Ground stopper

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One solid and two hollow stoppers made of glass ( from left to right ) with 14.5 mm and 29 mm
Ground stopper made of plastic

A ground - glass stopper is a glass stopper ground in the shape of a truncated cone , the outer surface of which is roughened to ensure a better hold and a more tight seal. It is used to close glass devices and vessels such as volumetric flasks , round flasks or laboratory bottles . The ground stopper forms with its ground inner part - the core - the counterpart to the ground outer part - the sleeve - of the vessel. Both parts together form a glass-on-glass closure. This type of closure is u. A. with standing or storage vessels in the chemical sector, often with liquid or crystalline and especially for aggressive substances that attack or dissolve other lid shapes. By vacuum grease which can tightness of the closure are improved. Ground-joint connections or stoppers are not suitable for strong alkalis , as these attack the glass surface.

As a rule, conical ground joints and associated plugs correspond to a general device standard . One then speaks of a normal cut or standard cut (abbreviated NS ). Standard sections have a defined pitch of 1:10. If a vessel or device with a standard ground joint is damaged, the upper part can be “blown” onto a new vessel by a glass blower or glass apparatus builder , thus saving the need to buy a new device.

Designs

Ground glass stoppers come in two main designs, solid stoppers and hollow stoppers.

Solid stoppers are made from a glass rod that is heated and molded into a glass blank by compression molding, which already contains the raw core and the handle of the stopper in one piece. In a further work step, the actual standard cut is created on the core of the plug by grinding.

Hollow stoppers are available with a pointed bottom or flat bottom, they are made from tubular glass, which is brought into the viscous state by heating and then manually blown into a stopper shape by a glass blower. Hollow plugs are characterized by their significantly lower weight, but are much more complex and therefore more expensive to manufacture. Hollow plugs also form the handle and core of the ground stopper. As with the solid plug, the core receives its standard cut in the grinding shop.

Conical ground joint plugs are also available made of polypropylene (PP) with sealing rings up to size NS 29/32 and sizes NS 34/35, NS 45/40 and NS 60/46 made of PE-LD . They are autoclavable (121 ° C). Also made of polytetrafluoroethylene (PTFE), solid with sealing rings. They are temperature-resistant up to 270 ° C and are available in the standard joint sizes NS 10/19, 14/23, 19/26, 24/29, 29/32 and 34/35.

Plug sizes according to DIN 12254 are:

  • NS 7/16, 10/19, 12/21, 14/23, 19/26, 24/29, 29/32
  • NS 34/35 and NS 45/40 (not according to DIN)

Individual evidence

  1. ↑ a b c Entry on Schliffe. In: Römpp Online . Georg Thieme Verlag, accessed on July 19, 2011.
  2. ↑ Martin Bultmann: Basics of the drug form theory: a guide to the lecture and practical course. 2nd edition 2003, ISBN 978-3-8330-0794-1 , p. 25.