US3916204A

US3916204A - Irradiating elongated material

Info

Publication number: US3916204A
Application number: US466756A
Authority: US
Inventors: Raymond Kenneth Swartz
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1974-05-03
Filing date: 1974-05-03
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28
Also published as: CA1031081A

Abstract

A plurality of conductors covered with crosslinkable insulation are advanced past an accelerator window with the stringup of each being accomplished to present a number of passes of each conductor to the accelerator beam and to cause uniform dosing of the insulation. A shutter associated with each conductor and spanning all the passes thereof is mounted for movement between the associated conductor and the accelerator to shield the conductor from the beam. When the supply of one of the conductors is about to be exhausted and requires a splice to a new supply, the line speed of that conductor is decelerated while the associated shutter is interposed between that conductor and the beam in synchronization with the line speed relative to dosimetry data to provide a constant dose exposure per pass during the splicing. The movement of the shutter is similarly coordinated with the acceleration of the conductor to line speed following the splicing operation.

Description

United States Patent [191 Swartz 1 IRRADIATING ELONGATED MATERIAL [75] Inventor: Raymond Kenneth Swartz, West Seneca, NY.

[73} Assignee: Western Electric Company, Inc.,

New York, NY.

[22] Filed: May 3, 1974 21 Appl. No.2 466,756

[52] US. Cl. 250/453; 250/492; 250/514 [51] Int. Cl. H01J 37/00 [58] Field of Search 250/514, 492, 493, 400, 250/453; 204/158 HE [56] References Cited UNITED STATES PATENTS 2,925,496 2/1960 Zoubek 250/453 3,144,552 8/1964 Schonberg.... 250/492 3,360,648 12/1967 Cornish 250/453 FOREIGN PATENTS OR APPLICATIONS 817,033 7/1959 United Kingdom 250/400 Primary Examiner+Craig E, Church Attorney, Agent, or FirmE. W. Somers Oct. 28, 1975 57 ABSTRACT A plurality of conductors covered with crosslinkable insulation are advanced past an accelerator window with the stringup of each being accomplished to present a number of passes of each conductor to the accelerator beam and to cause uniform dosing of the insulation. A shutter associated with each conductor and spanning all the passes thereof is mounted for movement between the associated conductor and the accelerator to shield the conductor from the beam. When the supply of one of the conductors is about to be exhausted and requires a splice to a new supply, the line speed of that conductor is decelerated while the associated shutter is interposed between that conductor and the beam in synchronization with the line speed relative to dosimetry data to provide a constant dose exposure per pass during vthe splicing. The movement of the shutter is similarly coordinated with the acceleration of the conductor to line speed following the splicing operation.

17 Claims, 11 Drawing Figures PRODUCT HANDLING DRIVE SYSTEM SHUTTER CONTROL LOGIC US. Patent Oct. 28, 1975 Sheet 1 of5 SHUTTER CONTROL LOGIC ODUCT HANDLING DRlVE SYSTEM U.S. Patent Oct. 28, 1975 Sheet2 ofS 3,916,204

US. Patent 0a. 28, 1975 Sheet 3 of5 3,916,204,

13a KOPUDOZNUU WETEIOZ Q mom zu 1Q mm mIw U.S. Patent Oct. 28, 1975 Sheet4 0f 5 3,916,204

PERPENDICULAR DISTANCE FROM THE WINDOW 2, MAX. MEGARAD READING CENTERLINE OF WINDOW X AXIS OF WINDOW /Y AXIS OF WINDOW BEAM WIDTH CENTERLINE OF WINDOW BEAM WIDTH US. Patent Oct. 28, 1975 Sheet5 of5 3,916,204

i i X AXIS PF WINDOW MAX. DOSE READING INCHES FROM VERTICAL WINDOW CENTER FIG. 9

MAX. MEGARD READING DEPTH MILS OFINSULATION 3,330,748 and 3,676,249.

IRRADIATING ELONGATED MATERIAL BACKGROUND OF THE INVENTION l. Field ofthe Invention This invention relates to irradiating elongated material, and more particularly, to methods of and apparatus for uniformly irradiation cross-linking the insulation of a plurality of conductors while providing for controllably' shielding selected ones of the conductors in a manufacturing environment to maintain a constant dose exposure per pass of each of the conductors independent of changes in line speed. v

2. Technical Considerations and Description of the Prior Art i In the telephone communications industry, the changing of a telephone number requires that a craftsman rearrange a connection of a conductor in a central office. These conductors must possess adequate tensile strength as well as being capable of withstanding abrasion during pulling thereof in the central office troughs as well as being fire resistant and capable of withstanding solder heat during the reconnection process. A priorly used three-layer structure, including polyvinyl chloride insulation, a textile layer and a fire retardant lacquer, has been replaced by a single layer of irradiation cross-linked insulating material as is shown in U.S. Pat. 3,623,940, issued on Nov. 30, 1971, in the names of Harold M. Gladstone and Leonard D. Loan. Also, see Sept., 1972, issue of the Bell Telephone Laboratories Record starting at page 239.

An improved irradiation cross-linked insulating composition is disclosed in commonly assigned application Ser. No. 292,469 filed Sept. 26, 1972, in the names of .l. R. Austin, L. D. Loan, N. W. Murray, Jr., W. A. Salmon and T. J. Szymczak now abandoned.

Technical problems have been encountered in the irradiation of the single layer insulation. The total radiation energy absorbed by a conductor is determined by the control of the accelerators operating parameters, the speed at which the conductor is passed through the beam exposure area, as well as the distance from the window to the conductor and the composition and thickness of the insulation.

Various prior art schemes have been patented as well as described in the literature and include, for example, the use of a figure-eight pattern with a single accelerator or the use of a single accelerator with a plurality of conductors being advanced along the longitudinal length of the accelerator window. The prior art also includes stacked accelerators with overlapping beams as well as multi-accelerators or a single accelerator positioned to irradiate different portions of the samearticle.

Other techniques involve the use of two accelerators arranged in alignment to oppose one another to irradiate, for example, a coated sheet (see U.S. Pat. No. 3,50l,390). This may suffice where the coated sheet approximates the size of the window. However, in the irradiation of conductors or other strand material, this arrangement of accelerators would tend to over-heat the opposing windows which are made of a very thin a material. The prior art includes other arrangements for irradiating conductors; For example, see U.S. Pat. Nos.

Those and other schemes aredescribed in commonly assigned application Ser. No. 304,458, filed Nov. 7,

1972, in the names of J. R. Austin, M. J. Brown andL.

many of the problems confronted by prior art devices and is specially suitable for irradiation cross-linking conductor insulation.

In a wire and cable manufacturing facility, it becomes economical to continue the irradiation process on a full-time basis. This necessitates the periodic splicing of the trailing end of a reel of a conductor, for example, the insulation of which has just been irradiation crosslinked, to the leading end of another supply reel. The problem here is that when the splicing occurs, the conductor insulation is exposed for an inordinately long period to the electron beam radiation. This causes an overdose and produces detrimental effects on the insulation.

