Elasticity spring strength

The press temperature influences the possible press time and therefore the capacity of the production line. The minimal press time has to guarantee that the bond strength of the still hot board can withstand the internal steam pressure as well as the elastic spring back of the board when the press opens or when the board leaves the continuous press. 

Fig. 5.9 (Chapter 5) depicts in its entirety the force or pressure diagram of a typical cycle of high-pressure agglomeration as a function of time. The effect of the two phenomena that are responsible for most problems associated with this technology, expansion of compressed air and/or elastic spring back, are shown to occur after having reached and take some time. The more important changes caused by these phenomena, however, are an increase in volume and porosity (Fig. 5.9) and the potential lowering of the product s structural integrity. In the best case, they will (only) lead to reduced strength, which may be corrected by a suitable post-treatment (e.g., coating.

The impact strength of certain plastics allows their assembly by stretching as click-and-spring work, clamping, snap-fit, etc. To make this task easier, the assembly angle must be sh low, generally lower than 30°, and the strain must be much lower than the elastic limit. 

Because of their particle shape and nature, cellulose and other plant based or organic drugs and pharmaceutical excipients often exhibit elastic properties. For that reason, as mentioned several times in this book (see, for example. Chapter 5 and Section 10.2), after fast compaction densified products may experience spring-back and loose structural integrity, strength, and/or quality as defined by a multitude of descriptions. To overcome possible problems, the rate of densification must be lowered to potentially unacceptable (technically and/or monetary) levels to allow conversion of temporary elastic alteration in shape and volume into permanent plastic deformation. 

The bulk modulus of rubber, which depends on the strength of the van der Waals forces between the molecules, is 2 GPa. Therefore, the compressive modulus of a rubber layer increases by a factor of a thousand as the shape factor increases from 0.2 (Fig. 4.3). The responses are not shown for S < 0.2 such tall, thin rubber blocks would buckle elastically (Appendix C, Section C. 1.4), rather than deforming uniformly. When laminated rubber springs are designed, Eqs (4.5) and (4.7) allow the independent manipulation of the shear and compressive stiffness. The physical size of the bearing will be determined by factors such as the load bearing ability of the abutting concrete material, or a limit on the allowable rubber shear strain to 7 < 0.5 and the compressive strain e < -0.1. 

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