Concepts in Energy Savings in Plastics Processing - ACS Symposium

2 Concepts in Energy Savings in Plastics Processing NICK R. SCHOTT University of Lowell, Lowell, MA 01854

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HOWARD DERBY GTE Laboratories, 40 Sylvan Rd., Waltham, MA 02154

Energy is defined as the capacity to do work. Based on the Carnot cycle, the theoretical energy required to do any form of work is constant. However, due to different efficiencies of various systems, the actual energy required to do the same work can vary depending on the system used. The ever increasing cost of energy has mandated the need to manufacture under reduced energy conditions. Plastics processing is just one manufacturing field where the potential for energy savings is being explored. Injection Molding Energy Requirements Energy is required to make injection molding machines do work. The theoretical energy required to produce a given part is constant for a given set of processing conditions. The processing energy is determined by the temperature to which a plastic resin must be raised to deform i t whereafter i t is injected into the cavity. The energy consists of three forms: 1) Sensible heat i.e. heat that is used to raise the temperature of the plastic resin from room temperature to its processing temperature; 2) latent heat (if any), the heat that is required to accomplish a phase change such as melting of a semi-crystalline polymer; and 3) the flow energy which is required to inject the material into the cavity. Heats of reaction can be neglected unless one has a thermoset resin. The flow energy is small in comparison to the sensible and latent heat, and one can estimate processing energy requirements from these two forms. Glanvill (1) lists the approximate total energy requirement at the processing temperature for many common thermoplastics. I f a l l i n j e c t i o n molding machines were 100 percent e f f i c i e n t , the energy r e q u i r e d to make a p a r t would be constant r e g a r d l e s s c f the machine used. No machine i s 100 percent e f f i c i e n t ; however, some systems are more e f f i c i e n t than o t h e r s . F i g u r e 1 shows a comparison of energy consumption f o r v a r i o u s i n j e c t i o n molding machines as reported by Reed P r e n t i c e Company (2) . The c a l c u l a t i o n s are based on 20 working days, 24 hours per day, 1 Kw/hp/hour

0-8412-0509-4/79/47-107-009$05.00/0 © 1979 American Chemical Society

Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

ENERGY

10

CONSERVATION

IN TEXTILE

A N D POLYMER

PROCESSING

55 50 45 40 35


30 25

-

20

-

15 —

•H

rH Ci

•H μ PQ

10 5 —

ο υ

s

C

u ω

U U

eu

cd

0) S5

*J •H Ο rH Φ pq

38.1

38.1

&

0 30.5 Figure 1.

30.5

22.8

53.3

22.8

Comparison of plastic infection molding machine energy consumption, 17S-225 clamp force (2)

Moving P l a t e n

toggle a c t i v a t i o n cylinder

Figure 2.

Schematic of hydraulic-mechanical imping

system



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and p u b l i s h e d machine horsepower r a t i n g s o f manufacturers. A c l o ser examination o f these data would show that the high energy con sumption machines have h y d r a u l i c motors f o r both the p l a s t i c a t i n g p a r t c f the molding c y c l e and f o r the clamping system. I f a sepa r a t e h y d r a u l i c motor i s used f o r the clamping system, then energy consumption w i l l be h i g h e s t . A s i n g l e h y d r a u l i c motor that f u r n i s h e s energy f o r both p l a s t i c a t i o n and clamping would be i n t e r mediate. The t c t a l energy consumption can be minimized i f one opts f o r a mechanical clamping system and a s i n g l e h y d r a u l i c motor. Mechanical clamping systems a r e commonly used on machines where t h i n w a l l e d parts w i t h very short c y c l e s a r e molded. A mechanical clamping system has a f a s t e r response than a h y d r a u l i c system and thus a s u b s t a n t i a l p a r t o f the c y c l e time can be saved w i t h a f a s t mold open-close o p e r a t i o n . T h i s can a l s o be a disadvantage s i n c e the f a s t mechanical toggle a c t i o n g i v e s a harder molding c l o s i n g which decreases the mold l i f e . H y d r a u l i c systems g i v e i n f i n i t e speed c o n t r o l i n c l o s i n g , extend mold l i f e , but a r e e x c e s s i v e po wer consumers f o r l a r g e machines w i t h h i g h clamping tonnages. Large machines oper&te best when a h y b r i d clamping system i s used. Here one uses l a r g e volume, low pressure h y d r a u l i c s to a c t i v a t e the toggle system and c l o s e the mold. Once the mold i s v i r t u a l l y c l o s e d , a low volume, h i g h pressure system a p p l i e s the clamping f o r c e (see F i g u r e 2 ) . Motor S e l e c t i o n i n I n j e c t i o n Molding In order to s e l e c t the most economical d r i v e f o r an i n j e c t i o n molding machine, the duty c y c l e must be c a l c u l a t e d (3) . T h i s c a l c u l a t i o n must be made f o r each s p e c i f i c a p p l i c a t i o n to determine the a p p l i c a b l e motor r a t i n g . A t y p i c a l duty c y c l e i s shown i n F i g u r e 3. The motor r a t i n g i s defined i n terms o f 1) Nameplate horsepower and s e r v i c e f a c t o r (SF) and 2) Breakdown torque i n terms o f f u l l l o a d . One f i r s t c a l c u l a t e s the RMS HP v i a Equation (1). RMS HP =

