According to the cause of mechanical sand sticking and the actual production conditions of the company, the process improvement direction is formulated to improve the structural strength of the sand core, reduce the micro pore size on the surface of the sand core and improve the cleaning capacity of the inner cavity.
| Category | Fire resistance/℃ | Bulk density/t · m ^ – 3 | Thermal expansion rate (%) | Specific heat capacity/kJ · (kg · K) ^ – 1 |
| Silica sand | 1710 | 1.4-1.5 | 1.5 | 1.130 |
| Baozhu sand | 1800-2000 | 2.05 | 0.13 | 1.423 |
Different from ordinary quartz sand (mainly composed of SiO2), Baozhu sand is made from high-quality bauxite through calcination, electric melting, granulation, screening and other processes. Its main composition is Al2O3. It can be seen from Table 1 that compared with silica sand, Baozhu sand has higher refractoriness and heat storage capacity, and its linear expansion rate is only about 1/10 of that of silica sand. In addition, Baozhu sand is spherical in shape, with good fluidity, smooth surface and compact structure, which is convenient for uniform coverage of the binder. Therefore, high structural strength and high temperature deformation resistance can be obtained by selecting Baozhu sand for core making.
| Amount of Baozhu sand added | Group I (silica sand: Baozhu sand=4:1) | Group II (silica sand: Baozhu sand=1:1) | Group 3 (silica sand: Baozhu sand=0 ∶ 1) |
| Cylinder hole wall thickness fluctuation/mm | 0.32～0.96 0.26～1.02 0.34～0.98 0.30～1.00 | 0.28～0.80 0.30～0.86 0.26～0.88 0.32～0.92 | 0.34～0.50 0.28～0.46 0.24～0.40 0.22～0.42 |
| Severity of sand sticking | 60%, difficult to clean | 35%, average cleaning difficulty | 5%, easy to clean |
During the process improvement, the deformation trend and sand sticking of the jacket sand core were verified by using different Baozhu sand addition ratios, as shown in Table 2. It can be seen from Table 2 that, with the increasing proportion of Baozhu sand, the degree of core deformation, the proportion of sand adhering and the difficulty of cleaning are generally decreasing, but the presence of silica sand still has a very significant impact on the verification results. In order to maximize the process stability and reduce the quality risk, we selected 100% Baozhu sand to shoot 2.7 CTI cylinder jacket sand core.