Ultrasonic curing

Ultrasonic welding is a frictional process that has been well established for heat welding thermoplastic parts. Like induction welding, it also has been adapted for curing structural adhesives such as epoxy. 

FIGURE 14.11 Equipment used in standard ultrasonic welding process. 

Rapid curing of structural epoxy adhesive by ultrasonic heating has been demonstrated successfully in recent work. The conversion of epoxy groups produced by ultrasonic curing for 50 s was almost 3 times higher than that obtained by thermal heating.51 

Adhesive Form Adherends Weld time, s strength, psi 

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In terms of equipment. McDonnell Douglas proposes an automated ultrasonic scanning system (AUSS) with 9 axes of motion, a 7 axes ultrasound system (ADIS-II) and a portable inspection system (MAUS II) for aerospace composite structure inspection [36], The ultrasonic resin analyser (URA 2002A from Quatro Technologies) can be used to measure the resin content in polymer based composites [10]. The UCMS-200 ultrasonic cure monitoring system from Micromet Instruments utilizes measurements of the ultrasonic sound speed to monitor changes in the viscosity, rigidity of composites. 

Sharma S and Luzinov I (2011), Ultrasonic curing of one-part epoxy system , J Compos Mater, 45, 2217-2224. doi 10.1177/0021998311401075. 

Nondestmctive testing (qv) can iaclude any test that does not damage the plastic piece beyond its iatended use, such as visual and, ia some cases, mechanical tests. However, the term is normally used to describe x-ray, auclear source, ultrasonics, atomic emission, as well as some optical and infrared techniques for polymers. Nondestmctive testing is used to determine cracks, voids, inclusions, delamination, contamination, lack of cure, anisotropy, residual stresses, and defective bonds or welds in materials. 

Polished steel substrates primed with plasma polymerized acetylene films were immersed into a stirred mixture of these materials at a temperature of 155 5°C to simulate the curing of rubber against a primed steel substrate. During the reaction, the mixture was continuously purged with nitrogen to reduce oxidation. At appropriate times between 1 and 100 min, substrates were removed from the mixture, rinsed with hexane ultrasonically for 5 min to remove materials that had not reacted, dried, and examined using RAIR. The RAIR spectra obtained after reaction times of 0, 15, 30, and 45 min are shown in Fig. 13. 

All four laminates were autoclave processed using the standard cure cycle discussed previously. After processing, all four laminates were ultrasonically inspected. The results are presented in Figure 10.13. As expected, the dry-hot precompacted laminate (Laminate 4) was... 

Hinrichs and Thuen [28] used ultrasonic attenuation to determine the proper time for pressure application during an otherwise traditional pre-established cure cycle. Because dielectric is an electrical property, it is influenced by moisture content and temperature as well as viscosity, so it may vary quantitatively. Ultrasonic measurements are also affected by other parameters (i.e., void content), but they are a mechanical measurement rather than an electric one. The ultrasonic sensors used by Hinrichs unfortunately were less reliable than the dielectric sensors. 

Kwan, K. M., and Benatar, A., Investigation of Non-Thermal Effects Produced by Ultrasonic Heating on Curing of Two-Part Epoxy Adhesive, Society of Plastic Engineers Annual Technical... 

Nondestructive Testing. Nondestructive testing (NDT) is far more economical than destructive test methods, and every assembly can be tested if desired. Several nondestructive test methods are used to check the appearance and quality of structures made with adhesives or sealants. The main methods are simple ones such as visual inspection, tap, proof, and more advanced physical monitoring such as ultrasonic or radiographic inspection. The most difficult defects to find are those related to improper curing and surface treatments. Therefore, great care and control must be exercised in surface preparation procedures and shop cleanliness. 

A series of five nanocomposite elastomer systems were prepared for this study incorporating 0, 1, 2, 4 and 8% (on total resin mass) of the organically modified montmorillonite clay Cloisite 6A. The appropriate level of Cloisite was dispersed in a starting resin blend of OH terminated PDMS (M -77,000 and Mn -550 g mol in a 3 1 ratio) by a combination of mechanical mixing and ultrasonic processing to give a nano-dispersion of clay platelets. The blend was subsequently crosslinked with a stoichiometric level of tetrapropoxysilane (TPOS) in the presence of 5% diphenylmethylsilanol (DPMS) chain terminator and 5% tin(II) 2-ethylhexanoate catalyst, cured in an open mould at 65°C for twenty minutes, then removed from the mould and post cured for a further fifteen hours at 65°C to give an elastomeric mat. 

Power ultrasound has also been found to be effective in the extraction of protein from meat [58]. Ultrasound disrupts the meat myofibrils and this releases a sticky exudate which binds the meat together. The binding strength, water holding capacity, product color, and yields were examined after treatment either with salt tumbling, sonication, or both. Samples which received both salt treatment and sonication were superior in all qualities. Similar results were obtained from a study of the effect of sonication on cured rolled ham [59]. Ultrasonic treatment enhanced the extraction of myofibrillar proteins leading to an increase in the strength of the reformed meat. 

Experiments were run to evaluate the effects of low level static (stretch) and dynamic (ultrasonic Irradiation) stress on water permeation of a WRT Neoprene. At the same time, the contribution of a partial silica filler In the place of black was determined. The materials were Identical zinc oxlde-magne-slum oxide-cured formulations except that one contained 30 phr black and the other contained 15 phr black and 15 phr silica. These were molded Into cups with 0.030 In. thick faces and 0.070 In. thick side walls which were then fitted over 3.5X salt water-filled glass cups and sealed with hose clamps. 

There are several reasons for the scatter of the data (a) nonhnear contributions of the transducers and measurement equipment are superimposed on the measurement effect (b) the samples bend during a test, producing both tensile and shear stress in the bonded interface and (c) there are expected to be statistical variations of the properties of the epoxy bonds themselves, due to different microstructures and curing. Furthermore, depending on the dynamic behavior of the interfaces, the deviation of the phases of the transmitted waves from their values in the nonhysteretic case must be taken into account in the evaluation of the interaction forces, especially if the ultrasonic excitation is high enough to obtain ultrasonic stresses comparable with the bond strength. 

The resin content in both composites is about 37% by weight. The porosity of the composites was characterized by ultrasonic C-scans. The test specimens of no measurable porosity were used. The resin specimens and the composite laminates were cured in a hydraulic press at 250 F and 75 psl for one hour, and subsequently postcured at the same temperature in the absence of pressure for another two hours. Additional curing for up to 16 hours in the case of HX-205 and F-185 resins showed no measurable changes in dynamic mechanical properties. 

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