USE

OF

SEALING

EFFICIENCY V.

I

OF

MATERIALS

TO

SCREW-ACTION

Ardashev

and

A.

M.

INCREASE

THE

MACHINES Korenev

UDC 62.762:[621.515.4+621.592.3]

The r e s u l t s of t e s t i n g s c r e w - a c t i o n e x p a n s i o n engines [1] and c o m p r e s s o r s [2] show that the p r i n c i p a l p a r t of the l o s s in p r o d u c t i v i t y and e f f i c i e n c y in t h e m is a s s o c i a t e d with g a s o v e r f l o w s through the gaps between w o r M n g e l e m e n t s of the m a c h i n e s . The magnitude of the t r a n s f e r a r e a of the gap s e c t i o n s d e pends on the q u a l i t y of f a b r i c a t i o n of the s c r e w s , the body, the b e a r i n g p a r t s , and the a s s e m b l y of the whole m a c h i n e , and a l s o on the p r o f i l e of the s c r e w peaks. Reducing the a r e a of the gap t r a n s f e r s e c t i o n is p o s s i b l e via t h r e e m e t h o d s : by i n c r e a s i n g the a c c u r a c y of f a b r i c a t i o n of i n d i v i d u a l p a r t s or the a s s e m b l y of the whole m a c h i n e ; by i n s t a l l i n g s e a l i n g bands " f e e l e r s " - at the ends and tops of the s c r e w teeth; or by placing a l a y e r of s e a l i n g m a t e r i a l on the s u r f a c e of the w o r k i n g e l e m e n t s of the s c r e w machine. -

When the f i r s t two m e t h o d s a r e used, the technology of f a b r i c a t i o n is m a d e m o r e c o m p l e x and the cost of the b a s i c m a c h i n e p a r t s is c o n s i d e r a b l y i n c r e a s e d . The t h i r d method of r e d u c i n g the t r a n s f e r a r e a of the gap s e c t i o n s is s i m p l e s t and c h e a p e s t . The g r e a t e s t effect is a c h i e v e d when a l a y e r of s e a l i n g m a t e r i a l is p l a c e d on the s u r f a c e of the worMng e l e m e n t s while the m a c h i n e is operating. In this e a s e , the t e m p e r a t u r e of the worMng e l e m e n t s is a l r e a d y s t a b i l i z e d and the l a y e r of s e a l i n g m a t e r i a l is l a i d down u n i f o r m l y on t h e i r s u r f a c e , c o m p e n s a t i n g for a l m o s t alI e r r o r s a s s o c i a t e d with f a b r i c a t i o n o r c a u s e d by temperature deformations. The t h i r d method was w o r k e d out in the N. ~. Bauman Moscow T e c h n i c a l College and was checked out e x p e r i m e n t a l l y on s c r e w - t y p e m a c h i n e s whose b a s i c d i m e n s i o n s a r e given in Table 1. F r o m the o p e r a t i n g conditions of s c r e w e x p a n s i o n engines, the following r e q u i r e m e n t s a r e i m