Casting defects are common problems in the production process of cylinder heads, which can affect the quality and performance of the final product. This article analyzes the causes of casting defects such as sand holes, misruns, internal burrs, and porosity in the 16V190 cylinder head, and proposes corresponding improvement measures.
I. Introduction
The cylinder head is one of the main components of a diesel engine. It not only withstands the high-temperature cyclic thermal shock load from the combustion chamber but also the cyclic impact load of high pressure in the combustion chamber. Therefore, the internal and external quality requirements of the cylinder head casting are relatively high.
II. Causes Analysis of Casting Defects
- Sand Holes
The sand hole defect in the 16V190 cylinder head casting refers to the presence of extra holes inside or on the surface of the casting after cleaning. Most of the time, the main reason for the sand hole is the improper operation during the mold assembly and box closing process. For example, the improper installation of the bolt hole core, the non-perpendicularity of the bolt hole core and the bottom surface of the core insertion, and the unstable lifting of the upper mold during box closing can all lead to the breaking of the bolt hole core and the falling of the sand core into the inner cavity of the mold, which is difficult to detect and causes the sand hole in the casting after pouring. In addition, the upper water cavity and the injector hole core use separate sand cores, which are bonded as a whole through foundry glue. There will inevitably be some cumulative errors in the sand core bonding. If there is floating sand or coating accumulation in the injector hole core seat, it will lead to the improper core insertion. Coupled with the poor control of the stability of the upper mold during the box closing process, the sand core may be broken or crushed, resulting in sand dropping and local sand hole defects in the casting after pouring. - Internal Burrs
The internal burr defect in the 16V190 cylinder head casting refers to the presence of irregular and uneven layers of “thin iron sheets” in the gas path, water path, or other parts. There are two main possible reasons for the formation of internal burrs. First, due to the complex structure of the water cavity of the cylinder head, the structural sand core in the water cavity is made by the hot box core shooting process. However, the coated sand is prone to shrinkage and sinking problems after being heated and softened, resulting in a thin shell layer of the sand core. During the natural cooling process of the sand core, it will shrink and generate capillary cracks. When the iron liquid is poured, the sand core will crack under the high-temperature thermal radiation of the iron liquid, causing the iron liquid to infiltrate into the sand core and form burrs of different degrees. Second, due to the complex structure of the water cavity of the cylinder head, the local wall thickness of the inner cavity is only 6 mm, and the intake core and the exhaust core need to be inserted through the water cavity core. This leads to the division of the water cavity core into two sand cores in the process design. In the later stage, the two sand cores are bonded with foundry glue according to the actual situation. This will make the bonding surface of the two sand cores not fit tightly enough, increasing the possibility of iron liquid infiltration and increasing the probability of internal burrs. - Misruns
The main reason for the misrun defect of the 16V190 cylinder head casting is the overflow of iron liquid at the parting surface during the pouring process, that is, the leakage of the box. In addition, it is also affected by the purity of the iron liquid, the pouring temperature, the correct placement of the filter sheet, and the air hole causing the leakage of the iron liquid. - Porosity
The main reason for the porosity defect of the 16V190 cylinder head casting is that a large amount of gas is generated when the resin and curing agent in the resin self-hardening sand are heated by the high-temperature iron liquid during the molding and core-making process. During the pouring process, the gas is 卷入 into the mold, and finally, the gas in the mold cannot be smoothly discharged, resulting in porosity in the casting after cooling and molding, and most of the pores are invasive pores.
III. Improvement Measures and Effects
- Improvement Measures for Sand Hole Defects
(1) Make a core insertion card board based on the actual situation to ensure that the sand core can be inserted in place. Since the cylinder head actually adopts the core assembly casting process, the core insertion card board should be made according to the actual core insertion, especially for the mating surface involving the height direction of the sand core, a height confirmation card board must be made to reduce the cumulative error of the core insertion and prevent the upper mold from crushing the bolt hole core and related sand cores during the box closing process, avoiding the breakage of the sand core during the core insertion process.
(2) Make an inner cavity wall thickness caliper and a 6 mm soft leather cord based on the casting structure. For the regular wall thickness dimensions, use the wall thickness caliper for inspection. For the irregular curved wall thickness of the airway, use the soft leather cord as an inspection feeler to pass through the curved cavity to ensure the minimum wall thickness dimension of the curved part, thereby ensuring that the relevant sand cores in the inner cavity are inserted in place and preventing the sand core from being crushed during the box closing process.
