GB2291688A - Sheathed steel pipe with conductive plastic resin - Google Patents

Abstract

A steel pipe (1) as the building block of structures is disclosed, which comprises a pipe body (1a) formed with film of plastic resin (1b) and a strip (1c) of conductive plastic resin that is formed along the entire length of the pipe body and made integral with the resin film extruding. The conductive strip (1c) readily discharges static electricity that may develop in a structure made of such pipes that are connected to have their conductive strips end-to-end, thereby grounding the structure. This design allows less use of expensive carbon black as the conductive material to prevent electrification. In addition, a variety of colours are used in the plastic resin to form the pipe surface for decorative purpose. The steel pipe may be used in structures for roller conveyors or chute rack storage units. <IMAGE>

Description

SHEATHED STEEL PIPE WITH CONDUCTIVE PLASTIC RESIN This invention relates in general to a tubular member as the building block to make structures, and particularly to such a member composed of a steel pipe sheathed with conductive plastic resin.

Structures, such as gravity-feed chute rack storage units and roller conveyors are made of steel pipes having with a small wall thickness and a diameter of 2832 millimeters, sheathed overall with an approximately 1 millimeter-thick film of plastic resin mixed with carbon black as the conductive additive to release electrostatic charge that may occur in the structure from operation. In typical applications, these conventional pipes may be made of SPCC-1 steel with a wall thickness of 0.7 millimeter.

However, the prior-art sheathed steel pipes with conductive plastic resin have been found to pose problems. For one, carbon black normally used as the conductive material for the film layer is expensive and its black color generates limitations when designers try to give a pipe structure decorative appearance. In addition, the film layer of carbon black does not resist impact well and easily fall from the sheathed surface.

To illustrate, if the width of carbon black forming is less than 5 millimeters, the pipe fails to show sufficient conductivity to prevent electrification.

Above 15 millimeters, the pipe costs too expensive and gives poor appearance due to its black tone.

It was these drawbacks of the conventional sheathed steel pipes with conductive plastic resin that gave rise to the present invention.

Accordingly the present invention provides a pipe including a metal pipe body sheathed with a film of plastic resin, and a strip of conductive plastic resin formed along the entire length of the pipe body.

Preferably, it is an object of the present invention to provide a sheathed steel pipe with conductive plastic resin which is not expensive and can also give colorful appearance. The pipe is sheathed overall with a film of synthetic resin that may be tinted in green or ivory.

A narrow strip of plastic resin mixed e.g with carbon black as the conductive additive is longitudinally formed along the length of the pipe, over the film forming, to make the pipe conductive to prevent electrification.

Other preferred features of the present invention are described in the accompanying claims.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: FIG. 1 is a perspective view of a sheathed steel pipe with conductive plastic resin designed in accordance with a first preferred embodiment of the present invention; FIG. 2 is a perspective view of a gravity-feed chute-rack storage unit constructed into a structure of sheathed steel pipes of FIG. 1, designed to shelve printed-circuit boards; FIG. 3 is a perspective view of a sheathed steel pipe of a second preferred embodiment according to the present invention; FIG. 4 is a perspective view of a section of a roller conveyor using steel pipes of FIG. 3, showing its core components; FIG. 5 is a cross-sectional view of the part of the structure of FIG. 4.

FIG. 6 is a perspective view of a sheathed steel pipe of square cross section with conductive plastic resin according to a third preferred embodiment of the present invention; FIG. 7 is a perspective view of a sheathed steel pipe of square cross section as a modified form of FIG. 6; FIG. 8 is a perspective view of a sheathed steel pipe of square cross section according to a fourth preferred embodiment of the invention; and FIG. 9 is a perspective view of a sheathed steel pipe of square cross section as a modified form of FIG. 8.

Preferred embodiments of this invention will be described in full detail in conjunction with the accompanying drawings.

In FIG. 1, a sheathed steel pipe with conductive plastic resin 1 manufactured according a first preferred embodiment of the present invention is shown.

The tubular body la is coated externally with an approximately 1-millimeter film 1b of a plastic resin such as Acrylate Styrene Acrylonitrile copolymer (ASA).

In addition, the tubular body la has a strip of synthetic resin lc formed over the longitudinal length of the resin film 1b along the entire length of the tubular body la.

After sheathing of the resin film lb, the pipe 1 ranges in diameter between 28 millimeters and 32 millimeters.

The resin film 1b may preferably be tinted in green or ivory to give decorative appearance.

The resin strip lc may preferably comprise a conductive plastic resin, such as Acrylonitrile Butadien Styrene copolymer (ABS) mixed with carbon black as the conductive additive, and measure 15 millimeters in width and 0.5 millimeter in thickness. The conductive resin strip Ic and the plastic resin film Ib may preferably be formed integrally by press extruding.

