Developments in Steel Casting Sand Binders 我国铸钢型砂粘结剂的一项新发展
Chinese metalcasters are faced with changing from a big
casting industry to a strong casting industry. In the devel- opment process of the steel casting industry, many new demands for sand binders are required to: • Reduce harmful gas emissions to satisfy the needs of envi- ronmental protection and industrial health and safety.
• Increase the recycling rate of used sand to maximize silica sand resources and reduce the discharge of waste sand.
• Reduce the cost of sand reclamation by using common and simple dry reclamation techniques to replace thermal and wet reclamation
• Avoid installing too much equipment and reduce energy consumption during production.
• Improve the properties of binders to improve casting quality and reduce production cost. Currently, the binders used in the Chinese steel casting
industry are mainly silicate (water glass) binder and alkaline phenolic resin. Some metalcasters also use furan resin(s) or urethane resins. Silicate binder—Silicate bonded sand for steel castings,
which has been used for around 60 years in China, has played an important role. Te preparation process for silicate binders is simple.
Tere are abundant resources for the manufacture of silicates, and their cost is low. Several methods are employed for moldmaking using
vacuum replacement hardening (VRH) and organic ester hardening processes. There are many advantages to using silicate as a
silicate as a binder such as: CO2 gas-hardening technology,
binder for sand, especially that no harmful substances are discharged. However, there are also some acute problems with the use of silicate-bonded sand, such as the dif- ficulty of shakeout, poor casting surface quality, difficult reclamation and low recycling rate. Te low recycling rate of used sand leads to large amounts of waste sand being discharged. Because silicate is a strong alkali and it is water soluble, the discharged waste sand can damage the environment and pollute surface water and groundwater. From an environmental protection standpoint, the use of silicate is a double-edged sword. Intensive research has been carried out worldwide on the
improvement of silicate binders; nevertheless, a satisfactory solution has not yet been achieved. With extensive use of various resin binders, the application of silicate binders has shown a downward trend. In recent years, due to the requirements of clean produc-
tion and environmental protection, the global metalcasting industry again focuses on various inorganic binders, and among them, silicate is considered first. It should be said that research on water-soluble silicate binders has entered a new stage, but of course, research in this respect has just started and has a long way to go.
和质量方面，也都有了明显的提升。但是，与其他工 业国家相比，我们在工艺过程控制、铸件质量、环保、 节能、减排等方面，仍然有颇大的差距。 今后，我们面临的任务是，尽快地实现我国铸造行 业‘由大到强’的转变。从而，在铸钢行业的发展过程 中，对型砂粘结剂也提出了很多新的要求，如： • 减少有害气体的排放，以适应环保和工业卫生方面 的要求；
• 提高旧砂的回用率，使硅砂资源得到充分的利用，并 减少废弃砂的排放；
• 降低旧砂再生的处理成本，以常用的干法再生代替热 法再生或湿法再生，以避免装设过多的辅助设备、 并降低生产中的能耗；
• 改进粘结剂的性能，以提高铸件的质量、并降低生 产成本。
目前，我国铸钢行业使用的型砂粘结剂，主要是硅酸 盐（水玻璃）和碱性酚醛树脂，也有一些企业采用呋喃 树脂或尿烷树脂，但为数不多。这里，只就硅酸盐和碱 性酚醛树脂作简要的分析。
1、关于硅酸盐粘结剂
我国铸钢行业采用硅酸盐粘结砂已有60来年的历 史。对于我国铸钢行业的发展，其作用和贡献是不可磨 灭的。
硅酸盐的制取工艺比较简单，原材料无匮乏之虞，价 格也相当低廉。
采用硅酸盐作型砂粘结剂，可以有多种造型工艺，
如：吹CO2硬化工艺、真空置换硬化工艺（简称VRH工 艺）和有机酯自硬工艺等。
硅酸盐粘结剂有很多优点，特别值得关注的是铸造生 产过程中不排放有害物质。但是，其在铸造生产中的应 用还存在一些棘手的问题，如落砂困难、铸件表面质量 较差、旧砂难以再生回用率低等。
旧砂回用率低当然导致废弃砂的排放量大。由于硅酸 盐的碱性很强，而且是水溶性的，排放的废弃砂会影响 周边的环境，并污染附近的水和地下水。因此，就环保 方面而言，这种粘结剂是一把双刃剑。
虽然，世界各国在硅酸盐粘结剂的改进方面都进行了 大量的研究工作，但长时间以来，都没有令人满意的解 决方案。在各种树脂粘结剂广泛应用的条件下，硅酸盐
May 2013
FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 63
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74