p o s e d on a s e a l i n g m a t e r i a h a b i l i t y to a d h e r e f i r m l y to the s u r f a c e of p a r t s ; high h a r d n e s s of the f i l m f o r m e d ; r e s i s t a n c e of the f i l m to w e a r (this p r o p e r t y depends d i r e c t l y on f i l m h a r d n e s s ) ; sufficient i m p a c t s t r e n g t h (which depends on the p l a s t i c i t y of the coating and i t s a d h e s i v e f o r c e to the m a t e r i a l ) ; p o s s i b i l i t y of u s e at t e m p e r a t u r e s c o r r e s p o n d i n g to the o p e r a t i n g r e g i m e of the m a c h i n e ; a s m a l l d r y i n g out t i m e ; and the p o s s i b i l i t y of i n j e c t i n g it in a s p r a y f o r m in the gas s t r e a m which is e n t e r i n g the machine. On the b a s i s of t h e s e r e q u i r e m e n t s , we s e l e c t e d a s s e a l i n g m a t e r i a l g l y p t a l p r i m e r G F - 0 2 0 , which is w i d e l y used in m a chine c o n s t r u c t i o n plants and is s e r v i c e a b l e under conditions of a c t i o n of a t m o s p h e r i c d u s t s , s o l a r r a d i a tion, or m a r i n e s p r a y , in a t m o s p h e r e s c o n t a m i n a t e d with i n d u s t r i a l g a s e s and d u s t s , at a i r t e m p e r a t u r e s f r o m - 6 0 to +60~ and at r e l a t i v e h u m i d i t i e s up to 95% at 25~ [3]. Acetone was used as the t h i n n e r f o r the GF-020. The s e a l i n g m a t e r i a l - GF-020 p r i m e r - is fed into the i n t a k e p o r t in a t o m i z e d f o r m by a m e t e r i n g device. F e e d of the p r i m e r into the w o r k i n g c h a m b e r of the m a c h i n e is b e s t effected in s m a l l p o r t i o n s , of about 40-50 cm 3, at i n t e r v a l s of about 15-20 rain. Under such a feed r e g i m e , the p r i m e r l i e s down as a thin l a y e r on the w o r k i n g s u r f a c e of the m a c h i n e and has t i m e to d r y out somewhat b e f o r e feed of the next p o r t i o n of p r i m e r . To e v a l u a t e the e f f e c t i v e n e s s of the method being d i s c u s s e d , d u r i n g an e x p e r i m e n t we r e c o r d e d a l l the p a r a m e t e r s which c h a r a c t e r i z e the o p e r a t i n g r e g i m e of an e x p a n s i o n engine. Constancy of i n s t r u m e n t r e a d i n g s upon f e e d of the next p o r t i o n of p r i m e r c h a r a c t e r i z e s the obtaining of m i n i m u m c l e a r a n c e s b e tween w o r k i n g m a c h i n e e l e m e n t s . T r a n s l a t e d f r o m K h i m i c h e s k o e i Neftyanoe M a s h i n o s t r o e n i e , No. 11, pp. 5-6, N o v e m b e r , 1971.

