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product news/產品新聞


Chill Vents Provide Seal With Innovative Insert Design 真空铸造法


Te use of vacuum is not new to diecasters. It was first


introduced a number of years ago. To date, the results have been rather inconsistent. Every diecaster knows the theory and advantages of vacuum assisted casting. Because of the turbulence of the alloy as it is forced at a high pressure into the die cavity and the complex shape of many casting molds, air and other gases are often trapped in the metal. Tis re- sults in porosity in some parts of the casting. Porosity causes more rejected castings than any other reason. Te real cost of rejected product is actually very high and,


more often than not, underestimated by the diecaster. Te total value of machine time lost while producing the rejected product is never recovered. It should be calculated as the selling price of good product made in an equal period, less only scrap recovery. If the casting is to be chromed, painted or powder coated


or if any part of the casting is very thin, any air or gas inclu- sions usually result in rejection. Porosity also affects the mechanical properties of the product. In structural applica- tions, it can act as a stress concentrator and create a site where cracks may occur. An additional problem is the fact that porosity in a cast-


ing may not always be immediately apparent. If discovered after secondary processing, customer dissatisfaction can be extreme. Te only solution is vacuum assistance.


Vacuum Valves


Before the injection shot occurs, a vacuum is drawn in both the shot sleeve and the mold cavity. The vacuum is maintained until the injection cycle is completed. Al- most all of the air is positively evacuated from the mold. A good vacuum in the mold cavity enables the alloy to flow into blind recesses in complex shapes. It also allows the fronts of the molten metal to merge freely, but only if it works properly. When vacuum was introduced in diecasting several years


ago, the diecaster needed an extreme application to justify its use, because the vacuum valve required so much main- tenance at that time. Te problem was compounded when the shot sleeve and plunger tip often did not work together well enough to create a secure seal. Tis resulted in air being pulled into the die cavity. Tis unfor- tunate situation was further worsened when the diecaster


利用真空对压铸制造商而言并不新奇,这种生产方式 多年前就已被引进。但直至今天,对该种方法的使用效 果仍各持己见。


每一位压铸制造商都了解真空压铸法的理论和优势。 由于合金被高速注入模腔时产生湍流,多数铸造模具形 状复杂以及空气和其他气体通常被困闭在金属中,不可 避免地导致一些铸件存在孔隙。因孔隙造成的铸件不良 率远高于其他原因。


不良品的实际成本非常高,而且这些成本往往被压铸 制造商低估。机器用于生产不良品的时间成本就从未被 考虑在内。这项成本应按相同时间内所生产的良品的售 价扣除废料回收成本进行计算。


如果铸造工序包含、镀铬、喷漆或粉末涂覆,或者 铸件的某一部分很薄,空气或其他气体混入就会造成 不良。孔隙同样会影响产品的力学性能。当存在孔隙 的产品被用于结构件时,其成为应力集中点,从而导 致部件断裂。


此外,铸件中的孔隙并非总是立即显现。如果在后续 处理过程中才发现,将会招致客户不满。唯一的解决方 法就是采用真空压铸。


真空阀


在压射金属前,压射缸与模腔均被抽成真空,真空状 态一直维持到压射循环完成。几乎所有空气都被有效排 出模具。保持模腔处于良好的真空状态可使合金流入复 杂形态模具内的盲点凹穴中,并且能使熔态金属正面自 由融合。


当数年前真空法被引入压铸行业时,因为当时真空阀 的维护要求很高,压铸制造商需要通过极端应用方式来 验证其适用性。但随之导致的问题是,压射缸与冲头配 合不良会导致密封性差,空气因而被带入模腔。不幸的 是,压铸制造商为解决气隙密封性问题而采用了重型润 滑剂或润滑脂这一 糟糕建议,导致问 题进一步恶化。润 滑剂常被带入真空 阀中,经常导致真 空阀失效。由此可 理解为何故障停机 率异常高。


即时是早几


Castool chill vents can increase quality and reduce scrap due to porosity.


在压射金属前,压射缸与模 腔均被抽成真空,真空状态 一直维持到压射循环完成。


86 | FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION December 2015


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