During the production of automotive cylinder blocks and cylinder heads, thin burrs known as veining defects often appear in the intake and exhaust ports, water jacket inner cavities, and hot spot internal corners. These burrs are difficult to clean due to their location inside the cavities. Veining defects in water jackets can impede the normal flow of cooling water, leading to engine cylinder scuffing in severe cases. Meanwhile, veining in intake and exhaust ports can affect the swirl characteristics of the air passages, significantly compromising engine performance. Therefore, resolving veining defects is crucial for automotive castings such as cylinder blocks and cylinder heads.

I. Causes of Veining Defects

At a temperature of 573℃, silica sand undergoes a crystalline transformation from β-quartz to α-quartz. The thermal stress caused by phase-change expansion leads to cracking on the surface of sand cores. Molten iron seeps into these cracks and solidifies, forming veining defects. Two basic conditions are required for veining to occur: first, the thermal stress generated by phase-change expansion exceeds the surface strength of the sand core; second, the molten iron remains in a liquid state with sufficient fluidity.

II. Measures to Resolve Veining Defects

(1) Reduce Sand Core Expansion

(2) Adjust Raw Sand Particle Size Distribution

If the particle size of raw sand is too concentrated, the overall expansion effect will be more pronounced. Generally, three-screen or four-screen sand is adopted. For automotive cylinder blocks and cylinder heads, scrubbed sand with a particle size of 0.355～0.154mm (50/100 mesh) is recommended, while raw sand with a particle size of 0.224～0.106mm (70/140 mesh) or finer should be avoided as far as possible.

(3) Improve the Room-temperature and High-temperature Strength of Sand Cores

With the same raw sand, the strength of sand cores depends on the type of binder and the sand core compaction degree. As cold-box cores are produced by high-pressure sand shooting, they have high compaction degrees, which leave little room for sand particle expansion at high temperatures, thus making veining defects more likely to occur.

(4) Role of Special Coatings

Chill coatings can accelerate the cooling and solidification of molten iron, which are generally suitable for automotive castings and easy to implement. However, their effect is not obvious for thick and large castings.

(5) Anti-veining Additives

Currently, there is a wide variety of anti-veining additives on the market, which are mainly divided into organic and inorganic types according to their compositions. The first type is a mixture of silicates and metal oxides, which has a low melting point. At high temperatures, it can form a glassy phase with silica sand to fill sand core cracks and prevent molten iron from penetrating into the cracks. This type of additive can be made into spherical particles, which have little impact on sand core strength, and the recommended addition amount is generally 1.0%～5.0%. The second type is organic additives, which require a smaller addition amount of 0.3%～1.5%, but have a more obvious impact on strength and produce a large amount of gas.

Xinda Anti-veining Additives stand out as the preferred solution for automotive casting enterprises with their innovative formula that perfectly avoids the shortcomings of traditional products. Its core advantages are reflected in three aspects: First, high-efficiency veining prevention. It adopts a synergistic effect of composite inorganic formula and organosilicon-fluorine coupling resin, which quickly forms a glassy phase to fill sand core cracks at high temperatures and inhibits the phase-change expansion of silica sand, thus blocking the formation of veining from the source. Field tests have shown that it can reduce the veining defect rate of cylinder blocks and cylinder heads by more than 90%. Second, low impact and high compatibility. The addition amount is only 0.8%～2.0%, which not only maintains the low interference of the spherical particle structure on sand core strength, but also optimizes the gas evolution amount through high-boiling inert solvents, making it far lower than that of similar organic additives in the industry. It is compatible with mainstream core-making processes such as cold-box and coated sand. Third, win-win situation of quality improvement and cost reduction. It does not require additional production equipment modification and can directly replace high-cost white corundum composite sand. While ensuring the cleanliness and dimensional accuracy of casting inner cavities, it reduces the cost of core-making sand, helping enterprises achieve maximum benefits in mass production. 

At present, Xinda Anti-veining Additives have been widely used in the production of complex castings such as automotive cylinder blocks and cylinder heads, and have won recognition from numerous OEM supporting enterprises with their stable performance.

With the continuous improvement of the automotive industry's requirements for engine performance, casting quality has become a key factor in the core competitiveness of enterprises. Anti-veining additives have become a must-have choice for solving veining defects due to their high efficiency, convenience and low cost advantages. With innovative technology and proven advantages in practical applications, Xinda Anti-veining Additives provide reliable support for the quality upgrade of castings, helping the industry break through production bottlenecks and achieve high-quality development.