Buttress thread
The buttress thread form, also known as the breech-lock thread form,[1] refers to two different thread profiles. One is a type of leadscrew and the other is a type of hydraulic sealing thread form. The leadscrew type is often used in machinery and the sealing type is often used in oil fields.
Contents |
[edit] Buttress thread in machinery
In machinery, the buttress thread form is designed to handle extremely high axial thrust in one direction. The load-bearing thread face is perpendicular to the screw axis.[2] or at a slight slant (usually no greater than 7°)[3] The other face is slanted at 45°. The resulting thread form has the same low friction properties as a square thread form but at about twice the shear strength due to the long thread base. This thread form also is easy to machine on a thread milling machine, unlike the difficult to machine square thread form. It can also compensate for nut wear using a split nut, much like the Acme thread form.[4]
Buttress threads have often been used in the construction of artillery, particularly with the screw-type breechblock.[1] They are also often used in vises, because great force is only required in one direction.[4]
[edit] Types
The image gallery below shows some of the types of buttress threads.
-
Simple buttress thread form[5]
-
The ANSI 45°/7° buttress thread form[6]
-
The British 45°/7° buttress thread form[7]
-
The 45°/5° buttress thread form[5]
-
The 33°/3° German "Sägegewinde" (saw tooth) buttress thread form[5]
[edit] Mechanics
[edit] Buttress thread in oil field tubing
In oil field tubing, buttress thread is a pipe thread form designed to provide a tight hydraulic seal. The thread form is similar to that of Acme thread[8][9] the force is transmitted almost parallel to the axis and thread is about the same strength as standard v threads.
[edit] References
- ^ a b http://books.google.com/books?id=gYZIAAAAMAAJ&pg=PA141
- ^ Barnwell, p. 163.
- ^ US patent 5127784, David Eslinger, "Fatigue-resistant buttress thread", issued 1992-07-07
- ^ a b Bhandari, p. 204.
- ^ a b c Oberg, p.1817
- ^ Oberg, pp. 1819–1820.
- ^ Timings, p. 127.
- ^ US patent 6893057, M. Edward Evans, "Threaded pipe connection", issued 2005-05-17 Figure 6.
- ^ Oil field glossary entry for buttress thread
[edit] Bibliography
- Barnwell, George W. (1941), The new encyclopedia of machine shop practice, Wm. H. Wise & Company.
- Bhandari, V B (2007), Design of Machine Elements, Tata McGraw-Hill, ISBN 9780070611412, http://books.google.com/?id=f5Eit2FZe_cC.
- Oberg, Erik; Jones, Franklin D.; Horton, Holbrook L.; Ryffel, Henry H. (2000), Machinery's Handbook (26 th. ed.), New York: Industrial Press Inc., ISBN 0-8311-2635-3.
- Timings, Roger Leslie (2005), Newnes Mechanical Engineer's Pocket Book (3rd. ed.), Newnes, ISBN 9780750665087, http://books.google.com/?id=IZdDk1cMlLcC.
