Casting is a manufacturing process that involves pouring molten metal into a mold to form a desired shape. However, during the casting process, various defects may occur, which can affect the quality and performance of the final product. In this article, we will focus on the analysis and improvement measures of casting defects in the 16V190 cylinder head.
I. Introduction
The 16V190 cylinder head is a critical component of a diesel engine. It not only withstands high temperatures and pressures during the engine’s operation but also requires a smooth internal surface and dense internal structure to ensure proper functioning. Therefore, the quality of the cylinder head casting is of utmost importance.
II. Casting Defects in 16V190 Cylinder Head
A. Sand Hole
The sand hole defect in the 16V190 cylinder head refers to the presence of unwanted holes on the internal or surface of the casting after cleaning. This defect is mainly caused by improper operations during the mold assembly and box closing process. For example, if the bolt hole core is not installed properly, not perpendicular to the bottom surface of the core, or if the upper mold is not lifted and placed smoothly during box closing, the bolt hole core may be broken, and the broken sand core may fall into the mold cavity, resulting in sand holes in the casting.
B. Inner Cavity Burr
The inner cavity burr defect in the 16V190 cylinder head is characterized by the presence of irregular and uneven layers of “thin iron sheets” in the gas path, water path, or other parts. There are two main reasons for this defect. Firstly, the complex structure of the water cavity in the cylinder head leads to shrinkage and cracking of the sand core during the cooling process, allowing the molten iron to infiltrate and form burrs. Secondly, the division of the water cavity core into two pieces and the imperfect bonding between them increase the possibility of molten iron infiltration, resulting in a higher probability of inner cavity burrs.
C. Misrun
The misrun defect in the 16V190 cylinder head occurs when there is an iron liquid overflow at the parting surface during the pouring process, resulting in incomplete filling of the mold. This defect can also be influenced by factors such as the purity of the iron liquid, the pouring temperature, the correct placement of the filter, and the presence of air holes that cause iron liquid leakage.
D. Porosity
The porosity defect in the 16V190 cylinder head is mainly caused by the generation of a large amount of gas during the pouring process due to the use of resin self-hardening sand for molding and core making. The gas is carried into the mold with the molten iron and cannot be smoothly discharged, resulting in the formation of porosity in the casting, and most of these pores are invasive pores.
III. Causes of Casting Defects
A. Sand Hole Causes
- Improper installation of the bolt hole core and unstable lifting of the upper mold during box closing can lead to the breaking of the bolt hole core and the falling of the broken sand core into the mold cavity.
- The use of separate sand cores for the upper water cavity and the injector hole core, along with the presence of floating sand or accumulated coating in the injector hole core seat, and unstable lifting of the upper mold during box closing, can cause the breaking or compression of the sand core, resulting in sand holes.
B. Inner Cavity Burr Causes
- The shrinkage and cracking of the sand core during the cooling process due to the complex structure of the water cavity, allowing the molten iron to infiltrate and form burrs.
- The imperfect bonding between the two pieces of the water cavity core, resulting in increased possibility of molten iron infiltration.
C. Misrun Causes
- Iron liquid overflow at the parting surface during the pouring process, which may be caused by the use of defective sand boxes or improper box closing.
- Factors such as the purity of the iron liquid, the pouring temperature, the correct placement of the filter, and the presence of air holes that cause iron liquid leakage can also affect the filling of the mold.
D. Porosity Causes
The resin and curing agent in the resin self-hardening sand generate a large amount of gas under the heat of the high-temperature molten iron. During the pouring process, the gas is carried into the mold and cannot be smoothly discharged, resulting in the formation of porosity in the casting.
IV. Improvement Measures
A. Sand Hole Improvement Measures
- Use of Core Insertion Cards
- Make core insertion cards based on the actual situation to ensure that the sand cores can be inserted in place.
- For the group core casting process used in this cylinder head, make height confirmation cards for the mating surfaces related to the height direction of the sand cores to reduce the cumulative error of core insertion and prevent the breaking of the bolt hole core and related sand cores during box closing.
- Wall Thickness Inspection Tools
- Make an inner cavity wall thickness caliper and a 6 mm soft leather cord.
- Use the wall thickness caliper to check the regular wall thickness dimensions, and use the soft leather cord as a check feeler to pass through the curved cavity to ensure the minimum wall thickness at the curved parts.
- This ensures that the relevant sand cores in the inner cavity are inserted in place and prevents the sand cores from being damaged during box closing.
- Quality Awareness Training
- Conduct regular quality awareness training to enhance the quality awareness of the operators.
- During the core insertion process, clean the floating sand or accumulated coating in the core seat one by one.
- After core insertion, check the perpendicularity of the bolt hole core one by one.
- During the box closing process, have a check whether the bolt hole core collides with the upper core seat to ensure a smooth box closing and prevent the breaking of the bolt hole core and other sand cores.
B. Inner Cavity Burr Improvement Measures
- Improve the Quality of the Water Cavity Core
- Control the shooting core temperature and holding time to ensure that the thickness of the core shell layer is greater than 5 mm.
- Before assembly, use alcohol-based zircon powder coating for two immersion coatings to improve the density, refractoriness, and strength of the sand core surface.
- Enhance the Quality Control of Water Cavity Core Insertion
- During core insertion, first, test-fit the upper and lower water cavity sand cores to check the mating condition of the mating surfaces.
- According to the shape of each part, appropriately trim the mating surfaces of the two sand cores to make the mating flat and minimize the mating surface gap.
