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DISCLAIMER
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
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d * ( I .
REPORT NO. RN-DR-0131
ENDURANCE TESTING OF TURBINE POWER CONTROL VALVE ACTUATOR BENDIX MODEL
NO. NT-D1, SN 17
NERVA PROGRAM CONTRACT SNP-1
N U C L E A R R O C K E T O P E R A T I O N S
N O T I C E This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express o r implied, or assumes any legal liability or responsibility for the accuracy, com- pleteness o r usefulness o f any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.
A E R O J E T - G E N E R A L C O R P O R A T I O N A S U B S I D I A R Y O F T H E G E N E R A L T I R E & R U B B E R C O M P A N Y
a
3 3 J J
a 13 3 13 J
REPORT NO. RN-DR-0131
ENDURANCE TESTING OF TURBINE POWER CONTROL VALVE ACTUATOR ]BENDIX MODEL
NO. NT-D1, SN 17
W. P . Harris
n
\ C. M. Rice Program Manager Nuclear Rocket Operations
iii
CONTENTS
a D
I. I n t r o d u c t i o n
11. Summary
111. Technical Discussion
A. Test Conditions
B. Endurance Test Setup
C. Sequence of Operat ions
D. Procedures and Resu l t s
APPENDIX
Bendix F a i l u r e Analysis of t h e Nutator Transmission of Turbine Power Control Valve Actuator Model NT-D1, Ser ia l No. 1 7
Page
1
1
3
3
3
12
13
TABLES
Table
1 Summary of Opera t iona l T i m e on Actuator No. 1 7 P r i o r t o t h e 4 Endurance T es t s I
Figure
1 2
3
4
5
6
7
8
9
FIGURES
Ac tua to r Test F i x t u r e Drawing and Photos
Schematic of T e s t Console
Schematic of Actuator Servoamplif ier
Block Diagram of Endurance T e s t Setup
In l and Torque Motor Command S i g n a l Inpu t
Amplif ier Gain Tests Before and A f t e r Temperature- Torque Cycling
Gain and Phase Lag vs Frequency Before TPCV Temperature-Torque Cycling T e s t
Gain and Phase Lag vs Frequency A f t e r TPCV Temperature-Torque Cycling Test
Amplitude Ra t ios Before and A f t e r Temperature- Torque Cycling T e s t
Page
5-7
a 9
10
11
1 4
16
17
18
\
i v
FIGURES (CONT. 1 Figure
li u
u
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11
1 2
1 3
14
15
16
17
18
19
20
21
22
23
Phase Angle Before and A f t e r Temperature-Torque Cycling Test
Time-Temperature P r o f i l e , TPCV Actuator Temperature-Torque Cycling Test, 1 4 June 1967
Beginning of Temperature-Torque Cycling T e s t
Low-Temperature P o r t i o n of Temperature-Torque Cycling T e s t
High-Temperature P o r t i o n of Temperature-Torque Cycling Test
End of Temperature-Torque Cycling T e s t
Actuator Output S h a f t A f t e r Temperature-Torque Cycling T e s t
Transmission Gear Teeth A f t e r Temperature-Torque Test, High Torque (400-in.-lb) Side
Transmission Gear Teeth A f t e r Temperature-Torque Test , Low Torque (80-in.-lb) S ide
Closeup of Gear Teeth A f t e r Temperature-Torque Test
Gear Motor Body Showing P o s t t e s t Sc ra t ch
Po ten t iome te r P o s t t e s t Schematic and Resu l t s (Terminals 1, 2 , and 3)
Potent iometer P o s t t e s t Schematic and Resu l t s (Terminals 1 6 , 1 7 , and 18)
P o s t t e s t V i e w s of Inpu t S h a f t Flange and Corresponding Temperature Samples
Page
19
22
23
24
25
26
28
30
31
32
33
35
36
37
R V
Li I. I N T R O D U C T I O N
R
The d a t a i n t h i s r e p o r t were obta ined from t h e Endurance Test p o r t i o n
of t h e q u a l i f i c a t i o n tes t program, which w a s performed on t h e Bendix
Model N T - D 1 Turbine Power Control Valve Actua tor , Se r i a l No. 1 7 and completed
i n t h e NRO Cont ro ls Laboratory on 1 5 June 1967.
The o b j e c t i v e s of t h e a c t u a t o r l i f e tes t are t o determine t h e s e r v i c e
l i f e of t h e a c t u a t o r under f u n c t i o n a l and environmental cond i t ions , w i t h t h e
except ion of r a d i a t i o n , t h a t s imula t e those expected dur ing a c t u a l engine
ope ra t ing cond i t ions and t o determine t h e r a t e of d e t e r i o r a t i o n of t h e
a c t u a t o r ' s performance i n t h e s e environments (Reference RN-S-0425).
11. SUMMARY
P r i o r t o t h i s t e s t , t h e tes t a c t u a t o r had been sub jec t ed t o 60.4 hours
of usage under va r ious cond i t ions . The endurance tes t cons i s t ed of s i n u s o i d a l
cyc l ing of t h e a c t u a t o r a t 0 .3 cps a g a i n s t a r e s i s t i v e to rque whose peak ampli-
tudes were 400 lb- in . i n t h e clockwise (opening) d i r e c t i o n , and 80 lb - in . i n
t h e counterclockwise d i r e c t i o n ( looking i n t o t h e a c t u a t o r ou tput s h a f t end) . \
During t h e torque c y c l i n g , t h e a c t u a t o r mounting f l ange temperature w a s reduced
dur ing a 1-hr pe r iod t o -230°F; i nc reased t o +600"F dur ing a 2 t o 2-112 h r
pe r iod , t hen w a s cooled t o 400"F, a t which p o i n t t h e torque cyc l ing w a s s topped .
L a t e r in format ion revea led t h a t t h e ou tpu t s h a f t had i n a d v e r t e n t l y reached
temperatures o f approximately 1000°F (1460"R). T o t a l t i m e of endurance t e s t
cyc le , i nc lud ing t h e t i m e t o r e t u r n t o ambient temperature and t o complete t h e
performance r e fe rence tes t w a s 8 h r . T o t a l t i m e of o p e r a t i o n f o r t h i s t e s t
a c t u a t o r i s 68.4 h r ; NDC51A, t h e c r i t e r i o n t o which t h i s model TPCV a c t u a t o r
w a s p rocured , e s t a b l i s h e d t h e ope ra t ing l i f e a t 20 h r .
P r e t e s t and p o s t t e s t d a t a , as w e l l as d a t a recorded dur ing t h e t e s t ,
were n o t s i g n i f i c a n t l y d i f f e r e n t . I n view of t h i s f a c t and t h e e x t e n s i v e
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p r i o r usage, t h e a c t u a t o r is considered t o have e x h i b i t e d s u f f i c i e n t endurance
f o r a p p l i c a t i o n i n t h e technology engine program.
Following t h e endurance test and during a test s t a n d to rque c a l i b r a t i o n
t e s t , i t was discovered t h a t t h e a c t u a t o r e x h i b i t e d l i m i t cyc l ing when s tepped
t o a c e r t a i n p o s i t i o n .
prone t o l i m i t cyc l ing a t i n t e r v a l s o f 1.3" of a c t u a t o r p o s i t i o n , w h i l e opera-
t i o n between t h e s e p o s i t i o n s appeared normal. The l i m i t cyc l ing w a s a t a
frequency of 25 cps and a t a 0.3" peak-to-peak amplitude.
of t h e a c t u a t o r revealed t r ansmiss ion gea r wear and rough-running bea r ings .
