Why MUST adopt filtration mesh in foundry

In casting production, the rejection rate of castings is 50 to 60%due to casting problems such as non-metallic inclusions. The inclusions do not only reduce mechanical properties of the casting, but also has a great influence on processability and appearance. For the purification of liquid casting alloys, reducing or filtering various non-metallic inclusions is an important technical measure to obtain good quality castings, and the use of casting filters has become an important auxiliary material for purification of liquid casting alloys.

The foundry industry generally uses stainless steel mesh, fiber filter mesh, straight hole filter mesh, foam ceramic filter mesh, etc. to purify molten metal. Fiberglass filter has become a more commonly used casting auxiliary material due to its low cost, simple production and convenient use. Fiberglass filter is made of fiber mesh cloth of various materials by impregnating resin and other bonding materials. Main function is to prevent macroscopic inclusions from entering the cavity and adsorb small inclusions. There are kinds of fiberglass filters for molten steel, iron, and aluminum according to the scope of use; according to different shapes, they can be divided into sheet, round, spherical, hat, barrel filters, etc. ; According to the different materials used, it can be divided into alkali-free mesh, medium-alkali mesh, high-silica mesh and other filters. One for cast aluminum is generally made of alkali-free mesh, for cast iron and steel is generally made of high-silica glass fiber mesh.

The mechanism of filtering the molten metal by casting filter mesh:

1. Rectification mechanism, filter screen is placed during the pouring process, the liquid metal liquid increases the resistance during pouring and changes the flow state, so that the liquid metal slowly flows into the mold cavity, it is not easy to generate eddy current, the filling is stable, and the secondary oxidation is reduced Slag inclusion is conducive to the floating of inclusions and the slag blocking function of the gating system.

2. Mechanical filtration, there are a lot of inclusions, slag and other large impurities in the molten metal. By selecting a filter screen with a suitable pore size, the inclusions larger than the pore size can be filtered out by mechanical methods.

3. Filter cake filtration. During mechanical filtration, many inclusions larger than the pore size are captured on the filter screen. With the increase of the number of inclusions, a filter cake is formed at the entrance of the filter screen. These filter cakes make the metal liquid flow finer, and have the function of filtering, which can be filtered twice.

4. Adsorption, the filter screen has a large specific surface area, and the metal liquid flow is divided into small liquid flow units through the filter screen, which increases the contact area between the metal liquid and the filter medium. A chemical reaction occurs on the surface of the filter and is adsorbed on the surface of the filter.

The efficiency of filtering the molten metal by casting filter mesh:

1. The use of the filter screen reduces the casting impurities by half and reduces the scrap rate;

2. Filter out impurities, reduce the adverse effects of impurities on the structure and properties of casting alloys, and improve the material properties of castings;

3. Improve the machining performance of castings;

4. Improve process yield;

5. Improve the surface quality of the casting, because the impurities are filtered out, the secondary oxidation is reduced, and the surface quality of the casting is improved.