Color coated plates are also called organic coating sheet or pre-coated steel sheet.
It is made of the metal coil (cold-rolled sheet, hot-dip galvanized sheet, aluminized sheet, high aluminum alloy sheet, stainless steel sheet, etc.) as the base material, coated or laminated with various organic coatings and plastic films on the surface.
It is widely used in the production of home appliances, furniture, and curtain wall sheet metal parts, and it is not used much in elevator manufacturing.
In the following, I will compile and summarize my understanding of color coated sheets and my company’s experience in the process of using color coated sheets, to hope colleagues in the elevator industry will have a better understanding of the characteristics and features of such raw materials.
Color coated sheet (Figure 1) is actually the processing of the spraying process at the raw material stage, its structure consists of substrate, chemical conversion layer, primer and topcoat.
Figure 1 Schematic diagram of the section structure of the painted panel
The basic structure and surface coating process are the same.
In the choice of substrate, cold-rolled steel sheet, hot-dip galvanized steel sheet, and hot-dip galvanized steel sheet can be selected as the substrate due to the different use environment.
Specific characteristics and application scenarios of various substrates are shown in Table 1.
Table 1 Characteristics and application scenarios of various substrates
|Cold rolled steel sheet||Poor corrosion resistance and low cost on its own||Lining parts of metal furniture, lamps, electrical boxes, etc.|
|Galvanized steel||It has a thicker zinc layer, which is suitable for the preparation of color-coated boards with high corrosion resistance and low decorative requirements.||Exterior siding, roofing panels, garage doors, etc.|
|Hot-dipped Al-Zn steel sheet||The production process is the same as that for hot-dip galvanized steel substrates, mainly regulating the composition of the molten plating solution, classified by the amount of aluminum content.||More corrosive outdoor environments|
The production process of color coated sheet
The production process of the color-coated sheet has developed from one coating and one baking to two coating and two baking.
Nowadays, most of the commonly used processes are two-coating and two-baking, and there are also three-coating and three-baking processes that require higher protection.
In addition, in order to enrich the color of the sheet, an embossing or transfer process is added to the original solid-color flat sheet, so that the color-coated sheets can produce more personalized products.
Color-coated sheets can be divided into three types: coated sheets, embossed sheets and printed sheets according to product types, as shown in Figure 2.
(A) Coated sheets
(B) Embossed sheets
(C) Printing sheets
Figure 2 Color-coated board product types
The production processes of the above three types of color coated sheets are similar, but the difference lies in the process of coating paint.
The production process of the color coated sheet is that the substrate enters the equipment in the form of a coil, and is connected with the previous roll of raw material through the first stitching process.
The process used in the stitching process is mainly welding.
Then the plate enters the looper process to release the stress of the plate, and adjust the flatness by releasing the internal stress, thereby preparing for the spraying of the primer.
Afterward, the material undergoes surface pretreatment (surface treatment, that is, the process of spraying the treatment liquid to achieve surface passivation), primer coating and baking.
This step is basically the same as the spraying process.
Then there is a fine coating, and the process difference of the three types of color-coated boards mentioned above lies in this.
Ordinary coated panels are mainly paint coating in the fine coating process.
If there is a requirement to achieve particle effects, aluminum powder or zinc powder can also be added to the coating.
The embossing plate adds a corresponding pattern roller at the exit to complete the embossing process.
For printing plates, transfer film technology is used in the fine coating process to obtain the established pattern.
After the plate is sprayed, the material will be coated with a protective film and flattened.
A more vivid process is shown in Figure 3.
Figure 3 Process of color coated sheet
In order to make the paint coating process more efficient, the production of color coated sheets adopts roller coating instead of pneumatic spray guns.
Its advantages are high production efficiency and uniform film thickness, but there are also unique coating defects.
The quality defects and cause analysis of color coated sheets are shown in Table 2.
Table 2 Quality defects and cause analysis of color coated sheets
|1||Roller paint surface is not smooth||The finished product is backlit and visible indentation is uneven along the running direction of the board||Uneven coating roller|
|Wrong roller speed ratio|
|Unsuitable coating roller hardness|
|Problem with thinner|
|2||Omission||Partially not painted on the painted surface||The original board is of poor quality|
|Deformation of coating roller|
|Improper pressure of belt roller speed|
|3||Convex||Rounded or oval bumps on paint surface||The original board degreasing effect is not good|
|Water on the painted surface|
|Poor defoaming of paint|
|4||Cavity||Visible background color or round shape on the 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 scaly||Paint leveling is not good|
|The parameter setting of the belt roll is not good|
|Improper paint viscosity|
|Paint roller damage|
|6||Particles||Particles appear on the board||Dust, foreign matter, particles|
|Mixed into paint|
|Unclean roll surface|
|7||Pinholes, bubbles||Small holes appear on the surface of the paint film due to solvent evaporation||Improper film thickness adjustment|
|Improper curing temperature|
|Improper adjustment of paint viscosity|
|8||Paint stripping||After the color steel coil is opened, the paint will fall off after a little rubbing||Paint baking humidity and time are not enough|
|9||Color difference||Different color from standard board||Insufficient stirring|
|Unsuitable curing temperature|
|Paint color is incorrect|
Advantages and disadvantages of color coated sheet application
A color coated board material has different applications in different industries, which must be related to its characteristics.
Color coated sheets are not widely used in the elevator industry because of their shortcomings and the lack of coordination with most elevator production processes.
The sheet metal parts of elevator parts are mainly concentrated in elevator cars, door systems and control cabinets, etc.
