Mill-shrinkage

Mechanical properties of PALF-reinforced natural rubber composites were studied in Bhattacharya et al. (1986) in which PALF addition increased hardness, compression set, tear resistance, and Mooney viscosity. However, elongation at break, mill shrinkage, and Mooney scorch time decreased. The use of resorcinol, hexamethylenetetramine, and silica is essential for PALF-rubber adhesion. PALF-reinforced... 

Although more and more zinc sheet and strip are produced in continuous mills, some is stiU produced by rolling slabs cast in open or closed book-type molds made of cast iron (124—127). The casting temperatures are between 440 and 510°C, mold temperatures between 80 and 120°C. The contact surfaces of the mold must be smooth and clean to allow unrestricted shrinkage of the cast slab. Mold lubricant is not necessary, but if used should be held to a minimum. Slabs cast in open molds must be skimmed immediately to remove surface oxide. Rolling slabs are cast 1.87—10 cm thick. 

In accordance with the test specifications, the area of char is that portion which shows definite decomposition or shrinkage, and is black to dark brown in color. However, the extent of the charred area is not always clearly distinguishable and this leads to variable reporting of the same charred area. The Class F fire test has been very useful in mill control work, permitting quick evaluation of mill surface coatings. 

As an alternative the test may be carried out in the laboratory scalemilling machine described in B.S. 1955 1953 (Fig. 11.11). The excess liquor is removed from the specimen, after determination of relaxation shrinkage, by passing the fabric through the rubber-covered rollers of a hand wringer, or in a hydroextractor, until the liquor retained is 55 to 60 per cent of the dry weight of the sample. The load is then wetted with 40 g of freshly prepared 5 per cent solution of sodium oleate. The sample is subsequently milled under the specified conditions and afterwards rinsed and measured under water in a tray. 

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