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Improvement of Sodium Silicate Binder by Syrup 



Source: internal company

In the past, the binder used in chemical hardening method was only sodium silicate, and its strength and surface strength were most suitable when modulus was 2. Even so, the ventilation time is relatively long and the collapse is poor. Therefore, it is necessary to add appropriate additives to improve the performance of sodium silicate. Through experiments on various organic materials, it is found that syrup has the lowest price and can improve the performance of sodium silicate. In addition, starch was also tested. 

Experimental method: 


                      Fig 1: Relationship between Syrup Addition and Compressive Strength               Fig 2: Strength Relationship between Sodium Silicate Concentration and Syrup Addition

The modified YHuan generator is used to put CO2 gas into the gas generator at a pressure of 60 mm water column high, and then the sample is ventilated. The sample uses No.7 Shi Ying powder, adds 5% sodium silicate, and then adds syrup or starch with different concentrations. In order to facilitate operation, water glass is mixed into 44%, 46%, 48%, 50% and 52%, then syrup or starch is added into 0%, 5%, 10%, 20% and 30%, starch is separated by 5% acetic acid, and then boiled and cooled. The aeration time and strength of these samples, the strength change after hardening and the residual strength after heating were all studied. 

Experimental results: 
The modulus of sodium silicate is 2 and the concentration is 50%. Add 0%, 5%, 10%, 20%, 30% syrup and 5% quartz sand for blending. The relationship between ventilation time and strength is shown in Fig 1. As the amount of syrup added increases, the concentration of sodium silicate binder decreases, i.e. The content of sodium oxide (Na2O) decreases. The hardening time is shortened and the hardening time is accelerated to reach the highest strength. When the amount of syrup added is 5%, the strength is the highest, reaching more than 20kg/cm2. When the syrup is added to 20% and 30%, the strength decreases again. The highest strength relationship between sodium silicate concentration and syrup addition is shown in Fig 2. Single water glass is used as binder, and the strength is the highest when the concentration is 46%. If syrup is added, the highest strength is when the concentration is 50%, and the highest strength is when 5% syrup is added to sodium silicate with various concentrations. When it is added to 20% and 30%, the strength decreases quickly. 

Placement Impact: 
When pure sodium silicate is placed in the air, its strength will gradually decrease with the increase of time, but if it is placed in a dry container with water at the bottom, there will be no such phenomenon. The residual strength after heating decreases with the increase of syrup addition. Although adding starch liquid can improve the strength, it is not as regular as syrup. It is probably due to improper mixing operation when adding starch liquid. Therefore, it is difficult to control the quality using starch liquid. 

When CO2 is used to harden sand mold, the hardening time of the water glass is shortened by adding syrup, and the strength and collapse property are improved. Low price and convenient use. However, starch liquid is not. If it is not mixed properly, the performance of molding sand will be affected.

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