Study On Inorganic Phosphate Foundry Binder

Inorganic phosphate is very valuable new resin foundry binder for its excellent knockout and environmental friendly features. But its poor stability, poor anti-wettability and low sticking power are still existed that limited its application in practice. In this paper, under the basis of summarizing advantages and disadvantages of present cast binders, necessities and problems of developing a new phosphate binder are presented, effects of such factors as neutralization degree of phosphate, modifier M and modifier B on properties of the binder are studied. Especially emphasized are the laws of no bake foundry sand and heat hardened sand. Conclusions are as follows.Tests show that stability and anti-wettability of binder have close relationship with neutralization degree, density and chemical compositions. The stability of the binder with low neutralization degree is better than that of the binder with high neutralization degree. But the anti-wettability of low neutralization degree binder is poorer than that of high neutralization degree binder. The stability of binder also has something to do with its density and chemical composition or modification. The higher the density of the binder, the poorer of its stability. Overdose of modifier M or B to binder is also harmful to stability. It is more favorable to stability that modifier M and B are existed in the binder at the same time than they are applied separately. Heat-cured product of binder is more hygroscopic than no bake product.Orthogonal experiment under special condition showed that modifier M has marked effect on properties of no bake sand. Other factors such as modifier B, phosphate concentration and aluminum hydroxide have some impact on properties of binder.It can be found by experiments that strengths of no bake sand are raised notably by binder that modified by modifier B. Modifier B can reduce the strength of no bake sand at high room temperature apart from condition of low room temperature that it can accelerate the reaction and strengthen the sand. Modest content of modifier M in binder has some improvement to anti-wettability of sand. But modifier B has not such notable effect. Electronic microscope shows that near cracks in no bake product there are fibrous shape substances formed when the samples are moistured in high humidity air for sometime. The fiber has high content of elements that contained in modifier M. That is to say, modifier M has the role of healing the crack.Effects of hardener types , the amount of hardener addition, ambient temperature and modifiers on hardening reaction speed of no bake sand are studied. It is known by testing work time of sand that the speed of metallurgical magnesium powder as a hardening agent is 2 times as that of fused magnesium powder. Insufficient hardener addition leads to low sand strength and poor anti-wettability for insufficient sand hardening. Overdose hardener addition leads to fast reaction, low sand strength but good anti-wettability. Moderate addition of hardener makes the sand have comprehensive performances. In low ambient temperature, hardening reaction speed is slow but can be quickened by applying binder that modified by modifier M so that the amount of hardener addition can be controlled low. In high ambient temperature, modifier M makes the reaction very fast and very low sand strength. Reaction speed is not affected by modifier B.The strength and anti-wettability of heat hardened sand are determined mainly by neutralization degree and amount of modifier B and modifier M in the binder. If the binder is modified only by modifier B, heat cured sand is strengthened notably and the anti-wettability is satisfactory under air with relative humidity 70% , but is unsatisfactory under air with relative humidity 80～90%. Again added is modifier M and content of the two kinds of modifier are high, the highest strength and best anti-wettability of sand can be obtained.The hardening speed of heat cured sand, sand strength and anti-wettability have close relationship with furnace temperature, time and modifiers.Effects of dry temperature and dry time on properties of heat cured sand and the relationship with binder composition are as follows: sands bonded by binders that are not modified have high strength when dry temperature is high and dry time is long, but their anti-wettability power is poor . Sands bonded by binders that are modified by B but not modified by M can be dried quickly and sand strength is high but anti-wettability power is also poor. Sands bonded by binders that are modified by M but not modified by B can also be dried quickly to obtain maximum strength, then the strength becomes lower when they are dried continually for more time. and sand strength is high but anti-wettability power is also poor. Sands bonded by binders that are modified by M as well as by B at the same time can be dried quickly to obtain maximum strength at low temperature and short time. But the anti-wettability of sand mold is best when they are dried at high temperature and long time. For samples of sizeφ30×30mm, the ideal drying parameters are temperature 200℃and time 20 minutes.The rapture of no bake sand "bridge" belongs detachment mode, so improvements should be paid attention to the surface quality of sand particles. The rapture of heat cured sand "bridge" belongs detachment and neck composite mode, improvements must be emphasized on binder as well as surface quality of raw sand.Carbon nanotube can be applied to strengthen the no bake sand, but too much tubes in the binder can accumulate together and are difficult to scattered...