CA1045580A

CA1045580A - Method of inerting the atmosphere above a moving product

Info

Publication number: CA1045580A
Application number: CA224,127A
Authority: CA
Inventors: Harden H. Troue; Donald W. Hunter
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1974-04-16
Filing date: 1975-04-08
Publication date: 1979-01-02
Also published as: FR2267826B2; JPS50138200A; GB1509725A; FR2267826A2; JPS547022B2; DE2516339A1; ES436611A1; NL7504481A; AU8014875A; NO751333L

Abstract

METHOD OF INERTING THE ATMOSPHERE
ABOVE A MOVING PRODUCT

ABSTRACT OF INVENTION

The method for inerting the surface of a moving product involves; passing a stream of inert gas, having a width at least equal to the width of the product, into an enclosure through which the product is to pass and in the direction of the product so as to impinge upon the product surface at a predetermined angle with respect thereto and having a velocity component in a direction opposing the advancing product and a magnitude at least substantially equal to the velocity of the product.

Description

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This in~ention relates to an improved method for inerting the surface o~ a cross-linkable polymeric product while the product is in motion.
To accomplish effective inerting in a dynamic system, the inerting procedure mu~t account for the air lying immediately above the product which, as the product moves, tends to be drawn with the product and along its surface. Hence, simply purging the work zone, although effective in a static system, is entirely inade~uate and unsuitable for the dynamic system.
Common to the dynamic inerting system disclosed in the above cited patent applicatlon and to the present invention is an enclosure including a treating chamber, which houses the source o~ radiant energy, an entrance ;~
tunnel leading to the treating chamber and adapted to receive the product, and an exit tunnel extending rearward from the treating chamber. Likewise, the design of the .- ~
inerting system to be disclosed herein adheres to the ' ' ' ' . .

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principles of the cited patent application concernlng the relevance o~ the inerting geometry to the dynamic sy~tem although directed to an improved method of pas~ing the inert gas into the enclosure~ The mean~ for inJecting the inert gas must take such ~orm as to provide a substan-tially unidirectional curtaln or stream o~ inert gas having a width at least equal to the width of the moving product and muRt be so oriented a~ ko direct the stream o~ gas toward the moving product so that the stream intersects with the surface o~ the product at a predetermined angle of inclination and with a component o~ velocity opposed to the movlng product. An elongated channel or slot formed ln the tunnel surface wall, as is shown in the afore-mentioned patent application, represents the pre~erred inert gas ln~ector mean~.
Heretofore lt wa~ necessary for the enclosure exlt tunnel to have a length sub3tantially greater than the entrance tunnel length. In thl~ manner the ma~ority of the inertlng gas wa~ ~orced to ~low out the entrance tunnel.
This method o~ controlllng gas flow direction proved to be ~atisfactory at low and moderate product line speeds o~ less than ? feet per min. However, at higher line speeds, o~
over ? feet per minute and up to about lO00 feet per minute, the length o~ the exlt tunnel becomesJ from a practical standpolnt, prohlbltive. It has now been dlscovered that the length o~ the exit tunnel can be 3igni~1cantly reduced and in ~act rendered ec~entially independent of the length ` of the entrance tunnel provlded that:

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~SS~ , (1) the inert gas stream is fed into the enclo-sure at an included angle of above about 45 degr-ees but below about ~5 degrees with respect to the longitudinal axis o~ the enclosure, said angle oriented such that the ~ issuing gas stream has a velocity cGmponent ln a direction - opposed to the directlon of the moving product;

