Internal lubrication

The various lubricants formulated into PVC to improve the processing can also enhance the performance of the stabilizet. In pigmented apphcations, calcium soaps, eg, calcium stearate, ate commonly used as internal lubricants to promote PVC fusion and reduce melt viscosity. This additive is also a powerfiil costabilizer for the alkyl tin mercaptide stabilizers at use levels of 0.2 to 0.7 phr. Calcium stearate can significantly improve the eady color and increase the long-term stabiUty at low levels however, as the concentration increases, significant yellowing begins to occur. 

By far the most common lead salt used for PVC stabilization is tribasic lead sulfate. It can be found either alone or combined with another lead salt in almost every lead-stabilized PVC formulation. Many of the combinations are actually coprecipitated hybrid products, ie, basic lead sulfophthalates. Dibasic lead stearate and lead stearate are generally used as costabilizers combined with other primary lead salts, particularly in rigid PVC formulations where they contribute lubrication properties dibasic lead stearate provides internal lubrication and lead stearate is a good external lubricant. Basic lead carbonate is slowly being replaced by tribasic lead sulfate in most appHcations due the relatively low heat stabiHty of the carbonate salt which releases CO2 at about 180°C during PVC processing. 

During some mol ding and extmsion operations, knit line failures, incomplete mold fill, die drag, and excessive heat buildup, ie, scorch, are problems. Many of these problems are reduced or eliminated by the addition of internal lubricants such as low mol wt polyethylene or Vanfre AP-2 Special, a product of R. T. Vanderbilt. 

Environment Internal Lubricating oii, 300°F (150 C) External Treated cooling water, 176 F (80°C)... 

It has been seen that internal lubricants are essentially low molecular weight flow promoters which, unlike plasticisers, have little effect on the... 

The Nash vacuum pump or compressor has only one moving part—a balanced rotor that runs without any internal lubrication. Such simplicity is possible because all functions of mechanical pistons or vanes are performed by a rotating band of liquid compressant. 

The lobes do not touch each other or the casing during operation. The separation is a few thousandths of a inch. There is no internal lubrication thus, the units can operate in a dry gas service. 

Because these machines require internal lubrication of the sliding-vane surface, no extreme effort is made to arrange special bearing and shaft seals, except that a gas seal of the conventional mechanical design is usually used to prevent gas from escaping to the outside or to prevent air inleakage in the case of vacuum service. For hazardous or... 

In most hydraulic components, the hydraulic fluid provides internal lubrication. Pump elements and other wear parts slide against each other on a film of fluid. Figure 40.14. 

By treating individually each of the above elements, the following occurs. The limit of the PV factor for each material or the internally lubricated materials for the constant wear of bearing is usually available from the supplier of the plastic. Neither the pressure nor the velocity should exceed a value of 1000. Thus, if the PV limit of acetal is 3000, the PV factor could be 1000 ft/min (300 m/min)... 

Additive, slip An additive modifier that acts as an internal lubricant which exudes to the surface of the plastic during and immediately after processing providing the necessary lubricity to reduce or eliminate coefficient of friction in molded parts, film, etc. products. 

Saturated hydrocarbons (waxes), fatty acids, metal soaps, fatty acid amides and esters (primarily Cig-Cis) act as internal lubricants, fluoro elastomers as external lubricants. Many other polymer additives, e.g. antistatic agents, antifogs, antioxidants, UV stabilisers, etc., act as lubricants in the barrel of the extruder once they are in the liquid form. 

Lubricants can be classified as internal or external lubricants. Internal lubricants should be partially miscible with the polymer at processing temperatures (i.e., behave similar to a plasticiser), but phase separate at ordinary temperatures. Whereas plasticisers are completely miscible with the bulk polymer, lubricants have a limited solubility. 

Examples of internal lubricants are fatty acid derivatives, e.g., stearates (for PVC), waxes and polyethylene oligomers containing polar groups obtained by partial oxidation. Not all polymers require lubricants LDPE, nylon and PET are self-lubricating. 

International Isocyanate Institute, 25 480 International Jamaica Agreement, 12 695 International kilogram, 26 239 International Lubricant Standardization and Approval Committee (ILSAC), 15 228-230... 

Figure 14.16 Mechanism by which poly(ether ester)s function as crystallization promoters. Such materials internally lubricate and plasticize the PET molecular chains, thus allowing reptation (i.e. chain folding) to occur more quickly...

Lubricants may be categorized by their chemical nature (Table 14.3), or may be classified according to their action into two basic groups external lubricants and internal lubricants. 

The effect of plasticizers has been explained by the lubricity, gel, and free volume theories. The lubricity theory states that the plasticizer acts as an internal lubricant and permits the... 

This generally depends on the type and amount of accelerator. The higher the accelerator the faster is the scorch. It can be made slow by the addition of retarders. Increasing softeners often slows down the onset of cure while at the same time improving internal lubrication in the compound. The higher the un-saturation in the rubber the faster is the scorch. 

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