Of course, the operation of the accelerator could be discontinued during splicing. Or, in the alternative, the advance of all of the conductors could-be discontinued during the splicing of any one or more of the conductors. Either of these alternatives detracts from manufacturing efficiencies.

Another solution would be to design a splicing process which isso rapid that the shutdown time is reduced, thereby minimizing the over-exposure of the conductor insulation which is directly in front of the window at the time of the splice Difficulties have been encountered in designing such a mechanical splicing process to avoid over-exposure.

It has been determined that the mostsuccessful approach would be to provide shielding facilities between the conductors and the radiation window during the splicing process. The shielding must be integrated with other parameters in order to result in a constant dose rate per pass of each of the conductors.

Several prior art patents show shielding facilities. In

SUMMARY OF THE INVENTION With these and other objects in mind, the present invention contemplates irradiating the covering of elongated materials by directing an electron radiation beam toward and into engagement with the elongated material strung up in a multi-pass path, advancing the elongated material along the path at a line speed to expose the elongated material to the beam while causing perturbation of the angle of incidence of the beam on the elongated material to dose uniformly the covering and regulating the exposure of the elongated material to the beam relative to changes in the line speed to provide a constant dose rate per pass independent of line speed changes.

In irradiation cross-linking the insulation of conductors, each of a plurality of conductors is advanced at a line speed back and forth in a figure-eight pattern past an accelerator window spanning the crossover points of the patterns to expose the conductors to the accelerator beam and to dose uniformly the insulation. Facilities are provided for shielding at least one selected conductor during a splicing processQBy reducing the line speed and simultaneously shielding the selected conductor substantially from the radiation beam of the continuously operated accelerator, the splice is made with assurance of protection from over-exposure. After a time interval, during which the splice is completed, the shielding is removed and the advance of the conductor brought up to line speed. The shielding and the re-exposure is accomplished in synchronization with the deceleration and acceleration to provide a constant dose rate per pass independent of line speed changes.

An apparatus embodying the principles of this invention for irradiating insulated conductors, in which a plurality of conductors are advanced past an accelerator window, includes a plurality of movable shutters, each of the shutters being associated with one of the conductors, and facilities for moving each of the shutters into a position between the accelerator window and the associated conductor and for moving the shutter from the position to expose the conductors to the accelerator window and radiation beam. Facilities are also provided for preventing radiation dosage from the unshielded portion of the accelerator window contacting that conductor which is shielded from the accelerator window by its associated shutter. Further, facilities are provided for coordinating the opening and closing of the shutters to provide for a constant dose rate per pass independent of line speed changes.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and features of the present invention will be more readily understood from the following description of specific embodiments thereof when read in conjunction with the accompanying drawings, in which:

FIG. 1 is an overall view in perspective of an apparatus embodying the principles of this invention for irradiation cross-linking the insulation of a plurality of insulated conductors while providing for a regulated shielding of the conductors during a splicing operation;

FIG. 2 is a plan view of the apparatus and showing the relative positions of the conductor string-up, the accelerator and the shielding facilities during the splicing of the conductors to prevent over-exposure of the conductors to the radiation beam;

FIG. 3 is an enlarged view in end elevation showing the apparatus of FIG. 2 with the shielding facilities located adjacent the accelerator window;

FIG. 4 is a plan view of a preferred embodiment of the shielding facilities;

FIG. 5 is an enlarged view in end elevation of the apparatus in FIG. 4;

FIG. 6 is an enlarged view in perspective showing two spaced banks of sheaves and illustrating the string-up of a twisted conductor pair in a modified figure-eight pattern;

FIG. 7 is an enlarged view in perspective showing portions of the two banks of sheaves and illustrating in simplified form the string-up of several loops of a strand material in a figure-eight pattern modified to facilitate the periodic reversing of the direction of travel of the strand material;

FIG. 8 is a graph which shows the width of the electron beam of the accelerator illustrated in FIG. 1 and plotted against the perpendicular distance from the ac: celerator window;

FIG. 9 is a graph showing surface dose as percent maximum dose reading plotted as ordinates against the distance along the elongated dimension of the window;

FIG. 10 is a normalized curve showing the beam width taken at a predetermined distance from? the accelerator window plotted against the percent maximum surface dose readingjand FIG. 11 is a depth-dose curve in which the ordinates represent the percent maximum rnegarad reading plotted against depth of penetration of the insulation of the conductor being passed a specific distance from the accelerator window.

DETAILED DESCRIPTION OF THE INVENTION Overall Description i I Referring now to FIG. 1, there is shown an apparatus designated generally by the numeral 20, which embodies the principles of this invention, for irradiating the insulation covering of ones of a plurality'of conductors 22-22. The apparatus 20 generally includes facilities for moving ones of the conductors 22-22 in a path adjacent radiation facilities which impinges a high energy electron beam on the conductors and facilities for insuring generally substantial uniformity of radiation dosage of the insultation notwithstanding changes in line speed for purposes of, for example, splicing.

Each of a plurality of the conductors 22-22 is strung up in a superimposed modified figure-eight path between sheave banks, designated generally by, the

numerals

23 and 24, and as disclosed in copendingcommonlyassigned application Ser. No. 304,458, filed in the names of J. R. Austin, M. J. Brown and L. D.. Loan on Nov. 7, 1972.now abandoned. An accelerator, designated generally by the numeral 25, which is positioned between the sheave banks 23 "and 24, is used to irradiation-crosslink the insulation of the strand material. The accelerator 25 is positioned to direct the radiation beam thereof at the crossover points of the figureeight string-up pattern (see also FIGS. 2 and'4).

Each one'of the conductors 22-22 is advanced from the left as viewed in FIG. 1 from a supply (not shown) into engagement with the sheave bank 23, then around the sheave bank 24 in the pl urali ty of groups of superimposed figure-eight paths. As the conductor 22 is moved from one group of figure-eight paths to another, the direction of travel in the figure-eight path is reversed. The use of the figure-eight path, and more specifically the modified figure-eight path, engenders a progressive screwing effect to cause the sections of the conductor 22 to turn about the longitudinal axes thereof to obtain a uniform dosing of'the insulation. In the preferred embodiment as disclosed: in the aboveidentified cope'nding application, twisted pairs of the conductors 22-22 are radiation cross-linked. The progressive screwing effect is even more pronounced when using the twisted pairs.

