Prepainted metal and the building industry: a machine manufacturer’s perspective through 40 years

The industrial use of coated coils has registered an impressive and constant growth in the past 40 years. The European Coil Coating Association (Ecca) statistical data on European production, highlight that from 1975 to 2010 the use of painted metal has increased in average 6,4% per year, form 144 million square meters in 1975 to 1,260 million in 2010. Few industrial sectors can report the same growth trend.

Production systems have evolved in parallel, with processes that had to take into account the new characteristics of painted metal, such as flexibility of the paint and resistance to abrasion.

In this article, I will cover the development and application of prepainted metal coils in the European market, and highlight micro-trends experienced in three specific fields of the building industry:

• Window frames
• Metal ceilings
• Aluminum rolling shutters

Click here for more information on roll forming machines for pre-painted materials.

Coil coating in the European market 1975-2015

From 1975 to 1990 the average growth rate has been 10,6% per year, with peaks over 30% between 1975 and 1983. Several sectors at that time were processing material that required subsequent finishing, and there was a strong will to skip the painting operation by moving to coated coils.

From 1990 to 2010 the yearly average growth rate has been 3,2%. In this case the growth is registered in square meters, corresponding to over 40 million more square meters every year.

About 70% of the production of coated coils is employed for building and construction applications (sandwich panels, rolling shutters, metal ceilings, cladding).

The cooperation between machine manufacturers with the material suppliers has been a key point for the success of the new materials: in fact, the painting applied to the base materials has several requirements:

• Resistance to the machining operations
• Flexibility of the paint for bending operations
• Consistency of the color over the years
• Resistance to wind, rain, hail, sun exposure
• Resistance to surfactants and cleaning products

In the first years, coated metals did not certainly comply to all these requirements: the coating technology had to improve its performance and processing equipment had to be adapted to the characteristics of these new materials.

Producing roll forming equipment since 1978 and focusing on painted and delicate materials, our company witnessed the evolution of the product, cooperating with research offices, experts, customers and suppliers.

The building sector has evolved, moving from standard to coated coils very quickly.

I want to focus on three industrial sectors, and show how the coated coils have been introduced and used: window frames, metal ceilings and rolling shutters.

Roll formed window and door frames

The picture below shows the evolution of a roll formed window frame.

1. Galvanized steel window frame profile (1973)
2. Galvanized and pre-treated metal window frame (1975)
3. Prepainted window frame (1977)
4. Galvanized steel window frame with thermal brake (2015)

The first profile, made out of galvanized steel, was produced in a roll forming line which could be easily closed by welding. These profiles had very well substituted the older frames in laminated steel, which had to be hot-dip galvanized to be used for external applications.

The second profile, in galvanized and pre-treated steel could no longer be welded because of the primer coating of the base metal: it had to be seamed mechanically. This profile had been improved for the application of a gasket and for improving the resistance to rainwater. The pre-treated material only needed cleaning before applying the Paint.

The third profile, in pre-painted steel is mechanically seamed: the form had to be adapted to the characteristics of the coated coil. In particular the bending radius had to respect the flexibility limits of the paint, in this case T3 (Standard EN 1396).

This standard on paint flexibility is particularly important for applications that involve the bending and roll forming of the sheet metal. In fact, if the bending radius is too small, the painted surface will show cracking that expose the metal underneath (left picture).

If the bending radius is correct, the result will appear as in the right picture, without any cracking. Prepainted window frames became very popular at the end of the seventies and until 1985.

The fourth profile is a composite element for external doors including thermal brake inserts, made out of galvanized steel. In this profile, the external elements that need to resist flection are in galvanized steel, or even stainless steel. The internal section is made out of a plastic material that creates a thermal brake and improves the thermal resistance.

Because of the strength of this composite profile, it is possible to create window frames with smaller transversal sections, improving the transparent surface of the window.

So, does this mean that prepainted materials are no longer being used for window frames? On the contrary: their use is increasing in the production of internal doors, safety doors, fire-rating doors, for all finishing profiles for window and door frames and for roof windows in coated aluminum: these are all profiles that are fully processed in line, taking advantage of the productivity of the punching and roll forming lines.

Roll-formed prepainted metal ceilings

Up to 1984 the market of metal ceilings in Italy was about 1500 tons per year, corresponding to about 1 million square meters.

In the following five years, machine manufacturers started producing compact and simple roll forming machines for slat ceilings. The equipment was supplied with 600kg of prepainted aluminum to start the production: with this integrated effort by machine manufacturers and producers of coated coils, the Italian market of metal ceilings expanded from 1500 to 9000 tons per year in 1989.

The market stabilized then to 5 to 6 million square meters per year. The metal ceilings products evolved from slat ceilings to open cell grid ceiling, T-grid ceilings and special panels, and the design of the products had to comply to new standards for reducing sound reflection (perforated panels).

At the same time, coated coils started to be used for external cladding (see picture in the header), and this further improved the use of coated coils in the building sector.

Click here for more information on roll forming systems for T-bars and metal ceilings.

Prepainted rolling shutters

In the rolling shutters sector, I want to analyze the evolution of the thickness of the material used in the international markets.

Over the years, this industry has segmented in three main markets:

1.   Premium products: high quality and resistance

2.   Quality products with 10-year warranty

3.   First price products, with low thickness and low mechanical characteristics - sometimes even hail or wind can damage the curtain

The following graph shows how the thickness of the different materials has evolved over the past 30 years.

In the rolling shutter business, different geographical markets have very different requirements: light shading, safety, privacy and so on.

In one of my next articles, I will focus on rolling shutter production systems, showing how production systems have evolved in two very different directions: high speed production systems complete with packaging, and coil-to-window customized production producing finished curtain right out of the production line.

Conclusions

As coated coils were introduced, the market urged machine manufacturers to evolve their production systems to take advantage of the leaner production cycle which eliminated the post-painting process.

In some cases such as in the external window frames, the market could take advantage of the prepainted material until new requirements (such as thermal insulation) forced to move back to galvanized materials.

In many fields, such as metal ceilings, external cladding, steel internal doors, rolling shutters and venetian blinds, prepainted metal is greatly improving the processing cycles, thanks to the cooperation between producers of coated coils, who continuously improved the mechanical performances and aesthetic of their materials, and machine manufacturers who adapted their equipment and design to comply to the characteristics of these new materials.