1. No-bake resin sand casting mostly uses phosphoric acid as the curing agent of high nitrogen furan self-hardening resin, and seldom uses the curing agent of low nitrogen furan self-hardening resin. This is because low nitrogen and high furfuryl alcohol resin, when acid is used as curing agent , The hardening speed is slow, the demolding time is long, and the strength is very low. The high nitrogen low furfuryl alcohol resin uses phosphoric acid as the curing agent to obtain the necessary curing speed. Moreover, the high nitrogen low furfuryl alcohol resin uses phosphoric acid as a catalyst to obtain good final strength. The reason for this result is mainly due to the poor miscibility of phosphoric acid and furfuryl alcohol, and the high affinity with water, so that the water contained in the resin and the catalyst and the water generated during the polycondensation reaction of the resin are not easily diffused and discharged, and phosphoric acid is formed as the core. The water droplets remain in the resin film and destroy the compactness of the resin film, so the strength is low. The high-nitrogen resin has good miscibility with water, and various kinds of water are not easy to concentrate into water droplets with phosphoric acid as the core. The resin film has a good structure and high strength.
2. Relatively speaking, the hard permeability of phenolurea resin is much better than that of furan resin sand, because the curing process of phenolurea resin is a polymerization reaction, and there is no small molecule water during curing, and there is no internal and external factors. The different volatilization speed of water causes the problem of inconsistent curing speed inside and outside. The curing process of furan self-hardening resin is a polycondensation reaction, and moisture is generated during the reaction. The different evaporation speeds of moisture inside and outside the core result in different curing speeds inside and outside. Therefore, its hardness and permeability are worse. This is also the reason why the curing speed of furan self-hardening resin sand is greatly affected by the relative humidity of the air.
3. High nitrogen furan resin can be used to produce cast aluminum and cast copper parts. Because aluminum and copper metal liquids hardly dissolve nitrogen, even if high nitrogen resin is used in the casting process, the nitrogen generated by the decomposition of the resin will not be affected by aluminum and copper. The liquid metal is absorbed so that nitrogen pores will not be formed due to the precipitation of nitrogen during the solidification process. Therefore, high-nitrogen resins can be selected for the production of cast aluminum and cast copper parts for the needs of collapse.
4. Self-hardening resin sand produces heavy castings. The pouring system is suitable to be made of ceramic pipes. The self-setting resin sand is used for modeling. When producing heavy castings, due to the long pouring time, the pouring system is heated for a long time in the high-temperature molten metal. Under the action, it is easy to cause the resin sand to collapse prematurely and lose its strength, causing sand washing defects. Therefore, for heavy castings, the pouring system should be made of ceramic pipes. At the same time, the pouring system, especially the sprue, is not easy to be coated. solve.
5. When no-bake resin sand is used for modeling and core making, when a batch-type sand mixer is used, the usable time of no-bake resin sand is longer than the period from no-bake resin sand from mixing and unloading to use up; When the continuous sand mixer is used for modeling and core making, the usable time of no-bake resin sand is longer than the period of time from the initial sand discharge position of the sand outlet of the sand mixer to the continuous sand discharge at this position again .
6. Relatively speaking, the draft angle of no-bake resin sand is larger than that of clay sand. The resin sand core has a certain degree of hardening strength when the mold is drawn, and it has no compromise. Generally, it cannot be knocked on the pattern and core box frame. To make the sand mold or sand core wall to achieve a loose pattern, the friction force is greater when the mold is drawn; the repairability of the resin sand mold and the sand core is poor, and it is difficult to repair once the sand mold and core are incomplete when the mold is drawn.
7. The no-bake resin sand process should have fewer shrunken risers and more air outlets for cast iron production. The resin sand mould has good rigidity and high sand mould strength at the beginning of casting. This makes it possible to utilize the graphitization expansion during the solidification of cast iron to effectively eliminate shrinkage. Porosity and shrinkage defects can realize less riser and no riser casting of gray cast iron and ductile iron. However, the amount of gas generated by the resin sand is limited. In order to facilitate the smooth discharge of a large amount of gas in the cavity during the pouring process, it is necessary to set more gas outlets. In principle, ∑F is required to be inside ∑F.
8. Theoretically, the higher the proportion of urea-formaldehyde resin in furan resin, the greater the final strength at room temperature. Therefore, when the furfuryl alcohol content is greater than 70% to 80%, the higher the furfuryl alcohol content, the lower the nitrogen content, and the higher the room temperature. The lower the intensity. However, with the increase of urea-formaldehyde resin, the water content of furan resin is relatively higher, which will reduce the curing speed and final strength. When the furfuryl alcohol content is less than 70% to 80%, the downward trend of the final strength of the resin exceeds the upward trend. Therefore, in general, when furfuryl alcohol contains 70% to 80%, the final strength of furan self-hardening resin sand at room temperature is the largest.
9. Using a curing agent with too strong catalytic activity or too much curing agent will lead to a too short pre-curing stage, and the random curly curly lumpy prepolymer in the resin has not been fully stretched and ordered, and it will be pre-polymerized by cross-linking. The substance is blocked in the body structure, so that a large number of active groups in the coil cannot participate in the reaction and cannot form a polymer with a high degree of polymerization. Therefore, although resin sand hardens faster and has higher initial strength, it will inevitably lead to a significant decrease in final strength.
