AU2001279961A1

AU2001279961A1 - Heat sealing apparatus for packaging machinery

Info

Publication number: AU2001279961A1
Application number: AU2001279961A
Authority: AU
Inventors: Simon Charles Martin; David Robert Seaward; Peter John Whitlock
Original assignee: Molins Ltd
Current assignee: Mpac Group PLC
Priority date: 2000-08-23
Filing date: 2001-08-17
Publication date: 2002-05-30
Anticipated expiration: 2021-08-17

Description

Heat Sealing Apparatus for Packaging Machinery

The invention relates to heat sealing apparatus for packaging machinery

and particularly, but not exclusively, to heat sealing apparatus for vertical, form,

fill and seal (VFFS) packaging machinery

VFFS machines usually produce filled and sealed bags from a flexible

packaging material, although they can be used to produce empty bags to be filled

and sealed subsequently A known configuration of VFFS packaging machine is

shown in Figure 1 In this machine, a web 18 of flexible packaging material is

fed over a forming shoulder 24 which causes it to form into a tube wrapped about

a vertically oriented filling pipe 26 The edges 27 of the web (Figure 2) are

sealed together in the longitudinal direction of the tube by a heat sealing device

36 to produce a backseal 29 The backseal is a continuous seal extending along

the length of the tubular web and is so-called because it can be found at the back

of the completed bag Subsequently, successive transverse seals are made at bag

length intervals by opposed transverse sealing jaws 42 The sealing jaws 42

typically carry a knife arrangement (not shown), which cuts through the area of

the transverse seal so that each transverse seal provides a top seal for a completed

bag 46 and a bottom seal for the bag immediately upstream thereof Product from

a product weigher 28 is fed down the filling tube 26 in synchronicity with the

sealing jaws so that each package contains a required amount of product Typically the heat sealing device 36 comprises heated wheels or belts which engage the tubular web and apply heat to the web as it is fed down the

forming tube past the backseal device

In order to obtain a good, strong, consistent seal, it is necessary to apply

heat evenly to the web This can be more critical in the case of some materials, for example polythene, than for others Heated wheels and belts have a certain

mass and thus a certain degree of thermal inertia, which makes it difficult, if not impossible, to change their temperature during the bag forming cycle Thus,

where the web feed speed varies during a bag forming cycle, it is not possible to correspondingly vary the amount of heat applied so as to provide even heating along the backseal The result can be burn-through of the mateπal at some points where the web is running relatively slowly, and/or no-seal at others where insufficient heat is applied due to decreased sealing time when the web is running fast

There have been proposals to form the backseal using a hot air backseal device Hot air backseal devices blow air over a heater and direct the heated air onto the backseal area by means of a nozzle The amount of heat applied has typically been varied to take account of different web speeds by varying the energy input to the heater, varying the airflow over the heater or selectively venting the heated air away from the seal area Known hot air backseal devices are disclosed in US5466326 and WO98/40202 The discussion of the background to the invention herein has been provided

simply to explain the context of the invention and it not to be taken as an

admission that any of the material referred to was known or part of the common

general knowledge in Australia or elsewhere in the world as at the priority date

of any of the claims

The invention provides heat sealing apparatus for forming a continuous

lengthways extending seal on a web of packaging material to be fed past said

apparatus, said apparatus comprising a nozzle connectable to a hot gas producer

which produces a flow of hot gas having a substantially constant temperature and

mass flow rate, a carrier for said nozzle and a drive for said carrier, the

arrangement being such that in use said nozzle can be controllably moved relative

to said web in accordance with variations in web feed velocity such that said flow

of hot gas from said nozzle can apply a substantially constant heat to said web to

form said lengthways extending seal

The invention includes form, fill and seal packaging apparatus, said

apparatus including a web feeder for feeding a web of packaging material over a

flow former, said web having lengthways extending edges and said flow former

being arranged to cause said web to adopt a generally tubular configuration

wherein said edges are disposed in generally adjacent relationship, and a heat

sealing device for forming a continuous seal adjacent said edges by which said

edges are held in said adjacent relationship, said heat sealing device comprising a nozzle connected with a hot air producer for directing a flow of hot gas at said

