14
The actual water content is best measured at
the same position as where the caliper was
measured.
Water from the felt conditioning system can
have an influence. Therefore try to measure
right after the nip and certainly before the felt
conditioning.
If there is much re-wetting of the felt at the press nip exit, the
measurement shows more water than there was in the mid-nip,
therefore wrongly indicating felt wear.
Hence it’s important to know which kind of press roll is used (blind
drilled rolls cause more re-wetting than grooved or suction rolls)
Blind drilled press roll
Grooved press roll
Low speed machines like board machines usually have considerable
re-wetting of the felt. This makes wear-calculation extremely
difficult.
Estimation of
current felt weight
(F
current
)
in fast running / nip dewatering machines:
F
current
= (1000 * h - water content) * 1.14 * re-wetting factor
(indicative) re-wetting factor for suction roll at high speed: 1.05
(indicative) re-wetting factor for for tissue felts:
1.16