1. The amount of resin and curing agent added in resin sand process
Adjustment of resin addition
Based on sand flow rate: first adjust the sand flow rate according to the nominal flow rate of the sand mixer, and then adjust the amount of resin added according to the sand flow rate. Usually the amount of resin added is controlled at 0.8%~1.2% of the weight of the molding sand, with the upper limit for thick and large pieces and the lower limit for small and medium pieces.
Consider the type of raw sand: the amount of resin added varies for different types of raw sand. For example, the amount of resin added to silica sand is generally 1.5%~1.8%, and the amount of resin added to chromite sand is 0.8%~1.2%.
Adjustment of curing agent addition
Reference temperature factors: The amount of curing agent added is related to the sand temperature and the ambient temperature of the workshop. It is generally 30%~50% of the amount of resin added. The lower limit is taken at high temperature and the upper limit is taken at low temperature.
Combined with the characteristics of castings: For large pieces with long sand placement time, the amount of curing agent added is taken at the lower limit to ensure that the resin sand has enough usable time.
In addition, it is necessary to weigh the flow of sand, resin and curing agent regularly, clean the liquid material pipeline every shift, and check the amount of liquid material added every week to ensure the accuracy of the amount added. At the same time, "a+b" curing agent can be selected or curing agents of different acidity models can be selected according to different seasons to ensure stable sand usable time and hardening speed.
2. Specific steps for adjusting the amount of resin and curing agent added in the resin sand process:
Preliminary preparation
Understand the process requirements: clarify the material, structure, size and production batch information of the casting. Different castings have different performance requirements for resin sand. For example, large thick-walled castings may require higher strength and longer usable time, while small thin-walled castings have higher requirements for hardening speed and surface quality.
Familiar with material properties: Master the performance characteristics of the resin, curing agent and raw sand used, including the type, viscosity, curing characteristics of the resin, acidity, reactivity of the curing agent, particle size, shape, mud content of the raw sand, etc.
Determine the initial addition amount
Reference to empirical data: According to the type of casting and the original sand, refer to the empirical data of similar processes to determine the initial addition amount of resin and curing agent. Generally speaking, the amount of resin added is usually 0.8% - 1.2% of the weight of the molding sand, and the amount of curing agent added is 30% - 50% of the amount of resin added.
Conduct test adjustments
Make samples: According to the initial setting of the amount of addition, make resin sand samples in the laboratory or production line. The preparation of the samples should simulate the actual production conditions, including sand mixing process, compaction method, etc.
Performance testing: The performance of the samples is tested, mainly including the test of indicators such as usable time, hardening time, and strength. The usable time can be determined by observing the time from the resin sand to the loss of fluidity after sand mixing; the hardening time can be measured by a special instrument to measure the time required for the resin sand to reach a certain hardness; the strength test is based on different requirements, and the test methods such as compressive strength, tensile strength or flexural strength are selected.
Adjust the amount of addition: According to the performance test results of the sample, adjust the amount of resin and curing agent added. If the usable time is too long or the hardening time is too slow, the amount of curing agent added can be appropriately increased; if the strength is insufficient, consider increasing the amount of resin added, but at the same time pay attention to the impact on the usable time and hardening time. On the contrary, if the hardening is too fast, the strength is too high but the usable time is too short, the amount of curing agent or resin added should be reduced.
Production verification and optimization
Small batch production: After the test adjustment obtains satisfactory results, small batch production verification is carried out. Observe whether the performance of resin sand meets the requirements of casting production under actual production conditions, including the moldability and demolding of sand molds, the surface quality, dimensional accuracy and internal quality of castings.
Continuous optimization: According to the feedback results of small batch production, the amount of resin and curing agent added is further optimized. During the production process, the performance of resin sand needs to be tested and adjusted regularly to ensure the stability of the process and the consistency of casting quality.
3. The hardening time and strength of resin sand are closely related to the resin. The specific relationship is as follows:
Hardening time
Resin type: Different types of resins have different hardening reaction mechanisms and speeds. For example, furan resin is cured by acid catalysis and has a relatively slow hardening speed at room temperature; while phenolic resin generally uses an alkaline curing agent, and the hardening speed may be faster than furan resin.
Resin addition amount: Within a certain range, the more resin is added, the shorter the hardening time. Because the resin content increases, the substances involved in the curing reaction increase, the cross-linking reaction speed is accelerated, and the hardening time is shortened. However, too much resin addition will lead to increased costs and may affect the quality of castings.
Strength
Resin properties: The molecular structure and properties of the resin directly affect the strength of the resin sand. Such as the molecular weight of the resin, the degree of cross-linking of the molecular chain, etc. Resins with a larger molecular weight and a higher degree of cross-linking can form a denser three-dimensional network structure, so that the resin sand has a higher strength.
Resin addition amount: Generally, as the amount of resin added increases, the strength of the resin sand will increase. Because more resin can better wrap the sand particles, form more bonding bridges between the sand particles, enhance the connection between the sand particles, and improve the overall strength. However, when the amount of resin added exceeds a certain value, the strength growth trend slows down, and the strength may even decrease due to the excessive thickness of the resin layer.
In addition, factors such as ambient temperature, humidity, and the type and amount of curing agent will also interact with the resin, indirectly affecting the hardening time and strength of the resin sand.
