Poor Parting Line

Fig. 4. Electron micrographs of L-Asp-LI and L-GIu-LI in hippocampus CAl from a hypoglycemic rat subjected to perfusion fixation. The tissue was treated with uranyl acetate before embedding in epoxy resin. The figure shows accumulation of immunoreactivities over synaptic vesicle clusters (sv) versus over cytoplasmic matrix (cm) in terminals making asymmetrical synapses on spines (s). Broken lines mark the houndary between the vesicle-rich and vesicle-poor parts of the terminals. Scale bar = 0.2 pm. (Modified from Gundersen et al., 1998.)...

Figure 11-19. Examples of parting line locations. The extreme right diagram shows that having sharp comers could cause poor dimensional control or possibly nonflat surfaces with inadequate mold cooling.

Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. They occur when melt flow fronts collide in a mold cavity. Material characteristics can affect the knitting of the melt fracture. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of part strength. 

The main problems with mica are poor knit line strength and impact resistance. When mica-reinforced plastic flows around inserts and rejoins on the other side, the knit line may only have 60% of the strength of the rest of the part. Impact resistance of mica-reinforced plastics is poor, as it is with talc and kaolin. These problems are often overcome by combinations of mica with glass fibers, acicular wollastonite, calcium carbonate or glass microspheres, and by special molding machinery. 

Inflation of the parison is normally accomplished with compressed air, but in some cases the vaporization of liquid nitrogen is used instead. If the air between the parison and the mold wall is not vented as the parison inflates, it will prevent the molten polymer from making uniform contact with the mold surface, resulting in poor surface finish. Slit-type vents may be provided at the mold parting line. 

One cmrent rule is the depth of the pocket is determined by multiple factors. These factors are plastic density, weight of part and parison, parison diameter, parison orientation, and pre-blow pressme. When the flash pocket is shallow, it causes extreme pressme at the parting line and machine pressure section and it causes difficulties in trimming off the flash. When the flash pocket is deep, it causes poor cooling. The poor cooling can cause a hot flash which softens and weakens the weld line [1]. 

The corrosion conditions can be different at the fluid line from the bulk condition. Aqueous liquids have a concave meniscus, which creates a thin film of liquid on the vessel wall immediately above the liquid line. Some corrosion processes, particularly the diffusion of dissolved gases, are more rapid in these conditions. Additionally, the concentration of dissolved gases is highest near the liquid surface, especially when agitation is poor. Locally high corrosion rates can therefore occur at the liquid line, leading to thinning in a line around the vessel. This effect is reduced if the liquid level in the vessel varies with time. Any corrosion tests undertaken as part of the materials selection procedure should take this effect into account. 

Common problems like insufficient filling-packing and poor dimensional control are often related to the gate size and design. Similarly, gate location is another important factor. They should be located in areas having heaviest cross-section of the part to assure fill-out and elimination of sink marks. Also their position should not facilitate the residual molded stress formation in the part, knit line formation. 

The relatively poor conductivity of a packed bed makes it difficult to get the heat of regeneration into the bed, either from a jacket or from coils embedded in the packing. This is more easily achieved by preheating the purge stream. Even in the best conditions, it takes time for the temperature of the bed to rise to the required level. Thermal regeneration is normally associated with long cycle times, measured in hours. Such cycles require large beds and, since the adsorption wave occupies only a small part of the bed on-line, the utilisation of the total adsorbent in the unit is low. 

Adequate vitamin A is also required for the health of the surface structures of the human body skin, the lining of the digestive system, lungs, and mouth. These structures, particularly the skin, are an important part of the human defense system against infection. When they are compromised, the human body becomes increasingly susceptible to infection, a profound problem in areas of poor public health resources. This story, and what has been done in response, is beautifully told in Philip Hilts book Rxfor Survival. ... 

Unfortunately, while these disorders can have a pernicious course (Jensen, 1998), the lack of early recognition, traced in part to poor training of front-line providers and to lack of reimbursement for comprehensive assessments (U.S. Public Health Service, 2000), has cre-... 

Paraffins function poorly as a solvent for some organic compounds. This fact can have various consequences. For example, gums, deposits, and fuel degradation products will not be dissolved or held in solution by high-paraffin-content fuels. As a result, gums and degradation products will fall from solution and settle onto fuel system parts such as storage tank bottoms and fuel system lines. The KB value for selected petroleum products is provided in TABLE 5-4. 

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