Exposed Drive Chains

Some chain drives are used on mobile equipment where the chain is exposed to the weather and other elements. These drives can only be lubricated manually. Most of these drives use engineering steel chain. Two typical examples are welded steel mill chains used to drive sludge collectors and heavy-duty offset sidebar chains for propel drives on power shovels. 

The chains used in such applications are often packed with extreme pressure grease at the factory. The purpose of this is to provide satisfactory lubrication only for the first few hours of operation. It is difficult to effectively lubricate these chains in service, and in some environments it is impractical. 

For example, these chains are often immersed in mud and water for a long lime without being cleaned or lubricated. Chains will rust rapidly under such conditions. In addition, internal rust and accumulated dirt may clog the chain clearances so that no lubricant can enter, even if it is applied. Joint flexure may also be impaired, resulting in poor sprocket action and reduced chain life. 

Chains used in such applications need to be cleaned and relubricated regularly. This can greatly increase their wear life and it may prevent chain failure from poor sprocket-chain interaction. 

Exposed drives sometimes have to work in abrasive environments. It is always good practice to lubricate these chains. Even though the abrasive mixed with lubricating oil forms a lapping compound, lubrication is recommended because the effects of no lubrication—galling, seizing, and scoring—can destroy the chain faster than abrasive wear. 

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Are all dangerous parts guarded, e.g. exposed gears, chain drives, projecting engine shafts ... 

The sprocket tooth form for engineering steel drive chains is specified in the ASME B29.10 standard. A drawing of the tooth form and the equations for computing the main dimensions are shown in Figure 4-36. It differs from the tooth form for roller chain in that the pitch line clearance and bottom diameter are slightly smaller than the theoretical root diameter. These differences permit the use of a less precisely made tooth form for engineering steel drive chains than the machine-cut tooth form for roller chains. Engineering steel chain drives are often operated in locations where mud, dirt, ore, rock dust, etc. get into the chain. These drives are often exposed to the weather. Pitch line clearance and the undercut bottom diameter both help provide proper chain-sprocket action under such adverse conditions. 

Many chains are also used on exposed drives on agricultural equipment. Food grade oils are sometimes used on these chains to prevent drips from contaminating the soil. 

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Msnual Lubrication. This method is recommended for small horsepower drives with low chain speeds. Open running chains should not be exposed to abrasive dirt. 

We encountered the properties of hydrophilic and hydrophobic molecules in our thoughts about driving forces for formation of three-dimensional protein structures. Specifically, proteins fold in a way that puts most of the hydrophobic amino acid side chains into the molecular interior, where they can enjoy each other s company and avoid the dreaded aqueous environment. At the same time, they fold to get the hydrophilic amino acid side chains onto the molecular surface, where they happily interact with that enviromnent. The same ideas are important for the double-stranded helical structure of DNA. The hydrophobic bases are localized within the double hehx, where they interact with each other, and the strongly hydrophilic sugar and phosphate groups are exposed on the exterior of the double helix to the water environment. Now, we need to understand something more about structural features that control these properties. 

Most (soluble) folded proteins have a hydrophobic core in which side-chain packing stabilises the folded state, and charged or polar side chains are placed on the solvent-exposed surface, where they interact with surrounding water molecules. It is generally accepted that rninirnising the number of hydrophobic side chains exposed to water is the principal driving force behind the folding process. 

A crosslinked polymer exposed to a thermodynamically compatible diluent absorbs solvent molecules. The driving force of the mixing process is mainly entropic. As the volume increases the network chains are deformed and an elastic retractive force develops. The chain deformation causes a decrease in the entropy, because the extended configuration of the chains is less probable. Equilibrium is achieved when these opposing forces are balanced. 

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