US3499141A - Self-shielded festoon for electron irradiation apparatus employing overlapping rollers having radiation blocking means - Google Patents

Description

March 3, 1970 s. F. KINGSLEY IH'AL 3,499,141

SELF-SHIELDED FESTOON'FOR'ELEC'IRON IRRADIATION APPARATUS EMPLOYING OVERLAPPING ROLLERS HAVING RADIATION BLOCKING MEANS Filed Nov. 13, 1967 4 Sheets-Sheet 2 FIG. 2

WWW HUN J03 49 INVENTORS 65 GORDON F. KINGSLEY ROBERT D. RAM /5W; 7%

ATTORN EY March 3, 1970 GS F. KINGSLEY 'Er-A 9,

SELF-SHIELDED FESTOON FOR ELECTRON IRRADIATIQN APPARATUS EMPLOYING OVERLAPPING ROLLERS HAVING RADIATION BLOCKING MEANS 4 Sheets-Sheet 3 GORDON F. KINGSLEY ROBERT D.

CRAM BY F ATTORNEY Filed Nov. 13, 19s? III March 3, 1970 s. F. KINGSLEY ETAL 3,499,141

SELF-SHIELDED FESTOON FOR ELECTRON IRRADIATION- APPARATUS EMPLOYING OVERLAPP-IN OLLERS HAVING RADIATION BLOC G MEANS Filed Nov. 13, 1967 4 Sheets-Sheet 4 fi g 8 g a U U U o O r 00'18 oo 8 (\I 5 g 1 8; criux Ii 2 i1! l\ a i5? I u If I l m 1 gx 835 x m 0 co x IO'IL FIG. 8

INVENTORS GORDON F. KINGSLEY ROBERT CRAM ATTORNEY 'IIO United States Patent 3,499,141 SELF-SHIELDED FESTOON FOR ELECTRON IRRADIATION APPARATUS EMPLOYING OVERLAPPING ROLLERS HAVING RADI- ATION BLOCKING MEANS Gordon F. Kingsley, Wellesley, and Robert I). Cram, Ipswich, Mass., assignors to High Voltage Engineering Corporation, Burlington, Mass, a corporation of Massachusetts Filed Nov. 13, 1967, Ser. No. 682,317 Int. Cl. G21f 7/00 U.S. Cl. 250-495 2 Claims ABSTRACT OF THE DISCLOSURE A self shielded flexible material irradiation apparatus using a flexible material apparatus which is positioned outside of the irradiation chamber so that adjustments may be made thereto for varying parameters, such as the material speed or tension without exposing the operator to potentially hazardous radiation.

BACKGROUND OF THE INVENTION Radiation processing has a wide variety of industrial and commercial applications including the curing of plastic material such as polyethylene. Many informative papers on radiation curing are available in the literature. Basically, however, such curing requires the exposure of the material to a beam of high energy electrons. One

method for irradiating flexible plies of polyethylene and the like is to thread the material back and forth through the beam over a series of rolls at each end of the irradiation field.

In the prior art this festooning of the material takes place within the region of hazardous radiation. Thus to make adjustments in the speed, tension, etc. of the material being irradiated or to change the material it is necessary that the machine be shut down thus leading to inefficiency and other losses.

The present invention was conceived against this background and is directed towards a machine permitting adjusting, tensioning, positioning etc. of the material being processed while the machine is in operation.

SUMMARY OF THE INVENTION Broadly speaking these and further advantages and features are realized in a machine provided with radiation proof walls, exteriorly positioned festooning apparatus and radiation traps thus permitting the safe and reliable use of such equipment in hitherto impossible locations.

