Hole-blind

Electrolytic plating rates ate controUed by the current density at the metal—solution interface. The current distribution on a complex part is never uniform, and this can lead to large differences in plating rate and deposit thickness over the part surface. Uniform plating of blind holes, re-entrant cavities, and long projections is especiaUy difficult. 

Although zinc has an appreciable vapour pressure at the temperatures of treatment, it is unlikely that zinc vapour plays any significant part in the diffusion process and it is generally accepted that the mechanism relies almost exclusively on intimate contact of hnely divided zinc dust with the steel surface. In spite of this requirement, coatings of even thickness and composition are obtained on the most intricate shapes, on fine threads, inside blind holes, and in the bore of small-diameter tubes. Large articles of uniform section, e.g. rods, tubes, etc. can be coated by this process. 

Blind hole In regard to molding products that include holes, it is important to ensure that sufficient material surrounds the holes and melt flows property. A core pin forming blind holes is subjected to the bending forces that exist in the cavity due to the high melt pressures. Calculations can be made for each case by establishing the core pin diameter, its length, and the anticipated pressure conditions in the cavity (3). 

When this type of flow pattern is impractical, an alternative may be a through hole or tube formation combined with a postmolding sealing or closing operation by spinning or ultrasonic welding. At the other extreme, consider a 1 /4 in. (0.6 cm) diameter core exposed to a pressure of 4,000 psi (28 MPa) with an allowance for deflection of 0.0001 in. (0.00025 cm) and determine how deep a blind hole can be molded under these conditions. 

Blind holes in molded plastics are created by a core supported by only one side of the mold. The length of the core and depth of the hole are limited by the ability of the core to withstand the bending forces produced by the flowing plastic without excessive deflection. For this reason, the depth of a blind hole should not exceed three times its diameter or minimum cross-sectional dimension. For small blind holes with a minimum dimension below 1/4 in., the L/D ratio should be kept to two. With through holes the cores can be longer, since the opposite side of the mold cavity supports them (3). 

Apparent (virtual) teaks quantities of gas will be liberated from hollovi/s and cavities inside cast parts, blind holes and joints (also due to the evaporation of liquids)... 

A great advantage of /me are spray is that it can he applied to almost anv plastic. Zinc arc spray, also suitable for prototypes and small lots of materials, is less suited lor very small parts and parts having blind holes or complex interior surlaces. or w here warpage is a problem. 

The cleaning may be carried out by solvent vapours, by immersion in the liquid phase—and by both methods in combination. Immersion also should overcome static attraction, but if this phase is not used a gun emitting deionized air under low pressure may be employed to clean individual parts and to take away debris. Agitation of components by ultrasonic means can be helpful in removing contamination from blind holes and recesses. 

Squeeze bottles, oil cans, and pressurized glue guns permit precise and speedy adhesive application. By adjusting the pressure, the rate of adhesive flow can be matched to the production rate. These devices can apply the adhesive or sealant inside a blind hole or limited-access area. The tip of the applicator can be used to deliver multiple spots of adhesive. 

Since supercritical fluids were chosen for their ability to penetrate small cracks and crevices, additional tests were performed to evaluate this characteristic. A test cube modeled after a similar fixture fiibricated by Ferranti Aerospace, was developed and manufactured to md in this study. The cube had a number of blind holes, tapped holes, dtannels and crevices to simulate actual hardware. Beryllium, 300 Series stainless steel and aluminum cubes were constructed to simulate the conunon metals found in the instrument. In addition, the sides of the cube were removable to facilitate deposition of the contaminants into these blind holes and crevices and later analysis of cleaning effectiveness. The base of the cube was equipped vrith a scanning electron microscope (SEM) mount so that the cube could be examined directly in the SEM. Figure 3 is a photograph of a test cube. Extensive evaluations with these test cubes indicated that supercritical fluids were indeed effective at removing contaminants from cracks and crewces. 

Pinholes, pits, blind holes, porosity, undercutting or similar depressions shall not exist in the finished surface of the weld before or after blast cleaning. 

In the case of blind holes, apply adhesive to the lower third of the borehole so that the adhesive will be pressed up on the (inner) walls of the threads when the screw or the stay bolt is tightened or even when a pin is bonded in place. 

This paper highlighted the recent efforts to apply three NDT methods, i.e., the infrared thermography. X-ray radiography, and industrial computed tomography (CT), to detect the blind holes in a C/SiC composite panel, and then to evaluate the abilities of these used NDT techniques for detecting the artificial defects. 

Preparation of the defect laminates with blind holes... 

Figure 1. Photograph showing the standard C/SiC sample with drilled blind holes on the other side.

For the composite panel with the drilled blind holes on the back side, a time sequence of thermal images was obtained by thermography. Figure 2 presents a series of thermographic results from t = 0.017s to 2.002s. These thermal images with time sequence exhibit a clear evolution of the hidden holes from invisibility to visibility at different depths. 

The blind hole can be measured in diameter and depth by thermography when the thermal intensity of each hole reached a maximum. The size measurement of each hole in the thermal image corresponds to a separate maximum time tp because the thermal intensity of each hole reached the maximum value at different time tp, depending on the diameter and depth as ... 

Figure 2. Thermal images of the blind holes in C/SiC sample with different times.

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