Sand casting, also known as sand molded casting, is a procedure that employs sand molds to form metal castings. In this type of casting process, there are six fundamental steps.
Firstly, a pattern is placed in the sand to create a mold, and then the pattern and the sand are integrated into what is termed a gating system. Next, the pattern is removed, the mold cavity is filled with the selected molten metal and permitted to cool and solidify. Eventually, the sand mold is broken apart and the final casting remains. Certain sand casting components demand a secondary machining process after casting.
Sand casting is capable of processing a broad spectrum of metals and alloys, such as iron, special alloy steel, titanium alloy, and others. Sand casting is a cost-efficient and effective technology, and it is generally flexible in terms of size and alteration of geometry design. Usually, secondary machining is necessary to enhance product accuracy.
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Capabilities of Sand Casting moulded by hand:
Max Size of Casting Molds: 1,500 mm × 1000 mm × 500 mm
Weight Range of Sand Castings: 0.5 kg – 500 kg
Annual Capacity of Sand Castings: 5,000 tons – 6,000 tons
Casting Tolerances: On Request or According to ISO 8062
Capabilities of Sand Casting by Automatic Molding Machines:
Max Size of Casting Molds: 1,000 mm × 800 mm × 500 mm
Weight Range of Sand Castings: 0.5 kg – 500 kg
Annual Capacity of Sand Castings: 8,000 tons – 10,000 tons
Casting Tolerances: On Request or According to ISO 8062
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Heat treatment: Quenching, Tempering, Normalizing, Annealing, Carburization, Nitration
Surface treatment: Anodizing, Zinc-plating, Polising, GeoMet, Zintek, Electrophoresis….etc
Testing Service: Chemical Composition, Mechanical Properties, Fluorescent or Magnetic Penetration Inspections (FPI, MPI), X-rays, Ultrasonic Testing, Dynamic and Static Balancing Testing
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Get a QuoteSand casting is a process of injecting liquid alloys into the mold to cool, solidify, and produce various castings. The vast majority of castings prepared by casting methods are treated as burrs and can only become famous machine parts after mechanical processing.
Only a few castings prepared by casting methods have dimensional accuracy and surface roughness that can meet the requirements of the parts and can be directly used as finished products or parts, while sand casting is usually not included in this list.
Sand casting is one of the basic technologies in modern equipment manufacturing industry and plays an extremely important role in national economic construction. It is common used in automotive parts casting, mechanic part casting, pulley casting and sports equipment casting. The level of casting and the quality of castings greatly affect the service life of products.
In various types of mechanical products, the importance of casting can be seen from the weight proportion of castings in the entire machine. For example, in machine tools, internal combustion engines, and heavy machinery, castings account for 70% to 4.90%; 60%~80% in fans and compressors; 60% to 70% in tractors;
Accounting for 40% to 70% of agricultural machinery; 20% to 30% in automobiles. Mining and metallurgy, engineering vehicles, machine tools, forging equipment, hydroelectric power, petrochemical industry, instrument equipment, agricultural machinery, light textile machinery, industrial and civil architecture, military weapons, ships and ships, aviation and aerospace, art sculptures, and even daily life tools cannot do without casting. Castings have been widely used in various fields.
Compared with other process methods, sand casting has the following significant advantages:
(1) Wide application range: The casting method is almost not limited by the structure, size, and complexity of the parts, and has a very wide application range, similar to various alloy castings with wall thickness ranging from a few millimeters to a few meters, length ranging from a few millimeters to more than ten meters, and mass ranging from a few grams to several hundred tons.
(2) Not limited by the types of metals or alloys: We are a great steel casting manufacturer in China. Our sand casting plant can produce cast steel, cast iron, as well as various aluminum alloys, copper alloys, zinc alloys, magnesium alloys, and titanium alloys. For the formation of brittle metals or alloys, casting is the only feasible and irreplaceable processing method.
(3) Low cost: Sand castings account for approximately 40% to 80% of the total weight in general machine production, while the cost only accounts for 25% to 30% of the total machine cost. The reasons for low cost are:
① easy to achieve mechanized production;
② Can utilize a large amount of waste and old metal materials;
③ Compared with forgings, its power consumption is small;
④ High dimensional accuracy, small machining allowance, can save machining time and metal.
Not all sand can be used for sand casting production. It must be based on the properties of the casting metal liquid, the size of the casting, and the casting wall thickness, casting mold, and adhesive characteristics of the workpiece, and should be reasonably selected based on the quality requirements of the casting and the economic efficiency of production. For example, Sand used for copper casting usually differs from that used for steel casting.
