Study on hardening time of self-hardening furan resin sand

Background
Furan resin self-hardening sand is very hard and easy to control, and the dimensional accuracy of castings is high. Therefore, the self-hardening resin sand process has been used to cast various metal castings, such as machine tools for machining and gas turbines for shipbuilding. Cast iron parts can be produced by self-hardening resin sand process. Today, the rapidly developing computer automation control technology accelerates the development and application of the self-hardening resin sand process.
However, furan resin sand has its own defects, and the use time and mold release time and final strength are greatly affected by changes in temperature and humidity, which tends to cause unstable production and adversely affect the production of the workshop. According to the mold materials applied by our company, the different ratio hardening curves of furan resin and benzenesulfonic acid curing agent in low temperature environment were studied, and the best ratio was determined. Based on this, the wood mold and metal mold resin sand were explored. The hardening trend is proposed to accelerate the hardening of the mold to guide the workshop production.
2. Experimental research
In this paper, furan resin, benzenesulfonic acid curing agent and regenerated silica sand used in our company are used as test materials. The parameters of each raw material are shown in Tables 1 to 3.


Instruments: electronic balance, automatic mixer, pressure tester, temperature and humidity meter, thermometer, stopwatch. The ambient temperature is 5 ° C, the ambient humidity is 30%, and the sand temperature is 15 ° C. 1000g sand was weighed by electronic balance. The proportion of resin added was 0.8% and 1.0% of sand weight. The curing agent was added to 30%, 35%, 40%, 45% and 50% of the weight of the resin respectively. Orthogonal test was made to produce φ40mm×40mm. Sand test block. Simultaneously record the operable time, the ejection time and the 24h compressive strength.
3. Test results and analysis
The testable measured time, die time, and strength data are shown in Table 4. table 5. The comparison is shown in Figures 1 to 3.





According to Fig. 1, it can be seen that the amount of curing agent is controlled at 30%~50%. With the increase of curing agent, the strength of thermal reclaimed sand gradually increases, reaching a maximum at 45%; the strength of mechanical reclaimed sand is gradually reduced, most The amount of curing agent added is 30%.
It can be seen from Fig. 2 that the amount of curing agent added is controlled at 30%~50%. With the increase of curing agent, the usable time of thermal reclaimed sand and mechanical reclaimed sand is gradually reduced, and the maximum available time curing agent is added. At 30%.
It can be seen from Fig. 3 that the amount of curing agent added is controlled at 30%~50%. With the increase of curing agent, the time of mold release of thermal reclaimed sand and mechanical reclaimed sand is gradually shortened, and the curing agent is added from 50%. The mold time is only 1/3 to 1/2 of the 30% added amount. According to the production needs of the site, the following requirements are imposed on the molding sand.
(1) The sand should maintain a certain final strength (small castings ≥ 2.0MPa, large castings ≥ 3.0MPa) to reduce core deformation and prevent casting sand.
(2) To ensure the necessary operation time, in order to place the core iron, cold iron and compact operation.
(3) In order to ensure smooth production on the spot, the core take-up time should be as short as possible to improve production efficiency.
(4) In the case of meeting the production requirements, the amount of binder should be added as low as possible, which not only saves cost, but also reduces the gas generated by the burning of organic binder during casting, improves the quality of castings and protects the environment.
Based on the above factors, the optimum liquid material ratio of mechanical reclaimed sand is 1.0% resin (accounting for sand weight), 30% curing agent (accounting for resin); the optimum liquid material ratio of thermal reclaimed sand is 1.0% resin (accounting for sand weight) ), 45% curing agent (accounting for resin).
Further tests, taking into account the differences in the time between the production of wood and metal molds on the site, using the wooden core box and the metal core box to prepare the samples, the compressive strength was measured every 1h, and the intensity change trend and the 24h before recording were recorded. The final strength, the results are shown in Table 6, Figure 4.



It can be seen from Fig. 4 that when the resin and curing agent are added in a certain ratio at 5 °C, the mold can be taken out from the pattern (1.5 MPa), and the mold can be taken out from the pattern (2 MPa). The hardening reaches sufficient strength and will not be deformed (see Figure 5); the metal mold takes 5 hours to be taken out, and the premature removal is not completely hardened, and extrusion deformation occurs (see Figure 6). The final strength is basically the same, about 3 MPa. 2 Simply increasing the acidity value of the curing agent does not significantly increase the hardening speed and shorten the mold release time.
According to this hardening trend, the on-site production can be arranged according to the different mold release time, avoiding the deformation of the core due to the insufficient hardening strength of the sand in the premature core, and the strength of the core is too late, and the mold is tightly bonded. It is difficult to mold, resulting in poor surface quality and delay in on-site production.
4. Conclusion
In the low temperature environment, when the furan resin and the benzenesulfonic acid curing agent are used as the binder, the following three experimental conclusions are obtained.
(1) The best liquid material of mechanical reclaimed sand is added as resin 1.0% (accounting for sand weight), curing agent 30% (accounting for resin); thermal reclaimed sand is the best liquid material added to resin 1.0% (accumulated sand weight), curing 45% (accounting for resin).
(2) The rest of the conditions are unchanged, simply increasing the total acidity value of the curing agent does not significantly shorten the mold release time. The internal reaction can be accelerated and the hardening can be accelerated by increasing the temperature of the pattern, the cold iron and the tooling temperature.
(3) When the conditions are the same, the mold time of the wood mold is greatly reduced compared with the metal mold, and the former is 1/2 of the latter.
references
[1] Bai Aixiang. Application and Latest Development of Self-hardening Resin Sand [J]. Research on Foundry Equipment, 2003.2(1): 38-42.
[2] Huang Tianyou. Casting Handbook Volume 4 Modeling Materials [M]. Beijing: Mechanical Industry Press, 2004: 156-162.
[3] China Petroleum and Chemical Industry Association. GB/T21872-2008 casting self-hardening furan resin sulfonic acid curing agent [S]. Beijing: China Standard Press, 2008.
About the author: Du Zhengzheng, Shared Equipment Co., Ltd.; Zhang Junyong, Ningxia Sharing Group Co., Ltd.

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