web, a carrier for said nozzle and a drive for said carrier, said drive being

arranged to controllably move said nozzle relative to the web in accordance with

variations in web feed velocity such that said flow of hot gas from said nozzle

applies a substantially constant heat to said web to form said continuous seal

The invention also includes a method of forming a continuous seal along

a moving web of packaging material, said method including moving said web at

a cyclically varying velocity, directing a flow of hot gas at said web, said flow

having a substantially constant temperature and volume flow rate, and cyclically

moving said flow relative to said web along a region to be sealed such that a

substantially constant heat is applied to said web to form said seal

The invention also includes form, fill and seal packaging apparatus, said

apparatus comprising means for feeding a web of heat sealable packaging material,

forming means arranged to cause said web to adopt a tubular configuration m

which opposed lengthways extending edges of the web are brought into a

juxtaposed relationship and heat sealing means for forming a continuous seal in

the region of said edges, said heat sealing means comprising means for directing

a flow of hot gas at said web to form said seal and being arranged to move said

flow relative to said web such that a substantially constant heat is applied to the

web

In order that the invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the drawings, in which

Figure 1 is a schematic side elevation of a vertical, form, fill and seal

packaging machine,

Figure 2 is a perspective view of a hot gas backseal device for the machine shown in Figure 1 ,

Figure 3 is a graphical representation of features of a bag making cycle using the machine of Figures 1 and 2, and

Figure 4 represents the motion of the transverse sealing jaws of the machine of Figure 1

Figure 1 is a schematic side elevation of a VFFS machine 10 for making and filling bags The machine comprises a frame 12 to the rear of which is fixed a mounting device 14 The mounting device 14 is arranged to receive a reel 16 of a packaging film such as polythene The reel is rotatably supported by the mounting device so that the film, or web 18, can be drawn from the reel by a nip roller drive 19 which is driven by a servo motor (not shown)

The web 18 passes upwardly from the mounting device through the nip roller drive 19 to a first roller unit 20, also mounted at the rear of the frame The roller unit 20 comprises one or more rollers (illustrated schematically as roller 22) around which the web is guided, and is arranged such that the web is directed towards the front of the frame 12 where it passes under a roller 23 before feeding onto a forming shoulder 24

The forming shoulder 24 is carried on a cylindrical filling tube 26 which

is supported on the front of the frame A weigher or other control device 28 is

mounted above the filling tube 26 and is arranged to drop predetermined amounts

of product down into the filling tube

The web passes over the forming shoulder 24 into an arcuate space

between the filling tube 26 and the forming shoulder The arrangement of the forming shoulder and filling tube is such as to cause the web to adopt a tubular

configuration about the filling tube Downstream of the forming shoulder, there is a heat sealing unit 36 which is positioned at the front of the machine and connected to the frame 12 by means of an L-shaped connecting arm 38, which is arranged to allow the sealing unit to be swung away from the filling tube when desired The heat sealing unit will be described in more detail below with reference to Figures 2 to 4 Two drive bands 40, or alternatively draw-off rollers, are arranged on opposite sides of the filling tube 26 to draw the web 18 downwardly towards opposed rotary sealing jaws 42 The sealing jaws are driven to rotate continuously by means of a servo motor (not shown) and are arranged to form transverse seals at bag length intervals The sealing jaws 42 carry a knife arrangement (not shown) which cuts through the transverse seals thereby separating completed bags 46 from the web The bag making machine has a control system 48 which is arranged to