Shielding facilities, designated generally by the numeral 50, are provided to prevent exposure of selected ones of the conductors 22-22 to the radiation beam during a splicing operation. The shielding facilities-50 include a shutter associated with each of the conductors 22-22, the shutter being adjacent theaccelerator or preferably adjacent the associated conductor. Provisions are made for programming the opening andlclosing of the shutter based on the string-up and accelerator geometry and the accompanying dosimetrycharacteristicsbased thereon. I

DESCRIPTION OF RADIATION EQUIPMENT Referring now to FIG. 1, there is shown the electron accelerator 25 suspended from rollers 2626 in such a way to facilitate positioning of the accelerator appropriately with respect to the conductor 22 for required irradiation dosage. The accelerator includes a scan magnet 28 interposed between an accelerator head 29 and a scan horn 31. A forward end of the scan horn 31 is covered with a metallic screen 32, commonly referred to as the window. The window 32 is capable of maintaining a vacuum within the acceleratorand yet is thin enough, e.g., 1 mil to permit electrons to pass therethrough without a great loss of energy. The window 32 is oriented so that the longitudinal dimension thereof, which is referred to herein as the window length, is substantially vertical. Of course, the orientation of the window in and of itself is not critical. What is important is the position of the window 32 relative to the path of the conductor 22.

The accelerator 25 is a 400 KEV rated, electron beam accelerator having a maximum beam current of 50 milliamperes. A frequency of 100 or 200 cycles per second is used to scan the beam over the window length which is approximately 48 inches. The electron beam is generated in a vacuum, scanned and then passed through the window 32 to impinge on the conductor 22, the insulation of which is irradiated in an air medium. Such an accelerator is available commercially from the Radiation Dynamics Company under the designation Dynamitron accelerator. The accelerator 25 generates a narrow beam of electrons which are scanned electromagnetically over the surface of the window. 32 to distribute the energy and limit the window and conductor heating.

RADIATION BEAM AND DOSAGE CONSIDERATIONS The apparatus 20 is designed to dose uniformly the insulation of the conductor 22 while optimizing use of the accelerator beam. Uniformity of closing is interpreted to mean a dose between predetermined minimum and maximum values. These values are chosen so that the insulation closed within that range will meet physical test requirements. In order to appreciate the shielding system 50 which cooperates with the other portions of the apparatus 20, it is necessary to consider the dosimetry characteristics of the system.

Of course, the cross-linking of the insulation, which includes a monomer and polyvinyl chloride, is a function of the insulation wall thickness and of the composition of the insulation. In some applications of methods and apparatus of this invention, the wall thickness of the strand material to be irradiation cross-linked is approximately seven to eight mils. However, in some ap plications, wall thickness may increase substantially, requiring greater dosage from the irradiation beam.

The accelerator rating and the spacing of the source of radiation from the conductor 22 are also important factors determinative of the total amount of energy absorbed in the exposure time. The exposure time is a function of the line speed.

Conductor speed is a major factor in determining the ultimate capacity of the process, and it must not be assumed that the greater the conductor speed, the better the process. The number of conductor breaks may be decreased by using a lowerline speed. A reduction in line speed also results in fewer conductor passes for the same beam current. thereby permitting a greater number of conductors to be run past the window 32. However, this increases the number of conductor handling systems, but a conductor break would result in a smaller percentage of the total capacity being lost and would not necessarily require shutting down the entire process.

The conductor handling and interfacing equipment also could be simplified for slower speeds. This more than offsets the cost of the extra payoffs and takeups. Also the simplification of the conductor handling equipment allows a reduction in the required floor space. 4 7

Effective beam utilization requires matching the beam to the geometry of the product and to the product during handling. There must be sufficient beam energy to not only penetrate the insulation of an insulated conductor 22 or a plurality of conductors in the form of a twisted pair or quad, but also to insure a minimum variation of dose with respect to depth throughout the passage of the product past the accelerator.

Reference is made to FIGS. 81] which display the v results of dosimetry studies, As can be seen in FIGS. 8 and 9, the electron beam diverges along both the X and Y coordinate axes, the X axis being that which is along the window length. However, the scattering of the beam in the Y direction is negligible near the window 32, but becomes more significant as the distance from the window increases.

Although the concentration 'of energy is much greater at distances closer to the window 32, the beam width adjacent the window is less than at some distance from the window (see FIG. 8). Beam width connotes beam width taken in a direction of the window width along the narrow direction. The total energy absorbed per conductor pass decreases for distances greater than approximately ten inches from the window 32. Presumably this is due to the energy loss'of the electrons in air becoming significant with respect to the total energy of the incident electrons at these distances.

A surface dose curve. (se'e FIG. 10) may be constructed at a particular distance from a window surface with the abscissa representing the beam width, and the ordinate, a surface dose reading with respect to the maximum dose received the conductor 22 at the window centerline, expressed in percent maximum dose. The point of maximum beam intensity occurs at the vertical and horizontal center of the window and for a narrow high intensity beam occurs adjacent the window 32. As the distance from the window 32 increases, with accompanying increase in beam width, the surface dose curve becomes flatter and the total beam intensity decreases (see FIG. 10).

Another factor which could affect the determination of the surface dose per conductor pass is a scattering of the beam in a vertical direction along the length of window 32. This could cause a change in dosage depending upon the position of the conductor pass with respect to its position along the length of the window 32. Since the scanning of the beam is accomplished in the vertical direction, no significant variation in dosage will be noticed unless a conductor pass is outside of the scanning length which is the area of constant dosage in the vertical direction. In the designated equipment, there are approximately 48 inches of uniform beam intensity along any one vertical plane normal to the window at the prescribed distance of the conductor 22 from the window 32 (see FIG. 9).

A depth-dose curve (see FIG. 11) may be constructed at a particular distance from a window surface. On this curve the abscissa represents the depth of penetration of the insulation in mils. The ordinate represents a relative close reading with respect to the maximum dose received from the conductor 22 at some specific depth and expressed in terms of percent maximum dose. The profile of the depth-dose curve shown in FIG. 11 varies with the design of the accelerator 25 and depends on such factors as window thickness, window material, the nature of the high voltage supply and the product being irradiated.

The point (or depth) of the highest energy absorption within the insulation can be linearly approximated for different distances from the window surface of the accelerator 25 for a constant high voltage. The depth of this maximum point of energy absorption decreases with increasing distances from the window 32. This is an indication that as the electrons travel through the air, the velocity thereof decreases, causing the incident energy to be lower. Also, because of this, as the distance from the accelerator window 32 increases to a determinate value, the surface dosage increases with respect to the maximum dose reading within the insulation.

There is a relationship between surface dosage and the perpendicular distance from the vertical and horizontal center of the window 32 for constant beam current and exposure time. For constant beam current and exposure time, there is a significant change in the energy absorbed within an insulation having a thickness of, for example, 8 mils. Depending upon the insulation wall thickness, the density of the insulation, accelerator operating parameters and the speed at which the productis passed through the beam, a distance may be found between the product and the window 32 which will optimize the energy absorbed. The constancy of max to min dose ratio throughout the thickness of the insulation is an indicator of the uniformity of the irradiation process.

In order to determine the energy absorbed within a given thickness of insulation on the moving conductor 22, the actual exposure time of a point on the insulation must be calculated. Knowing the exposure time and the average surface dose per unit time per particular conductor speed and distance from the accelerator window 32, the actual surface dose per pass can be determined.

