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Products and solutions, 2000-08-10, 02:00 AM

Krupp VDM gets Airbus into shape

From August 2000 the components of the rudder unit for the Airbus A330-200 will be produced in molds made of the material Pernifer 36 from Krupp VDM. The components are 13.50 meters high, up to 3.40 meters wide, 60 centimeters thick and weigh around 250 kilos. The consist of carbon fiber reinforced plastic (CFRP) and are among the largest fiber composite structures ever built for commercial aircraft. The parts have to meet stringent dimensional accuracy requirements, holding tolerances of only a tenth of a millimeter. Krupp VDM GmbH supplied around 90 tons of Pernifer 36 for the application.

Weighing ten tons each, the molds were manufactured in Varel, Lower Saxony, at the central production equipment plant of Airbus in Germany. The parts themselves are being made at the Stade site, which makes the rudder components for all Airbus planes. Because the parts are cured in the mold in an auto-clave at 180 degrees in a vacuum and at ten bars pressure, it is important for the mold material to behave as much as possible like the CFRP during heating and cooling.

Pernifer 36, a nickel/iron alloy, has a coefficient of linear expansion of 1.2 millionths of a meter per Kelvin (minimum at room temperature), which is equal to that of the plastic used for the rudder unit parts. Cracks or stresses, which could occur as a result of differing shrinkage rates of mold and part during cooling, are ruled out. During and after heat treatment the mold retains its dimensions so precisely that even steps or recesses can be integrated as force introduction points or to accommodate joint parts in the finished component.

Like other aircraft manufacturers, Airbus has been using molds of nickel/iron alloys like Pernifer 36 for smaller CFRP parts for a long time. For large parts like the rudder unit component however they have previously used molds made of the same material as the part. The change to the more expensive Pernifer mold was economic because it can be used over and over again indefinitely. By contrast, after about 100 uses CFRP molds have to be repaired after every individual heat treatment in the autoclave. Because joint parts and force application points can be molded directly into the rudder unit, manufacturing cost is lower and the strength of the overall structure is increased. It is planned to produce parts for the new Airbus A3 XX in molds made of Pernifer 36 as well.

As well as Pernifer 36, Krupp VDM GmbH supplies the nickel/iron alloys Pernifer 42 and Pernifer 2918 MS. Thanks to their low linear expansion these materials have proven themselves in numerous mold and die applications. Typical uses are molds for glass manufacturing, fixtures, housings for lasers and measuring equipment in automation technology.

Comparison of linear expansion coefficients of various materials
Material | Linear expansion coef-ficient in 10-6 K-1 | Notes
Pernifer 36 | 1,.2 | Minimum at RT
Pernifer 42 | 5.3 | Minimum at 350° C
Pernifer 2918 | 6.1 | Minimum at 400° C
Comparable materials
Stainless steel | 14.4
Aluminium | 23.8
CFRP | -0.8 ? 34 | Depending on direction, resin and fiber type
GFRP | 5.0 ? 7.0
Quartz glass | 1
Granite | 3.0 | Measuring tables

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