Irradiation apparatus for production line use

Details Irradiation apparatus for production line use Irradiation apparatus for production line use

1998-12-03

2001-02-20

Anderson, Bruce C. (Department: 2881)

Radiant energy

Supported for nonsignalling objects of irradiation

With source support

C250S453110, C250S492300, C250S496100

Reexamination Certificate

active

06191424

ABSTRACT:

FIELD OF INVENTION
This invention relates to irradiation equipment and in particular to compact, production-line sterilization equipment.
DESCRIPTION OF THE RELATED PRIOR ART
Manufacturers of sterile medical devices frequently use ionizing radiation to reduce the bioburden. Such radiation processing methods are also used for sterilizing, or rendering less harmful, other products such as foods, agricultural and waste materials and for crosslinking or scissioning polymers. Radiation may also be used for altering the physical properties of materials. Radiation sources for sterilization, scissioning and crosslinking typically include radioisotopes such as cobalt −60 or cesium 137, electron beam accelerators of energy greater than 1 MeV, or electron beam accelerators with heavy metal targets that convert the electrons into x-rays.
Typically, radiation processing is carried out after production and packaging of the product to be sterilized, at large sterilization plants, often located a considerable distance from the point of product manufacture. These high volume sterilization plants are expensive to build and very large in size, due to the thick radiation shielding and the need for a tortuous product transport path to prevent radiation leakage. In order to be cost-effective, this method of sterilization is generally used where a large volume of product is to be processed. As well, due to their size they cannot easily be integrated into the manufacturer's production line. Further, since these large capacity plants are often operated by independent service providing companies, a quality control system extending across more than one company is required. In addition, there can be a mixture of products processed at a given sterilization plant, which frequently results in the transfer from one product to another of undesirable characteristics such as odour.
An example of a typical large volume irradiator is described in U.S. Pat. No. 4,866,281 issued Sep. 12, 1989 and depicted in FIG.
1
. In this unit, the attenuation of the radiation which can escape along the product path is eliminated by the use of a maze structure extending between the radiation zone
1
and the product entry/exit point
2
. The size and complexity of the shield is therefore much larger than necessary to simply enclose the irradiation source and the product being irradiated.
In response to the demand for physically smaller systems, devices such as the one described in U.S. Pat. No. 5,557,109 issued Sep. 10, 1996 and shown as
FIG. 2
, were proposed. This system comprises a shielding unit
3
, an irradiation device
4
, a power supply, high frequency generator and modulator
5
, and a manipulator
6
. Products to be irradiated are placed in chamber
8
integral to manipulator
6
and the manipulator
6
is linearly received into the cavity
7
of shield
3
, so that the product to be sterilized is aligned with the irradiation device
4
. The related invention disclosed in U.S. Pat. No. 5,554,856 issued Sep. 17, 1996 uses a manipulator which can be rotated instead of linearly moved to place the product to be sterilized into the irradiation zone. While these devices do overcome the problem of size associated with earlier systems, they do not provide for a steady and continuous flow goods to be irradiated. These devices provide sequential rather than continuous processing, requiring labour and time-intensive product handling and the movement of a significant mass of the primary shield is necessary for the treatment of each unit processed. In the linear system for example, chamber
8
is accessed by moving the manipulator
6
which is constructed of a large slug of very dense and heavy shielding. Similarily, in the rotatable system, the manipulator is constructed from a large slug of shielding and has two chambers that must be loaded with product and rotated into the irradiation zone. The movement of the manipulator in both cases requires the acceleration and deceleration of a large mass of shielding, making neither system suitable for production line operations where higher throughput is required.
U.S. Pat. No. 5,009,654 issued Apr. 23, 1991 and shown in
FIG. 3
, discloses another sequential production line system whose primary purpose is to irradiate one part of an assembly while shielding other radiation sensitive parts. The essential components of this system include a shielding unit
9
, an irradiation device
10
, a conveyor system
11
, a carrier
12
, a piston cylinder
13
and an isolation fixture
14
. This system is designed to allow irradiation of a selected portion of a product to be irradiated by incorporating an isolation fixture
14
which comprises additional shielding to isolate the portion of the product to be irradiated. In operation, the carrier
12
is aligned with the piston cylinder
13
and the carrier
12
is lifted toward the irradiation device
10
. The isolation fixture
14
integral to carrier
12
is placed directly in line with the irradiation device, facilitating sterilization of a selected portion of the product. Although this system satisfactorily provides localized sterilization, it is not a general product ion line sterilization system which can accommodate continuous product throughput. The use of a piston cylinder
13
to physically lift the carrier
12
is necessary to ensure that only a selected portion of the product is sterilized and to ensure that any radiation produced is attenuated by the shielding unit
9
. However, lifting of the product unduly complicates the system and serves to reduce the volume of product which can be moved through the system.
A further attempt to provide production line sterilization is described in Swedish Patent Application 9602377-5 filed Jun. 14, 1996 which describes an apparatus for defocussing and bending an electron beam to provide simultaneous double-sided irradiation of a product stream. As shown in
FIG. 4
, in this device the main shield
15
encloses the radiation source and beam spreading system
16
, while a product handling system
17
delivers product to the radiation source
16
by means of a tortuous path designed to block radiation leakage. Due to the limitations of the product handling system and the shielding disclosed in this patent, this device is limited to processing products which are thin and flexible.
SUMMARY OF THE INVENTION
The present invention serves to overcome the deficiencies identified in the prior art. It is therefore the primary object of the present invention to provide a compact irradiation apparatus integral to a production line that can sterilize product received from a manufacturing process on a continuous basis.
The above object is achieved by providing an irradiation apparatus for production line use comprising:
(a) primary shield means for blocking radiation;
(b) secondary shield means for blocking radiation;
(c) an irradiation device; and
(d) conveyor means;
wherein said primary shield means further includes a central cavity therein and a channel extending therethrough which intersects the cavity and accommodates the conveyor means;
and wherein the secondary shield means comprises a plurality of discrete open containers, the containers having front and rear walls, the walls being substantially the size of the channel opening;
and wherein the primary and secondary shield means are of sufficient density to fully attenuate the radiation produced by the irradiation device;
and wherein the containers are integral to the conveyor means;
and wherein the irradiation device is disposed within the cavity to allow radiation of a product positioned in the containers as the containers pass through the cavity.
Preferably, the irradiation device is chosen from the group comprising electron accelerators, X-ray generators, and gamma-ray emitting radioisotopes.
More preferably, the conveyor means further includes a continuous track and drive means and the containers also integral to the conveyor means further include two pairs of wheels with each pair connected by an axle.
Conveniently, the continuous track is

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