- When inserting the upper water cavity core, first, evenly apply a layer of casting glue on the mating surface of the lower water cavity core, avoiding the exhaust groove. Then, close the upper water cavity core, apply a little pressure to make the casting glue squeeze to both sides, remove the upper core, and check the bonding condition of the two sand cores. Scrape off the excess casting glue and use casting glue to appropriately repair the areas that are not tightly bonded. Finally, close the upper sand core again and apply pressure to ensure that the mating surfaces of the two sand cores are sufficiently tight, reduce the possibility of molten iron infiltrating the sand core, and reduce the burrs in the water cavity.
C. Misrun Improvement Measures
- Prevent Leakage during Pouring
- During the molding process, check the condition of the sand boxes and other tooling. Do not use sand boxes that are missing or loose to prevent the overall sinking of the mold.
- Before box closing, place a ϕ4 mm sealing mud strip along the periphery of the lower mold’s parting surface, away from the sprue. When tightening the mold with box clamps, tighten them diagonally simultaneously to ensure uniform force on the mold.
- Control the Quality of Molten Iron and Pouring Process
- During the pouring process, control the quality of the raw molten iron and perform slag removal and skimming operations.
- Strengthen the slag blocking operation during pouring. The pouring ladle nozzle must be close to the pouring cup, quickly fill the pouring cup, and maintain the liquid level in the pouring cup to avoid turbulence, vortex, or even splashing during the filling process and prevent the blocking of the filter holes by slag during the pouring process.
- Ensure Correct Placement of the Ceramic Filter
- In the process design, place a ceramic filter at the junction of the sprue and the runner in the pouring system to play a role in slag blocking.
- When placing the ceramic filter, ensure that the inlet holes face the pouring cup to ensure that the molten iron flows smoothly through the filter holes and into the mold.
- Control the Ventilation Holes and Air Eyes
- Ensure that the air passages in the sand mold and sand core are unobstructed and make the ventilation holes in the sand core during the mold assembly process.
- Try to reserve the ventilation holes in the upper mold. Additionally, seal the area around the ventilation holes to prevent the molten iron from entering and causing iron leakage.
- Control the Pouring Temperature
- During the pouring process of the cylinder head, control the initial pouring temperature at the upper limit of the process (1390 °C).
- Insulate the molten iron in the pouring ladle with appropriate insulation materials to ensure a smooth and rapid pouring process and try to maintain the pouring temperature within the process requirements during the later stages of pouring.
D. Porosity Improvement Measures
- Optimize the Pouring System Design
- Ensure that the design of the inner runner is conducive to the smooth filling of the molten iron and the smooth escape of gas.
- Design the riser and air eyes in the correct position and in a reasonable quantity to facilitate the smooth discharge of gas from the mold.
- Control the Exhaust Function of the Sand Core
- Before sand core immersion coating, block the air passage holes to prevent the coating from blocking the air passages.
- After blocking, unblock all the air passage holes in the sand core head and the blocked air passage holes before immersion coating, and extend them to the thick parts of the sand core to pour out some broken sand in the sand core and ensure the smooth flow of the air passage in the sand core.
- Ensure Ventilation of the Sand Core and Mold
- Before core insertion, based on the position of the sand core head in the mold cavity, unblock the ventilation holes from the outside of the mold to the core seat.
- Apply casting glue in the core seat to block the gap between the core head and the ventilation holes. Apply casting glue around the ventilation holes to prevent the molten iron from entering the ventilation passages and blocking them during the pouring process, ensuring that the gas generated in the sand core can be smoothly discharged from the mold.
V. Effect of Improvement Measures
By implementing the above improvement measures, the occurrence of sand holes, inner cavity burrs, misrun, and porosity defects in the 16V190 cylinder head casting has been effectively avoided in the actual production process. The rejection rate of the cylinder head casting has decreased from the original 3.8% to 0.8%, achieving good implementation results.
VI. Conclusion
In conclusion, by analyzing the causes of the sand holes, inner cavity burrs, misrun, and porosity defects in the 16V190 cylinder head and taking corresponding improvement measures, the quality of the cylinder head casting has been effectively improved, and the rejection rate has decreased by 3%. It is crucial to pay attention to the details of the casting production process and control the quality of the casting. By reasonably designing and improving the casting process, standardizing the on-site operation requirements, and implementing relevant measures in place, the amount of scrap castings can be greatly reduced, the production efficiency can be improved, and the production cost can be lowered.
| Defect Type | Causes | Improvement Measures |
|---|---|---|
| Sand Hole | Improper installation of bolt hole core, unstable lifting of upper mold, presence of floating sand or accumulated coating in injector hole core seat | Use of core insertion cards, wall thickness inspection tools, quality awareness training |
| Inner Cavity Burr | Shrinkage and cracking of sand core, imperfect bonding between two pieces of water cavity core | Improve the quality of the water cavity core, enhance the quality control of water cavity core insertion |
| Misrun | Iron liquid overflow at parting surface, factors related to molten iron quality, incorrect placement of filter, blockage of air holes | Prevent leakage during pouring, control the quality of molten iron and pouring process, ensure correct placement of the ceramic filter, control the ventilation holes and air eyes, control the pouring temperature |
| Porosity | Generation of gas due to resin and curing agent in resin self-hardening sand | Optimize the pouring system design, control the exhaust function of the sand core, ensure ventilation of the sand core and mold |
In the future, continuous efforts should be made to further improve the casting process and quality control to ensure the production of high-quality cylinder head castings. Additionally, further research and development can be conducted to explore new materials and technologies to reduce the occurrence of casting defects and improve the performance and reliability of the products.