DESCRIPTION OF THE DRAWINGS FIGURE 1 shows an overall view of one embodiment of the present invention;

FIGURE 2 shows a sectional view of the acceleration portion of the apparatus of FIGURE 1;

FIGURE 3 shows a sectional view of the apparatus of FIGURE 1 taken at right angles to the view of FIG- URE 2;

FIGURE 4A is a graph of electron energy vs. range in steel;

FIGURE 4B is a graph of electron energy vs. range in lead;

FIGURE 5 shows the effect of angle of incident electrons in determining range;

FIGURE 6 shows a quarter section of the festooning apparatus and irradiation chamber of the apparatus of FIGURE 1;

FIGURE 7 shows details of the electron trapping arrangement and material feeder of FIGURE 6;

3,499,141 Patented Mar. 3, 1970 FIGURE 8 shows details of the festooning rollers used in the invention;

FIGURE 9 shows in section details of the festooning rollers used in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to the drawings and, more particularly, to FIGURE 1 there is shown an overall view of one model of the invention which is an integrally shielded electron beam processing machine for the irradiation of flexible sheets or films.

Basically the machine comprises a high voltage D.C. power supply 10 connected by a cable 11 to an integrally shielded electron beam assembly 12 coupled to an integrally shielded festoon assembly 13. A roll of material 129 is shown being fed into the machine. After processing the material is fed on to a take-up roll 121, With control panel 17 the equipment appears in this view as it is used on a factory production floor.

Preferably the power supply 10 is of the insulatingcore transformer type as shown in Dr. Robert J. Van de Graatfs patent, No. 3,187,208 dated June 1, 1965. Basically this supply is a three-phase transformer-rectifier with multiple secondary cores for each phase.

The power produced by supply 10 is delivered to the accelerator assembly 12 by a flexible coaxial cable 11 whose length is adjustable so that the supply may be placed at any desired position with relation to the remainder of the equipment. The console 17 may also be situated in any convenient place and will be connected to the other necessary assemblies by cabling (not shown).

Turning now to FIGURES 2 and 3., the electron beam assembly 12 will be discussed in greater detail. The assembly 12 comprises an accelerator subassembly 14, a shielded scanner chamber 15 and a chambered base 16.

The accelerator subassembly 14 comprises a cylindrical tank 20 within which there is contained a bushing 22 which passes through the distal end 23 of tank 20 and electrically couples cable 11 to an accelerator terminal shell 2% containing a transformer and a cathode (not shown). The cathode provides a supply of electrons which are electrostatically focused into a stream by suitable means (not shown), and accelerated by the multiple electrode accelerator column 25 located directly below the shell 24. The accelerated electrons pass in the form of a beam 21 out opening 26, provided in the proximal end 27, of tank 20, into the shielded evacuated scanner chamber 15. Directly after entering chamber 15 the beam 21 passes into an electromagnetic scanner 28 which continuously sweeps the beam 21 from side to side to form a wide, elongated, fan-line pattern 29. The widened beam of accelerated electrons passes out of chamber 15 via a thin metal foil window 30 located below the chamber 15 and within the base 16.

Such highly accelerated electrons are potentially hazardous to human life not only in themselves but especially because of the harmful X-rays produced when such electrons strike solid matter. The present invention contains these harmful radiations by providing the entire assembly with integral shielding which cannot be removed without causing shut-down of the electron source and hence of all radiation.

The present invention will first be described in reference to the embodiment shown in FIGURES 1 to 3. For purposes of illustration only, it will be assumed that a twenty milliampere electron beam will be accelerated to a maximum of 500 kilovolts and scanned 30 on either side of the beam centerline.

Since electrons become more hazardous after they are accelerated, the shielding disposed about the terminal shell need not have the large impedance required of the shielding made integral with the scanning chamher. However, the shell must be sufiiciently strong to accommodate a high pressure insulating gas. To meet both these requirements the tank is made in the shape of a double-Walled steel cylinder, formed of A1, inch steel sheets 31, separated by a 1 inch thick filling of lead 32, and having upper and lower ends 23 and 27 respectively formed from 2 inch thick steel plate. End 23 is in the form of a flat annular ring welded to the inner Wall of the cylinder 20 and has the terminal bushing 22 passing therethrough. The lower tank end 27 is a large circular disc which is welded to both walls of the tank 20. This disc is provided with orifice 26 aligned with the beam 21 and sealed off by column 25. Thus there is formed around the evacuated column a strong pressurizable tank which in operation is filled with 100 p.s.i. insulating gas. When electrons are generated at the cathode, they are accelerated by the field in column 25 and pass through orifice 26 as an electron beam 21 into scanner 28.

