Table 1. Levels of Each Production Factor Studied.

production factor	low level	center level	high level
PTFE wt %	20	35	50
rolling thickness setting	4 (thinner setting)		2 (thicker setting)
time stage 1 (min)	5	32.5	60
pressure stage 1 (Ton)	0.5	10.25	20
temperature stage 1 (°C)	80	140	200
time stage 2 (min)	5	32.5	60
pressure stage 2 (Ton)	0.5	10.25	20
temperature stage 2 (°C)	280	307.5	335
time stage 3 (min)	5	32.5	60
pressure stage 3 (Ton)	1	13	25
temperature stage 3 (°C)	300	317.5	335