GB2332867A - Fabricating steel structural members - Google Patents

Abstract

In a method of fabricating steel structural members from a number of components the components are protected against corrosion firstly by burning off contaminants, then by shot blasting the still hot components and finally applying a corrosion protection coating to the still heated component. The coating may be less than 2 mil thick and may be applied in a spray booth and then dried with hot air. The components are formed by cutting and working structural steel shapes or steel plate. After the corrosion protection treatment they are assembled and the assembly is delivered to a paint shop.

Description

"Improvements in and relating to steel structural members' Introduction The present invention relates to the fabrication of a steel structural member.

Generally such steel structural members are formed from a plurality of steel components and the steel structural members are then assembled at a building site into a larger structure usually with bolts or rivets.

There are ever recurring problems which arise in the fabrication of such steel structural members from a plurality of structural steel components.

Firstly, in this steel fabrication it is of vital importance that the various machining operations such as drilling and boring, cutting out of slots and structural shapes be generally manufactured and fabricated to a high degree of precision. For example, machining will often be required simply to cut a structural shape to a particular size, to mill or bore openings, or possibly to even cut out intricate patterns within such steel structural shapes which, for example, could be simply flat plates, I beams, rolled steel joists, channels, angles, bars and various other components of different cross sections. These sections are generally formed in rolling mills and are bought by the steel fabricators in lengths.

The structural steel is generally cleaned to remove scale, rust and other oxidation residues, hereinafter generally oxidation residues. Often this is carried out by shotblasting which additionally hardens the steel. However, this is often carried out early on in the production process so at the time the steel is worked it has by then acquired additional oxidation residues and indeed more importantly the present shot-blasting techniques, unless a considerable amount of money is spent on them, are relatively inefficient and do not provide a particularly good or smooth outside surface to the steel.

On the face of it the fact that the steel structural component does not have a smooth outer surface would appear to be somewhat irrelevant. However, in the fabrication of steel structural members from a plurality of structural steel components it is considered good practice to prime the components formed before full assembly of the steel structural member by welding and the like. The advantage of an anti-corrosion coating such as a priming paint is that portions of the steel structural member if they should become completely encased in metal will at least have received an initial priming coat and further it will ensure, presuming that the priming coat has been put on a totally clean and oxidation residue free surface, that the subsequent paint applied will adhere to the steel and will not then flake off. However, to achieve this one requires that the surface being primed be clean of all oxidation residues, scale and other contaminants.

A further problem has been experienced when a priming coat is applied to steel structural members before they are welded in that if a relatively thick film of a corrosion protection coating priming paint or the like has to be applied to the steel, such a thick film of paint inhibits somewhat the efficiency of subsequent welding operations and also tends to put too large a coating of paint on the bores of holes, etc. which again subsequently causes difficulty either on assembly within the workshop or on erection on site. There is thus a need to achieve some method by which the initial film of a corrosion protective coating should be relatively light. Unfortunately the rougher the external surface is, the thicker the film of paint required. Not alone does the thicker film cost more, but, as mentioned already, it causes difficulty in respect of subsequent fabrication.

A further problem with a poor surface finish is that rough surface finishes tend to get damaged, even when painted, more quickly than smoother surfaces. A rough surface often causes problems with claddings and where other components have to be subsequently attached thereto.

Finally while often of relatively little practical importance the smoother surface finish is more aesthetically pleasing and thus more acceptable to the customer who tends to think that a steel structural member with a smooth surface finish must of its nature be of a superior quality.

A further advantage of having a smooth outer surface is that very often many steel structures are not clad and various portions of the steel structural member may indeed remain permanently on view and then a good and high surface finish is all important.

