GB2300369A - Intumescent coating process for steel - Google Patents

Abstract

An off-site automated process for applying a fire resistant coating to structural steel comprising the steps of (i) pre-heating the steel to a pre-determined temperature sufficient to activate the curing of an intumescent material to be applied thereto, (ii) applying such an intumescent coating to the surface of the pre-heated steel and (iii) holding the coated steel in a controlled environment conducive to final curing of the coating from the steel surface outwards.

Description

COATING PROCESS This invention relates to a process of applying a fire resistant coating to a steel structure and more particularly, to an in-shop, automated process for applying an intumescent coating to a steel structure.

An intumescent coating provides a steel structure with protection from fire damage by swelling in temperatures above 2000C to form a carbonaceous char. Such coatings contain a spumific agent which decomposes together with the melting of the binder to liberate large volumes of non inflammable gases which expand the thermal insulating char typically 50 times by volume thereby protecting the underlying steel structure in the event of fire.

The on-site application of such coatings presents several problems in ambient weather conditions, wet trade overspray and solvent release all of which cause project programme difficulties.

Other methods of fire protection for structural steel have been proposed such as cementitious sprays, boards and encasement, however, none of these lend themselves to offsite application.

The present invention aims to provide an off site, automatic process for applying an intumescent fire protection coating in order to overcome or at least mitigate the above disadvantages.

According to one aspect of the present invention there is provided an off-site automated process for applying a fire resistant coating to structural steel comprising the steps of pre-heating the steel to a pre-determined temperature sufficient to activate the curing of an intumescent material to be applied thereto, applying such an intumescent coating to the surface of the pre-heated steel and holding the coated steel in a controlled environment conducive to final curing of the coating from the steel surface outwards. This has the advantage of avoiding or minimising the risk of spoiling the finish thereof, prevents premature skin formation and thereby facilitates solvent removal in a controlled manner.

According to another aspect of the invention there is provided an off-site automated process for applying a fire resistant coating to structural steel comprising the steps of conveying the steel into a coating apparatus including means for impingement and hot air blast heating of the structural steel to a temperature of about 500C, maintaining the throughput of steel therein at about 3000 kg/hr, conveying the thus heated steel into a coating chamber having means for delivering an intumescent coating material which is heat activated applying such an intumescent coating to the surface of the pre-heated steel to a controlled thickness as a single coat, and conveying the coated steel through a controlled air flow regime wherein the air temperature is in the range of from 800C to 1200C depending upon the steel section undergoing fire protection treatment.

The whole process of conveying the steel through the coating apparatus for fire protection is controllable to pass untreated steel into the apparatus and out again as fully fire-protected steel having at least 95% dry or cured coating within a period of only one hour.

Preferably the thickness of coating is about 1000 ym (wet coating thickness) and the coating is dried using a stoving oven.

Preferably the hot air used in the invention is heated by gas burners preferably located at the preliminary heating stage and optionally the hot air recovered therafter is reused or diverted to dry the coating in the final stage.

One embodiment of the present invention will now be described with reference to and as shown in the accompanying drawings in which: Figure 1 is a schematic view of a steel pre-heater used in accordance with one aspect of the invention; Figure 2 is a schematic view of a paint machine for use in the process as described; and Figure 3 is a schematic view of a stoving oven for use in the process as described.

One aspect of the present invention will now be described with reference to the accompanying Figures.

Fabricated steel (not shown) which is to be provided with an intumescent coating is blast cleaned and then fed into a pre-heater 1 as shown in FIgure 1. The steel sections are advanced towards the heater on a roller bed 2. The heater uses gas heated air as its heating medium and raises the substrate temperature of the steel from 50C to 500C. The temperature to which the steel is pre-heated is chosen according to the size and shape of the steel section. The steel is passed through the heater at a rate of about 3000 kg/hr. A further roller bed 3 carries the pre-heated steel sections from the heater.

After passing through the pre-heater, the heated steel substrate is passed through a finish paint machine 4 where a 1000y thickness, wet film of intumescent paint material is sprayed onto the substrate. The paint machine is preferably provided with 4 to 12 automatic airless spray guns (not shown) which deliver the intumescent paint from an external source to the steel section through a high pressure hose 5.

This coating is applied in one layer.

The paint machine also contains a water wall curtain system (now shown) of a standard type for the control of overspray and airborne particle removal.

