EP0531959A1

EP0531959A1 - Improved silenced device for blowing hot-dip-galvanized pipes

Info

Publication number: EP0531959A1
Application number: EP92115388A
Authority: EP
Inventors: Andrea Caronia; Giuseppe Brugali; Sergio Fulceri
Original assignee: TUBI DALMINE ILVA Srl
Current assignee: TUBI DALMINE ILVA Srl
Priority date: 1991-09-10
Filing date: 1992-09-09
Publication date: 1993-03-17
Also published as: ITRM910671A0; IT1249695B; ITRM910671A1

Abstract

The invention provides, for silencing the blowing of galvanized pipes, the inventive combination of a mobile element for gradual expansion of the steam with pressurization of the chamber for receiving the partially-expanded steam. In this manner the operating noise level can be reduced from over 130 db to less than 100 db.

Description

The present invention concerns an improved silenced device for blowing hot-dip-galvanized (HDG) pipes. More precisely, it concerns a device provided with a partial-expansion chamber for the blown steam, combined with a second chamber in which air is blown.
After pipes have been hot-dip-galvanized in a bath of molten zinc they are extracted and steam is immediately blown into them in order to produce a smooth inner surface that is free from runs and drips of solid zinc. The operation, which is known as blowing, is performed by introducing a violent jet of steam into one end of the pipe after the other end has been directed towards a box designed not only to permit expansion of the steam but also to collect the zinc that is blown off the inside of the pipe.
Though the operation is effective, its major drawback is that it is extremely noisy; indeed, it can be intolerable to the human ear. For large-diameter pipes the noise can easily exceed 130 db.
German patent 2 444 944 proposes to couple the free end of the pipe to a conical funnel heated to about 400°C, mounted on a plate forming part of a sound-proofed expansion box.
German patent 2 810 493 takes up the subject again, stating that the above solution cannot be utilized because of the need to heat the metal funnel and the fact that it only has a limited life, since it is subjected to continuous abrasion by the high-velocity zinc particles. The proposed solution apparently consists essentially in allowing the steam to expand in a closed sound-proofed chamber connected to the pipe via an opening and a movable collar fitted to the free end of the pipe.
British patent 2 081 836 proposes the use of a silencer located after the chamber which receives the free end of the pipe and collects the steam-borne zinc particles.
Another drawback of the known devices consists in that the zinc particles entrained in the steam are deposited as a condensate-moistened mass on the walls and on the bottom of the collection chamber. In this state the zinc readily oxidizes so it cannot be reused directly; indeed it is a downgraded recovery material whose market value is far lower than that of zinc metal.
The object of the present invention is to eliminate the drawbacks typical of the known installations for blowing galvanized pipes, by providing a simple, robust device that ensures a considerable reduction in the noise level of the blowing operation of the galvanized pipes, while at the same time permitting recovery of the dry zinc oxide dusts and zinc metal particles removed from the inside of the pipes.
According to the present invention, in a blowing plant for HDG pipes including a box with an opening to accommodate one end of the pipe to be blown, a steam-blowing device and a flue to remove fluids from the box, an improvement is introduced which consists in the coupling of an initial gradual partial-expansion chamber to a second total-expansion chamber, the latter being complete with pressurizing means.
The first chamber consists of an axially-mobile cylindrical tubular metal body with a flared internal cavity, set at the opening of the expansion chamber, the smaller part of the flare being directed towards the outside of the body and the larger part towards the inside of the chamber.
The second chamber consists of the expansion chamber, as known, while the pressurizing devices consist of means that are suitable for blowing air into the chamber. At least some of the air blowers are set inside the box so as to form a rising current of air directed towards the flue which, in its path, passes close to the larger opening of the cavity of the cylindrical metal body.
Other openings can be made in the box so that ambient air can be sucked inside the box as a result of the rising current of blown air.
The length-diameter ratio of the tubular body can advantageously be between 5/1 and 10/1, while the ratio between the areas of the larger and smaller openings of said flared cavity is in the 3/1 to 1.5/1 range.
Furthermore, the tubular body has a lapped inner surface and is equipped with vibration means.
With this structure the tubular body permits gradual partial expansion of the pressurized steam blown into the pipe to be treated, while the lapping of the internal surface and the vibration means virtually prevent particles of steam-entrained zinc from adhering to said inner surface or from damaging it.
Inside the total-expansion chamber there are inclined gratings positioned essentially at right-angles to one another and converging towards a horizontal screw whose axis is parallel to a plane containing the larger opening of the cavity practised in said tubular metal body. A metal plate is interposed between the end of the metal body, inserted in the chamber, and the grating facing onto said end and parallel thereto, so as to prevent steam-entrained zinc particles from blocking said grating, while at the same time permitting the blown air to pass beyond the grating without obstruction.
The present invention will now be described in relation to an embodiment a schematic view of which in a partially cutaway elevation is illustrated in the accompanying drawing purely for the purpose of exemplification and in no way limiting.
Box 1 defines a total-expansion chamber 2 and is provided with an opening 3. A tubular cylindrical body having a flared internal cavity forming a gradual partial-expansion chamber 4, has a smaller opening 5 and a larger opening 6, the end with opening 6 facing onto opening 3 into which it can be introduced; body 4 can be moved axially on guides with wheels or rollers 15 moved by a hydraulic ram 11 to accept in the smaller opening 5 one end of the pipe 7 to be blown. In body 4 openings 5 and 6 are suitably connected together to form a flared initial gradual partial-expansion cavity.
Body 4 also has a vibration means 10 which prevents the molten or pasty zinc particles from sticking to the inner walls which, moreover, are suitably lapped.
Inside the total-expansion chamber 2 there is a first grating 12 and a second grating 13 which are essentially perpendicular to one another and converge downwards towards a screw 16 whose shaft is horizontal and essentially parallel to the plane containing said opening 3. Between grating 13 and opening 3 there is a plate 14 parallel to and at a suitable distance away from grating 13.
Total-expansion chamber 2 also has means 17 for admitting air blown in under pressure and another opening 9 for the admission of ambient air which is sucked in by the stream of air coming from means 17.
In addition, the total-expansion chamber 2 has an opening 18 which communicates with flue 8 for evacuating the blown air.
In use, a metal pipe 7 is withdrawn from the HDG bath and rapidly positioned at the blowing station; the cylindrical metal body 4 is advanced by ram 11 and guides 15, so that one end of the pipe to be treated is inserted in the smaller hole 5 of said body, whose end with opening 6 must be inserted in opening 3 of the total-expansion chamber 2. At the same time air is blown into the total-expansion chamber 2 to form a rising current.
As already known, steam is introduced at high velocity into the galvanized pipe 7, so as to carry away any excess coating or drips or runs, etc. of molten zinc. The steam blast expands gradually and partially within tubular body 4 and finally, within the total-expansion chamber 2, where it encounters high pressure due to the air blown by means 17, thus greatly limiting the noise of the operation. On the other hand, the blown air not only helps to deaden the noise of the blowing, it also carries any very fine zinc particles through flue 8, so that these can be properly recovered downstream of the plant, while the largest particles fall towards plate 14 from whence they are conveyed towards screw 16 which transports them outside to be recovered.
As already indicated, this invention not only results in a considerable reduction in the noise involved in the blowing operation, it also has the important advantage of ensuring recovery of the steam-blown zinc, because the zinc particles are dried by the blown air, thus limiting oxidation, unlike what happens in the state-of-the-art technique where the zinc particles can build up in large wet masses where they are radically oxidized.
In a plant operating as per the invention, the following reductions in average noise levels have been measured using a manual noise-meter in a series of fixed positions located between four and eight meters from the blowing station:

Pipe dia. (inches) dBA before the invention dBA after the invention

1/2 113 93

3/4 118 94

1 126 96

1 1/4 128 96

1 1/2 > 130 95

2 > 130 96

2 1/2 128 96

3 125 95
The average level of oxidation of the blown zinc is 65% in the case of the invention, while previously it was around 95%.

Claims

Improved silenced device for blowing hot-dip-galvanized pipes (7), comprising a box (1) with an opening (3) which accomodates one end of the pipe (7) to be blown, steam-blowing means and a flue (8) to carry away the gaseous fluids from the box (1), characterized by the fact of including a coordinated coupling complex consisting of:
- an initial gradual partial-expansion chamber (4) in communication with

- a second total-expansion chamber (2)

- means (17) for pressurizing at least said second total-expansion chamber (2).
Device as per claim 1, characterized by the fact that the first gradual partial-expansion chamber (4) is formed by an axially mobile cylindrical tubular metal body having a flared internal cavity positioned opposite the opening (3) in the box (1), the smaller opening (5) of the flare being towards the outside and the larger one (6) towards the inside of said box (1).
Device as per claim 1, characterized by the fact that said means (17) for pressurizing at least the second total-expansion chamber (2) consists of devices for blowing air into the chamber itself and are at least partially positioned within the box (1) so as to form a current of air directed towards the flue (8).
Device as per claim 2, characterized by the fact that the length-diameter ratio of said tubular metal body is between 5/1 and 10/1, and the ratio of the areas of the larger (6) and smaller (5) openings is between 3/1 and 1.5/1.
Device as per claim 4, characterized by the fact that said tubular metal body has a lapped internal surface and means (10) for vibrating it.
Device as per claim 1, characterized by the fact that said box (1) contains inclined gratings (12,13) which are essentially perpendicular to one another and converge downwards towards a horizontal screw (16) whose shaft is parallel to a plane containing said larger opening (6).
Device as per claim 6, characterized by the fact that a metal plate (14) is interposed between said larger opening (3) and the grating (13) opposite to it, said plate (14) being parallel to and some distance away from said grating (13).