Lubrication processes

Lubricants. Process aids or lubricants promote smooth and rapid extmsion and calendering, prevent sticking to extmders or calender roUs, and impart good release properties to molding compounds. In some cases use of lubricants allow slightly lower processing temperatures (see Vinyl polymers). 

Cosmetics. Talc is widely used in baby and body powders, pressed powders, creams, and antiperspirants. Its softness, sHp, inertness (fragrance retention), and relative safety make this one of the oldest and most widely recognized appHcations for talc. Talc is also used in chewing gum as a detackifier and in tableting as a lubricating process aid. 

Extraction (discussed in Chapter 5) uses the selective adsorption of a component in a liquid to separate specific molecules from a stream. In application extraction may be coupled with its cousins, extractive distillation and azeotropic distillation, to improve extraction efficiency. Typical refinery extraction applications involve aromatics recovery (UDEX) and lubricants processing (furfural, NMP). Extractive distillation and azeotropic distillation are rarely employed in a refinery. The only... 

In conclusion, it may be said that a lot of literature has been published that favors the Frye and Horst mechanism of stabilization. Most of this is based on studies done on low-molecular weight model compound for al-lylicchlorines in PVC, i.e., 4-chloro-2-hexene. Although the large contribution of these studies toward understanding the mechanism of stabilization of PVC cannot be denied, the extrapolation of these results to the processes involved in the actual stabilization of the polymer should be done with extreme care. The polymer represents a complex mixture of macromolecules, which in the melt is not only physically a very different system compared to the low-molecular weight model compound, but invariably contains, apart from stabilizers, other additives, such as plasticizers, lubricants, processing aids, etc., that further complicate the situation. The criticism of the Frye and Horst mechanism is also based on solid experimental evidence, and hence, the controversy is still very much alive. 

The effective viscosity predicted with micropolar theory is in very close agreement with that found by experimental results in a previous work. This does not adequately assure that it is the only possible way to explain the traits of thin him lubrication, but it shows the roles the microstructure and microrotation of the particles will play in the lubrication process in the very thin him EHL situation. 

The first step in processing is usually powder mixing in a high speed, intensive mixer. PVC resin, stabilizers, plasticizers, lubricants, processing aids, fillers, and pigments are added to the powder blend for distributive mixing. 

Table V. Effect of Varying Lubricant/Processing Aid in PVC/PTHF Blends a...

Lubricant/Processing Aid phr Notched Izod Impact Strength (ft Ibs/in Notch)... 

Tribochemistry Tribochemistry is the science concerned with the chemical reactions in mineral and synthetic formulations affecting the tribofilm formation on metal surfaces during the boundary lubrication processes. What are the differences in the concept of electron sharing in the liquid processes and on metal surfaces ... 

Chemical compound added to a base oil to improve oil quality as any substance that aids in the lubrication process at the rubbing interface by functionality other than viscosity. Intermolecular energy of attraction between the separate molecules making up a homogeneous liquid or solid. The energy consists of contribution from Lifshitz-van der Waals components in all cases. 

As discussed earlier, lubrication of direct compression formulations is one of the more complex and difficult problems faced by a pharmaceutical scientist. The ideal lubrication operation provides the mildest mixing conditions that guarantee sufficient homogeneity of the lubricant. Magnesium stearate, provided as a finely divided powder, is one of the most widely used lubricants in the pharmaceutical industry. Many formulations are sensitive to the lubrication process when the formulation uses magnesium stearate powder. 

Singer IL (1992) Solid lubrication processes. In Singer IL, Pollock HM (eds) Fundamentals of friction macroscopic and microscopic processes. Kluwer Academic Publishers, London, p 237... 

L. Singer, Solid lubrication processes, in Fundamentals of Friction Macroscopic and Microscopic Processes, Elsevier, Amsterdam, 1992, pp. 237 261. 

Wilson, T.C. (1970) Qd Mist Lubrication Process and Novel Lubricating Qd Composition for Use Therein . US Patent 3,510,425. 

The present chapter deals with frictional behavior when lubricated surfaces rub against each other. In Chapter 7 attention was called to the distinction between viscous loss in a fluid film separating two solid surfaces and the friction of the surfaces rubbing directly against one another. In this chapter we shall discuss the type of lubrication in which the rubbing surfaces that carry the lubricant participate intrinsically in the lubrication process rather than merely as the geometric boundaries of the fluid film. The treatment of lubricated friction here will be mainly descriptive detailed analysis and discussion of theoretical models for lubricated frictional rubbing is reserved for subsequent chapters. 

No single description or definition adequately covers all lubricants or lubrication processes. For example, we have seen that a fluid can function as a lubricant by virtue of its viscosity as a liquid. We have also seen that a monomolecular film of stearic acid deposited on a metal surface acts as a lubricant and dramatically reduces the coefficient of friction. A polymeric substance such as polymethylmethacrylate when dissolved in an oil will increase its viscosity and improve its loadcarrying performance in the hydrodynamic lubrication process. Stearic acid dissolved in a carrier oil can effect a strong reduction in the coefficient of friction for metal rubbed against metal. 

In the discussions of the preceding section the breakdown of lubrication and the onset of scuffing at the critical temperature was accepted as an empirical fact, with little inquiry into the details of how and why temperature should affect the lubrication process. True, given... 

R. M. Matveevsky [56] discussed the influence of temperature on lubricant additive action in terms of whether the additive functions by an adsorption/desorption mechanism or by a chemical reaction mechanism. If the additive is a blend of two components, one of which acts via adsorption and the other by reaction, and if the critical temperature of desorption is lower than the temperature at which the rate of chemical reaction of the other additive will contribute substantially to the lubrication process, then the critical desorption temperature will control lubricant failure. Thus, if the load induces frictional heating at the rubbing interface so that the conjunction temperature exceeds the critical desorption temperature, this will be the critical failure load. But if the surface exposed by desorption of the first additive reacts with the second additive at the temperature prevailing there, the failure load will be raised. Cameron and his co-workers [48, 57] used these concepts, although not as explicitly proposed by Matveevsky, to explain the behavior of multicomponent compounded lubricants containing dibenzyl disulfide and a commercial calcium petroleum sulfonate as the additives. The failure temperature characteristic of the calcium sulfonate as the sole additive was 468 K (195 C), whereas failure with dibenzyl disulfide was observed at 543 K (270 C). With the two-component additive, incipient failure began at ca. 473-493 K, which seems to mark a balance between desorption of the sulfonate and chemical reaction of the disulfide. As the temperature increased above 493 K, the reactivity of the disulfide became more apparent and the coefficient of friction decreased, until at 543 K, the temperature observed for the failure of the disulfide alone, the rubbing pieces scuffed. 

Lubrication by solids is a well-recognized branch of lubrication technology, and the experienced practitioner finds little difficulty with the meaning of this designation when he sees it. But careful scrutiny shows that the distinction between lubrication by solids and other aspects of lubrication is not one of fundamental principles. Instead, the term as it is generally understood is applied to a collection of techniques characterized by one common feature the lubrication process is governed by the presence of a deliberately inserted solid substance in the rubbing interface. 

Source V. E. Arnold, Lubricants Processing Strategies, Paper FL-97-111, presented at the Fuels and Lubes Meeting of the National Petroleum Refiners Association, Houston, Texas, November 6-7, 1997. 

---