External lubrication

Extensional viscosity Extension cord External lubricant External plasticizers Exterol Exter press Exton... 

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. 

Poly(ethylene terephthalate). PET is a crystalline material and hence difficult to plasticize. Additionally, since PET is used as a high strength film and textile fiber, plasticization is not usually required although esters showing plasticizing properties with PVC may be used in small amounts as processing aids and external lubricants. Plasticizers have also been used to aid the injection mol ding of PET, but only at low concentrations. 

The success of the compaction operation depends pardy on the effective utilization and transmission of appHed forces and pardy on the physical properties and condition of the mixture being compressed. Friction at the die surface opposes the transmission of the appHed pressure in this region, results in unequal distribution of forces within the compact, and hence leads to density and strength maldistribution within the agglomerate (70). Lubricants, both external ones appHed to the mold surfaces and internal ones mixed with the powder, are often used to reduce undesirable friction effects (71). For strong compacts, external lubricants are preferable as they do not interfere with the optimum cohesion of clean particulate surfaces. Binder materials maybe used to improve strength and also to act as lubricants. 

Substituted Amide Waxes. The product of fatty acid amidation has unique waxlike properties (13). Probably the most widely produced material is N,1S7-distearylethylenediarnine [110-30-5] which has a melting point of ca 140°C, an acid number of ca 7, and a low melt viscosity. Because of its unusuaHy high melting point and unique functionaHty, it is used in additive quantities to raise the apparent melting point of themoplastic resins and asphalts, as an internal—external lubricant in the compounding of a variety of thermoplastic resins, and as a processing aid for elastomers. 

Laboratory tests and experience during use have demonstrated that the nylons have extremely good abrasion resistance. This may be further improved by addition of external lubricants and by processing under conditions which develop a highly crystalline hard surface e.g. by use of hot injection moulds and by annealing in a non-oxidising fluid at an elevated temperature (150-200°C for nylon 66). 

Alkanesulfonates act as an external lubricant in PVC, polystyrene, and engineering thermoplastics. They have a good release effect and assist flow. Addition is in the concentration range between 0.1 and 2.0 parts per 100 parts resin (phr). Because of their low volatility, alkanesulfonates are also used as a processing aid for high-melting engineering thermoplastics. 

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 external lubricants are metal soaps, paraffin waxes, silicones and fluoroplastics. 

These materials prevent adhesion between chilled rollers in film production or moulds for injection moulding. They behave like external lubricants, and should serve the following requirements ... 

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. 

Like flammable gas compressors, the external lubrication system for large air compressors can present a fire hazard. Oil flow rates above 25 gpm (95 Ipm) and or oil capacity greater than 100 gal (379 I) may require fire protection. 

A study was made of the effects of processing conditions and of blowing and nucleating agents and external lubricants on the apparent density, mechanical properties, linear thermal expansion coefficient and surface roughness of extruded cellular MDPE. Based on the results, recommendations were formulated for the properties of cellular MDPE pipes for the protection of light conducting cables. 16 refs. (Translation of Polimery, Tworzywa Wielkoczasteczkowe, No. 10, 1996, p.580). 

Some of these processing aids are incorporated into the bulk of the material rather than being directly applied to the surface and are known as internal release agents. In the process of migration to the surface they have an inevitable internal lubrication effect. Most internal lubricants also have an external lubricant effect, particularly at higher concentrations because usually some material finds its way to the exterior. 

Lubricants are often employed to facilitate the uniform transmission of forces and reduce undesirable friction effects during compaction. Lubricants may be classified as internal or external types [2]. Internal lubricants are materials which are added to the particulate feed not only to improve its flow properties (flow into the mold or die and rearrangement during compaction) but also to assist in the release of the final agglomerate from the mold or die. Internal lubricants are generally used in quantities of % to 2%. Internal lubricants, especially when used in excess, may interfere with the optimum cohesion of clean surfaces and reduce the strength of the agglomerates produced. External lubricants are materials used to prevent friction and wear at... 

Some fine particle fillers, such as silica gel or chalk, called as antiblocking agents, can also be classified as external lubricants. They make the separation of rolled films easier. 

Solids conveying is carried out in two steps the feed hopper and the back (entrance) portion of the screw. The feed hopper is an inverted cone or pyramid, in which solid pellets or powder flow downward from the force of gravity. If they flow poorly ( arcing or bridging ), the problem may be solved by installing a vibrator or a stirrer ( crammer/feeder ) in the hopper, or by coating the particles with a small amount of a chemical that acts as an external lubricant. ... 

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