CA1163844A - Curtain for shrouding welding operations - Google Patents
Curtain for shrouding welding operationsInfo
- Publication number
- CA1163844A CA1163844A CA000395903A CA395903A CA1163844A CA 1163844 A CA1163844 A CA 1163844A CA 000395903 A CA000395903 A CA 000395903A CA 395903 A CA395903 A CA 395903A CA 1163844 A CA1163844 A CA 1163844A
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- Prior art keywords
- curtain
- light
- eye
- arc
- declivities
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
A curtain for surrounding welding and cutting operations, especially electric arc welding and electric arc cutting operations to protect the eyes of otherwise unprotected observers. The curtain has one surface covered with declivities with faces disposed at angles to the plane of the sheet. Some light rays passing through the curtain are refracted and undergo a change of direction. This reduces the exposure of the retina to undesirable intensities by optically enlarging the small arc spot, and presenting the eye with general area illumination instead of pinpoint illumination.
A curtain for surrounding welding and cutting operations, especially electric arc welding and electric arc cutting operations to protect the eyes of otherwise unprotected observers. The curtain has one surface covered with declivities with faces disposed at angles to the plane of the sheet. Some light rays passing through the curtain are refracted and undergo a change of direction. This reduces the exposure of the retina to undesirable intensities by optically enlarging the small arc spot, and presenting the eye with general area illumination instead of pinpoint illumination.
Description
This application is a division of application 336~534J filed September 27, 1979.
This invention relates to welding curtains through which an object on the other side can be seen.
More particularly, this invention relates to a welding curtain which will enable an otherwise-unprotected observer to observe a welding scene on the other side with the greatest clarity consistent with the requisite safety from deleterious effects, even if the eye should fixate on the arc spot for an extended period.
The parent application is concerned with optimizing the trade-off between these two competing requirements by utilizing spectral space discrimina-tion using dyes, as described below. This may be used in combination with some or all of the following features:
I. Spatial frequency discrimination using surface refraction as des-cribed below;
II. Relative light intensity reduction by diffractive scattering, using surface or bulk index of refraction discontinuities as described below; and III. Pluorescent wavelength shifting, using fluorescent dyes as described below.
The present application relates to the use of spatial frequency discrmination. The other features can also be described for the sake of completeness.
Pertinent considerations are as follows:
SPATIAL FREQUENCY DISCRIMINATION
Radiations from 200 to 500 nm and even larger are potentially damaging to the eye, although the hazard decreases rapidly with increasing wavelength above 500 nm. In the band 200 to 400 nm the modeoE action of the 5~
potential injury is related to total amount of energy delivered to the eye.
Absorbing dyes which completely stop this energy band from penetrating the curtain are available as discussed later. The mode of action of the band of energy extending from 400 to 500 nm and even larger depends primarily on the energy-density at the retina of the eye. That is, a given amount of energy in the band 400 nm - and - larger, foc~sed on a small spot on the retina of the eye, may be a serious hazard, while if the same total amount of energy is spread out over a larger spot on the retina, it may be totally non-hazardous, even for extended longer-time viewing.
Thus, a selective broadening of the image of the minute arc spot on the retina, while leaving the diameter of the images of larger features in the scene relatively unchanged, so that sight and recognition of such features is perceived as "normal", could decrease the hazard below the danger point.
Consequently, the curtain may carry on its surface minute refracting elements, (sometimes called "declivities" herein) conveniently placed there by embossing or by reticulation. Bundles of light rays from the scene pass through the surface. The declivities on the surface make only a very small angle with the surface. The declivities should preferably be oriented at random. Thus a bundle of rays from any particular point in the scene is split up into a group of sub-bundles - those which passed through adjacent but dif-ferently oriented declivities of the curtain - and are brought to a focus on the retina as a number of partially superimposed images at and surrounding the location where the original image would be were there no declivities. The image of a small arc spot will thereby be spread out on the retina to enlarge its diameter, while the image of a large feature of the scene - a finger or hand or clamp, for example, would be spread out the same absolute amount but only a negligible relative amGunt and so would retain its nearly normal appearance _ 2 -1 ~B~844 in the scene. Thus the hazard to the eye from an overly bright minute source would be negated while still retaining satisfactory visual acuity of scenes through the curtain.
The net result is that the brightness of small minute features ~such as an arc spot) is preferentially reduced on the retina, while the brightness and appearance of larger features of the scene is essentially unchanged.
Thus, according to the present invention there is provided, in a weld-ing curtain of substantial area forming at least a portion of the perimeter of an area in which an electrical arc welding or an electrical arc cutting operation is conducted for the purpose of protecting the eyes of an observer located out-side of said perimeter from damage by light from said arcs, said curtain having a pair of surfaces spaced apart by a dimension of thickness, and being sufficiently clear for said observer to see through it an object of substantial size located inside said perimeter, the improvement comprising: one of said surfaces being substantially entirely covered with declivities each having a relatively minor surface extent and having faces disposed at angles to the plane of the sheet, whereby some rays of light, which pass through said one surface are refracted and undergo a change in direction thereby partially to de-focus an image.
SPBCTRAL SPACE DISCRIMINATION
The energy emitted by an electric welding arc is given out in the form of radiant energy. Such radiant energy consists of the simultaneous emission of electromagnetic waves whose wavelengths include every wavelength from less than 200 nanometers (nm) to more than 1,400 nm.
Among all the radiations, those of the ultraviolet (200 - 400 nm), and the shorter-wavelength part of the visible (400 to about 500 or 550 nm) are the most effective in producing damage to the eye. That is, the radiations whose wavelength is 500 nm and greater are relatively innocuous in causing damage even when they are present to as large an extent as the group from 200 1 ~63844 to 500 nm. Therefore a curtain or filter which stops all radiation from an arc operation between 200 and 500 nm while allowing the residual radiations from 500 to 1,400 nm to pass, will do away with the potentially hazardous 200 - 500 nm radiation, while allowing the longer ~500 to 1,400 nm) more innocuous radiation to pass through it. It is important to maximize the amount of the remaining non-hazardous radiations that pass through the curtain, because the ability to see the scene through the curtain depends on the amount of visible light which penetrates the curtain and reaches the eye.
There are thus two mutually contradictory requirements for a curtain which allows safe viewing of an electric welding or cutting arc scene. In order to minimize the potential eye hazard, the curtain should stop all wavelengths from 200 to 500 or 550 nm or larger. In order to maximize the ability to see the scene, the curtain should pass the maximum of those radiations which give rise to the sensation of sight (400 to 760 nm).
It has been determined as described later, that if the curtain transmission cut-off is between about 500 nm and about 580 nm sufficient visible light (with wavelengths between about 500 and about 760 nm) will reach the eyeJ
and little enough residual hazard will remain, so that such a curtain could constitute a safe and usable welding curtain for passers-by, adjacent workers, and supervisors.
RELATIVE LIGHT INTENSITY REDUCTION (SCENE CONTRAST EQUALIZATION) The normal mechanism of the human eye in protecting itself against a too-bright potentially hazardous over-illumination is an involuntary closing of the iris of the eye, and an aversion (of the direction of sight) of the eye. Neither of these reactions is effective in the normal circumstance of electric arc-weld scene viewing for persons to be protected by this invention such as adjacent workers, passers-by, and supervisors. This is because the ~ 4 ~
iris responds to the total illumination on the retina, and a very small bright spot surrounded by a dim field of view, is regarded by the eye-brain system as similar to a bright star in a dark sky, that is, as a "dark" scene, and the normal response is a maintainance of a wide-open iris.
The second natural protective mechanism - the involuntary aversion of the eye direction from a bright light source - is overcome by the conscious will of the observer to examine the scene in detail, because it is normally within his work-related duty to see and to study the details of the arc-welding in the scene.
It would, therefore, be desirable to ensure that the iris of the eye will diminish its aperture (pupil) while the arc is in operation.
Thus, the welding curtain may have discontinuities distributed throughout the matrix material, said discontinuities having an optical index of refraction which differs from the optical index of refraction of the material of which the curtain is primarily made by at least 0.2 units, where-by to scatter at least 5% and less than 50% of the light which passes through the curtain.
Most of the light from an arc spot will pass through the protective curtain in such a direction that its light would not be seen by the eye. How-ever, a fraction ~preferably about one-quarter) of this other-directed light is scattered by the curtain, and some part of the scattered light enters the eye from points of the curtain removed from the direct line of sight of the arc with respect to the eye. This scattered light from all parts of the curtain is seen by the eye, and forms a general illumination on all parts of the retina.
This general illumination, in combination with the residual normal illumination of the rest of the scene, triggers the normal iris - closing response due to a general, wide-spread illumination.
The net result of the scattering feature has been a decrease in scene contrast, that is, a reduction of bright spot intensity and a lightening of the surround, a general field-of-view illumination increase which causes the iris to contract, and a decrease in the brightness of the image of the arc spot on the retina, since some of the arc spot's brightness has been scattered away in passing through the curtain.
FLUORESCENT WAVELENGTH SHIFTING
It has been pointed out that it is desirable to decrease the amount of potentially harmful short wavelength light penetrating the curtain, and to increase the amount of longer wavelength visible light so that more details of the scene may be clearly seen.
This objective may be accomplished by incorporating a fluorescent dye material in the curtain. The characteristic feature of fluorescence is that when a ray ~strictly speaking, a quantum) of short wavelength light falls upon it, the short wavelength light may be totally absorbed and an equivalent amount of longer wavelength light will be emitted in all directions.
Thus the incorporation of an appropriately selected fluorescent dye will de-crease the amount of shorter wavelength light that penetrates the curtain, thereby further decreasing the hazard to the eye. Furthermore, the newly created fluorescent light, if one chooses a suitable fluor, will re-emit additional innocuous long-wavelength light, some of which will be redirected to the whole welding scene, add to the general illumination, and if the fluorescent color is chosen as will be described, will make its way unimpeded by the aforementioned sharp cut-off dye (the cut-off chosen to cooperate with the characteristic fluorescently emitted wavelength of the fluorescent dye material) through the curtain to give more visual brightness to the scene .
surrounding the welding arc.
