Influence of casting porosity
1. failure of metal continuity
2. less effective bearing area
3. Stress concentration and mechanical properties are easy to be caused near the air hole.
Porosity of casting
1. Intrusion pores: The gas accumulated on the surface of sand mold material intrudes into metal liquid to form
Gas source: water content, binder, various additives, etc
Characteristics of stomata: most of them are near the surface, with large size, and the inner surface of oval or pear shaped pores is oxidized.
Pore formation process:
Pouring – water vapor (one part is discharged from the parting surface and the vent hole, the other part is gathered on the surface as a high-pressure center point) – air pressure rises, dissolves into the metal – one part escapes from the molten metal – gate, and the rest is in the casting, forming a pore.
Prevent the occurrence of porosity: reduce the amount of molding sand (core sand) and increase the ability of mold exhaust.
2. Precipitated porosity: during the condensation process of gas dissolved in liquid metal, the gas will be precipitated due to the decrease of gas solubility, which will cause the formation of porosity in the casting.
The reason: metal melting and gas contact during pouring (H2 O2 NO CO, etc.)
Feature: wide distribution, very small pore size, affecting air tightness.
3. Reaction pore: the pore formed by gas generated by chemical reaction between molten metal and casting material, core support, cold iron or slag. For example: there is rust in cold iron, and pores are formed near the cold iron.Fe3O4 + C – Fe + CO
Prevent: the surface of cold iron core support shall be free of rust, oil stain and dry.
Casting Quality Control
1) Reasonable selection of casting alloy and casting structure.
2) Make reasonable technical requirements for castings (defects are allowed and regulations are provided).
3) Model quality inspection (model qualified – casting qualified)
4) Casting quality inspection (macroscopic, instrument)
5) Heat treatment of castings: eliminate stress, reduce hardness, improve machinability, ensure mechanical properties, annealing, normalizing, etc.
ABOUT KEVA
Keva Casting is a professional casting company that focuses on Construction, Machinery, Automobile, Hardware, Pipeline and many other industries.
We provide top quality products with the best service based on our complete production chain including our own mold design, advanced production techniques, and full management of the supply chain. Keva Casting has two factories located in Zhucheng, China's Shandong province.
We use "shell molding", which is a new technique that has been developed in recent years.This new technique has simplified production procedures and reduced air pollution compared with traditional sand casting and investment casting. Shell making and core making are faster to ensure production in enormous quantities. The dimensions and surface finishing are satisfactory for all kinds of industrial requirements. Besides supplying our own formwork & scaffolding systems, our casting products also supply OEM services in various industries.