## 4 Repair Technology  
The concept of the repair of the detachment of the shield fragment from the leading edge of the main rotor blade consists of the separation and bending of the shield fragment  
Figure 5: Sampling site and samples for DSC testing: (**a**) Bonding ply; (**b**) Rubber. Figure 6: Results of the DSC tests of the rotor blade edge components: (**a**) Bonding ply; (**b**) Rubber. from the rubber, proper drying and preparation of the surface for bonding (mechanical and chemical), application of properly selected adhesive, pressing the shield fragment to the edge, and conducting the appropriate thermal cycle of curing the adhesive. The process is shown step-by-step in Figure 7.  
In order to properly prepare the surface for bonding, the faulty shield must be separated from the rubber (Figure 7a). Based on the DSC analysis (Figure 6) and a number of tests, it was found that heating the shield to 110 \({}^{\circ}\)C softened the bonding paste so that it could be peeled off with a medical wooden spatula. It was tentatively assumed that an epoxy resin-based adhesive system, containing fillers to increase the viscosity of the bonding paste, would be used for bonding the shield during repair. When bonding, especially using epoxy resin-based systems, surface preparation is one of the most important parts of the bonding process. According to [24], a titanium surface before bonding can be prepared using various mechanical, chemical, and electrochemical methods. However, the most important issue is to create appropriate roughness on the prepared surface. In [24], an illustrative classification of bond strength and durability, from poor to excellent, was presented. Degreasing and then scrubbing with sandpaper affords irregular macroporosity to the surface [25]. According to the classification presented, roughening with sandpaper produces \"poor strength\" and \"poor durability\". In contrast, sandblasting yields uniform macro roughness, which translates to \"increased strength\" and \"adequate durability\" of the joint. \"Excellent properties\" are achieved by chromic acid anodizing [26] and other chemical treatments, such as sol-gel [9; 21; 27] or modified phosphate fluoride processes [28]. These methods produce a microporous surface coated with titanium compounds that is supersaturated with adhesive. Unfortunately, it is not feasible to use these  
Figure 7: Technological process of repairing the leading edge of a rotor blade: (**a**) Separation of the damaged piece of shield from the rubber; (**b**) Sandblasting; (**c**) Cleaning; (**d**) Drying; (**e**) Applying a primer; (**f**) Applying adhesive paste; (**g**) Curing; (**h**) Post-curing. methods in field workshop conditions. These methods require the use of toxic and chemically aggressive reagents (chromic acid VI) in appropriate proportions, and specialized apparatus in the case of anodizing. The use of aggressive chemicals, which, in an uncontrolled manner would penetrate the gaps created by a partially detached shield, could lead to the degradation of components during subsequent operation. In addition, in the case of selected fragments of partially detached shield, the use of electrochemical methods is technically very difficult. Therefore, the decision was made to treat the titanium surface in a way that is feasible in field workshop conditions, consisting of surface degreasing and sandblasting (Figure 7b). Sandblasting using a 6 mm-diameter nozzle, 0.4 mm-grade corundum sand, and 10 bar working pressure at 2 m\({}^{3}\)/min, resulted in a roughness of Ra = 1.05 \(\upmu\)m. Before this operation, the rubber was protected by isolation tape, which was removed after sandblasting. The surface after sandblasting should be washed with acetone to remove sand dust and oil residues (Figure 7c). Despite the use of oil separators in the pressure supply system of the sandblasting gun, there is a risk that trace amounts of oil mist from the compressor lubrication system may be present in the compressed air.