The welding curtain is preferably made utilizing an organic plas-tic matrix such as polyvinylchloride, which itself is opaque to certain undesirable wavelengths and which can act as a structural support and as a matrix for dyes, pigments, and additives which it may contain. One or both of its surfaces can be modified to provide the above surface refractive effects.
In the accompanying drawings which illustrate the structures and properties of certain prior art curtains and curtains embodying various of the above features:
Figure 1 is a graph showing the inter-relationship between the damage functions of ultraviolet, and of light induced retinal injury "blue-effect" light damage, the transmissivity of an ideal cut-off dye, and the photopic eye sensitivity function;
Pigure 2 is a graph showing the inter-relationship between the "blue-effect" light damage function curve, the photopic curve, and the transmissivity behavior of a group of curtains;
Pigure 3 shows the focusing action of the eye as it looks through a prior art curtain;
Figure 4 shows a view similar to Figure 3, but with the eye see-ing through one embodiment of curtain according to this invention;
Pigure 5 is a vignette showing the left hand surface of the curtain in Pigure 4;
Pigure 6 is a cross-section taken at line 6-6 in Pigure 5;
Pigure 7 shows the field of view and the response of an eye as it looks through a prior art curtain; and Figure 8 shows a view similar to Figure 7, but with the eye seeing through another embodiment of curtain according to this inven-tion.
Figure 1 is a graph illustrating some of the parameters that have been considered in the design of the present curtains. The abscissa is the wavelength of the radiation in nanometers ~nm) while the ordinate is the relative response of the eye to radiation and light and also the relative transmission of curtains at the various wavelengths. Graph line 10 shows the ultraviolet radiation damage function S. This line discloses that maximum damage is caused by radiation at about 270 nanometers.
Still, any radiation whose value is above zero anywhere along this graph line can cause some damage. For example, at about 225 nanometers the effect is about 1/7 as important as radiation at 270 nanometers. How-ever, it still constitutes a risk of damage rom ultraviolet radiation, although a lesser risk. The use of ultraviolet absorbers in plastics to absorb the ultraviolet radiation is per se. An ultraviolet absorber is conventionally used to preserve the plastic matrix, as well as to prevent transmission of ultraviolet light.
Graph line 11, shows the "blue-effect" light hazard function (B).
This graph line shows that retinal damage begins to be caused by radiation above about 400 nm, is maximum at about 440 nm, diminishes as a hazard through 600 r~, the hazard remaining constant at one thousandth of the maximum value rrom 600 to 1,400 n~. q~he greatest risk is at about 440 nm.
~owe-ver, any rs~iation within the indicated range of suf~icient intensity can cause retin 1 in~ury.
Graph line 12 is the photopic eye sensitivity function. This shows the sensitivity (V) of the eye to visible light. It rises from a zero value near 400 nm to a maximum at 555 nm and declines to near zero rear 760 nm. The more of the light as wei~hted by this response curve uhich can be transmitted, the 6reater will be the perception to the eye Or an object on the other side o2 the curtain.
Graph line 13 shows the transmissivity function of a theoretically perfect dye with a "cut-off" at approximately 491 nanometers. It has a rising segment 14. Especially this rising seg~ent, and indeed the whole line, de-fines what the dye will absorb and not pass, and what it will not absorb ana wlll pass. Speaking ~enerally, points beneath and/or to the right of the curve represent transmission. Points above and/or to the left, represent absorption. ~he rising segmcnt is the area of sharpest and greatest effect.
i A dye can be theorized, the rising segment of whose curve would be at either ¦ a shorter or longer wavelength than the one sho~n. If it were at a shorter wavelength, it would eive slightly more visible energy but would also pass a ¦ very significant additional amount Or "blue-4ffect" energy to the hazard of the viewer. Selection of a dye with a rising segment at a longer wavelength would reduce the "blue-effect" light hazard, but would also diminish the amount of visible light transmitted to the disadvantage of observer visibil-ity. Therefore, there is no perfect dye composition, and certainly no prac-tical dye composition, which will simultaneously entirely eliminate the "blue erfect" light hazard and entirely msximize the visible transmission. Accord-' ingly, there is a region 15 which is somewhat triangular in shape represent-_ 9 _ J`~
ing "blue-effect" light hazard which ~ill be transmitted even by the theoret-ically Ferfect curtain.
In Figure 2 there is shown another graph whose abscissa is wave-length in nznometers and whose ordinate is the relative tr~nsmission of the curtsins (~) and relative response of the eye (B) and (V). The purpose of this græph is to contrast the performance of one representa~ive em~odiment of this invention with some prior art welding curtains. The prior art cur-tains described have only dyes as their active constituents for the control of light, and therefore this comparison is made without the above discussed diffracting and scattering effects being included.
Graph line 20 shows the relative transmission o~ a curtain accord-ing to this invention, with ~yes only. It will be observed that the curve has a flat segment 21 whose ordinate vaiue is zero bet~een about 200 and about 500 nm, reaninB that it transmits no radiation between these ranges. It then has a rising seg~ent 22, as nearly vertical as can be devised by appropriate dye selection, from about ~ero tran~mission to about 80% tran~missicn. Limits 23, 24 and 24A are respectively shown at 1% at 450 nm, and at 5% at ~91 nm, and at 70% at 600 nm. To the right, above about 600 nanometers there is a generally flattened segment 25. This curve indicates that above about 600 nm about 75 to 85 percent of the light of various wavelengths is transmitted by the dyes, which is a very suitable value for a welding curtain.
Region 33 i8 also shown which indicates the transmission by the curtain o~ this invention oP residual "blue-effect" light. The absolute effect of the residu~l "blue-effect" light whose existence is indicated in Figure 2 by the somewhat triangular region 33, is obtained by a ~athematical weighting process. In each wavelength interval considered, (e.g. for this invention 500 to 505 nm, 505 to 510 nm, 510 to 515 nm, etc.) the value of the c~rtain dye transmission (T) in Figure 2 for segments in the respective line is multiplied by the value of (B), curve 28 in Fi~ure 2, ror the same wave-- length interval, and the product multiplied by the value of the spectral radiance of an arc source with a brightness similar to the su~ (L), for the same wavelength interval. The values of the final products (~LT) thus ob-tained for each wavelength interval are then summed. This total sum ~LT, is proportional to the total "blue-effect" light hazard to the eye from the residual "blue-effect" light passed by the curtain under consideration. The curtain of this embodiment will be seen to perform in a manDer which is rather close to the optimum de~ined by graph line 13 in Figure 1, although it cannot be expected that any economically priced commerically available dye will be P8 ideal in its absorption as the theoretical dye proposed by graph line 13 of Figure 1.
A~ will be discussed later, a useful method to characterize the relative rating of different curtains in safe6uarding the eye and in providing adequate vislbility i8 to compare the ratio of the total amount of visible energy transmitted by a welding curtain ( ~ VLT) with the total amount of potenti~lly hazardous ~'blue-effect" light energy ( ~ BLT) transmitted by the same curtain. The complete description Or the method of obtaining the value of the ratin8 factor wil1 take into account the necessary weighing functions such as lines 11 and 12 in Figure 1.
The spectral transmissivity of a curtain is a function o~ absorptive dyes in the matrix of the curt&in. The "perceived" color is not to be con-fused with "spectral~' color, even though the various curtain~ described do have a "color" which is perceived by the user. One refers herein to trans-mission and to cut-off strictly as a function of wavelength.
Assuming a suitable dye a useful curtain can be obtained, but such a curtain continues to involve the transmission of "blue-effect" light to the hazard of the observer. One problem with this "blue-effect" light is that ~ 163844 the eyeball is not strongly reactive to it. The light which constitutes the "blue-effect" li~ht hazard can have waveleng~hs longer or shorter than that of the spectral color blue. The perceived color blue does, however, charac-terize the color sensed in this regicn. ~here is little pain or other sensa-tion from it, and damage can be done because no protective action will be taken. This d m~ge is a function of energy per unit area incident on the retina. In a welding operation, it comes from a small source to which the pupil will not be adequately reacti~e, but the light is stror.gly focused by the eye, and this increases the area loading.
One tecbnique to assist and instruct the eye for its own protec-tion is shown in Figure 4, where a curtain 35 having a pair of surfaces 36, 37 is shown disposed between the eye 38 of an obser~er and a welding opera-tion 39. The welding operation i8 indicated by schematic welding rod 4O
adJacent to a workpiece 41 and eeneratin8 a fireball (arc) 42 which is the ~ource Or the light being protected against herein. The lens 43 of the eye is focused on a retina 44. An iris 45 ~orms a variable aperture to determine the amount of light which enters the eye through an area called the pupil.
More liEht i8 admitted when it i8 enlarged than when it is constricted.
Prlmary rays 46, 47 are shown impinging on a curtain 35.
A similar view is shown in Figure 3, where the same rays impinge on a prior art curtain 49. The prior art curtain i8 dyed but transparent, and has two smooth parallel surface~ 5O, 51. In Figure 3, rays 46, 47 are imaBed by the lens to form a central image 52 whose relative si~e is shown in solid o~al line lmmediately adJacent to the retina.
; In order to reduce the unit lcading on the retina it is useful to spread the lieht as much as possible for the same pupil area opening. In the embodiment illustrated in Figure 4 this is accomplished by reticulated or embossed declivities 53 on surfaces 54 PS shown in Figures 4-6. The purpose ,, ?~
1 16384~
of these variations from a planar surface i5 to provide surrace~refractive spreading of the beam. This will spread the image a~d reduce the unit load-ng.
For purposes of disclosure, dimpled declivities are ~ho~m, and their dimensions are greatly exaggerated. For purposes of the following specific eY.ample, the size of the fireball 42 is taken to be 6mm diameter, the distance from fireball 42 to curtain 35 or 49 is taXen to be 1.3m, and - the distance from the curtain to the eye 38 of the observer, is also 1.3m.
