Color-coated sheets, also known as organic-coated sheets or pre-coated steel sheets, are made from a metal coil that serves as the base material (cold-rolled sheets, hot-dip galvanized sheets, aluminized sheets, high aluminum alloy sheets, stainless steel sheets, etc.). The surface is coated or laminated with various organic coatings and plastic films.
These plates find wide application in the production of household appliances, furniture and sheet metal parts for curtain walls. However, they are not commonly used in elevator manufacturing.
In the following section, I will summarize my understanding of color coated sheets and share my company's experience in using them. I hope this information will help my colleagues in the elevator industry better understand the characteristics and characteristics of these raw materials.
The colored sheets (as shown in Figure 1) go through a spraying process in the raw material phase, which gives them a structure composed of substrate, chemical conversion layer, primer and finish.
Figure 1 Schematic diagram of the painted panel section structure
The basic structure and surface coating process are the same.
In terms of substrate selection, options include cold-rolled steel sheet, hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet, depending on the intended use environment.
For specific characteristics and application scenarios of each substrate, see Table 1.
Table 1 Characteristics and application scenarios of various substrates
| Substrate type | C characteristic | The applications |
| Cold rolled steel sheet | Low corrosion resistance and low cost alone | Coating of metal parts of furniture, lamps, electrical boxes, etc. |
| Galvanized steel | It has a thicker zinc layer, suitable for preparing colored plates with high corrosion resistance and low decorative requirements. | Exterior cladding, roof panels, garage doors, etc. |
| Hot Dip Al-Zn Steel Sheet | The production process is the same as that of hot-dip galvanized steel substrates, mainly regulating the composition of the cast coating solution, classified by the amount of aluminum content. | More corrosive external environments |
The production process of colored foil coating
The production process of color coated sheets has evolved from a single coating and baking process to a double coating and baking process. Today, the most commonly used processes involve two coatings and two firings, while some applications require higher levels of protection involving three coatings and three firings.
To enhance the color options available for these sheets, an embossing or transfer process can be added to the original solid color flat sheet. This process allows the production of more personalized and exclusive color-coated sheets.
Depending on the type of product, color coated sheets can be divided into three categories: coated sheets, embossed sheets and printed sheets, as illustrated in Figure 2.
(A) Coated sheets
(B) Embossed leaves
(C) Sheet printing
Figure 2 Types of color coated board products
The production processes of the three types of color plates mentioned above are similar, but the difference lies in the painting process.
The production process of colored sheets involves the substrate entering the equipment in the form of a coil and connecting it with the previous roll of raw material through the first sewing process, which mainly involves welding.
Subsequently, the board goes through the looping process to release tensions and adjust flatness, eliminating internal tensions, preparing for the application of the primer.
The material then undergoes surface pre-treatment, where treatment liquid is sprayed to passivate the surface, followed by priming and baking. This step is similar to the spraying process.
Then comes the fine coating process, where the difference lies in the production processes of the three types of colored sheets mentioned above.
In the thin coating process, common coated panels are mainly painted, and aluminum powder or zinc powder can be added to the coating to achieve particle effects if necessary.
For engraving plates, a corresponding pattern roll is added at the output to complete the engraving process.
For printing plates, transfer film technology is used in the thin coating process to obtain the established pattern.
After the board is sprayed, a protective film is coated and flattened. Figure 3 illustrates the process vividly.
Figure 3 Color coated sheet process
To improve the efficiency of the painting process, color coated sheets are now produced using roller coating instead of pneumatic guns. This method offers several advantages, such as high production efficiency and uniform film thickness. However, it also has unique coating defects that must be taken into consideration.
For a detailed analysis of quality defects and their corresponding causes in color coated sheets, see Table 2.
Table 2 Quality defects and cause analysis of color coated sheets
| No. | Defect | Phenomenon | Causes |
|---|---|---|---|
| 1 | The roller paint surface is not smooth | The finished product is backlit and the visible indentation is irregular along the running direction of the plate | Irregular Coating Roll |
| Wrong roller speed ratio | |||
| Inadequate coating roll hardness | |||
| Problem with thinner | |||
| two | Omission | Partially unpainted on painted surface | The original board is of poor quality |
| Coating roll deformation | |||
| Inadequate belt roller speed pressure | |||
| 3 | Convex | Rounded or oval bumps on the painting surface | The original degreasing effect of the plate is not good |
| Water on the painted surface | |||
| Poor paint defoamer | |||
| 4 | Cavity | Visible background color or round shape on painted surface | Bubbles during painting |
| Foreign matter on the surface of the coating roller | |||
| 5 | Uneven film thickness | The surface of the finished product is flaky | Paint leveling is not good |
| Belt roller parameter setting is not good | |||
| Inadequate paint viscosity | |||
| Paint roller damage | |||
| 6 | Particles | Particles appear on the board | Dust, foreign bodies, particles |
| Mixed in paint | |||
| Dirty roller surface | |||
| 7 | Holes, bubbles | Small holes appear on the surface of the paint film due to solvent evaporation | Incorrect film thickness adjustment |
| Inadequate curing temperature | |||
| Incorrect adjustment of ink viscosity | |||
| 8 | Pickling | After the colored steel coil is opened, the ink will fall off after rubbing a little | The moisture and cooking time of the paint are not enough |
| 9 | Color difference | Different color from the standard plate | Insufficient agitation |
| Inadequate curing temperature | |||
| The paint color is incorrect |
Advantages and Disadvantages of Color Coating Sheet Application
Color coated card material has diverse applications in different industries, which depend on its specific characteristics.
Due to its limitations and lack of compatibility with most elevator production processes, color coated sheets are not widely used in the elevator industry.
