36 Fluid Film Processing Applied to Manufacturing of Foam Core Insulating Panels VIJAY VIMAWALA
Kornylak Corporation, 400 Heaton Street, Hamilton, OH 45011
Kornylak Corporation's recent development of the Process Tunnel is expected to have a significant impact on a variety of operations in the plastic field. A number of lines incorporating this process have already been built and are in operation in the United States and abroad. Their spectacular performance indi cates that this development is indeed a breakthrough. This chapter will cover some of the technical aspects of this new process. To avoid repetition of our company's trade name we will, in this chapter, use a generic name to describe the equipment and its process. We will call it the "Fluid Film Process". The fluid film process permits a high speed continuous treatment of sheet, strip, panel and billet material requiring cooling, heating, pressure confinement or shape and surface control. Many products presently manufactured in molds or platen presses can now be much more rapidly produced continuously on machinery incorporating fluid film processing. The first major application of this process has been in the production of foam core panels used by the construction industry for the manufacture of roofing and sheathing panels. The use of urethane foam i n s u l a t i o n f o r r o o f i n g i n the U n i t e d States dates back t o the 1950 s. The e a r l i e s t machine was a f o u r - s i d e d Armorbelt pressure t u n n e l b u i l t i n 1958. T h i s machine produced a continuous r e c t a n g u l a r b l o c k of urethane foam which was cut t o l e n g t h and m u l t i p l e sawed t o d e s i r e d t h i c k n e s s e s and r o o f i n g f e l t was laminated to the cut s l a b s . This l i n e of machinery was soon f o l l o w e d by machines capable of pressures up t o 5 p s i (0.35 Kg/sq. cm) and panel widths t o 9 f t . (2.74 meters) (See F i g u r e 5 ) . These machines are w e l l known as double b e l t u n i t s which produce the major share of today's urethane foam panels f o r b u i l d i n g r o o f i n g and sheathing i n the USA. We a l s o know that through the years both designers and users have been concerned w i t h u n d e s i r a b l e f e a t u r e s of double b e l t u n i t s . Double b e l t l i n e s are l a r g e and massive. The s i z e i s necessary t o f
0097-6156/81/0172-05 5 3$05.00/ 0 © 1981 American Chemical Society
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accommodate the l a r g e d r i v e sprockets t o reduce the c h o r d a l a c t i o n of the b e l t c h a i n t o achieve a reasonably uniform b e l t speed. B e l t s must be of heavy duty c o n s t r u c t i o n t o prevent d e f l e c t i o n under the pressure of the expanding foam. A d e f l e c t i o n of .030 i n c h (0.76 mm.) i n each b e l t r e s u l t s i n a .060 i n c h (1.52 mm) d i f f e r e n c e i n panel t h i c k n e s s across the w i d t h of the panel. The h i g h pressure loads o f up t o 3000 l b s . (1364 Kg) per l i n e a l f o o t f o r a 4 f o o t (1.22 meter) wide conveyor r e q u i r e s a heavy duty frame t o avoid frame d e f l e c t i o n s which, added t o the b e l t d e f l e c t i o n s , f u r t h e r i n c r e a s e the inaccuracy of the p a n e l . These h i g h pressures r e q u i r e the use of a n t i f r i c t i o n r o l l e r s to a v o i d e x c e s s i v e d r i v e horsepowers. Even w i t h such e f f i c i e n t r o l l e r s , the d r i v e f o r a panel l i n e running a t 50 f t . / m i n . (15 meters/min.) i s 30 H.P. Tracks f o r the b e l t r o l l e r s must be machined and ground f o r panel t h i c k n e s s accuracy and power r e d u c t i o n . However, unless they a r e hardened or o f s p e c i a l wear and b r i n n e l l i n g r e s i s t a n t s t e e l , the continuous heavy r o l l i n g a c t i o n of the r o l l s soon wears a deep groove i n the track. Even w i t h frequent o r continuous l u b r i c a t i o n , the r o l l e r s subjected to heat and h i g h l o a d s , soon reach the end of t h e i r l i f e span, r e q u i r i n g replacement and expensive down time. Minute d i f f e r e n c e s i n alignment of adjacent conveyor s l a t s r e s u l t s i n b e l t marks which mar the appearance o f the f i n i s h e d panel. This i s i n s p i t e o f a l l the care p o s s i b l e t o b u i l d a p r e c i s i o n conveyor. Even though the d i f f e r e n c e i s only s e v e r a l thousandths of an i n c h , r e f l e c t e d l i g h t shows up the s l a t marks very d i s t i n c t l y . This c o n d i t i o n worsens as r o l l s and t r a c k s wear. Another important concern, i n view of the o i l c r i s i s , i s the extravagent use of energy nneded t o support t h i s chemical process and to move the panel through the process area. The heavy machinery and the b e l t pressure l o a d r e s u l t i n h i g h motor power requirements. More s e r i o u s , however, i s the i n e f f i c i e n c y of heat t r a n s f e r t o the b e l t and t o the product and the great l o s s o f heat from the b e l t t o the atmosphere. These and other needs f o r improvement were r e p r e s e n t a t i v e of the s t a t e of the urethane foam panel manufacturing a r t a t the time of i n t r o d u c t i o n of f l u i d f i l m processing. A l l o f these problems had been a concern t o my company d u r i n g i t s years of p i o n e e r i n g work w i t h foam panel p r o d u c t i o n . A number of piecemeal improvements were made through the y e a r s , but the grand s o l u t i o n , one which solved them a l l , came w i t h the development of the f l u i d f i l m process. The f l u i d f i l m process not only e l i m i n a t e s a l l of these problems but goes on t o add new advantages, most o f them of very s i g n i f i c a n t magnitude.