This bea r ing and gea r wear may have r e s u l t e d from temperatures a t t h e i n p u t
s h a f t t h a t were h ighe r t han o r i g i n a l l y planned. D i s c o l o r a t i o n of t h e s h a f t
and seal w a s evidence of t h e high temperature. However, inadequacies i n t h e
t r ansmiss ion gea r ing design appear t o be major and p o s s i b l y more s i g n i f i c a n t
c o n t r i b u t i n g f a c t o r s .
Fu r the r i n v e s t i g a t i o n r evea led t h a t t h e a c t u a t o r w a s
Subsequent disassembly
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111. TECHNICAL DISCUSSION
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A . TEST CONDITIONS
The test item was a Turbine Power Control Valve (TPCV) Actuator,
Bendix Model No. NT-D1, Bendix Part No* 2775030, Serial No. 17, (referred to
as the actuator in this report)-
Prior to the endurance test described in this report, the assembly
had been subjected to a total of 60.4 hr of actuation under various conditions
and for various purposes. Table 1 presents a summary of the data. 6
Included in the preceding value of 60.4 hr is a 4-hr endurance
test stand calibration period, during which the actuator was sinusoidally
cycled at 0 , 1 cps against an opposing torque of approximately - +80 lb-in. addition, during the last 1-1/2 hr of cycling, the actuator temperature
was reduced to -155°F before being returned to room temperature.
In
B. ENDURANCE TEST SETUP
Figure 1 shows the test fixture assembly. Schematics of the test
console, actuator servoamplifier, and a block diagram o f the test setup are
shown in Figures 2, 3 , and 4 . The actuator output shaft is coupled to a shaft
that passes through a dummy valve body to an Inland torque motor. The Inland
torque motor is capable of providing a resistive torque that can be modified to simulate actual TPCV resistive torque while the actuator is being sub jec t ed
to the simulated environments of temperature, pressure, and flow. Figure 5 shows a schematic of the Inland torque motor electrical system
The whole Inland torque mctor is enclosed in a pressure vessel and
is sealed to the dummy TPCV body on the side opposite from the actuator mount-
ing flange to preclude the need for a high-pressure rotating seal interface
between the two.
3 Page 3
iJ B
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TABLE. 1
SUMMARY OF OPERATIONAL TIME ON ACTUATOR NO. 1 7 PRIOR TO THE ENDURANCE TESTS
Ac t i v i t y
Assembly, Run-In, and Performance Tests
Acceptance Tests
Vib ra t ion Tests
Hot TPCV Valve Tes t ing
Humidity Test
Drop Test
Computer Work (Analog Engine Simulat ion)
Miscel laneous P res su re , Torque Tests
Endurance T e s t Stand C a l i b r a t i o n
T o t a l Tes t ing P r i o r t o Endurance T e s t
Hours
1 . 5
2.5
13.3
20.7
1 . 5
0 .3
7.5
9 . 1
4.0
60.4
*Unless o therwise noted a l l tests w e r e performed i n t h e NRO Cont ro ls Laboratory a t t h e Aero je t Nimbus f a c i l i t y
Comments
Performed a t Bendix -L
Performed i n "HI' area
D Page 4
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B I L 3 w I
0
v)
i
b t W
i!
I
I rl
2 7 M
d
F
m 0
U
0
c
PI a ki I
rl
Q a
I
rl
a 7
I MWLL 01 ACTUATOR 1
I I I I I ! ! ! !
III ' ! / i 1
M.NDIY MODIF PLWSCU CON *21137.93 OP
r3
m
I- a FtOATING _ _ _ SIGNALS (METER -1 ouvitr ON J M f JIS MUST NOT BE GROUNOLD)
Figure 2 - Schematic of T e s t Console
8
Figure 3 - Schematic of Actuator Servoamplifier
INLAND TORQUE MOTOR
\ MECHANICAL COUPLING
FUNCTION TPCV ACTUATOR GENERATOR
POWER IN (117V) POWER IN'
INPUT I-- - SIGNAL
J a
POSITION POSITION FEEDBACK \ \
INLAND POWER AMPLIFIER TPCV SERVO AMPLIFIER
Figure 4 - Block Diagram of Endurance Tes t Setup
Q
+15V- > 1 u -15V-
rs
B R
P
c.. 5 K \
I I
LOAD STAND POTENTIOMETER 1 1 . 5 K
24K -
24 K 1 .OK
1 . 5 K
- -
INLAND POWER AMPLIFIER
INLAND TORQUE MOTOR
-
Figure 5 - In l and Torque Motor Command S i g n a l Inpu t
8 11
The dummy TPCV body is f i t t e d w i t h a c o l l a r i n t h e v i c i n i t y of t h e
a c t u a t o r mounting f l a n g e , which i s s u i t a b l e f o r r e t a i n i n g l i q u i d n i t r o g e n f o r
l o w temperature , and wi th a wrap-around f l a n g e h e a t i n g element j u s t below t h e
LN c o l l a r f o r high-temperature cond i t ion ing . 2
During t h e temperature torque c y c l i n g tests, continuous r eco rd ings
were made of t h e a c t u a t o r command signal and feedback v o l t a g e s , of t h e In l and
to rque motor command s i g n a l v o l t a g e , and of t h e e i g h t thermocouples t h a t were
p o s i t i o n e d as fol lows: two were on t h e a c t u a t o r b a s e and one each was on t h e
a c t u a t o r gea r motor, a c t u a t o r po ten t iome te r base , In l and to rque motor b a s e ,
In l and torque motor top, h e a t exchanger, and helium gas i n l e t f i t t i n g . An
a d d i t i o n a l thermocouple w a s used as a high-temperature c o n t r o l l e r i n p u t signal.
I n a d d i t i o n , t h e a c t u a t o r i n l e t p r e s s u r e , t h e dummy TPCV body p r e s s u r e , and t h e
to rque motor enc losu re p r e s s u r e were cont inuously observed.
The test system e lec t r ica l s e t u p i s shown i n t h e schematic diagram
F igure 2.
C. SEQUENCE OF OPERATIONS
Following t h e i n s t a l l a t i o n of t h e a c t u a t o r i n t h e to rque motor
s t a n d , t e s t i n g w a s performed as fol lows:
1.
2.
3.
4. 5.
Amplif ier Gain T e s t
Performance Reference T e s t
a. S tep Response T e s t
b . Frequency Response T e s t
c. Threshold T e s t
Temperature Torque Cycling T e s t
Performance Reference T e s t (Repeat (2) above)
Amplif ier Gain Test
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D. PROCEDURES AND RESULTS
1. Amplif ier Gain Test
a. Procedure
With t h e a c t u a t o r i n s t a l l e d i n t o t h e test s t and b u t w i th
t h e s h a f t s p l i n e coupl ing disconnected (i.e., no l o a d ) , and no gaseous H e supply
t o t h e gear motor, a m p l i f i e r ou tpu t c u r r e n t w a s measured f o r v a r i o u s known
i n p u t vo l t ages .
b. Resu l t s
A curve of a m p l i f i e r g a i n i n m i l l i a m p s / m i l l i v o l t b e f o r e
and a f t e r t h e temperature-torque cyc l ing test is shown i n F igu re 6 .
i n d i c a t e t h a t t h e g a i n i s v i r t u a l l y l i n e a r i n t h e range t e s t e d , and no change
i n g a i n occurred du r ing t h e temperature to rque c y c l i n g test.
The curves
2. S t ep Response T e s t
a. Procedure
With t h e u n i t i n s t a l l e d as noted i n S e c t i o n 1II.D.l.a bu t
w i t h a c t u a t o r helium supply p r e s s u r e a t 215 p s i a , t h e a c t u a t o r w a s p o s i t i o n e d
t o 45" nominal (5 v o l t s on t h e r e c o r d e r command trace).
f u n c t i o n g e n e r a t o r , a 0.33 cps - + 1' squa re wave w a s superimposed on t h e nominal
p o s i t i o n s i g n a l .
