Document rBJ3kOam4aGka81jGk3XmopdE

FILE NAME: Railroads (RR) DATE: 1968 Apr DOC#: RR064 DOCUMENT DESCRIPTION: Gov Report - A Study of Frictional Characteristics of Composition Compared to Cast Iron Brake Shoes Conducted by the FAA Aeronautical Center  A SS O C IA T IO N OF A M E R I C A N R A I L R OA D RESEARCH DEPARTMENT R E P O R T NO. M R - 448 S T U D Y OF F R I C T I O N A L C H A R A C T E R IS T IC S OF C O M P O S IT IO N C O M P A R E D TO CAST IRON B R A K E SHOES A P R I L 1968 Office of R e s e a r c h D ir e c t o r AAR R E SE ARC H CENTER Chicago, Illinois 606l6 M R-448 44520- R a i l r o a d a t W a y c r o s s , G e o r g i a , b e g i n n i n g o n A p r i l 15, 1 9 8 8 a n d e n d i n g A p r i l 19, 19 68. T h e f i e l d w o r k w a s s u p p l e m e n t e d w i t h l a b o r a t o r y w o r k . c o n d u c t e d a : t n e AAR R e s e a rc h D e p a r t m e n t on the b ra k e shoe d y n a m o m e t e r m acnir.e wm cn has tne capability' of m e a s u r i n g stopping d i s t a n c e s u n d e r v a r io u s b r a k e snoe p r e s s u r e s . The f r ic ti o n a l e f fe c t f o r b r e a k a w a y r e s i s t a n c e of w h e e l s w a s a l s o s t u c i e a by the u s e of t h i s m a c h i n e . T h e braining f o r c e g e n e r a t e d by a n y bra.see s y s t e m is d e p e n d e n t u p o n two p r i m a r y f a c t o r s . T h e f i r s t of t h e s e f a c t o r s is the c o e f f i c i e n t o: f r ic ti o n b e t w e e n the Drake shoe and the w h e e l t r e a d and the s e c o n d is the a m o u r . : of p r e s s u r e a p plied to the shoe. F r i c t i o n b e tw e e n two given bodies is d i r e c t l y p ro p o r tio n a l to the p r e s s u r e . The c o e ffic ie n t of f r i c t i o n is c o n s t a n t for all p r e s s u r e s . H ow ever, w n e n t h e t r e a d s u r f a c e of t h e w h e e l r e a c h e s a h i g h t e m n e r a t u r e, t h e r e a r e s o m e v a r i a t i o n s m tn e c o e f f i c i e n t of f r i c t i o n c o m p a r e d w i t h t h e c o e f f i c i e n t c: f r i c t i o n tnat would be e x n e r i e n c e d at the l o w e r t e m p e r a t u r e s . In the c a s e of a lo c o m o tiv e m the type service co m p a ra b le to that investigated in the test reported herein, nigh te m p e ra tu re -h ig h speed c h a ra c te ris tic s would not be encountered. C onse quently, the v a r i a t i o n s in c o e f f i c i e n t of f r i c t i o n a r e due a l m o s t e n t i r e ly " t o the type ot m a t e r i a l in c o n t a c t with the w h e e l t r e a d . It i s a f u n d a m e n t a l a x i o m t h a t t h e f r i c t i o n a l r e s i s t a n c e i s p r o p o r t i o n a l to the load a p p lie d and t h a t it is i n d e p e n d e n t of the a r e a of the s l i d i n g s u r f a c e s . C o n s e q u e n t l y , a s w i l l be d i s c u s s e d in t h e d a t a of t h i s r e p o r t , t h e c o n t a c t a r e a of the brake shoes on the w heel tre a d does not re la te to the b ra k in g force g en erated so that it is-r.c; a fu n c tio n of w h e t h e r or not c l a s p or s in g le s h o e b r a k e s a r e used, but the p r e s s u r e ap p lied to the shoe u n d e r a given c o e ffic ie n t of friction that estab lishes the braking or stopping force. Acknowledgement s M r . J. W. H a w t h o r n e , A s s i s t a n t V i c e P r e s i d e n t , S e a b o a r d C o a s t D i n e Railroad, made available equipment and personnel for this stud'/. M r . W. E . Kirk, D i r e c t o r of R a ilr o a d E n g in e e rin g , W e s tm g h o u s e A ir B r a k e Co., fu rn is h e d i n s t r u m e n t s an d p e r s o n n e l . M r . J. G. Britton., M e c h a n i c a l E n g i n e e r , A A R R e search Center, coordinated the test data and su p e rv ise d its p re p a ra tio n for this r e p o r t . M r . O, W. K n o b l o c k , E n g i n e e r o f T e s t s , A A R R e s e a r c h C e n t e r , s u p e r vised the laboratory, work. PR O C E D U R E S AND IN STR U M EN TA TIO N A m e e t i n g w a s h e l d a t J a c k s o n v i l l e , F l o r i d a o n A p r i l 5, 1 9 o S to a r r a n g e a fie ld t e s t p r o g r a m f o r m a k i n g a n i n v e s t i g a t i o n of t h e b r a k i n g a b i l i t y of c o m p o s ition b ra k e shoes and c a s t iron b ra k e shoes on switching type and r oad-s witche r type l o c o m o t i v e s . T h i s m e e t i n g w a s a t t e n d e d by r e p r e s e n t a t i v e s of the S e a b o a r d Coast Dine, AAR R e s e a rc h D e p artm en t and W estinghouse A ir B rake Company. A t e n t a t i v e p r o c e d u r e 'f o r m a k i n g t p i s i n v e s t i g a t i o n w a s d e v e l o p e d w h i c h i s s h o w n a s F i g u r e 1. It w a s a g r e e d a t t h i s m e e t i n g t h a t e a c h o f t h e m a n u f a c t u r e r s of com position brake shoes would be re q u e s te d to supply c o m p o s itio n brake shoes