EP0117884B1 - Fibres de plomb, leur procédé de fabrication et matériaux de protection contre les rayonnements contenant ces fibres - Google Patents
Fibres de plomb, leur procédé de fabrication et matériaux de protection contre les rayonnements contenant ces fibres Download PDFInfo
- Publication number
- EP0117884B1 EP0117884B1 EP83102162A EP83102162A EP0117884B1 EP 0117884 B1 EP0117884 B1 EP 0117884B1 EP 83102162 A EP83102162 A EP 83102162A EP 83102162 A EP83102162 A EP 83102162A EP 0117884 B1 EP0117884 B1 EP 0117884B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- lead
- fibers
- tin
- lead fibers
- radiation shielding
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/005—Continuous casting of metals, i.e. casting in indefinite lengths of wire
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/06—Metallic powder characterised by the shape of the particles
- B22F1/062—Fibrous particles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/10—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying using centrifugal force
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F3/00—Shielding characterised by its physical form, e.g. granules, or shape of the material
Definitions
- the present invention relates to lead fibers melt-spun of lead containing tin as well as to a method of melt-spinning such lead fibers.
- the present invention further relates to radiation shielding materials for X-rays comprising these lead fibers.
- the prior art teaches methods of melt-spinning lead. These lead fibers are mainly used as radiation and sound shielding materials.
- the diameter of lead fibers made by conventional melt-spinning methods ranges from 150 to 200 microns. Fibers having a considerably smaller diameter are not available.
- Fibers with smaller diameters cannot by produced because when the fine lead fibers are extruded the small holes clog within a very short time, or the output decreases sharply. This problem is particularly noticeable in the process of spinning high-purity lead, such as lead with a purity of more than 99.9%.
- Japanese Patent Application No. 49-16168 discloses a method of avoiding the above-mentioned difficulties involved in the spinning of lead fibers. According to this method, the spinneret holes are prevented from clogging by the addition of alloy elements to the lead. Considerable amounts of an alloy element are used, namely 0.1 to 40% (by weight) of tin.
- the present invention is based on the concept that lead fibers with very small fiber diameters can be produced by melt-spinning the fibers of lead containing minimal amounts of tin only. This leads to high purity lead fibers with conspicuous advantages.
- the lead fibers according to the invention melt-spun of lead containing tin, are characterized in that the tin content of the lead is within the range of 50 to 500 ppm.
- the average fiber diameter is preferably less than 60 microns.
- the radiation shielding materials according to the invention comprise such lead fibers in which the tin content of the lead is within the range of 50 to 500 ppm.
- the lead fibers according to the invention are extremely flexible due to their very small diameter, and are therefore suitable for a variety of applications.
- the fibers are also highly resistant to corrosion:
- the lead fibers can be produced without any problems to do with the spinneret holes clogging up, which is a benefit of the low tin content.
- Figures 1 to 3 show X-ray photographs of Sheets A, B and C, respectively, made according to Example 7.
- the lead fibers of the present invention contain 50 to 500 ppm tin, and preferably 100 to 200 ppm tin.
- the lead fibers are produced by melt-spinning. Tin is added to the lead so that the amount of tin is within the range of 50 to 500 ppm. Since tin melts at about 232°C the mixture can be melted completely at 327°C, the melting point of lead. The fluid mixture is spun into fibers by being passed through spinneret holes having a desired diameter.
- spinneret holes can be prevented from clogging by the small amount of tin, holes with a very small diameter can be used without any problem.
- lead fibers with a diameter of 60 or 50 microns or even preferably below 30 microns can easily be spun.
- the lead fibers produced are extremely resistant to corrosion due to the characteristics of the tin.
- the lead fibers contain more than 500 ppm of tin, the advantageous effect as mentioned above is not increased, but the higher amount of tin is disadvantageous in view of the generation of characteristic X-rays.
- the tin can be mixed with the lead either in elemental form or as a compound.
- the lead fibers according to the invention since they are very fine and flexible, are especially suitable for radiation shielding material.
- the lead fibers can easily be fabricated into sheets which may be thin, thick, dense or coarse in their composition.
- the sheets are extremely resistant to corrosion and provide easy handling due to their flexibility.
- the lead fibers according to the invention are also especially suitable for producing composite materials comprising the lead fibers in chopped form and resin. It has been found that the extremely fine lead fibers according to the invention should be used in shorter length, preferably with an average fiber length of between 0.5 and 1.3 mm, compared to conventional thick lead fibers because the fine fibers entangle easily and form lumps, leading to non-uniform dispersion in the composite material.
- the fibers easily aggregate and form lumps when slightly pressed during production. During the mixing process with the resin, these fibers also form lumps resulting in a very poor dispersibility. On the other hand, when the fibers have an average length of less than 0.5 mm the fibers fly up in the air easily and are thus very inconvenient to handle.