By m e a n s of t h e
b. R e s u l t s
The fo l lowing d a t a show t h e response v a l u e s b e f o r e and
a f t e r t h e temperature to rque c y c l i n g test:
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3 1
330
2 00
100
0
100
2 00
3 00 0 BEFORE LIFE TEST
AFTER LIFE TEST I
-200 I
-1 00 0 + l o o . +2
0 UTPU TI MILL IA M PS
Figure 6 - Amplif ier Gain Tests Before and A f t e r Temperature- Torque Cycling
3 14
R
13 13
9
Before A f t e r
R i s e t i m e , s e c 0.025 0.015
Overshoot, % 16 .O 19 .o S e t t l i n g t i m e , sec 0.088 0.19
3. Frequency Response Test
a. Procedure
With t h e a c t u a t o r i n s t a l l e d as ind ica t ed i n
Sec t ion I I I .D.2 .a and by t h e use of a func t ion gene ra to r , a - 4- 1" s i n e wave w a s
superimposed on t h e nominal p o s i t i o n s i g n a l a t f r equenc ie s of .01, 0 .1 , 0.5,
0.8, 1, 2, 4 , 6 , 8 , 10 , 1 2 , 1 6 , 20, 25, and 30 cps . A Weston, Boonshaft , and
Fuchs Trans fe r Funct ion Analyzer, Model No. DA-410AY S/N 6001, w a s used i n t h e
tes t t o provide a d i g i t a l readout of t h e phase ang le and ampli tude r a t i o , from
which Bode p l o t s were obta ined .
b. Resu l t s
Figures 7 and 8 are p l o t s of amplitude and phase angle-
vs-frequency, r e s p e c t i v e l y , r e s u l t i n g from t h e tests made be fo re and a f t e r t h e
temperature torque cyc l ing tes t . Figure 9 i s a p l o t of t h e ampli tude r a t i o s
b e f o r e and a f t e r , and F igu re10 shows both phase l a g s f o r comparative purposes .
13 The be fo re and a f t e r f i g u r e s show t h a t t h e d i f f e r e n c e s
i n ga in and phase p l o t s are n o t s i g n i f i c a n t and can be a t t r i b u t e d t o normal
system n o n l i n e a r i t i e s and accuracy of measurements; i . e . , t h e s e d a t a i n d i c a t e d
no apprec iab le change i n performance r e s u l t i n g from t h e test.
The crossover frequency (where t h e phase l a g i s 90") i s
20.5 and 21.8 cps f o r t h e b e f o r e and a f t e r t e s t i n g , r e s p e c t i v e l y . The spec i -
f i c a t i o n r e q u i r e s t h a t the crossover frequency w i l l be g r e a t e r than 8 cps.
I
Page 15
FREQUENCY, Hz
F i g u r e 7 - Gain and Phase Lag v s Frequency Before TPCV Temperature-Torque Cycl ing Tes t
n -0
P
5
4
3
2
1
0
-1
-2 .1 1.0 10
FREQUENCY, HZ
Figure 8 - Gain and Phase Lag vs Frequency A f t e r TPCV Temperature-Torque Cycling T e s t
O0
5 0'
0 oo
5 0'
0 oo
100
c3
4 w v)
FREQUENCY, HZ
Figure 9 - Amplitude R a t i o s Before and A f t e r Temperature- Torque Cycl ing Tes t
FREQUENCY, HZ
Figure 10 - Phase Angle B e f o r e and A f t e r Temperature-Torque Cycl ing Test
3
s J 7 i
a 3 1
4. Threshold Test
a. Procedure
The i n i t i a l test cond i t ions were i d e n t i c a l t o t h o s e of
Sec t ion III.D.3.a, and t h e sine-wave frequency w a s 0 .1 cps . The amplitude of
t h e ' s i n e wave w a s i nc reased then decreased as r equ i r ed t o i n d i c a t e t h e pres-
ence o f , t hen t h e l a c k of response t o t h e command u n t i l t h e th re sho ld of t h e
response w a s determined.
b. Resu l t s
The th re sho ld be fo re and a f t e r t h e temperature torque-
cyc l ing tes t w a s - + 0.075'.
5. Temperature Torque Cycling Test
a. Procedure
3
3 3 a 3
The test u n i t ( s t i l l mounted on t h e s t a n d ) was connected
t o t h e test s t a n d torque motor by means of t h e s p l i n e d coupling.
t r i ca l p o r t i o n of t h e test s e t u p w a s i n accordance w i t h F igu res 2, 3 , 4 , and 5.
The elec-
With t h e test specimen e l e c t r i c a l l y ene rg ized and t h e
command po ten t iome te r s set at a nominal p o s i t i o n of 45" (5 v o l t s ) , a p r e s s u r e
of 215 p s i a w a s app l i ed t o t h e a c t u a t o r i n l e t .
w a s t hen inc reased t o 100 p s i w i t h a continuous slow b l e e d o f f through t h e hand
ven t valve (Figure 1).
The test s t a n d helium p r e s s u r e
The test s t a n d I n l a n d to rque motor command po ten t iome te r
w a s ene rg ized and a d j u s t e d t o n u l l relative t o t h e test s t a n d feedback
potent iometer . Then t h e to rque motor w a s energized.
3 Page 20
2 3 s a 13 J 3 I
3 s
a
a
3 1 a a s
Again, by means of t h e f u n c t i o n g e n e r a t o r , a 0.3 cps s ine
wave w a s superimposed onto the 45" command p o s i t i o n s i g n a l w i th s u f f i c i e n t
amplitude t o gene ra t e - + 240 lb- in . of t o rque a t t h e peak, (by d r i v i n g t h e test
s t a n d torque motor o f f i t s s e t p o i n t ) .
signal w a s then ad jus t ed s o t h a t t h e peak torque i n t h e TPCV opening d i r e c t i o n
w a s 400 lb-in. wh i l e t h e peak w a s 80 lb-in. i n t h e c l o s i n g d i r e c t i o n . This
mode of torque c y c l i n g w a s continued throughout t h e 5-hour d u r a t i o n of t h e
test , w h i l e t h e a c t u a t o r i n t e r f a c e f l a n g e temperature w a s f i r s t cooled t o
The tes t specimen nominal command
I -265"F, .then hea ted t o +600°F i n accordance w i t h t h e temperature-time p r o f i l e
shown i n Figure 11. Also as shown i n Figure 10 t h e ou tpu t s h a f t dynamic seal
p r e s s u r e w a s set a t 100 p s i a i n i t i a l l y , r a i s e d t o 200 p s i a during t h e warm up
pe r iod , t hen t o 300 p s i a during t h e h e a t soak pe r iod , and f i n a l l y reduced t o
atmosphere, a t which p o i n t h e a t i n g was terminated.
c. Resu l t s
During t h e temperature to rque c y c l i n g test , no changes
i n a c t u a t o r performance were ev iden t as i n d i c a t e d by t h e v a l u e s of a c t u a t o r
c u r r e n t and feedback v o l t a g e , t h e In l and torque motor preamp v o l t a g e i n p u t ,
and feedback s i g n a l s . F igu res 12, 13, 1 4 , and 15 show a c t u a l traces of t h e
i n d i c a t e d parameters taken (1) a t t h e beginning of t h e tes t , (2) du r ing t h e
l o w temperature phase, (3) during t h e h igh temperature phase, and (4) a t t h e
end of t h e test.