In general it is preferred that the tangents to the surfaces of the declivities do not exceed a dif~erence greater than about 8 minutes of arc from parallelism with what ~Tould be smooth planar surface parallel to surface 54. This is sho~m by angle 5~a ~Figure 6). Such an arrangement will give an image change corresponding to about a 4 minute of arc divergence on each side of the image of any obJect in the field of view. Such image en-lar~ement is a con6iderable part o~ the size of the otherwise unspread arc spot image size. Indeed for the dimension~ guoted the effect is to about ~uadruple the area on which the ener~y ~alls even though a brighter portion is still located in the center. The enlarged areas are shown as areas 55, 56, 57, 58 in Figure 4. ~his provide~ a gross enlargement in the image and spaces out the image rather similar to a range finder. The additional en-largement due to the 4 minutes of arc divergence on each side of a larger ob~ect of say 32 minutes of arc (a 25 mm obJect) will only raise the image size to that corresponding to an image appropriate to a 30 mm ob~ect. The 25 mm obJect would still be clearly recognizable. Even a smaller amount of ~preading ofthe incident rays causes a substantial reduction in unit loading on the retina. The effect thi surface treatment has on arc image intensity on the retina is described later. For si~plification of the optical effect the declivities have been sho~m on one side only. Declivities with half the , --angle (4 minutes of arc) and of the same size on both sides of the curtain would h~ve nearly the same effect.
The surface treatFent irregularity can be provided i~ man~ ways.
One way is to calendar a pattern all over the surface, and thiæ will produce predetermined shapes, which could be defined by planes to form pyranids and the like. Instead o~ sharp and planar bounded declivities, these may instead be dimpled structures ~Jith curved boundaries, conveniently provided as an "orange peel" surfacé known to all persons accustomed to calendaring sheets Or polyvinylchloride a~ the consequence of reticulation. Such a surface is shown in Figures 5 and 6, wherein the plurality of dimple-shaped concave declivities 53 are formed in the surface 54, as already described. Ihe sa~e criteria would apply to other types of surface irregularities, all of which are for convenience called "declivities", even though they may be convexly or concavely planar or curved in contour. It i8 not desirable to diffuse the imQge too greatly. The extent shown i6 optim~m.
If a greater anele is cho~en, the image~ o~ larger obJects are 0pread too much to be seen. If the declivities ~re too large (over a few millimeter in size) the image of the arc i8 not divided into parts and so it can not be sprena. If the decl~vities are too small (much less than a milli-meter) they tend to scatter light instead of slightly redirecting the bundlesof light. qhis would obscure the scene behind the curtain. Therefore the average decli~lty ought not to exceed about 1 ~m across, and may be smaller.
Another technlque to reduce the intensity of the image depends on in-body scatterin~, wherein about 25% of the light is likely to be scattere2, and about 67% (the re~aining 8% is due to surface reflection~ will pass through without any scattering at all to form an image. Thi~ class of scattering causes light from the arc to appear to come from the curtain itself. The curtain therefore becomes brighter, and this reduces the con-, trast between the background and the brieht arc, while at the same time itprovides illu~ination which causes the pupil to constrict. Materials fGr scattering are index of refraction discontinuities which may be particulateS
or voias whose index of refraction is different from that of the matrix material. The presently preferrea materials are fluorescent 7.inc oxide, zinc oxide, and titarium dioxide, all of whose indicies of refraction are above 2Ø The index of refraction of polyvinylchloride is about 1.5. Sim-ilarly, air may be utilized, being incorporated in the matrix as bubbles.
~he index of refraction Or air is 1Ø It is desirable for there to be a difference in index of refraction between matrix ard discontinuity of at least about 0.2 for best results.
This type of scattering will c~use every part of curtain 59 (Fig-ure o) to scatter light into the eye 38. In Figure 8, curtain 59 is sho~m with the surface treatment of ourtain 35 of Figure 4, and this is the pre-ferred embodiment. However, the surface treatment is ignored in Figure 8 ~or clarity in describing other features of the invention.
The result of the in-body scatterir,g iB that the scene perceived consists of a lower contrast (and about 25% lower arc-image intensity is the best embodi~er.t) fire~all against a relatively brighter (about four times more light ap~ears to be emitted by the curtain itself, compared with prior art curtains without this feature) background. Such scattering centers Or the type ~entioned tend to preferentially scatter the wavelengths which approx-imate their o~m size. Accordingly, for the purpose of scattering wavelengths Or light which p~ss throueh the curtain, particulates or cther discontinuities on the order of about 500 nm in size Ehould be utilized.
This class of scattering is sho~m in Figure 8 where ~isible light (including the "blue-effect" light) is shown as ray 70 impinging on discon-tinuities 71. Some of the visible light rays will of course pass directly through the curtain, but some ray5 will be scattered through the obser~rer's side of the curtain as sho~m by scatter rays 73 ard 7~.
Such scatter rays of course occur over t~e entire surface ar.d those scattered in the direction of the eye such as ray 75 are coll~cted by the pupil. Rays such as ray 72 may pass unscattered thrcugh the curtain directly to the eye. To the extent that scattered rays such as rays 73 and 74, and some rays ~hich are scattered reversely such as rays 76, 77 and 78, remove energy from the beam, they cause a diminution (about 25% reduction in the preferred embodiment) in the intensity of the beam ~rhich forms the image of the arc spot on the retina of the eye. The decreased intensity of the image of the arc spot formed on the retina represents a decreased hazard from the residual "blue-effect" light component of the ray.
Those forward-scattered rays such as ray 75 that happen to be directed precisely to~ard the eye, will be focused on the retina at places on the retina remo~ed from the location of the image of the arc spot 79, that i~, they ~rill be focused at about, or near 80 on the retina, and of course this is a wide-area effect from the entire surPace of the curtain. 5uch in-creased brightness in all of the curtain acting as a background and proJecting light to the retina over a wider area causes the iris to contract its diam-eter, ~till further diminishing the energy focused on spot 79 from the arcspot. This results in a further diminution (about 30% reduction due to iris constriction in the preferred embodiment) of the hazard from the residual "blue-effect" light component of the light from the ~rc spot.
Similarly, rearwara re nected scattered light shown by rays 76, 77 and 78 i8 directed into the region of the ~relding operation. There it may have struck some obJect 80, (ray 78 does this) ana then ha~e been returned as ray 81 through the curtain to the pupil, of course ray 81 may undergo some scattering itself. P~ays 78 ~rill ai~ in illuminating the booth, and the reflected ray 81 reaching the retina will further cause the iris to decrease its diameter with bene~icial results as ~ust described (as much as 5% reduc-tion due to iris constriction depending on the re~lective nature of obJects in the booth).
Still another means to protect the eye is to provide a fluorescent dye in the curtain which is responsive to the ultraviolet radiation. Ultræ-violet radiation will not pass through the curtain, but when an ultraviolet ray 85 impinges on a fluorescent dye particle 86 in the curtain, the energy Or the ray will be converted to visible fluorescent light shown by rays 87-92.
Forwardly extending rays ô7-89 behave in much the sa~e manner as rays 73-75 by illuminating the curtain and making it brighter so &S to instruct the eye-brain system to constrict the pupil, thereby to decrease the amount of energy which passes through the lens and onto the retina. This augments the effect o~ the scattering of light described above in diminishing the "blue-erfect"
light hazard from the focused arc spot on the retina. This e~ect can further reduce the apparent brlghtness Or the arc spot by an additional 5%.
Similarly some fluorescent light will be emitted back into the work area (rays 90, 91, 92), Ftrike an obJect 93 and be reflected by it as reflected ray 94 which can also reach the eye.
Dimension 95 indicates a constricted pupil caused by the constric-tion Or the iris due to this additional light.
The fluorescent dye is responsive only when it is near (a few microns from) the surface becQuse the ultraviolet absorber, present for another purpose, would absorb all the ultraviolet radiation that would stim-ulate the fluorescent dye. The fluorescent dye's response to ultraviolet stimulat1on is decreased with use, and as such must be continuously replen-ished at the surfnce. This is accomplished by using a mobile dye which dlffuses throu6h the body of the curt~ins and therefore allows fresh flores-cent dye to æppear near the surface as the existing dye is exhausted.
Figure 7 shous a prior art arrangement with a welding set-up an~ a conventional curtain 100 having only a dye and smooth sur~aces 101, 102. It is shown passing light 103 above about 350 nm and stopping ultraviolet rays 10~ and also passing visible light 105 in various directions. There i~
nothing to light up the curtain, so the iris remains unconstricted, as shown by dimension 107. Nothing is done to enlarge the image of the arc spot on the retina. For the same condition of relative location o~ arc, curtain and observer and for the same init al arc spot intensity, the potential "blue-erfect" light hazard is always greater than ~or a curts;in accordine to thisinvention.
ReferriDg to Figure 1, graph line 13 shows the characteristics of a dye whose transmis6ivity i5 0 from 200 nm to the cut-o~f wavelen&th Ac~
shown ~or ex~mple as 500 nm in the Pigure (segment 1~ nd whose transmis-sivity changes abruptly at ~c to 100% transmissivity from 500 to 1,400 nm.
On examining the changes in the relatlve values of graph lines 11 and 12 in Figure 1 in the vicinity of the cut-off wavelength, it is clear th~t i~ the cut-ofr wavelength were chosen as ~o~ewhat less than 500 nm, the contribution of "blue-efrect" lleht (line 11) would increase proportionately much re rapidly than the contribution of visible li~ht (line 12) would decrease. Conversely, if the cut-off were chosen at slightly larger wave-lengths than 500 nm, the contribution Or "blue-e~fect" light would decrease proportionately much les~ than the contribution Or visible light uould in-crease.
Hence, the cut-orf for a curtain aye should be chosen as far to the left in Fie~re 1 as is consistent with yielding an acceptable stare time for the use intended.
While the perfect cut-ofr filter (one in which the transmission 1 16384~4 changes from 0 to 100% completely at a given wavelength as in segment 14, Fi~ure 1) is not physically attainable, cut-ofr ~ilters can be made whose transition is sufficiently sharp, and whose transition from rel~tively opaque to relatively transparent takes place over a r.srro~T ~avelength band. A
desirable example Or such filters has a characteristic shown in Figure 2 as line 20. It will be noted that the se~ent 22 Or rapid rise is reasonably near to vertical, and that the cut-off "foot" 100 reduces the "blue-effect"
better than any of the "prior art" curtains whose spectra are shown in Figure
This invention relates to welding curtains through which an object on the other side can be seen.
