Ask A Scientist Materials Science Archive

name         Faye
status       educator
grade        K-3
location     MT

Question -   My students want to know how string is made?
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 The process is similar to making yarn, although usually with a 
tighter  twist.  The fiber, often cotton, is prepared for spinning 
by  cleaning debris out of the fluff, combing it so all the fibers 
are  aligned in parallel order, then spinning small bits at a time into 
a  long thin string.  Most string has at least 3 or 4 plies, made 
by  spinning/twisting together 3 or 4 of the long thin strings 
spun  previously.  Some string actually has the plies braided 
together  to make it stronger.  Plied string can be again plied with 
other  plied string to further strengthen the finished string.
 If you untwist a length of string, you may well find that each of 
the  three or four plies contains several fine, loosely spun, finer 
plies  which have been loosely twisted together.
 Materials used to make string or rope include: cotton, jute, 
hemp,  sisal, linen, various manmade fibers such as nylon and polyester.
  Rope walks were long narrow corridors where a team would twist 
together  long heavy strings to make ropes, such as are needed to secure 
ships at  piers.  One person would hold one end of the bundle being 
twisted  while the other person, standing far away, would twist the 
groups of  ends together.  When the twist is as tight as possible, that 
end  of the bundle is brought to the other end, allowing the rope to 
twist  on itself as it is doubled.  Both ends are secured to hold 
the  twist, and a strong rope has been formed.  When the lengths 
needed  for ship's ropes are involved I presume more than two people 
worked  together as those lengths would be difficult for only two people 
to  control.  For shorter lengths this process can be done by two  people.
  Strength in string or rope depends on several 
characteristics,  including the fiber used, the number of plies, the 
tightness of the  twist, the abrasion resistance of the fiber, which can 
be aided to some  degree by the twist, the thickness of the finished 
string or  rope.  You would not want to tie up an ocean liner with 
kite  string, nor would the rope used on the ship work very well when 
you  want to fly a kite.  Yet both are suitably strong for 
their  intended purpose.  Another consideration in designing the 
strength  of string/rope will be how strong the fiber is when wet, and 
how it is  affected by exposure to sun, heat, cold.
  Strength is not the only thing to consider.  Flexibility and durability 
are also important, as are many other attributes.

Korah A. Erbacher
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