(3) Regularly carry out quality awareness training to enhance the quality awareness of the operators. During the core insertion process, the floating sand or accumulated coating in the core seat should be cleaned one by one. After the core insertion, the perpendicularity of the bolt hole core should be checked one by one. During the box closing process, a special person should check whether the bolt hole core and the upper mold core seat collide, to ensure a stable box closing and prevent the upper mold from crushing the bolt hole core and other sand cores. - Improvement Measures for Internal Burr Defects
(1) To prevent the occurrence of internal burrs in the casting, efforts should be made to improve the quality of the water cavity core sand core itself. Control the process parameters such as the core shooting temperature and holding time to ensure that the thickness of the sand core shell layer is greater than 5 mm. In addition, before the mold assembly, the alcohol-based zirconium oxide powder coating should be used for two times of dipping to improve the compactness, refractoriness, and strength of the surface of the sand core.
(2) Strengthen the quality control of the details of the water cavity core insertion to ensure that the water cavity core is inserted in place. During the core insertion, first, perform the trial fit of the upper and lower water cavity sand cores, check the fit of the mating surfaces, and appropriately trim the mating surfaces of the two sand cores according to the shape of each part to make the fit flat and the gap of the mating surfaces minimized. Secondly, when inserting the upper water cavity core, first, evenly apply a layer of foundry glue on the mating surface of the lower water cavity core, avoiding the exhaust groove, and then close the upper water cavity core, apply a little pressure to make the foundry glue squeeze to both sides, remove the upper core and check the bonding situation of the two sand cores, scrape off the excess foundry glue, and finally, for the places where the bonding is not tight enough, use the foundry glue for appropriate repair, and close the upper sand core again and apply pressure to ensure that the mating surfaces of the two sand cores are tight enough, reduce the possibility of iron liquid infiltration into the sand core, and reduce the internal burrs in the water cavity. - Improvement Measures for Misrun Defects
(1) To prevent the leakage of the box during the pouring process, first, check the status of the sand box and other tooling during the molding process, and do not use the sand box with missing or loose parts to prevent the overall sinking of the mold. Secondly, before the box closing, place a ϕ4 mm sealing mud strip along the periphery of the lower mold parting surface, avoiding the pouring channel. When the box clamp tightens the mold, it should be tightened diagonally at the same time to ensure that the mold is evenly stressed.
(2) Control the quality of the iron liquid and the quality of the pouring process. During the pouring process, on the one hand, the quality of the raw iron liquid should be controlled, and the slag removal and cleaning work should be done well. On the other hand, the slag blocking operation during the pouring process should be strengthened. When 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, and even splashing during the filling process, and prevent the interruption of the pouring process from causing the molten slag to block the filter hole.
(3) Ensure the correct placement of the ceramic filter sheet. In the process design, a ceramic filter sheet should be placed at the lap joint of the sprue and the runner in the pouring system to play the role of slag blocking. When placing the ceramic filter sheet, it must be ensured that the inlet hole faces the pouring cup to ensure that the iron liquid flows smoothly through the filter hole and into the mold.
(4) Control the smoothness of the ventilation holes, air holes, etc., and ensure the proper post-processing. Ensure the smoothness of the air passages in the sand mold and sand core, and do a good job in making the ventilation holes of the sand core during the mold assembly process. The ventilation holes should be reserved in the upper mold as much as possible. In addition, the surrounding of the ventilation holes should be properly sealed to prevent the iron liquid from entering the ventilation holes and causing iron leakage.
(5) Control the pouring temperature. During the pouring process of the cylinder head, the initial pouring temperature should be controlled according to the upper limit of the process (1390 °C). The iron liquid in the pouring ladle should be insulated with appropriate insulation materials. The pouring process should be smooth, orderly, and rapid, and try to ensure that the pouring temperature in the later stage of the pouring is within the range required by the process. - Improvement Measures for Porosity Defects
(1) Improve the process and reasonably design the pouring system. During the process design, it should be ensured that the design of the inner gate is conducive to the smooth filling of the iron liquid and the smooth upward floating of the gas. The design of the riser, air hole, etc., should be in the correct position and reasonable quantity to facilitate the smooth discharge of the gas in the mold.
(2) Control the exhaust function of the sand core. Before the sand core is dipped, the airway holes should be blocked to prevent the coating from blocking the airway during the dipping process. In addition, all the airway holes in the core head of the sand core and the blocked airway holes before dipping should be opened and extended to the thick part of the sand core to pour out part of the broken sand in the sand core and make the airway of the sand core smooth.