MR-44 8 44520-4 ui t h e t y p e u s e d o n s w i t c h i n g and r o a d - s w i t c h e r l o c o m o t i v e s to t h e A A R R e s e a r c h D e p a r t m e n t fo r s t u d y of th e f r i c t i o n a l c h a r a c t e r i s t i c s of t h e s e s h o e s u sin g the brake shoe dynam om eter. . - The '.vestinghou.se A ir B rake C om pany a g re e d to supply' all in stru m en tatio n and m a n p o w e r to ru n the in stru m e n ta tio n for the field investigation as this com pany has sp e c ia l d e v ic e s w h ic h car. be used in such tests to quickly develop stopping d is t a n c e s , b r a k e c y l i n d e r p r e s s u r e s , s p e e d s , b r a k i n g r a t i o s , a n d d r a w b a r pul l . It w a s d e c i d e d t h a t t h i s i n s t r u m e n t a t i o n w o u l d be p l a c e d in a c a b i n c a r to be u s e d as an in stru m en t car during the field studies. The c ra k e c y lin d e r p r e s s u r e was m e a s u r e d by a B r e d F i a d e r Cc. tra n sd u c e r w h i c h h a d b e e n c a l i b r a t e d b y vVe s t i n g h o u s e A i r B r a k e C o m p a n y o n a d e a d w e i g h t t e s t e r f r o m 0 to 100 p s i . F i g u r e s 2 and 3 a r e v i e w s of th i s t r a n s d u c e r . T he o u t put of t h i s t r a n s d u c e r w a s r e c o r d e d o n a n E l e c t r o I n s t r u m e n t s , Lnc. 's XYY' R e c o r d e r Mode- No. 560. F i g u r e 4 shows a view of this r e c o r d e r and stooping d i s tance counter. The s p e e d in m i l e s p e r hour w as d e t e r m i n e d by using a r u b b e r - t i r e d a l u m i n u m w h e e l , 12 i n c h e s in c i r c u m f e r e n c e , w h i c h w a s d r i v e n by a w h e e l on the c a b i n c a r . F i g u r e s 5 a n d 6 a r e v i e w s of th i s d e v i c e . T h i s s m a l l w h e e l d r i v e s a S e r v o T ek P r o d u c t s Co. 's DC g e n e r a to r . This device also m e a s u r e d stopping distance w hich was c o n v e r t e d into fe e t and re a d on an electronic co u n ter m ounted in the c a b i n c a r . Tine s p e e d i n m i l e s p e r h o u r f r o m t h i s d e v i c e w a s r e c o r d e d on t h e XYY1 Recorder. T h e h o r i z o n t a l d i s t a n c e on the r e c o r d e r c h a r t s is t i m e ; a n d th e a m o u n t of t i m e f r o m i n i t i a t i o n of b r a k e a p p l i c a t i o n to a c o m p l e t e stop c a n be r e a d on the X Y Y ' c h a r t s . F i g u r e A. i n t h e A p p e n d i x i l l u s t r a t e s a n X Y Y ' r e c o r d e r c h a r t f o r r u n s 169 t h r o u g h 177 w h ic h a r e inclu d ed to i l l u s t r a t e the m e t h o d u sed . The o r d inate on this c h a r t sh o w s the brake cylinder p r e s s u r e in psi and the tr a m speed m m p h . The i n i t i a t i o n of b r a k e a p p l i c a ti o n s t a r t s the r e c o r d e r by a switch m o u n t e d on the i n d e p e n d e n t b r a k e v a lv e . F i g u r e 7 sh o w s a view of this s w i t c h in place on the b r a k e v a l v e . H o w e v e r , so i n s u r e a c c u r a c y , two o b s e r v e r s u s i n g stop w a t c h e s also m e a s u r e d the tim e f r o m brake application to the point at which motion had c e a s e d . A n o t h e r s p e e d o m e t e r was p l a c e d in the cab of the l o c o m o t i v e (see F i g u re 8) and the s p e e d fo r this in s tr u m e n t was d e te r m in e d by a n o th e r alum inum r u b b e r - t i r e d wheel, 24 inches in c irc u m fe re n c e , which drove another S ervo-T ek g e n e r a t o r . F i g u r e 9 is a v i e w of this w h e e l . T h e p o w e r f o r the i n s t r u m e n t a t i o n was obtained f r o m a B riggs and Stratton gasoline engine driving a M aster M ech a n i c s M a n u f a c t u r i n g C o . ' s 115 volt, 60 c y c le a l t e r n a t o r . T h i s p o w e r was fed to a H a r r i s o n 6 2 8 4 A D C p o w e r s u p p l y f o r i n s t r u m e n t o p e r a t i o n . F i g u r e 10 is a v i e w of the i n s t r u m e n t s e t - u p in the cabin ca r. The static d r a w b a r tests w ere conducted by installing a B aldw in-L im aH a m i l t o n 50, 000 l b . T*yype U - l l o a d c e l l b e t w e e n t h e l o c o m o t i v e s . T h i s l o a d c e l l h a d b e e n p r e v i o u s l y c a l i b r a t e d on an Olson U n i v e r s a l te stin g m a c h i n e at W estingn o u s e A i r B r a k e C o m p a n y . F i g u r e s 11 a n d 12 a r e v i e w s o f t h i s l o a d c e l l b e t w e e n two lo c o m o tiv e s . F i g u r e B in the Appendix shows the t r a c e s developed for live t r i a l s in R u n No. 281 R. T h is s e r i e s of ru n s w as m a d e to e s t a b l i s h the b re a k a w a y MR-448 520-5 r e s i s t a n c e o 1 the l o c o rn c 3 .v c Dr!;c 5 and the ab sc issa is the elapsed time Tr.e o r d i n a t e or o ra wo a r io rc e : building up the d r a w b a r tor Data/'for d e t e r m i n i n g brak in g