If equal surface or entrance dose readings are taken for different distances from the window 32, curves can be interpreted to determine total energy absorbed by the material. Knowing the surface dose and the energy absorbed at one specific distance from the window 32, surface dosage required to equal the total energy absorbed at different distances from the window may be determined. It must be realized that average distances are being used and that the distance through which the electrons travel to reach the conductor 22 vary over the width of the beam. By computing the surface dosage of the total energy absorbed, an optimum distance of the conductor 22 from the accelerator window 32 can be determined.

The total energy absorbed by the insulation is proportional to that area under the depth-dose curve (see FIG. 11). This becomes extremely critical for thin insulation walled conductors. In those instances, not only must sufficient radiation energy be absorbed to irradiation-crosslink the insulation, but the radiation must be uniform.

ARRANGEMENT OF RADIATION SOURCE AND CONDUCTORS Another consideration in attempting to maximize the production capabilities in the radiation facility is the path of travel of the conductor past the accelerator window 32. Many prior art devices cause the conductor 22 to be run longitudinally of the window length. The main advantage in running the passes along the length of the window 32 is that the beam exposure time per pass is increased, thereby allowing the number of conductor passes per string-up to be reduced. Notwithstanding this, it has been determined that the conductor pass should be run across the window 32, transversely of the longitudinal axis of the window.

The amount of energy to' which the conductor 22 is subjected is constant over approximately the entire scan length. Therefore, each individual conductor 22 being irradiated can have the same number of passes in front of the accelerator window 32. The energy distribution transversely across the width of the window 32 varies (see FIG. 8). Therefore, for vertical passes, each of the conductors 2222 being irradiated would have a different number of passes in front of the accelerator depending on its location with respect to the longitudinal axes of the window 32. Changes in electron filament or scanning could shift the point of maximum radiation intensity along the width of the window 32 at the point of the conductor 22 which in a preferred embodiment is spaced approximately 12 inches from the window. This would require changes to be made in the number of passes required per individual conductor if vertical passes along the width of the window 32 were used. Such change does not affect the string-up using passes transversely across the width of the window since there the passes are run perpendicular to the direction of scan.

Other advantages to a transverse path are outlined in the above-identified copending application, Ser. No. 304,458.

Positioning of the irradiation source relative to the conductor 22 is also important. As is shown in FIG. 1, a single irradiation source is used in cooperation with the unique string-up of the strand materials in the apparatus 20. Dual accelerators may be used to uniformly dose the insulation as disclosed in the copending application. The figure-eight pattern of the process described in the above-identified copending application is used with a single radiation source placed adjacent the cross-over points (see FIGS. 2 and 4).

If the properties of the resultant insulated conductor 22 are dose-related, then every lineal inch and every degree of circumferential surface of the conductor must receive the minimum dose of radiation. This is accomplished by advancing the conductor 22 with respect to the stationary accelerator 25 in such a way that each portion of the conductor insulation is exposed to at least a minimum amount of radiation.

Increasing exposure time per pass will increase the efficiency of dosage per pass with the accelerator 25. This can be accomplished by moving the conductor passes across the width of the window 32 at an angle to the beam pattern. Of course, as the accelerator 25 is positioned adjacent the crossover points of the figureeight pattern, then at least a portion of the path of the conductor is at an angle to the window 32.

In the above-identified application. a plurality of conductors 2222 may be simultaneously passed between 9 the accelerator and strung between the

sheave banks

23 and 24. Of course, the line speed and the proximity of accelerator 25 to the plane of the

sheave banks

23 and 24 must be adjusted to compensate for that exposure achieved by using the multiple pass pattern.

Considerations have been given to the string-up details between the

sheave banks

23 and 24 and has resulted in the use of a modified figure-eight pattern. This pattern is disclosed in detail in the above-identified application, and takes into account the peculiar problems relating to the radiation cross-linking of the insulation of the conductor 22 which has a circular cross section. The insulation thickness varies along chordal lines with respect to the direction of the incident electrons. Also, the conductive element of the conductor 22 causes some back-scattering of electrons and creation of X- rays which could change the characteristics of the depth-dose curves.

STRING-UP OF STRAND MATERIAL By coordinating the available beam current and the physical size of the sheave banks, the maximum number of conductors 2222 that can be physically placed along the scan line to the accelerator window 32 can be determined. There are a number of combinations within the limits of the beam rating of the accelerator 25 in which the conductor speed and a number of conductor passes in front of the accelerator can be varied to obtain the required dosage in the conductors 2222. The only criteria in conductor passes is that a minimum number must be allowed to guarantee against a dose variation within the insulation.

A delicate balancing must be achieved between the properties desired and the final product in the number of sheaves over which the conductor 22 is passed. It is desirable to pass the conductor 22 over as many sheaves as possible in order to be able to more uniformly dose the conductor. Also, by making multiple passes throughout the height of the window 32, it is possible to use a higher line speed. On the other hand, the more sheaves over which the conductor 22 is passed, the greater the degree of work hardening of the conductive element of the conductor which had priorly been annealed. This consideration would tend to cause a reduction in the number of sheaves.

The conductors are advanced through a plurality of passes transversely past the window 32 by the use of, for example, sheaves 4la-4le and 42a-42e which are mounted rotatably individually on spindles 43 and 44 (see FIG. 6). Each of the sheaves 41 and 42 are quadra sheaves, each having four grooves formed therein and are described in detail in the above-identified application, Ser. No. 304,458.

Only a portion of the window 32 need be allocated to one of the conductors 2222. Sufficient passes of one of the conductors 2222 may be made past that portion of the window 32 to satisfy the dosage requirement. This, of course, permits the use of the remaining portions of the window 32 for the radiation of plural passes of additional conductors and optimizes beam utilization.

Approximately twelve inches of the window 32 are allocated to each of the conductors 2222. Each 12 inch span is -allocated to the associated groups of quadra sheaves 41a-41e and sheaves 42a-42e (see FIG. I).

As can be seen in FIG. 7, the conventional figureeight pattern is modified such that as the conductor 22 10 is removed from one level or one of the quadra sheaves to the next one of the quadra sheaves, there is a straight (S) as opposed to a diagonal path between the spaced

sheave bands

23 and 24. In other words, the pass S is parallel to a line intersecting the axes of the

spindles

43 and 44 and normal thereto.

This causes the conductor 22, which is moved in a figure-eight pattern in the next level, to be in a reverse direction as that in the preceding level. As a result, the radiation of the insulation of the conductor 22 tends to become more uniform. Since the pass of the wire is an alternate figure-eight pass, patterns are in opposite directions, alternate ones of the sheave sets are turned rotatably in opposite directions.

It should be realized while the principle embodiment is concerned with uniformly dosing insulation throughout the cross-sectional area thereof, that this invention is not so limited. The use of the accelerator together with the string-up and handling of the conductor 22 may be used to uniformly dose the surface of the conductor.