More particularly, this invention relates to a welding curtain which will enable an otherwise-unprotected observer to observe a welding scene on the other side with the greatest clarity consistent with the requisite safety from deleterious effects, even if the eye should fixate on the arc spot for an extended period.
The parent application is concerned with optimizing the trade-off between these two competing requirements by utilizing spectral space discrimina-tion using dyes, as described below. This may be used in combination with some or all of the following features:
I. Spatial frequency discrimination using surface refraction as des-cribed below;
II. Relative light intensity reduction by diffractive scattering, using surface or bulk index of refraction discontinuities as described below; and III. Pluorescent wavelength shifting, using fluorescent dyes as described below.
The present application relates to the use of spatial frequency discrmination. The other features can also be described for the sake of completeness.
Pertinent considerations are as follows:
SPATIAL FREQUENCY DISCRIMINATION
Radiations from 200 to 500 nm and even larger are potentially damaging to the eye, although the hazard decreases rapidly with increasing wavelength above 500 nm. In the band 200 to 400 nm the modeoE action of the 5~
potential injury is related to total amount of energy delivered to the eye.
Absorbing dyes which completely stop this energy band from penetrating the curtain are available as discussed later. The mode of action of the band of energy extending from 400 to 500 nm and even larger depends primarily on the energy-density at the retina of the eye. That is, a given amount of energy in the band 400 nm - and - larger, foc~sed on a small spot on the retina of the eye, may be a serious hazard, while if the same total amount of energy is spread out over a larger spot on the retina, it may be totally non-hazardous, even for extended longer-time viewing.
Thus, a selective broadening of the image of the minute arc spot on the retina, while leaving the diameter of the images of larger features in the scene relatively unchanged, so that sight and recognition of such features is perceived as "normal", could decrease the hazard below the danger point.
Consequently, the curtain may carry on its surface minute refracting elements, (sometimes called "declivities" herein) conveniently placed there by embossing or by reticulation. Bundles of light rays from the scene pass through the surface. The declivities on the surface make only a very small angle with the surface. The declivities should preferably be oriented at random. Thus a bundle of rays from any particular point in the scene is split up into a group of sub-bundles - those which passed through adjacent but dif-ferently oriented declivities of the curtain - and are brought to a focus on the retina as a number of partially superimposed images at and surrounding the location where the original image would be were there no declivities. The image of a small arc spot will thereby be spread out on the retina to enlarge its diameter, while the image of a large feature of the scene - a finger or hand or clamp, for example, would be spread out the same absolute amount but only a negligible relative amGunt and so would retain its nearly normal appearance _ 2 -1 ~B~844 in the scene. Thus the hazard to the eye from an overly bright minute source would be negated while still retaining satisfactory visual acuity of scenes through the curtain.
The net result is that the brightness of small minute features ~such as an arc spot) is preferentially reduced on the retina, while the brightness and appearance of larger features of the scene is essentially unchanged.
Thus, according to the present invention there is provided, in a weld-ing curtain of substantial area forming at least a portion of the perimeter of an area in which an electrical arc welding or an electrical arc cutting operation is conducted for the purpose of protecting the eyes of an observer located out-side of said perimeter from damage by light from said arcs, said curtain having a pair of surfaces spaced apart by a dimension of thickness, and being sufficiently clear for said observer to see through it an object of substantial size located inside said perimeter, the improvement comprising: one of said surfaces being substantially entirely covered with declivities each having a relatively minor surface extent and having faces disposed at angles to the plane of the sheet, whereby some rays of light, which pass through said one surface are refracted and undergo a change in direction thereby partially to de-focus an image.
SPBCTRAL SPACE DISCRIMINATION
The energy emitted by an electric welding arc is given out in the form of radiant energy. Such radiant energy consists of the simultaneous emission of electromagnetic waves whose wavelengths include every wavelength from less than 200 nanometers (nm) to more than 1,400 nm.
Among all the radiations, those of the ultraviolet (200 - 400 nm), and the shorter-wavelength part of the visible (400 to about 500 or 550 nm) are the most effective in producing damage to the eye. That is, the radiations whose wavelength is 500 nm and greater are relatively innocuous in causing damage even when they are present to as large an extent as the group from 200 1 ~63844 to 500 nm. Therefore a curtain or filter which stops all radiation from an arc operation between 200 and 500 nm while allowing the residual radiations from 500 to 1,400 nm to pass, will do away with the potentially hazardous 200 - 500 nm radiation, while allowing the longer ~500 to 1,400 nm) more innocuous radiation to pass through it. It is important to maximize the amount of the remaining non-hazardous radiations that pass through the curtain, because the ability to see the scene through the curtain depends on the amount of visible light which penetrates the curtain and reaches the eye.
There are thus two mutually contradictory requirements for a curtain which allows safe viewing of an electric welding or cutting arc scene. In order to minimize the potential eye hazard, the curtain should stop all wavelengths from 200 to 500 or 550 nm or larger. In order to maximize the ability to see the scene, the curtain should pass the maximum of those radiations which give rise to the sensation of sight (400 to 760 nm).
It has been determined as described later, that if the curtain transmission cut-off is between about 500 nm and about 580 nm sufficient visible light (with wavelengths between about 500 and about 760 nm) will reach the eyeJ
and little enough residual hazard will remain, so that such a curtain could constitute a safe and usable welding curtain for passers-by, adjacent workers, and supervisors.
RELATIVE LIGHT INTENSITY REDUCTION (SCENE CONTRAST EQUALIZATION) The normal mechanism of the human eye in protecting itself against a too-bright potentially hazardous over-illumination is an involuntary closing of the iris of the eye, and an aversion (of the direction of sight) of the eye. Neither of these reactions is effective in the normal circumstance of electric arc-weld scene viewing for persons to be protected by this invention such as adjacent workers, passers-by, and supervisors. This is because the ~ 4 ~
iris responds to the total illumination on the retina, and a very small bright spot surrounded by a dim field of view, is regarded by the eye-brain system as similar to a bright star in a dark sky, that is, as a "dark" scene, and the normal response is a maintainance of a wide-open iris.
The second natural protective mechanism - the involuntary aversion of the eye direction from a bright light source - is overcome by the conscious will of the observer to examine the scene in detail, because it is normally within his work-related duty to see and to study the details of the arc-welding in the scene.
It would, therefore, be desirable to ensure that the iris of the eye will diminish its aperture (pupil) while the arc is in operation.
Thus, the welding curtain may have discontinuities distributed throughout the matrix material, said discontinuities having an optical index of refraction which differs from the optical index of refraction of the material of which the curtain is primarily made by at least 0.2 units, where-by to scatter at least 5% and less than 50% of the light which passes through the curtain.
Most of the light from an arc spot will pass through the protective curtain in such a direction that its light would not be seen by the eye. How-ever, a fraction ~preferably about one-quarter) of this other-directed light is scattered by the curtain, and some part of the scattered light enters the eye from points of the curtain removed from the direct line of sight of the arc with respect to the eye. This scattered light from all parts of the curtain is seen by the eye, and forms a general illumination on all parts of the retina.
This general illumination, in combination with the residual normal illumination of the rest of the scene, triggers the normal iris - closing response due to a general, wide-spread illumination.
The net result of the scattering feature has been a decrease in scene contrast, that is, a reduction of bright spot intensity and a lightening of the surround, a general field-of-view illumination increase which causes the iris to contract, and a decrease in the brightness of the image of the arc spot on the retina, since some of the arc spot's brightness has been scattered away in passing through the curtain.
FLUORESCENT WAVELENGTH SHIFTING
It has been pointed out that it is desirable to decrease the amount of potentially harmful short wavelength light penetrating the curtain, and to increase the amount of longer wavelength visible light so that more details of the scene may be clearly seen.
This objective may be accomplished by incorporating a fluorescent dye material in the curtain. The characteristic feature of fluorescence is that when a ray ~strictly speaking, a quantum) of short wavelength light falls upon it, the short wavelength light may be totally absorbed and an equivalent amount of longer wavelength light will be emitted in all directions.
Thus the incorporation of an appropriately selected fluorescent dye will de-crease the amount of shorter wavelength light that penetrates the curtain, thereby further decreasing the hazard to the eye. Furthermore, the newly created fluorescent light, if one chooses a suitable fluor, will re-emit additional innocuous long-wavelength light, some of which will be redirected to the whole welding scene, add to the general illumination, and if the fluorescent color is chosen as will be described, will make its way unimpeded by the aforementioned sharp cut-off dye (the cut-off chosen to cooperate with the characteristic fluorescently emitted wavelength of the fluorescent dye material) through the curtain to give more visual brightness to the scene .
surrounding the welding arc.
The welding curtain is preferably made utilizing an organic plas-tic matrix such as polyvinylchloride, which itself is opaque to certain undesirable wavelengths and which can act as a structural support and as a matrix for dyes, pigments, and additives which it may contain. One or both of its surfaces can be modified to provide the above surface refractive effects.
In the accompanying drawings which illustrate the structures and properties of certain prior art curtains and curtains embodying various of the above features:
Figure 1 is a graph showing the inter-relationship between the damage functions of ultraviolet, and of light induced retinal injury "blue-effect" light damage, the transmissivity of an ideal cut-off dye, and the photopic eye sensitivity function;
Pigure 2 is a graph showing the inter-relationship between the "blue-effect" light damage function curve, the photopic curve, and the transmissivity behavior of a group of curtains;
Pigure 3 shows the focusing action of the eye as it looks through a prior art curtain;
Figure 4 shows a view similar to Figure 3, but with the eye see-ing through one embodiment of curtain according to this invention;
Pigure 5 is a vignette showing the left hand surface of the curtain in Pigure 4;
Pigure 6 is a cross-section taken at line 6-6 in Pigure 5;
Pigure 7 shows the field of view and the response of an eye as it looks through a prior art curtain; and Figure 8 shows a view similar to Figure 7, but with the eye seeing through another embodiment of curtain according to this inven-tion.
Figure 1 is a graph illustrating some of the parameters that have been considered in the design of the present curtains. The abscissa is the wavelength of the radiation in nanometers ~nm) while the ordinate is the relative response of the eye to radiation and light and also the relative transmission of curtains at the various wavelengths. Graph line 10 shows the ultraviolet radiation damage function S. This line discloses that maximum damage is caused by radiation at about 270 nanometers.