J-

Σ

||^

(1)

Table 1 summarizes these c a l c u l a t i o n s f o r the t y p i c a l duty c y c l e shown i n F i g u r e 3. The r e q u i r e d motor horsepower i s given i n Equation (2). Required motor HP - (RMS Load) (1.1)

(2)

The above r e l a t i o n s h i p allows f o r a ± 10 percent v o l t a g e v a r i a t i o n and the p a r t i c u l a r motor h e a t i n g , p a r t i c u l a r l y a t peak loads a t 90 percent v o l t a g e . For example ( r e f e r to Table 1) RMS HP =

2

JZHP T Ι'ΣΤ

= 118980.38 = 47.8 HP II 52.05


(3)

12

ENERGY

CONSERVATION IN TEXTILE

A N DP O L Y M E R

PROCESSING

-Complete Cycle120

Max. Hp = 108

100 U

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α CO u ο

80 60 40 20

H2 7U 20

10

30

40

9 50

Time, Seconds Figure 3.

Typical injection molding duty cycle (3)

Table I T a b u l a t i o n f o r Duty Cycle C a l c u l a t i o n (see F i g u r e 3) (Ref. 3)

Part of Cycle

Time sec (T)

HP

1

1.5

18.8

2

4.0

108.0

46656.0

3

3.0

16.0

768.0

4

0.5

18.8

176.72

5

14.8

65.5

63495.7

6

20.0

16.0

5120.0

HP* Τ 530.16

7

1.25

18.8

441.8

8

2.0

16.0

512.0

9

5.0

16.0

1280.0

52.05

118980.38


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Savings

Required motor HP - (47.8)(1.1) 1)


2)

- 52.3 HP

13 (4)

S e l e c t i n g a 50 HP motor with a 1.15 SF; the usable HP - 50 (1.15) = 57.5 HP S e l e c t i n g a 60 HP with a 1.0 SF; usable HP = 60 (1.0) = 60 HP

From a thermal viewpoint e i t h e r r a t i n g i s s u i t a b l e f o r the required load. Torque requirements must a l s o be considered. The motor must be capable of c a r r y i n g the peak horsepower (torque) value from the duty c y c l e at 90 percent v o l t a g e . Motor breakdown torque i s r e duced by the square of the v o l t a g e . The r e l a t i o n s h i p i s given i n Equation (5). Motor % BDT

= Peak Load HP χ 100 - Peak Load HP χ 121 NP HP(.9) NP HP

(5)

Z

For example, u s i n g : 1)

2)

50 HP with 1.15

60 HP with 1.15

SF: % BDT = 108 χ 121 = 261% 50 SF: % BDT

« 108 χ 121 = 218% 60

(6)

(7)