provide suitable control signals for synchronising the operations carried out by

various parts of the machine The control system can be of any known type and

may, for example, comprise a PLC

Referring to Figure 2, the heat sealing unit, or backseal device 36, includes

a nozzle 50 positioned opposite and adjacent the filling tube 24 The arrangement

is such that the edges 27 of the tubular web, which are to be joined to form a

continuous backseal 29, pass between the nozzle and the filling tube as the web

is fed downwardly towards the sealing jaws 42

The nozzle 50 is carried on an endless band 52 which is supported by two

pulleys 54 The pulleys 54 are mounted one above the other with their respective

axes of rotation in parallel spaced apart relationship One of the pulleys is

connected to the output shaft 56 of a servo motor 58 and serves as a drive pulley

for the band 52

The servo motor 58 receives control signals from the PLC 48 which cause

it to rotate the output shaft 56 back and forth thereby reciprocating the nozzle in

the lengthways direction of the filling tube The arrangement of the band 52 and

the pulleys 54 is such that the nozzle remains at a fixed distance from the filling

tube 26 as it reciprocates

The nozzle is connected by a pipe 60 to a hot air blower 62 In the

embodiment, the pipe and blower are carried with the nozzle by the endless band 52 Alternatively, the blower may be mounted on the machine frame 12 and

connected with the nozzle bv means of suitable flexible ducting

The hot air blower includes an electrical resistance heater together with a

fan which blows air over the heater The hot air blower includes a poteniometer

64 by which the current supplied to the heater can be controlled to set a desired

output temperature A temperature sensor 66 is mounted in an aperture provided

in the pipe 60 to sense the air output temperature and provides a signal to the

control circuitry of the blower which is used to switch the heater to maintain the

desired temperature In addition to, or as an alternative to the poteniometer,

means may be provided for controlling the mass air flow through the blower

These means could take the form of a speed control for the fan or a means for

venting the airflow to the heater

The hot air blower may in principle be any commercially available product

and the inventors have successfully tested prototype apparatus using a Leister Hot-

Air Tool 3000, Model 8D 1

In use, the operator of the machine programmes the desired operating

parameters into the PLC 48 and sets the hot air blower 52 to produce heated air

at a desired flow rate and output temperature for the sealing operation The

operating parameters to be entered into the PLC will include the operating speed

of the machine in bags per minute (bpm), the bag length and the seal time The

seal time, or sealing interval, is the time required for the transverse sealing jaws to produce a reliable transverse seal 42 The seal time will at least in part be

dependent on the thickness of the web 18 and the type of material from which the

web is made The operator will additionally enter the sealing length 70 (Figure

4), unless this information is stored in the PLC The sealing length is a function

of the geometry of the sealing jaws and is the length of the web travel during

which the sealing jaws will engage the web From this information the PLC

generates a control sequence, referred to herein as a cam profile, which will

govern the motion of respective servo motors which drive the transverse sealing

jaws and the nip rollers 19

An example of a part of the cam profile produced by the PLC is shown in

Figure 3, which is a plot of velocity in mm/s and time in seconds In the

example, bags having a length of 300mm are to be produced at the rate of 60bpm

so that the cycle time for producing each bag is 1 second The sealing interval

for the sealing jaws is 0 5 seconds Based on the desired sealing time and the

sealing length 70, the PLC determines the velocity of the web feed during the

sealing interval In the example the sealing length is 60mm and therefore the web

feed velocity during the sealing interval would be 120mm/s, which is indicated as

V_MIN in Figure 3

Since 60mm of the 300mm bag length is fed during sealing interval, the

other 240mm must be fed through in the remaining 0 5 seconds of the bag making

cycle In order to achieve this, the web is accelerated rapidly to a maximum velocity (shown as V_MΛX in Figure 3) and then decelerated to V _I ready to commence the next bag making cycle In the example, V_V1ΛX is 840mm/s

From the foregoing description it will be appreciated that during a bag

making cycle, the web travels relatively slowly at a constant rate during the

sealing interval and at a much faster rate, which typically varies substantially continuously, during the remainder of the cycle

The hot air blower delivers air at a substantially continuous rate and temperature and in order to ensure that a substantially continuous amount of heat

is applied to the web as the web speed varies, the servo motor 56 is actuated to cause the nozzle to reciprocate in synchronisation with the web feed cam profile In more detail, the PLC determines a velocity offset, which is the average velocity of the web over a bag cycle The PLC provides the necessary control signals for the servo motor such that the relative velocity between the nozzle and the web remains substantially constant, matching the velocity offset throughout the bag making cycle

