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deposited on the surface of a driven cooled roll. There are

usually several rolls in series (normally called ‘‘chill

rolls’’), arranged to cool the polymer by conduction, or

direct contact.

Conduction cooling is quicker than convection cooling,

and this has an effect on the clarity of the ﬁlm. Because

convection cooling (quenching of blown ﬁlms) is relatively

slow, more and larger crystals form in the ﬁlm, as com-

pared to those formed in the casting method. Because

interfaces between crystals scatter light, blown ﬁlm tends

to be more hazy than cast ﬁlm. This ‘‘haze factor’’ normally

rules out use of blown ﬁlm where clarity is very important,

such as food overwrap applications. Because conduction

cooling is more uniform and rapid than convection cooling,

cast ﬁlm has less gauge variation than blown ﬁlm. This

superior ﬂatness means the ﬁlm can be handled better in

subsequent converting operations such as multicolor

printing and laminating. These operations are performed

at high speeds and cast ﬁlm is preferred to minimize

scrap.

Gauge Randomization

In practice, perfectly ﬂat ﬁlm cannot be made, due to die

geometry and machine tool constraints. Blown-ﬁlm thick-

ness variations of 77% and cast-ﬁlm thickness variations

of 73% are typical. Variations in thickness are frequently

evidenced by gauge bands. If relatively small variations

become signiﬁcant at the ﬁlm winder or at a later con-

verting process (printing, laminating), adjustments must

be made to distribute them. In the blown method, varia-

tions in the ﬁlm are usually randomized by rotating or

oscillating the die to distribute the gauge variations over

the ﬁnished web. In cast ﬁlm, because a ﬂat web with two

free edges is produced, the downstream winder with edge

trim slitters is normally oscillated across the ﬁlm, winding

only a portion of the cast web (see Slitting and rewinding).

This generates waste ﬁlm that must be recycled or

scrapped.

It is common to measure sheet and ﬂat-ﬁlm thickness

automatically after the die, compute and average thick-

ness, and use the signal to control screw speed and thus

control thickness in the linear direction. Special casting

and sheet dies that operate in conjunction with a compu-

ter and a thickness-measuring gauge automatically con-

trol the ﬁlm thickness across the width of the die as well.

Wider lines and thinner layers are the current interest

in ﬁlm extrusion. Dies are becoming wider and layers are

shrinking as ﬁlm extruders look to optimize properties and

output as economically as possible. Extrusion Dies Indus-

tries (EDI) report that 3.1 m dies have grown to 4.7 m and

even 5.3 m. It is hoped that cast prolypropylene ﬁlms

could then compete with biaxially oriented polypropylene

(BOPP). For the clarity that is achieved with BOPP, the

ﬁlm used must be quenched rapidly. This is achieved by

Figure 7. Blown-ﬁlm line.

Figure 6. Cast-ﬁlm line.

438 EXTRUSION

running the chill roll slowly. At EDI, the Multiplier feed

block makes ﬁlms with hundreds of layers possible. Kiefel

says customers are looking past dies to its Perfect Cool

system in order to produce more layers. Most of the bulk

equipment used at present is still three layers (5).

RIGID SHEET EXTRUSION

Film thicker than 0.010 in. (0.25 mm) is normally deﬁned

as sheet (see Films, plastic). It is thermoformed (see

Thermoforming) into objects that hold their shape, a

property that ﬁlm does not possess. Extruded sheet is

thermoformed into cups, lids, containers, packaging blis-

ters, automotive panels, signs, and windows. The machin-

ery required for the manufacture of sheet usually extrudes

the polymer horizontally into a nip formed by two har-

dened cooling rolls that deﬁne the ﬁnal product thickness

and surface. Additional rolls and a conveyor for more

cooling and pull rolls and a winder or shear complete the

sheet extrusion line (see Figure 8). The extruder is often

vented to remove low levels of moisture from polystyrene

and ABS. Sheet is traditionally extruded horizontally from

a die similar to a ﬂat-ﬁlm die, but with specially designed

interior ﬂow surfaces to suit the particular polymer.

Restrictor bars are usually used for added gauge unifor-

mity (see Figure 9). Sheet dies are often more massive, to

minimize distortion.

The takeoff unit for extrusion of sheet usually consists

of a cooling and polishing unit (C & P unit) having three

driven, highly polished, chrome-plated rolls; a roller

conveyor; and a pair of driven rubber-covered pulloff

rolls. The C & P unit serves three functions: cooling,

polishing, and gauge control. In some cases, one or two

of the chrome-plated rolls are embossed to yield a

sheet with speciﬁc surface qualities. Roll diameter is

contingent on the output of the extruder, the linear speed

of the equipment, and the level of heat transfer required.