A t a b u l a t i o n of p r i c e s and r a t i n g s would l e a d one to the pro per motor s e l e c t i o n . The motor should be s i z e d to operate a t high e f f i c i e n c y over the a n t i c i p a t e d duty c y c l e . T h i s allows f o r a mi nimum power f a c t o r c o r r e c t i o n . In the low duty p a r t of the c y c l e , a s m a l l e r motor i s more e f f i c i e n t . I t i s s t r o n g l y recommended that the power f a c t o r c o r r e c t i o n be used to make the motor operate at i t s peak e f f i c i e n c y over the t o t a l c y c l e . Buyers have a ten dency to o v e r s p e c i f y the r e q u i r e d HP which r e s u l t s i n l e s s than peak e f f i c i e n c y . U t i l i t y Requirements i n I n j e c t i o n Molding Machines A c t u a l s t u d i e s of u t i l i t y requirements i n i n j e c t i o n molding were c a r r i e d out by Olmsted (4). He found that the s i n g l e g r e a t est expense i n operating the machine i s the cost of the e l e c t r i c a l power. His data show that about h a l f the energy consumed goes i n to p l a s t i c a t i n g the r e s i n . A l s o , h i s c a l c u l a t i o n s show that the RMS HP r a t i n g f o r the motor i s v i r t u a l l y unchanged by the shot size. This means that a smaller motor with s p e c i a l design f e a tures to supply high torque requirements to take care of peak loads w i l l do an adequate job (see Table 2 ) . C a l c u l a t i o n s as pre sented by Olmsted are u s u a l l y based on a constant l o a d . Thus, the s i z e of the motor i s u s u a l l y overestimated by 1/4 to 1/3.



Totals

Screw Return Die Open Hydr. Eject. Open Dwell

Impulse

Ram Dwell

Ram In

Die Lock

Die Close

Machine Action

RMS hp = 22.4

0

0

C

0

28.91

8.4

25.9

1.0 3.0

7.3

25.9

0.97

15.5

7.3

8.4

5.0 0.2

36.4

36.4

7.3

hp

Power

1.91

0.15

1.18

sec

psi

Screw 0 both 250 Screw 0 both 1500 Screw 0 both 1500 Screw 0 small 1500 Screw 0 both 250 Screw 2000 small 1500 Screw 0 both 250 Screw 2000 small 1500 Screw 0 small 1500

Cycle Time

10-oz shot Pump Pressures

62.8

14487.1

211.6

670.8

51.7

10397.5

10.6

352.8

2530.6

198.7

2

hp sec

(Power) χ time

z

RMS hp = 23.1

0

Screw 0 small 1500

0

Screw 0 both 250 Screw 0 both 1500 Screw 0 both 1500 Screw 0 both 1500 Screw 0 both 250 Screw 2000 small 1500 Screw 0 both 250

psi

4-oz shot Pump Pressure

11.63

1.0

0

0.97

6.2

0.2

1.0

0.93

0.15

1.18

sec

Cycle Time

8.4

18.5

7.3

25.9

7.3

8.4

36.4

36.4

7.3

hp

Power

6198.2

70.5

342.2

51.7

4159.0

10.6

70.5

1232.2

198.7

62.8

2

hp sec

z

Power χ time

C a l c u l a t i o n s to Estimate Power Required on an I n j e c t i o n Machine to mold 10 and 4 oz. shots o f High Impact Styrène (Ref. 4 ) .

Table I I


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Olmsted's study showed that other major sources of energy consumption i n a d d i t i o n to the e l e c t r i c a l motors a r e the heater bands on the b a r r e l , the scrap g r i n d e r motor, the a i r compressors for general p l a n t use and f o r hopper l o a d e r s , motors i n mold c h i l l e r s , and pump motors and heaters i n mold temperature u n i t s . Energy savings can be accomplished by running hot runner or runnerl e s s molds. This e l i m i n a t e s to a l a r g e extent the r e g r i n d i n g of scrap and e l i m i n a t e s the c a p i t a l investment i n the g r i n d e r .