The velocity offset (average velocity of the web) in the example given is 300mm/s and thus the servo motor is driven to maintain a relative velocity of 300mm/s between the nozzle and the web The velocity profile of the nozzle is shown in Figure 3 by curve 74, a negative velocity indicating movement in the opposite direction to that of the web and a positive velocity indicating movement in the same direction as the web Referring to Figure 3, it will be seen that during the sealing interval the nozzle moves upwards in the opposite direction to the web

at a velocity of 180mm/s, thereby maintaining a relative velocity of 300mm/s

between the web and the nozzle After 0 5 seconds, the nozzle starts to accelerate

maintaining a velocity offset of 300mm/s and reaching a peak velocity of

540mm/s when the web speed reaches V_MΛ

By driving the nozzle 50 to maintain the relative velocity of the nozzle and

web at the average web velocity, it is possible to ensure that each unit area of web

which is a part of the backseal 29 takes the same amount of time to pass the

nozzle and thus since the heat output by the hot air blower is substantially

constant, a constant heat is applied along the length of the backseal Accordingly,

provided the hot air blower is set to direct the correct amount of heat at the web,

the seal produced should be of a consistent quality along its length despite

significant variations in the web speed during each bag making cycle

It will be understood that by moving the nozzle in synchronisation with the

web velocity as illustrated in Figure 3, the effect is of having a fixed nozzle, with

the web moving past at a constant velocity

The machine 10 incorporating a hot air backseal device 36 has been tested

by the applicant and found to produce good quality, consistent backseals even

when sealing polythene in a bag making cycle having a 10 1 velocity ratio on the

web

It will be understood that many modifications may be made to the web feed arrangement shown in Figure 1 and that the machine may incorporate any

conventional web feed arrangement For example, in place of the nip rollers 19,

the reel may be driven in cooperation with the drive bands 40 and tensio ng

rollers and dancer arm rollers may be incorporated as desired

In Figure I , the machine is shown having one set of transverse sealing

jaws The machine may have more than one set of jaws as is known in the art

and in place of the rotary jaws indicated, the machine may be provided with any

form of jaw arrangement used in continuous motion VFFS machines For

example, the machine may have two sealing jaws which move along opposed D-

paths or substantially rectangular paths Such arrangements will be recognised by

those skilled in the art and accordingly, will not be described in detail herein

It will be appreciated that the drive for the hot air backseal device is not

limited to a servo motor In principle any form of drive which permits the nozzle

to be controllably moved could be used An example of an alternative drive is a

stepper motor

It will be understood that many forms of control device may be provided

for governing the motion of the various moving parts in the machine For

example, in the embodiment, the nip roller drive 19, sealing jaws 42 and endless

band 52 are each driven by a respective servo motor The PLC provides control

signals for the servo motors so that the motion of the various parts is

synchronised Each servo motor may have its own motion controller which is fed with control signals from the PLC Alternatively, the PLC may be suitably equipped to incorporate the motion control function, in which case it would

communicate directly with the servo motors These aspects of the control of the machine will be readily understood by those skilled in the art and thus a

comprehensive description of the various alternatives and modifications to the control systems and hardware for the machine and in particular the backseal

device will not be provided herein

It is to be understood that whilst the hot air backseal device 36 has been

illustrated and described in conjunction with VFFS machinery, it can equally be used in conjunction with horizontal form, fill and seal (HFFS) machinery Since the application of the device to HFFS machinery will be readily apparent to those skilled in the art, no specific description of such application is provided herein.