Another problem arises in the final painting of such steel structural members in that either they have to be painted in expensively constructed painting booths by operatives wearing protective clothing incorporating breathing apparatus, or they have to be painted out of doors which nowadays is generally unacceptable. When painted in workshops without painting booths, the environmental damage and indeed the general problems arising therefrom are such as to make such a painting method totally unacceptable. At the same time, such structural members are not by their nature adapted for any form of automatic spraying in spray booths such as may be adopted for mass produced structural frame members such as for car parts, machinery parts and the like. Almost certainly such painting has to be done by an operative carrying a spray painting gun or the like piece of apparatus. These painting methods of their nature are such that there is a considerable amount of surplus paint that does not get onto the member being painted, nor indeed it is possible in many instances to more than crudely dispose of the paint and provide totally separate spray painting enclosed areas with as much extraction equipment as can be provided, together with providing the operative with enclosed suits incorporating breathing apparatus. The amount of work that can be carried out using such breathing apparatus is considerably less than can be carried out by an operative who is not required to wear and use such equipment. All forms of breathing apparatus lead to fatigue and thus to reduced operative efficiency and performance.

A further problem is that of general mechanical handling.

To have an efficient fabrication assembly and to ensure that the various problems as listed above are tackled, it is vital that the various components can be moved around the fabrication shop easily and efficiently and further they can be moved with optimum regard to worker safety.

The present invention is directed towards providing an improved method of fabrication of a steel structural member from a plurality of steel structural components that will overcome the aforesaid problems and further the invention is directed towards providing an imported steel structural member fabricating assembly.

Statements of Invention According to the invention there is provided a method of fabricating a steel structural member from a plurality of steel structural components including a corrosion protection operation for each formed component at a corrosion protection station characterised in that the method includes: burning off contaminants and the loosening or removal of oxidation residues by applying naked flame directly to the component; a steel shot-blast mechanical cleaning of the heated component to remove any remaining oxidation residues and to flatten undesirable metal protrusions to form a smooth surface profile; and an application of a corrosion protection coating to the still heated component.

The advantage of the present invention is that an initial burning off of contaminants such as, for example, lubricating oils left by drilling operations, grease or dirt generally, together with the removal scale by heat is that all of these are removed prior to the shot-blasting operation, so that the shot-blasting operation is more efficient. Further since the steel is sent directly from the heating or burning off operation to the shot-blasting operation, the shot-blasting mechanical cleaning process is much more efficient on a dry heated component than it would be on a colder component where any scale, rust or other oxidation residues, or, indeed oil and dirt that had not been burnt off or had fallen of from the steel would have hardened again against the steel, however, since the shot-blasting takes place when the components are still warm very quickly any residue left on the steel is removed by the shot-blasting and the shot-blasting can take place to provide the smoothest possible surface on the component. Shot-blasting on a heated surface is a desirable surface treatment method. Finally, since the priming coat or application of a corrosion protective coating takes place on the still heated component, the coating will dry quicker, adhere quicker to the component and generally will provide a better and more efficient operation.

Ideally the burning off takes from 1 to 6 minutes. It has been found once burning off under direct flame takes place for up to six minutes that any possible scale, residues, etc. have been burnt off. It may not be necessary to subject the steel structural component to more than 2.5 to 3 minutes of heat.

In one embodiment of the invention the shot-blast cleaning leaves metal peaks of less than 1.5 mil. This is a relatively smooth surface which facilitates the adherence of the corrosion protection coating.

In one method according to the invention the corrosion protection coating is less than 2 mil thick. The advantage of this is that a very light coating of paint can be applied to the steel structural component because of the high surface finish provided on the steel structural component. This thin layer of corrosion protection coating ensures that subsequent operations and welding are not impeded. Ideally after the application of the corrosion protection coating the formed structural steel component is subjected to a hot air drying process.

In another embodiment of the invention prior to the corrosion protection operation, the initial steps are performed of: moving a structural steel shape to a cutting machine to cut the steel shape into the required length of basic structural component; moving the basic structural component to a metal working station; carrying out all metal cutting and forming operations at this metal working station; and moving the formed component to the corrosion protection station.

By ensuring that only one machine in effect after the initial cutting operation is used to form the structural steel component it is possible to ensure that the steel structural component is manufactured to the highest level of tolerance. The more operations carried out by separate machines, the more likelihood there is for inaccuracies to occur. It will be readily appreciated that the operation involved in transferring a workpiece to and from different machines and effecting different operations thereon as well as being time-consuming and expensive, must frequently lead to inaccuracies which are particularly exacerbated by the relatively large size of many of the steel structural components being worked on.