SHIELDING SYSTEM As is shown in FIG. 1, four conductors 2222 are simultaneously advanced past the accelerator 25. During the irradiation process, it is logical to assume that ones of the conductors will become exhausted from the supply and that a splicing to a new source of supply of conductor must be made. Obviously, the process could be conducted so that all the supplies are depleted at one time and the operation of the accelerator discontinued. However, this would require additional down time of the accelerator prior to beginning the cycle again while all the splices are made. It is more efficient to splice sequentially ones of the conductors rather than all simultaneously.

Problems present themselves during the splicing process. For example, in some installations the accelerator beam current has been reduced during the splicing process. But here, where four conductors are simultaneously exposed to the irradiation and where the splicing of only one is being conducted, then reduction in the beam current would affect the irradiation process with respect to the other three conductors. Clearly, there is a need for a technique for splicing the conductor 22 in an irradiation environment without affecting the irradiation cross-linking of the other conductors.

This has been accomplished by using a shielding system, designated generally by the numeral 50 (see FIG. 1), for selectively shielding one of the conductors 2222 which is to be spliced. Moreover, this is conducted in synchronization with the acceleration and deceleration of the line speed in order to maintain a constant close exposure per pass of the conductor 22 independent of line speed to uniformly dose the insulation.

In one embodiment now in use, the shielding system 50 includes a reciprocally mounted shutter 51 associated with each of the conductors 2222 (see FIGS. 2 and 3) and mounted for movement transversely across the width of the window 32. As can be seen in FIGS. 1 and 2, each of the shutters 51-51 is connected to a rod 52 and a rack 53 longitudinally extending from a support member 54. The shutter configuration shown in FIG. 1 is a preferred embodiment, but the support and control facilities shown in FIG. 1 are applicable for both embodiments to be described. Each of the racks 53-53 is meshed with a pinion (not shown) in the support member 54 driven by an associated one of a plu- 11 rality of motor drives 56-56.

Moreover, each of the shutters Sl-Sl is arranged so that it is immediately adjacent the window 32 (see FIG. 3). Because the shutter 51 is immediately adjacent the window 32 in this embodiment, the shutter need be only as wide as the window (refer to FIG. 2 and FIG. 8). The shutters 51-51 which are used in this arrangement are water-cooled.

It will be recalled that the conductors are approximately twelve inches from the window 32. As can be seen in FIG. 3 with the shutters adjacent the window 32, when the shutter 51 for the selected one of the conductors 13, which is about to be spliced, is moved into position to shield a portion of the window 32, the conductor, which is presumably shielded, is still exposed to portions of the radiation from that portion of the window directly above and below that shutter which has been operated.

In order to avoid this, a plurality of collimator plates 57-57 (see FIG. 3) are used and fixedly mounted with respect to the window 32. The collimator plates 57-57, which number one more than the number of conductor groups being simultaneously irradiated, are transverse of the X-axis of the window 32, are normal to the window, have a configuration approximately identical to that of the beam pattern (see FIG. 2), and extend from beyond the window slightly beyond the plane of the conductors 22-22. By using the collimator plates 57-57, the movement of the shutters 51-51 across the aligned portion of the window 32 effectively blocks the radiation from adjacent unshielded portions of the window from engaging with the selected one of the conductors 22-22 between the adjacent ones of the collimator plates and about to be spliced.

While the use of the collimator plates 57-57 is beneficial in preventing radiation during splicing, the plates result in a reduction in the efficiency of the radiation process. Because the plates 57-57 extend transversely from the window 32 slightly beyond the conductors 22-22 (see FIG. 3), the conductors of any one group do not benefit from the dispersion effect of the portions of the beam which irradiates the adjacent groups of conductors. While the use of the plates 57-57 advantageously yields excellent uniform dosing results, the loss in efficiency may be as high as 40% and may require additional passes. The actual efficiency loss is a function of the distance of the conductor 22 from the accelerator window 32 and the spacing between adjacent ones of the plates 57-57.

In a preferred embodiment, the shielding includes a plurality of shutters 61-61 mounted for movement adjacent the conductors 22-22 rather than adjacent the window 32 (see FIGS. 4 and 5). Because of this and because the shutters in the preferred embodiment are in the shape of a U or C-shaped channel, collimator plates are not required. The legs of the C or U extend slightly beyond the plane of the conductors 22-22. Moreover, in the preferred embodiment, because of the distance of the shutters from the window 32, water cooling is not required. However, since the beam pattern widens as the distance from the window -32 increases (see FIG. 8), the shutters 61-61 in the preferred embodiment must be substantially longer than the shutters Sl-Sl and cover the entire beam width at the conductor pass.

Prior art processes make it appear to be completely unobvious to shield the conductor 22 from the radiation beam in the manner described. The shielding must be controlled and coordinated to control the dosimetry "12 in order to obtain uniformity of dosimetry during the splicing. Some prior art installations reduce the beam current during the splicing and then increase the beam as the line speed is increased. This is impossible in the highly efficient multiconductor radiation setup since desirably all of the conductors 22-22 are not being spliced simultaneously. Hence, the irradiation thereof must continue during the splicing of the selected one of the conductors. I

In order to control the opening and closing of the

shutters

51 or 61, the shielding system 50 includes a shutter control logic system 66 which is connected to the drive motors 56-56 and a product handling drive system 67 which is connected to the logic system. Feedback signals indicative of line speed are transmitted from the drive system 67 to the shutter control logic 66 to control the motor drives 56-56 for closing or opening of the

shutters

51 or 61. There are also feedback provisions for signals indicative of the shutter position to the logic system 66 and thence to the product handling drive system.

It is extremely important that the closing and opening of the shutters 61-61 be coordinated with the line speed in order to obtain a constant dose exposureper pass and hence maintain the uniformity of dosage. Line speeds of approximately 2,000 feet per minute are used with the preferred embodiment. Moreover, the deceleration and acceleration of the line before and after the splicing is controlled to be non-linear so that the decrease and increase, respectively, of the line speed is linear. r

The acceleration and deceleration of the preferred embodiment is from approximately 2,000 feet per minute down to a zero line speed in approximately 7-8 seeonds with the splicing occurring normally during a twenty second to one minute interval. Then, the line speed is started up again to go from zero to 2,000 feet per minute within 7-8 seconds, during which time the shutter 61 must be opened. The shutter 61 is generally caused to be closed and opened in a period of 6-7 seconds.

The coordination of the movement of the shutters 61-61 with respect to line speed must be made because of the shape of the beam intensity curve. Moreover, this coordination is also a function of the location of the conductor 22 with respect to the window 32. The closer the conductor 22 is to the window 32, the smaller the beam width and the greater the concentration. Hence, because the curve is more steep adjacent the window 32 rather than spaced therefrom, the more critical is the coordination of line speed and shutter speed for those conductors closer to the window. This problem arises when the thicker-walled insulation requires more radiation dosage and, hence, must be passed more adjacent the window 32 than those conductors with the thinner walled insulation.

