Casting defects in cast iron parts

The terms and definitions of casting defects, the classification and coding methods of casting defects, and the classification and explanation are mainly applicable to cast iron castings produced by sand molds. Cast iron castings produced by other casting methods can refer to them.

According to the line classification method and hierarchical classification method, casting defects were classified into four levels: class, grouping, subgroup, and specific defect. And standardized the coding method, established a code structure diagram, and provided examples for explanation. The codes and names of defect classification, defect grouping, and defect subgroups have been described.

A detailed description of specific defects in casting was provided, including multiple meat defects, pore defects, cracks, cold insulation defects, surface defects, incomplete defects, size or shape errors, inclusions or structural abnormalities, and detailed explanations were given at different levels. The main content includes the code, name, and characteristics of specific defects, which were described with pictures. During the preparation process, a large amount of domestic and foreign materials and literature were consulted, and compared and verified with the description and definition of casting defects in the casting industry, so as to make the description of defects in the standard more scientific, reasonable, and effective. During the preparation process, the opinions of multiple casting industry experts were combined with the actual production of casting, and some defects that appeared in the production of non cast iron parts, uncertain defects, or duplicates with other content were deleted; Due to the fact that heat treatment defects are not casting defects, the heat treatment defects in the ISO standard have been removed; Integrate some similar or consistent defects; Adjusted the relevant names and explanation level images of some defects to make them more accurate; Added some common defects in production that were not mentioned in the standards.

These types of defects can be roughly divided into three categories, mainly including winged or trimmed succulent defects, chunky meat defects, and other succulent defects.

(1) Defects such as flying wings or edges that do not change the basic dimensions of the casting, mainly thin flying wings (or edges) on the parting line or core head
The defect is mainly caused by the gap between the mold and the sand core; The raised veins on the surface of the casting are sand mold cracks caused by severe shrinkage of the molding sand And cause; Inner corner flying wing refers to the thin metal protrusion at the inner corner, which divides the rounded corner into two parts. This defect is mainly caused by mold sand cracks leading to the outflow of molten iron.
(2) The main dimensions of the casting have been changed due to flying wings and edge defects, mainly caused by the lifting of the casting at the parting line, resulting in thick flying wings and other defects in the casting Flying wings caused by cracks in position. This type of defect is mainly caused by the floating and lifting of the core or the cracking of the mold, resulting in flying wings.

(1) Sand expansion defects, where there is excess metal on the inner and outer surfaces of the casting, such as sand expansion on the outer surface or inner surface, near the inner gate or straight There is excess metal sand at the bottom of the pouring channel. This type of defect is mainly caused by the sand mold not being compacted or not completely dried.
(2) The excess metal produced by crushing the sand mold (core) during molding, which is formed by the damage of the sand mold (core), is called sand squeezing; The excess flesh on the surface of the casting caused by the collapse of the upper mold, i.e. the collapse of the box (mold); The succulence (scattered) on the lower surface of the casting, i.e. the scarring at the bottom; Local sand blocks of the sand mold fall off The blocky metal protrusions formed, namely sand shedding; The rough and fleshy surface of the inner corner area of the casting, namely the sanding and scarring of the inner corner; Surface formed by sand core fracture Noodle is succulent, that is, the sand core is crushed.
(3) Other meat defects. Smooth surface small metal nodules, forming approximately spherical nodules on the surface of castings, right angles, or some inner walls (exudates). These defects are generally exudates, mainly caused by the graphitization of eutectic crystals and the precipitation of dissolved gases in molten iron; The residual blocky and fleshy texture of the sprue is mainly caused by structural design issues or styling.

Casting porosity and pinholes

(1) Holes are usually located within the wall of the casting and do not extend to the surface of the casting. They can only be identified by special methods, equipment, or crushing the casting. They are mainly pores and pinholes with smooth walls and varying sizes of holes, isolated or clustered irregularly existing inside the casting; Placing metal sheets into the mold Pores caused by preset foreign objects and pores with slag inclusion in the nearby area.
(2) Holes located on or near the surface of the casting, most of which are exposed or at least connected to the surface of the casting. These types of holes are usually of varying sizes, appearing individually or in groups, usually on or near the surface, and have glossy inner walls; Or located at the inner corner of the casting, often extending to the interior of the casting Hot spot pores at the corners; Surface pinhole defects may be small pores (holes) on the surface of the casting, with more or less extension. These types of defects are usually discovered after sandblasting or mechanical processing; Cracked pinholes are usually small narrow cracks that exist on the surface or at the edges It can only be discovered after mechanical processing.

Shrinkage and porosity of castings

(1) Sometimes, open pores extend into the interior of the casting, and the open shrinkage pores are usually open funnel-shaped pores with dendritic crystal groups on the inner wall Weaving; Internal corner shrinkage hole, usually a hole with sharp edges, located at the rounded corner or gate position of thick castings.
(2) Completely internal pores in the casting: internal shrinkage pores, usually irregular pores, and the pore walls are usually dendritic structures; Centerline shrinkage,
Usually a hole or porous area along the central axis.
(3) The porous structure caused by a large number of small pores is mainly due to changes in volume during the solidification process. Almost invisible pores to the naked eye Holes: macroscopic shrinkage, microscopic shrinkage, shrinkage porosity, and casting leakage, usually dispersed dendritic shrinkage pores on the cross-section of the casting.

