Air blister

Air blisters generally occur due to trapped air during the processing of the rubber in the calender or extruder or during hand building up of the products. The remedial measures to be undertaken are 1) Modify process temperature or pressure, 2) Feed the calender or extruder with adequate rubber stock, 3) Prick out visible blisters when the compound is in unvulcanized state, and 4) Use bleeder cords between metal and the rubber sheets applied at the welded places in the rubber lining process. 

Air blisters can be avoided easily in thinner sheets that can be plied up to the required thickness, rather than one step calendering of a thicker sheet that induce formation of air blisters during calendering. 

In air, blister agents Lewisite and Mustard-Lewisite will be broken down by compounds that are found in the air, but they may persist in air for a few days before being broken down. 

The back pressure is intended to ensure that a sufficiently high level of homogeneity is attained by the melt during plasticising. This involves uniform temperature distribution, and the absence of air blisters or gas blisters. 

If the back pressure is too low, this will become noticeable through big variations of the compound pack during holding pressure from batch to batch (as a result of air blisters). If the component s weight is measured, too low a back pressure shows up through the underweight components which appear from... 

During the injection, air is entrapped in the melt and appears as a hollow (air blister) on the moulded part. Primarily there are two factors responsible for this defect ... 

On this meter ease, there are dovetail guides on the four side faces. The varying wall thickness caused the meeting of flowpaths resulting in an air blister in the vicinity of the gate. This is shown in Figure 9.42. The following measures were adopted to try and remove this air blister ... 

In order to remove the air blister even at faster initial injection speeds, the mould clamping force, which had previously been set very high (too high) was reduced until satisfactory ruiming was achieved again. This example shows that a mould clamping force which is not too high, and which is satisfactorily set,... 

It was decided to remove the air blister by a simpler method as shown in Figure 9.44. A gas vent was groimd, 8.0 mm wide and 0.3 mm thiek. The convergence point, with the air, could now be forced out, and it was possible to manufacture good components. 

Pure phenol is a colourless crystalline substance, having m.p. 43°, and b.p. 182° on exposure to air, it slowly sublimes, and on exposure to light, develops a pink colour. It has a characteristic odour, and a limited solubility in water. Phenol in dilute aqueous solution has strongly antiseptic properties, but the crystalline substance should not be allowed to come in contact with the skin, as it may cause severe blistering. 

Blister Elevation of the surface of a plastic caused by trapped air,... 

Air pockets or bubbles are left on the surface of all concrete. Good vibration and placing techniques will reduce their number but not eliminate them. Many air pockets have a small opening on the surface in relation to their size. Paints will not penetrate into such holes, with the result that air or solvent is trapped and subsequent expansion will cause the coating to blister. In addition, some air pockets are covered with a thin layer of cement that also has no strength and will cause loss of adhesion. 

The solid produced is called blister copper. It has an irregular appearance due to air bubbles that enter the copper while it is still molten. Blister copper is impure, containing small amounts of several other metals. 

The copper product is known as blister copper because of the appearance of air bubbles in the solidified metal. In the hydrometallurgical process, soluble Cu2+ ions are formed by the action of sulfuric acid on the ores. Then the metal is obtained by reducing these ions in aqueous solution either electrolytically or chemically, by using an inexpensive reducing agent that has a more negative standard potential than that of copper, such as hydrogen or iron (see Section 14.3) ... 

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