Twin teeth

Tooth dysplasia, twin teeth, or root anomalies (Fig. 13.22) ... 

Healy WB, Ludwig TG. 1968. Barium content of teeth, bone and kidney of twin sheep raised on pastures of differing barium content. Arch Oral Biol 13 559- 563. 

Highly viscous polymeric reactions (e.g., the hydrolytic polyamide reaction) are often carried out in a gear-pump reactor (Tadmore and Klein, 1970). This type of reactor is often difficult to operate because the clearance of the gear teeth is increased by wear caused by flow and the reaction process. For smaller viscosity of the melt, a screw reactor or a twin-screw extruder is often used. Sterbecek et al. (1987) used a twin-screw extruder (i.e., Wemer-Pfleiderer extruder ZSK 83) for studying fast ion-catalyzed polymerization (6-caprolactam) in a melt. They indicated that power input and quality of product in such a reactor depends on the slot width between reactor wall and impeller in a twin screw extruder. They provided an optimum design of a twin-screw reactor for a fast ion-catalyzed polymerization in a melt. 

Fig.13.22. Blocked twin tooth 13. By CT the differentiation of a real twin tooth from two teeth projecting only on each other was possible...

The experimental results foimd in literature for the friction coefficient between gear teeth cannot be predicted from the lubricant traction curves obtained in twin disc machine tests imder full film lubrication regime. 

The numerical results obtained are compared with results extrapolated fi om twin disc machine lubricant traction curves and with results obtained from real gear tests. The correlation between numerical and experimental gear results is quite good, putting into evidence the need to consider mixed film lubrication, surface roughness, lubricant non-Newtonian behaviour and contact temperature in order to predict realistic values of the friction coefficient between gear teeth. 

Figure 3 shows the average friction coefficients between gear teeth measmed in those tests, which are significantly smaller than the ones extrapolated from twin-disk machine traction curves shown in the same figure. That difference is quite significant at high loads. 

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