Still, any radiation whose value is above zero anywhere along this graph line can cause some damage. For example, at about 225 nanometers the effect is about 1/7 as important as radiation at 270 nanometers. How-ever, it still constitutes a risk of damage rom ultraviolet radiation, although a lesser risk. The use of ultraviolet absorbers in plastics to absorb the ultraviolet radiation is per se. An ultraviolet absorber is conventionally used to preserve the plastic matrix, as well as to prevent transmission of ultraviolet light.
Graph line 11, shows the "blue-effect" light hazard function (B).
This graph line shows that retinal damage begins to be caused by radiation above about 400 nm, is maximum at about 440 nm, diminishes as a hazard through 600 r~, the hazard remaining constant at one thousandth of the maximum value rrom 600 to 1,400 n~. q~he greatest risk is at about 440 nm.
~owe-ver, any rs~iation within the indicated range of suf~icient intensity can cause retin 1 in~ury.
Graph line 12 is the photopic eye sensitivity function. This shows the sensitivity (V) of the eye to visible light. It rises from a zero value near 400 nm to a maximum at 555 nm and declines to near zero rear 760 nm. The more of the light as wei~hted by this response curve uhich can be transmitted, the 6reater will be the perception to the eye Or an object on the other side o2 the curtain.
Graph line 13 shows the transmissivity function of a theoretically perfect dye with a "cut-off" at approximately 491 nanometers. It has a rising segment 14. Especially this rising seg~ent, and indeed the whole line, de-fines what the dye will absorb and not pass, and what it will not absorb ana wlll pass. Speaking ~enerally, points beneath and/or to the right of the curve represent transmission. Points above and/or to the left, represent absorption. ~he rising segmcnt is the area of sharpest and greatest effect.
i A dye can be theorized, the rising segment of whose curve would be at either ¦ a shorter or longer wavelength than the one sho~n. If it were at a shorter wavelength, it would eive slightly more visible energy but would also pass a ¦ very significant additional amount Or "blue-4ffect" energy to the hazard of the viewer. Selection of a dye with a rising segment at a longer wavelength would reduce the "blue-effect" light hazard, but would also diminish the amount of visible light transmitted to the disadvantage of observer visibil-ity. Therefore, there is no perfect dye composition, and certainly no prac-tical dye composition, which will simultaneously entirely eliminate the "blue erfect" light hazard and entirely msximize the visible transmission. Accord-' ingly, there is a region 15 which is somewhat triangular in shape represent-_ 9 _ J`~
ing "blue-effect" light hazard which ~ill be transmitted even by the theoret-ically Ferfect curtain.
In Figure 2 there is shown another graph whose abscissa is wave-length in nznometers and whose ordinate is the relative tr~nsmission of the curtsins (~) and relative response of the eye (B) and (V). The purpose of this græph is to contrast the performance of one representa~ive em~odiment of this invention with some prior art welding curtains. The prior art cur-tains described have only dyes as their active constituents for the control of light, and therefore this comparison is made without the above discussed diffracting and scattering effects being included.
Graph line 20 shows the relative transmission o~ a curtain accord-ing to this invention, with ~yes only. It will be observed that the curve has a flat segment 21 whose ordinate vaiue is zero bet~een about 200 and about 500 nm, reaninB that it transmits no radiation between these ranges. It then has a rising seg~ent 22, as nearly vertical as can be devised by appropriate dye selection, from about ~ero tran~mission to about 80% tran~missicn. Limits 23, 24 and 24A are respectively shown at 1% at 450 nm, and at 5% at ~91 nm, and at 70% at 600 nm. To the right, above about 600 nanometers there is a generally flattened segment 25. This curve indicates that above about 600 nm about 75 to 85 percent of the light of various wavelengths is transmitted by the dyes, which is a very suitable value for a welding curtain.
Region 33 i8 also shown which indicates the transmission by the curtain o~ this invention oP residual "blue-effect" light. The absolute effect of the residu~l "blue-effect" light whose existence is indicated in Figure 2 by the somewhat triangular region 33, is obtained by a ~athematical weighting process. In each wavelength interval considered, (e.g. for this invention 500 to 505 nm, 505 to 510 nm, 510 to 515 nm, etc.) the value of the c~rtain dye transmission (T) in Figure 2 for segments in the respective line is multiplied by the value of (B), curve 28 in Fi~ure 2, ror the same wave-- length interval, and the product multiplied by the value of the spectral radiance of an arc source with a brightness similar to the su~ (L), for the same wavelength interval. The values of the final products (~LT) thus ob-tained for each wavelength interval are then summed. This total sum ~LT, is proportional to the total "blue-effect" light hazard to the eye from the residual "blue-effect" light passed by the curtain under consideration. The curtain of this embodiment will be seen to perform in a manDer which is rather close to the optimum de~ined by graph line 13 in Figure 1, although it cannot be expected that any economically priced commerically available dye will be P8 ideal in its absorption as the theoretical dye proposed by graph line 13 of Figure 1.
A~ will be discussed later, a useful method to characterize the relative rating of different curtains in safe6uarding the eye and in providing adequate vislbility i8 to compare the ratio of the total amount of visible energy transmitted by a welding curtain ( ~ VLT) with the total amount of potenti~lly hazardous ~'blue-effect" light energy ( ~ BLT) transmitted by the same curtain. The complete description Or the method of obtaining the value of the ratin8 factor wil1 take into account the necessary weighing functions such as lines 11 and 12 in Figure 1.
The spectral transmissivity of a curtain is a function o~ absorptive dyes in the matrix of the curt&in. The "perceived" color is not to be con-fused with "spectral~' color, even though the various curtain~ described do have a "color" which is perceived by the user. One refers herein to trans-mission and to cut-off strictly as a function of wavelength.
Assuming a suitable dye a useful curtain can be obtained, but such a curtain continues to involve the transmission of "blue-effect" light to the hazard of the observer. One problem with this "blue-effect" light is that ~ 163844 the eyeball is not strongly reactive to it. The light which constitutes the "blue-effect" li~ht hazard can have waveleng~hs longer or shorter than that of the spectral color blue. The perceived color blue does, however, charac-terize the color sensed in this regicn. ~here is little pain or other sensa-tion from it, and damage can be done because no protective action will be taken. This d m~ge is a function of energy per unit area incident on the retina. In a welding operation, it comes from a small source to which the pupil will not be adequately reacti~e, but the light is stror.gly focused by the eye, and this increases the area loading.
One tecbnique to assist and instruct the eye for its own protec-tion is shown in Figure 4, where a curtain 35 having a pair of surfaces 36, 37 is shown disposed between the eye 38 of an obser~er and a welding opera-tion 39. The welding operation i8 indicated by schematic welding rod 4O
adJacent to a workpiece 41 and eeneratin8 a fireball (arc) 42 which is the ~ource Or the light being protected against herein. The lens 43 of the eye is focused on a retina 44. An iris 45 ~orms a variable aperture to determine the amount of light which enters the eye through an area called the pupil.
More liEht i8 admitted when it i8 enlarged than when it is constricted.
Prlmary rays 46, 47 are shown impinging on a curtain 35.
A similar view is shown in Figure 3, where the same rays impinge on a prior art curtain 49. The prior art curtain i8 dyed but transparent, and has two smooth parallel surface~ 5O, 51. In Figure 3, rays 46, 47 are imaBed by the lens to form a central image 52 whose relative si~e is shown in solid o~al line lmmediately adJacent to the retina.
; In order to reduce the unit lcading on the retina it is useful to spread the lieht as much as possible for the same pupil area opening. In the embodiment illustrated in Figure 4 this is accomplished by reticulated or embossed declivities 53 on surfaces 54 PS shown in Figures 4-6. The purpose ,, ?~
1 16384~
of these variations from a planar surface i5 to provide surrace~refractive spreading of the beam. This will spread the image a~d reduce the unit load-ng.
For purposes of disclosure, dimpled declivities are ~ho~m, and their dimensions are greatly exaggerated. For purposes of the following specific eY.ample, the size of the fireball 42 is taken to be 6mm diameter, the distance from fireball 42 to curtain 35 or 49 is taXen to be 1.3m, and - the distance from the curtain to the eye 38 of the observer, is also 1.3m.
In general it is preferred that the tangents to the surfaces of the declivities do not exceed a dif~erence greater than about 8 minutes of arc from parallelism with what ~Tould be smooth planar surface parallel to surface 54. This is sho~m by angle 5~a ~Figure 6). Such an arrangement will give an image change corresponding to about a 4 minute of arc divergence on each side of the image of any obJect in the field of view. Such image en-lar~ement is a con6iderable part o~ the size of the otherwise unspread arc spot image size. Indeed for the dimension~ guoted the effect is to about ~uadruple the area on which the ener~y ~alls even though a brighter portion is still located in the center. The enlarged areas are shown as areas 55, 56, 57, 58 in Figure 4. ~his provide~ a gross enlargement in the image and spaces out the image rather similar to a range finder. The additional en-largement due to the 4 minutes of arc divergence on each side of a larger ob~ect of say 32 minutes of arc (a 25 mm obJect) will only raise the image size to that corresponding to an image appropriate to a 30 mm ob~ect. The 25 mm obJect would still be clearly recognizable. Even a smaller amount of ~preading ofthe incident rays causes a substantial reduction in unit loading on the retina. The effect thi surface treatment has on arc image intensity on the retina is described later. For si~plification of the optical effect the declivities have been sho~m on one side only. Declivities with half the , --angle (4 minutes of arc) and of the same size on both sides of the curtain would h~ve nearly the same effect.
The surface treatFent irregularity can be provided i~ man~ ways.
One way is to calendar a pattern all over the surface, and thiæ will produce predetermined shapes, which could be defined by planes to form pyranids and the like. Instead o~ sharp and planar bounded declivities, these may instead be dimpled structures ~Jith curved boundaries, conveniently provided as an "orange peel" surfacé known to all persons accustomed to calendaring sheets Or polyvinylchloride a~ the consequence of reticulation. Such a surface is shown in Figures 5 and 6, wherein the plurality of dimple-shaped concave declivities 53 are formed in the surface 54, as already described. Ihe sa~e criteria would apply to other types of surface irregularities, all of which are for convenience called "declivities", even though they may be convexly or concavely planar or curved in contour. It i8 not desirable to diffuse the imQge too greatly. The extent shown i6 optim~m.