Claims

Claims

1 Heat sealing apparatus for forming a continuous lengthways extending seal

on a web of packaging material to be fed past said apparatus, said apparatus

comprising a nozzle connectable to a hot gas producer which produces a flow of

hot gas having a substantially constant temperature and mass flow rate, a carrier

for said nozzle and a drive for said carrier, the arrangement being such that in use

said nozzle can be controllably moved relative to said web in accordance with

variations in web feed velocity such that said flow of hot gas from said nozzle can

apply a substantially constant heat to said web to form said lengthways extending

seal

2 Apparatus as claimed in claim 1 , further comprising a hot air producer

connected to said nozzle and carried by said carrier

3 Form, fill and seal packaging apparatus, said apparatus including a web

feeder for feeding a web of packaging mateπal over a flow former, said web

having lengthways extending edges and said flow former being arranged to cause

said web to adopt a generally tubular configuration wherein said edges are

disposed in generally adjacent relationship, and a heat sealing device for forming

a continuous seal adjacent said edges by which said edges are held in said adjacent relationship, said heat sealing device comprising a nozzle connected with

a hot air producer for directing a flow of hot gas at said web, a carrier for said

nozzle and a drive for said carrier, said drive being arranged to controllably move

said nozzle relative to the web in accordance with variations in web feed velocity

such that said flow of hot gas from said nozzle applies a substantially constant

heat to said web to form said continuous seal

4 Apparatus as claimed in claim 3, wherein said web feeder feeds said web

substantially continuously at cyclically varying velocities and said nozzle is moved

such that there is a predetermined relative velocity between said nozzle and said

web

5 Apparatus as claimed in claim 4, wherein said relative velocity is

substantially constant

6 Apparatus as claimed in claim 3, 4 or 5, wherein said drive is arranged to

cause said nozzle to reciprocate generally parallel to said adjacently disposed

edges

7 Apparatus as claimed in any one of claims 3 to 6, wherein said hot air

producer is earned by said carrier 8 Apparatus as claimed in any one of claims 3 to 7, wherein said drive

includes a servo motor

9 Apparatus as claimed in any one of claims 3 to 8, comprising a control

device for said drive, said control device being arranged to provide a control

signal for said drive, said control signal being a function of said web feed

velocity

10 Apparatus as claimed in claim 9, wherein control device is programmable

1 1 Apparatus as claimed in claim 9 or 10, wherein said control device

provides a control signal such that a relative velocity between said web and said

nozzle substantially equal to an average velocity of said web is maintained

12 A method of forming a continuous seal along a moving web of packaging

mateπal, said method including moving said web at a cyclically varying velocity,

directing a flow of hot gas at said web, said flow having a substantially constant

temperature and volume flow rate, and cyclically moving said flow relative to said

web along a region to be sealed such that a substantially constant heat is applied

to said web to form said seal 13 A method as claimed in claim 12, comprising reciprocating said flow of

hot gas in a lengthways direction of said seal

14 A method as claimed in claim 12 or 13 comprising determining an average

velocity of said web and moving said flow relative to said web so as to maintain

a relative velocity between said web and said flow which relative velocity is

substantially equal to said average velocity

15 Form fill and seal packaging apparatus, said apparatus comprising means

for feeding a web of heat sealable packaging material, forming means arranged to

cause said web to adopt a tubular configuration in which opposed lengthways

extending edges of the web are brought into a juxtaposed relationship and heat

sealing means for forming a continuous seal in the region of said edges, said heat

sealing means comprising means for directing a flow of hot gas at said web to

form said seal and being arranged to move said flow relative to said web such that

a substantially constant heat is applied to the web

16 Apparatus as claimed m claim 15, wherein said heat sealing means

comprises outlet means connected with hot air producing means and mounted on

transport means 17 Apparatus as claimed in claim 16, wherein said forming means includes pipe means around which said web is wrapped to cause it to adopt said tubular

configuration, said transport means being arranged to reciprocate said outlet means parallel to a longitudinal axis of said pipe means

18 Apparatus as claimed in claim 16 or 17, wherein said transport means moves said outlet means such that a relative velocity substantially equal to an average velocity of said web is maintained between said web and said outlet

means

19 Apparatus as claimed in claim 18, comprising a programmable control means for said transport means