(2) the inert gas flow rate exiting from the entrance and exit tunne} respectively is held to below a critical volumetrlc flow level per unit Or tunnel width for each speclfic inert gas composition; and ~3) the inert gas velocity component opposing the moving product has a magnitude ~ubstantially equal to and pre~erably greater than the velocity of the moving product.
The speciflcation of any given production line ~ facility and tunnel design parameters outlined in the pre-; viously clted patent may then govern khe total enclosure design length with the inert gas in~ector inclination angle and flow rate chosen to satisfy the hereinabove stated conditions. Moreover, by ~atis~ying the above stated conditions, occasional instability ln the direction o~
inert gas ~low within the enclosure, w~lch has been noted to occur particularly at higher operatlng speeds, has been ellminated.
It has been further demonstrated that, provided the above noted conditions are satlsfied, the ~tream of " : '. ~: ' ' '' ,, ,' '.
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inert gas can be introduced into the enclosure either up-stream of the treating chamber as is shown ln khe a~ore-mentloned patent applicatlon or, i~ des~red, downstream o~ the treatlng chamber. The latter arrangement has been found to be particularly advantageous in applications where the product consists of a plurallty Or entlties each of finlte length and where the product thickness varies .
over at least about one-quarter lnch in depth.
Accordingly, lt is the principal ob~ect Or the present inventlon to provide a method for maintainlng a substant~ally inert atmosphere at the surface o~ a moving product as it moves through the interior o~ an enc:Losure.
It is a ~urther ob~ect Or this invention to pro-vide a method of inertlng the sur~ace o~ a moving product at product travel speeds of up to about 1000 feet per min.
and regardless of whether the product is of a contlnuous `' length or represents one Or a plurality of entitles each of flnite length and thickness.
Other ob~ects and advantages will become appar-ent ~rom the rollowing detailed de~criptlon when taken in connection with the accompanying drawings o~ which:
~igure 1 is a diagrammatic illuRtration in long-itudlnal section of a treatment enclosure ~or lrradiating . .
a moving product ln an atmosphere to be controlled in accordance with the teachlngs oP the present invention;

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Figure 2 is an exploded view of the inert gas in~ector showlng the pre~erred angle of inclination ~or the in~ector relatlve to the longitudinal axis of the enclosure; .
Figure 3 is an illuatrative isometric o~ a por-tion of either tunnel of the enclosure of Figure 1 in -~
which the inert gas in~ector is located wlth a sectlon~:
thereof cut-away to illustrate the lateral orientation of the inert gas in~ector relative to the. width o~ elther tunnel respectively.
Re~erring to Figure 1-3 inclusive in which the treatment enclosure 10, ~or lrradiating the moving product P, i~ diagrammatlcally illustrated and comprises a treat-ing chamber 12 which hou~es a ~ource o~ radiant energy ..
(not shown?; an entrance or inlet tunnel 14 located up-stream o~ the treating chamber 12 in the directlon Or the :.:
moving product P; and an exit tunnel 16 extendin~ down-. I stream of the treatlng chamber 12. The term "tunnel" ~or purpo~es of the pre~ent disclo~ure is de~ined a~ a hollow pa~sageway Or uni~orm cro~s-~ectlon which may either have a sel~-enclosed perlphery or a partially enclosed periphery whlch become~ ~ub~tantlally fully enclosed ~hen the moving product P 18 pre~ent and whlch preferably con~orms to the de3ign parameters outlined ln the aforementioned patent application. For simpllcity o~ illu~trationg the medium 18, whlch may represent, for example, a conveyor belt sur~ace ~or advancing the product P through the en~ .:
closure 10~ hown rormlng the physical bottom of the ;~,, , :