These parts are also commonly used welding process, and pay more attention to appearance quality.
Most elevator companies still organize production in a decentralized manner, which increases the risk of collision and scratching of raw materials during the turnover process.
In addition, anti-corrosion ability needs to be considered as appearance parts.
The production characteristics of these elevator sheet metal parts more or less restrict the use of color coated sheets.
The specific shortcomings of color coated sheets in the elevator industry are as follows:
⑴ The forming performance is slightly worse.
The raw material of color coated sheet is mainly galvanized sheet, and its material characteristics are harder than cold-rolled sheet.
In addition, to protect the coating on the surface of the material, a protective film needs to be added to the surface of the raw material, and the processing of sheet metal parts with a film requires higher requirements for the flexibility of the coating film.
These situations are reflected in the bending process and will affect the achievement of bending accuracy.
⑵ Corrosion of the notch.
Since the color coated sheet is first coated with paint and then the product is made, it will inevitably appear to be similar to the corrosion of the galvanized sheet.
Although it does not affect the appearance and use of the surface, the performance in the salt spray test does not meet the requirements.
⑶Poor welding performance.
After the color coated board product is processed and formed, there is also an insulating protective film covering the surface of the paint film because the surface is covered with a paint film, so the color coated board processing basically cannot apply the welding process.
If applied forcibly, serious welding defects and occupational health and safety problems will occur.
⑷ Limitation of plate thickness.
Since the production process of color coated board needs to be carried out with a coating roller, it requires the material to have good flexibility.
In the past, the material thickness of color coated sheets was within 1mm.
After the process was improved, the thickness of the color coated board was increased to 1.5mm.
Board thickness is increasing, and application scenarios and production costs will be greatly increased.
Therefore, there are very few color coated sheets above 1.5mm on the market.
⑸ Process dispersion can easily lead to product defects.
Both color coated sheets and brushed stainless steel require surface coating, but the surface of color coated sheets is more fragile and cannot be repaired when scratched.
If the dispersion process is used for production, multiple loading and unloading and turnover will make the surface of the color coated sheet easy to scratch, and this quality defect is irreversible.
This situation makes color coated sheets have a greater quality risk during use.
The shortcomings of color coated sheet limit its application range.
However, its advantages are also very obvious,
The biggest advantage of the color coated sheet application is that the product can be shipped directly after it is offline, without spraying or outsourcing.
This can greatly shorten the cycle and the inventory of semi-finished products as well as reduce the backlog of funds, which is very necessary for companies pursuing low inventory.
It is shown in the following 4 points:
1) In today’s increasingly serious environmental issues, many spraying plants will be shut down due to environmental audits, resulting in supply disruptions.
The production of color coated sheets is carried out in steel plants, and the processes are all made of environmentally friendly materials, and the material utilization rate is very high.
The good environmental performance makes its production basically not affected by environmental inspections.
2) Due to the efficient production process, compared with outsourcing spraying, the cost of using color coated sheets is lower than the comprehensive cost of steel spraying.
3) The coating process is continuous, and the film thickness and color difference are strictly controlled by the equipment.
The product consistency is very good.
The materials of the same manufacturer are basically free from color difference problems.
This is for elevator door panels and wall panels that emphasize splicing appearance are very important.
4) The base material of color-coated plate is galvanized plate, coupled with surface coating paint, its surface anti-corrosion ability is much stronger than steel plate spray paint.
Application of color coated board in the elevator industry
As far as elevator companies are concerned, the use of color coated plates must be combined with their own actual conditions to effectively avoid their shortcomings and enlarge their advantages.
For the disadvantages of poor welding performance and easy scratching of color-coated sheets, the use of automated production equipment can effectively reduce the impact.
Our company adopts a fully automated production model of automation equipment and robots to produce color coated elevator door panels.
The head structure is eliminated on the product, and the welding process is replaced by a riveting process, thereby effectively avoiding the above shortcomings.
In the application process, the mechanical properties of the color-coated plate are generally stable, and the abnormal processing conditions are not serious.
In the actual test, the yield strength of the color-coated plate is better than that of the SPCC plate, and its deformation is smaller in the elevator door impact test.
Since the author’s company does not have a spraying production line and requires outsourcing spraying, the application of color-coated plates can reduce the production cycle of 3 days and nearly 40% of the inventory of semi-finished products, which brings great benefits to the company.
Of course, we also face 4 problems in use:
(1) Since the color-coated sheet is not a conventional sheet, its price has no reference target, so users need to communicate closely with suppliers about price changes.
(2) It needs to pay attention to the choice of protective film, especially in the case of automated production.
The choice of the protective film is critical because the safety risk of film release is great.
(3) If choosing two or more suppliers to supply color-coated sheets of the same color, the color difference standard should be formulated.
The key is that the color palette management needs to be improved.
(4) Since there is a minimum purchase amount of raw materials, do not hope that all colors of the company’s products use color coated sheets, which may cause a large backlog of materials.
Competition in the elevator market is becoming increasingly fierce, and product cost has become an important weapon for companies in addition to product performance.
Many manufacturers are trying to make a fuss on the raw materials.
443, 201, color coated sheets and composite steel sheets have all entered the elevator industry in response to market changes.
Unlike other sheets, color coated sheets have reduced costs and partially improved quality under certain scenarios.
To achieve the above effects, companies need to have sufficient production capacity and technical capabilities to support them.
Using color-coated boards is a more reasonable product improvement plan for the author.
But it does not mean that all companies can achieve the same results.
I hope that readers can analyze their own situation realistically and find a set of applications that are beneficial to them.