Curing, rubber belts

The duck is glued in thin layers (plies) with a rubber compound and vulcanized (cured). The number of plies used to make a belt and their quality defines the strength of the belt (e.g. 3 ply x 32 or 3 ply x 34, etc.). 

Rubber blends with cure rate mismatch is a burning issue for elastomer sandwich products. For example, in a conveyor belt composite structure there is always a combination of two to three special purpose rubbers and, depending on the rubber composition, the curatives are different. Hence, those composite rubber formulations need special processing and formulation to avoid a gross dissimilarity in their cure rate. Recent research in this area indicated that the modification of one or more rubbers with the same cure sites would be a possible solution. Thus, chlorosulfonated polyethylene (CSP) rubber was modified in laboratory scale with 10 wt% of 93% active meta-phenylene bismaleimide (BMI) and 0.5 wt% of dimethyl-di-(/ r/-butyl-peroxy) hexane (catalyst). Mixing was carried out in an oil heated Banbury-type mixer at 150-160°C. The addition of a catalyst was very critical. After 2 min high-shear dispersive melt mix-... 

Any method of vulcanising rubber products which proceeds without interruption from start to finish as compared to the method of vulcanising separate batches of products or sections of a product. Continuous vulcanisation processes include the cold curing of proofed cloth, the vulcanisation of belting and flooring, of cables and certain extruded products by either the Liquid Curing Medium, Fluid Bed, Microwave, or Hot Air techniques. 

Steel belts are used to transport rubber profiles through the liquid salt medium in the LCM (liquid cure medium) baths. These belts, either used singly or in multiples are often used in conjunction with chain driven roller systems. Steel belts, in the high temperatures of a LCM medium expand considerably, and the multiple belt system helps to overcome this problem to some degree, by allowing easy adjustment for overall length. The belts used in these systems are customised to the particular equipment and normally can only be sourced from the original equipment manufacturer. 

Another cure system consideration is the compound scorch behavior. Prior to vulcanization, rubber is plastic-like and can be processed into desired shapes such as tires, hoses, belts, or other articles. The time available to accomplish this processing depends laigely on the cure system and is referred to as the scorch time. If a compound cures prematurely during the processing step, it usually becomes useless scrap. Therefore, a key requirement of the vulcanization step is to minimize premature vulcanization or scorch (Fig. 4). 

Since EPDM rubber is costly and the price fluctuates widely, high filler and oil loadings are resorted to, to achieve relatively low cost compounds. But these compounds tend to have poor strength and abrasion resistance. High quality stocks, especially those with peroxide cures, are considerably more expensive than NR, BR or SBR stocks. EPDM is used in belts and hoses meant for conveying hot materials because of its excellent heat resistance. Its excellent chemical resistance makes it a preferred rubber for specialty belts, chemical hoses and pump liners. 

This system involves the use of some form of heating by air or steam in a chamber in a manner such that the vulcanization occurs immediately after the rubber is formed in an extruder or calender. This is a suitable process for extruded profiles and calendered sheets and conveyor belts. Liquid curing method (LCM) is also a continuous process which involves the use of suitable hot liquid baths in which extruded profiles can be passed through and vulcanized continuously. Items can be cured rapidly at temperatures from 200°C to 300°C however the compounds must be suitably designed to prevent porosity as this is a common problem with any extrudate. Suitable materials for curing medium includes bismuth-tin alloys, an eutectic mixture of potassium nitrate and... 

Most of the silicone rubbers used in the food industry are based on polydimethyl vinyl silicone and these materials have very good high- and low-temperature properties. It is their high-temperature resistance that enables them to be used for seals and tubing, for example, in drinks vending machines up to 100 °C. Cold cured silicones are used as release coatings on items such as food transportation belts and for sweet moulds. 

Used for sulfur-cure, mineral-filled rubber applications. Silica-filled tires with lower rolling resistance, longer lasting, heat resistant belts or hoses, and light weight shoe soles are some of the typical uses. 

Typically, the compounded rubber stocks need to be further processed for use. The process could be an injection or transfer molding into a hot mold, where it is cured. Extrusion of the rubber stock is used to make hose or tire treads and sidewalls. Another common process is calendaring, in which a fabric is passed through rolls where rubber is squeezed into the fabric to make fabric-reinforced rubber sheets for roofing membranes, belting or body plies for tires. The actual construction of the final product can be quite complex. For example, a tire contains in excess of six different compounded elastomeric stocks. All the components must be prepared and assembled with high precision so that the final cured product can operate smoothly at high speeds and last over 50,000 mi. 

In each step of vulcanization, the section of the belt to be vulcanized is gripped and stretched hydraulically to minimize or eliminate elongation during use. The difliculties of press cure may, however, be avoided by adopting continuous vulcanization with a Rotocure equipment in which the actual curing operation is carried out between an internally steam heated cylinder and a heated steel band. Rotocure is also useful for the vulcanization of transmission belts and rubber sheeting. 

Uses Post vulcanization stabilizer for sulfur cures of NR, IR, SBR, and NBR used in tire treads, sidewalls, and general industrial prods, incl. belting and inj. molded goods bonding promoter for rubber-based steel adhesion Trade Name Synonyms Duralink HTS [Flexsys http //www.fiexsys.com, Harwick Std. Distrib. http //WWW. harwickstandard. com]... 

Uses Rubber for use in tire inner tubes/liners/curing bladders, pharmaceutical closures, mech. goods, conveyor belts/hosing antivibration mounts food/drug seals adhesives in closure-sealing gaskets for food containers in food-contact articles for repeated use... 

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