Stuffing box
The stuffing box or gland (in Switzerland: package ), formerly stuffing box named because as a sealing material, among others felt was used is a sealing element of mechanical engineering . It seals a rotating shaft or a reciprocating rod from a housing against the acting liquid or vapor pressure , as well as against penetrating dirt or escaping lubricant .
In order to extend the service life, stuffing boxes were traditionally only tightened to the extent that a small amount of leakage occurred. In the case of a seal against water, cooling and lubrication of the seal were achieved at the same time. A small cloud of steam could often be seen on the spindles of the fittings of pipelines for steam and the stuffing boxes "hissed" a little. The stuffing box can also be loosened prior to a movement of the shaft or actuating rod, as a result of which it becomes leaky but has little friction, while it is tightened again after the movement for better sealing. Highly compressed gases are problematic.
A stuffing box consists of the stuffing box packing (the actual seal) and a stuffing box gland (a flange-like sleeve) with which the stuffing box packing is pressed axially by means of screws or springs. In the case of elastic sealing material, the axial compression also results in radial compression of the stuffing box packing on the shaft. The sealing gap can thus be set to a minimum that is adapted to the operating conditions. A small leak cannot be completely ruled out. Due to the large contact area, combined with the high pressure required for a low-leakage seal, stuffing box packings cause a relatively high level of friction.
Stuffing box packings are used as an economical sealing solution in pumps and agitators and as spindle seals in control valves . The former blue and white asbestos have been replaced by modern materials such as aramid, graphite, PTFE and similar. Packs are usually braided by machine with the addition of various lubricants and impregnating agents. Tallow and wax were traditionally used, among other things .
The machine-braided, self-lubricating stuffing box packing was invented by Feodor Burgmann in Dresden in 1884.
Stuffing boxes were also used in piston steam engines , especially in steam locomotives. The passage of the piston rod through the cylinder cover required a vapor-tight seal. The stuffing box rings were initially made mainly on a graphite and asbestos basis , with the spread of the superheated steam engine, later mainly cast iron packing rings were used.
Nowadays, more modern components are usually used for this sealing purpose: the radial shaft sealing ring, colloquially the Simmerring (registered trademark of Freudenberg & Co, Weinheim) or the mechanical seal for pressure seals . However, the newer components cannot be used everywhere.
Since the sealing pressure is pressed from the outside via the gland follower, a large number of suitable materials are available (fiber materials, graphite ...), some of which can also be used at high temperatures and aggressive media, for which the elastomer seals predominantly used today (for example O-rings , radial shaft seals, etc.) are no longer suitable. Another advantage is that by tightening the gland follower, leakages caused by wear of the sealing material can be reduced again.
In limited applications, the old stuffing box technology is still used sensibly. Traditionally, a ship's drive shaft , for example, has been sealed at the bushing through the ship's hull or at the inner end of the stern tube by means of stuffing boxes. The ship's shaft runs in the stern tube . The stuffing box is usually made of rubber or a felt packing and is soaked with grease. The preload of the sealing packing is axially adjustable. It must not be set too tightly in order to reduce the friction of the shaft. The stuffing box is usually refilled with grease once a year. On large ships, the stuffing box is also made of metal.
See also
literature
- Wolfgang Tietze: Handbook Sealing Practice. 3rd edition, Vulkan Verlag GmbH, Essen 2003, ISBN 3-8027-3301-0 .
- Klaus Joachim Soiné: Handbook for water masters. 4th edition, R. Oldenbourg Verlag, Munich Vienna 1998, ISBN 3-486-26392-7 .
- Ralph-Harry Klaer (Ed.): Practical manual for industrial fittings 2003. Vulkan Verlag GmbH, Essen 2003, ISBN 3-8027-2729-0 .
Web links
- fachwissen-dichtungstechnik.de (accessed on January 2, 2017)