High-capacity multiple-zone temperature control units

are often built into the C & P unit, which must be of

rugged construction to eliminate vibration. Sheets up to

approximately 0.050 in. (1.3 mm) thick can be wound

onto rolls; thicker sheet is cut to desired lengths. In

some cases the sheet is pulled directly into a thermo-

forming machine, providing an in-line, pellet-to-part

operation.

FOAM SHEET EXTRUSION

Extruded polystyrene foam (see Foam, extruded polystyr-

ene) sheet material used for making egg cartons, meat and

vegetables trays for fast-food packaging, and similar

applications continues to ﬁnd new uses, ranging from

decorated picnic ware to coated and laminated sheets.

Polyoleﬁn foams are used for packaging materials (see

Foam cushioning), insulation, and wire coverings. Most of

the world’s extruded foam is produced on tandem-extru-

sion equipment. Although the extrusion process is rela-

tively straightforward, special equipment and controls are

needed.

The ﬁrst extruder has a long barrel and is used to mix a

nucleating agent uniformly throughout the melt of a base

polymer. The nucleator, typically a selected ﬁller, controls

foam cell quality. In effect, it creates imperfections in the

polymer melt, forming nucleation centers for cells to

originate.

About two-thirds down the primary extruder barrel,

the gas blowing agent is introduced. At this point the melt

is homogeneous and at a pressure of 3500–4000 psi (24.1–

27.6 MPa). Fluorocarbons are the usual agents, often

blended with hydrocarbons, such as butane or isopentane,

to reduce costs (6). Carbon dioxide blended up to 35% with

either ﬂuorocarbons or hydrocarbons reduces material

costs still further.

The product mix is fed through a screen changer for

ﬁltering. Then the mix, still under pressure, is fed into a

larger extruder that cools and discharges the product

under conditions to allow extrusion through the annular

die. This is achieved through use of a low-speed screw

rotating in a barrel cooled by high ﬂow rates of water.

Foaming occurs only outside the die lips.

The foamed tube is expanded to 3.5–4 times its dia-

meter and extruded horizontally over an internal cooling

and sizing mandrel that cools and orients the foam and

supports the tube as it leaves the die. After the tube passes

Figure 8. Sheet line.

EXTRUSION 439

along the mandrel and a slitting unit, the two webs are

pulled through nip rolls. From the nip rolls the webs are

wound on either dual-spindle turret-type or cantilevered

winders. Large-diameter reels are required to handle

foam sheet.

Sheet weight per inch (or centimeter) is governed by

the amount of blowing agent incorporated in the mix.

Sheet thickness is determined by adjustment of the die

lips and the take-off speed of the nip rolls. Sheet orienta-

tion is controlled by a combination of die gap, blow-up

ratio, and line speed.

Accurate metering equipment is needed for a good

ﬁnished product. The blowing agent system calls for

sophisticated controls to safely handle high-pressure gas

products on the production line. The difﬁculties of operat-

ing a two-extruder system have been reduced through the

use of microprocessors that automatically monitor and

control a multitude of functions on the extrusion line.

BIBLIOGRAPHY

J. A. Gibbons, ‘‘Extrusion’’ in M. Bakker, ed., The Wiley Encyclo-

pedia of Packaging Technology, 1st edition, John Wiley & Sons,

New York, pp. 282–289; 2nd edition, A. J. Brody and K. S.

Marsh, eds., pp. 370–378.

Cited Publications

1. C. Rauwendall, ‘‘Extrusion’’ in The Mark Encyclopedia of

Polymer Seience and Technology, 2nd edition, John Wiley &

Sons, Hoboken, NJ, 2003.

2. M. Gray, British Patent 5056 (1879).

3. V. Royle and J. Royle, Jr., U.S. Patent 325,360 (1885).

4. Z. Tadmor and I. Klein, Engineering Principles of Plasticating

Extrusion, Reinhold, New York, 1970.

5. T. Deliglio, ‘‘Processing Technology, Extrusion,’’ Modern Plas-

tics Worldwide, 28–36 (September 2008).

6. M. Xanthos and D. B. Todd, ‘‘Plastics Processing’’ in The Kirk–

Othmer Encyclopedia of Chemical Technology, Vol. 19, John

Wiley & Sons, Hoboken, NJ, 2006, p. 549.

EXTRUSION COATING

MICHAEL G. ALSDORF

Extrusion Group, Egan

Machinery

Updated by Staff

INTRODUCTION

Extrusion coating is a process in which an extruder forces

melted thermoplastic through a horizontal slot die onto a

moving web of material. The rate of application controls

the thickness of the continuous ﬁlm deposited on the

paper, board, ﬁlm, or foil. The melt stream, extruded in

one or several layers, can be used as a coating or as an

adhesive to sandwich two webs together.

Equipment for extrusion coating and laminating lines

is normally associated with product groups, with some

overlapping between groups. Substrates or web handling

characteristics distinguish the difference among plastic

ﬁlms, paper, and paperboard combinations.