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F i g u r e 1 shows a cross s e c t i o n through a f l u i d f i l m process panel production l i n e . A i r i s introduced through the porous p l a t e n s u r f a c e s . The a i r forms a .005" (0.127 mm) t h i c k f i l m of r a p i d l y moving a i r , enveloping the panel f o r maximum heat t r a n s f e r and p r e v e n t i n g p h y s i c a l contact of the panel w i t h the p l a t e n s . The p l a t e n s are separated by p r e c i s e gage b l o c k s to achieve accurate t h i c k n e s s and to permit the production of a broad range of panel t h i c k n e s s e s . A f l u i d f i l m process l i n e i s shown i n F i g u r e 2. I t i s a s e r i e s of modules, each c o n s i s t i n g of the p a i r of p l a t e n s i l l u s t r a t e d i n the previous s l i d e . Each module i s 5 f e e t (1.524 meters) long and each can have c o n t r o l s to a d j u s t the temperature and pressure of the e n t e r i n g a i r . Thus, knowing the p r o f i l e of temperature and pressure needs of a s p e c i f i c foam chemical formul a t i o n , the l i n e can be adjusted f o r optimum o p e r a t i o n and minimum energy waste. The f o l l o w i n g are some of the other r e v o l u t i o n a r y f e a t u r e s of the process: FASTER MORE ACCURATE SMOOTH SURFACE MODULAR CONTROL HIGHER PRESSURE LOWER ENERGY USE HIGHER TEMPERATURE LOWER MAINTENANCE QUIETER SAFER COMPACT INTERCHANGEABLE WITH DOUBLE BELTS Each of these i s discussed i n d e t a i l below: Faster Foam panels have moved t h r u the t u n n e l i n a smooth e f f o r t l e s s manner at any speed we have t r i e d . Meanwhile, e x i s t i n g "wet-end" and c u t o f f equipment have been s t r a i n e d to c a p a c i t y . Because of these wet end and c u t o f f l i m i t a t i o n s , the top speed t e s t e d at the w r i t i n g of t h i s paper, has been 170 f t . / m i n . (52 meters/min.) However, there appears to be no apparent l i m i t to the speed c a p a b i l i t y of the process, and f o r t h i s reason, we are i n the process of developing the a u x i l i a r y equipment f o r higher speeds. N a t u r a l l y , as the l i n e speed i n c r e a s e s there develops a need f o r i n c r e a s i n g the l e n g t h of the l i n e to permit complete cure of the foam. This new speed c a p a b i l i t y , now presents a challenge to the chemical manufacturers and formulators to develop f o r m u l a t i o n s which w i l l match the machine. This challenge has been passed on to the i n d u s t r y , but meanwhile we are l o o k i n g i n t o other t e c h n o l ogies to speed the c u r i n g process of e x i s t i n g f o r m u l a t i o n s .
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Figure 2. Fluidfilmprocess line.