ratio of the l o c o m o t i v e s w a s o o t a m e d by using a d y n a m o m e t e r b r a k e s h o e a n d i n s t a l l i n g i t m e a c h b r a k e n e a d f o r t h e u p - < t y p e ox locomotive. The shoe forces at various brake cylinder p r e s s u r e s were m e asu red on a Budd SR -4 s ta tic s tr a in indicator. F ig u r e 13 is a view of tne d y n a m o m e te r s h o e i n p l a c e a n d F i g u r e s 14 a n d 15 a r e v i e w s of t h e t e s t o p e r a t i o n . s m s d y n a m o m e t e r b ra k e s h o e was c a lib ra te d on a B aldw in u n i v e r s a l T e s tin g Machine in the test la b o ra to ry of the Seaboard Coast Line R ailroad a: W a y cro ss, Georgia. The c o m p o s itio n crake shoes used on the sw itch ers and road-sw itching type l o c o m o t i v e s of the S e a b o a r d C o a st L in e a r e of the h i g h f r i c t i o n type. This type of b ra k e sh o e is c o v e r e d by AAR S p ecific atio n M - 9 2 o - 6 5 . The s p ec ific atio n r e q u ir e s that the b r a k e shoes m eet conditions re la ted to the stopping distance f r o m v a r i o u s i n i t i a l s p e e d s u s i n g a l i g ht b r a k i n g l o a d of 2 , 000 lb. b r a c e s h o e f o r c e a n d a h e a v y b r a k i n g l o a d of 6, 000 lb. b r a k e s h o e f o r c e . T h e s p e c i f i c a t i o n a l s o i n c lu d es a s i m u la te d g r a d e te s t in which a w h e el on the b r a k e shoe d y n a m o m e t e r is ro ta te d continuously a g a in st the brake shoe to d e te r m in e the b ra k in g force under these conditions. The b ra k e shoe c v n a m o m e te r at the AAR R e s e a r c h D e p a r t m e n t is equipped to m a k e s t o p t e s t s u n d e r th e h e a v y b r a k i n g t y p e c o n d i t i o n s a n d t e s t s of b r e a k a w a y friction can also be m ad e using the d y n a m o m e te rs attached to this m achine. A s e r i e s of t e s t s w a s m a d e w ith c o m p o s i t i o n b r a k e s h o e s w h i c h w e r e of the s a m e design and type as those u sed in the field te sts at W ay cro ss, G eorgia. The p r o c e d u re for d e te r m in in g the stop distance u nder the heavy b ra k in g serie s d esc rib ed in A A R S p e c i f i c a t i o n M - 9 26- 65 w a s u s e d to m e a s u r e the s t o p p i n g d i s t a n c e with the v a r i o u s g o e s of b r a n s shoes. The s tatic coefficient of f r i c t i o n was d e t e r m i n e d by o b s e r v i n g the d e f l e c t i o n of the d y n a m o m e t e r p e n w h e n the w h e e l was r o t a t e d a g a m s t a b r a k e s h o e w i t h a f o r c e a p p l i e d r a n g i n g f r o m 2, 5 8 7 t o 6, 0 0 0 l b. T h e brake force value obtained from the dyn am o m eter is directly convertible to static coefficient of f r ic tio n . RESULTS The field t e s t s w e re conducted on the W a y c ro s s F r e i g h t L ea d on the J a c k s o n v i l l e m a i n l i n e of t h e S e a b o a r d C o a s t L i n e R a i l r o a d s t a r t i n g o n A. p r i l 1 5, 19 68 . S t o p p i n g t e s t s w e r e b e g u n th e f o l l o w i n g d a y a n d c o n t i n u e d t h r o u g h A p r i l 19, 1968. A list of th o se in a t t e n d a n c e is shown in T able 1 and show s the days curing w hich th e y w e r e p r e s e n t f o r the fie ld i n v e s t i g a t i o n s . T a b l e 2 s h o w s a s c h e d u l e of the t e s t s as they w e r e c o n d u c te d on the d iffe re n t ty p es of l o c o m o t i v e s , b ra k e shoe a r r a n g e m e n t s , a n d b r a k e s h o e s . F i g u r e 16 is a co p y of a d a t a s h e e t p r e p a r e d for r e c o r d i n g the stop test inform ation. A s i m i l a r f o r m of d a t a sheet was used for re c o rd in g in fo rm a tio n in the locom otive static d ra w b a r te s ts . * STOP DISTANCE TESTS Stop distance tests were conducted with locom otives used m switching s e r v i c e a t s p e e d s u p t o 14 . 5 m o h . T h e t e s t t r a i n i n e a c h c c . s e c o r . s i s t e ti of t h e l o c o m o t i v e , i n s t r u m e n t c a r J 5 C L US 4-1) a n d a t r a i l i n g L a i d o f i, o b i t m s m i s u p of MR-448 44520-6 15 g o n d o l a c a r s l o a d e d w i t h s c r a p m e t a l . T h e g o n d o l a c a r s w e r e e q u i p p e d w i t h pi am. b e a r i n g s . F i g u r e 17 s h o w s t h e g o n d o l a c a r s u s e d f o r t h e s t o p d i s t a n c e tests. The tram lin e was connected throughout the train and c h a rg e d with air. However, for the s t o p t e s t s only, the ind ep en d e n t b r a k e w a s u s e d to stop the tra m and to actuate i n s tr u m e n ta tio n m e a s u r i n g stooping tim e , d i s t a n c e and brake cylinder p r e s s u r e build-uo. Siv T y p e L o c o m o t i v e s w i t h Gl a s n B r a k e A r r a n g e m e n t T w o l o c o m o t i v e s of the SW-9 t y p e (1, 200 HP) w e r e s e l e c t e d to m a k e to o d i s t a n c e t e s t s and to c o m p a r e the s t o p p i n g c a p a b i l i t i e s of c o m p o s i t i o n s h o e s with ca st i r o n flan g e d s h o e s . L o c o m o t i v e No. 155 w h i c h w a s e q u i p p e d w ith the c a s t i ro n H a n g e d s h o e s , h a d a r a i l w e i g h t o: 247, 100 l b . , 34 p s i b r a k e c y l i n d e r p r e s s u r e a n d a t h e o r e t i c a l b r a k i n g r a t i o of 56. 