Study On Dgeba Resin Coated Sand For Shell Process

Resin Coated Sand is processed using cold or hot method with silicon sand attached to its surface a layer of resin film, and the method of foundry using Resin Coated Sand is called Shell Process. The castings of Shell Process are of both high dimensional accuracy and low surface roughness. The Shell Process is the major method of making cores at present, and is used widely in automotive castings.Diglycidyl ether of bisphenol-A (DGEBA) epoxy resin is thermoset polymer that exhibits excellent adhesion, high strength, resistance to chemicals and low cure shrinkage. In this paper, epoxy resin was used as adhesive of Resin Coated Sand, dicyandiamide (DICY) was used as curing agent with accelerant to improve the cure rate.FTIR was used to monitor the curing reactions between epoxy resin and dicyandiamide. The addition of accelerant has significantly accelerated the cure rate of the system. When the resin/curing agent ratio was 100: 6, the cure rate of the system without accelerant was 1997s, while the cure rate was speeded to 93 s with accelerant added at 150°C. DSC was used to calculate the activation energy of the system with and without accelerant. The activation energy was 103.9kJ/mol before adding accelerant and the figure was 63.2kJ/mol after accelerant added calculated by Kissinger Equation. The presence of accelerant significantly reduced the activation energy of the reaction, thus notably increased the cure rate of the system.Epoxy resin has good adhesive strength and high cohesive energy, however, because of the highly crosslinked three-dimensional network structure formed between epoxy resin and curing agent, the toughness of the cured system is relatively poor. In this paper, carboxyl-terminated butadiene acrylonitrile (CTBN) was used to modify epoxy resin. A comparative study of Fourier transform infrared (FTIR) spectra showed the modification as a result of chemical reactions between epoxide group, curing agent and CTBN. Satisfactory improvements in impact strength as well as lap shear strength were observed in the prepared blend systems. The development of two-phase morphology for the CTBN-modified systems was evident from scanning electron microscope (SEM). The neat epoxy matrix showed smooth and glassy fractured surfaces, which accounted for its poor toughness, as there was no energy dissipation mechanism operating here. The fractured surfaces of all modified epoxies with CTBN incorporation showed two-phase morphology with a rigid continuous phase and a dispersed rubbery phase of isolated spherical particles. The particle size increased with increasing the content of CTBN. Many toughening mechanisms have been proposed to explain rubber toughened epoxies. Different mechanisms like crazing, rubber bridging and shear deformation of the rubber particles have been proposed and these mechanisms were thought to act alone or in combination, to produce the toughening effect in rubber-modified epoxies. The addition of CTBN speeded the cure rate and lowered the softening point of epoxy resin, and also increased the tensile and fiexural strength of Resin Coated Sand. The best overall performance was obtained when the rubber content was 20%.Compared to traditional novolac type Resin Coated Sand, CTBN modified epoxy resin type Resin Coated Sand has the following advantages:1. Better mechanical properties. The tensile and fiexural strengths were increased by 16% and 11% respectively compared to traditional novolac type Resin Coated Sand.2. Increased the collapsibility of Resin Coated Sand. The applications of Resin Coated Sand could be further widened.3. Increased the covering property of Resin Coated Sand. The modifications of epoxy resin lowered the softening point and increased the fluidity and covering property of Resin Coated Sand.4. Better anti-self-adhesion properties. The epoxy resin type Resin Coated Sand had not agglomerated at room temperature for 3 months.5. More environmental and health friendly. The reaction between traditional novolac and HMTA is polycondensation, there is a large amount of ammonia produced when curing. However, the reaction between epoxy resin and dicyandiamide is addition polymerization, there is no release of gas molecules during the reaction. Therefore epoxy resin is quite environmental friendly.