After the accelerated electrons pass through scanner 28 into chamber 15, they strike the window 30 and most pass therethrough into the material 120 being irradiated. Some electrons however upon striking the window, the material being processed, or the underlying bed 65 of base 16 become deflected or produce X-rays which emanate, from the struck material, at various angles. These potentially harmful radiations must not be permitted to pass out of the apparatus unless attenuated or reduced to a safe level. To this end. he walls of chamber 15 and base 16 are made to attenuate the electrons and harmful X-radiations and reduce them to safe levels, that is below 2.5 millirads per hour.

In order to properly design the walls of chamber 15 it is necessary to call to mind that the penetrating ability, or range, of such electrons in most materials is short but the range of X-radiation generally increases with its en ergy and decreases with the density of the material being struck. This relationship is shown graphically in FIG URES 4A and 4B. By expressing the range in terms of half value layers, the energy in terms of the generating electron, and using the general absorption equation any worker, skilled in the art, can determine the wall thickness necessary to attenuate the generated X-rays below 2.5 millirads/ hour. It should be understood, however, that since the X-ray energy and density generally increases with electron beam energy and current, the thicknesses given in the specific embodiments described herein are illustrative only for a 500 kev. 20 milliampere beam and that for most energetic beams thicker walls would be required. Conversely, with less energetic beams a thinner wall could be utilized.

As is well known, the penetration depth taken normal to the surface is dependent on the incident angle of the radiation with respect to the surface being struck. In other words the point at which the radiation is attenuated to a safe level is determined by the angle at which it strikes the surface. This may be better understood from FIGURE 5. In this figure the path of an incident ray of radiation striking a surface 33 is shown by the dotted line 34. X is the distance from the surface at which the ray is attenuated to a safe level when R is the range of the radiation when it has an initial energy E and 6 is the angle of the incident beam with respect to the surface 33. Thus under these circumstances X R Sin 0 With this information one may readily calculate the necessary impedance in terms of the thickness required for the chamber Walls.

For ease of fabrication slabs of mild steel was selected for the walls of chamber 15. These slabs were welded together such that a vacuum could be maintained in the chamber. The general shape of channel 15 resembles the center zone of a truncated pyramid as shown in FIGURES 2 and 3. The configuration shown in these views was chosen to provide sufficient width for a beam and for the scanner 28 while matching the upper surface of the chamber to the tank 20 for vacuum purposes. Thus the inner surface of the sidewalls 40 and 41 of chamber 15 were inclined at an angle of 66 to the horizontal. Since radiation intensity is inversely proportional to the square of the distance from the source and since with increasing 0 the distance X becomes smaller, the chamber walls 40 and 41 can be made thinner as they recede from the window 30. Thinning these walls at their upper points realizes a considerable savings in both weight and cost of material.

To obtain proper matching between the chamber and tank and yet retain a suflicient thickness for protection against radiation leakage, the outer surface of the walls 40 and 41 were tapered at an angle of 50 to the horizontal. In the actual machine, built in accordance with the invention, the walls 40 and 41 were each 7 inches thick at their top and 13 inches thick at their widest point 43. In order to properly align the chamber in the base 16, and yet retain sufiicient shielding, the outer surface of the chamber walls 40 and 41 were cut on a vertical line from point 43 to the bottom and an eight inch high square ring 4 of 3 inch thick steel was welded around the chamber. As shown in FIGURE 6, this ring 44 is provided with a plurality of L shaped ports 18 which enter the interior of chamber 15 at right angles to the beam but emerges through the lower edge of ring 44 in the direction of the beam so that it can engage an aligned tapered pin 19 secured to the upper surface 60 of base 16. To assure good vacuum sealing of port 18 when assembly 15 is situated on base 16 the pin 19 is provided with a deformable gasket 42. The ring further shields the clearance space 45 provided between the chamber 15 and the base shield 16.