As a l r eady i n d i c a t e d , according t o t h e r e s u l t s of t h e
b e f o r e and a f t e r performance r e f e r e n c e tests, appa ren t ly no s i g n i f i c a n t changes
i n a c t u a t o r performance occurred as a r e s u l t of t h e test . Bode p l o t s of t h e
frequency d a t a f o r both t h e b e f o r e and a f t e r performance r e f e r e n c e tests are
shown i n F igu res 7 through10 f o r purposes of comparison as i n d i c a t e d i n L Sec t ion I11 .D. 3.b.
Page 21
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TIME, HOURS
F i g u r e 11 - Time-Temperature P r o f i l e , TPCV A c t u a t o r Temperature-Torque Cyc l ing T e s t , 1 4 June 1967
3
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3
3 1
3
\ ,ZERO TORQUE
Figure 1 2 - Beginning of Temperature Torque Cycling T e s t
8
D 2 3
3 3
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Figure 13 - Low-Temperature P o r t i o n of Temperature-Torque Cycling T e s t
24
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c3 Figure 1 4 - High-Temperature P o r t i o n of Temperature-Torque
Cycling T e s t
D 25
ZERO TORQUE
Figure 15 - End of Temperature-Torque Cycling
ia 2 6
3
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id
a
13
Following t h e endurance test and du r ing a subsequent
t o rque c a l i b r a t i o n tes t , a l i m i t cyc l ing of t h e a c t u a t o r w a s encountered a t
one s p e c i f i c a c t u a t o r p o s i t i o n ( i n t h e v i c i n i t y of t h e 45' set p o i n t used du r ing
t h e test) .
b e made t o l i m i t c y c l e a t o t h e r p o s i t i o n s as w e l l .
t h e a c t u a t o r w a s prone t o l i m i t cyc l ing a t approximately 1.3" i n t e r v a l s of
a c t u a t o r p o s i t i o n throughout i t s e n t i r e 90' o p e r a t i n g range, a t a frequency
and amplitude of approximately 25 cps and 0.3" peak-to-peak, r e s p e c t i v e l y .
(Note a l s o t h a t from t h e r e s u l t s of t h e a m p l i f i e r g a i n tes t , t h e a c t u a t o r s e r v o
a m p l i f i e r ga in had no t changed du r ing t h e test) .
This cond i t ion prompted a sea rch t o determine i f t h e a c t u a t o r could
The sea rch r evea led t h a t
I n view of t h e preceding circumstances, i t was concluded
t h a t some change may have occurred w i t h i n t h e a c t u a t o r du r ing ( o r a f t e r ) t h e
temperature to rque cyc l ing test , and an i n v e s t i g a t i o n of t h e i r r e g u l a r per-
formance w a s made.
Examination of t h e a c t u a t o r when i t w a s removed from t h e
endurance test s t a n d r evea led t h a t d i s c o l o r a t i o n w a s v i s i b l e on t h e a c t u a t o r
ou tpu t s h a f t and t h e a c t u a t o r mounting f l a n g e (Figure 1 6 ) .
s h a f t coupl ing appeared t o have been sub jec t ed t o severe h e a t i n g .
Also t h e ou tpu t
Subsequent disassembly of t h e a c t u a t o r r evea led t h e
fol lowing:
1. D i s c o l o r a t i o n of t h e ou tpu t s h a f t had p rogres sed t o
t h e i n s i d e f a c e of t h e s h a f t , l e a v i n g t h a t area a gold c o l o r .
2. The a c t u a t o r b e a r i n g s w e r e somewhat rough - - running, L ,' p a r t i c u l a r l y those a t t h e a c t u a t o r ou tpu t end.
a Page 27
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3. The a c t u a t o r t r ansmiss ion gear t e e t h appeared t o
have been f r e t t e d o r g a l l e d , a cond i t ion t h a t w a s most ev iden t a t o r n e a r t h e
ends of t h e t e e t h . I n a d d i t i o n , some of t h e t e e t h appeared t o have been
shaved down t h e f a c e , w i th :he shaving ( i n each case) depos i t ed n e a r t h e
r o o t of t h e t o o t h (Figures 17 , 18, and 19) .
t o b e t h e most severe on t h e d r iven gear . The cond i t ion was more severe on
t h e s i d e r e s i s t i n g t h e 400 lb-in. torque load , which w a s app l i ed during t h e
temperature to rque c y c l i n g tes t .
This shaving c o n d i t i o n appeared
4 . Manual r o t a t i o n of t h e gea r motor r equ i r ed an
i r r e g u l a r a p p l i c a t i o n of torque (with r e s p e c t t o p o s i t i o n ) .
measurement of torque provided t h e fol lowing d a t a :
Subsequent
a. Running torque; 18 t o 25 in.-grams, clockwise; 20 t o 30 in.-grams, counterclockwise.
b . Breakaway torque: 29 in.-grams, clockwise; 32 in.-grams, counterclockwise (maximum).
5. On disassembly of t h e g e a r motor, t h e f a c e of t h e
gea r t e e t h had some d i s c o n t i n u i t y of t h e molybdenum d i s u l f i d e coa t ing .
t h i s c o n d i t i o n w a s only v i s i b l e under h igh magn i f i ca t ion , and probably had no
adverse e f f e c t on gea r motor ope ra t ion .
However,
6 . The gea r motor body had a s m a l l groove running
around t h e i n l e t s i d e of one of t h e d r i v i n g gea r cavities.
p a r t i c l e had been lodged between t h e t i p of a too th and t h e body dur ing a
p o r t i o n of t h e g e a r ' s r o t a t i o n (Figure 20)
Apparently a
4
7. A test of t h e two po ten t iome te r s w a s conducted t o
determine i f they had been s u b j e c t t o adve r se e f f e c t s du r ing t h e temperature
to rque c y c l i n g test.
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Page 29
a
n
Figure 1 7 - Transmission Gear Teeth A f t e r Temperature-Torque Test, High Torque (400-in.-lb) S ide
30
a
Figure 18 - Transmission Gear Teeth After Temperature-Torque Test, Low Torque (80-in.-lb) Side
, 31
n
D Figure 1 9 - Closeup of Gear Teeth A f t e r Temperature-Torque T e s t
32
A
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Figure 20 - Gear Motor Body Showing P o s t t e s t Scra tch
33
The test cons i s t ed of a s t anda rd l i n e a r i t y check I
desc r ibed schemat i ca l ly i n Figures 21 and 2 2 . -. L
The r e s u l t s of t h e s e tests are a l s o shown i n t h e s e
f i g u r e s . The d a t a are t y p i c a l f o r po ten t iome te r s of t h i s t ype and are w i t h i n
s p e c i f i c a t i o n l i m i t s .
6 . P o s t t e s t Evaluat ion
a. Test Temperature
As a l r eady i n d i c a t e d , due t o t h e degree of d i s c o l o r a t i o n
of t h e a c t u a t o r i n p u t s h a f t , compared w i t h t h a t of t h e i n p u t f l a n g e (which w a s
instrumented) , i t was suspected t h a t t h e s h a f t reached h i g h e r temperatures
during t h e endurance test than those recorded a t t h e f lange. To make an
approximate de t e rmina t ion of t h e s h a f t temperature, a series of Incone l samples
were s u b j e c t e d t o 2-hour helium atmosphere soaks, a t temperatures ranging from
600°F t o 1500'F i n increments of 100'. The helium w a s t aken d i r e c t l y from t h e
supply system used f o r t h e endurance tes t , D i s c o l o r a t i o n of t h e samples
r e s u l t e d i n a c o l o r spectrum (Figure 2 3 ) and v a r i o u s p a r t s of t h e a c t u a t o r
were compared w i t h t h i s spectrum. The comparison i n d i c a t e d t h a t t h e i n p u t
s h a f t temperature reached approximately 900° t o lOOO'F ( conse rva t ive ly ) . Figure 2 3 shows areas on t h e ou tpu t s h a f t t o g e t h e r w i th t h e corresponding
L,
/
sample ,
t h e loss of o r c
b. Transmission Gear Tooth Wear
Because of t h e uneven t r ansmiss ion gea r t o o t h wear, and
lange i n gea r t o o t h s u r f a c e t h a t w a s d e t e c t e d fol lowing t h e
endurance tes t , t h e t r ansmiss ion design w a s reviewed as a p o s s i b l e c a u s a l
f a c t o r .