M a t e r i a l Usage Reduction S u b s t a n t i a l energy savings may a l s o be r e a l i z e d by reducing the amount o f m a t e r i a l that goes i n t o a given p a r t . Part weight reductions greater than 40 percent a r e p o s s i b l e by proper p l a c e ment o f r e i n f o r c i n g r i b s i n redesigned p a r t s (5) . Weight savings are a l s o r e a l i z e d i f one uses s t r u c t u r a l foam p a r t s . Here the weight r e d u c t i o n i s 0 to 30 percent. In each case energy i s saved by processing l e s s m a t e r i a l and a l s o by saving the inherent f u e l value o f the m a t e r i a l i t s e l f . One Pump I n j e c t i o n Molding Machines Olmsted concluded i n h i s study that the number and s i z e o f the e l e c t r i c a l motors could make a s i z e a b l e d i f f e r e n c e i n the energy consumption o f the i n j e c t i o n molding machine. A similar study by F l i c k n e r (6) confirms t h i s . He analyzed the energy savings o f a one pump i n j e c t i o n molding machine. Most conventional systems use two pumps to provide high speed clamp movement, i n j e c t i o n and e x t r u s i o n . However, only one pump i s loaded a t a time, with the second pump i d l i n g . The i d l i n g pump becomes an energy waster as i t provides no u s e f u l work during the i d l i n g time. The study shows that an i d l i n g pump can draw s e v e r a l horsepower. F i gures 4 and 5 i l l u s t r a t e the d i f f e r e n c e i n energy consumption o f a one pump versus a two pump system. F i g u r e 4a shows the power consumed when the clamp pump i s i d l i n g , w h i l e the second pump i s used f o r i n j e c t i o n and p l a s t i f i c a t i o n ( e x t r u s i o n ) . The Kw used during i d l i n g are wasted. F i g u r e 4b shows the Kw consumed when the i n j e c t i o n pump i s i d l i n g , w h i l e the clamp pump i s used f o r clamp movement. The combined i d l i n g Kw o f the clamp and e x t r u s i o n pumps i s wasted power. Figure 5 shows the power consumption o f a one pump system. The only i d l i n g Kw occur during the i n j e c t i o n low p o r t i o n of the c y c l e , which appear minimal. A comparison o f F i gures 4 and 5 shows the energy savings o f the one pump d i v e r t system. Proper machine c y c l e s e t t i n g s a r e a l s o important f o r energy savings. The i n j e c t i o n speed c o n t r o l system ( a v a i l a b l e on new machines as an o p t i o n o r as a r e t r o f i t on o l d machines) optimizes the speeds a v a i l a b l e f o r s p e c i f i c time i n t e r v a l s . The i n j e c t i o n high volume pump i s a v a i l a b l e f o r a f i x e d time p e r i o d and i s then dropped out o f the system. T h i s time p e r i o d should c o i n c i d e w i t h


ENERGY

1 0 0

Γ

CONSERVATION

ΓΝ T E X T I L E

A N DPOLYMER

PROCESSING

r-Clamp Fwd. Pressure B u i l d up


(Kw)

.Clamp Rev.

Idling

I////////

/ / / / / / /

-Time-

2

- I n j e c t i o n High - I n j e c t i o n Low Extruder Run

60

(Kw)

rH

4 Or-

M

Idling

2d-

1////7////1 -Time-

U s e f u l Work

• Figure 4.

Wasted Energy

Two pump system: (a) clamp pump, Kw use; (b) injection extruder pump, Kw use



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the f i l l i n g of the p a r t . A f t e r the c a v i t y i s f i l l e d , a pressure c o n t r o l mode takes over which ce.n be h e l d with the i n j e c t i o n low volume pump. This e l i m i n a t e s blowing the high volume pump over a r e l i e f v a l v e , which i s an energy waster. The blowing of pump volume over a r e l i e f v a l v e a l s o adds heat to the h y d r a u l i c o i l . The o i l temperature must be kept below 150°F Ç4) which i s the safe o p e r a t i n g temperature f o r pumps. Heat exchangers are provided to c o o l the h y d r a u l i c o i l . These r e q u i r e up to 35 gpm f o r a 400 ton machine. A high water usage becomes an energy waster and adds to the o p e r a t i n g c o s t s . F l i c k i n g e r (6) s t a t e s that many operator c o n t r o l s a f f e c t the energy consumption of a machine. The heater band c o n t r o l s , i f set too high, can waste energy as w e l l as overheat the p l a s t i c mater i a l , thus d e l a y i n g c y c l e time. Keeping the h y d r a u l i c o i l too c o l d r e s u l t s i n wasting water and leads to increased o i l pumping c o s t s s i n c e the o i l v i s c o s i t y increases w i t h decreasing temperature. Timer s e t t i n g s need be c a r e f u l l y s e t so that pumps are not kept under load longer than necessary. Pressure s e t t i n g s should be set as low as p o s s i b l e . Figure 6 shows the r e l a t i v e energy consumption f o r v a r i o u s c o n d i t i o n s of a r e l a t i v e machine c y c l e (HPM 220 ton machine). I t i s up to the operator to i n s u r e that the above energy conservation procedures be used. Energy Savings v i a Stack Molding and Double Shot Molding

