How to deal with casting defects of titanium screws?

The titanium alloy forgings used on the space shuttle mainly include: high-pressure vessels, wing leading edges, oil pressure pipelines, engine thrust brackets, etc.

①High pressure vessel.

The pressure vessel used on the space shuttle must withstand a high pressure of (2.1~3.5)×10Pa. The wall of the vessel is actually a composite structure, which uses titanium as the substrate and is reinforced with aromatic organic fibers. The fiber applies a pre-stress (compressive stress) to the titanium substrate. This structure can make the pressure vessel weigh 35% lighter than a single-layer all-titanium vessel. Both the container material and its welding wire use Ti6Al4V alloy.

② Wing.

The maximum temperature of the front edge of the wing can rise to 538℃, which is unbearable by aluminum alloy, and the FeNi-based alloy is too heavy, so Ti6Al-4V alloy is used. The wing is fixed on the wing supporting structure with the same fixture mechanism, and the fixture also uses Ti6Al4V alloy.

③Hydraulic piping.

There are a large number of hydraulic pipelines on the space shuttle, and T3A2.5V alloy seamless pipes are used for piping, which can reduce the weight of the pipeline by 40%.

④ Engine thrust bracket.

At the back of the space shuttle, there is a thrust bracket supporting three main engines (Figure 29), through which 510t of thrust can be transmitted to the space shuttle. The thrust bracket is made of high-strength titanium alloy, and at the same time, boron epoxy resin is used for composite on its surface. The specific elastic modulus of boron epoxy resin is higher than that of Ti6A4V alloy, but the thermal expansion coefficient of the two is similar. The boron epoxy resin composite layer can improve the rigidity of the thrust member.

⑤Other parts.

Due to the high specific strength of titanium, titanium materials are used in the space shuttle for the rear elevator fixture, external container fixture, the upper part of the frame/tail conversion device, and the sealing fins on the upper surface between the wings and elevons.
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