Page 3 4
N T - D l POT
- Y AXIS
Figure 21. Potentiometer Posttest Schematic and Results I (~erminals 1, 2, and 3)
Figure 22. Potentiometer Posttest Schematic and Results (~erminals 16, 17, and 18)
B P
P
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I, -- .-
700°F - NO COLOR CHANGE
SLIGHT GOLD 8r30"F - TINGE SHOVING
900°F - DEFINITE GOLD COLOR WITH TRACES OF PURPLE
1000°F -DEEP BLUE AND PURPLE
1100°F - PREDOMINANTLY BLUE
1200°F - BLUE TO GREEN
1400°F - LIGHT GREEN TO BLACK
1500°F - DEEPER GREEN- BLACK
P 0 ST-T E ST V I E W SH 0 W I N G MA TC H I N G PORT I ON 'JF OUTPUT S H A F T F L A N G E EXPOSURE OF INCONEL SPECIMENS IN
COMPARISON OF COLOR CHANGES WITH
A HELIUM ATMOSPHERE ,
1' ' d
CLOSE UP OF 900'!F COLOR SAMPLE AND CORRESPONDING OUTPUT S H A F T COLOR CORRESPONDING OUTPUT S H A F T COLOR
CLOSE UP OF.1OOO'F COLOR SAMPLE AND
0 FiKurt 2 3 - I ' o s t t e s t V i e w s of Input S h a f t Flange and
Corrempondlng Temperature Samples
37
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Although i t was apparent t h a t t h e i n i t i a l choice of b a s e
materials and h e a t t reatment of t h e gear t e e t h l e f t room f o r improvement,
spec t rog raph ic a n a l y s i s of t h e shavings found nea r t h e r o o t of t h e t e e t h
i n d i c a t e d t h e shavings d i d n o t c o n t a i n i r o n , i .e. , no 17-4 PH s teel b a s e
material. Rather , t h e shavings were composed mainly of s i lver , w i t h traces of
molybdenum and s i l i c o n , which are c o n s t i t u e n t s of t h e gea r t o o t h c o a t i n g on ly ,
( a s i l ve r p l a t e w i th baked-on molyd i su l f ide c o a t i n g ) .
t h e r e f o r e , must b e considered adequate, d e s p i t e t h e merits of t h e i n i t i a l
choice.
The b a s i c gea r material,
c. Gear Tooth Configurat ion
R e l a t i v e t o gear t o o t h c o n f i g u r a t i o n , a p re l imina ry
lox - s i ze l ayou t of t h e t e e t h i n mesh i n d i c a t e d t h a t due t o a d i f f e r e n c e i n t h e
p r e s s u r e a n g l e of t h e output and i n p u t g e a r s , t h e sha rp c o m e r s of gea r t o o t h
t i p s were c o n t a c t i n g t h e mating t e e t h and causing s c u f f i n g o r shaving down
of t h e f aces .
13
A subsequent ex tens ive i n v e s t i g a t i o n of t h i s p o s s i b i l i t y
w a s accomplished a t Bendix, t h e r e s u l t s of which s u b s t a n t i a l l y v e r i f i e d pre-
l imina ry f i n d i n g s by Aerojet . A complete r e p o r t of t h i s Bendix s tudy i s con-
t a i n e d i n Bendix Research Labora to r i e s Report No. CA-23105, " F a i l u r e Analysis
o f t h e Nutator Transmission of Turbine Power Control Valve Actuator Model
NT-D1, Serial N o . 17," which is included i n t h i s r e p o r t as Appendix A.
d. Seal
Of i n t e r e s t i n t h e a c t u a t o r post-endurance test evalua-
t i o n w a s t h e cond i t ion of t h e seal.
D Page 38
. . . - - - - . . . . . - . . - - . -. . . . . . . -. . . . . . . . . . . . .
a Microscopic examination of t h e seal showed i t t o b e i n
good cond i t ion .
outgassed carbon b inde r material due t o t h e high-temperature environment.
seal s u r f a c e was a 4 microin. f i n i s h wi th a 6 microin. c i r c u m f e r e n t i a l s c r a t c h ,
which probably d id no t a f f e c t t he s e a l i n g func t ion .
Some bui ldups were p r e s e n t , which appeared t o be carbon o r
The
7. Conclusions
D
Q
a. The r e s u l t s of t h e endurance t e s t i n g desc r ibed i n t h i s
r e p o r t , t o g e t h e r w i th t h e ex tens ive ope ra t ing t i m e t h e t e s t a c t u a t o r S / N 1 7
w a s s u b j e c t e d t o b e f o r e t h e s ta r t of t h e Endurance T e s t , v e r i f y t h a t t h e u n i t s
u s e f u l l i f e i s s i g n i f i c a n t l y longe r than w i l l b e r equ i r ed f o r t h e XE t e s t i n g
a p p l i c a t i o n . I n a d d i t i o n t h e high-temperature environmental cond i t ions t o
which t h e a c t u a t o r w a s sub jec t ed during t h e temperature to rque c y c l i n g test
w e r e much more severe than had been o r i g i n a l l y intended.
b. Despi te t h e preceding conclusion, t h e tests helped t o
reveal inadequacies i n t h e a c t u a t o r t r ansmiss ion gea r des ign , which l e d t o
corresponding improvement of f u t u r e hardware. S p e c i f i c a l l y t h e n u t a t i n g gea r
has been redesigned wi th (1) a l a r g e r p r e s s u r e ang le , (2 ) a decreased addendum,
and (3) r a d i i a t t h e t i p s and a decreased r o o t r a d i u s , a l l of which are
in t ended t o e l i m i n a t e t h e shaving a c t i o n . Appendix A shows t h e d e t a i l s of
t h e s e changes.
The changes w i l l b e e f f e c t i v e on t h e Model NT-D2
a c t u a t o r s t h a t are s h o r t l y t o b e d e l i v e r e d . Therefore , i t i s recommended t h a t
t h e endurance test desc r ibed i n t h i s r e p o r t be repeated us ing t h e new design.
Also, t h e test equipment i s t o b e modified so t h a t t h e i n p u t s h a f t temperature
w i l l b e used f o r c o n t r o l i n p l a c e of t h e va lve -ac tua to r i n t e r f a c e f l a n g e , i n
o r d e r t o e l i m i n a t e overheat ing.
Page 39
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APPENDIX
BENDIX FAILURE ANALYSIS O F THE NUTATOR TRANSMISSION OF TURBINE
POWER CONTROL VALVE ACTUATOR MODEL NT-D1, SERIAL NUMBER 1 7
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ATTACHMENT
FAILURE ANALYSIS OF THE NUTATOR TRANSMISSION OF TURBINE POWER CONTROL VALVE ACTUATOR MODEL NT-D1, SERIAL NUMBER 17
INTRODUCTION
After completing one life cycle in the life test, TPCV actuator, Model NT-D1, Serial No. 17 was found to limit-cycle. The rotation of the output shaft was checked and found to be running rough. Aerojet- General personnel carefully disassembled the actuator and examined the transmission. Metal chips were discovered at the bottom of the gear teeth of the output gear, and the gear teeth faces appeared as though they were abnormally worn over about one-third of their area.
parts, particularly the transmission gears, and to review the history of the actuator.
transmission of actuator Serial No. 1 7 . Included in the following sections are a description of the failed gears, a history of actuator No. 17, a history of the nutator transmission for TPCV actuators, an analysis of the gear teeth geometry, a review of gear materials, and conclusions and recommendations.