I 9 1972 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article c a n n o t be reproduced for any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00.

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Fig. 1. D e p e n d e n c e of a d i a b a t i c e f f i c i e n c y c o e f f i c i e n t , ~ a d (a), a n d of a c t u a l v o l u m e t r i c p r o d u c t i v i t y , V a (b), of e x p a n s i o n m a c h i n e on d e g r e e of e x p a n s i o n , Gi (~ = P i / P f , w h e r e Pi a n d pf a r e the gas p r e s s u r e s at the e n t r a n c e a n d exit to the e x p a n s i o n engine): - - - ) b e f o r e d e p o s i t i o n of s e a l i n g m a t e r i a l ; - - ) a f t e r a p p l i c a t i o n of s e a l i n g m a t e r i a l ; 1) n 1 = 4500 r p m ; 2) n t = 12,000 r p m . Fig. 2. R e s u l t s of c h e c k i n g s t r e n g t h of s e a l i n g m a t e r i a l l a y e r : 1) at n 1 = 9000 r p m ; V a = 143 m 3 / h ; 2) at n 1 = 12,000 r p m ; V a = 200 m a / h .

TABLE1 E E

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i00

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A s p r i m e r i s fed into the e x p a n s i o n m a c h i n e and the t r a n s f e r a r e a of the gaps d e c r e a s e s , the flow of gas e s c a p i n g f r o m the high p r e s s u r e zone to the low p r e s s u r e zone d e c r e a s e s c o n s i d e r a b l y , due to which the a d i a b a t i c e f f i c i e n c y r i s e s . If the v a l u e of the a d i a b a t i c e f f i c i e n c y c o e f f i c i e n t of the e x p a n s i o n m a c h i n e with c l e a n r o t o r s on e x p a n d i n g a i r f r o m 2.5 to 1.0 arm, a t a n i n i t i a l t e m p e r a t u r e of 293~ w a s 0.47 at a m a s t e r r o t o r r p m , nl, equal to 4500 r p m , and 0.68 when n~ = 12,000 r p m , t h e n a f t e r d e p o s i t i n g a l a y e r of s e a l i n g m a t e r i a l the a d i a b a t i c e f f i c i e n c y c o e f f i c i e n t a t t a i n s v a l u e s of 0.65 and 0.86, r e s p e c t i v e l y (Fig. 1). The m a x i m u m v a l u e of the a d i a b a t i c e f f i c i e n c y c o e f f i c i e n t , which c o r r e s p o n d s to a m i n i m u m t r a n s f e r gap s e c t i o n a r e a , was o b t a i n e d a f t e r i n j e c t i n g 300 cc of p r i m e r into the e x p a n s i o n e n g i n e . In the g e n e r a l c a s e , the flow r a t e of p r i m e r into the m a c h i n e d e p e n d s on the g e o m e t r i c d i m e n s i o n s of the w o r M n g e l e m e n t s and the m a g n i t u d e of the c l e a r a n c e s b e t w e e n them. A f t e r the c h a r a c t e r i s t i c s had b e e n r e c o r d e d , the e x p a n s i o n m a c h i n e was t a k e n a p a r t for v i s u a l i n spection. Upon e x a m i n a t i o n it was found that a l l the s c r e w s u r f a c e s and body b o r i n g s w e r e c o a t e d with a c o m p a c t p r i m e r l a y e r of v a r i o u s t h i c k n e s s e s . The g r e a t e s t t h i c k n e s s of the s e a l i n g l a y e r w a s i n the s p a c e s of the m a s t e r a n d the d r i v e n r o t o r , that is, i n t h o s e p l a c e s w h e r e c o n t r o l of the c l e a r a n c e gap m a g n i t u d e i s e s p e c i a l l y difficult.

