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Aerospace

 

Introduction

Components installed in aircraft are subject to strict quality guidelines. Specifically, components that can cause catastrophic damage to the aircraft in the event of a failure are subject to special guidelines. For this purpose, a separate approval procedure was established to qualify suppliers. Approvals such as EN9100 or NADCAP are standard in the supplier industry. The heat treatment of these components is called the "Special Process" in the said approvals and thus shows that in terms of quality, special attention is paid to these processes. In order for the components, e.g. from the landing gear or aircraft turbines, to withstand the loads, appropriate heat treatment is one of the core processes in addition to the correct design, production and material selection.

Heat treatment after following standards and norms:

  • AMS 2759
  • AMS 2759 /1 - 9, 11, 12
  • AMS 2750
  • Customer's specific norms after checking

Parts

Landing gear

The landing gear of an aircraft consists of wheels, tyres, rims, brakes and the corresponding suspension. The landing gear supports the aircraft during take-off on the one hand, and is one of the most important elements when landing, since high forces are exerted on all landing gear parts at that time. In addition to the impact load, the landing gear is exposed to high kinetic and potential energies during landing.

With the aid of targeted heat treatment processes, strength-increasing properties of the landing gear can be achieved.

Crank shafts

Crankshafts convert linear movements of a piston into a rotary movement. They must therefore withstand the loads generated during flight operations and are exposed to both compressive and tensile forces as well as radial forces. Accordingly, it must be ensured that a crankshaft has sufficient bending and torsional strength and that the bearing points have a good load-bearing capacity.
A surface or heat treatment of crankshafts may be necessary to improve the material properties in order to meet the higher requirements in the aerospace sector. Suitable thermo-chemical processes are Gas Nitriding R.NIT+®, Nitrocarburizing R.NIT+®, Plasma Nitriding PLASNIT® and Case Hardening R.CARB+®. The addition of nitrogen results in an increase in strength and a build-up of compressive stresses, which leads to improved load-bearing capacity of the crankshaft. During Case Hardening R.CARB+®, the surface layer is carburised to achieve higher strength.

Bearings

Bearings are components that connect machine parts and slide or roll over each other. They enable moving and stationary components to be connected and transmit forces. A distinction is made between plain and roller bearings.
In the aerospace industry, ball, roller or needle bearings are subject to high loads. The rolling elements and the bearing shells, between which the rolling elements are pressed, in particular, are subject to high stresses. In the long run, this load leads to wear and thereby limits the service life of the parts.
The resistance generated can be reduced by adequate heat treatment, low-friction material combination and lubrication. The RÜBIG hardening techniques Gas Nitriding R.NIT+® and Plasma Nitriding PLASNIT® or Case Hardening R.CARB+® as well as Vacuum Hardening R.VAC+® increase the strength of the parts. Moreover, bearing rings can only withstand constant rolling of the rolling element without damage after heat treatment.
A surface coating can be used to minimise friction. The PLASTIT® Hard Coating processes are particularly suitable for this.

Camshafts

Camshafts control the intake and exhaust valves of internal combustion engines. Therefore, camshafts are exposed to high wear and contact loads as well as increased friction loads. A suitable combination of wear resistance, toughness and strength is essential for this. Due to the geometry (long shaft, small diameter), the component is at risk of distortion during heat treatment. Low temperature processes (<550°C) such as Gas Nitriding R.NIT+® and Plasma Nitriding PLASNIT® minimise the resulting heat distortion.

Pumps

Pumps are used to transport liquids. In internal combustion engines or aircraft engines, pumps are usually used for transporting coolant or fuel. Gear pumps are used to transport fuel, particularly in the aerospace sector. The gears used are exposed to high forces at the edge and require heat treatment.

Heat treatment improves both the strength and the wear behaviour of the component. These properties can be adjusted with the aid of specific heat treatment processes. Particularly the Case Hardening R.CARB+® and Nitriding PLASNIT® and R.NIT+® are used here.

Engine blades

Due to their shape and rotary motion, engine blades are used to draw in and compress air (compressor) or, if the function is reversed, to generate a rotary motion when air flows out (turbine). In aircraft engines, turbine blades are heavily loaded due to the high temperature, especially after the fuel has burned, when the hot air stream escapes.

Specific heat treatment processes can be used to adjust the strength-increasing and wear-resistant properties of engine blades. Particularly VH and BBB are used here.

Turbine shafts

Turbine shafts are required to transmit rotary movements and torques and to fix or mount rotating parts such as turbine blades. Unlike axes, shafts transmit torque. Depending on the design of the engine, the shaft structure can be different (e.g. single, coaxial, multi-part).
Due to the high stress, a suitable and carefully executed heat treatment and material selection is indispensable. RÜBIG Hardening Technology offers heat treatment processes tailored to the component requirements in order to increase the service life and safety of turbine shafts.

Valves

Valves seal the combustion chamber of aircraft engines with internal combustion engines. Here, a distinction is made between intake valves that open the combustion chamber of the aircraft engine and exhaust valves that open and close the exhaust outlet. These are controlled by one or more camshafts. Valves operate under the influence of aggressive gases, extreme temperatures and are exposed to strong frictional forces. They are both thermally and mechanically stressed parts. Defective valves can lead to overheating and melting in the engine compartment.
Heat treatment is used to achieve high wear and corrosion resistance, high temperature resistance and scale resistance and thus significantly extend the service life of these parts. The following processes are suitable for this: e.g. Gas Nitriding R.NIT+® and Plasma Nitriding PLASNIT® or Case Hardening R.CARB+® and Vacuum Hardening R.VAC+®.

Gearwheels / Planetary Gears

Gears are used for the transmission of torques. The transmission can be done as a rotary movement (two gears) or, paired with a gear rack, as a linear movement. The requirements for gears are different. On the one hand, a high hardness must be achieved for the rolling movement and the forces occurring on the tooth surface; on the other hand, a tough core is required for the transmission of force. Shock loads and abrupt increases in torque complete the requirement profile.

In planetary gears, several gears are installed in a rotating frame and orbit a centrally located sun gear. The sun wheel transmits the energy to the planet wheels. Basically planetary gears serve as transmission stages and are often used in the aerospace sector as reduction gears for turbofan engines (e.g. Boeing 747). With such engines, the majority of the feed motion is generated by a fan, which is controlled by a planetary gear.

Heat treatment improves both the strength and the wear behaviour of the component. Planetary gear units are used for very high reduction ratios. This causes very high loads on the gears. These properties can be adjusted with the aid of specific heat treatment processes. In particular, Case Hardening R.CARB+® and Nitriding PLASNIT® and R.NIT+® are used here.

Cylinders / Cylinder head

Cylinders and cylinder heads are made of aluminium in modern aircraft engines. A cylinder head comprises inlet and outlet channels, the valve control for gas exchange processes and channels for cylinder head cooling. The cylinders, which act as a link between the housing and cylinder head and at the same time provide the frame for the piston stroke movement, are often cooled exclusively with air and are accordingly equipped with cooling fins.
Since temperatures of over 250°C can be reached in the area of the combustion chamber, this can lead to thermal fatigue in the long term. Toughness and strength values play a decisive role in counteracting the high loads. These can be homogenised by suitable heat treatment. The RÜBIG ALU mainly offers T6 and T7 states for the heat treatment of aluminium castings. T6 and T7 states convince by the short throughput times with highest quality.

Various parts

Other components that can be heat-treated in aircraft include: Suspensions, joints, seats, galley, div. Test parts, div. Parts of utility wagons, airfield test systems and others.

Services Heat treatment
Services of the Heat Treatment division at a glance: