- Email: [email protected]
Mechanical seal with angular sealing surfaces
Patents Seal d e s i g n with bi-directional pumping
• I.'zl
/
Patent number: US397996 P u b l i c a t i o n date: 4 t h S e p t e m b e r 1996 Inventor: D Johnston Applicant: Freudenberg-NOK General Partnership Previous s h a f t seals h a v e b e e n formed from c o m p r e s s i v e elastomeric materials. Shaft seals typically seal liquid, s u c h as a l u b r i c a t i n g oil, from a side o p e n e d to a t m o s p h e r e . N o r m a l l y s u c h seals are u s e d w i t h a r o t a t i n g s h a f t s u p p o r t e d b y a b e a r i n g or other m e a n s . Several seals have b e e n developed u s i n g a p u m p i n g action, a n d i n c l u d e s o m e type of d e s i g n o n the seal face - ie. the face c o n t a c t i n g the s h a f t acts to p u m p the seal fluid b a c k t o w a r d s the sealed area. D e s i g n s i n c l u d e ribs or groove p o r t i o n s o r i e n t e d relative to the direction of s h a f t rotation. This m e a n s p u m p i n g a c t i o n only o c c u r s w h e n the fluid s h a f t is r o t a t i n g i n one direction. Additionally seals have p r e v i o u s l y b e e n m a n u f a c t u r e d of e l a s t o m e r i c or flexible m a t e r i a l s w h i c h allow the seal to stay i n c o n t a c t with the s h a f t d e s p i t e c o n c e n t r i c i t y a n o m a l i e s . Seal w e a r is a n i n e v i t a b l e c o n s e q u e n c e . This p a t e n t d e s c r i b e s a seal, (Figure 2), with a seal e l e m e n t , formed of a semi-rigid m a t e r i a l
F i g u r e 3. S i n u s o i d a l u n d u l a t i o n s i n t h e s e a l face, c r e a t e a bidirectional pumping action.
s u c h as PTFE. The seal e l e m e n t e x t e n d s radially toward the shaft w h e n n o t fitted. W h e n the shaft is i n s e r t e d the seal flexes a b o u t a section, (Figure 3). The seal face, p r e s s e d a g a i n s t the shaft, h a s a n s i n u s o i d a l u n d u l a t i n g surface, w h i c h u n d e r s h a f t r o t a t i o n give a forward or p u m p i n g m o t i o n toward the oil side of the seal. The stroke of the u n d u l a t i o n s is b e t w e e n 0.05 a n d 1 m m d e p e n d i n g on the fluid. A c i r c u l a r b a n d , also e n g a g e s the s h a f t c i r c u m f e r e n c e to act as a static seal w h e n s t a t i o n a r y . This seal is p a r t i c u l a r l y u s e f u l with reversible type motors, w h i c h r o u t i n e l y r e q u i r e the s h a f t to operate in b o t h forwards a n d reverse directions.
Mechanical seal with •
'
N
,:
~o
i~
,
F i g u r e 2. T h e s e a l f l e x e s o v e r t h e shaft, creating a wavy seal face.
14
sealing surfaces Patent number: US5577739 P u b l i c a t i o n date: 2 6 t h N o v e m b e r 1996 Inventor: A Ciotola This i n v e n t i o n d e s c r i b e s a n improved m e c h a n i c a l seal, with stationary and rotating faces of
silicon c a r b i d e a t e q u a l a n d o b l i q u e a n g l e s to the s h a f t axis (Figure 4). T h e seal s u r f a c e s oppose e a c h o t h e r a n d are forced together b y e l a s t o m e r i c m e a n s to form a m e c h a n i c a l seal. This effect is c l a i m e d to r e s u l t i n a seal w h i c h resists leakage particularly when u s e d i n a p p l i c a t i o n s w h e r e there is large e q u i p m e n t , h i g h p r e s s u r e , a n d eccentric r o t a t i o n . The conical c o n f i g u r a t i o n is believed to c a u s e t h e seal to t e n d to self align, p r e v e n t i n g the f o r m a t i o n of wide t r a c k i n g of t h e o p p o s i n g seal e l e m e n t s . This c a n lead to p r e m a t u r e seal leakage. A n elastic m e t h o d is u s e d to exert a n axial force o n at l e a s t o n e of t h e e l e m e n t s . The seal c a n b e m a d e of single piece e l e m e n t s or as a split m e c h a n i c a l seal w h e r e each rigid s e c t i o n is m a d e of two c i r c u m f e r e n t i a l pieces, a n d e a c h elastic piece h a s o n e split.
\
i
7 ' Sf/ lj/ III
./il /// /// is, / 987
%,,.%%~-: , £ ~ / / /747
/. SBJ~
"/45
F i g u r e 4. T h e c o n i c a l d e s i g n helps the seal to self-align.
A d d i t i o n a l l y the p a t e n t i n c l u d e s a v e r s i o n w h e r e the seal c a n be c o n n e c t e d to a s t a t i o n a r y h o u s i n g b y c o n n e c t o r clips (Figure 5). E a c h clip is c o n n e c t e d to a bolt e x t e n d i n g from the h o u s i n g , a n d c o n t a c t s a radial s u r f a c e of the s t a t i o n a r y c o m p o n e n t s . A n u t s e c u r e d to t h e bolt p r e s s e s the clip down. E a c h clip c o m p r i s e s a n axial e x t e n s i o n located b e s i d e the bolt, with thee
Sealing Technology No. 39
Webwatch Compression s l e e v e for an expandable seal
~38
Patent number: EP747619 P u b l i c a t i o n date: 1 1 t h D e c e m b e r 1996 Inventor: W Skinner Applicant: P r e s s - S e a l G a s k e t Corporation
~
~
Figure 5. C o n n e c t o r c l i p s c a n b e u s e d t o affix t h e s e a l t o t h e housing.
bolt being between the axial extension and the stationary element. The axial extension prevents the clip from rotating axially away from the stationary component as the bolt is tightened against it.
An apparatus is presented which radially expands a tubular gasket into compressive sealing engagement with the wall of an opening. Figure 6 shows a reinforced concrete manhole riser or monolithic base, with a pipe opening in a sidewall. To seal the pipe with the hole a gasket apparatus is used which comprises an elongated sleeve of elastomer such as rubber or neoprene. A conventional screw-type a n n u l a r clamping band clamps one end of the gasket against the outer surface of the pipe. At the opposite end, a radially expandable split sleeve, 20,
m
~
p
i
p
~
s
:
d
by
expands to compress the gasket against the wall of the opening. A sliding sleeve, 24, made of nylon, hypalon or polyester is also provided to act as a slip plate for the compression sleeve. This lowers the magnitude of the force required to expand the compression sleeve because the coefficients of friction have been reduced. Greater equalisation of compression of the material in the gasket is also facilitated, thus creating a more positive seal.
Webwatch Apple Rubber P r o d u c t s http://www.applerubber.com
Yei S h i e n E n t e r p r i s e http: //www.yeishin. corn /
A comprehensive listing of its design and m a n u f a c t u r i n g capabilities appears on Apple Rubber's impressive site. Submit an Engineering Assistance Request tbr an online response to specific queries. Its trade show schedule is listed, and Technical Corner carries useful O-ring troubleshooting and selection advice. Well worth a browse.
Yei Shin has been a m a n u f a c t u r e r of oil seals and cavity moulds since 1985. Its m a n u f a c t u r i n g process is profiled, and several hydrodynamic design aids are provided, along with an extensive 8-page seal application catalogue. Unusually, the company also compares its current productivity levels to its overall capacity.
Feodor Burgmann http://www.burgmann.com/
Classy presentation from the Wolfratshausen-headquartered mechanical seals manufacturer. Offered in both English and German, the site contains good b a c k g r o u n d information on the company, its activities, corporate structure, and most recent product developments. The frames-style structure is especially effective in the Product Field section.
Sealing Technology No. 39
Ferrofluidics http: //www. fero. c o m /
Ferrofluidics has created an elaborate and impressive homepage. The concepts behind its ferrofluidic sealing technology are fully explained, and typical applications discussed. Standard and metric size data is included. Alternative uses for ferrofluids, such as in stepper motors and inertai dampers are also described.
15
• I.'zl
/
Patent number: US397996 P u b l i c a t i o n date: 4 t h S e p t e m b e r 1996 Inventor: D Johnston Applicant: Freudenberg-NOK General Partnership Previous s h a f t seals h a v e b e e n formed from c o m p r e s s i v e elastomeric materials. Shaft seals typically seal liquid, s u c h as a l u b r i c a t i n g oil, from a side o p e n e d to a t m o s p h e r e . N o r m a l l y s u c h seals are u s e d w i t h a r o t a t i n g s h a f t s u p p o r t e d b y a b e a r i n g or other m e a n s . Several seals have b e e n developed u s i n g a p u m p i n g action, a n d i n c l u d e s o m e type of d e s i g n o n the seal face - ie. the face c o n t a c t i n g the s h a f t acts to p u m p the seal fluid b a c k t o w a r d s the sealed area. D e s i g n s i n c l u d e ribs or groove p o r t i o n s o r i e n t e d relative to the direction of s h a f t rotation. This m e a n s p u m p i n g a c t i o n only o c c u r s w h e n the fluid s h a f t is r o t a t i n g i n one direction. Additionally seals have p r e v i o u s l y b e e n m a n u f a c t u r e d of e l a s t o m e r i c or flexible m a t e r i a l s w h i c h allow the seal to stay i n c o n t a c t with the s h a f t d e s p i t e c o n c e n t r i c i t y a n o m a l i e s . Seal w e a r is a n i n e v i t a b l e c o n s e q u e n c e . This p a t e n t d e s c r i b e s a seal, (Figure 2), with a seal e l e m e n t , formed of a semi-rigid m a t e r i a l
F i g u r e 3. S i n u s o i d a l u n d u l a t i o n s i n t h e s e a l face, c r e a t e a bidirectional pumping action.
s u c h as PTFE. The seal e l e m e n t e x t e n d s radially toward the shaft w h e n n o t fitted. W h e n the shaft is i n s e r t e d the seal flexes a b o u t a section, (Figure 3). The seal face, p r e s s e d a g a i n s t the shaft, h a s a n s i n u s o i d a l u n d u l a t i n g surface, w h i c h u n d e r s h a f t r o t a t i o n give a forward or p u m p i n g m o t i o n toward the oil side of the seal. The stroke of the u n d u l a t i o n s is b e t w e e n 0.05 a n d 1 m m d e p e n d i n g on the fluid. A c i r c u l a r b a n d , also e n g a g e s the s h a f t c i r c u m f e r e n c e to act as a static seal w h e n s t a t i o n a r y . This seal is p a r t i c u l a r l y u s e f u l with reversible type motors, w h i c h r o u t i n e l y r e q u i r e the s h a f t to operate in b o t h forwards a n d reverse directions.
Mechanical seal with •
'
N
,:
~o
i~
,
F i g u r e 2. T h e s e a l f l e x e s o v e r t h e shaft, creating a wavy seal face.
14
sealing surfaces Patent number: US5577739 P u b l i c a t i o n date: 2 6 t h N o v e m b e r 1996 Inventor: A Ciotola This i n v e n t i o n d e s c r i b e s a n improved m e c h a n i c a l seal, with stationary and rotating faces of
silicon c a r b i d e a t e q u a l a n d o b l i q u e a n g l e s to the s h a f t axis (Figure 4). T h e seal s u r f a c e s oppose e a c h o t h e r a n d are forced together b y e l a s t o m e r i c m e a n s to form a m e c h a n i c a l seal. This effect is c l a i m e d to r e s u l t i n a seal w h i c h resists leakage particularly when u s e d i n a p p l i c a t i o n s w h e r e there is large e q u i p m e n t , h i g h p r e s s u r e , a n d eccentric r o t a t i o n . The conical c o n f i g u r a t i o n is believed to c a u s e t h e seal to t e n d to self align, p r e v e n t i n g the f o r m a t i o n of wide t r a c k i n g of t h e o p p o s i n g seal e l e m e n t s . This c a n lead to p r e m a t u r e seal leakage. A n elastic m e t h o d is u s e d to exert a n axial force o n at l e a s t o n e of t h e e l e m e n t s . The seal c a n b e m a d e of single piece e l e m e n t s or as a split m e c h a n i c a l seal w h e r e each rigid s e c t i o n is m a d e of two c i r c u m f e r e n t i a l pieces, a n d e a c h elastic piece h a s o n e split.
\
i
7 ' Sf/ lj/ III
./il /// /// is, / 987
%,,.%%~-: , £ ~ / / /747
/. SBJ~
"/45
F i g u r e 4. T h e c o n i c a l d e s i g n helps the seal to self-align.
A d d i t i o n a l l y the p a t e n t i n c l u d e s a v e r s i o n w h e r e the seal c a n be c o n n e c t e d to a s t a t i o n a r y h o u s i n g b y c o n n e c t o r clips (Figure 5). E a c h clip is c o n n e c t e d to a bolt e x t e n d i n g from the h o u s i n g , a n d c o n t a c t s a radial s u r f a c e of the s t a t i o n a r y c o m p o n e n t s . A n u t s e c u r e d to t h e bolt p r e s s e s the clip down. E a c h clip c o m p r i s e s a n axial e x t e n s i o n located b e s i d e the bolt, with thee
Sealing Technology No. 39
Webwatch Compression s l e e v e for an expandable seal
~38
Patent number: EP747619 P u b l i c a t i o n date: 1 1 t h D e c e m b e r 1996 Inventor: W Skinner Applicant: P r e s s - S e a l G a s k e t Corporation
~
~
Figure 5. C o n n e c t o r c l i p s c a n b e u s e d t o affix t h e s e a l t o t h e housing.
bolt being between the axial extension and the stationary element. The axial extension prevents the clip from rotating axially away from the stationary component as the bolt is tightened against it.
An apparatus is presented which radially expands a tubular gasket into compressive sealing engagement with the wall of an opening. Figure 6 shows a reinforced concrete manhole riser or monolithic base, with a pipe opening in a sidewall. To seal the pipe with the hole a gasket apparatus is used which comprises an elongated sleeve of elastomer such as rubber or neoprene. A conventional screw-type a n n u l a r clamping band clamps one end of the gasket against the outer surface of the pipe. At the opposite end, a radially expandable split sleeve, 20,
m
~
p
i
p
~
s
:
d
by
expands to compress the gasket against the wall of the opening. A sliding sleeve, 24, made of nylon, hypalon or polyester is also provided to act as a slip plate for the compression sleeve. This lowers the magnitude of the force required to expand the compression sleeve because the coefficients of friction have been reduced. Greater equalisation of compression of the material in the gasket is also facilitated, thus creating a more positive seal.
Webwatch Apple Rubber P r o d u c t s http://www.applerubber.com
Yei S h i e n E n t e r p r i s e http: //www.yeishin. corn /
A comprehensive listing of its design and m a n u f a c t u r i n g capabilities appears on Apple Rubber's impressive site. Submit an Engineering Assistance Request tbr an online response to specific queries. Its trade show schedule is listed, and Technical Corner carries useful O-ring troubleshooting and selection advice. Well worth a browse.
Yei Shin has been a m a n u f a c t u r e r of oil seals and cavity moulds since 1985. Its m a n u f a c t u r i n g process is profiled, and several hydrodynamic design aids are provided, along with an extensive 8-page seal application catalogue. Unusually, the company also compares its current productivity levels to its overall capacity.
Feodor Burgmann http://www.burgmann.com/
Classy presentation from the Wolfratshausen-headquartered mechanical seals manufacturer. Offered in both English and German, the site contains good b a c k g r o u n d information on the company, its activities, corporate structure, and most recent product developments. The frames-style structure is especially effective in the Product Field section.
Sealing Technology No. 39
Ferrofluidics http: //www. fero. c o m /
Ferrofluidics has created an elaborate and impressive homepage. The concepts behind its ferrofluidic sealing technology are fully explained, and typical applications discussed. Standard and metric size data is included. Alternative uses for ferrofluids, such as in stepper motors and inertai dampers are also described.
15