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More Accurate Where +1/32 i n c h (+0.8 mm) has been the standard t h i c k n e s s t o l e r a n c e f o r 4 f o o t (1.22 meter) wide panels produced i n double b e l t l i n e s , the standard f o r the f l u i d f i l m process i s +0.010 i n c h (+0.25 mm). At times, an accuracy w i t h i n +.005 i n c h (+.127 mm) has been achieved. Such accuracy i s p o s s i b l e because of the p r e c i s i o n and r i g i d i t y of the t u n n e l c o n s t r u c t i o n . The p l a t e n s are r e i n f o r c e d weldments, s t r e s s r e l i e v e d a f t e r welding and then ground and chrome p l a t e d . They are separated by p r e c i s e gage b l o c k s to form the two faces of the t u n n e l . D e f l e c t i o n i s p r a c t i c a l l y non-existant s i n c e the foam pressure on the p l a t e n i s balanced by the f l u i d pressure w i t h i n the p l a t e n r e s e r v o i r . The f l u i d f i l m i s a c c u r a t e l y c o n t r o l l e d to m a i n t a i n i t at a normal working t h i c k n e s s of 0.005 i n c h (0.127 mm). This new accuracy, i n a d d i t i o n to easing the job of meeting customer s p e c i f i c a t i o n s i s a l s o an o p p o r t u n i t y f o r savings i n c o s t l y chemicals, p a r t i c u l a r l y s i g n i f i c a n t f o r t h i n panels. In the case of a 0.125 i n c h (3 mm) t h i c k p a n e l , a 0.040 i n c h (1 mm) saving i s equal to 1/3 of the t h i c k n e s s . Smoothness B e l t marks and the u s u a l random plane s l a t impressions are non-existant on f l u i d f i l m process panels. The absence of conveyor b e l t s and the extremely accurate t u n n e l , produce a smooth continuous s u r f a c e on both s i d e s of the panel. This f e a t u r e combined w i t h the improved t h i c k n e s s accuracy opens the door to many new markets which were p r e v i o u s l y denied f o r the l a c k of acceptable appearance and accuracy. Lower Energy Use Energy c o n s e r v a t i o n stems from the f o l l o w i n g f e a t u r e s of the f l u i d f i l m process: 1) More e f f i c i e n t heat t r a n s f e r 2) Absence of heat l o s s e s 3) F r i c t i o n - f r e e movement of panel Each of these energy conserving f e a t u r e s i s reviewed i n d e t a i l below: More E f f i c i e n t Heat T r a n s f e r . In the c o n v e n t i o n a l double b e l t system, hot a i r i s normally introduced i n t o each conveyor body. This a i r heats the b e l t s which i n t u r n t r a n s f e r the heat to the product. The equation f o r heat t r a n s f e r c o e f f i c i e n t f o r t h i s process i s shown i n F i g u r e 3. In the f l u i d f i l m process, the heat i s s u p p l i e d v i a the hot a i r f i l m which i s i n d i r e c t contact w i t h the product. In a d d i t i o n , the r a p i d movement of the a i r f i l m f u r t h e r i n c r e a s e s
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heat transfer coefficient
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1
κ
1
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h
3
h
l
h
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1 5.2
2
&
h
3
are transfer coefficient of the film on both sides of the conveyor slat and the panel skin surface.
1 1
559
1.34
1
L is the plate thickness (inches) 1.34
Κ is the conductivity coefficient of the plate
= .435 BTU / degF / hour / square foot Reference - M A R K S HANDBOOK Figure 3.
