|
Robot welding is used for the fabrication of regeneratively cooled nozzle
extensions. These nozzles are constructed entirely from tubes, spiral
wound around a mandrel and automatically precision welded together into
the nozzle profile.
The nozzle of the HM-7 rocket engine, used on Ariane 1 to 4 is produced
this way. The Ottobrunn Production Centre has produced more than 160
nozzles for this third stage engine since 1979.
The nozzle of the HM-7 thrust chamber comprises 242 rectangular section
cooling tubes having a wall thickness of 0,32 mm. The width of each
tube varies along its length to optimise on coolant flow properties,
thereby enabling a uniform heat distribution throughout the nozzle.
The tubes are welded together to form an integral spiral-welded nozzle
structure without the use of any filler material.
Each nozzle has a welded seam length of approximately 730 metres (about
the length of seven football fields).
Our robot welder produces about 10 nozzles per year. One of its main
features is a laser-led TIG welding head that detects the welding gap
between tubes as well as any tube offset and regulates the welding parameters
accordingly.
The finished nozzle and engine. The HM-7 uses a regenerative cooling
system for the combustion chamber and throat assembly, i.e. most of
the liquid hydrogen flow is routed through 128 longitudinal channels
integrated in the double-wall structure. The nozzle is cooled by a simple
process known as dump cooling, whereby remaining hydrogen flow is routed
to the 242 spiral-welded tubes forming the nozzle structure, then escapes
through 726 micro-nozzles set along the base of the nozzle rim. Although
these gases do not undergo combustion, they are heated during their
trip and contribute to the overall thrust.
|