Three types of lines for extrusion coating and laminat-

ing are thin-ﬁlm or low tension applications at operating

web tension levels of 8–80 lbf (35.6–356 N), paper and its

combinations in the middle range of 20–200 lbf (89–887 N),

and high tension for paperboard applications at 150–

1500 lbf (667–6672 N).

In extrusion laminating, a ﬁlm of molten polymer is

deposited between two moving webs in a nip created by a

rubber pressure roll and a chrome-plated steel chill roll. In

this continuous operation, rolls of material are unwound,

new rolls are automatically spliced on the ﬂy, and the

surface of the substrate is prepared by chemical priming

or other surface treatment to make it receptive to the

extrusion coating and to help develop adhesion between

the two materials (see Figure 1).

Pressure and temperature on the web and extrudate

combine to produce adhesion. The substrate normally pro-

vides the mechanical strength to the resultant structure,

and the polymer provides a gas, moisture, or grease barrier.

As materials, especially for food packaging, become

more complex with ever-increasing performance stan-

dards, coating lines become more complicated. The re-

quirements for new extrusion coating lines are high

productivity, extreme ﬂexibility, and labor-saving compu-

terized and robotized equipment. Modern extrusion coat-

ing lines must be able to process the speciality resins that

offer greater adhesion, allowing line speeds to be in-

creased. The most common coating resins used is low-

density polyethylene, but extends to ethylene–vinyl

acetate, ethylene–acrylic acid, polypropylene, high-

density polyethylene, and ionomers (1).

APPLICATIONS

Products from extrusion coating/laminating lines have six

main market classiﬁcations: liquid packaging, ﬂexible

Figure 9. Cutaway of sheet die with restrictor.

440 EXTRUSION COATING

packaging, board packaging, industrial wraps, industrial

products, and sacks.

Liquid Packaging

Liquid packaging utilizes a single web-coated lightweight

board, or a combination of board, plastic, and aluminum

foil, for semirigid containers for milk, juices, water, oils,

processed foods, sauces, cheese products, and aseptic

packaging of liquids. The polyethylene-coated milk carton

was largely responsible for the emergence of the extrusion

coating industry in the 1960s, and as more commercial

uses were found for polyethylene-coated materials, the

industry grew rapidly (see Polyethylene; Cartons,

gabletop).

In the 1980s, aseptic packaging made strong inroads

in replacing traditional metal and glass containers (see

Aseptic packaging). The sterile ﬂexible ‘‘paper bottle,’’

which extends the shelf life of dairy products for months

without refrigeration, is a major alternative form of

packaging (2) (see Shelf life). It is also used to package

fruit juices.

Although aseptic packaging systems differ, most of

them use paperboard–foil–plastic composite material

that is formed to shape, sterilized, and ﬁlled with a sterile

liquid or semiliquid product under the sterile conditions.

Customized extrusion-coating lines, complete with in-line

laminating stations, are used to produce an almost un-

limited variety of shapes, sizes, and printing options for

aseptic and other packaging materials.

Flexible Packaging

The ﬂexible packaging classiﬁcation covers the combina-

tion of plain, printed, or metallized ﬁlms, papers, poly-

mers, and foil, used for protection, unitizing, dispensing,

or holding of commodities. These include medicine and

pharmaceutical supplies, foods, chemicals, hardware,

Figure 1. Simple extrusion-coating line.

EXTRUSION COATING 441

liquids, notions, sterile products, and meats. Flexible

packages also include wrappers for fast food, the bag

for ‘‘bag-in-box’’ containers, and the multilaminated web

for Glaminate tube packaging (3) (see Bag-in-box, dry;

Bag-in-box, liquid; Tubes, collapsible; Multilayer ﬂexible

packaging).

Flexible packaging lines are processing progressively

thinner substrates of polyester, oriented polypropylene,

and metalized materials (see Film, polyester; Film, or-

iented polypropylene; Metallizing). The light-gauge pre-

printed substrates used for snack foods require minimum

tension to ensure that preprinted webs are not distorted.

Machines to create these new structures are becoming

increasingly complex. Thinner coating layers are more

difﬁcult to extrude on the coating machine, and often the

coating head itself must be engineered to handle a variety

of coating materials (see Figure 2).

Flotation drying, using air on both sides to ﬂoat the

web, is widely used in ﬂexible package manufacturing

because it handles light ﬁlms well. Improved drying

efﬁciency compared with roll-support dryers allows higher

line speeds.

Board Packaging

In board packaging, heavyweight boards are coated, lami-

nated, and then formed into boxes (folding cartons) for

packaging detergents, tobacco, liquor, frozen foods, and

bakery products (see Cartons, folding). Microwaveable

and radiant oven trays (4) and ice cream cartons are

also in this category. The plastic-coated containers protect

against grease, moisture, and gas. Release characteristics

can also be provided.