- the spun fibers are cut immediately after solidification during spinning, using a rotary cutter next to the spinning facilities. They are then filtered through a sieve adjacent to the rotary cutter and only those lead fibers having the predetermined length are selected.
- the fibers of the present invention are extremely well-suited for use in radiation shielding material, having extremely high X-ray shielding power in spite of the thin fabric construction.
- garments or aprons as commercially available are made up of a number of X-ray shielding sheets which contain powder of lead metal or a lead compound dispersed in a high polymer.
- a fine powder of lead or a lead compound cannot be blended into a resin to achieve a specific gravity greater than 0.2. If more powder is added the sheets become too weak to be used properly.
- the lead equivalent amounts only to a value of 0.08 (mm Pb) at the thickness of 0.5 mm, according to the JIS Z-4501 standard test method. This value is too low for proper shielding of X-rays.
- a composite material mainly used for sound shielding which comprises lead fibers with diameters extending from a minimum of 100 microns upwards, and normally in the range of 200 to 500 microns. Compared to lead powder, these fibers allow a significantly higher lead content to be achieved when incorporated in a high polymer, so that values of 5.5 of specific gravity can be reached.
- the radiation shielding material according to the present invention being preferably a composite material composed of lead fibers blended with synthetic resin, wherein the lead fibers have an average diameter of less than 60 microns and the composite material has a minimum specific gravity of 4.0, does not show such a pin-hole effect.
- the lead equivalent is often used to compare X-ray shielding powers of various materials, whereby the lead equivalent is represented by "the thickness of lead substrate to which the X-ray shielding power is equivalent". The greater the lead equivalent is, the higher the X-ray shielding power is.
- the lead equivalent value In order to obtain maximum X-ray shielding power, the lead equivalent value must be increased by providing material with higher specific gravity and especially the X-ray absorbing material, which is the lead, must be uniformly dispersed.
- the uniform dispersion is essential because even if the lead equivalent value is increased, if there are pin-holes which allow the X-rays to penetrate the shielding sheet locally, such sheet is fatally defective for X-ray shielding purposes.
- the extremely fine lead fibers of the present invention can easily be homogeneously dispersed into resin and, even though a large amount of the lead fibers is added, the strength and the flexibility of the sheet remain unaffected.
- the diameter of the lead fibers exceeds 60 microns, the homogeneous dispersibility is lower, which then leads to a number of pin-holes which allow the X-rays to penetrate easily the shielding sheet itself.
- thermoplastic and thermosetting resins that are usually applicable for conventional composite materials may also be used with the lead fibers of the present invention.
- thermosetting resins include, for example: epoxy, phenol, unsaturated polyester and polyimide resins.
- Crosslinking agents, catalysts or any other additives may be used with any of these resins.
- thermoplastic resins are, for example: polyvinyl chloride, polyolefin, polyamide and polyester. Any suitable additives such as plasticizers, fillers, thermostabilizers, flame retarders, pigments, etc. may be used with these resins.
- the composite materials comprising chopped lead fibers and resin of the present invention normally have a specific gravity of more than 4.0 and particularly more than 4.5.
- the lead fibers are homogeneously dispersed.
- the lead equivalent values measured by the JIS Z-4501 standard test method were significantly higher than those measured for any of the conventional lead powder blended composite material, and yet the composite material comprising the lead fibers is totally free of pin-holes which would allow X-rays to penetrate.
- thermosetting resins Even a composite material comprising any of the thermosetting resins, if made into a very thin sheet having a thickness of less than 0.5 mm, provides sufficient shielding power against X-rays. In addition, it is very easy to handle owing to its excellent flexibility. Thus, a vast variety of applications is possible.
- Preferred radiation shielding sheets can, for example, be made by any of the following methods, without being limited thereto.
- the lead fibers are mixed, for example, with polyvinyl chloride resin in any desired proportion.
- a suitable plasticizer is added before the mixture is completely blended, thereby using a Banbury mixer.
- the blended material is pressed between rolls that are provided with a predetermined gap so that the blended material can be shaped into a sheet.
- woven, knitted or spun-bonded fabric composed of either the natural fiber or a man-made fiber to be laminated on or in the composite material so that the sheet strength can be increased.
- Tin metal (Sn shot, made by Fukuda Kinzoku Hakufun Kogyo KK) was added to molten lead metal of 99.9% minimum purity.
- the sum of the content of Sb and Sn was less than 10 ppm so that the amount of the Sn in the lead fiber had the values as shown in the following table.
- the mixed metals were melted at 385°C and fed to spinning equipment provided with a spinneret comprising five holes each having a diameter of 0.05 mm.
- the material was then extruded through the spinneret at 380°C by pressurized inert gas. Lead fibers with a diameter of 30 to 40 microns were produced in this manner.
- lead fibers having very high purity can stably be produced although a very minimal amount of tin is present.
- tin metal was added to lead metal with a minimum purity of 99.9%, whereby the sum of the content of Sb and Sn was less than 10 ppm at 345°C so that the Sn content became 100 ppm.
- the melted metal was then spun through holes each having a diameter of 0.05 mm.
- This mat was then rolled onto a pipe with a diameter of 10 cm. Owing to its high flexibility, the mat could be tightly rolled onto the pipe. This high flexibility is very advantageous because such sheets can be used for radiation shielding of radioactive pipes.
- a light metal mixture was prepared for spinning according to Example 4. After being melted at 345°C, the fluid metal was spun using a spinneret having holes with a diameter of 0.05 mm. With these lead fibers having a diameter of 30 to 40 microns, a web with a weight of 7.5 kg/m 2 was produced.
- Very fine lead fibers having a diameter of 30 to 40 microns produced according to Example 4 were cut by a cutter in order to obtain chopped fibers. Chopped fibers of several lengths were produced by varying the diameter of the cutter screen.
- lead fibers having an average length in the range of 0.5 to 1.3 mm show excellent dispersibility and are good to handle.
- a mixture was first prepared by adding the fibers to polyvinyl chloride resin. After adding a plasticizer, the mixture was sufficiently stirred by a Banbury mixer. The mixture was then extruded through a gap between rollers, whereby two sheets having a specific gravity of 4.2 (sheet A) and 4.7 (sheet B) were produced.
- the JIS Z-4501 standard test method revealed a lead equivalent of 0.14 (sheet A) and 0.17 (sheet B).
- Photographs were made by 100 KVP X-ray tube voltage. They showed that the sheets were of a homogeneous quality without containing any pin-holes at all and providing totally effective radiation shielding characteristics.
- lead fibers having a diameter of 70 microns and a length of 1 mm were mixed with polyvinyl chloride resin and a sheet having a thickness of 0.5 mm was prepared (sheet C).
- the specific gravity was 4.7 and the lead equivalent value 0.14.
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Nanotechnology (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Nonwoven Fabrics (AREA)
Claims (8)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP83102162A EP0117884B1 (fr) | 1983-03-04 | 1983-03-04 | Fibres de plomb, leur procédé de fabrication et matériaux de protection contre les rayonnements contenant ces fibres |
DE8383102162T DE3367867D1 (en) | 1983-03-04 | 1983-03-04 | Lead fibers, a method of producing same and radiation shielding materials comprising same |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP83102162A EP0117884B1 (fr) | 1983-03-04 | 1983-03-04 | Fibres de plomb, leur procédé de fabrication et matériaux de protection contre les rayonnements contenant ces fibres |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0117884A1 EP0117884A1 (fr) | 1984-09-12 |
EP0117884B1 true EP0117884B1 (fr) | 1986-11-26 |
Family
ID=8190331
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP83102162A Expired EP0117884B1 (fr) | 1983-03-04 | 1983-03-04 | Fibres de plomb, leur procédé de fabrication et matériaux de protection contre les rayonnements contenant ces fibres |
Country Status (2)
Country | Link |
---|---|
EP (1) | EP0117884B1 (fr) |
DE (1) | DE3367867D1 (fr) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DK444985A (da) * | 1984-10-08 | 1986-04-09 | Johnson Matthey Plc | Fremgangsmaade ved fremstilling af metalliske materialer |
DE50113474D1 (de) * | 2001-08-28 | 2008-02-21 | Jl Goslar Gmbh | Strahlenschutzformkörper und seine Verwendung |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3967739A (en) * | 1971-11-24 | 1976-07-06 | Itogihan Company, Ltd. | Apparatus for supplying thin, flat articles |
US3845805A (en) * | 1972-11-14 | 1974-11-05 | Allied Chem | Liquid quenching of free jet spun metal filaments |
DE2461243A1 (de) * | 1974-12-23 | 1976-06-24 | Kernforschung Gmbh Ges Fuer | Bleimatte zum abschirmen von gammastrahlen |
US4190095A (en) * | 1976-10-28 | 1980-02-26 | Allied Chemical Corporation | Chill roll casting of continuous filament |
US4170257A (en) * | 1978-03-03 | 1979-10-09 | National Standard Company | Method and apparatus for producing filamentary articles by melt extraction |
-
1983
- 1983-03-04 DE DE8383102162T patent/DE3367867D1/de not_active Expired
- 1983-03-04 EP EP83102162A patent/EP0117884B1/fr not_active Expired
Also Published As
Publication number | Publication date |
---|---|
DE3367867D1 (en) | 1987-01-15 |
EP0117884A1 (fr) | 1984-09-12 |
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