Q,8)

The preceding d i s c u s s i o n has shown that a s i g n i f i c a n t p o r t i o n of the e l e c t r i c a l energy i n i n j e c t i o n molding i s used i n the oper a t i o n of the clamping system. The amount of clamping f o r c e i s determined by the p r o j e c t e d area of the p a r t s and runners. The relationship i s : Clamping Force = (melt pressure) (Area)

(8)

By s t a c k i n g two c a v i t i e s on top of each other one can mold twice the number of p a r t s w i t h the same tonnage and e s s e n t i a l l y the same energy consumption f o r the clamping p a r t . Due to s l i g h t l y l a r g e r runners and slower f i l l i n g speed per c a v i t y one should a c t u a l l y consider a 15 to 20 percent e x t r a tonnage allowance. O v e r a l l one s t i l l v i r t u a l l y doubles the output of each machine. S u i t a b l e p a r t s to be molded are t h i n w a l l p a r t s with l a r g e surface area such as o\*ercaps f o r c o f f e e cans or margarine tubs. A second energy saving a p p l i c a t i o n i n v o l v e s double-shot molding. This technique i s used to mold p a r t s that have e i t h e r d i f f e r e n t c o l o r s of the same m a t e r i a l or d i f f e r e n t m a t e r i a l s i n the same p a r t . U s u a l l y two p l a s t i e a t i n g u n i t s are used w i t h a two c a v i t y mold. The t o o l i n g c o n s i s t s of a two c a v i t y mold with the c a v i t i e s mounted to r o t a t e 180 degrees. Energy savings and l a b o r savings are r e a l i z e d s i n c e only one machine and one operator are involved.


ENERGY

CONSERVATION IN TEXTILE

^Clamp

A N D POLYMER

Fwd. & P r e s s u r e B u i l d Injection

PROCESSING

Up

High

Injection

Low

Extruder

Run

(Kw)


Clamp Rev.

Figure 5.

One pump divert system: clamp and injection pump, Kw use

100 80

(Kw)

6

0

40 20 0

if

1 '

*ΰ XI ι Η 60 £ • Ή Ή Ο É

60 c α •Η S Η îj • O r Η Figure 6.

ι

ι

ι i ι

0) CO U

. . α) Φ < · -U *J Ό pti 0 ) r H » - i C N C n co ο ο ρ Η C0 0) 0) Μ · Ν 0) φ 0J Φ Φ - n r ) 4 J ft Ν CÎ β β β H M C C X r H O O O O O Η Η W U Ï 5 N N N N

Kw requirement for various conditions during the machine cycle (for total system)


2. scHOTT

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Savings


Energy Savings i n Drying Operations Many polymeric m a t e r i a l s are hygroscopic and p i c k up atmosp h e r i c moisture which must be removed by d r y i n g p r i o r to processi n g . C a l l a n d (9) c a l c u l a t e d the energy that i s r e q u i r e d f o r drying most thermoplastic r e s i n s . These data have been compared with the processing energy that i s reported f o r i n j e c t i o n molding i n G l a n v i l l ÇL). The data a r e presented i n Table 3. The energy consumed i n d r y i n g can represent 1/3 to 1/2 o f the t o t a l p r o c e s s i n g energy. However, because o f heat l o s s e s i n the dryer to the s u r roundings, the d r y i n g e f f i c i e n c y i s assumed to be only 50 percent (10) and the a c t u a l d r y i n g energy i s equal to the p r o c e s s i n g energy. Table I I I T y p i c a l Processing and Drying Energy Requirements f o r Thermoplast i c s (Ref. i a n d 9) . Material ABS Acrylic Acetal Acetate But\rate Nylons

Polycarbonate LD Polyethylene Polyethylene with Carbon Black Polypropylene Polyimide Styrene PVC SAN

Processing Energy (Btu/100 l b / h r ) 14,000 to 17,000 12,500 18,000 12,500 12,000 27,500 to 32,500