With the thicker wall insulation and in close, up to, for example, 7 inches from the window 32 to the conductor 22, there may be problems in obtaining the correct coordination. It would appear from dosimetry studies that the shutter 61 should be moved rather quickly at the base of the intensity curve and then be decelerated rapidly during the sharp slope or high energy concentration portion of the curve (see FIG. 10). However, this changing of the shutter speed complicates the controls, increasing the cost of the installation. A more sophisticated shutter arrangement and movement thereof 'may be required.

As the distance from the window 32 increasesQth shape of the surface dose curve (see FIG. ),flattens,

so that at approximately l4to 16 inches from the window the curve is relatively flat. This facilitates the coordination of the opening and closing of the shutters.

61-61 with the acceleration and deceleration of line speed. This may be coordinated linearly with ease. This justifies removing the conductors 2222 outwardly from the window 32 to a point where the surface-dose curve begins to flatten. Then, a constant shutter speed can be maintained.

In a normal non-irradiation installation, there is a constant rate of acceleration which gives a non-linear .change of line speed to zero and from zero to line speed. This results in a non-linear line speed. In the irradiation technique set out hereinbefore, there is a non-linear acceleration in order to give a linear increase or decrease of line speed. The only non-linear parameter that must be dealt with then is the beamintensity curve, and this may be accounted for by delaying the opening and closing of the

shutters

51 or 61 as may be required.

Once the distance from the window 32 to the conductors 2222 is set, the depth-dose curve configuration is established and coordination must be made with the beam-intensity curve which relates to surface dose. The beam intensity curve effects the design of the shutter arrangement. If through proper coordination, the beam intensity is maintained uniformly, then there is assurance of uniformity of dosage internally.

it should be observed from the arrangement of the shutters 6l6l together with the multi-conductors 2222 and the multi-passes thereof that there is still string-up by. canting alternate ones of the sheaves 41-41 and. associated ones of the sheaves 42 42. This causes longitudinal turning of the conductor 22 and sequentially different circumferential portions of the insulation to be presented to the accelerator 25 as the conductor 22 is advanced therepast. Moreover. different portions of the insulation are presented-to the accelerator as between successive figure-eight patterns to cause a more uniformdistribution of dosage of radiation. The canting of the sheaves generally is only necessary during the simple loop string-up. It has been observed that-when a single conductor 22 is moved in a figuresome blockage of the radiation beam from the conduc:

tors. This occurs because of the closeness of the adjacent ones of the shutters 61-61 when in the closed position with parts of the beam dispersion from adjacent groups of unshielded conductors 2222 striking the legs of the C-shaped shutters, which tend to act as reduced-size collimator plates. It has .been estimated there is approximately a 10 percent loss in the irradiation striking the conductor 22 because of this interference. This contrasts to an approximate loss with the collimator plate arrangement. 7

This interference is a maximum when an unshielded conductor 22 is bordered on each side by a shielded conductor. in that situation,'the depending legs of the shutters 61-61 act to reduce the irradiation on the unshielded conductor 22 from beam dispersion.

The critical dimension is that between adjacent ones of the shutters 61-61. In the preferred embodiment, a conductor group occupies approximately l2 inches of. window length. If a smaller dimension were used, the shutters 6l61 would be closer together, thereby increasing the interference and beam dispersion and hence increasing the loss. With a reduced section distance, the conductors are closer together. This is especially critical when, for example, more than one shutter is closed at the same time with the one conductor 22 being moved while each adjacent one thereofis being spliced.

LONGITUDINAL TURNING OF CONDUCT ORS In order to substantially eliminate the dose variation during the normal irradiation, perturbation of the angle of incidence of the beam on the insulated conductor 22 is caused as it is passed adjacent theaccelerator window 32. This may be accomplished in the simple loop eight pattern over uncanted sheaves, that a progressive screwing effect occurs. This is similar, in effect, to the canted sheave arrangement and causes the conductor to be turned about the longitudinal axes to present sequentially different portions of the insulation to the .window 32 as the conductor is advanced therepast.

The rotation of the conductors 2222 is synchronous with the advancement of the conductor. The use of the shutter arrangement permits line splicing of a selected one of the conductors 2222 while continuing .the irradiation cross-linking of the other ones of the conductors. This is a tremendous assist in maintaining the efficiency of theoperation, while at the same time continuing to uniformly dose the insulation of the conductors. ln effect, this reduces-the radiation dosage to which the conductor insulation is exposed as the speed of the conductor is reduced and then after the splice occurs and the line speed is increased, increases the radiation dosage again to that normal for the general run of the conductors past the accelerator 25.

It is tobe understood that the above-described arrangements are simply illustrative of the principles of the invention. Other arrangements may be devised by those skilled in the art which will embody the principles of the invention and fall .within the spirit and scope thereof. i 7

What is claimed is:

l. A method of irradiating uniformly cross-linkable covering of ones of a plurality of elongated materials, which includesthe steps of:

directing an electron radiation beam toward and into t engagement with a plurality of elongated materials,

beach of which is strung up in a multi-pass path;

advancing each of the plurality of elongated materials along the associated path at a line speed to ex pose simultaneously the plurality of elongated materials to the beam, while causing perturbation of the angle of incidence of the beam on the elongated materials to dose uniformly the covering; and

regulating individually the exposure of each of the plurality of elongated materials to the beam relative to changes in the line speed to provide a con-,

stant dose rate per pass independent of line speed changes.

2; A method of irradiating uniformly cross-linkable covering of ones of a plurality of elongated materials, which includes the steps of: 1

directing an electron radiation beam toward and into engagement with a plurality of elongated materials,

I each of which is strung up. in a multi-pass path;

advancing each of the plurality of elongated materials along the associated path at a line speed to expose the elongated materials to the beam,'while causing perturbation of the angle of incidence of the beam on the elongated materials to dose uniformly the covering; decelerating the advance of a selected one of the elongated materials and subsequent to a time inter-' val, accelerating the selectedone of the elongated materials to the line speed; while 7 shielding the selected one of the elongated materials from the radiation bea-m during the time interval and then re-exposing the selected one of the elon gated materials to the radiation beam, the shielding and re-exposure being accomplished in synchroni-' zation with the deceleration and acceleration, respectively, to provide a constant dose rate per pass independent of line speed changes and thereby continue the uniform dosing of the covering during the deceleration and acceleration.

3. The method of claim 2,wherein the elongated material is dosed uniformly throughout the cross-sectional area thereof. I

4. The method of claim 2, wherein the advancing'ofthe elongatedmaterial is accomplished to include a periodic reversing of the direction of travel around the path and the rotation of the elongated material-about the longitudinal axes thereof as the elongated material is advanced along the path, the rotation being effective to present different rotational orientations of the elongated material to the beam as the elongated material is advanced along the associated path. r

5. The method of claim 2, wherein each of the elongated materials includes a twisted pair of conductors which are strung up in a path around spaced strand engagement surfaces, the engagement of the conductors with the strand engagement surfaces causing the pair to be turned about longitudinal axes thereof to cause the insulation thereof to be uniformly dosed and crosslinked. I a l 6. The method of claim 2, wherein each of the elongated materials is a strand materialwhich is strung-up in a plurality of figure-eight paths in superimposed spaced relation to each other transversely of the elon-' gated dimension of the radiationbeam, the beam being directed along the crossover points of the figure-eight paths, each plurality of figure-eight paths being discontinued intermittently to provide a pass between spaced strand engagement surfaces which is parallel to a line joining the axes of rotation of the strand engagement surfaces to cause'the direction of travel of the strand material in the figure-eight paths before and after the aforementioned pass to be in opposite directions.