952

To d e t e r m i n e t h e s t r e n g t h of t h e c o a t i n g of s e a l i n g m a t e r i a l , w e c a r r i e d out t e s t s of t h e e x p a n s i o n m a c h i n e o v e r 110 h, in 66 h of w h i c h it o p e r a t e d a t n 1 = 12,000 r p m , and in 44 h of w h i c h it o p e r a t e d a t 9000 r p m . T h e s t a t e of t h e c o a t i n g l a y e r c o u l d be j u d g e d f r o m c h a n g e in flow r a t e of the g a s p a s s i n g t h r o u g h t h e m a c h i n e . [n F i g . 2 we show t h e r e s u l t s of t h e t e s t s . No c h a n g e in flow r a t e of t h e g a s p a s s i n g t h r o u g h t h e m a c h i n e w a s o b s e r v e d a f t e r t h e t e s t t i m e , w h i c h i n d i c a t e s t h a t t h e l a y e r of s e a l i n g m a t e r i a l w a s p r e s e r v e d . It s h o u l d b e n o t e d t h a t , d u r i n g t h e t e s t p e r i o d , t h e m a c h i n e w a s f r e q u e n t l y s t o p p e d and w a r m e d up to t h e s u r r o u n d i n g t e m p e r a t u r e (the t e m p e r a t u r e of t h e r o t o r s in t h e o p e r a t i n g m a c h i n e w a s 250-240~ T h u s , a t e m p e r a t u r e f l u c t u a t i o n in t h e w o r k i n g m a c h i n e e l e m e n t s w i t h i n the l i m i t s of 45-50~ e s s e n t i a l l y has no e f f e c t on t h e s t r e n g t h of t h e G F - 0 2 0 p r i m e r l a y e r . In s c r e w m a c h i n e s w h i c h o p e r a t e u n d e r other r e g i m e s ( c o m p r e s s o r s , f o r e x a m p l e ) , t e m p e r a t u r e f l u c t u a t i o n s of t h e p a r t s and of t h e g a s o v e r a w i d e r a n g e a r e p o s s i b l e . To e v a l u a t e t h e s t a b i l i t y of t h e p r i m e r l a y e r u n d e r s u c h c o n d i t i o n s , a d d i t i o n a l s t u d i e s a r e r e q u i r e d . If t h e l a y e r of s e a l i n g m a t e r i a l i s s t a b l e e v e n f o r a few h u n d r e d h o u r s of m a c h i n e o p e r a t i o n , t h e e c o n o m i c e f f e c t f r o m u s e of t h i s m e t h o d w i l l p r o v e to b e a p p r e c i a b l e . To r e s t o r e t h e s e a l i n g l a y e r in t h e w o r k i n g c h a m b e r of t h e m a c h i n e , it i s n e c e s s a r y to p e r i o d i c a l l y s u p p l y s m a l l p o r t i o n s of the s e a l i n g m a t e r i a l . F o r t h i s p u r p o s e , i n d u s t r i a l s e t ups s h o u l d b e p r o v i d e d w i t h v e r y s i m p l e m e t e r i n g d e v i c e s h a v i n g a s p r a y n o z z l e . T h e m e t h o d d e s c r i b e d w a s a l s o t e s t e d on a t w o - s t a g e c o m p r e s s o r , in o p e r a t i o n on h e l i u m . The r o t a t i o n r a t e s of t h e l e a d r o t o r s in t h e f i r s t a n d s e c o n d s t a g e s w e r e the s a m e , and equal to 15,500 r p m . T h e d e s c r i b e d v o l u m e of s t a g e I, Vhi, w a s 1342 m 3 / h . B a s i c D a t a O b t a i n e d in T e s t i n g C o m p r e s s o r s Before depositing l a y e r of s e a l i n g material Excess pressure, kg/cm2: on i n t a k e : stage I ...................... s t a g e II . . . . . . . . . . . . . . . . . . . . . on d i s c h a r g e : stage I ...................... s t a g e II . . . . . . . . . . . . . . . . . . . . . Temperature, ~ in i n t a k e of s t a g e s I a n d II . . . . . . . . . . in d i s c h a r g e : of s t a g e I . . . . . . . . . . . . . . . . . . . . of s t a g e II . . . . . . . . . . . . . . . . . . . . C o m p r e s s o r output, k g / h . . . . . . . . . . . Delivery coefficient ...............

After deposition of s e a l i n g m a terial layer

0.65 2.35

0.6 2.2

2.35 5.3

2.2 6.0

20

20

236 239 0 0

170 172 193.5 0.557

A s e v i d e n t f r o m t h e d a t a g i v e n , the t e m p e r a t u r e on c o m p r e s s i o n w a s c o n s i d e r a b l y r e d u c e d , a n d t h e d e l i v e r y c o e f f i c i e n t r o s e f r o m 0 to 0.557. C o n s e q u e n t l y , the m e t h o d d e s c r i b e d c a n b e u s e d to i n c r e a s e the d e l i v e r y c o e f f i c i e n t a n d t h e e f f i c i e n c y c o e f f i c i e n t of s c r e w c o m p r e s s o r s . T h i s m e t h o d can be u s e d both f o r e x p a n d e r s and a l s o f o r c o m p r e s s o r s c r e w m a c h i n e s , a n d a l s o f o r double-rotor machines with synchronizing link pinions which operate without a working lubricant.

LITERATURE I.

2. 3.

CITED

A. M. Korenev and V. I. Ardashev, in. Proc. N. E. Bauman Moscow Higher Technical College [in Russian], No. 124, Moscow (1967). I. A. Sakun, Screw Compressors [in Russian], Mashinostroenie, Moscow-Leningrad (1970). M. M. Gol'dberg et al. (editors), Handbook on Paint and Varnish Coatings in Engineering [in Russian], Mashinostroenie, Moscow (1964).

953