Bendix personnel visited Aerojet-General to examine the actuator
This attachment presents the detailed failure analysis of the
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1 DESCRIPTION OF NUTATOR GEARS OF TRANSMISSION UNDER ANALYSIS A sketch of the transmission (Part No. 2775033) used in the Model
In this sketch the output NT-D1 TPCV actuators is shown in Figure 1-1. gear (Part No. 2775728) and the nutating gear (Part No. 2775815) under analysis are indicated. cones of the two gears which is also the theroretical point about which the nutating gear nutates. are indicated.
Noted in the sketch is vertex of the pitch
The plus and minus direction of rotation
1.1 Output Gear (Part No. 2775728)
Of the two gears, the output gear showed the most significant signs of wear. the‘teeth, but the areas at the outer and inner portions of the tooth face showed signs of aggravated wear or scuffing. On almost every tooth face that would be in contact when moving against the 400 in-lb load, there was an area at the outer portion of the tooth face that showed signs of scuffing with a metal chip at the bottom of tooth face. This area had the most significant signs of wear. It is not known at this time whether the chips at the bottom of the teeth are chips of the base metal of the gear or of the plating applied in the lubrication process. The metal chips can be seen in the photograph of the gear in Figure 1-3. inner portion of the tooth faces but they were not nearly so severe as those at the outer portion.
There was tooth contact throughout the entire length of
(See Figure 1-2.)
There were a lso indications of scuffing on the
On the faces in contact when opposing the 80 in-lb load, there were signs of scuffing and metal chips on the inner portion of almost every tooth face. nearly every tooth, the wear was not so severe as on the outer portion of the opposite face. portion of the tooth face and metal chips in occasional teeth.
(See Figure 1-4.) Although there were metal chips in
There were also signs of scuffing at the outer
1.2 Nutating Gear (Part No. 2775815) The nutating gear showed less signs of aggravated wear than
the output gear. There was tooth contact along the entire length of tooth, but there were signs of scuffing at the inner and outer ends of the tooth face. (See Figure 1-5.) ‘filere were metal chips at the bottom of a few of the teeth, but these instances were relatively minor in comparison to the output sear. (See Figures 1-6 and 1-7.)
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Figure 1-1 - Transmission Assembly (Part No. 2775033)
F i g u r e 1-2 - O u t p u t Gear ( P a r t No. 2775728)
Figure 1-3 - Chips a t Bottom of 400 in-lb Face of Output Gear
Figu re 1-4 - Chips a t Bottom of 80 in-lb Face of Output Gear
Figure 1-5 - N u t a t i n g Gear ( P a r t No. 2775815)
Figure 1-6 - Nutating Gear, Showing Wear
Figure 1-7 - Nutating Gear, Showing Wear
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HISTORY OF ACTUATOR S/N 17 Prior to the life tests of actuator S/N 1 7 , the actuator was sub-
jected to and used in a number of tests. tests totaled 61 hours. The tests included vibration, frequency response, stall torque, and checkout tests of the actuator and the use of the actuator in engine simulation, test-stand checkout, and hot-valve tests. The life test was initiated without the refurbishment of the actuator.
The operating time in these
In the life test, the actuator was mounted on a turbine power control valve that has been made part of the test fixture. The butter- fly shaft was coupled to an Inland torquemotor to allow torque loads to be accurately programed and applied. To simulate temperature the turbine power control valve body was heated using a Calrod heater. Cryogenic temperatures were produced by cooling the valve body and actuator with liquid nitrogen. During the life tests the torque load was 400 in-lbs in a CCW and 80 in-lbs in CW direction. The input command to the actua- tor was a 0.3-cps sine wave with 6-degree peak-to-peak amplitude. The actuator position was 45 degrees. The time-temperature profile of the life cycle is shown in Figure 2-1. Also indicated in the figure is the output shaft dynamic seal pressure. The temperature indicated in the Figure was that measured by a thermocouple attached to the actuator at a dynamic-seal mounting screw. A life cycle was approximately five hours. Actuator performance was evaluated before and after the life cycle. After the cycle was completed, it was found that the actuator would limit-cycle and that the rotation of the output shaft without pneumatic power was rough. The actuator was carefully disassembled. The trans- mission gears of the actuator were found to be as described in Sectionl. The total operating time of the actuator was approximately 70 hours.
10
F i g u r e 2-1 - Tempera tu re P r o f i l e i n T,ife-Test C y c l e
3 HISTORY OF TRANSMISSION DESIGN
The n u t a t o r t ransmiss ion has been used i n a l l Turbine Power Con- t r o l Valve Actuators s i n c e the i n i t i a t i o n of t h e B series of TPCV actua- t o r s . The t ransmiss ion of t h e B-series a c t u a t o r s was designed t o meet t h e requirements of BRL a c t u a t o r s p e c i f i c a t i o n DS-563. load as func t ion of va lve p o s i t i o n w a s def ined. The maximum valve load torque w a s 248 in- lbs ; t h e f r i c t i o n load w a s 60 in- lbs ; and t h e i n e r t i a load of t he va lve w a s considered n e g l i g i b l e . a c t u a t o r w a s n o t def ined. The t ransmiss ion designed had a r a t i o 82 : l and w a s capable of handl ing a 10 in- lb inpu t torque. The gears of t h e t ransmiss ion were made of 17-4PH. This material was s e l e c t e d f o r i t s high f a t i g u e and y i e l d s t r e n g t h combined wi th i t s e x c e l l e n t r e t e n t i o n of d u c t i l i t y a t cryogenic temperatures. The gear geometry, cone angle , p re s su re angle , and p i t c h s e l e c t e d f o r t h i s i n i t i a l t ransmiss ion and the material s e l e c t e d have been used i n a l l subsequent n u t a t o r trans- missions b u i l t f o r TPCV ac tua to r . Transmission P a r t No. 2151312 w a s used i n t h e Models NT-B2 and NT-B3 a c t u a t o r s . Two t ransmiss ions of t h i s design were l i f e t e s t e d . The f i r s t t r a n s h i s s i o n w a s run under maximum load a t cons tan t speed f o r fou r hours and t h r e e minutes. A t t he completion of t h e t e s t i n g of t h i s t ransmiss ion , t h e gears showed s i g n i f i c a n t s i g n s of wear. A number of minor changes, inc luding t h e inc reas ing of t h e f a c e width of t h e gea r s , were made i n t h e second t rans- mission. The second t ransmiss ion w a s sub jec t ed t o tests of temperature shock, constant- load endurance, and low-temperature c y c l i c load endurance i n which a peak load of 383 in- lbs w a s appl ied . Tests of t h i s t r ans - mission were concluded a f t e r 7.33 hours. While t h e r e were i n d i c a t i o n s of wear a t the conclusion of t h e tests of t h e second t ransmiss ion , they were n o t considered excessive. The d e t a i l s of t he t e s t i n g of t h e t rans- mission are presented i n r e p o r t number BPAD 863-4-15122R.
The NT-B4 a c t u a t o r used t ransmission P a r t No. 2775005. This t ransmiss ion w a s e s s e n t i a l l y t h e same t ransmiss ion as P a r t No. 2151312 except t h a t t h e s i n g l e double-row angular-contact bear ing w a s rep laced wi th a p a i r of angular-contact bear ings .
The a c t u a t o r
The duty cyc le of t h e
I n t h e Model NT-C a c t u a t o r s , some ref inements w e r e made i n t rans- mission design. geometry remained unchanged.