Industrial Wraps

Industrial wraps cover the range of heavy or reinforced

papers, ﬁlms, or boards used for products in which the

extrusion-coated material may be added to other media

used for products such as composite cans, drum liners,

soap wrappers, and sheet overwraps for a variety of baled

materials (see Cans, composite). The coated product is not

necessarily used as a unit container, but as a wrapper or

part of a protective structure.

Industrial Products

The industrial products classiﬁcation takes in extrusion-

coated or laminated material serving various industry

requirements. Products include photographic-base papers,

substitutes for bitumen coatings, base papers for silicone

coatings, insulation backing, automative carpet coating,

and metallized ﬁlm balloons. Also in this category are

functional laminates like credit cards and printed circuit

boards, decorative laminates such as wallpaper, and dis-

posables like tablecloths and various hospital and surgical

supplies. As with industrial wraps, these products may or

may not be associated with packaging.

Sacks

Sacks cover materials for multiwall paper bags and plas-

tic-coated rafﬁa. Intermediate tension lines produce

coated scrim that is woven from tapes of oriented poly-

ethylene or polypropylene. These materials are used for

heavy-duty sacks and tarpaulins; and they have applica-

tions in building, recreational, and agricultural areas (see

Bags, paper; Bags, heavy-duty plastic).

A miscellaneous classiﬁcation would include coated

foam used in the fast-food industry.

MACHINERY

Obviously, no single coating line can produce all the

foregoing products. Today, various types of machinery

are manufactured to produce coated and laminated pro-

ducts using substrates ranging from 0.4-mil (10-mm) ﬁlm

to 246 lb/3000 ft

(400 g/m

) board, with coating weights

4.3–49 lb/3000 ft

(7–80 g/m

), at widths 76.2–787 mil (300–

3100 mm), and at speeds 1.1–33 ft/s (0.33–10 m/s).

The most important consideration in web processing or

web handling equipment is the determination of the

practical range for the system—the maximum and mini-

mum unwind and winder roll diameters, maximum and

Figure 2. High-speed extrusion-coating line used to produce ﬂexible packaging-type materials.

442 EXTRUSION COATING

minimum web-tension forces, splicing speeds, core dia-

meters, and other process needs.

The unwind basically takes material in roll form and

processes it continuously over a series of idler or driven

rolls with a suitable amount of tension in order to mini-

mize wrinkling yet not produce deformation. A dancer or

transducer roll can be used for tension control; DC regen-

erative drives and electric or pneumatic brakes are used

where applicable. Similar considerations apply to the

infeed holdback when levels of tension required differ

from those of the in-line operations. These sections tend

to isolate tension transients from the unwinding roll.

Electrostatic treatment and ﬂame treatment are avail-

able for enhancing surface tension or wettability condi-

tions of the inert substrates prior to applying aqueous

solutions (1). The direct/reverse gravure coater can be

used for either priming, coating, or printing. Chemical

priming is used mostly in ﬂexible-packaging lines to

promote adhesion between the extrudate and substrates

such as cellophane, polyester, ionomer, nylon, or polyoleﬁn

ﬁlms (see Film articles). Infrared preheating and vacuum

rolls provide the means to dry the PVDC-coated web and

effect proper web handling.

Air-ﬂotation, driven-roll, idler-roll, or drum-support

dryers are selected depending on the strength, support,

or tension required for the substrates. Recirculation of

heated air in the dryers is a common energy conservation

practice in all these dryers. The single-roll web guide at

the dryer exit and chill or pull rolls are needed for special

web processing requirements.

The extrusion laminator along with the extruder-and-

die system is the heart of the process. The backup chill

roll, rubber roll, and large-diameter chill roll form a three-

roll system. Two-roll laminators can be used for heavy

substrates or paper-board applications. As the moving web

enters the nip section, it is coated, laminated, or both.

Ozone in close proximity to the entering web is used for

oxidation of the molten polymer for improved adhesion in

high bond level applications. Most of the heat is removed

from the coating or laminate by the chrome-plated chill

rolls. Chill rolls normally are steel and are constructed

with a double-shell arrangement and spirally bafﬂed.

Outer shells of aluminum have been used for high coating

weights. High-velocity chilled water is circulated to main-

tain a temperature rise between inlet and outlet of 2–41F

(1–21C).

The coated or laminated structure is normally edge-

trimmed at the laminator by razor, score, or shear cutting.

Trim removal systems are installed just after the lamina-

tor. Slitting can also be done just prior to winding at a

turret or single-drum winder.

Auxiliary unwinds can be located on, near, or over the

extrusion laminator to provide a secondary substrate for

laminating at the nip where the extrudate acts as an

adhesive. These unwinds can consist of single-position or

turret assemblies with ﬂying splices for aluminum foil,

oriented polypropylene or polyester ﬁlm, paper, or paper-

board substrates.