(3) Do a good job in the ventilation of the sand core and the mold. Before the core insertion, according to the position of the core head of the sand core in the mold cavity, open the ventilation hole from the outside of the mold to the core seat, apply the foundry glue in the core seat to block the gap of the core head, and apply the foundry glue around the ventilation hole to prevent the iron liquid from entering the ventilation hole and blocking the airway during the pouring process, so that the gas generated in the sand core cannot be smoothly discharged from the mold.
IV. Conclusion
By taking corresponding improvement measures, the occurrence of sand holes, internal burrs, misruns, porosity, and other defects in the 16V190 cylinder head casting has been effectively avoided in the actual production process, and the scrap rate of the cylinder head casting has decreased from 3.8% to 0.8%, achieving good implementation results.
In conclusion, for the typical casting defects such as sand holes, internal burrs, misruns, and porosity in the cylinder head, analyzing the causes of the relevant problems according to the actual situation and taking corresponding solutions can effectively improve the quality of the cylinder head casting. The scrap rate of the cylinder head casting has decreased by 3%. Considering the control of the details quality in the casting production process of the cylinder head has a direct impact on the quality of the cylinder head casting, combining production experience and practice, reasonably designing and improving the corresponding casting process, standardizing the requirements of on-site operations, formulating relevant measures and implementing them in place can greatly reduce the scrap of castings, improve production efficiency, and reduce production costs.
| Defect Type | Causes | Improvement Measures |
|---|---|---|
| Sand Holes | Improper operation during mold assembly and box closing, such as improper installation of bolt hole cores, non-perpendicularity of bolt hole cores, and unstable lifting of the upper mold during box closing. Also, problems with the bonding of sand cores, such as floating sand or coating accumulation in the injector hole core seat, and improper core insertion. | Making a core insertion card board, a wall thickness caliper, and a soft leather cord to ensure accurate core insertion. Regularly conducting quality awareness training to enhance operators’ awareness. Cleaning the floating sand and accumulated coating, checking the perpendicularity of bolt hole cores, and ensuring a stable box closing process. |
| Internal Burrs | The complexity of the water cavity structure leads to thin shell layers of the sand core, which causes capillary cracks during cooling and cracking during iron liquid pouring, allowing iron liquid to infiltrate and form burrs. Also, the division of the water cavity core into two sand cores and the imperfect bonding between them increase the possibility of iron liquid infiltration. | Improving the quality of the water cavity core by controlling the core shooting temperature and holding time, and using alcohol-based zirconium oxide powder coating for dipping. Strengthening the quality control of water cavity core insertion, including trial fitting, trimming the mating surfaces, applying foundry glue properly, and checking the bonding situation. |
| Misruns | Leakage of the box during pouring, which is affected by factors such as the purity of the iron liquid, the pouring temperature, the correct placement of the filter sheet, and the blockage of air holes. | Checking the status of the sand box and tooling during molding, placing a sealing mud strip before box closing, and tightening the box clamp diagonally. Controlling the quality of the iron liquid, strengthening the slag blocking operation during pouring, ensuring the correct placement of the ceramic filter sheet, controlling the ventilation holes and air holes, and controlling the pouring temperature. |
| Porosity | The generation of a large amount of gas during the molding and core-making process with resin self-hardening sand, which cannot be smoothly discharged from the mold during pouring. | Improving the design of the pouring system to ensure smooth filling of the iron liquid and the smooth discharge of gas. Controlling the exhaust function of the sand core by blocking and opening the airway holes. Ensuring the ventilation of the sand core and the mold by opening ventilation holes and applying foundry glue to prevent blockage. |
V. Future Prospects
In the future production of 16V190 cylinder heads, we should continue to pay attention to the quality control of casting processes and strictly implement the improved measures to ensure the stability and reliability of product quality. At the same time, we can also explore the application of new technologies and materials to further improve the performance and quality of cylinder heads.
For example, we can consider using advanced simulation software to optimize the casting process and predict potential defects in advance, so as to take corresponding preventive measures. Additionally, we can research and develop new types of coatings and materials to improve the surface quality and corrosion resistance of cylinder heads.
Furthermore, strengthening the training and management of operators is also crucial to ensure the correct implementation of operating procedures and the improvement of product quality. We should establish a sound quality management system to monitor and evaluate the production process in real time, and continuously improve and optimize the process based on the feedback.
In conclusion, by continuously improving the casting process, strengthening quality control, and exploring new technologies and materials, we can further reduce the occurrence of casting defects, improve the quality of 16V190 cylinder heads, and meet the higher requirements of the market and customers.