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Choosing the wrong color steel plate, pitted millions

 

“At about 2010, a proprietor asked for an innovative color steel roof. I was invited to investigate the status quo of roof construction and put forward proposals for roof innovation. Accompanied by Party A, I was stunned when I climbed the outdoor ladder to the roof. : On the roof of about 8 thousand square meters, there are rust spots of different sizes at an even distance of about 3 to 4 meters. Some areas have been rusted through, and there are small holes to see the interior! Walking on the roof, I can only Be careful to step on the roof purlins as much as possible, perhaps at least on the roof that does not appear to be rusted, and dare not step on it, legs trembling...

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The owner's two workshops of 8,000 square meters each have such rusty roofs. Innovative roofing, coupled with strikes during construction, cost a total of several million yuan. "

Owners of non-steel structure occupations who have not experienced steel structure infrastructure construction. The time when they need to purchase color steel plates to build a factory is like going to a vegetable farm and want to buy a local chicken, but they don’t know the difference between foreign chickens and local chickens. They can never tell the seller. Say: Come, untie the rope that binds the chicken and see if it can fly 2 meters high...

 

In fact, understanding the coating of color steel plates is not much messier than understanding the interior wall coatings of various levels in our own home decoration, which is very easy. Next, we will be able to popularize the common sense of color steel plates in 10 minutes, so that you can prevent you from being scammed by millions.

 

Color steel plate composition

Mainstream color steel plates are generally composed of base steel plate + galvanized/galvanized + color coating.

 

Therefore, when we purchase color steel sheets, we look at the composition of these three materials: the raw material and thickness of the base steel sheet, the amount of galvanized steel, and the composition of the color coating.

 

1. Base material steel plate

 

Raw material, thickness, the raw material of the base steel plate has a yield strength from 300Mpa to 550Mpa, and a thickness from 0.3mm to 0.8mm.

 

The selection of raw materials and thickness is to serve the bearing capacity of the color steel plate. Because each supplier's plate type is different, and the purlin distance required by each supplier is different, it is impossible to give a universal specification.

 

Main stream uses more: roof panel thickness 0.6mm, wall outer panel thickness 0.5mm, inner lining board (installed behind the purlin) 0.35mm

 

2. Substrate plating

 

The content of aluminum-zinc or zinc-plated in the anti-corrosion coating ensures the anti-corrosion function of the color steel plate.

 

Galvanizing, galvanizing, the vivid sequence of chemical elements in middle school chemistry, remember the formula for recitation?

 

Potassium calcium sodium magnesium aluminum, zinc iron tin lead hydrogen, copper mercury silver platinum.

 

Married to my beautiful woman, she has a slender body and a total of 100 catties.

 

The vividness of steel is not as good as aluminum and zinc. Therefore, if aluminum and zinc are plated on the surface of the steel plate, the aluminum and zinc will be oxidized first; then the aluminum oxide and zinc oxide produced will form a dense maintenance film on the surface of the steel to maintain the inner layer. The steel plate is not corroded. Therefore, the amount of galvalume/galvanization ensures the corrosion resistance of the color steel plate.

 

There are two types of anti-corrosion coatings: galvanized (55% aluminum in the meantime) and galvanized. In the meantime, the anti-corrosion function of galvanized zinc is better. If it is used for the roof panel, it can directly use the original color of galvanized galvanized without color coating. Of course, it can also add color coating on galvanized; the anti-corrosion function of galvanized is slightly worse. , But because aluminum is expensive, zinc is cheap, and the amount of galvanized coating is increased, it is also a good choice for the anti-corrosion function of color-coated color steel plates.

 

For decades, galvanized and galvanized as anti-corrosion coatings have been confirmed by many constructions around the world: the amount of galvanized (55% aluminum) 150g/㎡ can basically ensure the anti-corrosion life of color steel plates for more than 15 years ( Even if there is no color coating to cover); and the amount of galvanized 275 g/㎡, it can ensure the anti-corrosion life of the color coated board for more than 15 years (the color coating is required to cover). Of course, the prerequisite is that there is no corrosive gas in the internal environment and the external natural environment. If the natural environment often has salt spray, metal dust in the building, acidic volatile gas, etc., it will greatly accelerate the corrosion of the color steel plate. Under such harsh conditions, consider using better anti-corrosion aluminum-zinc-magnesium-plated color steel plates, and even Stainless steel plate.

 

3. Variety of coating

 

The service life of color steel plate largely depends on the type of coating. Different types of coating materials have different prices.

 

Variety and film thickness of top coat, Variety and film thickness of primer

The appearance color of the color steel plate is realized with color coating. The outer appearance of the color steel plate is called the front side, and the other side is naturally the reverse side. Regardless of whether it is front or back, the coating contains two layers of primer and topcoat. Generally, the thickness of the topcoat on the front of the outer panel is 20μm and the primer is 5μm; the thickness of the topcoat on the front of the inner panel is 15μm and the primer is 5μm.