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enclosure 10. It should be understood, however, that the bottom of the ~nclosure 10 may be formed in any manner and is, in fact, preferably established by the moving product itself where the product is continuous.
The product P may represent a chemical coating or a coated substrate and may be of a continuous length such as a web or of a finite length. In the latter in-stance the product P would actually be presented to the enclosure for treatment as a series of abutting or spaced entities. For purposes of the present invention any source of radiation may be employed to treat the product P within the treating chamber 12 of the enclosure 10 although an internally cooled or non-cooled source is preferred. Pre-ferred sources of actinic radiation are low pressure ultra-violet mercury tubes and/or germicidal lamps.
Inert gas G. is supplied from an inert gas plenum chamber 19 and passed through an inert gas injector 20 into the enclosure 10. The source of supply for delivering the gas to the plenum chamber 19 is n~t shown. The inert gas injec~or20 is orientecl wi~h respect to the longi~udinal axis of the enclosure 80 that its shorter axis intersects with the longitudinal axis forming the acute angle " '~" ;
as shown in Figure 2. Angle 'lc~ll is defined as the angle ... ..
form~d between the stream of inert gas G, issuing from the gas injector 20, and the longitudinal axis of the enclosure ;
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10 along which the product P is intended to travel and shvuld lie within a range of above about 45 degrees but below about 85 degrees and be oriented within such range such that the gas stream has a velocity component in a ` direction opposing the moving product and of a magnitude at least about equal to the velocity o the product. The gas injector 20 may be fabricated by orming a slot in the top surface of th~ enclosure 10, as shown in Figures 1 and

3 respectively. The longer or longitudinal axîs of the gas injector 20 should lie substantially parallel to the width of either tunnel 14 and 16 respectively as i9 shown in Figure 3 ; It has been taught that dynamic inerting requires a non-tur~ulent non-mixing inert gas 10w within the interior of the enclosure 10. It has now been dis-; covered thatthe required non-turbulent non-mixing flow within the enclosure 10 is assured regardless of product speeds up to about 1000 feet per min. by the combination of:
introducing inert gas into the enclosure 10 in the form of a substantially unidirectional stream; appropriately direc- ~
ting the inert gas stream toward the advancing product P at ;
the preferred angle " ~"; and maintainlng an inert gas volumetric 10w per unit of ~unnel width, which is limited, or each inert gas composition, to a maximum level out of each tunnel 14 and 16 respectively. For an inert gas of substantially nitrogen th~ volumetric flow per unit of tunnel width out from each tunnel 14 and 16 respectively ~"':' ' ' . ' ~ ~ .
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~ ~ S S 8 must be below about 650 cu.ft./hr. per foot of tunnel wldth. For helium the maximum level is about 5000 cu.ft./hr. per foot of tunnel width and ~or carbon dioxide the maxlmum level is about 360 cu.ft./hr. per ~oot Or tunnel width. The above levels were determined mathe-matlcally and con~irmed experimental~y. It should be noted that the above levels are independent of tunnel height and independent of product speed at least up to about 1000 feet per mln.
Moreover, it has ~urther been discovered that substantially all of the air carried with the advancing product P, upon approaching the inlet openlng 22 of the enclosure 10, may be strlpped of`f the product sur~ace and dlverted away from the enclosure 10 provlded thak; the inert gas veloclty component, in the direction opposing the moving product P, has a magnitude ~ubstantially equal to or greater than the veloclty of the moving product P.
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This is based upon a study made o~ the atmosphere within the enclosure 10. Measurements of the oxygen levels within the enclosure 10 have ~hown levels of 50 to 100 ppm and ~enerally less than 500 ppm under typical operating condi-tions at line speeds in the range o~ about 300 to about 1000 feet per minute. '~
As previously stated, the lnclined position of the inert gas injector 20 provides a pre~erenkial direction for the lnert ga~ ~low toward the upstream end o~ the en-closure 1~. This pre~erence has been shown to exist not only when the in~ector 1~ located in the forward tunnel 14 ' ,' , 9 ,: :
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but also when located in the exit tunnel 16. The injector can be as equally effective when located in the exit tunnel 16 as it is when positioned in the entrance tunnel 14 but not necessarily at the same angle of inclination. Moreover, although the entrance tunnel 14 should still have a length which extends from the inlet 22 downstream to the injector 20 a distance equal to at least ten times the smallest cross-sectional dimen-sion of the tunnel opening; the length of the exit tunnel 16 no longer must bear any relationship to the length of the entrance tunnel 14.
The faster the product travels through the en-closure 10 the more the injector should depart from a vertical position, i.e., the angle of inclination "c~ "
should become smaller. An angle Ic~" o below about 45 degrees, however, significantly raises,the danger of estab-lishing a venturi effect at the rear of the enclosure causing air to be drawn into the enclosure 10 through the exit tunnel 16. The preferred angle for speeds above 200 feet per minute is about 60 degrees.