8 p e r c e n t . L o c o m o t i v e No. 147 w a s used for tests with c o m p o s i t i o n shoes and w e ig h e d 246, 600 lb. B r a k e cy lin d er p r e s s u r e s u s e d on L o c o m o t i v e No. 147 w e r e 27 p s i g i v i n g 45. 0 p e r c e n t b r a k i n g r a ti o a n d 53 p s i r e s u l t i n g in 55. 2 p e r c e n t b r a k i n g r a t i o . T h e d a t a f r o m t h e s e stop d is ta n c e te s ts a r e plotted m F i g u r e 18. T his plot s h o w s t h a t at sp eeds b e low 4 m p h , the s t o p p i n g d i s t a n c e w as i n d e p e n d e n t of the t y p e of s h o e u s e d at the brace pressures investigated. t o 90 f t . s t o p p i n g d i s t a n c e . S t o p p i n g t h e t e s t t r a i n f r o m 4 m e n r e q u i r e d SO ft . , At speeds exceeding 4 mph, the com position brake sh o es show a definite trend toward sh o rten ed stopping distances and this trend b e c o m e s m ore pronounced a s t ne i n i t i a l s p e e d i n c r e a s e s . F o r e x a m p l e , s t o p p i n g f r o m a s p e e d of 10 m p h u sing c o m p o s i t i o n s h o e s an d 27 p s i b r a k e c y l i n d e r p r e s s u r e r e q u i r e d 510 ft. c o m p a r e d to 775 ft. r e q u i r e d fo r the l o c o m o tiv e e q u ip p e d with c a s t i r o n sh o es with a higr.er b r a k i n g r a t i o a n d 34 p s i b r a k e c y l i n d e r p r e s s u r e . In th e c a s e of the c o m p o s i t i o n s h o e a r r a n g e m e n t w i t h 33 p s i b r a k e c y l i n d e r p r e s s u r e , l o c o m o t i v e w h e e l S l i c i n g o c c u r r e d ( s e e F i g u r e 18) w h e n m a k i n g a s t o p f r o m 5. 8 m p h , i n d i c a t i n g a Gracing ra tio for the co n ditions u n d e r which this lo c o m o tiv e w a s u s e d to step the t r a m that cannot be e x c e e d e d without r i s k of sliding w heels. CP-1 L o c o m o t i v e s (1, 500 HP) with C l a s p B r a k e A r r a n g e m e n t L o c o m o t i v e s No. 773 and No. 805 of this s a m e type a n d h a v in g cla s p b r a k e a r r a n g e m e n t s w e r e u s e d in the s t o p p i n g d i s t a n c e t e s t s . L o c o m o t i v e No. 775 w as e q u i p p e d w i t h c a s t i r o n b r a k e s h o e 3 a n d h a d a b r a k e c y l i n d e r p r e s s u r e of 45 p s i w.mch p r o v i d e s 52. 3 p e r c e n t b r a k i n g r a t i o b a s e d on a r a i l w e i g h t of 247, 900 lb. L o c o m o t i v e No. 8 0 5 w e i g h e d 244, 900 lb. a n d w a s e q u i p p e d w i t h c o m p o s i t i o n b r a k e sn o es. T h e b r a k e c y l i n d e r p r e s s u r e s on L o c o m o t i v e No. 805 w e r e v a r i e d f r o m 27 p s i p r o d u c i n g 31. 6 p e r c e n t b r a k i n g r a t i o to 45 p s i g i v i n g 52 . 9 p e r c e n t b r a k i n g r a ti o . D a t a f r o m f i v e s e r i e s of stop t e s t s on the G P - 7 l o c o m o t i v e s with b r a k e a r r a n g e m e n t a r e s h o w n in g r a p h i c a l f o r m in F i g u r e 19- T h e d a t a s h o w n - i n F i g u r e 19 i n d i c a t e t h a t t he s t o p d i s t a n c e f r o m 4 m p h f o r the c a s t i r o n shoe a n d f o r the t h r e e h i g h e s t b r a k e c y l i n d e r p r e s s u r e s in the c o m p o s i t io n shoe a r r a n g e m e n t w e r e b e t w e e n 80 to 100 ft. With a b r a k e c y l i n d e r p r e s s u re of 27 p si f o r t h e c o m p o s i t i o n shoe, the sto p d i s t a n c e i n c r e a s e d to 142 As t-.e i n i t i a l s p e e d i n c r e a s e d , the c o m p o s i t i o n shoe'-; s h o w e d a m o r e : l a v e ; a b l e t r e n d MR-44S 44520-7 toward sh o rter stopping distance when com pared with cast iron shoes. Above 5. 2 m o h , t h e s t o p p i n g d i s t a n c e s o b t a i n e d w i t h c a m no s it i o n s h o e s ( e x c e p t t o r t h e a r r a n g e m e n t - w i t h 27 p s i b r a k e cy lin d e r p r e s s u r e ) w e re c o n s i d e r a b l y b e tte r than the c a s t i r o n s h o e b r a k e . At 10 m p h , t he c a s t i r o n s h o e w a s e q u i v a l e n t to t h e c o m p o s i t i o n s h o e w i t h 27 p s i b r a k e c y l i n d e r p r e s s u r e a n d a t s p e e d s a b o v e 10 m p h , all of t h e c o m p o s i t i o n sh o e a r r a n g e m e n t s p r o v i d e d a b e t t e r s t o p p i n g d i s t a n c e c o n d i t i o n t h a n t he c a s t i r o n s h o e s . At a n i n i t i a l s p e e d of 10 m p h , f o r e x a m p l e , t he s t o p p i n g d i s t a n c e w a s 