Orifice viscometers

Orifice. Orifice viscometers, also called efflux or cup viscometers, are commonly used to measure and control flow properties in the manufacture, processing, and appHcation of inks, paints, adhesives, and lubricating oils. Their design answered the need for simple, easy-to-operate viscometers in areas where precision and accuracy are not particularly important. In these situations knowledge of a tme viscosity is uimecessary, and the efflux time of a fixed volume of Hquid is a sufficient indication of the fluidity of the material. Examples of orifice viscometers include the Ford, Zahn, and Shell cups used for paints and inks and the Saybolt Universal and Furol instmments used for oils (Table 5). 

Orifice viscometers should not be used for setting product specifications, for which better precision is required. Because they are designed for Newtonian and near-Newtonian fluids, they should not be used with thixotropic or highly shear-thinning materials such fluids should be characterized by using multispeed rotational viscometers. 

Some orifice viscometers, such as the Shell dip cup and the European ISO cup, which resembles a Eord cup with a capillary, have long capillaries. These cups need smaller kinetic energy corrections and give better precision than the corresponding short-capiHary viscometers. However, they are stiU not precision instmments, and should be used only for control purposes. 

Table 5. Some Orifice Viscometers Used in Industry...

Oriented polystyrene film, 23 408-409 Orifice mixing columns, 16 712 Orifice plates, 11 657-659 26 680 Orifice viscometers, 21 729-730 ORIGEN code, 19 673 Orimulsion, 3 769... 

It Is unfortunate that the description of his viscometer, and the emphasis on laminar flow appeared too late to Influence Redwood, Eagler and Saybolt who designed orifice viscometers In the mid 1880 s. (Ref. 4 Chapter 2). 

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