Web turnover systems, pull rolls, coaters, infrared

heating, dryers, and web processing steps after the extru-

sion laminator are designed according to product needs.

Thickness measuring devices include infrared and scan-

ning of clear webs.

There are two basic winding techniques. The turret

winder or center wind system is used for most ﬂexible

packaging materials. Tension is controlled by a dancer or

transducer roll. The same design criteria for unwinds

also applies to winders. The type of web, operating speed,

tension range, and roll buildup must be properly con-

trolled to wind up a satisfactory roll. Paper and paper-

board products can be wound by surface methods on a

single-drum winder.

All-plastic constructions require more advanced web

controls. Many converters utilizing traditional wood cel-

lulose substrates are specifying that their new coating

lines must be able to handle all-plastic ﬁlms. Wider

tension ranges and air ﬂotation dryers are two principal

requirements of these convertible systems.

Other features being incorporated into various lines

include DC-regenerative unwinds and infeed holdback

drives for prices and low-level tension, direct/reverse

gravure coaters for aqueous PVDC coating, infrared pre-

heating, and vacuum rolls for web controls.

In the production of photographic-base papers, exact-

ing speciﬁcations and special criteria for pigmented poly-

mers are needed to produce coated materials that

constantly provide high-quality photographs. The concept

of tandem operations or coating two sides of a substrate in

one pass can be applied to many ﬂexible-packaging lines

that produce combinations of paper, extrusion lamination

to aluminum foil, and extrusion coating a polymer for heat

sealing. Higher-operating line tensions can be used in

producing structures with paper for granulated or pow-

dered mixes and freezer-wrap or sugar-pouch materials.

Polyethylene is not the only resin used for lamination or

coating. Polypropylene, ionomer, nylon, ethylene–acrylic

acid (EAA), ethylene–methacrylic acid (EMA), and ethy-

lene–vinyl acetate (EVA) can also be part of a converter’s

inventory of resins.

Single-unit pilot coating lines feature an entire coating

system preassembled and prewired at the factory and

mounted on a structural steel base. These lines can be

completely enclosed and have applications for the develop-

ment of products such as the retort pouch, aseptic packa-

ging, vacuum packaging, and other extended shelf-life

oduct

s used to replace conventional glass and metal-can

packages; they can also be used in the development of many

types of medical-grade extrusion coatings (3).

Stainless steel is used when extreme cleanliness is

required. The ‘‘cleanroom’’ machines are designed so

that any metallic particles generated by machine friction

are either contained or swept away by laminar air ﬂow.

Stainless steel is also used when lines are frequently

washed with solvents that could remove conventional

paint.

A typical pilot coating line consists of an unwind,

coating heat, air-ﬂotation dryer, dryer exit tension control,

cooling station, extrusion coater, and rewinder, all aligned

on a one-piece steel frame. Pilot coating lines are designed

to handle narrow web widths and can be built so that

components are cantilevered instead of being supported

by traditional side-frames. The spindles, idler rolls, force

EXTRUSION COATING 443

transducers, and air-ﬂotation bars are all mounted on a

vertical backplate.

Extrusion-coating lines are experiencing increased

automation. Raw material and roll stock can now be

selected from a controlled inventory, delivered to the

line, and handled through robotics (see Robots). The entire

operation can be monitored and controlled by computer

(see Instrumentation/controls).

Drives are under computer process control, and there

have been advances in digital drives and in energy-

efﬁcient AC inverters. While a number of different drive

systems have been installed and operated, the multimotor

DC system is predominantly used for extrusion coating

equipment. These drives can consist of as many as 10

motors in one line with a single control to bring the web up

to operating speed. The tandem follower is another drive

or computer feature whereby the extruder will increase or

decrease in rate with line speed in order to maintain a

ﬁxed coating weight as the line speed is changed.

BIBLIOGRAPHY

Michael G. Alsdorf, ‘‘Extrusion Coating’’ in The Wiley Encyclope-

dia of Packaging Technology, 1st edition, John Wiley & Sons,

New York, 1986, pp. 289–293; 2nd edition, 1997, pp. 378–381.

Cited Publications

1. R. J. Ashley, ‘‘Extrusion Coating’’ in D. E. Packham, ed., The

Handbook of Adhesion, John Wiley & Sons, Chichester, UK,

2005.

2. J. G. Brennan and B. P. F. Day, ‘‘Packaging’’ in J. G. Brennan,

ed., Food Processing Handbook, Wiley-VCH, Weinheim,

Germany, 2006.

3. M. Schlack, ‘‘Extrusion Coaters Gear for New Packaging

Action,’’ Plast. World, 42 (July 1984).

4. M. J. Kirwan, ‘‘Folding Cartons’’ in M. J. Kirwan, ed., Paper

and Paperboard Packaging Technology, Blackwell Publishing,

London, 2005.