10. After pouring the sand mold and core with phosphoric acid as the curing agent, the phosphoric acid cannot be decomposed and destroyed under the heat of the molten metal, and the phosphate is deposited on the surface of the sand grains, which is difficult to be removed by regeneration, resulting in a decrease in the strength of the resin sand prepared by the reclaimed sand A lot, and increase the expansion of the mold, which increases the tendency of sand inclusion.
11. Due to the high water content in the acid-hardened resole resin, when the crosslinking reaction occurs, in addition to the water produced by the resin itself, a large amount of water will be released. This water will dilute the hardener and make the reaction very slow. . Increasing the free acid content of the hardener will make the hardening speed faster, but it will reduce the strength of the self-hardening sand a lot. Therefore, the hardening speed must be ensured, and the strength of the resin sand must not be greatly reduced. Total acid value. Since the free acids of inorganic acids are generally higher, for acid-hardened resols, organic acids with high total acidity and low free acid content should be used as curing agents.
12. Since the acid-cured resole resin is formed by the condensation of benzoic acid and formaldehyde under the action of an alkaline catalyst, the alkaline catalyst is neutralized with an acid and made weakly acidic before leaving the factory. Therefore, the resin is not as sensitive to acidic hardeners as furan resins, and the crosslinking reaction occurs when the acid concentration is quite high. In addition, the water content of this resin is very high, generally around 15% or higher in some aspects. When the cross-linking reaction occurs, in addition to the synthetic water produced by the resin itself, a lot of water that is mutually soluble with the resin is also released. The water will dilute the hardener. The more resin added to the self-hardening sand, the stronger this dilution effect will be. Therefore, to maintain the same curing speed, the hardener has to be added. Therefore, for resole phenolic resin self-hardening sand, the addition amount of hardener should be calculated as a percentage of the resin, that is, the addition amount of acid hardening resole phenolic resin sand curing agent should increase with the increase of resin addition.
13. The hardening reaction of the resin in the mold and core just after the mold and the new repair is still in the initial stage. If it encounters the water (solvent) in the water-based paint, it will affect the normal hardening process (for the phenolurethane self-hardening resin, it is not The reacted two-component polyisocyanate can react with moisture and become ineffective); if alcohol-based coatings are used, they must be ignited immediately after coating, which will also cause unreacted resins to overburn. These will affect the surface stability of the mold and core.
14. Due to the high alkalinity of alkaline phenolic resin (the base PH value is usually 11-13), the resin contains more alkali (usually potassium hydroxide), and the alkali in the resin easily interacts with silica sand to generate a low melting point during casting The molten silicate adheres firmly to the sand grains and is difficult to remove, which makes it difficult to remove and makes it difficult to regenerate old sand.
15. When choosing the type of resin, the following factors of the casting should be considered:
15.1 The material of the casting. When the materials of castings (steel castings, high-alloy cast irons) have a high tendency to produce nitrogen holes, low nitrogen or nitrogen-free resins should be selected; when the materials of castings (spheroidal graphite cast irons, gray cast irons) have a low tendency to produce nitrogen holes For black metal, you can choose medium nitrogen resin; for copper and aluminum parts that are insoluble in nitrogen, you should choose high nitrogen resin.
15.2 The weight, wall thickness, and pouring temperature of the casting. When the weight of the casting is heavier, the wall is thicker, and the pouring temperature is high, a resin with high furfuryl alcohol content and low urea-formaldehyde content should be selected to make the high temperature strength of the core meet the needs; low pouring temperature, light weight, thin-walled castings, If the required high temperature strength is low, resins with higher urea-formaldehyde content can be selected to reduce costs.
15.3 The structure of the casting. Castings are prone to thermal cracking, so it is advisable to use high-temperature and low-temperature resin as a binder. For steel castings that are prone to hot cracking, alkaline phenolic resin should be used instead of furan nitrogen-free resin as the binder; castings are prone to cold cracking, and good collapsibility should be used as the binder.
Sanzhuji equipment manufacturing specializes in the production of Sand casting equipment, no-bake resin sand mixer, sand reclamation equipment, Flip the die winch, dust collector, Casting system, and systematically customized solutions based on the amount of casting sand recovery. At the same time, it provides equipment installation training to ensure sand Reclamation equipment operates safely and efficiently.
Qingdao Sanzhuji Equipment Manufacturing Co., Ltd. specializes in the production of Green Sand Molding Line,Self-hardening sand molding line,foundry machines,Sand molding machine,Sand casting equipment,sand mixer,GS high efficiency rotary mixer,Resin sand mixer,no-bake resin sand mixer,Jolt squeeze molding machine/Jolt-squeezing moulding machines,Multi- Piston Moulding Machine/Hydraulic multi-piston moulding machine,sand casting molding machine,sand reclamation equipment，foundry molding machine,flaskless moulding machine,shot blasting machine,dust collector,according to the amount of old sand recovered Carry out plan customization, and provide sand reclamation equipment installation, commissioning, and training. Welcome guests to visit the factory.