If a greater anele is cho~en, the image~ o~ larger obJects are 0pread too much to be seen. If the declivities ~re too large (over a few millimeter in size) the image of the arc i8 not divided into parts and so it can not be sprena. If the decl~vities are too small (much less than a milli-meter) they tend to scatter light instead of slightly redirecting the bundlesof light. qhis would obscure the scene behind the curtain. Therefore the average decli~lty ought not to exceed about 1 ~m across, and may be smaller.
Another technlque to reduce the intensity of the image depends on in-body scatterin~, wherein about 25% of the light is likely to be scattere2, and about 67% (the re~aining 8% is due to surface reflection~ will pass through without any scattering at all to form an image. Thi~ class of scattering causes light from the arc to appear to come from the curtain itself. The curtain therefore becomes brighter, and this reduces the con-, trast between the background and the brieht arc, while at the same time itprovides illu~ination which causes the pupil to constrict. Materials fGr scattering are index of refraction discontinuities which may be particulateS
or voias whose index of refraction is different from that of the matrix material. The presently preferrea materials are fluorescent 7.inc oxide, zinc oxide, and titarium dioxide, all of whose indicies of refraction are above 2Ø The index of refraction of polyvinylchloride is about 1.5. Sim-ilarly, air may be utilized, being incorporated in the matrix as bubbles.
~he index of refraction Or air is 1Ø It is desirable for there to be a difference in index of refraction between matrix ard discontinuity of at least about 0.2 for best results.
This type of scattering will c~use every part of curtain 59 (Fig-ure o) to scatter light into the eye 38. In Figure 8, curtain 59 is sho~m with the surface treatment of ourtain 35 of Figure 4, and this is the pre-ferred embodiment. However, the surface treatment is ignored in Figure 8 ~or clarity in describing other features of the invention.
The result of the in-body scatterir,g iB that the scene perceived consists of a lower contrast (and about 25% lower arc-image intensity is the best embodi~er.t) fire~all against a relatively brighter (about four times more light ap~ears to be emitted by the curtain itself, compared with prior art curtains without this feature) background. Such scattering centers Or the type ~entioned tend to preferentially scatter the wavelengths which approx-imate their o~m size. Accordingly, for the purpose of scattering wavelengths Or light which p~ss throueh the curtain, particulates or cther discontinuities on the order of about 500 nm in size Ehould be utilized.
This class of scattering is sho~m in Figure 8 where ~isible light (including the "blue-effect" light) is shown as ray 70 impinging on discon-tinuities 71. Some of the visible light rays will of course pass directly through the curtain, but some ray5 will be scattered through the obser~rer's side of the curtain as sho~m by scatter rays 73 ard 7~.
Such scatter rays of course occur over t~e entire surface ar.d those scattered in the direction of the eye such as ray 75 are coll~cted by the pupil. Rays such as ray 72 may pass unscattered thrcugh the curtain directly to the eye. To the extent that scattered rays such as rays 73 and 74, and some rays ~hich are scattered reversely such as rays 76, 77 and 78, remove energy from the beam, they cause a diminution (about 25% reduction in the preferred embodiment) in the intensity of the beam ~rhich forms the image of the arc spot on the retina of the eye. The decreased intensity of the image of the arc spot formed on the retina represents a decreased hazard from the residual "blue-effect" light component of the ray.
Those forward-scattered rays such as ray 75 that happen to be directed precisely to~ard the eye, will be focused on the retina at places on the retina remo~ed from the location of the image of the arc spot 79, that i~, they ~rill be focused at about, or near 80 on the retina, and of course this is a wide-area effect from the entire surPace of the curtain. 5uch in-creased brightness in all of the curtain acting as a background and proJecting light to the retina over a wider area causes the iris to contract its diam-eter, ~till further diminishing the energy focused on spot 79 from the arcspot. This results in a further diminution (about 30% reduction due to iris constriction in the preferred embodiment) of the hazard from the residual "blue-effect" light component of the light from the ~rc spot.
Similarly, rearwara re nected scattered light shown by rays 76, 77 and 78 i8 directed into the region of the ~relding operation. There it may have struck some obJect 80, (ray 78 does this) ana then ha~e been returned as ray 81 through the curtain to the pupil, of course ray 81 may undergo some scattering itself. P~ays 78 ~rill ai~ in illuminating the booth, and the reflected ray 81 reaching the retina will further cause the iris to decrease its diameter with bene~icial results as ~ust described (as much as 5% reduc-tion due to iris constriction depending on the re~lective nature of obJects in the booth).
Still another means to protect the eye is to provide a fluorescent dye in the curtain which is responsive to the ultraviolet radiation. Ultræ-violet radiation will not pass through the curtain, but when an ultraviolet ray 85 impinges on a fluorescent dye particle 86 in the curtain, the energy Or the ray will be converted to visible fluorescent light shown by rays 87-92.
Forwardly extending rays ô7-89 behave in much the sa~e manner as rays 73-75 by illuminating the curtain and making it brighter so &S to instruct the eye-brain system to constrict the pupil, thereby to decrease the amount of energy which passes through the lens and onto the retina. This augments the effect o~ the scattering of light described above in diminishing the "blue-erfect"
light hazard from the focused arc spot on the retina. This e~ect can further reduce the apparent brlghtness Or the arc spot by an additional 5%.
Similarly some fluorescent light will be emitted back into the work area (rays 90, 91, 92), Ftrike an obJect 93 and be reflected by it as reflected ray 94 which can also reach the eye.
Dimension 95 indicates a constricted pupil caused by the constric-tion Or the iris due to this additional light.
The fluorescent dye is responsive only when it is near (a few microns from) the surface becQuse the ultraviolet absorber, present for another purpose, would absorb all the ultraviolet radiation that would stim-ulate the fluorescent dye. The fluorescent dye's response to ultraviolet stimulat1on is decreased with use, and as such must be continuously replen-ished at the surfnce. This is accomplished by using a mobile dye which dlffuses throu6h the body of the curt~ins and therefore allows fresh flores-cent dye to æppear near the surface as the existing dye is exhausted.
Figure 7 shous a prior art arrangement with a welding set-up an~ a conventional curtain 100 having only a dye and smooth sur~aces 101, 102. It is shown passing light 103 above about 350 nm and stopping ultraviolet rays 10~ and also passing visible light 105 in various directions. There i~
nothing to light up the curtain, so the iris remains unconstricted, as shown by dimension 107. Nothing is done to enlarge the image of the arc spot on the retina. For the same condition of relative location o~ arc, curtain and observer and for the same init al arc spot intensity, the potential "blue-erfect" light hazard is always greater than ~or a curts;in accordine to thisinvention.
ReferriDg to Figure 1, graph line 13 shows the characteristics of a dye whose transmis6ivity i5 0 from 200 nm to the cut-o~f wavelen&th Ac~
shown ~or ex~mple as 500 nm in the Pigure (segment 1~ nd whose transmis-sivity changes abruptly at ~c to 100% transmissivity from 500 to 1,400 nm.
On examining the changes in the relatlve values of graph lines 11 and 12 in Figure 1 in the vicinity of the cut-off wavelength, it is clear th~t i~ the cut-ofr wavelength were chosen as ~o~ewhat less than 500 nm, the contribution of "blue-efrect" lleht (line 11) would increase proportionately much re rapidly than the contribution of visible li~ht (line 12) would decrease. Conversely, if the cut-off were chosen at slightly larger wave-lengths than 500 nm, the contribution Or "blue-e~fect" light would decrease proportionately much les~ than the contribution Or visible light uould in-crease.
Hence, the cut-orf for a curtain aye should be chosen as far to the left in Fie~re 1 as is consistent with yielding an acceptable stare time for the use intended.
While the perfect cut-ofr filter (one in which the transmission 1 16384~4 changes from 0 to 100% completely at a given wavelength as in segment 14, Fi~ure 1) is not physically attainable, cut-ofr ~ilters can be made whose transition is sufficiently sharp, and whose transition from rel~tively opaque to relatively transparent takes place over a r.srro~T ~avelength band. A
desirable example Or such filters has a characteristic shown in Figure 2 as line 20. It will be noted that the se~ent 22 Or rapid rise is reasonably near to vertical, and that the cut-off "foot" 100 reduces the "blue-effect"
better than any of the "prior art" curtains whose spectra are shown in Figure
2, and in which the "foot" is not minimized.
A st desirable dye would have its most nearly vertical segment corresponding to segment 14 in Figure 1 displaced from 491 nm, and ~ould have as sharp a cut-off as possible on the shorter wavelength side, marked 103 in Figure 1. Ihe sharp cut-o~f at the rOot is far more important than a ~harp cut-off at the high transmisslon end Or the transition, marked 102, since ror a real curt~in dye the unavoidable 810pe 0~ the segment correspond-ing to se6ment 14 in Fieure 1, or segment 22 in Figure 2 has carried the lonE
~-avelength shoulder far to the right of the wavelength 491 nm. The additional contribution to hazard from blue li~ht (B, Figure 1, line 11) at the top cut-off wavelen~th is rery small; the chenge in luminous effect depending on V
(Fieure 1, line 12) is pro~ortionally not great.
The consequence Or this analysis is that the most userul ayes for the curtains under consideration must have a steep rise (compare se6ment 14 in Fieure 1), a sharp foot (CODIpare foot 100 in Figure 2), and the steep rise should take place at a wavelength removed rroTr. 491 nm. The lnst part Or the requirement comes about since the sensitivity of the ratio ~VLT/~BL~ is greatest at 491 nm, relatively slight changes in the concentration Or the dye in the curtain, and hence in the transmissivity, will shift the value ~VLT/~BLT unacceptably due to unavoidable manufacturing process variations.
1 ~63844 "L" represents the spectrAl radiance of the source.
A description of a dye for optimum curtain manufacture i8 best done by specifying design points in the curve oP Figure 2.