Sheet metal components used in elevator manufacturing are primarily found in elevator cabs, door systems, and control cabinets. These parts commonly undergo welding processes and require a high standard of appearance quality.
Most elevator companies continue to organize their production in a decentralized manner, which increases the risk of damage to raw materials during transport.
Additionally, the ability to resist corrosion should be considered for parts with an emphasis on appearance.
The production characteristics of elevator sheet metal parts restrict the use of color-coated sheets to a certain extent.
Color coated sheets used in the elevator industry have some shortcomings, listed below:
(1) Slightly lower forming performance
The main raw material used for color coated sheets is galvanized sheet, which has a harder material characteristic than cold-rolled sheets. In addition, to protect the surface coating of the material, a protective film is added to the surface of the raw material. Sheet metal parts processed with film require greater flexibility of the coating film. These situations affect the bending process and can impact bending accuracy.
(2) Notch corrosion
Because color coated sheet is first coated with paint before the product is manufactured, it can appear similar to the corrosion of galvanized sheets. Although it does not affect the appearance or use of the surface, its performance in the salt spray test may not meet the requirements.
(3) Poor welding performance
After the color coated card product is processed and formed, the surface of the paint film is covered with an insulating protective film. Therefore, the processing of color coated plates cannot apply the welding process. If the welding process is forced onto the product, serious welding defects and occupational health and safety problems may occur.
(4) Plate thickness limitation:
The process of producing colored panels requires the material to have good flexibility, as it needs to be coated with a roller. In the past, the thickness of color coated sheets was limited to 1 mm. However, after process improvements, the thickness of color-coated boards was increased to 1.5 mm. Although increasing board thickness expands application scenarios, it also significantly increases production costs. Therefore, there are very few color coated sheets above 1.5mm available on the market.
(5) Process dispersion can easily lead to product defects:
Both color-coated sheets and brushed stainless steel require surface coating. However, the surface of color-coated sheets is more fragile and cannot be repaired once scratched. If the dispersion process is used for production, multiple loading, unloading and rotation will make the surface of the color-coated sheet vulnerable to scratches. Unfortunately, this quality defect is irreversible, making color coated sheets subject to quality risks during use.
The limitations of color coated sheets limit their application range. However, its advantages are significant. The most significant benefit of using color-coated sheets is that the product can be shipped directly after being offline, without spraying or outsourcing. This reduces cycle time and inventory of semi-finished products and reduces backlog, which is crucial for companies seeking low inventories.
The following points demonstrate the advantages of using color coated sheets:
- In light of increasingly serious environmental problems, many spray plants are being closed due to environmental audits, leading to supply disruptions. However, as the production of colored coated sheets is carried out in steel mills using environmentally friendly materials and with a high rate of material utilization, their production is not significantly impacted by environmental inspections.
- Thanks to its efficient production process, the cost of using color coated sheets is lower than the comprehensive cost of steel spraying.
- The coating process is continuous and the equipment strictly controls the film thickness and color difference, ensuring excellent product consistency. Additionally, materials from the same manufacturer typically do not present color difference issues, which makes them particularly important for elevator doors and wall panels, where a uniform appearance is crucial.
- The base material of color coated sheets is galvanized sheet, and together with surface coating paint, its surface anti-corrosion ability is much stronger than that of steel sheet spray paint.
Application of color coated board in elevator industry
To effectively avoid deficiencies and take advantage of color-coated plates, elevator companies must match their use to their specific conditions.
One of the disadvantages of color-coated sheets is poor welding performance and susceptibility to scratches. However, the use of automated production equipment can significantly reduce these problems.
In our company, we use fully automated production models, which involve the use of automation equipment and robots to produce colored coated elevator door panels. By eliminating the head structure and replacing the welding process with a riveting process, we can effectively avoid the problems mentioned above.
During the application process, the mechanical properties of color coated plates remain stable and abnormal processing conditions are rare.
In our real-world tests, color-coated boards showed better yield strength than SPCC boards and also exhibited smaller deformations in elevator door impact tests.
As our company does not have a spraying production line and outsourcing is necessary, the use of colored sheets reduced our production cycle and almost 40% of our stock of semi-finished products by three days. This has brought significant benefits to our company.
There are, of course, four issues we need to address when using color coated sheets:
(1) Since color coated sheets are not conventional sheets, their prices have no reference point. Therefore, users need to communicate closely with suppliers regarding any price changes.
(2) It is essential to pay attention to the choice of protective film, especially when using automated production. Protective film selection is critical due to the significant safety risks associated with film release.
(3) If choosing two or more suppliers to supply color coated sheets of the same color, a color difference standard should be formulated. The key here is to improve your color palette management.
(4) As there is a minimum purchase value for raw materials, it is not viable to use colored plates for all of the company's products. This can result in a significant buildup of materials.
Completing missions
Competition in the elevator market is becoming increasingly fierce, and product cost has become an important factor, in addition to product performance, for companies to gain a competitive advantage.
To stay ahead in the market, many manufacturers try to make a difference by focusing on the raw materials used in their products. Responding to market changes, 443, 201, color coated sheets and composite steel sheets were introduced into the elevator industry.
Compared to other types of sheets, color coated sheets have the advantage of reducing costs and improving quality in certain scenarios. However, for companies to achieve such effects, they need to have sufficient production capacity and technical capabilities to support them.
In the author's opinion, the use of color coated sheets is a reasonable product improvement plan. However, it is important to highlight that not all companies are able to achieve the same results.
Therefore, it is crucial that the reader analyzes their own situation realistically and finds a set of applications that are beneficial to their business.
