Rubber calendaring

Mortality associated with acrylonitrile exposure was evaluated as part of a study of 15 643 male workers in a rubber plant in the United States (Akron, Ohio) (Delzell Monson, 1982). Included in the analysis were 327 workers who were employed for at least two years in the plant between 1 January 1940 and 1 July 1971, and who had worked in two departments where acrylonitrile was used, i.e., 81 worked only in the nitrile rubber manufacturing operation where exposures to 1,3-butadiene (see this volume), styrene (lARC, 1994a) and vinylpyridine also occurred and 218 only in the department where the latex was coagulated and dried. [No information on levels of exposure to acrylonitrile was provided ] Mortality among these workers was assessed through 1 July 1978 and compared with age- and calendar-time-specific rates for white men in the United States. SMRs were 0.8 ( = 74 95% CI, 0.7-1.0) for all causes of death, 1.2 ( = 22 95% CI, 0.8-1.9) for all cancers combined, 1.5 ( = 9 95% CI, 0.7-2.9) for lung cancer, 4.0 ( = 2 95% CI, 0.5-14.5) for urinary bladder cancer and 2.3 ( = 4 95% CI, 0.6-5.8) for cancers of the lymphatic and haematopoietic system. SMRs for lung cancer by duration of employment were [1.0] (4 observed, 3.8 expected) [95% CI, 0.3-2.7] for < 5 years, and [3.3] (5 observed, 1.5 expected) [95% CI, 1.1-7.8] for 5-14 years. No case was observed with duration > 15 years. 

The compounded rubber stock will be further processed for use. The process could be injection or transfer molding into a hot mold where it is cured. Tire curing bladders are made in this fashion. 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 or body plies for tires. The actual construction of the final product can be quite complex. For example, a tire contains many different rubber components some of which are cord or fabric reinforced. All of... 

An impactor can crush the muscle tissues or any part of the human anatomy. Sometimes two rotating objects can cause crushing of body parts when they are moving toward each other. Common examples include meshing gears, belts running over pulleys, cables on drums, chains on sprockets, rollers on manual type washing machines, and rolls on rubber mills or paper calendars. 

Unimofl. [Bayer Miles] Hithalaies plasticizers for PVC, calendaring, extrusion, iig. molding, VC copolymers, PVAc, surf, coadi adhesives, rubber, NC ethyl cellulose, CAB, acrylic surf, coatings, all resins, pdymediactylate, robbw. 

When rubber is deformed during processing operations such as extrusion or calendaring, its inherent elasticity will cause some subsequent recovery. A fundamental material constant characterizing this tendency is, defined in Eqs. (6.12) and (6.14). Elastic recovery is also reflected in die swell, D, defined as the ratio of the flnal and initial dimensions perpendicular to the flow. Die swell is governed by the normal force, although predictions of D for an arbitrary deformation are not possible. However, for steady-state flow there are approximate relations between D and the first (primary) normal force (Tanner, 1970),... 

Coran, 1978). During this test, fully mixed but unvulcanized rubber is contained in a heated cavity. Imbedded in the rubber is a rotating disc. Viscosity is continuously measured (by the torque required to keep the rotor rotating at a constant rate) as a function of time. The temperature is selected to be characteristic of rather severe processing (extrusion, calendaring, etc.). 

The importance of scorch control cannot be overemphasized. Present-day tire plants could not compete without good control of scorch resistance or processing safety as it is commonly called. Such safety is necessary in order to rapidly process rubber mixes at high temperatures (through extrusion, calendaring, etc.) into preforms for molding (e.g., tire components). 

Processing the fabrics and steel cord and coating them with rubber at the calendaring operation. 

Among Ihe most commercially prevalent of these alloys is the PVC-NBR blends, the properties of which approach those of thermoplastic elastomers. Since nitiile elastomers are well established in conventional elastomer applications such as hoses, belts, and calendared goods, these alloys are found in many of the same fabricated products. NBR s are available in a variety of molecular weights, gel levels, comonomer rahos, and in physical forms ranging from powders to crumb rubber to slabs or bales of rubber. Alloys of these polymers are commonly found in automotive dashboard skins, wire and cable compounds, water and fuel hoses, and oil resistant boots and outerwear, among others (83). 

FIGURE 23 (a) Applying rubber to fabrics, (b) Profiling by means of a four-roll engraving calendar. 

Calendaring is the forming operation in which the rubber compound is sheeted or spread evenly onto fabric. The calendar is a heavy-duty machine equipped with three or more chrome-plated steel rolls that revolve in opposite directions (Fig. 23). The rolls are heated with steam or circulated water the gearing allows the rollers to operate at variable speeds like the mill rolls. Fabric or wire is passed through the calendar rolls, and compound is applied above and below to fully cover the material. 

The amount of compound deposited onto a fabric or steel cord is determined by the distance between rollers and is monitored by Beta Gauges. Each cord is insulated on all sides with rubber. The finished treatment or calendared steel cord sheet is cut to length and angle for tire building. Key compound requirements in calendaring operations are minimum shrinkage, optimum tack... 

The first mixer was an annular container with a spiked rotor for rubber compounding (Hancock 1823). The calendar/two-roll mill was patented by Chaffe in 1836 and manufactured by Farrel Co. A counterrotating twin-shaft internal mixer... 

Hard rubber Rubber Made by mixing natural rubber, rehydrated precipitated silica, and sulfur. This is then extraded and calendared, vulcanized under water, and dried. Finer pore diameter (0.2 pm average), relatively lower electrical resistance, excellent oxidation resistance, retards antimony transfer... 

Strips or dollies of EPDM rubber compound of maintained viscosity can be fed to the first roll nip of a 3 bowl calendar. The thickness of the sheeting is adjusted by operating the motorised roll nip adjustment device fitted on the machine. 

The term process aid is a general description for any material that will improve one or more aspects of the processing behaviour of rubber. These materials generally improve the flow behaviour, providing smooth surface finish to calendared or extruded products. Typical process aids include the following material types ... 

Low sieve residues are important for all but the most undemanding of rubber applications. Coarse impurities may result in die blockage on extrusion, pinholes in calendared sheet and abrasive wear to processing equipment generally. In application they may act as failure sites in tension or on flexing, may cause failure electrically in cables, and cause leakage of gas or fluid through membranes. 

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