The transmission vs wavelen~th cur~e (Figures 1 and 2) should have limits as follows:
Limit 23: at 450 nm, the relative transmission should not be ereater than 0.01 (1%).
Limit 24: at 491 nm, the relative transmission should not be greater than 0.05 (5%).
Limit 24a: at 600 nm, the relative transmission should be at least (70%).
This relates only to an organic plastic matrix with dye, with cmooth surfaces, and without any scattering function. These additional runctions will improve the curtain even without the optimum dyes. Figures 1 and 2 illustrate only the dye's function.
Control and variation of per~issible stare time i9 accomplished by mean~ of.the rollowing procedures.
I. ~PECTP~L SPACF DI8CRIMI~ATION
The dye composition and concentration i9 ~aried so that the segment corresponding to line 14 in Figure l is displaced sensibly parallel to it-selr, but to the right or left.
II. SPATIAL FREQUENCY DISTRIBUTIOM
Surface refraction i9 used to preferentially reduce the bri6htness of the image Or the small arc spot on the retina, and thererore decrease the sum ~BLT on the retina, while leaving the intensity of large reatures of the scene sensibly unchanged.
III. PEATURES OF SCENE CONTRAST EQUALI2ATION
Surface and volume scattering reduce the ~alue of BLT and VLT, and `~;,,,~.
1 16~844 cause the curtain to scatter light to the general field of vie~. This causes the iris to contract and diminishes tke size of the pupil of the eye, and so the energy delivered to the retina at the i~age location of the ~rc spot is further diminished.
IV. FEATU~ES OF FLUORESCENT ~IAYELENGTH S~IFTING
This will add to the illumination of the scene, further reducine the si~e of the pupil, hence the energy delivered to the retina at the image location of the arc spot is further diminished. On the other hand, the value of ~T will be increased because some of the fluorescent light falls on the scene and increases the general visible-light level by which features of the scene are seen. ~his last factor can offset some or all of the loss of ~VLT
caused by scattering discussed in III directly above, but it does not change the effect of III in diminishing ~BLT.
In Table I there is shown a list of materials of construction with which it is possible to make the best known mode of curtain, and also to melke curtains of le6ser but stlll adequate performance, and to make some advan-tages of the invention available even in curtalns ha~in~ dyes which do not function accordlng to the crlteria of this inventlon.
In describing the dyes, considerable difficulty is encountered, because their compositions tend to be regarded by thelr manufacturers as trade secrets. In general, metallic azo dyes, a well-known type of dye, are preferred for their stabllity. Curtains with such dyes should last a con-slderable time wlthout undue fadir~g, because metallic azo dyes are quite resistent to fadlng. ~lowever, e~ny type of dye with a suitable cut-off ln accordance with meeting the criteria o~ this lnvention, can be used instead of the exemplary dyes disclosed herein.
As to the scattering materials, their size is selected to approx-imate the wavelength preferentially to be scattered. The most appropriate ...
materials are any o~ the following: air bubbles, zinc oxide powder, fluo-rescent zinc oxide powder, titanium dioxide powder, or ~ixtures of the~.
Fluorescent zinc oxide performs a dual function of both scattering and fluorescin6 ' The fire retardant is selected in addition to its major function, for havir~ an optical index of refraction nearly equal to that of the base polymer. Then the mixture is as transparent as the ~atrix.
The organic plastic matrix i9 preferably polyvinylchloride. It works well, is well-understood, and has a suitable life. Of course other transparent organic plastic materials could be used instead. Polyvinyl-chloride is given ~erely as an example of a large number of suitable ~ate-rials.
The plasticizers will be those known in the art for use with the selected ~atrix material.
Ultraviolet absorbers are well-known, and nead no detailed descr~p-tion here.
BECT MODE CURTAIN (with reference to Table I). Percentages are by weight and are approximate:
The ider.tified "Base Polymei": 41~
DOP plasticizer : 41%
The ~etallic azo dye identified as Sc-39-3 g/g bright orange : 1-1/3%
The ~luorescent oranee dye identified as C507XX Product No. 40-26-2 : 1/2%
The identified rluorescent zinc oxide phosphor, particle size about 500 nm : 0.17 The identified UV absorber : 1~
Tkeidentified fire retardant : 15%
1 i638~4 This curtain will be providea with declivities on both of its surfaces, produced by reticulation.
CT~ER CUPT~INS:
l. The "2nd choice" ~luorescent orange dye may be substituted for the fluorescent dye in the best mode curtain.
2. The "2nd choice" pig~ent ttitam um dioxide), zinc oxide, or air bubbles oP the same size, may be substituted for the fluorescent zinc oxide.
A st desirable dye would have its most nearly vertical segment corresponding to segment 14 in Figure 1 displaced from 491 nm, and ~ould have as sharp a cut-off as possible on the shorter wavelength side, marked 103 in Figure 1. Ihe sharp cut-o~f at the rOot is far more important than a ~harp cut-off at the high transmisslon end Or the transition, marked 102, since ror a real curt~in dye the unavoidable 810pe 0~ the segment correspond-ing to se6ment 14 in Fieure 1, or segment 22 in Figure 2 has carried the lonE
~-avelength shoulder far to the right of the wavelength 491 nm. The additional contribution to hazard from blue li~ht (B, Figure 1, line 11) at the top cut-off wavelen~th is rery small; the chenge in luminous effect depending on V
(Fieure 1, line 12) is pro~ortionally not great.
The consequence Or this analysis is that the most userul ayes for the curtains under consideration must have a steep rise (compare se6ment 14 in Fieure 1), a sharp foot (CODIpare foot 100 in Figure 2), and the steep rise should take place at a wavelength removed rroTr. 491 nm. The lnst part Or the requirement comes about since the sensitivity of the ratio ~VLT/~BL~ is greatest at 491 nm, relatively slight changes in the concentration Or the dye in the curtain, and hence in the transmissivity, will shift the value ~VLT/~BLT unacceptably due to unavoidable manufacturing process variations.
1 ~63844 "L" represents the spectrAl radiance of the source.
A description of a dye for optimum curtain manufacture i8 best done by specifying design points in the curve oP Figure 2.
The transmission vs wavelen~th cur~e (Figures 1 and 2) should have limits as follows:
Limit 23: at 450 nm, the relative transmission should not be ereater than 0.01 (1%).
Limit 24: at 491 nm, the relative transmission should not be greater than 0.05 (5%).
Limit 24a: at 600 nm, the relative transmission should be at least (70%).
This relates only to an organic plastic matrix with dye, with cmooth surfaces, and without any scattering function. These additional runctions will improve the curtain even without the optimum dyes. Figures 1 and 2 illustrate only the dye's function.
Control and variation of per~issible stare time i9 accomplished by mean~ of.the rollowing procedures.
I. ~PECTP~L SPACF DI8CRIMI~ATION
The dye composition and concentration i9 ~aried so that the segment corresponding to line 14 in Figure l is displaced sensibly parallel to it-selr, but to the right or left.
II. SPATIAL FREQUENCY DISTRIBUTIOM
Surface refraction i9 used to preferentially reduce the bri6htness of the image Or the small arc spot on the retina, and thererore decrease the sum ~BLT on the retina, while leaving the intensity of large reatures of the scene sensibly unchanged.
III. PEATURES OF SCENE CONTRAST EQUALI2ATION
Surface and volume scattering reduce the ~alue of BLT and VLT, and `~;,,,~.
1 16~844 cause the curtain to scatter light to the general field of vie~. This causes the iris to contract and diminishes tke size of the pupil of the eye, and so the energy delivered to the retina at the i~age location of the ~rc spot is further diminished.
IV. FEATU~ES OF FLUORESCENT ~IAYELENGTH S~IFTING
This will add to the illumination of the scene, further reducine the si~e of the pupil, hence the energy delivered to the retina at the image location of the arc spot is further diminished. On the other hand, the value of ~T will be increased because some of the fluorescent light falls on the scene and increases the general visible-light level by which features of the scene are seen. ~his last factor can offset some or all of the loss of ~VLT
caused by scattering discussed in III directly above, but it does not change the effect of III in diminishing ~BLT.
In Table I there is shown a list of materials of construction with which it is possible to make the best known mode of curtain, and also to melke curtains of le6ser but stlll adequate performance, and to make some advan-tages of the invention available even in curtalns ha~in~ dyes which do not function accordlng to the crlteria of this inventlon.
In describing the dyes, considerable difficulty is encountered, because their compositions tend to be regarded by thelr manufacturers as trade secrets. In general, metallic azo dyes, a well-known type of dye, are preferred for their stabllity. Curtains with such dyes should last a con-slderable time wlthout undue fadir~g, because metallic azo dyes are quite resistent to fadlng. ~lowever, e~ny type of dye with a suitable cut-off ln accordance with meeting the criteria o~ this lnvention, can be used instead of the exemplary dyes disclosed herein.
As to the scattering materials, their size is selected to approx-imate the wavelength preferentially to be scattered. The most appropriate ...
materials are any o~ the following: air bubbles, zinc oxide powder, fluo-rescent zinc oxide powder, titanium dioxide powder, or ~ixtures of the~.
Fluorescent zinc oxide performs a dual function of both scattering and fluorescin6 ' The fire retardant is selected in addition to its major function, for havir~ an optical index of refraction nearly equal to that of the base polymer. Then the mixture is as transparent as the ~atrix.
The organic plastic matrix i9 preferably polyvinylchloride. It works well, is well-understood, and has a suitable life. Of course other transparent organic plastic materials could be used instead. Polyvinyl-chloride is given ~erely as an example of a large number of suitable ~ate-rials.
The plasticizers will be those known in the art for use with the selected ~atrix material.
Ultraviolet absorbers are well-known, and nead no detailed descr~p-tion here.
BECT MODE CURTAIN (with reference to Table I). Percentages are by weight and are approximate:
The ider.tified "Base Polymei": 41~
DOP plasticizer : 41%
The ~etallic azo dye identified as Sc-39-3 g/g bright orange : 1-1/3%
The ~luorescent oranee dye identified as C507XX Product No. 40-26-2 : 1/2%
The identified rluorescent zinc oxide phosphor, particle size about 500 nm : 0.17 The identified UV absorber : 1~
Tkeidentified fire retardant : 15%
1 i638~4 This curtain will be providea with declivities on both of its surfaces, produced by reticulation.