7. The method of claim 2, wherein each of the'elongated materials is a strand'material, the shielding of the selected one of the groups of strand materials is accomplished by providing an effective barrier to the radiation beam immediately adjacent to each of the conductors and which extends substantially the width of the beam in the plane of the pass, the advancing of the strand materials being accomplished at a distance. from the window such that a constant velocity of the barrier during deceleration and acceleration of the strand material causes a constant dose exposure per'pass and the continuation of a uniform dosing of the covering.

8. The method of claim 2, wherein each of the elongated materials is'a strand material, the shielding of the selected one of the strand materials is accomplished by providing an effective movably mounted barrier to the radiation beam immediately adjacent a window aligned with the selected one of the strand materials and through which the beam passes, the barrier extending essentially the width of the window, further providing a't'a constant velocity, during acceleration of the line speed, to open the barrier.

10. An apparatus for irradiating uniformly cross-linkable covering of ones ofa plurality of elongated materials, which includes:

means for stringing up each of a plurality of elongated materials in' a'multi-pass path; means for directing an electron radiation beam toward and into engagement with each ofa plurality of elongated materials alongat least a portion of the associated path;

means for advancing each of the plurality of elon-- gated materials along the associated path at a line speed to expose simultaneously the plurality of elongated materials to the beam while causing perturbation of the angle of incidence of the beam on the elongated materials to dose uniformly the covering; and i means for regulating individually the exposure of each of the plurality of elongated materials to the beam relative to changes in the line speed to provide a-constant dose rate per pass independent of line speed changes. 1 ll. An apparatus for irradiating uniformly cross-linkablecovering of ones of a plurality of elongated materials,which includes: I r

means for stringing up each of a plurality of elongated materials in a'multi-pass'path;

means, includingta window, for directing an electron 1 radiation beam toward and into engagement with the plurality of elongated materials;

means for advancing each of the plurality of elongated materials along the associated pathat a line speed to expose :the elongated materials to the beam, while-causingperturbation of the angle of incidence of the beamonthe elongated materials :to dose uniformly the'covering;

means for decelerating the advance of a selected one of the elongated materials and subsequent to a time interval, accelerating the selected one of the elongatedrnaterials to the line speed; while means for shielding the selected one of the groups of elongated materials from the radiation beam during the time interval and then re-exposing the selectedone of; the groups to the radiation beam, the

shielding and re-exposure being accomplished in synchronization with the deceleration and acceleration, respectively, to provide a constant dose rate per pass independent of line speed changes and thereby continue the uniform dosing of the covering during the deceleration and acceleration.

12. The apparatus of claim 11, wherein the elongated strand material is dosed uniformly throughout the cross-sectional area thereof.

13. The apparatus of claim 11, wherein each of the elongated materials includes a twisted pair of conductors, the engagement of which with the means for stringing up the strand material being effective to cause the strand material to be turned about the longitudinal l7 axes thereof.

14. The apparatus of claim 11, wherein each of the elongated materials is a strand material, the shielding means including a barrier associated with each of the strand materials and adjacent the window and having a width approximately equal to the window width; the apparatus further including means for mounting movably each barrier to move the barrier transverse of the window; and

a plurality of auxiliary barriers normal to the window and extending therefrom into a configuration approximately equal to that of the beam intensity pattern and extending slightly beyond the associated strand materials, there being an auxiliary barrier adjacent the first and last pass of each strand material of the plural strand materials; and

. means for cooling each of the movably mounted barriers.

15. The apparatus of claim 11, wherein each of the elongated materials is a strand material andthe shielding means includes a barrier associated with and adjacent each of the strand materials, each barrier being in the shape of a channel with legs normal to the window and extending beyond the associated strand material to shield effectively the associated strand material during the interval of time while others of the strand materials continue to be exposed; the apparatus further including means for mounting movably each barrier to move the barrier transverse of the window.

16. The apparatus of claim 15, wherein the means for stringing up the strand material causes the strand material to be rotated about the longitudinal axes thereof to present the strand material in sequentially different orientations to .the beam as the strand material is advanced in successive ones of the figure-eight loops past the window and for causing the periodic reversing of the direction of travel around the pattern, and wherein the shielding means causes each of the barriers to be moved after a preset delay at a constant velocity during deceleration of the line speed to interpose the barrier between the window and the associated conductor and after a preset delay to move the barrier at a constant velocity during acceleration of the line speed to open the barrier.

17. The apparatus of claim 15, wherein the means for stringing up the strand material includes spaced strand engagement surfaces, each of the strand engagement surfaces including two spaced banks of sheaves with the coaxial axes of the sheaves being parallel to the longitudinal axes of the window, the strand material being a conductor strung-up around said sheaves in a plurality of superimposed generally figure-eight paths in spaced relation to each other with the elongated dimension of the window substantially normal to the plane of the figure-eight paths, the beam directed toward the crossover points of each of the figure-eight paths and the beam being oriented with respect to the superimposed adjacent layers such that each layer is exposed to substantially the same radiation dose, the stringing up of the conductors between associated ones of the sheaves in superimposed figure-eight paths including the periodic interruption of the figure-eight pattern to include a run along a path parallel to a line joining the axes of rotation of the spaced sheaves to cause the strand material to be moved in opposite dipath parallel to the axes.

Claims

1. A method of irradiating uniformly cross-linkable covering of ones of a plurality of elongated materials, which includes the steps of: directing an electron radiation beam toward and into engagement with a plurality of elongated materials, each of which is strung up in a multi-pass path; advancing each of the plurality of elongated materials along the associated path at a line speed to expose simultaneously the plurality of elongated materials to the beam, while causing perturbation of the angle of incidence of the beam on the elongated materials to dose uniformly the covering; and regulating individually the exposure of each of the plurality of elongated materials to the beam relative to changes in the line speed to provide a constant dose rate per pass independent of line speed changes.

2. A method of irradiating uniformly cross-linkable covering of ones of a plurality of elongated materials, which includes the steps of: directing an electron radiation beam toward and into engagement with a plurality of elongated materials, each of which is strung up in a multi-pass path; advancing each of the plurality of elongated materials along the associated path at a line speed to expose the elongated materials to the beam, while causing perturbation of the angle of incidence of the beam on the elongated materials to dose uniformly the covering; decelerating the advance of a selected one of the elongated materials and subsequent to a time interval, accelerating the selected one of the elongated materials to the line speed; while shielding the selected one of the elongated materials from the radiation beam during the time interval and then re-exposing the selected one of the elongated materials to the radiation beam, the shielding and re-exposure being accomplished in synchronization with the deceleration and acceleration, respectively, to provide a constant dose rate per pass independent of line speed changes and thereby continue the uniform dosing of the covering during the deceleration and acceleration.

