Presented at the Pulp and Paper Association Meeting

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ELIMINATION OF STRUCTURAL RESONANCE

TO ALLOW PAPER MACHINE SPEED UP


Presented at the Pulp and Paper Association Meeting


Montreal, Canada




BACKGROUND


Irving Paper, Inc., located in Saint John,
N.B., is a privately owned company. There
are two pape
r machines


330” which
produce both newsprint and specialty news.
No. 2 P.M. was built in 1972 and the original
design speed for the dryer section was 3000
FPM. The machine has run fairly
consistently at 3150 FPM; however, slight
frame and soleplate mo
vement was visible at
this speed.

SCOPE

In the fall of 1991 excessive vibration at 1 x
RPM of the dryer cans was being
experienced in the 4
th

Dryer Section. Speed
of #2 Paper Machine was contemplated in the
range of 3400 FPM from the current 3150
FPM. Ba
lancing of the dryers was
recommended; however the test data
indicated a structural resonance in the
support base of the paper machine. The 4
th

Dryer Section was modeled on computer
(FEA) and various modifications were tested
in order to move the structur
al resonance
above 4000 FPM.

DISCUSSION OF ACTIONS AND
RESULTS

Vibration Readings taken in the fall of 1991

model of the support base was created within
a Finite Element Modeling (FEA) program to
extrapolate the probably characteristics of the
resonance. The results of these tests are
shown in Figure 7.



Figure 7


FEA Extrapolated Resonance
Response Curve

PROBLEM RESOLUTION

Step 1
:

Develop a computer model that
machines the existing structure (Finite
Element Analysis).

Transducers were mounted on

the support
columns and dryer frame. Transducer
locations were measured and documented
(figure #8) for reference within the FEA
computer model.

confirmed what could be seen visually. The
4
th

Dryer Section was moving above
comfortable levels. The 4
th

dryer section is
gear driven on the back
side and the general
concern was of a machine catastrophe caused
by gear failure then roll and dryer felt failure.


Figure 1


4
TH

Dryer Section #2 P.M.

Vibration readi
ngs of the 4th Dryer Section
taken in preparation for paper machine
speedup, compared to a two year old paper
machine of similar design (figure 1, 2 and 3)
show a difference in magnitude of twenty
times higher.




Figure 8
-

Transducer

Location on Frame
Structure

Vibration Measurements were taken at
different operating speeds and an operating
structural modal was developed. An FEA
model was then developed and adjustment
were performed until the FEA model matched
the indicated operatin
g structural modal
responses recorded in the field (figure #9).


Figure 9
-

Frame Movement During
Operation

Step 2
: Try different changes to the structure
to bring the

structural resonance above 4000
FPM.

Different designs were proposed to change
the resonance of the structure. The designs
ranged from a full wall to cross bracing
(figure #10).

Figure 2


Vibration 4
TH

Dryer Section


Figure 3


Comparison Vibration on Two
Year Old Machine

The recommended solution, due to the
dominance of one x dryer RPM vibration,
was to balance all ten dryers in the 4
th

Dryer
Section. Two methods for balancing the
dryers were investigated:


A
)



The Conventional Method



Drive
each dryer can independently similar
to the regular roll balancing method.

B)



Dynamic Balancing by the Impact
Method

-

This is a two
-
phase
approach to Dryer balancing
developed by Pretech.

Phase I



conduct a baseline vibration audit of
the dryer sections to determine the
operational integrity of the machine.
Acquire a balance profile of each
dryer and determine its residual
unbalance level when compared to the
remaining dryer cans. The dr
yers are
then scheduled for balancing based on
their synchronous magnitudes and
dynamic phase responses when
compared to the neighboring cans.
Phase II



Impact testing of the
scheduled dryer cans is conducted to
determine the structural dynamic
influence

coefficients between dryer
can, bearing housing and structural
support base. This is accomplished
using a calibrated force hammer. The

Figure 10


Frame Movement according to
Structural Modifications.

Due to the amount of paper, which drops into
the basement, rope runs and access, height
required for forklifts a modified “A” frame
design was decided on. The “A” frame using
computer modeling is rated for 3400 FPM.

Step 3
: Modify the Structure in the field.