25,000 to 30,000

25,000 12,000 7,000 to 15,000 12,000 to 15,000

Drying Energy (Btu/100 l b / h r ) 5460 5120 6143 5120 6485 15,358 12,970 9,215 7,508 4,780 6,826 8,191 10,239

for for for for for

Nylon Nylon Nylon Nylon Nylon

6 66 610 11 12

7,167 6,484 4,095 3,754 4,788

One can see that the e l i m i n a t i o n o f the d r y i n g o p e r a t i o n r e presents a l a r g e p o t e n t i a l energy saving. As a f i r s t step, one can use a hopper dryer so that p e l l e t s that a r e a t the e l e v a t e d d r y i n g temperature a r e f e d to the machine. T h i s e l i m i n a t e s the heat l o s s to the surroundings which occurs i n tray d r y e r s . Drying may be e l i m i n a t e d e n t i r e l y i n c e r t a i n instances as d e s c r i b e d i n two recent developments. HPM (11.) has developed a vented i n j e c -


20

ENERGY

CONSERVATION

IN

TEXTILE

A N D POLYMER

PROCESSING

t i o n molding machine which d e v o l a t i l i z e s the melt through a vent port s i m i l a r to vented e x t r u s i o n . The d r y i n g step i s eliminated and the energy i s saved. Lord (12,) r e p o r t s a second method that e l i m i n a t e s d r y i n g . He has shown that c e r t a i n molds can be modi f i e d i n t h e i r v e n t i n g systems and p r e s s u r i z e d to prevent the f o r mation of splay marks (the moisture of undried r e s i n that wants to come out of s o l u t i o n as the pressure i n the mold c a v i t y i s r e l e a sed) . He found that p r e s s u r i z i n g the c a v i t y with N2 o r CO2 up to 50 p s i g was e f f e c t i v e f o r molding undried ABS m a t e r i a l .


Recovery of Waste Heat A f i n a l thought concerns the: energy savings a s s o c i a t e d with the recovery of waste process heat f o r space h e a t i n g purposes. In i n j e c t i o n molding the heat removed from the mold by the c h i l l e r water i s u s u a l l y l o s t to the surroundings. This waste heat can be used to heat i n j e c t i o n molding p l a n t s as reported by Haas (13). The waste heat i s recovered i n a heat pump type water c h i l l e r and blown i n t o the f a c t o r y area. A s i m i l a r system has been developed f o r other commercial i n s t a l l a t i o n s as r e p o r t e d by Waters (14). Conclusions The preceding d i s c u s s i o n has shown that energy savings i n p l a s t i c s p r o c e s s i n g are p o s s i b l e i n the area of machine m o d i f i c a t i o n , new process machinery, p r o c e s s i n g o p e r a t i o n o f the machine i t s e l f , and i n the area of weight r e d u c t i o n by p a r t r e d e s i g n and foaming of the r e s i n .

Literature Cited 1. Glanville, A.B., Plastics Engineer's Data Book, p. 20, Indus trial Press, New York (1971). 2. Reed Prentice Bulletin, Package Machinery Co., East Longmea dow, MA 01028. 3. G.E. Bulletin GEP-363, General Electric Company, Schenectady, New York. 4. Olmsted, B.A., Modern Plastics, p. 31 (March 1966). 5. Crate, J . H . , Engineering Design with DuPont Plastics, E.I. DuPont De Nemours & Co., Wilmington, Del. 19898. 6. Flickinger, W., "Energy Saving, One Pump Divert Systems", in HPM Now, (Fall 1977), HPM Corp., 820 Marion Road, Mount Gilead, Ohio 43338. 7. Husky Newsletter, (Feb. 1978), "Stack Mold Developments", Husky Injection Molding Limited, P.O. Box 1000, Bolton, On tario, Canada L0P 1A0. 8. Sesko, R.F., Plastics Machinery and Equipment, 7, 43 (June 1978). 9. Calland, W.N., SPE ANTEC, 17, 306 (May 1971). 10. McLeod, John, "The Drying of Hygroscopic Thermoplastics", Bulletin by Thoreson-McCosh, Inc., Troy, Mich. 48084. 11. DeCapite, R., and C.S. Gudermuth, "The Vented Reciprocating Screw Plasticator", HPM Corporation, Mt. Gilead, Ohio 43338. 12. Lord, H.A., SPE ANTEC, 24, 83, Washington, D.C., (April 1978). 13. Haas, Ν., SPE J . 23, No. 2 (Feb. 1967). 14. Waters, C . E . , Applications Erg. Corp., Elk Grove Village, Ill. RECEIVED February 8, 1979. Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Concepts in Energy Savings in Plastics Processing - ACS Symposium

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