Raw and auxiliary materials
1. Raw sand is the main body of coated sand. The requirements for raw sand are: high fire resistance, less volatiles, high particle strength, and generally choose natural silicon sand, which is mainly due to its rich reserves, cheap price, which can meet the casting requirements.Only the special required castings shall use special sand (such as zirconium sand, chromite, ceramite sand, magnetite sand, etc.) as the original sand of coated sand:
The general requirements for silicon sand are:
A.SiO2: Casting iron and non-ferrous casting sand are above 90% and steel casting above 98%.
B. Aacidic sand is better than alkaline sand.
C. Mud content was <0.3%.
D. Grain size distribution: 3 sieve concentration degree and 5 sieve dispersion degree should be used.
E. Granticle: choose silicon sand with good rounas far as possible, angular coefficient should be less than 1.3.
Usually silica sand can meet the requirements by secondary scrub, but in order to improve the performance of coated sand, silica sand can be acid washed or high temperature active treatment (900-1200℃ burn).
2. Binding agent
Currently, thermoplastic phenolic resins are commonly used as binders,
raw and processed material
raw and processed material
The performance requirements of thermoplastic phenolic resin are:
A. Polymerization speed (hot plate method): 25-75S
B. softening point (universal method): 90-105℃
C. Fluidity (inclined plate method): 60-110mm
D. Free phenol content (bromide method): 4%
The performance of binder has an important impact on the quality of coated sand, people have been committed to study how to improve the performance of phenolic resin, foreign has developed different properties of special resin, such as high strength low air resin, easy to break resin, also used modified polyester resin instead of phenolic resin, but not get comprehensive promotion, is still widely used modified phenolic resin.In recent years, China has developed rapidly in the research and development of phenolic resin for coated sand. Shandong Chemical Plant, Qingdao Chemical Plant and Jinan Shengquan Co., Ltd. have developed high strength phenolic resin, fast poly and fast break phenolic resin, etc., but compared with developed countries, there is still a certain gap.
3. Curing agent, lubricant and additives
The conventional curing agent of coated sand is Ultoppine, which is 5% -20% of resin.In order to meet some special requirements (such as anti-shell, fast convergence, etc.), some enterprises have developed special curing agents.
The lubricant is to prevent agglomeration and improve the fluidity and moulding of coated sand. Mainly have calcium stearate, stearic acid milling ammonium.Lubricants should be as high as possible to prevent coating sand during use.
The main function of additives is to improve the performance of coated sand. At present, the widely used additives are mainly high temperature resistant additives, easy to break out additives, enhanced toughness additives, anti-sticky sand additives and wet additives.Many film sand factories have unique additive formula, the performance of additives plays an important role in the production of special film sand, is one of the core competitiveness of the film sand market.
Since 1977, due to the vigorous development of China's machinery, electronics, light industry, instrument, transportation and other industrial departments, the demand for casting mold is more and more in quantity, the quality requirement is getting higher and higher, and the supply period is getting shorter and shorter.
High production efficiency: high machine productivity, such as domestic J 3 horizontal cold air die cast aluminum 600~700 times every eight hours; die cast aluminum life, one die cast aluminum, die cast aluminum clock alloy, life can reach hundreds of thousands of times, even millions of times; easy to realize mechanization and automation.