Thickness, adhesive controlling

Specifications and Test Methods. The American Society of Electroplated Plastics pubHshes a comprehensive book covering most technical aspects of testing and control (24). A number of ASTM standards have been issued that cover thickness, adhesion, and thermal-cycling resistance of the total plated film. Some specifically for plated plastics include ... 

The study of corrosion is essentially the study of the nature of the metal reaction products (corrosion products) and of their influence on the reaction rate. It is evident that the behaviour of metals and alloys in most practical environments is highly dependent on the solubility, structure, thickness, adhesion, etc. of the solid metal compounds that form during a corrosion reaction. These may be formed naturally by reaction with their environment (during processing of the metal and/or during subsequent exposure) or as a result of some deliberate pretreatment process that is used to produce thicker films or to modify the nature of existing films. The importance of these solid reaction products is due to the fact that they frequently form a kinetic barrier that isolates the metal from its environment and thus controls the rate of the reaction the protection afforded to the metal will, of course, depend on the physical and chemical properties outlined above. 

Plasma surface treatment of many polymers, including fabrics, plastics, and composites, often occurs. The production of ultra-thin films via plasma deposition is important in microelectronics, biomaterials, corrosion protection, permeation control, and for adhesion control. Plasma coatings are often on the order of 1 100 nm thick. 

General Process Considerations. To be useful, a CVD process must produce thin films with reproducible and controllable properties including purity, composition, film thickness, adhesion, crystalline structure, and surface morphology. The growth rates must be reasonable, and the deposition must not have significant impact on the microstructures already formed in the substrate. The deposition time must be sufficiently short, and the temperature has to be low enough so that dopant solid-state diffusion does not smear the results of previous processing steps. 

The adhesive layer thickness was controlled within the limits 5 x 10 to 3 X 10 cm, and the cemented materials were IKhlSNlOT steel and aluminum. The thickness of the substrates h, their moduli E, and the linear thermal expansion coefficients a were... 

Bondline thickness. The control of bondline thickness is essential for high-power devices. A thin bondline is required since thickness is directly proportional to the junction-to-case thermal resistance, Qjq (see Ch. 2). Specially formulated solvent-based hybrid adhesives can produce uniform bondline thicknesses of one mil or less. Small hard spacers, acting as shims, added to paste adhesive formulations, have also been used to control thickness.The use ofpreforms instead of paste adhesives also assures reproducible thicknesses provided uniform pressure and temperature are applied during curing. 

The design loading is a short-term permanent loading only. The joint will be located at an indoor environment at room temperature. The adhesive is applied manually using a spatula and the adhesive layer thickness is controlled using copper wires. The adhesive and adherend mechanical values have been determined by testing. 

The quality of the coating (e.g. crystal size, porosity, smoothness, thickness, adhesion to base metal) is influenced mainly by bath composition, pH and temperature, although initial metal surface structure, cleaning and pre-treatment can also be important. In addition to accelerators, other additives may be included in bath formulations to control crystal nucleation, wetting of the metal surface and the metal ion concentration. 

The quantized friction would be a direct result of the multiple discrete values of the adhesion-controlled contribution to the total friction, and could be a common feature for fluids able to form thin film-layered structures. The results described by Smith et al. could account for discontinuities in friction across thin films as a function of the number of layers, particularly under boundary lubrication regimes with varying liquid film thickness across the contact zone between rough surfaces. 

Tape-cast brazing alloys are flexible, and when laminated to an adhesive layer they can be applied to the surfaces to be brazed even in very complex and convoluted areas. The metallic powders are mixed with the organic components and the slurry is tape-cast in a very conventional manner. The thickness is controlled by the setting of the doctor blade. A wide variety of thicknesses are used for this application, although most of the tapes are in the 0.254 to 1 mm thickness range. 

Doctor roll. The gap between the pick up roll and the coating roll is adjustable and this determines the adhesive add-on. It is possible to apply thick adhesives up to 50,000 mPas and control accurately the adhesive thickness which may vary from 10 to 150 g/m. This system allows also to apply fluid adhesives at very high speed and low add-on (2 to 50 g/m ) (Fig. 40 and 48). The doctor roll reduces foaming because it squeezes the foam bubbles which could result from the agitation of the adhesive. Doctor rolls are always used in sophisticated roll coaters, when an accurate add-on is required and for high speeds. 

The coating and curing processes are depicted schematically in Fig. 4 More detailed information about application, thickness and adhesion control can be found in Ref... 

The thick-flhn limit of the lubricant dispersion surface energy is yf = 13 mJ/m [22]. The dispersion component of the surface energy of the slider is Yi. For the uncoated slider, yf = 43 mJ / m, and the coated slider values are given in table 4.10. The adhesion stress is listed in table 4.13. Further discussion of adhesion-controlled friction is given in the literature [23]. 

D-3983. Test Method for Measuring Strength and Shear Modulus of Non-rigid Adhesives by the Thick Adheiend Tensile Lap Specimen (Fig. 11). For measuring the properties of lower-mod-ulus, more rubbeiy adhesive films. Glueline thickness is controlled by shims. Developed for wood but applicable to metals and other substrates also. 

The Institute has many-year experience of investigations and developments in the field of NDT. These are, mainly, developments which allowed creation of a series of eddy current flaw detectors for various applications. The Institute has traditionally studied the physico-mechanical properties of materials, their stressed-strained state, fracture mechanics and developed on this basis the procedures and instruments which measure the properties and predict the behaviour of materials. Quite important are also developments of technologies and equipment for control of thickness and adhesion of thin protective coatings on various bases, corrosion control of underground pipelines by indirect method, acoustic emission control of hydrogen and corrosion cracking in structural materials, etc. 

Additional improvements have been incorporated since 1966 with the availabihty of thinner float glass. Glass thickness and interlayer thickness have been studied to optimize the product for occupant retention, occupant injury, and damage to the windshield from external sources (30,31). The thinner float glass windshields are more resistant to stone impacts than the early plate glass windshields. The majority of laminated windshields are made of two pieces of 2—2.5 mm aimealed glass and 0.76 mm of controlled adhesion interlayer. 

AppHcation of an adhesion-promoting paint before metal spraying improves the coating. Color-coded paints, which indicate compatibiHty with specific plastics, can be appHed at 20 times the rate of grit blasting, typically at 0.025-mm dry film thickness. The main test and control method is cross-hatch adhesion. Among the most common plastics coated with such paints are polycarbonate, poly(phenylene ether), polystyrene, ABS, poly(vinyl chloride), polyethylene, polyester, and polyetherimide. 

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