490 ft. for c o m p o s i t i o n s h o e s with 45 p s i b r a k e c y l i n d e r p r e s s u r e . The c a s t iro n shoe u n d er the s a m e conditions of b r a k e c y l i r o e r p r e s s u r e o u t w it h s l i g h t l y l o w e r b r a k i n g ra ti o , h a d a stoD d i s t a n c e of 725 it. G P -7 l o c o m o t i v e s with Single Shoe B rake A r r a n g e m e n t A. G P - 7 l o c o m o t i v e w i t h a s i n g l e s h o e b r a k e a r r a n g e m e n t a n d s ition s h o e s was c o m p a r e d with L o c o m o tiv e No. 773 which had a c l a s p m e n t a n d c a s t i r o n s h o e s . . A.s p r e v i o u s l y d e s c r i b e d , L o c o m o t i v e No . . , 3 w e i gtoh e d 247, 900 lb. and h a d a 45 p si B rake cy lin d e r p r e s s u r e r e s u l t i n g m a br eaing ra tio oi 52. 3 p e r c e n t . T h e s i n g l e s h o e a r r a n g e m e n t w i t h a c o m p o s i t i o n s h e e in p l a c e is s h o w n m F i g u r e 20 a n d w a s a p p l i e d to G P - 7 L o c o m o t i v e No. 79 6. T h is l o c o m o t i v e w e i g h e d 248, 200 lb. a n d b r a k e c y l i n d e r p r e s s u r e s of 45 p s i to 74. 5 ps : v/ere inv estig ated in this study. These brake cylinder p r e s s u r e s re su lted , n ssnectively, in a b r a k i n g r a t i o r a n g e of 26. 1 p e r c e n t to 43. 6 p e r c e n t . The c o m p a riso n between the stopping distances with c a s t iron shoes and c o m p o s i t i o n s h o e s is show n g r a p h i c a l l y in F i g u r e 21. The s t o p d i s t a n c e c u r v e s on t h i s g r a p h f o r L o c o m o t i v e No. 796 is s i m i l a r to the c u r v e s d e v e l o p e d by the locom otive having the clasp com position shoe brake a rra n g e m e n t. At crake cylin der p r e s s u r e s a b o v e 58.5 psi, the c o m p o sitio n shoe lo c o m o tiv e s have substantially the s a m e stopping capabilities fr o m 4 m ph as the cast iro n shoe equipped l o c o m o tive. T h i s s t o p p i n g d i s t a n c e r a n g e s f r o m 85 to 108 ft. f r o m a n i n i t i a l s p e e d of 4 m p h . A bove 10 m p h , all of the t e s t s with the c o m p o s i t i o n s h o e s t h r o u g h o u t the e n t i r e r a n g e of b r a k e c y l i n d e r p r e s s u r e s p r o v i d e d b e t t e r s t o p p i n g d i s t a n c e s th an c a s t i r o n s h o e s a l t h o u g h L o c o m o t i v e No. 79 6 w a s e q u i p p e d w i t h a si n g le s h o e brake a r r a n g e m e n t m com parison with the clasp a rra n g e m e n t on Locomotive No. 773. At 8 m p h , e x c e p t f o r .t h e c o m p o s i t i o n shoe l o c o m o t i v e with 45 psi b r a k e c y lin d e r p r e s s u r e , the stopping d istan ce s for the co m p o sitio n sh o es was e q u iv a l e n t to o r b e t t e r t h a n t h e c a s t i r o n s h o e p e r f o r m a n c e . F o r e x a m p l e , a: a n i n i t i a l s p e e d of 8 m p h , t h e s t o p p i n g d i s t a n c e f o r t h e c o m p o s i t i o n s h o e w i t h 74. 5 p s i b r a k e c y l i n d e r p r e s s u r e w a s 322 ft. c o m p a r e d to the 422 ft. s t o p p i n g d i s t a n c e i r o m the sam e initial speed for the cast iron shoe. C o m p a r i s o n of C o m p o s i t i o n Shoe T y p e s on the SW-9 L o c o m o t i v e T h e s t o p p i n g d i s t a n c e d a t a s h o w n in F i g u r e 18 w a s o b t a i n e d with a C o b r a B ra k e Shoe, Type V-149 m a rk e te d by W estinghouse Air B r a k e Co. A brake shoe d e sig n fo r the sam'bbe application is sold by Griffin Wheel Co. and is called the A nchor Shoe, Type H-71-6. These shoes w ere com pared u n d e r the same condi tio n s o n L o c o m o t i v e No. 147, an S W -9 type s w i t c h e r . T h e s h o e s w e r e c o m p a r e d using 27 psi b r a k e cylinder p r e s s u r e re su ltin g in a 45.0 p e r c e n t bra.king ratio. 1 h e s p e e d a n d s t o p d i s t a n c e i n f o r m a t i o n i s s h o w n m F i g u r e 2 2 .'.such ... u v s t h a t M R -448 44520-8 th ese two b r a n d s of c o m p o s i t i o n b r a k e s h o e s p r o d u c e d the s a m e s t o p d i s t a n c e c u r v e i n d i c a t i n g n o d i f f e r e n c e 'i n s t o p p i n g c h a r a c t e r i s t i c s b e t w e e n t h e s h o e s t e s t e d . C o m p a r i s o n of -Brake Shoe T y p e s on the G P - 7 T y n e L o c o m o t i v e w i th oingie 5noe Braking A r r a n g e m e nt T h e i n f o r m a t i o n p r e s e n t e d m F i g u r e 21 f o r t h e c o m p o s i t i o n s h o e s on L o c o motive No. 79b was b a s e d on the C o b r a B r a k e Shoe, T ype V-1Q3, m a r k e t e d by Wesim.ghouse Air B ra k e Co. Two other co m p o sitio n b ra k e shoes w e re used tor com parison with the C o b ra type shoe using a single shoe a r r a n g e m e n t on l o c o m o tive l-o. 796. T h e s e s h o e s w e r e the A n c h o r Tim e H - 2 5 - 2 s h o e s o l d by C-rUtin Whet- Co. a n d the C o m e t T y p e C - 1 5 8 s h o e p r o d u c e d by A b e x C o r e . All ct t h e s e shoes w e r e s tudied u s i n g a b r a k e c y lin d e r p r e s s u r e of 67. 5 n s i r e s u l t i n g m a bra.-tir.g r a t i o of 39. 2 p e r c e n t . T h e d a t a d e v e l o p e d i n t h i s s e r i e s c: t e s t s a r e p r e s e n t s : in F i g u r e 23. The c u r v e s for sto p p in g d i s t a n c e s r e s u l t i n g f r o m the u s e of all tr.ree b r a k e s h o e ' t y p e s follow a s i m i l a r p a t t e r n and w i t h i n the l i m i t s of r e p r o d u c e u i t y , it: a p p e a r s t h a t t h e - t h r e e b r a k e s h o e t y p e s c a n b e c o n s i d e r e d e c u i v a i e n t for tats type of ap p lic a tio n . STATIC DRAWBAR TESTS S tatic d r a w b a r te s t s w e r e co n ducted on e a c h type of l o c o m o t i v e by v a r y in g the crake c y lin d er p r e s s u r e and noting the d r a w b a r pull load d e v e lo p e d on the d y n a m o m e te r co u p ler when the wheels on which the b ra k e was ap p lied on the test locomotive first began to rotate. Since the d y n am o m eter coupler limit was 50, C.O l b . , w h i c h w a s b e l o w t h e f o r c e s t h a t w o u l d d e v e l o D w i t h t h e b r a k e o n a l l w h e s - s , t h e b r a k e s w e r e a p p l i e d t o o n l y o n e t r u c k of t h e t e s t l o c o m o t i v e . -The bra.-ie a p p l i c a t i o n w a s m a d e to t h e l e a d t r u c k in on e s e r i e s of t e s t s a n d to the trai-mg tru ck m a second series. The tests were begun at 0 b ra k e cylinder p r e s sure ;o d e t e r m i n e the t r a i n r e s i s t a n c e of the. l o c o m o t i v e at s t a r t i n g . F i g u r e 24 snow: the a r r a n g e m e n t u se d on the static d ra w b a r pull te s ts in w hich L ocom otive No . _:>5, a n S W - 9 t y p e , i s b e i n g t e s t e d f o r b r e a k a w a y r e s i s t a n c e . L o c o m o t i v e No. - /3, a G P - 7 ty p e, w a s u s e d to p r o v i d e th e d r a w b a r p u l l a n d b r e a k a w a y f o r c e to X c c o m o t i v e No. 155. F i g u r e 25 s h o w s a s i m i l a r a r r a n g e m e n t w h e r e L o c o m o tive ho. 79b with a single shoe b ra k e rig g in g a r r a n g e m e n t is b e in g pulled by L o cc m o tiv e No. 805 th ro u g h the d y n a m o m e t e r d r a w b a r a r r a n g e m e n t . F i g u r e 26 is a p l o t of the d a t a o b t a i n e d in s t a t i c d r a w b a r t e s t s . The s c a t t e r 01 p a n t s s h o w s t h e w i d e r a n g e of v a l u e s d e t e r m i n e d a t e a c h b r a k e c y l i n d e r p r e s sure setting. The total r e s is ta n c e to b re a k a w a y fo r c e r e p r e s e n t e d by the d r a w b a r pull is s h o w n in F i g u r e 26 and includes b r a k e shoe r e s i s t a n c e an d lo c o m o tiv e t r a i n r e s i s t a n c e . F i g u r e 27 show s static d r a w b a r c u r v e s d e v e lo p e d b y s u b t r a c t i n g the loccm otive tr a in r e s i s t a n c e with no b ra k e applied f r o m the v a lu e s obtained with the crak e applied u n d e r v a r io u s b rak e c , . m a e r p r e s s u r e s . T a b le 3 shows the average v a lu e s for s ta rtin g re s is t a n c e for the five l o c o m o tiv e s u s e d in the te s t when no b r a k e was a p p lied . T h e s e v a l u e s r a n g e f r o m 625 lb. f o r L o c o m o t i v e No. .96 t o 6, 250 lb. f o r L o c o m o t i v e No. 7 7 3 . T h e l o c o m o t i v e s o n w h i c h t h e c a s t iron sn oes had bee n applied and w o r n - i n p r i o r to m a k in g the t e s t s had a s o m e w h a t higner s t a t i c r e s i s t a n c e than the l o c o m o t i v e s on w hich c o m p o s i t i o n shoes had b een aPF-:ed and w o r n - in p r i o r to test. This v a ria tio n in the l o c o m o t iv e t r a m r e s i s t a n c e MR-448 44520-9 is ?.r. e f f e c t t h a t a p p e a r s t o d e v e l o p b e c a u s e t h e c o m p o s i t i o n s h o e d o e s n o t c r e a t e a b u i l d - u p of b r a k e sh o e m e t a l on the w h e e l t r e a d an d c o n t i n u o u s l y keeps the w heel tread m a r e la t iv e ly s m o o t h condition. With c a s t iron, shoes, the brake shoe m e ta l develops a ro u g h e n e d t r e a d condition b e c a u s e oi the lo c a liz e d heating and a b r a s io n which o c c u rs during b ra k e applications. This diffe ren c e in tr e a d condition may explain in p a r t the v a r i a t i o n in starting r e s i s t a n c e found b e tw e e n tne locom otives equipped with the two ty p es of shoes. R e f e r r i n g to F i g u r e 27, it is e v i d e n t t h a t the b r a k e c y l i n d e r p r e s s u r e fo r a locom otive equipped with c o m p o sitio n shoes which is r e q u ir e d to develop the sam e b r e a k a w a y r e s i s t a n c e a s a l o c o m o t i v e e q u i p p e d with c a s t i r o n s h o e s , is s o m e w h a t g r e a t e r . T h i s e f f e c t d e v e l o p s f r o m t n e f a c t t h a t t he c o e f f i c i e n t cl f r i c t i o n of c a s t iron on s te e l at e x t r e m e l y low speeds a p p r o a c h i n g z e r o is high, w n e reas the coeiiicient of f r ic ti o n of c o m p o s i t i o n s h o e s on s t e e l w h e e ls is m o r e u niform over a wide speed range and does not in c re a s e at v e ry low speeds approaching zero. L o c o m o t i v e s No . 1 4 7 a n d 3 0 5 w h i c h w e r e , r e s p e c t i v e ! ' / , an. S W - 9 a n a C- P - 7 t y p e both having clasp b ra k e s , showed esse n tia lly the s a m e b re a k a w a y resistance. 3 o th of t h e s e l o c o m o t i v e s w e r e e q u i p p e d with c o m p o s i t i o n b r a k e sh o e s. L o c o m o tive No. 79 6, a G P - 7 t y p e r o a d s w i t c h e r e q u i p p e d w i t h a c o m p o s i t i o n single sho e brake arra n g e m e n t, showed a m ark ed ly lower value c: breakaw ay resistance for all b r a k e c y l i n d e r p r e s s u r e s . The s a m e c o m p a r i s o n did not a p p l y in the c a s e of l o c o m o t i v e s e q u i p p e d w ith c a s t iro n c l a s p shoe b r a k e a r r a n g e m e n t as is evident i r o m t h e p l o t t e d d a t a . L o c o m o t i v e No . 155, an. S W - 9 t y p e s w i t c h e r , s h o w e d a m u c h h i g h e r s t a t i c r e s i s t a n c e th ro u g h o u t the r a n g e of b r a k e c y l i n d e r p r e s s u r e s te s te d t h a n did G P - 7 L o c o m o t i v e No. 773 w h ic h was a l s o e q u i p p e d with a c la s p brake arrangem ent having cast iron shoes. D E T E R M IN A T IO N OF BRAKE F O R C E S A. d y n a m o m e t e r b r a k e s h o e w a s u s e d t o s t u d y t h e b r a k i n g p r e s s u r e s on. tne lo c o m o tiv e s u s e d in the field test-w ork. The th e o re tic a l b ra k in g p r e s s u r e w a s c o m p u t e d a n d t h e c u r v e f o r t h i s s t a k i n g , f o r c e is s h o w n o n F i g u r e 28 f o r G P -7 l o c o m o t iv e s u s e d in the tests. ' T his stu d y was not m a d e for the SW-9 locom otives b ec au se the d y n a m o m e te r brake shoe was dam aged and required extensive re p a ir. This w o rk is scheduled to be conducted at a la te r time. F ig u r e 28 a l s o s h o w s t h e v a r i a t i o n of s h o e f o r c e w i t h b r a k e c y l i n d e r p r e s s u r e as determ in ed by the d y n a m o m e te r brake shoe. The ra n g e s of shoe fo rce for e a c h brake cylinder p r e s s u r e used are quite large. This can be explained by a difference in the brake rigging efficiency durmg any p a r t i c u l a r t e s t . W ith the v i b r a t i o n of l o c o m o t i v e m o v e m e n t , it is e x p e c t e d that the b r a k i n g f o r c e w o u ld have a m o r e n a r r o w r a n g e than is shown m F ig u r e 28. T h is f i g u r e a l s o s h o w s t h a t t he shoe f o r c e r a n g e s f o r L o c o m o t i v e No. 773, with th e c a s t i r o n s h o e c l a s p b r a k e , is s i m i l a r to the s h o e f o r c e r a n g e f o r e a c h of the G P - 7 locomotives equipped with composition shoes. T h e r e is n o t s u f f i c i e n t d i f f e r e n c e in the i n f o r m a t i o n d e v e l o p e d in this s t u d y of b r a k i n g f o r c e s to i n d i c a t e t h a t o n e t y p e of b r a k e s h o e a r r a n g e m e n t or s h o e t y p e has an advantage over the other types tested. v R-44`8 44520-10 'OIIV . l\ The fiv e-ty p es of high i n c u o n c o m p o sitio n fcrske s h o e s s tu d ie d in the f i e l d i n v e s t i g a t i o n s w e r e a l s o s t u d i e d on t h e b r a k e so oe d y n a m o m e t e r m a c n i n e at the AAR R e s e a r c h L a b o r a t o r y . This w o rk was divided into s to p d is ta n c e tests and static c o e f f i c i e n t of friction tests. The b ra ce shoe p r e s s u r e was 6, 000 I 'd . p e r s h o e a n d s i n g l e s h o e t e s t s w e r e u s e d i : r t h e s t o p p i n g d i s t a n c e cata. T h e w h e e l l o a d or. r a i l was e o u i v a l e n t to 20, ; . . lb. 3 : od D i s t a n c e T e s t s T he stop d i s t a n c e t e s t s w e r e c o n d u c t e d in a c c o r d a n c e w ith tr.e sch e d u le f or h e a v y b r a k i n g t e s t s d e s c r i b e d m A A R S p e c i f i c s : : :r. M . - 9 2 6 - 6 5 . A 3 3 - m. c i a m e t e r w ro u g h t s te e l w h e el was used in th ese testa r e q u i r i n g th at tne Drake shoes be m a c h in e d to the approxim ate wheel radius emee the sh o e s u sed m the se s tu d ie s w e r e d e s i g n e d for lo c o m o tiv e s having a l a r g e r w h e e l d i a m e t e r than 33 in. T h e w h e e l t r e a d was hig h ly p o l i s h e d with a s p e c i a l b r a k e s h o e "and ea ch b r a k e shoe w a s iv o rn -ir. on the wheel to obtain a good b e a r i n g condition. P rio r to e a c h s t o p - d i s t a n c e run, the w heel tr e a d was cooled to a t e m p e r a t u r e not e x c e e d in g a m a x i m u m of 125F. Data for each b ra k e shoe type from the stop-c:stance te s ts w ere avera t e d f o r e a c h i n i t i a l s p e e d a n d t h i s i n f o r m a t i o n i s p r e s e n t e d i n T a b l e 4. AT i n itial s p e e d s of 10 a n d 30 m p h , all of th e b r a k e s h o e s w e r e w i t h i n t h e r a n g e of scop-distance v a lu e s g iv e n in the Specification. At these s p e e d s t h e r e was little difference noted in the s top-dis tanc e p erfo rm an c e among the b r a k e snoes studied. At 50 m p h i n i t i a l s p e e d , t h e b r a k e s h o e s g e n e r a l l y w e r e w i t h i n t h e p r o p e r r a n g e of v a l u e s t a k i n g i n t o a c c o u n t s l i g h t n o r m a l d e v i a t i o n s f r o m e x p e r i m e n t a l e r r o r . Shoe K - 2 6 - 4 was an e x c e p t i o n at this speed v/ith the a v e r a g e sto p p in g distan ce b e i n g 1, 6 9 2 f t . . H o w e v e r , a l l s t o p s m a d e a t 10 a n d s i m p h w e r e s u r p r i s i n g l y c o n s i s t e n t . T h e m a j o r e x c e p t i o n in t h e 50 a n d 70 m e n s t o p t e s t w a s t h e G r i f f i n H-26-4 shoe. Other than this variable, all results were consistent. Static C o effic ien t of F r i c t i o n Tests The m e a s u r e m e n t of static and k in etic f r ic tio n at l o w s p e e d s is difficult and is likely to show w ide variations, p a r ti c u la r l y when usin g a s i m u la te d w heel and b ra k e shoe a s s e m b l y . No laws on fric tio n a r e absolute in p r a c t i c e and each one is m o d ifie d f o r c e r t a i n c i r c u m s t a n c e s . The co eificien t of f r i c t i o n , as was seated e a r l i e r , is i n d e p e n d e n t of the s p e e d of m o v e m e n t b e t w e e n t h e tw o c o n t a c t s u r f a c e s . S o m e e x p e r i m e n t s have show n that the time of c o n t a c t of the s u r f a c e s a i f e c t s t h e c o e f f i c i e n t of f r i c t i o n . T h e c o e f f i c i e n t c: f r i c t i o n is s l i g h t l y g r e a t e r lor sm all e n s u r e s on la rg e areas than for high p r e s s u r e s on s m a l l a re a s. With all of t h e s e v a r i a b l e s in c o m b i n a t i o n with the v a r i a b l e r e s u l t i n g f r o m f r i c t i o n in the b r a k e rig g in g , t h e r e h a s been a r e a s o n a b l e d e g r e e of c o n s i s t e n c y in the r e a d ings obtained d u rin g the la b o ra to ry tests. T a b l e 5 s h o w s the s t a t i c coe fficient of f r ic t:;:i for v a r i o u s c o m p o s i t i o n s h o e s a n d o n e c a s t i r o n b r a k e s h o e . It w i l l be note:: t h a t t h e V - L 0 3 c o m p o s i t i o n MR r 448 445 2 'ONS 1. B raking force developed by the b ra k e s y s te m is d e p e n d en t open the f u n d a m e n t a l s of coefficient of fr ic ti o n of the b r a k e shoe cr. t he w h e e l a n d p r e s s u r e a p p l i e d o n t he s h o e . 2- The stopping d is ta n c e s m e a s u r e d in the test c o v e r e d by the x c r e g o i n g d a t a a r e i n d e p e n d e n t of the type b r a k e s h o e o r w h e t h e r single or clasp b rak es are used, provided that o ro o e r coefficient c: m o t i o n of b r a k e s h o es and b r a k e shoe p r e s s u r e a r e u s e d in Ir.t d e s i g n . 3. B r a k e s h o e p r e s s u r e s that- d e v e l o p r e s t r a i n i n g f o r c e s g r e a t e r tr.an c a n be w i t h s t o o d by the w h e e l - r a i l c o n t a c t will r e s e k 'in the tendency to re d u c e braking effort and c a u se slid fiat w h e e ls . 4. B ra k e s y s t e m s should be designed and m a in ta in e d for the type of b r a k e shoe it is d e s i r e d to use. 5. Wide v a r i a t i o n s in the c o e f f i c i e n t of f r i c t i o n of c o m p o s i t i o n bra.-te s h o e s of the m a n u f a c t u r e r s ' s h o es that w e r e t e s t e d w e r e no: shown to exist in this investigation. 6. The c o e ffic ie n t of fric tio n v a lu e s for the c a s t i r o n sh o e c o m pared with the com position shoes are sufficiently s im ila r to p e r m i t u s e of e i t h e r type of shoe p r o v i d e d p r o p e r b r a k e c y l i n d e r p r e s s u r e is m a in ta in e d and suitable le v e r ratios a r e u s e d in the design. D irector Apprcved, As s is tans Vice P r e s id e n t Approved for R elease, Vice P resident P r i n t e d and d i s t r i b u t e d by the A s s o c i a ti o n of A m e r i c a n R a i l r o a d s , Chicago, I l l i n o i s . No p a r t of t h i s r e p o r t m a y be r e p r o d u c e d w i t h o u t f i r s t o b t a i n i n g p e r m i s s i o n f r o m t h e Vice. P r e s i d e nt - R e s e a r c h, A A R R e s e a r c h C e n t e r , 3140 5. F e d e r a l S t r e e t , C h i c a g o , I l l i n o i s 6061 b.