Lubricants, function

A key limitation to the application of the monolayer as a boundary lubricant is the sensitivity to temperature. Molecules are desorbed from the surfaces as the temperature rises, and the coverage ratio would drop to zero above 200 ° C at which the monolayer becomes completely ineffective. Boundary lubrication functions at high temperature regions rely mainly on chemical reactive hlms. 

One very common beneficial interaction involving an excipient is the interaction between magnesium stearate and the metal of tablet punches and dies, or the equivalent parts on a powder encapsulation machine. Magnesium stearate is an example of a boundary lubricant. As such it has a polar head and a fatty acid tail. It is believed that the polar head of the magnesium stearate is oriented toward the die wall or tablet punch face. In these ways it is able to reduce the ejection force (the force required to eject the tablet from the die after compaction) and prevent sticking to the punch faces. The other boundary lubricants, e.g., calcium stearate and sodium stearyl fumarate, will also function in a similar manner. However, the so-called liquid film lubricants function in a very different manner (19). 

Of these predictions, 5 was pure provocation I didn t believe it at the time, and indeed it is clearly absurd. At the molecular level, lubrication functions by sliding, not rolling. No molecule, certainly not a hollow one, could act as a frictionless undeformed rolling element, and in any case would need a molecularly smooth track on which to do so. The other predictions seemed to me about right for Daedalus challenging, but not obviously beyond belief. 

Scenario Suppose a company that currently manufactures disposable razors and shaving lubricants is developing a new product that combines both shaving and lubricating functions in one. The new design is for a disposable razor that houses shaving gel in a hollow handle. The gel is automatically dispensed through a porous pad just below the blades. Since the product is disposable, the amount of gel in the handle should be matched to the life of the blades. 

The idea was to integrate lubricating functions and surface wetting functions into the same silicone oil, so that efficient transfer to the mold surface is assured at the same time as excellent wetting and therefore release performance. 

The product at this stage is suitable for simple lubricating functions. However, engine lubricants are called on to meet many demands in addition to lubrication, which requires blending and several additives. 

Boundary lubrication describes processes which can occur at surfaces in relative motion to reduce friction and also control wear under conditions where fluid film formation is not possible. Boundary lubrication functions by several mechanisms... 

Before 2001, the components used for specific lubricant functions had remained relatively consistent since the introduction of ashless dispersant technology in the 1960s. However, recently introduced emissions legislation mandates the use of exhaust after-treatment for both gasoline and diesel light vehicles in many parts of the developed world, and this requirement affects component selection for modern formulations. 

The long-chain structure by itself, as exemplified by n-aliphatic hydrocarbons, shows no extreme-pressure lubricant functionality. Evidently the additive action is connected with the carboxylate ester and the sulfide structures. To demonstrate this, Dorinson isolated an ester/ sulfide component from sulfurized methyl undecylenate, identified its structure, synthesized an organosulfide-ester with this structure, and showed that the lubricant additive activity was the same for the fraction separated from sulfurized methyl undecylenate end for the synthetic material. The data, summarized ib Fig. 11-15, were obtained tiy pin-and-disk wear tests with hardened steel rubbing specimens and show the effect of contact pressure on the depth-rate of wear. The significant feature is the change from a low rate of wear, relatively insensitive to increase of pressure in the range 0.276-1.724 GPa (40,000-250,000 Ib/in ), to pressure-sensitive increase of wear rate at 1.724 GPa and higher. 

GC-44-14. [Stepan/PVO] Dipenu-eiythritol ester lubricant, functional fluids for aviation, automotive, and military formulated lubricants arid gas turbine engine oils. 

Earlier tribological measurements (12) make an evaluation possible of the structural influence on the lubrication. At first the stability of the structure versus temperature is important for the lubricant function and the pertinent problem in this case is thermal stability with added glycerol (12). Table I shows the interesting fact that the temperature for the transition to liquid form is increased by the addition of glycerol. 

The mechanism of lubricant function is complex and still not very clear. Briefly speaking, lubricants are able to improve the surface characters of particles (small in size and large in surface area). In detail, there are three main aspects as follows ... 

Fatty amides. Fatty amides possess unique mold release properties. Simple primary fatty amides are used as slip and mold release agents primarily in polyolefins but also in a variety of other polymers. The more complex bis-amides, such as ethylene bis-stearamide, offer mold release as well as internal and external lubricity functions in materials such as PVC and ABS. 

Liquid lubricants are the most widely used. The most common are petroleum oils, synthetic fluids, and animal or vegetable oils. Many other fluids can fulfill a lubrication function under special conditions when the use of oils may be precluded. 

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