Rapid casting sand blank forming of tractor small parts

The die-free casting precision forming machine uses the milling method to complete the processing and forming of sand mold and sand core. Before processing, it is necessary to prepare sand blanks corresponding to different cores. The small batch manufacturing of tractor small parts needs to make sand billets of different sizes and shapes through manual modeling. Sodium silicate sand and phenolic resin sand are easy to shape by hand to make sand blanks of different shapes. The following process tests are carried out for the sand blank forming method.

(1) Properties of sodium silicate sand and forming process of sand blank. Water glass sand mold is made by mixing silica sand and water glass in proportion in the sand mixer. The cost is low and the production process is simple. The sand blank is suitable for processing into sand mold or sand core with low strength requirements and no thin-wall structure. The water content, air permeability, tensile strength and compressive strength of sodium silicate sand are tested, and the performance test and processing test of sodium silicate sand are carried out. When the amount of sodium silicate is 5% ~ 6%, the strength is about 1 MPa after standing for 48 hours; With the increase of sodium silicate content, the permeability of sand block becomes poor, and hard blocks appear in the sand block, resulting in serious wear of cutting tools. The processing test was carried out on the sand block with 6% water glass addition. The strength of the processed sand core met the core modeling requirements. No obvious wear of the tool was found after 200 h processing (the blade material of the tool is PCD). The manufacturing process of sodium silicate sand blank is formulated as follows:

① Select 50 / 100 mesh quartz sand and weigh;

② Weigh an appropriate amount of sodium silicate according to 6% by mass;

③ Add quartz sand into the sand mixer and stir, and slowly and evenly add water glass until it is evenly stirred;

④ Use 50 mesh screen to filter out hard particles and conduct modeling. Large sand core needs to add core bone to improve strength and increase exhaust channel;

⑤ It is cured with CO2 and can be used for processing after standing for 24 hours.

(2) Properties of phenolic resin sand and sand block forming process. Through the performance test of resin sand, the forming method of phenolic resin sand block is optimized for the processing of sand core with high strength requirements, and the problem of sand core fracture in the process of core assembly is solved. When the resin addition is 2%, the strength is 3.6 MPa after standing for 48 h. Through the molding sand performance test, the manufacturing process of phenolic resin sand blank is determined as follows:

① Calculate the size and quality of the sand blank, prepare the core box die and adjust it to the required size;

② Cpi-1600 and cpii-2600 are used for the resin, and the addition amount is 1% respectively. The addition amount of curing agent CP Ⅲ – 3595 / 3550 is 1% ~ 6% of cpi-1600. The addition amount of curing agent is adjusted according to the curing time;

③ Mix the molding sand and binder in the sand mixer for 1 min. the interior of the sand mixer needs to be cleaned, otherwise the screen must be used to filter out the large hard blocks in the sand after sand mixing;

④ Fill the sand into the core box mold with fixed size. If there is exhaust demand and higher strength demand, embed the core bone, tamp and scrape the sand, and check whether the height meets the minimum height requirements of the sand block;

⑤ It can be used for processing after standing for 24 h.

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