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For a slower moving product below 200 feet per min. and particularly a discontinuous product~ it is more desirable to operate at a higher angle Or incllnation llmited however to below about ~5 degrees, pre~erably at about 75 degrees. At this angle any slight perturbation ln flow which might develop due to a thicknes~ varlation in product P o~ greater than one-quarter inch or due to a sudden change in product speed will not upset the pre~-erential flow condition out o~ the entrance tunnel 14.
Although the method o~ the present invention ;~ has been described with reference to a single in~ector 20, lt i5 obvious that a tandem combination o~ ln~ectors may be used provided that the stipulated condltions of, maximum volumetric ~low, total velocity component oppos-ing the moving product and range of incllnation angle be observed. In the latter respect, lt is also apparent that the in~ector 20 need not be fabricated so as to be stationary in orlentation. Instead, an ad~ustable in~ec-tor means may be employed for a~lxing any deslred angular orientation within the prescribed range. It should be , . . .
further understood that it will be apparent to one o~
ordinary sklll in the art to suggest mlnor variations and modi~cations without departing from the scope and - ~pirit o~ the invention as is hereby claimed. ~' ,"~ .
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Claims

WHAT IS CLAIMED IS:

1. A method of maintaining a substantially inert atmosphere at the surface of a moving product as it moves at any given speed up to about 1000 feet per minute through the interior Or an enclosure including a treating chamber and a first and second tunnel with the first tunnel located upstream of said chamber relative to said moving product and the second tunnel located downstream of said chamber;
said method comprising the steps of:
(a) passing a stream of inert gas, having a width at least about equal to the width of said product into said enclosure;
(b) directing said stream of inert gas toward the advancing product so that said stream impinges on the surface of the moving product to form an acute angle with respect to such surface of above about 45 degrees and below about 85 degrees; and (c) orienting said angle such that said gas stream has a velocity component in a direction opposed to the advancing product and a magnitude at least substantially equal to the velocity of the moving product.

2. A method as defined in claim 1 wherein said treating chamber houses a source of actinic radiation con-sisting of at least one ultraviolet radiating lamp.

3. A method as defined in claim 2 wherein said inert gas is nitrogen and further comprising the step of passing said nitrogen stream at a flow rate such that the maximum volumetric flow out of each tunnel respectively is below about 650 cu.ft./hr. per foot of tunnel width.

4. A method as defined in claim 3 wherein said stream of nitrogen is introduced into the enclosure up-stream of said treating chamber.

5. A method as defined in claim 4 wherein when said product is moving at a speed of less than 200 feet per minute said angle should be oriented at about 75 degrees,

6. A method as defined in claim 4 wherein when said product is moving at a speed of above about 200 feet per minute said angle should be oriented at about 60 degrees.

7. A method as defined in claim 2 wherein said inert gas is helium and further comprising the step of passing said helium stream at a flow rate such that the maximum volumetric flow out of each tunnel respectively is below about 5000 cu.ft./hr. per foot of tunnel width.

8. A method as defined in claim 7 wherein said stream of helium is introduced into the enclosure upstream of said treating chamber.

9. A method as defined in claim 2 wherein said inert gas is carbon dioxide and further comprising the step of passing said carbon dioxide stream at a flow rate such that the maximum volumetric flow out of each tunnel respec-tively is below about 360 cu.ft./hr. per foot of tunnel width.

10. A method as defined in claim 9 wherein said stream of carbon dioxide is introduced into the enclosure upstream of said treating chamber.