What is a pre-painted steel coil?

The pre-painted steel coil is a roll of thin steel plate coated with paint, supplied in rolls or sheets as a unit to the barrel factory to be used directly in the production of steel plates without further coating. The substrate steel plate is generally a 0.2–2.0 mm thick steel coil, with a maximum width of up to 2 m. Mainly cold-rolled steel, hot-dip galvanized, or electro-galvanized steel plate. Here is Ral 1050 Galvanized Prepainted Steel Coil.

Development and application of pre-painted steel coil

Pre-painted coil technology was initially developed in the 1930s in the United States. The first is an alkyd resin paint applied to a 0.2mm thick, 50mm wide steel strip used to replace the board for the window panel shutters. Recovery from the trauma of WWII led to the building industry's prosperity after the war. Taking advantage of this opportunity, a pre-coated coil was produced as a lightweight and low-cost building material. Simultaneously, when the postwar economy recovered, scientific and technological achievements in the production of pre-coated coils offered a material and technical foundation.

At present, there are more than 300 pre-coated coil production lines in the world, with an annual production capacity of 15 million tons. The field of use has been expanded from building materials to automobile manufacturing, ship interior decoration, household appliances, containers, drinking utensils, and other aspects. Currently, at home and abroad, it has begun to be used in the field of packaging, especially in the metal container manufacturing industry, which is popularizing the application.

The main reason for the rapid development of precoated coil is that it has good economic benefits and adapts to the needs of social and economic development. First of all, it will be the traditionally manufactured products coated into raw materials, steel plate continuous coating, not only to facilitate the surface treatment and coating quality control but also because it is not easy to produce coating defects at the edges of the dead ends and get the best coating quality. Secondly, the traveling speed of the thin steel plate in the coating line is generally 40–100 m/min; the fastest has reached 240m/min, and the production efficiency is far greater than the finished product coating.

Third, when the paint film is curing, the painted flat plate in the oven, through the furnace capacity utilization rate, is higher than the finished product coating. Baking volatile solvents can be collected and introduced into the burner incineration, where they will be reused as heat, resulting in a total energy consumption of only one-fifth to one-sixth of the finished product coating. Finally, the emissions from the production are easy to centralize, such as the oven exhaust gas being treated by the incinerator, and the organic solvent content is less than 50 ppm.

Pre-painted steel coil production process

The production process of pre-painted steel coil is mainly divided into three major parts, i.e. introduction, pretreatment, painting, and lead-out.

1. Introduction

Introducing equipment such as uncoiling, shearing, stitching, storage sleeves, etc., which loosens the raw material coils and connects them to supply thin steel sheets to the unit continuously and at an even speed.

2. Pre-treatment

The role of pretreatment is to clean the coated steel plate and apply surface treatment, to improve corrosion resistance and adhesion of the paint film.

3. Painting

The coating is the heart of the unit, and it typically coats two baking operations at the same time, namely coating primer, baking, coating paint, and baking. Because of the various requirements of the items, they can also be coated on only one baking or only one side. Paint is typically applied using a reverse roller coating structure. The advantage of this method is that you may acquire a variety of paint film thicknesses by modifying the thin steel plate traveling speed and paint roller speed ratio, as well as the paint roller and paint roller gap.

To get a good view of the full curing of the film, the oven temperature is controlled in sections; the temperature of each section is determined by the variety of paints used, the thickness of the steel plate, and the time through the oven. Because it is a double-sided coating, after coating the steel plate in the furnace, it cannot have support, so the general use of a hanging or air-floating oven.

After adding laminating machinery, some materials require a top-coat furnace in addition to liquid paint. You can laminate plastic film on the base plate, then coat and activate the adhesive using the top coat roller coating machine and baking oven. The coating can be printed or embossed once other auxiliary devices are attached. A coating of peelable protective film or a layer of wax is applied to the pre-coated board to protect the paint film during transit, processing, and installation.

4. Lead out

Lead out will be the product in rolls or cut into single sheets according to the required size.