When selecting, important indicators such as the purity, mud content, particle composition, particle shape, and sintering point of the raw sand are mainly considered.
The mass fraction of the part with particle diameter less than 0.020mm (20μm) in the original sand is collectively called the mud content of the original sand. The mud content of the raw sand has a great influence on the strength, air permeability and refractoriness of the molding sand. A considerable part of the mud contained in the original sand is often not clay minerals, and its bonding properties are much worse than ordinary clay, which reduces the performance of the molding sand. The higher the mud content of the raw sand, the higher the cost of the sand core and mold shell. Therefore, for oil sand, resin sand and raw sand used for investment casting shells, the mud content is best controlled below 0.3%.
The particle composition of sand used in sand casting includes particle size, distribution, particle shape and surface morphology. The particle composition of raw sand has a great impact on the strength and air permeability of the molding sand, as well as the dimensional accuracy and surface quality of the casting mold. It is one of the important performance indicators for judging the quality of the sand used for manufacturing.
The particle composition of the sand used for sand casting is determined after sieving with a casting standard sieve. China’s GB/T9442-2010 stipulates that the standard screen consists of 12 screen numbers and a total of 12 layers of chassis, as shown in the table below. The sieve number corresponds to the American ASTM standard and represents the number of sieve holes per unit inch length, referred to as mesh.
| Mesh No./No. | 6/1 | 12/2 | 20/3 | 30/4 | 40/5 | 50/6 |
| Mesh size/mm | 3.35 | 1.70 | 0.850 | 0.600 | 0.425 | 0:300 |
| Mesh No./No. | 70/7 | 100/8 | 140/9 | 200/10 | 270/11 | chassis/12 |
| Mesh size/mm | 0.212 | 0.150 | 0.106 | 0.075 | 0.053 |
The different contour shapes of various sand grains can be clearly seen using an optical binocular stereomicroscope. The grain shapes of raw sand used for sand casting are roughly divided into three categories, namely round, polygonal and angular, which are represented by the symbols “O”, “口” and “△” respectively, as shown in the figure below.
a). round sand b). polygonal sand c). angular sand
If one shape of raw sand is mixed with particles of other shapes, as long as it does not exceed 1/3, it will still be represented by the grain shape symbol of the main particle; otherwise, it will be represented by two symbols, and the larger number of grain shape symbols will be used. Ranked first, for example, □-△, □-O, etc.
The particle shape of sand used in sand casting is related to its mineral composition and formation process. Natural silica sand, such as river sand, lake sand, etc., are generally round or quasi-circular due to mutual friction during hydraulic transportation; mountain sand and silica sandstone are mostly polygonal; while broken artificial silica sand is sharp-angled.
In order to produce sand castings, not only advanced and reasonable casting processes and equipments need to be adopted, but also the structure of the parts themselves must meet the requirements of sand casting production, while ensuring the quality of the castings and simplifying the casting process.
The performance of the part structure that adapts to the requirements of sand casting process and ensures the quality of the castings is called the castability of the part structure.
The main steps for designing a qualified cast part include: a. Functional design; b. Modifying and simplifying the design based on casting experience; c. Metallurgical design (selection and applicability of casting materials); d. Considering cost-effectiveness.
When analyzing the castability of the part structure, it is necessary to first consider ensuring the quality and usage requirements of the castings, and prevent the tendency to pursue simplification of the casting process unilaterally.
The casting process plan should be formulated according to the actual production conditions and the production batch of the castings. It involves conducting a process analysis of the parts that are planned to be produced by the casting method.
After comparing various possible schemes, it is formulated based on real and possible conditions. The reasonableness of the structure of the casting is closely related to the type and performance of the casting alloy, the quality requirements and the quantity of the casting, the casting process method, and production conditions.
Under the premise of ensuring performance, in order to avoid defects such as incomplete pouring and cold shut, the casting should not be too thin. Each type of casting alloy has its appropriate wall thickness range. If chosen properly, it can not only ensure the mechanical performance requirements of the casting but also facilitate casting production, while also saving metal materials and reducing the weight of the casting.
The appropriate wall thickness should enable the casting to meet the requirements of mechanical properties without causing casting defects. Under certain casting conditions, the minimum thickness that a casting alloy can fill the mold is called the minimum wall thickness of the casting alloy.