Surface defects of castings

Surface defects include casting surface wrinkles, surface roughness, surface grooves, depressions, sand sticking, and scarring.
(1) Surface wrinkling defects of castings, including wrinkling skin, refer to large-scale wrinkling of castings; Elephant skin wrinkled skin refers to a network of uneven folds on the surface Wrinkle; Snake shaped wrinkled skin refers to continuous wavy wrinkles, with the edges of the wrinkles located on the same plane, and the surface of the casting is smooth.
(2) Surface roughness, such as abnormally rough surface, refers to surface roughness with a depth greater than the size of sand particles. These types of defects are generally high-pressure molding defects.
(3) Surface grooves of castings, including grooves, refer to grooves of varying lengths and mostly branching, with smooth bottom and edges; Rat tail, deep fingertips
A groove with a degree of up to 5 mm, and a folding formed at one edge more or less covers the groove; Pitted surface refers to the surface of the entire casting being filled with pits or spots.
(4) Surface depression of castings, such as shrinkage, refers to the surface depression of castings near the hot spot.
(5) Deep depressions on the surface of castings, such as top collapse and box extrusion, refer to deep depressions that usually account for the majority of the lower part of the casting.
(6) Adhesive sand, including chemical adhesive sand, refers to the solid adhesion of the sand layer to the casting surface; Hot bonded sand refers to the melted adhesive parts on the surface of castings Sand; Mechanical sand sticking refers to a mechanical mixture of sand particles and metal adhered to a part or entire surface of a casting.
(7) Rough sheet-like metal protrusions, usually parallel to the surface of the casting, including sand inclusions and scars, refer to rough sheet-like metal protrusions parallel to the surface of the casting, which can be removed with a chisel; Coating scar refers to the flat metal protrusion on the surface of a casting caused by the peeling of the coating on the sand mold or sand core.

Partial absence of castings

(1) The appearance deviation of the casting relative to the pattern, including insufficient pouring, mainly refers to the basic integrity of the casting except for slightly circular edges and corners; Poor coating and improper shaping can cause deformation of the edges or contours of castings.
(2) The casting has serious deviations from the design, including severe insufficient pouring, which refers to incomplete casting caused by early solidification; Underfilled, due to insufficient liquid metal, resulting in incomplete castings; Running fire and mold leakage (leakage box) refer to incomplete castings caused by the loss of liquid metal from the mold after pouring; Excessive shot blasting refers to severe material loss caused by excessive shot blasting.

Standard applications

Sand casting refers to the casting method of producing castings in sand molds. Steel, iron, and most non-ferrous alloy castings can be obtained by sand casting method
Get it. Due to the low cost and easy availability of molding materials used in sand casting, mold making Easy to manufacture, suitable for single piece production, batch production, and mass production of castings Can be applied. For a long time, it has been a basic process in casting production.In the sand casting process, due to the complexity of its process Sex, whether it is structural design, quality of casting raw materials, or process operation Production may affect the final quality of castings, leading to various issues Defects. During the processing or use of cast iron parts, it is possible to produce a Fixed appearance quality, internal quality, and usage quality issues, while cast iron parts Quality has a direct impact on the performance of the mechanical products it applies to, and once it is released Defects are likely to cause mechanical accidents, thereby affecting the overall product Quality and service life. There are many reasons that can cause defects in cast iron parts The forms of sinking also have their own characteristics, so through defect analysis, We can quickly identify the cause of the defect and improve production Only by scientifically classifying defects can the process be improved or the technical level be improved Naming is necessary to successfully identify the causes and mechanisms of defects, thereby
Find a solution to the defect. Only by continuously solving defects and reducing castings The unqualified rate is the only way to continuously improve the overall quality of the casting industry Ping promotes the development of the casting industry. Currently, there is no clear definition in China regarding this matter The standard for describing the classification and naming of casting defects, and the development of this standard Can promote the overall quality level improvement of the casting industry and reduce casting production The production cost of the product improves the economic efficiency of the casting enterprise.With the development of China’s economy, especially its accession to the WTO Later on, the international trade cooperation in the casting industry has become increasingly broad The naming and definition of casting defects vary among different countries, so in casting There may be differences in the determination of casting defects in international trade and exchange cooperation Disputes and objections. To achieve consistency in identifying casting defects internationally and The judgment is urgent. At present, there is no classification and naming of casting defects in China Class standards. This project is a standard project for casting foundations and actively adopts it Developed the international advanced standard ISO/TR16078 to standardize the casting defects of cast iron parts Classification and explanation of defects, and comparison with internationally recognized casting defect classification and The naming convention maintains universality.

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