Soft Plastic Forming

The water content for soft plastic forming methods ranges from 20 to 30 wt%, which produces complete filling of pores by water and can result in some additional free water that separates the particles in the structure [22,31]. Soft plastic forming techniques include high-volume mechanical techniques such as jiggering, jollying, and ram pressing

Soft Plastic Forming

and low-volume hand techniques such as throwing and wheel turning [27]. The imposed pressure range for soft plastic forming is 0.1-0.75 MPa (15-110 psi) [26]. The soft plastic forming techniques of jiggering and jollying are used to form objects that have a center of radial symmetry conducive to forming by rotation, such as dinner plates, cups, mugs, and flowerpots. During jiggering, the plastic mass is placed on a rotating form that determines the profile of the product and a tool is brought down to cut away excess material from the back (Fig. 11a) [31]. Jollying is similar to jiggering, except that in this case the tool determines the inner profile of the product and the form serves as a physical support [26]. Typically, objects such as dinner plates are formed by jiggering, while objects such as teacups and mugs are formed by jollying. Similarly, ram pressing employs two forms that are pressed together, but without rotating tooling [26]. Ram pressing can be used to form a variety of shapes including dinner plates (Fig. 11b).