Unfortunately many of these errors become cumulative. It is possible that after a structural steel component has been worked on by a large number of machines in separate sequential steps that the dimensional accuracy of the steel structural component is unacceptable.

In a still further method according to the present invention prior to the application of the corrosion protection coating the initial steps are performed of: delivering steel plate to a cutting machine station to cut the plate into a required basic outline shape; moving the cut plate to a metal working station; carrying out all other metal cutting and forming operations at this metal working station; and moving the structural steel component so formed to the corrosion protection station.

Again the advantage is of one of operation on steel plates ensures that gusset plates, base plates, connecting plates and the like between different steel structural members are accurately formed so that when they are included in the subsequently fabricated steel structural member and brought out on site for erection accurate interengagement can be achieved.

Preferably according to the present invention, after the application of the corrosion protection coating: the components are collated to provide the components for the one steel structure; the components are assembled into the one steel structure; and the steel structure is delivered to a paint shop.

In one embodiment of the invention, there is provided a steel structural member fabricating assembly comprising: a cutting machine station; a metal working station; a corrosion protection station; a conveyor assembly for feeding structural steel shapes to the cutting machine and metal working stations and for feeding the structural steel components so formed to and from the corrosion protection station: characterised in that the corrosion protection station comprises: in combination a metal burning and heating station feeding directly to a shot blasting machine and in turn to a coating station.

The advantages of having the one composite corrosion protection station are manifold. Firstly, it ensures that there is not wasteful heating of components, secondly by delivering steel structural components directly from burning off and shot-blasting one ensures a rapid, accurate removal of all forms of contamination and the provision of the smoothest possible surface is achieved.

Further, by then carrying out the corrosion protection coating operation there is no time for any oxidation to occur on the steel structural component and thus it is painted at its optimum surface condition. Ideally the corrosion protection station includes a hot air painting drying means in the coating station.

Further the structural steel fabrication assembly comprises a final painting station having: a workpiece support mounted above the ground; underground extraction ducts having inlets between the workpiece support; and extractor fans for removing surplus paint into the ducts.

The advantage of this painting station will be immediately apparent since it is now possible for the painting to take place in the open, as it where, without disturbing other workers. For the operatives carrying out the painting it obviates the need for special breathing equipment or the like. Extraction through the ground is by far and away the best way of doing this, since generally speaking the spray painting will be carried out by directing spray lances or the like downwards onto the surface of the steel structural member and thus towards the ducts where any residual spray paint will be drawn away.

It has been found in practice the atmosphere is so clean as not to require the use of breathing apparatus or masks.

While masks and even some breathing equipment may be desirable heavy duty equipment will not be essential.

Ideally the ducts lead to a paint filter and recovery which allows the paint to be recycled.

Ideally the conveyor assembly comprises: a plurality of main conveyors arranged in substantially parallel and spaced apart relationship; and sets of at least a pair of parallel transfer conveyors mounted transversely between the main conveyors.

The advantage of having crossing conveyors, namely by having the transfer conveyors is that the components can be moved around the fabrication shop easily and without any risk of injury to workers.

Ideally the transfer conveyor comprises: a carrier member mounted on a carriage; means for driving the carriage; and means for raising the carrier above the carriage and the main conveyors.

By being able to raise the carrier member forming part of the transfer conveyor ensures that workpieces can be moved not just simply between adjacent parallel main conveyors, but between any parallel main conveyor.

In a further embodiment of the invention the transfer conveyor comprises: a pair of opposed channels housing carriage support wheels; a pair of spaced apart support arms each pivotally mounted at one end on the carrier and also on the carriage; an endless chain mounted adjacent and below the channels between sprocket wheels, the chain being split with one end connected to the carriage and the other to one of the support arms remote from its pivotal connection to the carriage and on the side of the carriage remote from the carrier; a chain drive; means for tensioning or slackening the chain to raise or lower the carrier.

The use of what is in effect an endless chain and combining with the drive the raising and lowering function of the carrier has been found to be most effective.

Detailed Description of the Invention The invention will be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a plan view of a steel structural member fabricating assembly according to the invention; Fig. 2 is an enlarged plan view of portion of Fig. 1 and identified by the arrow II in Fig. 1; Fig. 3 is an enlarged plan view of a corrosion protection station forming part of the assembly and identified by the arrow III in Fig. 1; Fig. 4 is an enlarged plan view of the plate metal working station forming part of the assembly and identified by the arrow IV in Fig. 1; Fig. 5 is an enlarged plan view of a paint shop forming part of the assembly and identified by the arrow V in Fig. 1; Fig. 6 is an enlarged plan view of part of the corrosion protection station according to the invention; Fig. 7 is a side view of the corrosion protection station illustrated in Fig. 6; Fig. 8 is a perspective view of portion of the paint shop; Fig. 9 is a sectional view in the direction of the arrows IX-IX of Fig. 8; Fig. 10 is a plan view of portion of the conveyor assembly used in the invention; Fig. 11 is a side view part diagrammatic view of a transfer conveyor forming part of the conveyor assembly in the raised position; Fig. 12 is a view similar to Fig. 11 showing the transfer conveyor in the lowered position; Fig. 13 is a sectional view of the transfer conveyor illustrated in Fig. 11; Fig. 14 is a sectional view of the transfer conveyor as illustrated in Fig. 12.

Referring to the drawings there is illustrated a steel structural member fabricating assembly indicated generally by the reference numeral 1 housed within a building equipped with overhead gantries not shown. Outside the building 2, there is a steel stock holding yard 3 having overhead gantries shown in outline 4 feeding three conveyors 5, 6 and 7 which project through the building 2.

Two of the conveyors 5 and 6 feed cutting machine stations 8 incorporating metal saws. Between the two conveyors 5 and 6 there is mounted a third conveyor 9.

A further conveyor 10 is provided in the building 2 and feeds to and from a corrosion protection station indicated generally by the reference numeral 11. The conveyor 9 feeds metal working stations 12. The conveyors 5, 6 and 9 also feed a further plate metal working station 13.

A plurality of cross conveyors 14 are provided between the various conveyors, 5, 6, 7, 9 and 10 to transfer from one conveyor to the other. The building 2 has a number of designated fabrication areas 15 and also incorporates a painting station indicated generally by the reference numeral 16. There are numerous transfer rollways, overhead gantries and the like for the handling of equipment and workpieces which are not identified.

The cutting machine stations 8, the metal working stations 12 and the plate metal working stations 13 are all of conventional construction and don't require any further description.

Referring now specifically to Figs. 3, 6 and 7 there is illustrated the corrosion protection station 11. The corrosion protection station 11 is mounted over the conveyor 10 and comprises a metal burning and heating chamber 30 containing a shot-blasting machine 31 which feeds directly into a spray painting booth 32 which then feeds into an air drying chamber 33. The burning and heating chamber 30 comprises a plurality of gas pipes 40 carrying burners (not shown). Extraction ducts 42 are provided.

The shot-blasting machine 31 is essentially of conventional construction and again includes exhaust ducts 43 and delivers out from the conveyor 10 into the spray painting booth 32 which again is of conventional construction and again is provided with an extraction duct 44. The spray painting booth 32 feeds directly into the hot air chamber 33.

Referring now specifically to Figs. 5, 8 and 9 the painting station 16 comprises an ordinary open portion of the building 2 which while it obviously contains air extraction ducts and the like is not specifically constructed in the conventional manner of an enclosed spray booth. The painting station comprises a plurality of trestles 50 to mounted above grids 51 which acts as the cover for ducts mounted below them. The ducts are in turn connected to air extract fans which connect with filters and paint recycling apparatus (not shown).

Referring to Figs. 10 to 14 inclusive, there is provided a conveyor assembly which comprises the main conveyors as previously described and the transfer conveyors.

In Fig. 10 there is illustrated main conveyors 5 and 6 and transfer conveyors 14. All the main conveyors are of the same construction and each main conveyor comprises a framework 60 mounting driven rollers 61 which are driven by an endless chain drive in conventional manner and do not require any further description.

Each transfer conveyor 14 comprises a pair of sets of opposed channels 70 housing between them a carriage 71 mounted on rollers 72. The carriage has mounted by pivots 74 thereon support arms 75 and 76 which in turn pivotally mount a carrier 77. One of the supports arms 75 is connected at 78 to a drive chain 80 which is led between sprockets 81 and 82 one of which is a driven sprocket, the drive being conventional. The sprocket 82 is slidable by an hydraulic ram 85 back and forth in the direction of the arrow A (Figs. 11 and 12) to tension the chain 80. The other support arm 76 has mounted thereon a chain contacting guide 86. The chain 80 is connected at 87 to the carriage 77. A return spring 90 is mounted between the carriage 77 and the support arm 75.

In use with the chain 80 in the position illustrated in Fig. 11 the carrier is raised and the transfer conveyor 14 can be used to transport steel from one main conveyor to another. Once the tension is removed from the chain 80 as illustrated in Fig. 12 the carrier 77 will be lowered.

The carriage 71 can be moved by the chain 80 in either the raised or lowered position.

In operation, structural steel shapes such as beams, channels, angles, bars and plates are delivered from the steel stock holding yard 3 to one of the conveyors 5, 6 or 7. The conveyors 5 and 6 deliver the uncut lengths which would in general be the various steel sections, angles, channels, RSJs, etc. to the two cutting machine stations 8 where they are cut to length. Then the length of structural steel is delivered to the appropriate metal working station 12 where the various cutting, drilling boring machining operations are performed. Then the formed structural steel component is delivered to the corrosion protection station 11 by the conveyor 10 and is delivered firstly into the burning and heating chamber 20 where any dirt adhering to the component is burnt off together with any oil, grease or tool lubricant which may be adhering thereto. Further any scale, rust or other oxidation residues will generally be completely burnt off so as to fall away therefrom. The steel component generally progresses through the burning and heating chamber is about 5 meters long at a relatively slow pace so that it remains therein for ideally 2.5 to 3 minutes, though in some instances this time can be reduced or increased depending on the size of the component and thus times of the order of 1 to 6 minutes are often required.

The main objective is to ensure that there is sufficient time to burn off all contaminants. The now heated component is delivered to shot-blasting machine 31 which essentially removes any residues still adhering to the surface of the component and dresses the surface so as to leave the surface relatively smooth without any metal peaks exceed 1.5 mil. Because most of the contaminants have already been removed from the component and the component is heated the shot-blasting is much more efficient than is conventionally the case. The component is hot and dry and thus the surface of the component can be easily dressed by the shot-blasting and an exceedingly smooth surface finish is obtained without any contaminants being forced back onto the surface of the component as is often the case with conventional shot-blasting. Still progressing along the conveyor 10 the components are delivered into the spray painting booth 32 where they are painted in conventional manner. Subsequently they are delivered from the spray painting booth 32 into the hot air drying chamber 33. However, because the components have a relatively smooth surface, it is possible to put the minimum amount of paint or anti-corrosion protective liquid onto the component and thus avoid any problems with subsequent handling and fabrication work such as welding.

Generally speaking the layer of paint is of the order of under 5 mil thick and preferably is under 2 mil. After the component has been treated, it can be delivered from the conveyor 10 onto the conveyor 7 and from thence to various fabrication assembly areas 15.

Where it is desired to cut plate or bend plate to form a particular section such as for example in an angle master machine, the plate is delivered from the steel stock holding yard, directly onto the conveyor 7 and down to the plate metal working station 13 where it is formed, cut, drilled, etc. in conventional manner. It can then be delivered onto the conveyor 10 for subsequent treatment at the corrosion protection station 11.

After the steel structural member has been fabricated in the relevant fabrication area 15 from the structural steel components, whether they be structural steel shapes or plates, the formed component is then delivered to the painting station 16. It should be noted that the painting station 16 as mentioned already is simply an open building. The components are laid on the trestles 50 and are spray painted by operatives using spray guns and generally speaking some form of breathing mask. Since the spraying takes place downwardly and the duct are extracting the paint downwardly through the grids 51 there is relatively little paint in the atmosphere. Thus, the painting essentially takes place in the open, without contamination of the atmosphere. The surplus paint is delivered into the ducts and from thence to the filters and extraction plant where it can be recycled.

Claims (20)

1. CLAIMS 1. A method of fabricating a steel structural member from a plurality of steel structural components including a corrosion protection operation for each formed component at a corrosion protection station characterised in that the method includes: burning off contaminants and the loosening or removal of oxidation residues by applying naked flame directly to the component; a steel shot-blast mechanical cleaning of the heated component to remove any remaining oxidation residues and to flatten undesirable metal protrusions to form a smooth surface profile; and an application of a corrosion protection coating to the still heated component.
2. 2. A method as claimed in claim 1 in which the burning off takes from 1 to 6 minutes.
3. 3. A method as claimed in claim 2 in which the burning takes from between 2.5 to 3 minutes.
4. 4. A method according to any preceding claim in which the shot-blast cleaning leaves metal peaks of less than 1.5 mil.
5. 5. A method as claimed in any preceding claim in which the corrosion protection coating is less than 2 mil thick.
6. 6. A method as claimed in any preceding claim in which after the application of the corrosion protection coating the formed structural steel component is subjected to a hot air drying process.
7. 7. A method as claimed in any preceding claim in which prior to the corrosion protection operation the initial steps are performed of: moving a structural steel shape to a cutting machine to cut the steel shape into the required length of basic structural component; moving the basic structural component to a metal working station; carrying out all metal cutting and forming operations at this metal working station; and moving the formed component to the corrosion protection station.
8. 8. A method as claimed in any of claims 1 to 6 in which prior to the application of the corrosion protection coating the initial steps are performed of: delivering steel plate to a cutting machine station to cut the plate into a required basic outline shape; moving the cut plate to a metal working station; carrying out all other metal cutting and forming operations at this metal working station; and moving the structural steel component so formed to the corrosion protection station.
9. 9. A method as claimed in any preceding claim in which after the application of the corrosion protection coating: the components are collated to provide the components for the one steel structure; the components are assembled into the one steel structure; and the steel structure is delivered to a paint shop.
10. 10. A steel structural member fabricated in accordance with the method of claims 1 to 9.
11. 11. A steel structural member fabricating assembly of the type comprising: a cutting machine station; a metal working station; a corrosion protection station; a conveyor assembly for feeding structural steel shapes to the cutting machine and metal working stations and for feeding the structural steel components so formed to and from the corrosion protection station: characterised in that the corrosion protection station comprises: in combination a metal burning and heating station feeding directly to a shot-blasting machine and in turn to a coating station.
12. 12. A steel structural member fabricating assembly as claimed in claim 11 in which the corrosion protection station includes a hot air painting drying means in the coating station.
13. 13. A steel structural member fabricating assembly as claimed in claim 11 or 12 in which there is provided a final painting station having: a workpiece support mounted above the ground; underground extraction ducts having inlets between the workpiece support; and extractor fans for removing surplus paint into the ducts.
14. 14. A steel structural member fabricating assembly as claimed in claim 13 in which the ducts lead to a paint filter and recovery unit.
15. 15. A steel structural member fabrication assembly as claimed in any of claims 10 to 13 in which the conveyor assembly comprises: a plurality of main conveyors arranged in substantially parallel and spaced apart relationship; and sets of at least a pair of parallel transfer conveyors mounted transversely between the main conveyors.
16. 16. A steel structural member fabrication assembly as claimed in claim 15 in which the transfer conveyor comprises: a carrier member mounted on a carriage; means for driving the carriage; and means for raising the carrier above the carriage and the main conveyors.
17. 17. A steel structural member fabrication assembly as claimed in claim 16 in which the transfer conveyor comprises: a pair of opposed channels housing carriage support wheels; a pair of spaced apart support arms each pivotally mounted at one end on the carrier and also on the carriage; an endless chain mounted adjacent and below the channels between sprocket wheels, the chain being split with one end connected to the carriage and the other to one of the support arms remote from its pivotal connection to the carriage and on the side of the carriage remote from the carrier; a chain drive; means for tensioning or slackening the chain to raise or lower the carrier.
18. 18. A steel structural member fabrication assembly as claimed in claim 17 in which the other support arm projects below the carriage to slidably engage the chain.
19. 19. A steel structural member fabrication assembly as claimed in claim 17 or 18 in which the carrier is spring biased to lie on the carriage.
20. 20. A steel structural member manufactured in the steel structural fabrication assembly as claimed in any of claims 11 to 17.