NDC-51A. I n t h i s s p e c i f i c a t i o n , a maximum ou tpu t torque of 600 in- lbs and l i f e of 20 hours were s p e c i f i e d . t ransmiss ion w a s redesigned b u t gear geometry and material were r e t a ined .
The f a c e width of gears w a s increased b u t t h e gear
The Model NT-D1 a c t u a t o r s were designed t o AGC s p e c i f i c a t i o n
No duty cyc le was s p e c i f i e d . The
The t ransmiss ion of t h e Model NT-D2 a c t u a t o r is e s s e n t i a l l y t h e same as t h a t of Model NT-D1 ac tua to r . I n t h e s p e c i f i c a t i o n f o r t h e Model NT-D2 a c t u a t o r , AGC 90080, maximum torque is 600 in- lb; t h e actua- t o r l oad as func t ion of p o s i t i o n is def ined; a l i f e of 100 hours is s p e c i f i e d ; no duty cyc le is i nd ica t ed .
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7
3 1 13
4 ANALYSIS OF GEAR GEOMETRY
4 . 1 D e s c r i p t i o n of Gear Mesh
A schemat ic diagram of t h e g e a r t e e t h i s shown i n F i g u r e 4-1. The p i t c h l i n e s of t h e g e a r s are d e s c r i b e d by cones whose ver t ices are c o i n c i d e n t when t h e g e a r s are p r o p e r l y mated. The p i tch-cone a n g l e of t h e n u t a t i n g g e a r is l a r g e r than t h e p i t c h cone a n g l e of t h e r o t a t i n g g e a r . When t h e t r a n s m i s s i o n i s assembled, t h e c e n t e r l i n e s of t h e g e a r s are d i s p l a y e d by a n a n g l e e q u a l t o t h e d i f f e r e n c e i n t h e p i tch-cone a n g l e s . The g e a r s , t h e n , are meshed a t t h e p i t c h l i n e on one s i d e of t h e g e a r b u t are n o t meshed on t h e d i a m e t r i c a l l y o p p o s i t e s i d e of t h e g e a r . A s e c t i o n a l view t a k e n p e r p e n d i c u l a r t o t h e p i t c h l i n e of t h e meshed g e a r d e s c r i b e s t h e s p e c i f i e d p r e s s u r e a n g l e . I n o p e r a t i o n , t h e c e n t e r l i n e of t h e nuta- t i n g g e a r d e s c r i b e s a cone w i t h t h e v e r t e x a t t h e p i tch-cone v e r t e x . t h e g e a r n u t a t e s , i t becomes disengaged from t h e o u t p u t g e a r a t one p o i n t and becomes meshed a t a n o t h e r p o i n t . There i s a one-tooth d i f f e r e n c e between t h e n u t a t i n g and o u t p u t g e a r s , and f o r each n u t a t i o n c y c l e , t h e o u t p u t g e a r i s advanced 1/N of a r e v o l u t i o n (where N is t h e number of t e e t h on t h e o u t p u t g e a r ) .
A s
4.2 Gear Geometry as P r e s e n t e d on Drawings 2775815 and 2775728
The n u t a t i n g g e a r and t h e o u t p u t g e a r are manufactured a c c o r d i n g t o drawings 2775815 and 2775728, r e s p e c t i v e l y . I n o r d e r t o o b t a i n proper o p e r a t i o n of t h e g e a r se t , t h e p i tch-cone and p r e s s u r e a n g l e s of t h e g e a r t e e t h must b e a c c u r a t e l y machined and t h e p r o p e r t o o t h c o n f i g u r a t i o n must b e g e n e r a t e d . The g e a r t e e t h and s p a c e s can b e con- s i d e r e d t r u n c a t e d pyramids as i l l u s t r a t e d i n F i g u r e s 4-2 and 4-3. The t o o t h s p a c e s (and t h u s t h e t e e t h ) may b e g e n e r a t e d u s i n g a form t o o l ( m i l l c u t t e r o r g r i n d i n g wheel) . The v e r t e x of t h e form-tool a n g l e (Fig- u r e 4-4) moves a long t h e l i n e AC of F i g u r e 4-3. It i s t o b e n o t e d t h a t t h e l i n e AC is a t a d i f f e r e n t a n g l e from t h e p i t c h l i n e . The c u t t i n g - t o o l a n g l e i s t h e r e f o r e d e f i n e d when viewing t h e t o o t h s p a c e a l o n g t h e l i n e AC, and must b e d i f f e r e n t from t h e p r e s s u r e a n g l e which is d e f i n e d by viewing t h e s p a c e a l o n g t h e p i t c h l i n e . On drawings 2775815 and 2775728, t h e n , t h e t o o t h s p a c e a n g l e s are g i v e n as 1 9 d e g r e e s , 28 minutes , 46 seconds, and 20 d e g r e e s , 35 minutes , 1 5 seconds , and should b e u s e d . f o r g e a r manufac tur ing o n l y . I f t h e g e a r s are c u t w i t h t h e s e a n g l e s a l o n g t h e p r o p e r a n g l e f o r t h e l i n e AC ( F i g u r e 4-3), t h e p r o p e r p r e s s u r e a n g l e should b e o b t a i n e d when t h e g e a r s are mated.
4 .3 A n a l y s i s of Gear Geometry
An a n a l y s i s of t h e p r e s e n t g e a r geometry w a s performed to d e t e r m i n e i f t h e d imens iona l i n f o r m a t i o n g i v e n on drawings 2775815 and 2775728 w a s c o r r e c t . The e q u a t i o n s t o o b t a i n t h e p r e s s u r e a n g l e from t h e g i v e n dimensions were d e r i v e d u s i n g t h e s k e t c h e s shown i n F i g u r e s 4-5 and 4-6. R e f e r t o F i g u r e 4-5; t h e f o l l o w i n g e q u a t i o n s were d e r i v e d f o r t h e n u t a t i n g g e a r ( P a r t No. 2775815):
I 13
3
3 13 7
3 1 3
a 3
NUTATING GEAR 83 TEETH
\ 58.82 DEGREES
60 DEGREES
OUTPUT (ROTATING) GEAR 82 TEETH
PITCH CONE VERTEX
- ._ - - - A & ___- -_
1 CENTER LINE OF
OUTPUT GEAR
- 4 -_ \
CENTER LINE ---7- OF __ NUTAT I N C GEAR
PITCH LINE OF ROTATING
y h P I T C H LINE OF NUTATING GEAR
/ '
// / /!