Ports 18 and pins 19 also serve to make the unit safe. Removal of the shielded chamber 15 from base 16 immediately causes pin 19 to withdraw from port 18 which permits air to flow into chamber 15 and thence to subassembly 14. Destruction of the vacuum and the presence of an atmosphere containing oxygen around the cathode cause it to be immediately consumed thus stopping the beam before the scanning chamber can be raised to a height sufiicient to expose anyone to the radiation. Thus the device is fail safe in the event repairs are attempted while the beam is still on.

Since the angle of the incidence of any radiation directed towards the front and back walls 47 and 48 will be very slow in any region higher than ring 44, these walls need not exceed 4 inches in thickness.

Ring 44 transmits the weight of the unit to the base shield 16. The window assembly 49 is secured to walls 47 and 48 by bolts 51. Cooling air is supplied to the window assembly 49 through a coupling 50. Located between the bottom of chamber 15 and the window assembly 49 is gasket 46 of suitable deformable material such as Indium, which makes this joint vacuum tight.

The upper portion 61 of the base 16 also has a sub stantially square ring configuration. In detail, for the described apparatus, this portion 61 has a height of 16 inches and a wall thickness of 12 inches.

Adequate protection is afforded around the air supply coupling 50 which passes through an opening in the base shield by providing around the coupling and the air duct 53 a bearing plate 52 made of 4 inch thick lead. The air duct 53 (shown in phantom) passes in a single labyrinth fashion through this bearing plate 52 and to parallel the side of the window 30.

As is well known in the art, it is necessary that a vacuum be maintained in the device between the cathode and the window. To this end suitable vacuum tight seals have been provided at the various assembly joints and means provided in the back wall 48 of chamber for evacuating this region. These means consist of a port 35 provided in the rear wall, a vacuum flange 36 around the port, an ion pump 37 and a vacuum valve 38 for coupling on a roughing pump (not shown). To prevent any possible stray radiation from passing out of the port 35, a baffle plate 39 of 1" lead is provided in front of ion pump 37.

The forward wall 47 is also provided with a port 57 through which the scanner 28 can pass. This port 57 is sealed with a plug 58 of the same thickness as the wall 47. A plurality of electrical feed through connectors 54 and screw means 55 for adjusting the scanner pass through this plug.

FIGURES 6 through 9 illustrate additional details of the machine and in particular portray the details of the festooning apparatus.

The chambered base 16, as previously noted, comprises an upper portion 61 and a lower portion 65, both of which are made sufiiciently thick enough to annenuate impinging radiation to an acceptable level. Provision is made, in the base 16, for the passage of multiple plies of the material 120 through the base by having in each end of the base, in line with each festoon assembly 13, large openings 63. To prevent-the escape of radiation through these openings 63, a plurality of magnets 80 through 85 are fitted therein, the thickness of which is made sutficient to attenuate impinging X-rays. Slits 8011 through 84a are left between these magnets which permit the introduction of the material 120 into the base. These slits should have the smallest possible width to reduce, to the lowest possible level, the probability that X-rays could pass therethrough without suffering attenuation due to reflection. Electrons are impeded in their passage through these slits by virtue of the magnetic field which exists between the magnets and extends across the slits.

Although it is improbable that X-rays or electrons will pass through these slits without suffering attenuation to a suitable level a further precaution is provided by the rollers 68 to 72 and 68a to 72a and blocks 98 to 98:: which are positioned in the festooning assembly 13 so as to overlap the slits and thus block any escaping radiations.

To assure attenuation of the radiations and yet permit free and easy conveyance of the material 120 through the base the rollers are arranged as shown in FIGURE 8. These rollers consist of separately rotatable portions, an inner core, consisting of an axle 101 covered with a lead sheathing 100, and an outer stainless steel shin 102.

The axle (and sheathing) is rotatable supported in a journal block 104 by bearing 103. Independently carried by the same journal block 104 is the stainless steel skin 102. Because the journal block 104, afi'ixed to a drive shaft 105 through bearing 108 supported by bearing retainer 107 and channel 106, is directly coupled to the gear train 78 and because the core (axle 101 and sheathing 100) is rotatable in the journal block, each segment of the roller may rotate at different speeds without aflFecting the transmission of the material 120.

