Prevention
According to the subsequent processing and assembly situation, thicken the diameter of the boss or add reinforcing ribs to ensure the structural strength of the boss. Refine the casting cleaning operation process, formulate detailed operation standards, and conduct targeted training for cleaning operators
3. Effect of Improvement Measures
Defect Type
Before Improvement
After Improvement
Cold Shut
High occurrence rate
Solved
Gas Porosity
5.4%
Reduced to about 2%
Damage
High occurrence rate
Significantly reduced
4. Conclusion and Prospect
In the production of gantry cylinder blocks, various casting defects such as cold shut, gas porosity, and damage are prone to occur. Through optimization measures such as the pouring system, exhaust system, and process parameters, the quality of the casting has been significantly improved. Future research can focus on further optimizing the casting process to reduce shrinkage defects and improve the overall quality of the cylinder block. It is also necessary to continuously explore new materials and technologies to meet the higher requirements of the automotive industry for cylinder block performance.