444 EXTRUSION COATING

FILLING MACHINERY, BY COUNT

Accurate measuring is imperative in packaging to avoid

costly overage and shortages that are now prohibited by

law. As a basis for measurement, most packaging lines use

either the weight of the package (see Checkweighing) or

the number of pieces in the package. This article pertains

to methods used to produce packaging that contain a

speciﬁed number of pieces. Modern automatic counting

systems are based on concepts that evolved in ancient

times. They all are encompassed three basic functions that

are as follows: parts representation, parts detection, and

product handling.

PARTS REPRESENTATION

Counting is used to determine the amount of a speciﬁed

batch and the method used to achieve this begins by

selecting a basic system of representation. Systems of

representation are used in all forms of counting. Units

can be represented by ﬁngers and toes, knots in a rope, or

as in the packaging industry, they can be pulses of elec-

trical current generated from specially designed detection

units. Over the years, humans have engineered quick and

accurate ways of counting, but no method is as accurate as

a single-ﬁle count of an individual unit of product.

PARTS DETECTION

The next step in counting is detecting the unit of product

to be counted. A person detects the product either by sight

or by touch. Machines are designed to operate on the same

principles and use either optical systems (sight) or non-

optical systems (touch).

Optical Systems. An optical system operates much like

a human eye. A photosensitive receiving device is estab-

lished, and the unit of product to be counted is passed

within detection distance of it. There are many models of

optical systems used in packaging, but most are based on

either a simple digital photocell system or an intricate

electronic analog detection unit.

In the photocell system, the breaking of a light beam

fed to the photocell receiver indicates that a unit of

product has passed through the detection zone. The break

is then recorded as the counting of one unit of product.

This method of detection is perfect for most product

applications that meet speciﬁcations for light-blocking

systems, but it is limited by the fact that the light source

fed to the receiver must be completely blocked out before

detection is recognized. This method is not efﬁcient with

transparent, overlapping, or bicircular objects (such as

clear plastic), two pieces of material riding on top of each

other, or objects with holes, which may trigger the photo-

cell more than once.

Another approach to optical detection is the analog

photo-optic system. This system is fast, ﬂexible, and

accurate, because certain parameters must be established

and met before detection is recorded. The Photo Optic

Shadow Detector (Sigma Systems, Inc.), for example,

detects the dimensions of a speciﬁed shadow made by

the unit of product when fed through the detection zone.

Each shadow of a detected unit must meet certain para-

meters before being recorded. The parameters can be

entered into the computer portion of the counting system

to compensate for objects such as ﬂat washers and O rings,

which would trigger a photocell system twice, or clear

plastic, which would not block out a light source but would

cast a shadow that could be detected.

Nonoptical Systems. The nonoptical methods of parts

detection are similar to human touch. The touch methods

generally involve escapement devices, electrical contact, or

magnetic-ﬁeld contact. The escapement device is usually

fully mechanical and is similar to an analog machine. Each

unit of product must be of a speciﬁc shape and size. The

product is fed into a receiving device that ﬁts those exact

parameters and then is discharged and recorded as a

speciﬁc unit of product. This process is equivalent to

placing dominoes in a box made just for dominoes. If only

ten dominoes ﬁt, then the unit of product would be

recorded as ten units. This system is accurate, but it offers

little ﬂexibility. It commonly is used for high-speed count-

ing of uniform products such as pills and tablets.

Another nonoptical method is the electrical-contact

method, in which an electrical switch is triggered each

time a part comes in contact with the switch. The part is

then recorded as one unit of product. The response time

and the ability of the product to actuate the mechanical

switch-triggering device greatly affects the accuracy and

ﬂexibility of this type of system. The magnetic system is

another touch-system method. Each unit of product to be

counted must come in contact with or disturb the mag-

netic ﬂow being transmitted from a magnetic source. As

each unit of product is fed through the magnetic ﬁeld, it is

recorded as a counted unit.

Coupled with the detection system is a process known

as discrimination (e.g., a farmer counting cows knows how

to exclude sheep). This process has hampered the auto-

mated counting system greatly, because once this vital

function leaves the dependability of the human senses,

accuracy often suffers. Only two of the detection systems

mentioned earlier can discriminate and are as follows: the

photo-optic-analog system and the escapement-device sys-

tem. In both, certain parameters must be met before a unit

of product is recorded; the other systems record any item

that is detected. Engineers have been working for years to

improve the efﬁciency of the detection system to ensure an

accurate count.

445

PRODUCT HANDLING

In almost every counting system, the process of getting the

product to the detection zone and then moving it away

from the zone must be achieved, whether the detection

zone goes to the product or the product comes to the zone.

