How to convert 2 or gates (x1 V x2 V x3) to NAND How can I convert a clause of size 3 that is made of 2 OR gates 

example:                 

(x1 OR x2 OR x3 )


to one or more clauses of size 4 made only of NAND gates and not gates? So without parentheses inside the clauses.

examples:      

(x1 NAND x2 NAND x3 NAND x4) 
(not x1 NAND x2 NAND not x3 NAND not x4) AND (x1 NAND x2 NAND x3 NAND x4)


additional notes:
The original question asked is to prove that 4-SATCNF (A CNF expression that can be satisfied, with clauses of size 4 and with NAND gates between the 4 terms.) is NP-Complete by showing the polynomial reduction of 3-SAT &lt;=p 4-SATCNF. I'm stuck at the part where I need to find a function for the reduction. I suppose the function should be something around the form showed above, if not can somebody helped me find the good function? 

Thank You 

Articles that I consulted so far:

3-Sat to 4-sat polynomial conversion: https://www.csie.ntu.edu.tw/~lyuu/complexity/2012/20121106s.pdf

NAND Conversion:
https://en.wikipedia.org/wiki/NAND_logic
(x1 or x2 or x3) = (not x1 NAND not x2 NAND True NAND not x3)