The brake housing is the rack of the brake device on which the brake disc and cylinder block are mounted. The brake housing is basically a cylinder body with a flange. The torque of the brake is transmitted to the landing gear by the flange of the brake housing or the torque pin of the cylinder seat, so the brake housing is also called the torque barrel. In the early stage, 2A11 hard aluminum alloy forgings (such as J-7 main engine wheel, etc.) were used for brake housing materials, and then 2A80 (old brand LD8) was used to forge aluminum alloy (such as Yun 8). The pressure plate is also made of LD8 forged aluminum alloy. Alloy steel and titanium alloy are used in the brake housing to adapt to the increase of aircraft load level. The main wheel of yun7 is the first product to use 30CrMnSiA alloy steel, and the home-made main wheel of 154 is the first to use TC11 titanium alloy. Many models have applied titanium alloy brake housing, which has the advantages of light weight and high strength, but its disadvantages are high price and poor processing technology. In addition, measures should be taken to prevent titanium brittle in machining and use of titanium alloy parts
Titanium alloy brake housing
From the analysis of operating conditions, the brake case bears the thrust produced by the piston, the torque of the brake acting on the brake disc, and the thermal stress and high-temperature oxidation corrosion of the brake. In addition, it is possible for the aircraft to be put into use when the brake wheel temperature is high, which requires that the brake shell material can withstand a certain high temperature, that is, high temperature endurance and good creep performance. Alloy steel and titanium alloy can better adapt to the harsh conditions of disc brake of heavy-duty aircraft.
Titanium alloy with low density and high strength is an effective measure to reduce weight. TC11 and TC21 are the main titanium alloy used in the brake case. TC11 titanium alloy is a kind of -titanium alloy with good comprehensive performance. Its nominal composition is Ti-6.5 al-3.5 Mo-1.5 ZR-0.3 Si. It has excellent thermal strength under 500℃ and higher room temperature strength
The alloy also has good thermal processing properties (including conventional process properties and superplasticity), and can be welded and machined in various ways. At present, the heat treatment and isothermal forging of TC11 titanium alloy have been developed rapidly with the continuous expansion of its application. The alloy has good corrosion resistance.
However, similar to some titanium alloys, it has a certain sensitivity to thermal salt stress corrosion. The alloy is mainly used in the manufacture of compressor disc, blade, drum and other parts of aeroengine, and also in the manufacture of aircraft structural parts. The maximum long-term operating temperature of the alloy is 500℃ by thermal deformation and heat treatment in the -region. The semi-finished products are bar, forgings and die forgings.
Titanium alloys are sensitive to surface defects and stress concentration, especially those with high strength, so stress concentration should be paid attention to. During the first application of a certain type of airplane wheel brake housing, due to the lack of understanding of the characteristics of TC11 and the poor design consideration, the brake housing clamp broke during the application (low cycle fatigue fracture). . TC21 titanium alloy, whose nominal composition is Ti-6al-2Zn-2SN2Mo-1.5 CR-2NB, is a newly developed high-strength damage tolerance titanium alloy in China, which has been successfully applied in various types of aircraft. From the analysis of mechanical properties at room temperature, except impact toughness, TC11 and TC21 have similar mechanical properties at room temperature without significant difference. The high temperature performance of TC21 titanium alloy at 500℃ is slightly higher than that of TC11 disk die forgings specified in the standard. At present, performance standards of TC21 materials have not been included in relevant standards or manuals.