The aim of the conductive strip Ic is to release the electrostatic charge that may occur in the steel pipes I, grounding the pipe structure in which steel pipes 1 are connected with their conductive resin strips lc aligned end-to-end.

h plurality of vertical and horizontal steel pipes 1 may be connected and assembled into a gravity-feed flo-rac storage nit to shelve printea-circuit boards, as shown in Fig. 2.

The storage unit comprises a rack framework 2 including a pair of upright sides, each build with a number of steel pipes 1 jointed end-to-end through largely L-shaped corner joints 3a, 3b, 3c and 3d which should be made of conductive metal or conductive plastic resin material, into a trapezoid.

The framework 2 may be supported on casters 4 to make the storage unit easy to move.

A plurality of T-joints 6, which are also made of conductive metal or conductive plastic resin material, couple the paired sides 5 to form the upright front and rear sides of the storage unit in which the steel pipes 1 are connected end-to-end with a plurality of T-joints 7a and cross joints 7b that are made of conductive metal or conductive plastic resin material.

With this arrangement, the front side of the storage unit, as shown in FIG. 2, has a plurality of substantially rectangular frames composed of horizontal and vertical steel pipes 1 and joints 7a, 7b between the trapezoidal sides 5.

The rectangular frames form ports 8 through which printed-circuit boards are loaded or unloaded out of the chute storage unit.

Each loading/unloading port 8 has therein a layer of leveled pairs of chute rails 9 that extend between the front and rear sides of the storage unit and tilted downward toward the front side to keep printed-circuit boards P in the manner of gravity-feed storage. In the drawing, the guide rails 9 are shown on the one side of the pairs alone for brevity's sake. With this arrangement, separate loading/unloading ports 8 in a chute storage unit may be labeled to hold different kinds of electronic boards P.

In addition, each loading/unloading port 8 is provided with a detection lamp 10 that may preferably be mounted at a mid-point in the top pipe of the port, which is lit up to help storehouse workers located particular ports 3.

Preferably, a pair of a photoelectric scanner and a mirror, both not shown, are installed at aligned locations across the loading/unloading port for each pair of chute rails 9.

The associated scanner-and-mirror combination detects the loading or unloading of a printed-circuit board P as the board blocks the beam from the scanner to the mirror when a warehouse worker is attending at a particular port 8. The scanners and the detection lamps 10 are connected through cables, not shown, to a central computer program, not shown, which keeps track of loadings or unloadings for a chute storage unit, and energizes a buzzer, not shown, to warn if an attempt is made to access the wrong port 8.

Moreover, in the bottom horizontal pipe section 1 of one of the side trapezoids 5 is provided with a largely inverted U-shaped grounding terminal 12 with a lead 11 to discharge static electricity that may develop from friction by sliding printed-circuit boards P against their respective chute rails 9 when they are loaded or unloaded. In the structure of the illustrated chute storage unit, the electrostatic charge that may occur in the steel pipes 1 will be let to discharge through the grounding terminal 12 and lead 11 via the conductive joints 3a, 3b, 3c, 3d, 6, 7a, 7b.

It must be noted that, in this particular embodiment, printed-circuit boards P are stored horizontally between chute rails 9 that are mounted in the vertical pipes of the loadingiunloading ports 8.

However, this is a matter of choice, and in a modified form of gravitv-feed storage unit, the boards P may be stored in vertical position, between the top and bottom pipes l of the ports 8.

In addition, in an alternative modification, the grounding terminal 12 and lead 11 may be replaced by casters 4 that are made of an electrically conductive plastic resin matri31 zz rund he chute storage unit.

This design would help avoid inconvenience on a scattered storage floor where the trailing lead 11 can be caught by obstructs when the storage unit has to be wheeled around.

Referring then to FIG. 3, a second preferred embodiment of a sheathed steel pipe with conductive plastic resin 16 is shown. The pipe 16 comprises a pipe body 16a having a thickness of 0.7 millimeter, sheathed in the outside surface with a 1 millimeter-thick film of plastic resin 16b, such as ASA.

A parallel pair of ribs 16c are longitudinally formed along the entire length of the steel pipe 16, and may preferably made integral with the resin film 16b. After sheathing of the plastic resin film 16b, the pipe 16 measures a range of 28-32 millimeters in diameter.

- In an alternative modification, the pipe 16 may be provided with a single longitudinal rib, instead of the paired ribs 16c.

A strip of conductive synthetic resin 16d is formed over the resin film 16b along the longitudinal length of the pipe body 16a, and preferably measure 15 millimeters in width and 0.5 millimeter in thickness. The resin for the strip 16d may preferably be an ABS mixed with carbon black as the conductive additive.

In addition, the conductive strip 16d and the plastic resin film 16b may preferably be formed integrally by press extruding. Furthermore, the strip 16d may be formed parallelly with the paired ribs 16c, spaced from the ribs for a distance of approximately one-fourth of the circumference of the pipe body 16a.

The resin film 16b may be tinted in green or ivory to give decorative appearance.

As with the earlier embodiment, the conductive strip 16d causes electrostatic charge occurring in the pipe 16 to discharge.

Preferring next to IS. t and 5, a fragmental section of one of the roller frames of a roller conveyor, using pipes 16a of FIG. 3, is shown in perspective and cross-sectional views.

The roller conveyor consists of a pair of upright side frame 17 between which a plurality of endless beltdriven rollers are rotatably disposed in a horizontal plane to carry cargoes on a moving surface, which may comprises a steel pipe 16 of FIG. 3 and a sheathed steel pipe with conductive resin material 18.

More specifically, the steel pipe 18 comprises a tubular body 18a having a wall thickness of 0.7 millimeter, formed in the outside surface with a film of synthetic resin 18b such as ASA approximately 1 millimeter in thickness. After sheathing the plastic resin film 18b, the pipe 18 measures a diameter of 28-32 millimeters in diameter.

The resin film 18 may be tinted in green or ivory.

A single stretch of rib 18c is formed along the entire length of the tubular body 18a, and may be formed integrally by extruding with the film 18b. The rib 18c is formed to have a size that allows the pipe body 18a to snap into the paired ribs 16c of the steel pipe 16 to form the roller frame 17 of dual pipes, to thereby strengthen the structure of the roller conveyor.

When a pipe 16 and a complementary pipe 18 is connected through their respective ribs 16c, 18c to form a roller conveyor side frame 17, the conductive strip 16d should be made to face inwardly in the conveyor to avoid immediate exposure of the conductive surface for safety's sake.

In the roller conveyor side frame 17, the steel pipe 16 may preferably be mounted to lay above the complementary steel pipe 18, with or without supportive legs, not shown, mounted below the frame.

A plurality of roller holders 19 made of a conduc tive composite resin material which may be composed of AbS mixed wth lac ~lac. > as the conductive additive and polycarbonate, are mounted along the steel pipe 16 of the conveyor side frame 17, at spaced intervals, on both sides of the conveyor.

Each roller holder 19 has a base member 20 composed of a C-shaped clutch 20a that snaps onto the steel pipe 16 and a largely U-shaped pocket 20b to removably receive therein the end of a conveyor roller 22 through an end member 21.

The end member 21 comprises a largely inverted L-shaped engaging member 21a and a hub member 21b that is mounted to extend perpendicular with the longitudinal axis of the roller conveyor body. The pocket 20b is engaged with the end member 21 with the perpendicular portion of the L-shaped member 21a inserted into the vertical slip of the pocket.

The roller holder 19 holds the conveyor roller 22 rotatably in the pocket 20b of the base member 20. The conveyor roller 22 is a tubular member 23 comprising a steel pipe 23a having a thickness of 0.7 millimeter, and coated in the outside surface with an approximately 1 millimeter-thick film of conductive synthetic resin 23b.

The conductive resin for the film 23b may be PE mixed with carbon black as the conductive additive.

After pipe surface extrusion with the resin film 23b, the conveyor roller 22 measures a range of 28-32 millimeters in diameter.

In addition, the conveyor roller 22 has an end cap 24 that is sized to fit into the pipe body 23 at the end of the roller. The end cap 24 is made of the same conductive resin that makes as the film 23b for the roller 22. Also, the end cap 24 has an axial hole 24b into which the hub 21b is inserted to enable the roller holder 19 rotatably hoids the roller 22 through the end member 21.

A largely inverted-U shaped grounding terminal 26 is mounted around the steel pipe 16 to ground the roller conveyor through a Dead 25.

The end cap 24 may preferably be provided with a pulley 24b that is concentrically mounted around the periphery of the end cap. The pulley 24b is driven by a drive pulley, not shown, through an endless belt of a round or V-shaped cross section, not shown, passed about the pulley 24b, to turn the conveyor roller 22 about its axis.

Static electricity developed in the conveyor rollers 22 as they turn will be discharged through the grounding terminal 26 and lead 25 via the conductive roller holders 19 and the conductive resin film 16d of the steel pipes 16 that make up the roller side frames 17.

With roller conveyors thus built according to the present invention, there will be little danger of injury for factory operators at work or damage to the products carried over the roller due to static electricity.

TABLE 1 Room Room Electrostatic potential (V) Run temperature moisture This Conventional No. ( C) (%) invention conveyor 1 25 76 0 6000 2 26 71 100 - 200 5000 - 6000 3 26 76 200 4500 4 32 63 0 - 200 7600 5 32 63 100 - 200 10500 6 27 75 200 6000 7 27 60 200 - 300 8000 8 30 50 700 8000 9 32 57 200 5000 TABLE 1 shows the result of a series of testing, carried out over a number of days under different atmospheric conditions of temo erature and moisture, to compare the readings of electrostatic potential occurring in a roller conveyor made of sheathed pipes according to the present invention and that in a conventional roller conveyor. The mean of measuring electrostatic potential is used a model KSD-0102 digital voltage gauge manufactured by Kasuga Denki KK.

The TABLE 1 shows how less electrostatic potential was in the roller conveyor of sheathed steel pipes of this invention, compared with the conventional conveyor.

In this particular embodiment, the roller side frames 17 uses a double-pipe assembly comprises conductive resinsheathed steel pipes 16 and resin film-sheathed steel pipes 18 longitudinally bonded together by their ribs 16c, 18c. However, this design is a matter of choice, and the side frames 17 may comprises a structure of sheathed steel pipe with conductive synthetic resin 16 of FIG. 3.

In an alternative modification, the side frames 17 of a roller conveyor may be a dual-pipe structure built of conductive resin-sheathed steel pipes similar to ones 1 depicted in FIG. 1 and complementary ribless resinextruded steel pipes laid parallel with the former.

The roller conveyor may not need to have conductive resin-coated pipes 16 built into on all sides frames thereof or the entire length of each side frame depending on the type of cargoes to be handled or the entire mechanical structure.

In FIG. 6, a sheathed steel pipe with conductive resin material 30, made according to a third embodiment of the invention, is shown. The pipe 30 comprises a pipe body of square cross section 30a extruded with a film 30b of synthetic resin. A longitudinal strip of conductive synthetic resin 30c is press-coated along one side of the square pipe body 30a, which is integral with the resin film 30b.

As a modified form of the resin-sheathed pipe 30, a strip of conductive resin 32c is press-extruded on the resin film 32b of the resin-sheathed pipe 32, along a corner of the pipe body 32a in FIG. 7, instead of the side of a pipe as shown in FIG. 6.

The aim and the manner in which the sheathed conductive-resin layered square pipes 30 (FIG. 6), 32 (FIG. 7), along with their general dimensions, are essentially similar to the round cross-section pipe of FIG. 1, and will not be described here for brevity's sake.

Referring to FIG. 8, a resin-sheathed square crosssection pipe 34 includes a pair of ribs 34d bonded to one side of the square tubular body 34a. The purpose of the paired ribs 34d is essentially similar to that of the paired ribs 16c of FIG. 3 and will here not be discussed for brevity's sake. The pipe 34 also includes a resin film 34b and a longitudinal conductive strip 34c all of which are similar to the round pipe 16 of FIG. 3.

With respect to FIG. 9, a modified form of the resin-sheathed square steel pipe 36 is shown, in which a conductive-resin strip 36c is formed along a corner of the square pipe body 36a. The pipe 36a also includes a film of synthetic resin 36b that is integrally formed by press extruding with the conductive strip 36c.

It will be clear from the above that a structure made of sheathed steel pipes with conductive plastic resin manufactured according to the invention is grounded to discharge static electricity that may occur in the structure. In addition, the pipe costs less since the expensive carbon black, which is used as the conductive material for grounding the pipe structure, is coated only in a narrow longitudinal strip in the pipe circumference, not the entire pipe external surface as in conventional structure pipes. In addition, the pipe according to the invention leaves a wider freedom of color design for the pipe external surface since the narrow conductive slip of black carbon leaves a wider area to brin the pipe in a variety of tints of plastic resin for at,-ac-~ve decoration.

Claims (8)

CLAIMS:

1. A pipe including a metal pipe body sheathed with a film of plastic resin, and a strip of conductive plastic resin formed along the entire length of the pipe body.

2. A pipe according to claim 1 wherein the strip is integral with the extruded plastic film.

3. A pipe according to claim 1 or claim 2 wherein the conductive plastic resin strip has a width ranging from 5 millimetres to 15 millimetres.

4. A pipe according to any of the above claims, wherein the pipe is round in cross section.

5. A pipe according to any one of claims 1 to 3, wherein the pipe is square in cross section.

6. A pipe according to any of the above claims including one or more ribs extending along the length of the pipe.

7. A pipe substantially as any one embodiment herein described with reference to figure 1 and figures 3 to 9 of the accompanying drawings.

8. A pipe framework including one or more pipes according to any of the above claims.