Aflixed to each gear 109 of gear train 78 is a small clutch 110 which will maintain each roller at a desired speed, independently of the speed of the other rollers.

If desired the rolls of festoon assembly can be laminated and consist of an outer steel shell 11 and an inner lead shield 99. Also a gear train cap 113 can be provided.

The material 120 is fed into the machine as shown in FIGURE 6 beginning at roller 68a crossing to roller 68 and thence back to roller 69a. This passing back and forth of the material 120 continues until it finally passes roller 72 after which it passes over an idler roller 72 and out of the festooning assembly cover 77.

Because of the complete protection aflorded by the machine, of the invention, the material 120 may be fed into the machine while it is in operation, that is while the beam 21 is passing through the window 30.

Feeding of the material into the machine is facilitated by affixing a relatively stiif leader of paper, cardboard, nylon, or the like to the end of the material 120. This leader will be guided through the base and by the rollers by guide channels and lips such as through 97, shown in FIGURE 7.

The leader material shown should, of course, be thin enough to easily pass through the slits 80a to 84a but can be considerably thicker than the material and long enough to extend past rollers 68 and 68a. Because the pillow blocks 107 are spring loaded in channel 106 by a spring loading mechanism which consists of a spring 115, and a plug 116 retained in extension 114 by cap 117.

Additional features of the present invention include a labyrinth passageway 62 in base 16 for the removal of spent cooling gas. By means of a coupling 63 this exhaust passageway may be connected to an exhause system (not shown) for discharging these gases at a remote location.

Having now shown and discussed each unique feature of the present invention it is desired that the invention not be limited by the specific details disclosed herein only by the appended claims.

What is claimed is:

1. An apparatus for electron irradiation of goods comprising an enclosed, evacuated chamber having afiixed thereto means for producing a beam of electrons with energies in the KeV range or greater, along an axis of said chamber, scanner means, in said chamber, for expanding said beam to form an elongated fan-line configuration, a beam transparent window means comprising an elongated narrow pane element positioned in a wall of said chamber transverse to said beam to permit transmittal of said beam out of said chamber, into a chambered base and transport means, positioned adjacent said chambered base, to convey goods, to be irradiated, through said base and transversely through said beam after said beam passes through said window, each of said means and said base having integral shielding therewith of sufficient density and thickness to attenuate X-rays created in said means to a level below 2.5 millirads per hour, said transport means comprising a real for rotatably supporting a roll of flexible sheet material, a festooning apparatus, for passing flexible sheet material under said beam, positioned outside of said base, means for introducing said sheet material into the festooning apparatus, and means for taking up said material after its passage through the beam, said festooning apparatus comprising a plurality of rollers positioned on each side of said base for supporting a plurality of layers of said flexible material through the path of said beam, the axis of each roller being parallel to the long dimension of said expanded beam, roller means and gears coupled to each roller and to one another to synchronize each of said rollers with its adjacent rollers, guide means, for directing and maintaining said material along predetermined paths through said base, magnetic electron trapping means located in said base parallel to the long dimension of said expanded beam and between said beam and said rollers to create a magnetic field transverse to said material to trap electrons traveling parallel to said material, and means for attenuating X-rays generated in said base by said beam to a level below 2.5 millirads per hour, said attenuating means comprising said rollers, overlapping one another, and a pair of blocking members, arranged to overlap the rollers adjacent said blocking members to block the line of sight through said base.

2. The apparatus of claim 1 wherein said rollers each comprise an axle bearing a lead rotatably mounted at each end within a closed stainless steel cylinder, said cylinder being supported at each end by journals fitted within channels, spring loading means on said journals 7 8 Within said channel to permit one degree of freedom Of 3,144,552 8/ 1964 Schonberg at al. 250-495 movement of said pournals, roller means and gears. 3,433,947 3/1969 Emanuelson et a1. 25049.5

References Cited RALPH G. NILSON, Primary Examiner UNITED STATES PATENTS 5 C. E. CHURCH, Assistant Examiner 2,722,620 11/1955 Gale 25049.5 2,858,442 10/1958 Dewey 2s0 49.5

2,993,120 7/1961 Emanuelson 25049.5 250-108

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