in Vol. 5 - May Issue - Year 2004
De-lacquering with Shotblasting Technology–Custom Made for Aircraft
The surface of each of these engine parts is shot peened at the production stage as well as later during service and maintenance works.
The special shotblasting system to automatically de-lacquer rotor blades processes about 12 m
SNECMA and EADS are using this shot peening system to increase resistance of material fatigue of engine parts.
De-lacquering radomes: In the system layers of paint on radome covers for civil and military aircraft are removed without chemical additives quickly and economically
The radome is shotblasted with a special shotblasting media that is based on wheat starch. A special software makes the robot hand follow the contour of the component automatically.
In January 2004 Vapor Blast, the French manufacturer for shotblasting technology became part of Rösler Oberflächentechnik GmbH, Untermerzbach. This international manufacturer of slidesanding and shotblasting technology is a well known and respected player with its know-how concerning shotblasting processing solutions, mainly for the aviation industry, and now being part of Rösler world wide coverage can further extend its activities in this area. The civil and military aviation and space industry are the key areas of activity where Vapor Blast has held a leading position for many years, especially in the French market. The new Rösler subsidiary can rely on more than 50 years of experience in developing and manufacturing special shotblasting systems for cleaning, de-lacquering, delaminating and hardening blasting by means of shot peening. Leading manufacturers and operators of aircraft such as SNECMA Group, Air France, EADS, Messier Bugatti are among Vapor Blast’s customers.
Surface finishing in the aviation and space industries requires high technological standards and stringent safety regulations. For reasons of cost-calculation, aircraft manufacturers and airlines also expect cost effective plants and processes for servicing and maintenance, and in this area, custom automation is becoming more and more important.
The lifetime of an aircraft is about 25 years, and during this period it will be completely de-lacquered at least three times. This happens in the course of service and maintenance. Individual parts that are heavily used, such as radomes, which protect sensitive radio or radar systems at the aircraft’s nose, or a helicopter’s rotor blades are de-lacquered and delaminated even more often. Using a chemical process to speed up the process it used to take three days to manually de-lacquer a helicopter’s rotor blades, which can be up to 16 m long. This process is no longer used, partly because of cost, and partly because of environmental concerns. Today, depending on size, a rotor blade can be de-lacquered in a special shotblasting system within 40 minutes. The system is a development of Vapor Blast, a well-known and respected French manufacturer of shot blasting systems that recently became part of the Rösler organization. Vapor Blast developed the automatic shotblasting system in 1995. It is being used by many helicopter manufacturers, and can de-lacquer 12m² of rotor blade surface per hour, fully automatically, producing an even surface, with full blade protection. The speed is reached by means of two special rotary jets that during the process blast simultaneously on either side of the blade, thus ensuring an even blasted surface.
The shotblasting media used is made from plastic that effectively and carefully cleans the surface. One of the system’s special features is that it can be used for rotor blades made from metal as well as for those made of compound materials. In order to ensure repeatability, together with the desired variability during processing, the shotblasting system has been equipped with a new type of programming. This makes it possible depending on the process requirement to control the shotblasting energy via a pre-selection system. The computer supported control system monitors the machine settings and readjusts them if necessary. This includes control of the shotblasting media. Contaminated media is continuously collected and processed, with re-charging of shotblasting media being carried out automatically from the media storage container.
De-lacquering of Complex Geometries
A further example of a special de-lacquering method by means of shotblasting technology again demonstrates the high profitability of custom made automated solutions. It is the de-lacquering of radomes, the housings that are mounted at the nose of civil and military aircraft to protect the radar systems. Radomes consist of high-quality GfK-material, protected with a special lacquer against extreme weather conditions and corrosion. In the course of regular maintenance work the lacquer must be removed in order to examine the condition of the radome. Lacquer removal by means of a chemical process is no longer carried out for environmental reasons; thorough sanding is time consuming and may take up to three days. With the fully automated solution developed by Vapor Blast the processing time for one radome can be reduced to just one hour. It is possible to remove the protective lacquer very precisely and carefully off a surface area of 5 m² per hour using the robot-controlled jet. In order to follow the contours of the components automatically and precisely, Vapor Blast has developed special programmable software.
A laser sensor on the robot’s hand reports the surface structure of the component to the system. The working curve is then automatically calculated, and the required distance, angle and speed sent to the robot.
All parameters are recorded on a data sheet. The shotblasting media used together with a special fine jet, consists of wheat starch. This system is used for any type of radome, in military and civil aviation. To de-lacquer large radomes, as are used on the Boeing 747, or engine covers as well as smaller rotor blades, a similar fully automated system was developed. In this instance the robot is mounted on the ceiling on a mobile axis, in order that a larger shotblasting area can be covered.
Peening of Engine Parts
Shot peening is now an indispensable process used in the manufacture and maintenance of aero engine parts. Treatment with shot peening increases the resistance against material fatigue; therefore slimmer and lighter parts can be used. Shot peening requires exactness and reproductability. Both are decisive features, in order to comply with the regulations implemented by the manufacturers of aircraft to achieve the highest level of safety and profitability. The universal hardening shotblasting robot system developed by Vapor Blast for EADS, SNECMA and other aero engine companies for manufacture, repair and maintenance work ensure absolute precision and reproductability through a special fully automated process control. The weight of the used shotblasting media is measured continuously, and sensors monitor the flow of shotblasting media. Twenty sensor readings per second make it possible to guarantee an even (+/- 2%) flow of shotblasting media. This however was not good enough for Vapor Blast and SNECMA for them to ensure constant quality results.
Therefore, this system has an electronic Almen-reading which constantly monitors the intensity of the shotblasting stream. This normally happens only selectively using Almen strips; the additional expense for the strips can be saved by using the electronic system. The system can be used to process a wide range of engine parts, improving and/or restoring their endurance limit. The system can be fully programmed; it works automatically and complies with the specifications of the aviation and space industry. Part of the system is a 6-axle robot for jet manipulation and a rotary table.
During the process, the shotblasting media undergoes an integrated classification system, it is sorted according to size and shape, processed continuously and brought back into the cycle, thus ensuring the highest possible integrity of the peening process in all operations of the process.
High pressure wet blasting at 4000 bar
De-lacquering without using chemicals, together with wet blasting, have become some of the most common processes in the aviation industry. A special high-pressure procedure working at 4000 bar and with a throughput of 20 liters per minute can reduce processing time to one tenth (3 hours instead of 30 hours). There are many advantages to using wet blasting:
-The process time to remove the layers is reduced – in some cases by twenty times as compared to conventional systems.
-In many cases the parts do not need to be masked.
-The procedure is environmentally friendly. The only residue that occurs is the paint layers removed from the cleaned surface and the paper filter. The processing water can be re-used after filtering.
-No deformations, minimal wear with less than 0.008 mm as compared to 0.018 mm when using conventional processing procedures.
-Highest processing precision, no wear of shotblasting media, no chemical additives.
Because of the advantages described this procedure is experiencing increased demand from manufacturers of maintenance systems for military or civil aviation technology.