This system of product movement is known as product

handling. The product is usually brought to the detection

zone, and in packaging, all of the methods bring the

product to the zone in single ﬁle. There are various ways

to do this. One is vibratory feeding, which is designed to

vibrate a track or bowl ﬁlled with product, which in turn

causes the product to vibrate along a designated path or

ramp. The tracks or ramps narrow as the product nears

the detection zone in order to create a single ﬁle. These

feeding systems are the most ﬂexible, because most objects

lend themselves to vibration.

Another method is the belt or V-belt system. The

product is placed in a master container and discharged

onto a belt system. The width of the belt track is narrowed

to allow only one part to pass at a time to achieve single-

ﬁle feeding. Product handling plays an important role in

the counting process, because even the most reﬁned

counting system will be inaccurate if the product is not

presented to the detection zone in a manner acceptable to

the detection device.

Many approaches to product feeding exist, but most

counting systems allow free entry and exit of product

through the detection zone. In packaging, however, it is

sometimes necessary to retain all or part of the amount

counted for a speciﬁc function. The retention is known as

accumulation or partial accumulation. The accumulation

functions usually are determined or predetermined by a

manual function, in which an accumulation parameter, i.e.,

the amount of product desired, is assigned to the counting

unit. The counting unit usually must meet the assigned

parameters before permitting the accumulation functions

to discharge the retained product. This function is essential

when a manufacturer wants to place a predetermined

amount of product into a speciﬁc-size container, e.g., accu-

mulating 20 tablets, then discharging them into a package

or bottle. It also plays an important role in the packaging

process, because most packaging machines are intermit-

tently cycled by the signal received from the counting

system when the accumulation function discharges pro-

duct. Most containers are aligned under the accumulation

chute to receive the allotted amount of product.

As electronic technology advances, the ability to count

and discriminate parts will improve. However, the attain-

able operating speeds will depend on the speed with which

the unit of product can be fed into the detection mechan-

ism and the speed of the product-handling system. The

performance of any counting system must be objectively

evaluated on its ability to count accurately and its adapta-

tion to the intended use.

BIBLIOGRAPHY

‘‘Filling Machinery, by Count,’’ in David Madison, ed., The Wiley

Encyclopedia of Packaging Technology, 1st ed., by Sigma

Systems, Inc., pp. 294–295.

FILLING MACHINERY, LIQUID, CARBONATED

The method for ﬁlling carbonated liquids (primarily beer

and soft drinks) differs from other ﬁlling techniques (see

Filling machinery, still liquid), because it is accomplished

under pressure and uses the container as part of the

control of net contents. Carbonated beverages, which

tend to foam, require ﬁlling techniques that ensure the

retention of the required carbonation levels in different

sizes of cans and bottles. It is imperative that the carbo-

nated liquid be processed in a way that prevents excess

foaming, which would result in uncontrolled ﬁlling levels

as well as impaired closing of the vessel.

The ﬁlling machine (ﬁller) consists of a rotating bowl

with a valve and CO

pressurization control, ﬁlling valves

that attach to the perimeter of the bowl, a tabletop that

contains the controlling technique for feeding in and taking

away the container, a closing section that applies either a

bottle closure or a can end, and a drive system that keeps all

components in proper synchronization with each other.

The bowl must control the pressure on the liquid within

it, yet be at a pressure lower than that of the system that

feeds it. With this system, a continuous supply of product

is assured with the least amount of turbulence. The level

within the bowl is maintained by a simple ﬂoat valve or

similar device.

The ﬁlling valves embody the applied technology in-

volved in ﬁlling carbonated products. Almost all of the

machinery manufacturers of note employ the same prin-

ciples with some variation in the mechanical interpreta-

tion of the concepts. To understand the valve’s function, it

is necessary to follow it through the various ﬁlling stages

described in the following paragraphs.

The vessel is presented to the ﬁlling valve to ensure

complete intimacy between both surfaces. This process is

controlled by a pneumatic pressure system that holds the

vessel ﬁrmly against the valve, yet tenderly enough to

avoid crushing the thin metal cans or light plastic bottles.

The container rotates with the ﬁller valve, and a me-

chanical trip actuates the valve to permit CO

from the

upper part of the bowl (above the liquid level) to pressurize

the container. The pressure in the container is now equal to

or somewhat lower than the pressure in the bowl.

The valve is then actuated into the next stage, which

permits the product to ﬂow into the prepressurized con-

tainer gravimetrically. During the ﬁlling phase (as ﬂuid

enters the vessel), it is essential that the CO

in the

container be displaced. This displacement is accomplished

through a vent tube, which is normally in the center of

the valve and protruding downward into the vessel. As the

product ﬁlls the vessel, it ultimately rises to seal off the

vent tube or ball check. This stops the ﬁlling process

because pressures in the bowl above and in the container

below have reached an equilibrium.