CT~ER CUPT~INS:
l. The "2nd choice" ~luorescent orange dye may be substituted for the fluorescent dye in the best mode curtain.
2. The "2nd choice" pig~ent ttitam um dioxide), zinc oxide, or air bubbles oP the same size, may be substituted for the fluorescent zinc oxide.
3. Dioctyl aze~ate may be substituted ror the DOP pl~sticizer.
4. The "2nd choice" metallic azo dye may be substituted for the Pirst choice ~ye.
5. The curtains with diPferent dyes, the scattering materials, or sur-Pace treatment, or both, can be provided.
TABLE I
, AMOUNT
PURPOSE OF USED IN MA~UFAcquRERs COM Ol~ MATERIAL GENERA~ t~ANUFACTURERS CURTAIN ~AME AND
IN CURTAIN - ~AME PART NUMBER % W~. LOCATION
Ba6e Polymer Poly Vlnyl PVC 75 to 35% Conoco Chemicals Chloride POLYM~R typically Div. oP Con-(PVC) 41% tinental Oil Co.
Houston, Texa~
Pla~ticizer Dioctyl DOP 25 to 50% Mobay Chemical Phthalate Pla6ticizer typically Corp.
(D.O.P.) 41% Pittsburg, Pa.
~Di-2-Ethyl-hexyl phtha-late]
Orange Dye with Metallic Sc-39-3 9/~ l/2 to 7-K Color Corp.
cut-ofP at 540 nm Azo Bright Orange 1-l/2% ~ollywood, Ca.
and high light typically 6tability l-l/3%
~, TABLE I CON~'D
MATERIALS OF CONSTRUCTION
AMOUNT
PURPOSE OF USED IN M~UFACTURERS
COMPONENT ~TERIAL GE~7ERAL MANUFACTUP~ERS CURTAI~T -NA~ A~D
IR CURTAI~T NAME PART NUMBER % WT. LOCATIO~
Fluorescent Hetero- c5a7xx 1/4 to 1% Shannon Luminous orange dye with cyclic oil Product ~o. typically M~terials Inc.
cut-o~f at 540 soluble 40-26-2 1/2% Xollywood, Ca.
nm stimulated by mobile 300 nm to 400 nm emits at 420 nm to 600 nm with peak at 550 nm Light scattering Fluore~- Ottalume 0.05 to Ottawa Chemical Fluorescent Pigment cent 2100 M O.5% Div. of Ferro 0.5 to 2 micron Zinc Oxide typically Corporation Dia. stimulated by Phosphor 0.17% Toledo, Ohio.
250 nm to 400 nm emits at 500 nm W Absorber 2-Hydroxy- W -Chek ~ 1/2 to lg Ferro Ottawa 4-N- AM300 typically Corp.
Octoxy- 1~ Toledo, Ohio.
benzo-phenone Fire Retardant Barium Me~a Busan ll-Ml 10 to 20~ Buckman Labora-Index of Refraction Borate typically tories Inc.
1.5 Pigment 15% Memphis, Tenn.
Oran~e Dye wlth cut- MetPllic Fylam Orange~ 1/2 to Pylam Products off at 540 nm, and Azo 727782 1 1/2Z Co~pany, Inc.
hi~h light stability typically Queens Village, (2nd choice) 1-1/3% ~ew York 926-4461 Ingham Fluorescent Orange Alcohol C507 x 1/4 to 1% Shannon Luminous Dye with cut-off at Soluble typically Materials Inc.
540 nm, ~timulated 40-25-3 1/2% Hollywood, Ca.
by 300 nm to 400 n~
and emlt~ at 420 nm to 600 nm with peak at 550 nm (2nd choice) ks ~o~
`, TABLE I CONT~D
MATERIALS OF CONSTP~UCTIOM
~.~OUNT
PURPOSE OF USED IN MANUFACTURERS
COMPONENT ~ERIAL GENERAL MANUFACTURERS CURTAI~ NAME AND
IN CURTAIM ~U~IE PART ~ ~BER f WT. LOCA~IOM
-Light Scattering Titanium RF-3 0.05 to Mew Jersey Zinc Pigmcnt . Dioxide O.5% Company 0.5 to 2 Micron typically Bethlehem, Dia (2nd choice) 0.17% Pennsylvania Plasticizer Dioctyl Plastolein 25-50% Emery Industries (2nd choice) Azelate go58 typically Cincinnati, Ohio (DOZ) DOZ 41%
~Tr~
,
TABLE I
, AMOUNT
PURPOSE OF USED IN MA~UFAcquRERs COM Ol~ MATERIAL GENERA~ t~ANUFACTURERS CURTAIN ~AME AND
IN CURTAIN - ~AME PART NUMBER % W~. LOCATION
Ba6e Polymer Poly Vlnyl PVC 75 to 35% Conoco Chemicals Chloride POLYM~R typically Div. oP Con-(PVC) 41% tinental Oil Co.
Houston, Texa~
Pla~ticizer Dioctyl DOP 25 to 50% Mobay Chemical Phthalate Pla6ticizer typically Corp.
(D.O.P.) 41% Pittsburg, Pa.
~Di-2-Ethyl-hexyl phtha-late]
Orange Dye with Metallic Sc-39-3 9/~ l/2 to 7-K Color Corp.
cut-ofP at 540 nm Azo Bright Orange 1-l/2% ~ollywood, Ca.
and high light typically 6tability l-l/3%
~, TABLE I CON~'D
MATERIALS OF CONSTRUCTION
AMOUNT
PURPOSE OF USED IN M~UFACTURERS
COMPONENT ~TERIAL GE~7ERAL MANUFACTUP~ERS CURTAI~T -NA~ A~D
IR CURTAI~T NAME PART NUMBER % WT. LOCATIO~
Fluorescent Hetero- c5a7xx 1/4 to 1% Shannon Luminous orange dye with cyclic oil Product ~o. typically M~terials Inc.
cut-o~f at 540 soluble 40-26-2 1/2% Xollywood, Ca.
nm stimulated by mobile 300 nm to 400 nm emits at 420 nm to 600 nm with peak at 550 nm Light scattering Fluore~- Ottalume 0.05 to Ottawa Chemical Fluorescent Pigment cent 2100 M O.5% Div. of Ferro 0.5 to 2 micron Zinc Oxide typically Corporation Dia. stimulated by Phosphor 0.17% Toledo, Ohio.
250 nm to 400 nm emits at 500 nm W Absorber 2-Hydroxy- W -Chek ~ 1/2 to lg Ferro Ottawa 4-N- AM300 typically Corp.
Octoxy- 1~ Toledo, Ohio.
benzo-phenone Fire Retardant Barium Me~a Busan ll-Ml 10 to 20~ Buckman Labora-Index of Refraction Borate typically tories Inc.
1.5 Pigment 15% Memphis, Tenn.
Oran~e Dye wlth cut- MetPllic Fylam Orange~ 1/2 to Pylam Products off at 540 nm, and Azo 727782 1 1/2Z Co~pany, Inc.
hi~h light stability typically Queens Village, (2nd choice) 1-1/3% ~ew York 926-4461 Ingham Fluorescent Orange Alcohol C507 x 1/4 to 1% Shannon Luminous Dye with cut-off at Soluble typically Materials Inc.
540 nm, ~timulated 40-25-3 1/2% Hollywood, Ca.
by 300 nm to 400 n~
and emlt~ at 420 nm to 600 nm with peak at 550 nm (2nd choice) ks ~o~
`, TABLE I CONT~D
MATERIALS OF CONSTP~UCTIOM
~.~OUNT
PURPOSE OF USED IN MANUFACTURERS
COMPONENT ~ERIAL GENERAL MANUFACTURERS CURTAI~ NAME AND
IN CURTAIM ~U~IE PART ~ ~BER f WT. LOCA~IOM
-Light Scattering Titanium RF-3 0.05 to Mew Jersey Zinc Pigmcnt . Dioxide O.5% Company 0.5 to 2 Micron typically Bethlehem, Dia (2nd choice) 0.17% Pennsylvania Plasticizer Dioctyl Plastolein 25-50% Emery Industries (2nd choice) Azelate go58 typically Cincinnati, Ohio (DOZ) DOZ 41%
~Tr~
,
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a welding curtain of substantial area forming at least a portion of the perimeter of an area in which an electrical arc welding or an electrical arc cutting operation is conducted for the purpose of protecting the eyes of an observer located outside of said perimeter from damage by light from said arcs, said curtain having a pair of surfaces spaced apart by a dimension of thickness, and being sufficiently clear for said observer to see through it an object of substantial size located inside said perimeter, the improvement comprising: one of said surfaces being substantially entirely covered with declivities each hav-ing a relatively minor surface extent and having faces disposed at angles to the plane of the sheet, whereby some rays of light, which pass through said one sur-face are refracted and undergo a change in direction thereby partially to de-focus an image.
2. A curtain according to claim 1 in which said angles are less than about 8 minutes of arc.
3. A curtain according to claim 1 in which the declivities have non-planar surfaces.
4. A curtain according to claim 3 in which the declivities are formed by reticulation.
5. A curtain according to claim 1 in which the declivities are formed on both surfaces of the curtain, the said angles being less than about four min-utes of arc.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000395903A CA1163844A (en) | 1978-09-27 | 1982-02-09 | Curtain for shrouding welding operations |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US94616378A | 1978-09-27 | 1978-09-27 | |
| US946,163 | 1978-09-27 | ||
| CA000336534A CA1121192A (en) | 1978-09-27 | 1979-09-27 | Curtain for shrouding welding operations |
| CA000395903A CA1163844A (en) | 1978-09-27 | 1982-02-09 | Curtain for shrouding welding operations |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1163844A true CA1163844A (en) | 1984-03-20 |
Family
ID=27166425
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000395903A Expired CA1163844A (en) | 1978-09-27 | 1982-02-09 | Curtain for shrouding welding operations |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1163844A (en) |
-
1982
- 1982-02-09 CA CA000395903A patent/CA1163844A/en not_active Expired
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| MKEX | Expiry |