Figure 4-1 - Schematic Diagram of Transmission Gear Mesh
14
ON ?ITCH CONE
T I T C H COKE VERTEX
F igu re 4-2 - Typica l Gear Tooth
Figure 4-3 - Typica l Tooth Space
VERTEX
CUTTING TOOL ANGLE
F i g u r e 4-4 - Sketch of Gear-Cutting Tool
Figure 4-5 - Schematic Diagram of Geometry for Nutating Gear (Part No. 2775815) (83 Teeth)
,
CENTER LINE 4 OF GEAR
PITCH L I E
PITCH CONE VERTEX
Pi-gure 4-6 - Schematic Diagram of Geometry for Output Gear (Part No. 2775728) (82 Teeth)
SPACE
D
i3 D
D
R
6J
d tan = -
d tan 8 = - R4
R1 = r tan (4 - 4,)
where
, = pitch cone angle
$1 = angle of line AC (Figure 4 - 3 )
8 = pressure angle
O 2 = cutting tool angle
Other dimensions are as shown on the sketches. Substituting equations (21, ( 3 ) , and ( 4 ) into equation (1) results in
which can be simplified to
tan 8 = cos (4 - $1) tan e 2
Equation ( 6 ) , then, relates the pressure angle to the pitch-cone angle, the cutting-tool angle and the angle along which the form tool is moved while cutting the tooth space. Similar relations can be obtained for the output gear using Figure 4 - 6 . angle of the gear is
The final equation for the pressure
tan 8 ' = cos (I$l' - 6 ' ) tan B 2 ' (7)
0 20
3 3 J 3 3 3
3 3 3 1 3 3 3 3 3 3
where t h e angles are as def ined above. pu t gear . )
The d a t a g iven f o r manufacturing t h e two gea r s is as fo l lows:
(Primed q u a n t i t i e s r e f e r t o out-
Nutat ing Gear
$ = 30 deg
= 27.3486 deg $1
C12 = 19.4794 deg
Output Gear
4 = 31.175 deg
I = 33.6806 deg $1
= 20.5875 deg O2
Calcu la ted p res su re angles f o r t h e n u t a t i n g and output gea r s are 19.4588 degrees and 20.5655 degrees , r e s p e c t i v e l y . It is seen, t h e r e f o r e , t h a t t h e manufacturing dimensions given on t h e drawings do no t r e s u l t i n a p res su re ang le of exac t ly 20 degrees as s p e c i f i e d . p roper ly mesh a t t h e p i t c h l i n e when assembled i n t h e t ransmiss ion .
I n o rde r t o o b t a i n a clearer p i c t u r e of how t h e gea r s mesh, t he gear geometry w a s ca l cu la t ed a t r = 1.25 inches and r * 1.62 inches ( inner and o u t e r r a d i i of t h e gear t e e t h measured along t h e p i t c h l i n e ) . Typical gear mesh f o r t h e two r a d i i are shown i n F igures 4-7 and 4-8, which are drawn s e v e r a l t i m e s s i z e . It i s seen from t h e s e f i g u r e s t h a t , due t o t h e improper ang le s , t h e gea r s do no t mesh along t h e p i t c h l i n e . It is a l s o seen how t h e r o t a t i n g gear can be "shaved" by t h e n u t a t i n g gear as t h e two come i n t o mesh. t h e t e e t h of t h e gea r s can bottom on t h e r a d i u s of t h e spaces a t t h e smaller va lues of r a d i u s r . This c o r r e l a t e s wi th t h e wear p a t t e r n of t h e f a c e s of t h e t e e t h of both gea r s .
The t ransmiss ion gea r s can be reworked t o o b t a i n t h e same pres su re ang le by reworking t h e n u t a t o r gear only.
The gea r s w i l l no t
Addi t iona l ly , F igure 4-7 i n d i c a t e 6 t h a t
The t e e t h can be
3 3 21
Figure 4-7 - Typical Gear Mesh at r = 1.25 inches
--
83 TEETH @~7#7W6 GEB~?)
Figure 4-8 - Typical Gear Mesh at r = 1.62 inches
a
n
J
a
1
machined a t a s l i g h t l y l a r g e r ang le than t h e 19 degrees , 28 minutes, 46 seconds s p e c i f i e d on drawing 2775815. a l s o have t o be decreased t o prevent i n t e r f e r e n c e a t t h e bottom of t h e r o t a t i n g gear space. be broken wi th a s l i g h t r ad ius t o he lp a l l e v i a t e any "shaving" a c t i o n . I t may a l s o be d e s i r a b l e t o deepen t h e nu ta t ing gear space by decreas ing t h e r o o t r ad ius . shimming a t assembly t o a s s u r e coincidence of t h e pitch-cone vertices.
The addendum of t h e t e e t h will
A t t h e same time, t h e co rne r s of t h e t e e t h should
With t h e s e modi f ica t ions , t h e n u t a t i n g gear w i l l r e q u i r e
24
1 I 1 J
3 1
1 1
3
5 GEAR MATERIALS The physical properties of a group of stainless steels that warrant
consideration for this application, including the 17-4PH stainless steel presently being used, are presented in Table 5-1. presented in this table have sufficient physical strength and ductility.
All materials
It has been indicated that the galling characteristics of the gear material may have an effect on the short life achieved by the failed parts. good wear characteristics; thus is recommended for the making of gears. The Armco Steel Corporation has conducted galling tests on various stainless steels in which loads causing galling were determined. The results of these tests are included in Table 5-1. The data indicates that the 410- or 416-series of stainless steels have greater resistance to galling than 17-4PH. The report also indicates that improved galling characteristics, approaching that of the 410 and 416 steels, could be achieved with 17-4PH by using mating parts with differing hardnesses.
The 17-4PH stainless steel is considered to have relatively
In the TPCV actuator application, the mating parts are lubricated with a dry-film lubricant, and environmental and load conditions differ considerably from those of the galling tests. Therefore, it is difficult to evaluate with any degree of certainty the effect of the galling char- acteristics of the materials on the life they achieve. This is not to say that in future designs it would not be advisable to change the material from 17-4PH to either a series 410 or 416 stainless steel.
25
Table 5-1 - Material Review for Nutator Gears
Characteristic 17-4 PH
Tempering Temperature 900 925 1025* I
1150
Tensile Room Temp. 190,000 170,000 155,000 135,000 S trenx th -320'F 1263,0001 I I Yield Room Temp. 110,000 155,000 145,000 Strength 243,000
in Two Inches -320'F IZOD Impact Room Temp. **-20 15-35 (f t-lb). -320'F I
105,000
16 >l
30-50
6000 6000 5000 Galling Load (psi) *** i 20,000 30,000
* ** Temperature of 11-4 PH used in present gears Minimum impact properties for 17-4 PH in position 900 +re not acceptable.
April 20, 1955 issue of "Steel" Magazine. ***"Stainless Steel Galling Characteristics," H. Tanczyn, Armco Steel Corporation,
1 J '
1 I 1 I 1 WJ 7
I
I
J
3 3
6 CONCLUSIONS AND RECOMMENDATIONS
It was concluded from the failure analysis that scuffing of the gear teeth and the resulting metal chip at the bottom of gear teeth was due to the difference in the pressure angle of the nutating and output -'mars arid the sham corners on the gear tooth tips. The chips found at the bottom of the teeth are probably chips of the plating material from Yagnaplate process used to lubricate the gear teeth. The conclusion that the chips are from the plating process is drawn because it is not probable that the base material of gears would generate a chip, since both gears are of the same hardness. The plating material is soft in comparison to the base material and therefore a gear tooth with a sharp corner could shave the softer material.
In support of the foregoing conclusion, it is also concluded that it is unlikely that the galling characteristics of the base material contributed significantly to the failure. The gear teeth of the trans- mission are lubricated with a dry-film lubricant that actually prevents the contact of the base materials and lowers the coefficient of friction between the contacting faces of the gear teeth. Once the dry-film lubri- cant has deteriorated to the point where the base materials of the two gears come into contact, the transmission efficiency should decrease and the wear of the gear teeth increase. It is questionable to what ex- tent that galling characteristics of the base material would limit the life of a transmission after the base materials come into contact. A review of materials indicated that the 416-series stainless steel did have better resistance to galling and could be substituted for the 17-4PH material presently being used.
It was noted in reviewing the history of the transmission design that the actuator duty cycle, loads, and environments as a function of time, have never been defined or specified. Therefore, it is not possi- ble to establish the adequacy of the transmission for this application.
It is recommended that gear teeth of the nutating gear be changed to have the same pressure angle as the output gear and that the corners on the tips of the gear teeth be broken. It is not possible to predict to what extent the life of the transmission will be improved by correct- ing the pressure angles and breaking the sharp corners of the gear teeth. This can be established only through testing of the transmission. It is also recommended that the required duty cycle of the actuator be established and be made part of the actuator specification to allow adequacy of the transmission to be determined.
27