After exiting the paint machine 4, the steel substrate is carried along a roller bed 6 between the coating machine 4 and a stoving oven 7 where the solvents are removed and the material is dried to 95% hard dry by weight before being removed from the oven. This drying stage is achieved by a combination of air flow over the material which is typically in the region of 10 metres per second and the heating of the material and substrate with air temperatures in the range of 800C to 1200C being used depending upon the steel section passing through the oven.

Finally, the material is removed from the oven 7 and placed onto a transfer table (not shown) for loading onto a trailer and delivery to the site.

The typical cycle time for a steel structure passing through the above process is approximately 1 hour from preheating of the steel to removal from the stoving oven.

The pre-heating and stoving of the material dries the coating from the inside out to ensure that the film does not form a skin of dry material on the surface which locks in solvents and keeps the material soft in the middle whilst being touch dry on the surface.

The thus pre-coated structural steel is then transported to the site to be erected. It will be appreciated that as the above described coating process is carried out prior to the structural steel being delivered to the site this significantly reduces the usual down time encountered in erecting the structure according to previous on-site fire-protection procedures. Furthermore, since the steel is already fire-protected on delivery there can be no time lost if the ambient weather conditions are not conducive to the drying of the intumescent coating in the field.

The coatings also provide the internal steel structure with protection against corrosion without the further requirement of an anti-corrosion primer. A sealer coat can be added to give fuller protection when required for external steel structures.

Claims (6)

1. An off-site automated process for applying a fire resistant coating to structural steel comprising the steps of pre-heating the steel to a pre-determined temperature sufficient to activate the curing of an intumescent material to be applied thereto, applying such an intumescent coating to the surface of the pre-heated steel and holding the coated steel in a controlled environment conducive to final curing of the coating from the steel surface outwards.

2. An off-site automated process for applying a fire resistant coating to structural steel comprising the steps of conveying the steel into a coating apparatus including means for impingement and hot air blast heating of the structural steel to a temperature of about 50 C, maintaining the throughput of steel therein at about 3000 kg/hr, conveying the thus heated steel into a coating chamber having means for delivering an intumescent coating material which is heat activated applying such an intumescent coating to the surface of the pre-heated steel to a controlled thickness as a single coat, and conveying the coated steel through a controlled air flow regime wherein the air temperature is in the range of from 80"C to 1200C depending upon the steel section undergoing fire protection treatment.

3. A process according to claim 1 or 2, wherein the coating is applied to a thickness of about 1000 ym (wet coating thickness) and the coating is dried using a stoving oven.

4. A process according to any one of the preceding claims, wherein the hot air used in the invention is heated by gas burners preferably located at the preliminary heating stage and optionally the hot air recovered therafter is re-used or diverted to dry the coating in the final stage.

5. A process according to any one of the preceding claims, wherein the coating is dried to 95 dry weight within a period of one hour.

6. An off-site automated process as defined in claim 1 for applying a fire resistant coating to structural steel substantially as hereinbefore described.

6. An off-site automated process for applying a fire resistant coating to structural steel substantially as hereinbefore described.

Amendments to the claims have been filed as follows 1. An off-site automated process for applying a fire resistant coating to structural steel comprising the steps of pre-heating the steel to a pre-determined temperature sufficient to activate the curing of an intumescent material to be applied thereto, applying such an intumescent coating to the surface of the pre-heated steel and holding the coated steel in a controlled environment conducive to final curing of the coating from the steel surface outwards.

2. An off-site automated process for applying a fire resistant coating to structural steel comprising the steps of conveying the steel into a coating apparatus including means for impingement and hot air blast heating of the structural steel to a temperature of about 50 C, maintaining the throughput of steel therein at about 3000 kg/hr, conveying the thus heated steel into a coating chamber having means for delivering an intumescent coating material which is heat activated applying such an intumescent coating to the surface of the pre-heated steel to a controlled thickness as a single coat, and conveying the coated steel through a controlled air flow regime wherein the air temperature is in the range of from 800C to 1200C depending upon the steel section undergoing fire protection treatment.

3. A process according to claim 1 or 2, wherein the coating is applied to a thickness of about 1000 ijm (wet coating thickness) and the coating is dried using a stoving oven.

4. A process according to any one of the preceding claims, wherein the hot air used in the invention is heated by gas burners preferably located at the preliminary heating stage and optionally the hot air recovered therafter is re-used or diverted to dry the coating in the final stage.

5. A process according to any one of the preceding claims, wherein the coating is dried to 95% dry weight within a period of one hour.