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the t r a n s f e r r a t e . The formula f o r the f l u i d f i l m t r a n s f e r i s shown i n F i g u r e 4. At a temperature of 180°F (82°C) and a conveyor s l a t t h i c k ness of 0.375 i n c h (9.5 mm), the f l u i d f i l m heat t r a n s f e r r a t e i s approximately 4 times that of the double b e l t u n i t . Absence of Heat Losses. There are two major heat l o s s e s i n a double b e l t system. One i s the leakage of hot a i r through the gap between the conveyor b e l t and the conveyor body. The combina t i o n of i n e f f i c i e n t heat t r a n s f e r p r e v i o u s l y e x p l a i n e d and the s i z e of the gap around the e n t i r e p e r i p h e r y of the conveyor on both s i d e s , wastes most of heat fed i n t o the conveyor to the atmosphere. The second l o s s i s by r a d i a t i o n from the b e l t . The b e l t , which i s of heavy c o n s t r u c t i o n f o r r i g i d i t y and f l a t n e s s i s a very s i g n i f i c a n t heat s i n k . Some of t h i s heat t r a n s f e r s to the panel where i t i s needed and some where i t i s not needed. The remainder i s l o s t to the atmosphere by r a d i a t i o n d u r i n g i t s i d l e r e t u r n to the input end. T h i s l o s s can be reduced by i n s u l a t i o n but the problem of removing and r e s t o r i n g t h i s i n s u l a t i o n f o r i n s p e c t i o n and maintenance access makes i t i m p r a c t i c a l . A measurement on a double b e l t revealed a 20°F (11°C) l o s s i n b e l t temperature d u r i n g the r e t u r n run. The f l u i d f i l m system completely e l i m i n a t e s the heat s i n k / r a d i a t i o n l o s s s i n c e the p l a t e n s remain s t a t i o n a r y . The heat i n the p l a t e n i s r a d i a t e d i n t o the product. The r e s e r v o i r behind the p l a t e n i s easy to i n s u l a t e and t h i s i n s u l a t i o n remains i n p l a c e w i t h no hinderance to i n s p e c t i o n or maintenance. Further, s i n c e the heat i s c o n t r o l l e d i n zones corresponding to the need p r o f i l e of the formulation, there i s no w a s t e f u l input of energy i n t o the product. The reduced t h i n f i l m leakage l o s s at the perimeter i s easy to c o l l e c t and r e c i r c u l a t e . Because of the d i f f i c u l t y i n c a l c u l a t i n g comparative data, we have c o l l e c t e d data from o p e r a t i n g l i n e s . To compare heat l o s s e s , we have data from comparable double b e l t and f l u i d f i l m lines. The o p e r a t i n g c o n d i t i o n s f o r both u n i t s were the same: 50 f e e t (15.24 meters) long l i n e producing 4 f e e t (1.22 meters) wide panel at 50 f t . / m i n (15.24 meters/min.) and a 160°F (71°C) s k i n temperature. The heat input i n t o the double b e l t l i n e was 333,000 BTU/hr. (84,000 Kg c a l o r i e s / h o u r ) and i n t o the f l u i d f i l m l i n e was 121,000 BTU/hr. (30,500 Kg c a l o r i e s / h r . ) . This the f l u i d f i l m l i n e operates w i t h a 64% saving of heat i n p u t . At a working pressure of 3 p s i (0.21 Kg/Sq.cm) i n a 50 f o o t (15.24 meters) long l i n e , a 4 f o o t (1.22 meters) wide panel i s subjected to a t o t a l b e l t l o a d of 86,400 l b s . (39,273 Kgms.). With a c o e f f i c i e n t of f r i c t i o n of 0.001 f o r the r o l l e r supported b e l t s assuming the use of l u b r i c a t e d r o l l e r b e a r i n g s , the t o t a l b e l t p u l l i s 86.4 l b s . (39 Kgms.), r e q u i r i n g a 15 HP d r i v e f o r each b e l t a t a 50 f t . / m i n . (15.24 meters/min.) p r o d u c t i o n speed.
τ
1
IT
J
χ2
*2
Figure 4.
.435
=
"
6.2
h = transfer coefficient of panel skin surface 2 = transfer gain due to velocity of Process Film
U = heat transfer coefficient
Advantage of Process Tunnel over conventional Double Belt is
= 2.7
υ=
Figure 5. Edgemold Foamboarder center seam of split bottom belt is tight in the process zone. The belts diverge at the discharge end to free panel from the side restraint blocks.
