How do they extract kernels from sunflower seeds in mass production?
By using a dehuller machine. See:
http://www.youtube.com/watch?v=-hegzzj9Rzk
or
http://www.buhlergroup.com/global/en/products/dehuller-dgba.htm

How does a dehuller work? I don't know, but it seems that Google does:


  The most popular decorticator for sunflower is proposed by the Bühler
  Cie. It consists in a rotating blade that propels the seeds by
  centrifuge force against a wall. It functions on one impact. It is
  designed for partial removal of hulls because due to its principle, it
  is not able to carry out a good dehulling without increasing the force
  of the impact. The kernel oil content is so high in sunflower that
  under the violence of he chock, some oil can be transferred to the
  hulls and is lost. Moreover, increasing the rotating speed of such
  dehuller drives to increase the production of fines that are difficult
  to separates from hulls. Another mono-chock kind of dehuller is
  air-jet impact where the propelling of the seeds is done by a strong
  current of air. Multi-chocks dehullers like the Ripple mill improve
  the dehulling quality because they carry out several impacts on the
  achene with milder violence and enable en enhanced separation of hulls
  without generating an excess of fines.


See: http://www.creol.fr/CTMSite/creol/us/travaux/img/dehulling_3.pdf

See also: http://www.buhlergroup.com/northamerica/downloads/DGBA_Sunflower_Dehuller.pdf for some schematics of the inside of the machine and some insights about the way it works.