Sodium silicate-bonded sand for casting and hardening method thereof

Abstract

The invention discloses sodium silicate-bonded sand for casting and a hardening method thereof, and relates to the technical fields of casting modeling technology and sodium silicate modification. Thesodium silicate-bonded sand for casting comprises the following components: crude sand, sodium silicate, a hardening accelerator and / or a modifier and / or ester, wherein the hardening accelerator is one or more of salt, acid and alcohol; the modifier is one or more of phosphate, aluminate and a hydrophobic agent; and the ester comprises one or more of organic acid ester such as glyceryl diacetate,glyceryl triacetate, glyceryl acetate and the like as well as inorganic acid ester such as dimethyl carbonate, propylene carbonate, glycerol carbonate and the like. By adding the hardening accelerator and the modifier, the amount of the sodium silicate added is reduced, the hardening speed of the sodium silicate-bonded sand is accelerated, the sand mold moisture resistance is improved, and the sand mold collapsibility is improved.

Description

technical field [0001] The invention relates to the technical field of casting molding technology and water glass modification, in particular to a method for preparing water glass sand for casting and its hardening method. Background technique [0002] Water glass is an aqueous solution of an alkali metal silicate; usually, water glass refers to sodium water glass. Unmodified water glass is ordinary water glass, and modified water glass is modified water glass. Common water glass and modified water glass are collectively referred to as water glass below. [0003] Water glass sand is a mixture made of water glass as a binder and raw sand. The commonly used water glass sand hardening method is CO 2 hardened and ester hardened. [0004] CO 2 The principle of hardened water glass sand is: sodium silicate is hydrolyzed to generate sodium hydroxide and silicic acid, sodium hydroxide and CO 2 The reaction produces sodium carbonate, the content of sodium hydroxide decreases, the...

AI Technical Summary

Problems solved by technology

[0007] 1. The amount of water glass added is high: the surface of the sand is covered with a layer of water glass film, and the water glass on the outer layer of the water glass film will 2 A layer of silica gel film is formed under the action of the silica gel film, and the formation of the silica gel film hinders the CO 2 React with the water glass inside the silica gel film. When the sand mold is hardened to the pouring strength, the percentage of the water glass that participates in the reaction is about 62%, and the percentage of the water glass that does not participate in the reaction is about 38%, so that the water glass has no To give full play to the bonding effect, the amount of water glass added (about 6%-8%) must be increased to achieve the required pouring strength

[0008] 2. The sand mold collapse is extremely poor: on the one hand, due to the high amount of water glass added, the sand mold collapse is poor; on the other hand, due to the Na in the water glass during pouring, 2 SiO on the surface of O and sand grains at high temperature 2 The reaction produces sodium silicate, and the sand particles are firmly bonded together, resulting in poor collapsibility of the sand mold; due to the extremely poor collapsibility of the sand mold, it is difficult to regenerate the water glass sand, which can only be used as back sand after crushing, and 30- 50% of new sand is used as surface sand, 50-70% of old sand is used as back sand, and 30-50% of old sand needs to be discharged to the outside, resulting in serious alkaline environmental pollution

[0009] 3. The sand mold is easy to absorb moisture, and the sodium ions on the surface of the silica gel can absorb water molecules, causing cracks in the bonding bridge, resulting in moisture absorption of the water glass sand, reducing the strength of the sand mold, and causing various casting defects

[0011] 1. Sand mold hardening speed is slow

[0012] 2. The sand mold has poor collapsibility. When pouring, the Na in the water glass 2 SiO on the surface of O and sand grains at high temperature 2 The reaction produces sodium silicate, and the sand particles are firmly bonded together, resulting in poor sand mold collapse

Due to the poor collapsibility of sand molds, the recycling rate of sodium silicate sand is reduced. The recycling rate of old sand is about 75%, and about 25% of old sand needs to be discharged to the outside, resulting in a certain amount of alkaline environmental pollution.

[0013] 3. The sand mold is easy to absorb moisture, and the sodium ions on the surface of the silica gel can absorb water molecules, causing cracks in the bonding bridge, resulting in moisture absorption of the water glass sand, reducing the strength of the sand mold, and causing various casting defects