Ground zones

Standard Joint Size Number Approximate Diameter at Small End (mm.) Computed Diameter at Large End of Ground Zone (mm.) Approximate Length of Ground Zone (mm.)... 

Size Designation Nominal Diameter OF Ground llEMISPlIEllE Nominal Diameter AT Upper End of Ground Zone Nominal Bore... 

Size designation Approximate diameter at small end (mm) Computed diameter at large end of ground zone (mm) Approximate length of ground zone (mm)... 

Cones are made in three types. The first is closed at the small end of the ground zone and is used for stoppers. The second is open at the small end and is used for general purposes. The small end of the ground zone is extended as a tube in the third type this tube may be cut off at an angle and is known as a drip tip (see Fig. 11.2). 

Sockets are also made in three types, the first two differ only in the diameter of the tube extending beyond the small end of the ground zone. The third type has a short tube, or cup, attached to the large end (Fig. 11.3). 

Cones and sockets should, after cutting, have a length of tube left, not less than the length of the ground zone. The heating should not extend to the ground zone. The finished glassware should be oven-annealed. 

Several factors influence the stability and deformation of improved ground zones and supported structures during and after an earthquake (PHRI 1997 JGS 1998 MitcheU et al. 1998). Some of the more important factors are discussed below. 

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