The minimum allowable wall thickness that a casting alloy can fill the mold is related not only to the type of casting alloy but also to the casting method, the size and shape of the casting, pouring temperature, and the thermophysical properties of the mold. Under the conditions of ordinary sand mold casting, the minimum allowable wall thickness of the casting is shown in the following table:
| Alloy Type | Outline Dimensions Of Sand Castings | |||||
| 200 | 400 | 400 -800 | 800~12.50 | 1250-2000 | 2000 | |
| Carbon Steel | 8 | 9 | 11 | 14 | 16~18 | 20 |
| Low-Alloy Steel | 8-9 | 9=10 | 12 | 16 | 20 | 25 |
| High Manganese Steel | 8-9 | 10 | 12 | 16 | 20 | 25 |
| Stainless Steel, Heat-Resistant Steel | 8～10 | 10-12 | 12-16 | 16～20 | 20-25 | — |
| Gray Iron | 3-4 | 4-5 | 5-6 | 6-8 | 8～10 | 10-12 |
| Inoculated Chain Iron (Above Ht300) | 5-6 | 6-8 | 8-10 | 10~12 | 12-16 | 16~20 |
| Nodular Cast Iron | 3~4 | 4-8 | 8~10 | 10~12 | 12～14 | 14 -16 |
| High Phosphorus Cast Iron | 2 | 2 | — | — | — | — |
| Alloy Type | Outline dimensions of sand castings | |||||
| <50 | 50-100 | 100-200 | 200-400 | 400-600 | 600-800 | |
| Malleable Iron | 2.5-3.5 | 3~4 | 3.5 ～4.5 | 4.0～4.5 | 5~7 | 6~8 |
| Aluminum Alloy | 3 | 3 | 4-5 | 5~6 | 6~8 | 8～10 |
| Brass | 6 | 6 | 7 | 7 | 8 | 8 |
| Magnesium Bronze | 3 | 5 | 6 | 7 | 8 | 8 |
| Tin-Free Bronze | 6 | 6 | 7 | 8 | 8 | 10 |
| Magnesium Alloy | 4 | 4 | 5 | 6 | 8 | 10 |
| Zinc Alloy | 3 | 4 | — | — | — | 一 |
In the design of sand casting structures, it is often encountered that two or three walls are connected. Properly designing the wall connection is of great significance to preventing casting defects such as shrinkage cavities, shrinkage porosity, cracks, deformation, sand sticking, and improving casting quality. Heat nodes should be minimized and dispersed, and wall intersections should be avoided.
Castings with uneven thickness will form larger internal stresses during cooling, which can easily cause defects such as shrinkage cavities, shrinkage porosity, and cracks. Therefore, unnecessary thick sections should be eliminated and the arrangement of ribs should minimize intersections to prevent the formation of hot spots, as shown in the figure below.
a) un-reasonable b) reasonable
During casting, the inner wall of the casting has poorer heat dissipation conditions, slower solidification speed, and lower mechanical properties compared to the outer wall.
At the same time, thermal stress is easily generated at the junction of the inner and outer walls during the casting process, leading to cracks in the casting.
For alloy castings, shrinkage cavities and shrinkage porosity are also prone to occur. Therefore, the inner wall of the casting should be thinner than the outer wall to ensure uniform cooling of the inner and outer walls, reduce internal stress, and prevent cracks. The improvement of the structure of a sand casting is shown in the figure left.
Sand casting is a metal casting process that involves pouring molten metal into a sand mold cavity to create a desired shape. The sand mold is created by packing sand around a pattern or a replica of the desired part, which is then removed to leave a cavity. The molten metal is poured into the cavity and allowed to solidify, after which the sand mold is broken apart to reveal the finished casting.
Sand casting can be used with a wide range of metals and alloys, including aluminum, bronze, brass, iron, steel, and many others. The choice of material depends on the specific application and performance requirements of the finished product.
Sand casting offers several advantages over other casting methods, including:
The maximum size and weight of a sand casting depend on several factors, including the size and capacity of the foundry equipment, the complexity of the part geometry, and the type of metal being cast.
The lead time for sand casting production varies depending on the complexity of the part design, the size of the production run, and the availability of materials.
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Quality control measures in sand casting typically include visual inspection, dimensional measurements, and non-destructive testing (NDT) methods such as X-ray, ultrasonic, and magnetic particle inspection. These measures ensure that the castings meet the required specifications and performance standards.