The “A” frame structure was installed in the
field on September 7, 1992 (figure #11). The
structure has a temperature paint insulation to
minimize soleplate deflection.


Figure 11


“A” Frame Structure
Reinforcing

The installment of the “A” Frame Structure
required a preliminary 8 Hour Shut followed
by a 48 Hour Shut one month later.

The long
excitation spectrum and response are
measured and analyzed
simultaneously. The final correction
weights can now be ca
lculated for
each dryer.


In comparing the two methods for
cost/dryer along with the amount of
downtime required was investigated
(figure 4).


Figure 4


Comparison of
Balancing Costs

The maximum time available for shutdown
on #2 P.M. was 72 hours and a restriction
was put on the amount of funds available.
Dynamic Balancing by the Impact Method
was chosen as the most cost
-
effective course
of actions.

PROBLEM IDENTIFICAT
ION

Readings following completion of Phase I
and Phase II of Dynamic Balancing by the
Impact Method distinctly showed a structural
resonance problem. Phase I testing
established each dryer unbalance magnitude
and phase. Figure 5 shows a plot of the
phase

components obtained.

Shut was during a previously planned Labor
Day Shut and did not cause any unplanned
Paper Machine downtime.


Figure 12


Reduction in Vibration
According to
Speed

CONCLUSION

The installation of the “A” frame to
structurally modify #2 Paper Machine 4
th

Dryer Section, has successfully tuned the
structure for all speeds tested up to 3400 FPM
(figure #12).

Over the past year vibration readings taken on
the solepla
te of the 4
th

Dryer Section has not
increased indicating the structure is stable.
Additionally, the dryer balance responses
have decreased with the increased structural
stiffness. Nevertheless, if paper machine
speed up is again contemplated further work

is necessary to balance certain dryer cans and
remove or replace those felt rolls which are
sensitive to roll wipe at the new desired
speed.

Dryer balancing using the Impact Method
results in not only identifying the residual
unbalance condition of the dr
yer cans, but
also affords a general overall view of the

Figure 5
-

Phase Angle of Forcing
Function

As can be seen in Figure 5, the phase
relationship between the 4
th

section dryer
cans indicated that t
he position of the
unbalance vector for both the bottom and top
dryers were al within the same quadrant.
Although this condition could exist,
statistically it is very improbable. Further
analysis confirmed that the dryers were
responding to a structural
resonance in the
paper machine support base.


Figure 6
-

Response of Structure to
Varying Paper Machine Speeds

Machine speed tests were conducted between
2800 FPM to 34
00 FPM to determine the
structural resonance of the 4
th

dryer section.
The data indicated a non
-
linear response of
the basement concrete columns and soleplate
as graphed in Figure 6; thus confirming the
presence of a structural resonance within the
structural condition of the subject paper
machine. While conventional methods will
reduce the unbalance vector, machine speed
up may still not be possible. Depending upon
the machine’s structural r
esponse and
resonance characteristics, the primary
machine forcing function at dryer rotation
speed may be amplified and result in
unacceptable levels of vibration throughout
the machine support and frame structures.

IMPORTANT CONSIDERATION

Resonance is a
problem quite often seen with
independent support structures and should be
kept in mind when looking at high 1 x RPM
vibration readings in dryer section. Dryer
unbalance may be the forcing function but
structural resonance is the amplifier.

Structural sta
bility and acceptable dryer
balance condition are only the beginning
process in any machine speed up. Other
factors such as available fourdrinier
production levels, felt roll stability and
winder speeds must be considered;
nevertheless a stable paper mach
ine
foundation and frame structure is a must.

NOTE: This paper was previously
presented in

Chatham at the Canadian
Machinery Vibration (CMVA) meeting,
March 1993.

REFERENCES

1.



Journal: Guha


Majumdar, S. and



Woury, M. “Dynamic Analysis o
f



Paper Machine Foundations,”



Tappi, Journal, 69
-
73;August, 1992.

2.

Paper: Borhaug, J. Ph.D.,
“Methodology of Dynamic Balancing
by Impact Method,” Pretech, 1
-
4,
January, 1991.

suppor
t base. A very elementary

3.

Report: Morin, Eric, “PM2 Condition
Test,” Valmet,

Figure 4.1.13, January,
1992.

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