Although the container is still in an intimate seal with

the valve, another external latch actuates an internal

chamber in the valve, which closes the connection to the

bowl (both the liquid portion and the CO

charge above it)

and simultaneously vents the container to atmosphere.

446 FILLING MACHINERY, LIQUID, CARBONATED

This step maintains control of the product in the container

during the depressurizing step and assures that the

product will be virtually foam-free when the container is

removed from contact with the valve.

The tabletop, which employs an exit star wheel (not

generally used on can ﬁllers), sweeps away the lowered

package from the rotating bowl and transfers it into the

closing section at tabletop height. If the container is a can,

then it is closed in the closing machine by an ‘‘end,’’ which

is rolled and seamed in place (see Can seamers) integrally

with the can body with forces great enough to withstand

high internal pressures. Bottles can be closed with a pryoff

or twistoff crown; a rolled-on aluminum closure, which is

threaded in place using the threaded portion of the bottle

as a mandrel, or a prefabricated threaded closure applied

by standard technique (see Capping machinery; Closures).

Carbon dioxide dissolves more readily in cold water

than in hot water; thus, to keep foaming at a minimum

and ﬁlling speeds at a maximum, it has been common to

run beer and soft drinks as close to 321F(01C) as is

practicable. To save the energy consumed by refrigeration,

ﬁllers have been introduced that operate at ambient

temperatures. Controlling the CO

in the carbonating

and ﬁlling stages means these operations must be accom-

plished at above-normal pressures, which complicates the

internal parts of the ﬁlling valve and reduces rates of

speed. The production rates of modern ﬁllers have in-

creased to approximately 2000 12-oz (355-mL) cpm and

reportedly 1500 16-oz (473-mL) glass bpm. These in-

creased rates of output are made possible by the use of

programmable computers and new advanced instrumen-

tation. Precise ﬁll heights in the containers are controlled

by the length of a vent tube in a bottle ﬁller and ball check

technique in a can ﬁller. However, because of minor

variations in the dimensions of glass and plastic bottles,

more variability exists in volumetric content than in the

exact volumetric measurement technique sometimes em-

ployed in ‘‘still’’ liquid ﬁlling.

BIBLIOGRAPHY

‘‘Filling Machinery, Liquid, Carbonated’’ in W. R. Evans, ed.,

The Wiley Encyclopedia of Packaging Technology, 1st ed., by

Coca-Cola Bottling of New York, p. 300.

FILLING MACHINERY, LIQUID, STILL

F. B. FAIRBANKS

Horix Manufacturing Company,

Pittsburgh, Pennsylvania

This article deals with the ﬁlling of noncarbonated liquids

intended for packaging and distribution into rigid and

semirigid preformed containers, such as glass bottles,

sanitary cans, plastic bottles, and preformed paper car-

tons. Form/ﬁll/seal packaging is not discussed (see the

Form/ﬁll/seal, horizontal; Form/ﬁll/seal, vertical; Therm-

form/ﬁll/seal articles), and the information relates only

indirectly to such applications as the ﬁlling of paper cups

in vending machines.

Liquid-ﬁlling machines are classiﬁed here in terms of

two fundamental characteristics: ﬁlling principle em-

ployed (see Table 1) and container-positioning method

used (see Table 2). Except for a few speciﬁc restrictions

(discussed below), the two characteristics are indepen-

dent, but certain combinations are not commercially avail-

able. Packagers can select from a wide range of ﬁllers,

however. Among the members of the U.S. Packaging

Machinery Manufacturers Institute (PMMI) alone, 61

companies offer liquid ﬁllers (1), and this ﬁgure does not

include machines made in other countries.

METHODS OF FILLING

In Table 1, the methods of ﬁll are divided into two primary

categories: the sealed-container system, in which the ﬁll-

ing device seals positively against the container; and the

unsealed-container system, in which the container is left

open to the atmosphere during the ﬁll process.

Sealed Container Filling System. In sealed-container ﬁll-

ing, there are seven distinctly identiﬁable types of ﬁllers.

All sealed-container ﬁllers ﬁll to a controlled level in the

container.

Table 1. Methods of Container Filling

Type of Container Filling Method

Sealed container Balanced pressure

Gravity

Gravity–vacuum

Counterpressure

Unbalanced pressure

Vacuum

Prevacuumizing

Gravity

Pressure

Unsealed container Level sensing

Piston volumetric

Cylinder vertical, closed ends

Cylinder vertical, open-end inlet

Cylinder horizontal, single-ended

Cylinder horizontal, double-ended

Rolling-diaphragm volumetric

Displacement-ram volumetric

Volume cup

Turbine-meter volumetric

Positive-displacement-pump volumetric

Peristaltic-pump volumetric

Weight

Gross weight

Net weight

Time

Controlled-pressure head

Constant-volume ﬂow

Overﬂow

FILLING MACHINERY, LIQUID, STILL 447