3. The method of claim 2, wherein the elongated material is dosed uniformly throughout the cross-sectional area thereof.

4. The method of claim 2, wherein the advancing of the elongated material is accomplished to include a periodic reversing of the direction of travel around the path and the rotation of the elongated material about the longitudinal axes thereof as the elongated material is advanced along the path, the rotation being effective to present different rotational orientations of the elongated material to the beam as the elongated material is advanced along the associated path.

5. The method of claim 2, wherein each of the elongated materials includes a twisted pair of conductors which are strung up in a path around spaced strand engagement surfaces, the engagement of the conductors with the strand engagement surfaces causing the pair to be turned about longitudinal axes thereof to cause the insulation thereof to be uniformly dosed and cross-linked.

6. The method of claim 2, wherein each of the elongated materials is a strand material which is strung up in a plurality of figure-eight paths in superimposed spaced relation to each other transversely of the elongated dimension of the radiation beam, the beam being directed along the crossover points of the figure-eight paths, each plurality of figure-eight paths being discontinued intermittently to provide a pass between spaced strand engagement surfaces which is parallel to a line joininG the axes of rotation of the strand engagement surfaces to cause the direction of travel of the strand material in the figure-eight paths before and after the aforementioned pass to be in opposite directions.

7. The method of claim 2, wherein each of the elongated materials is a strand material, the shielding of the selected one of the groups of strand materials is accomplished by providing an effective barrier to the radiation beam immediately adjacent to each of the conductors and which extends substantially the width of the beam in the plane of the pass, the advancing of the strand materials being accomplished at a distance from the window such that a constant velocity of the barrier during deceleration and acceleration of the strand material causes a constant dose exposure per pass and the continuation of a uniform dosing of the covering.

8. The method of claim 2, wherein each of the elongated materials is a strand material, the shielding of the selected one of the strand materials is accomplished by providing an effective movably mounted barrier to the radiation beam immediately adjacent a window aligned with the selected one of the strand materials and through which the beam passes, the barrier extending essentially the width of the window, further providing fixed shielding barriers extending normally to the window and between adjacent ones of the strand materials to prevent the shielded one of the strand materials from being exposed to beam dispersion from the adjacent ones of the strand materials.

9. The method of claim 8, wherein the movably mounted barrier is moved, after a preset delay, at a constant velocity during deceleration of the line speed to close the barrier, and is moved, after a preset delay, at a constant velocity, during acceleration of the line speed, to open the barrier.

10. An apparatus for irradiating uniformly cross-linkable covering of ones of a plurality of elongated materials, which includes: means for stringing up each of a plurality of elongated materials in a multi-pass path; means for directing an electron radiation beam toward and into engagement with each of a plurality of elongated materials along at least a portion of the associated path; means for advancing each of the plurality of elongated materials along the associated path at a line speed to expose simultaneously the plurality of elongated materials to the beam while causing perturbation of the angle of incidence of the beam on the elongated materials to dose uniformly the covering; and means for regulating individually the exposure of each of the plurality of elongated materials to the beam relative to changes in the line speed to provide a constant dose rate per pass independent of line speed changes.

11. An apparatus for irradiating uniformly cross-linkable covering of ones of a plurality of elongated materials, which includes: means for stringing up each of a plurality of elongated materials in a multi-pass path; means, including a window, for directing an electron radiation beam toward and into engagement with the plurality of elongated materials; means for advancing each of the plurality of elongated materials along the associated path at a line speed to expose the elongated materials to the beam, while causing perturbation of the angle of incidence of the beam on the elongated materials to dose uniformly the covering; means for decelerating the advance of a selected one of the elongated materials and subsequent to a time interval, accelerating the selected one of the elongated materials to the line speed; while means for shielding the selected one of the groups of elongated materials from the radiation beam during the time interval and then re-exposing the selected one of the groups to the radiation beam, the shielding and re-exposure being accomplished in synchronization with the deceleration and acceleration, respectively, to provide a constant dose rate per pass independent of line speed changes and thereby conTinue the uniform dosing of the covering during the deceleration and acceleration.

13. The apparatus of claim 11, wherein each of the elongated materials includes a twisted pair of conductors, the engagement of which with the means for stringing up the strand material being effective to cause the strand material to be turned about the longitudinal axes thereof.

14. The apparatus of claim 11, wherein each of the elongated materials is a strand material, the shielding means including a barrier associated with each of the strand materials and adjacent the window and having a width approximately equal to the window width; the apparatus further including means for mounting movably each barrier to move the barrier transverse of the window; and a plurality of auxiliary barriers normal to the window and extending therefrom into a configuration approximately equal to that of the beam intensity pattern and extending slightly beyond the associated strand materials, there being an auxiliary barrier adjacent the first and last pass of each strand material of the plural strand materials; and means for cooling each of the movably mounted barriers.

15. The apparatus of claim 11, wherein each of the elongated materials is a strand material and the shielding means includes a barrier associated with and adjacent each of the strand materials, each barrier being in the shape of a channel with legs normal to the window and extending beyond the associated strand material to shield effectively the associated strand material during the interval of time while others of the strand materials continue to be exposed; the apparatus further including means for mounting movably each barrier to move the barrier transverse of the window.

16. The apparatus of claim 15, wherein the means for stringing up the strand material causes the strand material to be rotated about the longitudinal axes thereof to present the strand material in sequentially different orientations to the beam as the strand material is advanced in successive ones of the figure-eight loops past the window and for causing the periodic reversing of the direction of travel around the pattern, and wherein the shielding means causes each of the barriers to be moved after a preset delay at a constant velocity during deceleration of the line speed to interpose the barrier between the window and the associated conductor and after a preset delay to move the barrier at a constant velocity during acceleration of the line speed to open the barrier.

17. The apparatus of claim 15, wherein the means for stringing up the strand material includes spaced strand engagement surfaces, each of the strand engagement surfaces including two spaced banks of sheaves with the coaxial axes of the sheaves being parallel to the longitudinal axes of the window, the strand material being a conductor strung-up around said sheaves in a plurality of superimposed generally figure-eight paths in spaced relation to each other with the elongated dimension of the window substantially normal to the plane of the figure-eight paths, the beam directed toward the crossover points of each of the figure-eight paths and the beam being oriented with respect to the superimposed adjacent layers such that each layer is exposed to substantially the same radiation dose, the stringing up of the conductors between associated ones of the sheaves in superimposed figure-eight paths including the periodic interruption of the figure-eight pattern to include a run along a path parallel to a line joining the axes of rotation of the spaced sheaves to cause the strand material to be moved in opposite directions in the figure-eight loops before and after the path parallel to the axes.