What is sand casting?

Sand casting is a casting method to produce castings in a sand mold. Steel, iron, and most non-ferrous alloy castings can be obtained by sand casting. Because the molding materials used in sand casting are cheap and easy to obtain, and mold manufacturing is simple, it can adapt to the single-piece production, batch production, and mass production of castings. It has been the basic process of casting production for a long time.

Metallurgical Content

Technological Process

Sand casting is the most popular and simplest type of casting, which has been used for centuries. Sand casting is used to make large parts such as manganese steel, chrome steel, gray cast iron, ductile iron, stainless steel, and other types of steel. The main steps include painting, mold, core making, modeling, melting and pouring, cleaning, etc.

Step 1. Make Drawings

The traditional method is to obtain casting drawings and send them to the foundry. This process can be done in the quotation. Nowadays, more and more customers and foundry manufacturers use CAD instead. In our foundry, you can send your drawings or sample products to us, our engineer will recheck or measure the drawings.

Step 2. Make Patterns

In sand casting, the mold is made of wood or other metal materials. In this process, we ask our engineers to make the mold size slightly larger than the finished product, and the difference is called shrinkage allowance. The purpose is to ensure that the molten metal solidifies and contracts by acting on the mold to prevent cavities during casting. In our foundry, we make patterns by wood and glass fiber reinforced plastics.

Step 3. Core Making

Core making is a casting with an internal surface formed by placing resin sand particles in a mold. Therefore, the gap between the core and the mold eventually becomes casting.

Step 4. Forming

A set of mold needs to be prepared in the melting process. Molding usually involves the support frame of the mold, pulling the mold out to separate it during casting, melting the previously placed core in the mold, and then closing the mold opening.

Step 5. Cleaning

The purpose of cleaning is to remove sand, grinding and excess metal from castings. Welding, desanding can improve the casting surface appearance, burned sand and scale are removed to improve the surface appearance of casting. Excess metal and other risers are removed. Further welding, grinding and other steps. Finally, check its defects and comprehensive quality.

Step 6. Modify

Reprocessing before shipment. According to the requirements of different customers, we can do heat treatment, surface treatment, additional inspection, and so on.

Core Types

In order to ensure the quality of castings, the cores used in sand casting are usually dry cores. According to the different binders used in the core, the core can be divided into clay sand core, oil sand core, and resin sand core.

Clay Core

A simple core made of clay sand.

Oil Sand Core

The core made of core sand with dry oil or semi-dry oil as the binder is widely used. The viscosity of the oil is low, the mixed core sand has good fluidity and is easy to be compacted during core making. However, the strength of the newly made core is very low. Generally, the core should be carried on by the profiling supporting core plate, and then it should be dried in the oven at 200 ~ 300 ℃ for several hours, and the oil will be oxidized by air to harden it. The disadvantages of this method are: the core is easy to deform in the process of demoulding, handling, and braking, which leads to the reduction of casting dimensional accuracy, long baking time and high energy consumption.

Resin Sand Core

Various cores made of resin sand. The shape and dimension tolerance of the core can be ensured by taking out the core after hardening in the core box. According to the different hardening methods, the manufacturing of resin sand core is generally divided into three methods: hotbox core, shell core, and cold box core.

  1. Hotbox core making: appeared in the late 1950s. Furan resin is usually used as core sand binder, in which latent hardening agent (such as ammonium chloride) is added. In the process of core making, the core box is kept at 200-300 ℃. After the core sand is injected into the core box, ammonium chloride reacts with free formaldehyde in the resin at a higher temperature to form acid, which makes the core harden quickly. It takes about 10-100 seconds to establish the demolding strength. By using the hotbox core method, the size accuracy of the core is relatively high, but the process equipment is complex and expensive, energy consumption is high, the emission of irritating gas, and the working conditions of workers are also very poor.
  2. The shell core is made by the hot method with coated sand, which has high strength and good quality;
  3. Cold box core method: appeared in the late 1960s. Urethane resin was used as a core sand binder. In this method, the core box is not heated, and the core can be hardened by blowing amine steam into it for a few seconds. This method is superior to the hotbox method in energy, environment, and production efficiency. In the mid-1970s, the furan resin cold box method of blowing sulfur dioxide hardening appeared again. Its hardening mechanism is completely different from that of the urethane cold box method, but its technological characteristics, such as rapid hardening and high core strength, are roughly the same as those of the urethane cold box method.

Sodium Silicate Sand Core

The sand cores made of sodium silicate as the binder can be divided into the following types: sodium silicate CO2 method, ester hardening sodium silicate self-hardening method, sodium silicate methyl formate cold box method.

 

Our foundry chooses the sodium silicate sand core.

Sand Casting Application In Qiming Machinery

Qiming Machinery uses sand casting to cast most of our wear parts, which include: