MXPA98000288A - Rolled formation of structural steel profiles with galvanized coating - Google Patents

Abstract

The structural steel profiles such as channels, having a material thickness greater than 2 millimeters, are formed in a roll to a predetermined profile with partially bent corners, galvanized in line, and then formed in roll in addition to the final shape. The preformed profile has convex surfaces facing up allowing a rapid detachment of excess galvanizing material. By preforming the corners before galvanizing, the elongation of the surface in the galvanization layer is minimized and the cracking is eliminated. This is improved by the constant length bending of the corners on the preform and roll forming operations.

Description

"ROLL FORMATION OF STRUCTURAL STEEL PROFILES WITH GALVANIZED COATING" TECHNICAL FIELD This invention relates to the roll forming of structural steel profiles with galvanized coating and has been particularly designed even when not only for the roll forming of profiles of a hot rolled steel strip.

BACKGROUND OF THE INVENTION It is well known to provide in-line galvanization of the steel sections such as the round tube where the section is formed to essentially the desired shape and then passed through an in-line electroplating bath or pan to provide the coating of the material galvanizing which is typically zinc. This works well for most of the closed sections but problems have been encountered with some open profile shapes, such as the channels, to obtain an even coating of the galvanizing material after the bath due to the difficulty in rapidly blowing the excess material from several areas of the section.

It has also been known to form open structural profiles of galvanized steel by taking the pre-galvanized flat steel strip and roll that strip to the desired profile, eg angle or channel sections by the conventional roll forming process. The joining of the flat strip in the roll forming process nevertheless imposes significant elongations of the outer surface of each formed corner when the strip is sufficiently thick to form a structural profile. (Through this description the term "structural profile" is taken to refer to profiles formed from a strip having a thickness generally greater than 2 millimeters). To deal with this situation, the industry standard has been to use a zinc coating where the galvanizing material incorporates alloys such as aluminum and where the base metal strip to which the galvanized coating has been applied is already formed. either through the process of cold rolling or by hot rolling, collecting and oiling. The combination of the cold-rolled steel base layer and the significant percentages of alloy in the zinc coating when properly applied according to the known processes results in a thin and useful galvanizing layer over the base metal which can support the significant elongation required in corner bending during roll forming of structural profile.

However there are three occasions in which the manufacturing process in which the zinc coating can not always be applied correctly according to the most desirable parameters and in such cases are less ductile coatings than desired which in some cases may crack due to the significant lengthening of the outer surface during the roll forming process. This problem can also exist where the strip has been galvanized in simpler electroplating operations which do not use aluminum alloys or where the parent material has a surface which can be seen as highly reactive to the galvanizing process (such as a burst strip). with shots).

When both the cold-rolled and hot-rolled base material is used it is desirable to provide a method for forming a structural section where some concession can be made for less than the ideal zinc coating parameters so that the formation of the The desired shape after the galvanization takes place does not result in unacceptable levels of cracking in the zinc layer.

The present invention therefore provides a method for manufacturing a continuous section of steel having a structural profile incorporating at least one corner of a predetermined included angle and a coating of electroplating material, said method comprising the steps of: forming a strip in roll of material to a preformed profile wherein said corner is partially bent at an included angle significantly greater than the predetermined included angle, applying said coating of galvanizing material by passing said preformed profile through an in-line galvanization phase, cooling rapidly the profile that comes out of the galvanization phase in line, and also roll up the profile to the desired structural profile.

In one form of the invention the steel strip comprises hot rolled steel strip.

Preferably the hot rolled steel strip is struck with shot to clean its surface before galvanizing.

Preferably the steps for forming the corner in the preformed profile and further forming the roll to form the corner at the predetermined included angle together comprise the constant length bending of the corner.

Preferably the preformed profile is configured such that the or each corner is partially bent at an included angle sufficiently similar to the corresponding predetermined included angle so that the formation of the additional roll of the profile to the desired structural profile does not cause a significant elongation in the coating of the galvanizing material.

BRIEF DESCRIPTION OF THE DRAWINGS In spite of any other forms that may fall within its scope a preferred form of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows a number of typical profiles capable of being manufactured by the method according to the present invention.

- Figure 2 shows the preformed profile of an attempted angle section.

Figure 3 shows the preformed profile of an attempted channel section.

Figure 4 is a partial section through a partially formed corner that is being bent according to the constant length method.

Figure 5 is a similar view showing the completed corner.

Figure 6 is a partial cross section through a partially formed corner that is being bent according to the constant radius method; Y Figure 7 is a similar view of the completed corner.

MODE FOR CARRYING OUT THE INVENTION In the preferred form of the invention, "Open profiles" so-called are formed into a roll to any desired shape incorporating at least one corner of a predetermined included angle. Such included angle is typically a 90 degree angle and the typical profiles formed according to this method are shown in Figure 1. As can be seen from the examples given a number "of different profiles can all be formed having at least one corner of 90 degrees and some with additional corners of more than 90 degrees or, in the case of the Sigma profile, corners of less than 90 degrees included angle.

The method for forming such profiles and others according to the invention is similar but will be described specifically in relation to the equal angle profile and the channel profile.

Figure 2 shows the preformed profile 1 of an equal angle section where the base steel strip has been bent to a corner having an included angle of 100 degrees before galvanizing by an in-line process.

Similarly in Figure 3 the section of a preformed channel 2 is shown wherein the two corners of the channel have been preformed by bending through an angle of 60 degrees, for example to form an included angle of approximately 120 degrees before the galvanization process. The fabric section 3 of the channel has also been formed to a convex configuration facing upwards before the in-line galvanization process.

In each case the corner, or corners of the section are partially bent at an included angle significantly greater than the included included angle in the final profile shape. In the case of the equal angle section as shown in Figure 2, the included angle of the preformed profile is 100 degrees, with significantly greater than 90 degrees of final included angle being in the equal angle section. Similarly, the included angle for each corner of the channel section is 120 degrees in the preformed section being significantly greater than the 90 degrees of the finally formed channel section. The change in the angle included between the preformed profile and the final section is therefore significant, and much greater than the few degrees of change that can take place through the formation of the roll in the reshaping to eliminate distortions that may have occurred in a galvanization of hot embedment of load of black profiles formed net or almost net.

By means of roll forming the steel strip for the preformed profiles described before the galvanization, the amount of deformation required to complete the formation of the desired profile after the galvanization is significantly limited and the amount of elongation required on the outer surface of a particular corner is therefore restricted. By restricting the elongation on the outer surface of the corner, the integrity of the galvanizing layer can be maintained.

It is also a feature of the invention that formation to the shapes shown before galvanization allows the preformed profile to be designed for ease of discarding galvanizing material from the profile either by air rings or by a cleaning process . Typically preformed profiles in the galvanizing phase can be designed to not include any horizontal flat surfaces that could result in undesirable stagnation of the galvanization layer which should be kept as thin and consistent as possible both for economic reasons and to reduce the possibility of cracking during the final roll formation to the desired last profile.

It is also preferred to roll form each corner of the profile by the "constant length" method rather than the "constant radius" method. This can be explained with reference to Figures 4 to 7 in which Figures 4 and 5 show the method of constant length of forming a fold in two phases, before and after the galvanizing operation and similarly Figures 6 and 7 show The two phases in the formation of a corner according to the constant radio method.

Even when the corner or fold shown in the Figures 5 and 7 is the same in the last profile, the method for bending results in different degrees of elongation of the metal on the outer surface of the fold. In the formation of constant length the steel is bent to a first internal radius Rp over a length of metal L. After galvanizing the corner is bent to the desired degree by tightening the bend over the same length L to a tighter inner radius Rf.

By contrast using the constant radius method of forming the bend, the folded preformed profile is first formed at the radius R over the length Lp as shown in Figure 6. After the galvanization the fold is further developed over the two sections external by doubling an additional length dL on each side of the initial length Lp to give a total bend length Lf over the same original radius R.

Using the constant radius method the outer surface of the metal over the length of the bending Lp will not require any further elongation after the galvanizing process but the outer surface over the dL lengths will require a significant elongation leading to a potential cracking in the galvanizing layer.

By way of contrast, the method of constant bending length shown in Figures 4 and 5 will require a uniform elongation of the outer surface of the metal strip in the post-galvanization bending, but this degree of elongation will be significantly less than the elongation over the bends. dL lengths in the configuration shown in Figure 7.

In order to maintain the overall amount of elongation required in the galvanization layer to a minimum and thus reduce the opportunity for cracking it is desirable to combine the bending operations previously described with reference to Figures 2 and 3, with the length method bending constant.

Using the combination of bending to a preformed profile before galvanizing and the method of constant length of bends it has been found that it is possible to reduce the elongation on the outer surface of the steel and therefore in another galvanizing layer by a significant amount and to avoid cracking in the coating of the galvanizing material on the outside of the corners.

Claims (7)

R E I V I ND I C A C I O N S

1. A method for manufacturing a continuous section of steel containing a structural profile incorporating at least one corner of a predetermined included angle and a coating of galvanizing material, said method comprising the steps of: Roll forming a strip of steel to a preformed profile wherein said corner is partially bent at an included angle significantly greater than said predetermined included angle, applying said coating of galvanizing material by passing said preformed profile through a galvanizing step in line, quickly cooling the profile that comes out of the galvanization phase in line, and also forming in roll the profile to the desired structural profile.

2. A method as claimed in clause 1 characterized in that the steel strip comprises the hot-rolled steel strip.

3. A method as claimed in clause 2, characterized in that the strip of hot rolled steel is struck with a shot to clean its surfaces before galvanizing.

4. A method as claimed in any one of any of the preceding clauses characterized in that the steps for forming the corner in the preformed profile and the formation of additional roll to form the corner to the predetermined included angle together comprise the constant length joint of the corner.

5. A method as claimed in any of the preceding clauses characterized in that the preformed profile is configured such that the difference between the included angle of the corner in the preformed profile and the corresponding predetermined included angle of the finished profile is sufficiently low to avoiding cracking in the coating of the galvanizing material on the outside of said corner during said further roll forming of the profile to the desired structural profile.

6. A method as claimed in any of the preceding clauses characterized in that the preformed profile is configured for ease of detachment of the galvanizing material in excess of the profile after passing through the in-line galvanization phase.

7. A method as claimed in clause 6 characterized in that the preformed profile is configured to eliminate any flat horizontal surfaces. E S U M E N Structural steel profiles such as channels, having a material thickness greater than 2 millimeters, are formed in a roll to a predetermined profile with partially bent corners, galvanized in line, and then roll formed in addition to the final shape. The preformed profile has convex surfaces facing up allowing a rapid detachment of excess galvanizing material. By preforming the corners before galvanizing, the elongation of the surface in the galvanization layer is minimized and the cracking is eliminated. This is improved by the constant length bending of the corners on the preform and final roll forming operations.