Classification of Screw Threads – Application Of Screw threads
Classification Of Screw Threads
Screw threads having various applications can be classified as follows
1. According to location
- external screw thread (on bolts etc.)
- internal screw thread (in nuts etc.)
2.According to configuration
- straight (helical) – most common, e.g., bolts, studs etc.
- taper (helical), e.g., in drill chuck
- radial (scroll) as in self centering chuck
3 . According to the direction of the helix
- right hand (common)
- left hand (occasionally)
4. According to form
- vee thread (600 or 550 angle) – most common
- acme thread (290)
- square thread (generally in power screws)
- buttress thread (45o)
- worm thread (290 ~ 400)
- semicircular (groove section) thread being used in recirculating type bolts, screws.
5. According to standard
- BSW (British Standard Whitworth); thread – size is designated by TPI (threads per inch)
- metric thread; thread size is specified by pitch or lead (in mm)
6. According to number of start
- single start – most common
- multi-start (2 to 4)
7. According to spacing of threads
- TPI (no. of threads per inch), e.g. 12 TPI
- pitch (or lead) – distance between two successive threads (or length of travel of the nut for one rotation of the screw), in mm
8. According to compactness or fineness of threads
- general threads (with usually wide thread spacing), pipe threads (more densed desired)
- fine threads (generally for leak proof)
9. According to segmentation
- full threads (common)
- half turns as in half nuts
- sector thread – e.g., in the jaws of lathe chucks.
Read More: Lead Screw Mechanism -types , Advantages
General Applications Of Screw Threads
The general applications of various objects having screw threads are :
• fastening : screws, nut-bolts and studs having screw threads are used for temporarily fixing one part on to another part
• joining : e.g., co-axial joining of rods, tubes etc. by external and internal screw threads at their ends or separate adapters
• clamping : strongly holding an object by a threaded rod, e.g., in c-clamps, vices, tailstock on lathe bed etc.
• controlled linear movement : e.g., travel of slides (tailstock barrel, compound slide, cross slide etc.) and work tables in milling machine, shaping machine, cnc machine tools and so on.
• transmission of motion and power : e.g., lead screws of machine tools
• converting rotary motion to translation : rotation of the screw causing linear travel of the nut, which have wide use in machine tool kinematic systems
• position control in instruments : e.g., screws enabling precision movement of the work table in microscopes etc.
• precision measurement of length : e.g., the threaded spindle of micrometers and so on.
• acting as worm for obtaining slow rotation of gear or worm wheel
• exerting heavy force : e.g., mechanical presses
• conveying and squeezing materials : e.g., in screw conveyor, injection moulding machine, screw pump etc.
• controlled automatic feeding in mass production assembly etc.
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