>
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ο
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Χ
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to
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In the f l u i d f i l m p r o c e s s , where the panel f l o a t s i n a enveloping f i l m of a i r , v e r y l i t t l e f o r c e i s needed t o move the panel. Higher Temperatures Some f o r m u l a t i o n s , such as i s o c y a n u r a t e s , r e q u i r e or b e n e f i t from temperatures h i g h e r than normally p o s s i b l e i n double b e l t l i n e s . An o p e r a t i n g temperature of 350°F (82°C) has been necessary f o r some f o r m u l a t i o n s . P r o d u c t i o n temperatures can be achieved w i t h i n 60 minutes. The d i f f i c u l t y i n meeting t h i s requirement on a double b e l t l i n e r e s u l t s from the much l e s s e f f i c i e n t heat t r a n s f e r and the e x c e s s i v e heat l o s s e s . A f u r t h e r problem on double b e l t l i n e s has been the a c c e l e r a t e d wear of bearings a t h i g h e r temperatures as explained l a t e r under the t o p i c that f o l l o w s . Maintenance Maintenance requirements of the t u n n e l are minimal because of the e l i m i n a t i o n of moving p a r t s . The troublesome and frequent l u b r i c a t i o n of r o l l e r s and bearings i s completely e l i m i n a t e d . This i s a f o r t u n a t e improvement s i n c e the h i g h temperatures shorten the l i f e of l u b r i c a n t s and the h i g h pressure load on the r o l l e r s cause b e a r i n g breakdown and wears grooves i n the supporting t r a c k s . Proper l u b r i c a t i o n p r a c t i c e c a l l s f o r removal of spent grease and replacement. The replacement schedule depends p r i m a r i l y on speed, hours of o p e r a t i o n s and temperature. This renewal p e r i o d i s halved f o r each 25°F (14°C) i n c r e a s e i n temperature. For example, a l u b r i c a n t l i f e of 1000 work hours at 150°F (66°C) i s reduced t o 500 hours a t 175°F (79°C) and only 250 hours a t 200°F (93°C). F a i l u r e t o observe a proper schedule on double b e l t u n i t s has r e s u l t e d not only i n d e s t r u c t i o n of bearings and r o l l e r s but a l s o damage t o the b e l t s l a t s , the t r a c k s and d r i v e sprockets and a c o s t l y shutdown of the l i n e . Quieter As o p e r a t i n g speeds get h i g h e r the metal t o metal c o n t a c t of r o l l e r s and t r a c k add c o n s i d e r a b l y t o the p l a n t n o i s e l e v e l . Since q u i e t n e s s i s recognized as a d e s i r e d and mandatory c o n d i t i o n of the workplace, the s i l e n t o p e r a t i o n of the f l u i d f i l m system i s another of i t s many important advantages. Safer An ominous s a f e t y hazard i s present on double b e l t l i n e s a t the e n t r y t h r o a t formed by the two conveyors. I t l o c a t i o n i n the area of g r e a t e s t a c t i v i t y - paper e n t r y , paper f o l d i n g , chemical laydown and d i s t r i b u t i o n i s a constant hazard t o workers
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i n the area. This i s p a r t i c u l a r l y so i f an operator attempts to adjust a paper w r i n k l e or a f a u l t y f o l d . Or he might grab f o r an obj ect which had f a l l e n on the lower paper and was about to enter double b e l t and cause c o n s i d e r a b l e damage to the b e l t s or to i t s e l f . Further down the l i n e , hazard i s g r e a t l y reduced, but some i s present because of the exposed edges of the moving b e l t s , p a r t i c u l a r l y a t p o i n t s where they pass by s t a t i o n e r y supports and braces a t the three moving l e v e l s a t the panel l e v e l and at the top and bottom i d l e r e t u r n l e v e l s . The f l u i d f i l m process has no moving p a r t s i n the pressure zone. Compact The o v e r a l l thickness of a f l u i d f i l m s e c t i o n when s e t f o r a 5 i n c h (127 mm) t h i c k panel i s only 24 inches (610 mm). This i n c l u d e s 2 inches of i n s u l a t i o n on top and bottom exposed surfaces of the l i n e . The r e s u l t i n g i n s t a l l a t i o n i s only waist high p e r m i t t i n g easy v i s i b i l i t y and communication across the l i n e . Interchangeable With Double B e l t s The f l u i d f i l m processor can match any s i z e , speed, formul a t i o n c a p a b i l i t y , temperature, pressure, energy use, c o n t r o l , and duty c a p a b i l i t y of a double b e l t conveyor f o r the production of c e l l u l a r panel produced of urethane, cyanurate or p h e n o l i c and two f l e x i b l e s k i n s . I t w i l l e a s i l y f i t i n t o the same space and as a replacement may then o f f e r the c a p a b i l i t y of higher speeds, higher d e n s i t i e s , greater accuracy, smoother s u r f a c e and greater core m a t e r i a l v e r s a t i l i t y . In a d d i t i o n , i t s quietness s a f e t y and reduced maintenance make the replacement a welcome change. In review i t appears that the new f l u i d f i l m process o f f e r s i n s u l a t i o n panel manufacturers and chemical companies an opport u n i t y to i n c r e a s e output, r a i s e q u a l i t y , enter new markets and reduce costs a t a time when improved i n s u l a t i o n o f f e r s the best immediate r e l i e f from r i s i n g costs and u n c e r t a i n s u p p l i e s of fuel. New experiments with the f l u i d f i l m process are c o n t i n u i n g and new t e c h n i c a l data i s s t i l l being developed a t the time of w r i t i n g t h i s paper. Some of t h i s data, i f a p p r o p r i a t e w i l l be added a t the conference. RECEIVED May 1, 1981.
