Quality Control of Precision Casting Water Glass Shell Shelling Process
Precision casting is one of the most commonly used processes for art casting. This paper discusses the quality control requirements and production management of precision cast water glass shell. Practice has proved that by strengthening the shell process in the key process control and quality of the integrated control of factors, so that product quality and yield has been significantly improved.
Water glass; precision casting; shelling; process; control
The water glass binder is inexpensive and the shelling cycle is short, so the water glass shell precision casting process is widely used in our country, but the water glass shell precision casting is still expensive compared with the traditional sand casting, and the process is complicated and produced. Longer cycle problems. The shell as one of the most critical factors affecting the quality of castings, how to effectively control its quality, is of great significance. The following are the same as the "
In this paper, we will discuss the quality of the shell and improve the quality of the casting and the purpose of improving the quality of the casting. In this paper, we will discuss the quality of the shell and the quality of the finished product. The
Selection and Control of Raw Materials
Quality control of water glass adhesive
Precision casting used for sodium water glass. The main performance parameters of water glass are modulus (M), density (ρ) and viscosity, where M is an important parameter of water glass, which can be expressed by the following formula. M = w (SiO2) / w (Na2O) 1.032, where w (SiO2), w (Na2O) are SiO2, Na2O,% by mass, and 1.032 is the ratio of Na2O to SiO2 relative molecular mass. The following are the same as the "
The water glass density ρ indirectly represents the concentration of Na2O.mSiO2. M depends on the relative content of SiO2 and Na2O, and the height of ρ determines the content of SiO2. M and ρ directly affect the surface strength of the shell, room temperature strength, high temperature strength and residual strength. In the production, the water glass M is generally controlled at 3.0 to 3.4, the surface coating ρ is controlled at 1.25 to 1.28 g / cm3. The reinforcement layer ρ is controlled at 1.30 to 1.34 g / cm3. When M and ρ do not meet the requirements, with acid or alkali to adjust M, water or high density of water glass to adjust ρ. Viscosity is also a more important performance parameters of water glass, it directly affects the performance of coatings and shells, the impact of water glass viscosity factors such as modulus, density, temperature, water glass viscosity increases with the M, the density increases, The temperature decreases and rises. The following are the same as the "
Due to the presence of free SiO2 in the water glass, stored for a certain period of time, SiO2 deposition in the bottom of the container, resulting in water glass modulus decreased. Therefore, in the course of the use, in addition to the water glass unloading test once, after 24 hours of storage should be re-test once to ensure that the water glass to meet the requirements.
Influence and Control of Powder on Shell Quality
Paint in the powder particle size should be appropriate, coarse powder coating, the paint precipitation quickly, poor process stability, resulting in rough casting surface. And too fine powder on the impact of the larger layer of paint, paint is not easy to control, resulting in wax coating on the coating is too thick, corner, groove accumulation at the serious, hardened impermeable, shell by roasting, the inner surface powder off, Sand and sand and other defects significantly increased. In the actual production, select the appropriate powder for the average particle size of 35 ~ 50μm. This powder preparation of the paint, both to improve the powder ratio, but also improve the process stability.