The casting of titanium and titanium alloys using metal patterns are usually made of gray cast iron (HTl50 or HT200), cast steel (ZG200 -- 400), cast copper (pure copper or brass), and very small amounts of refractory metals (such as molybdenum). With the exception of refractory metals, the melting point of these materials is lower than that of titanium, and they can be used for casting titanium alloys for the following reasons:
(1) The thermal conductivity of these materials is higher than that of titanium, and the heat generated by pouring titanium liquid into the cast mold is quickly transferred away;
(2) The thermal conductivity of titanium is low, and the liquid titanium immediately solidifies to form a thin shell after the contact between the mold and the mold surface, which can effectively increase the temperature gradient of the mold holding.
The above several metal casting materials have advantages and disadvantages:
(1) welded titanium tube supplier believes Cast iron has good rigidity, easy processing, low price, long life, and is stable to molten titanium at low temperature. At the same time, it contains flake graphite structure, so the titanium liquid is good for its wettability, which is conducive to the filling of titanium liquid and the forming of the casting. Its disadvantages are high coefficient of linear expansion and low melting point. Therefore, it is usually only suitable for making the outer mold of castings, not used as the core.
(2) Cast steel is similar to cast iron in that it is stronger and more durable than cast iron, but has slightly greater deformation than cast iron.
(3) The thermal conductivity of cast copper is very high, but the strength is low, the rigidity is poor, can only be used for the manufacture of small parts of the mold, the price is high, generally rarely used.
(4) refractory metal has high temperature resistance, high hardness and wear resistance, but it is very brittle, expensive and bad machinability. Molybdenum is mainly used as the punch of die casting.
The key of metal mold casting lies in the design of the mold, which is directly related to the quality and dimensional accuracy of the casting, the life of the mold, the processing and manufacturing cost of the mold. In addition to following the principles of ordinary metal pattern design, the characteristics of titanium and titanium alloy casting must be considered in the design, which can be summarized as follows:
(1) Bottom injection should be adopted as far as possible;
(2) An open gating system shall be adopted;
(3) Try to use centrifugal casting, according to the requirements of centrifugal casting design of metal casting structure and fixing mode.
In order to reduce the cost of the metal type and improve the service life of the metal type, the metal type can be combined with the machining graphite type. Inlaid graphite block can be used for cavity parts that are difficult to mold and easy to damage, and machined graphite type can be used for all pouring systems. The casting of titanium alloy artificial joint is a combination of metal and machined graphite. The machined graphite parts must be roasted at a high temperature (not more than 400℃) before pouring, and it is best to roast them in a vacuum at 950-1000 ℃ for 1.0-2.0 h to remove the adsorbed gas.