 

A. Variety of top coat

 

On the market, mainstream finishes are divided into:

 

Polyester (PE), silicon modified polyester (SMP), high weather resistance polyester (HDP), KYNAR@500: 70% polyvinylidene fluoride (PVDF), polyester (PE, PolyEster)

 

PE coatings have outstanding adhesion to raw materials, color-coated steel plates are easy to process and shape, are inexpensive and have many products, and there is a lot of room for choice in color and gloss. Under direct exposure to the general environment, the anti-corrosion period is 7 to 8 years. The UV resistance of the polyester coating and the powdering resistance of the coating film are poor, and the color will fade and chalk in a few years.

 

Silicone Modified Polyester (SMP, Silicone Mobified Polyester)

 

Using Silicone resin and polyester with excellent color persistence and heat resistance for the denaturation response, the UV resistance and chalking properties of PE are improved, and the anti-corrosion life of SMP is extended to 10-12 years, and the corresponding price is also higher than that of PE. high. However, because Silicone resin is not optimistic about the adhesion and processability of raw materials, the paint may peel during the cold pressing of the sheet, so SMP color-coated steel sheet is not suitable for sheet types that require multiple cold pressing.

 

High Durable Polyster (HDP, High Durable Polyster)

 

The highly weather-resistant polyester resin developed in the beginning of 2000 uses monomers containing cyclohexane structure to achieve the balance of flexibility, weather resistance and cost of the resin, and uses non-aromatic polyhydric alcohols and polybasic acids to reduce the UV exposure of the resin. The absorption of light reaches the high weather resistance function of the coating. It can reach 60%~80% weather resistance of PVDF coating, and the weather resistance in the field can reach 15 years. High weather-resistant polyester coatings have been recognized by the market at home and abroad, with outstanding cost performance. Because the price of high weather-resistant polyester is not much different from that of silicon-modified polyester, but the functions are improved a lot, generally more high-weather-resistant polyester (HDP) is selected to make silicon-modified polyester (SMP) available in the market. It's less common.

 

KYNAR@500: Containing 70% polyvinylidene fluoride (PVDF, PolyVinyliDene Fluoride)

 

PVDF is classified as a kind of fluorocarbon coating, which is the oldest and most widely used one among fluorocarbon coatings. Because PVDF has a strong bond energy between the chemical bond and the chemical bond, the coating has very good corrosion resistance and color persistence. It is a first-class product in the color-coated steel coating for construction industry, and the molecular weight is large. Straight bond structure, so in addition to chemical resistance, mechanical functions, UV resistance and heat resistance are also outstanding. Under normal circumstances, its anti-corrosion life can be as long as 20-25 years, and its color will not fade.

 

B. Variety of primer

 

The primer is generally selected based on the product's use, application occasion, processing level, and matching with the topcoat. The film thickness of the primer is generally 5 μm. The main primer is divided into:

 

Epoxy resin (EP, EPoxy resin)

Polyester (PE, PolyEster)

Polyurethane (PU, PolyUrethane)

Epoxy resin (EP, EPoxy resin)

Easy to peel and short lifespan.

Polyester (PE, PolyEster)

 

The UV resistance and the powdering resistance of the coating film are poor, but the primer for the lining board is satisfactory.

 

Polyurethane (PU, PolyUrethane)

 

Among the primers, polyurethane has the characteristics of chemical resistance, abrasion resistance, durability, and flexibility. It is the best primer in all aspects.

 

Regarding the color steel plate, the top coat and primer on the front and back of the outer panel, the top coat and primer on the front and back of the inner panel, and the top coat and primer on the sandwich panel, too many combinations will not be listed. I am afraid I confused myself in the process of listing.

 

If the description of popular science in the front is not intuitive enough, let me get a powerful and common package for you to choose.

 

A. Packages for big-name foreign companies and high-end private companies:

 

Roof panel—thickness 0.6mm; aluminum-zinc plating above 150g/㎡, original color;

 

Wall panel-thickness 0.5mm; aluminum-zinc plating 150g/㎡ or galvanized 275g/㎡; primer polyurethane, topcoat Kynar@500;

 

Inner lining board—thickness above 0.35mm; aluminum-zinc plating 100g/㎡ or galvanized 180g/㎡; primer polyester and topcoat are highly weather-resistant.

 

B. Useful and progressive enterprise package:

 

Roof panel—thickness 0.6mm; aluminum-zinc plating 150g/㎡, original color;

 

Wall panel—thickness 0.5mm; aluminum-zinc plating 150g/㎡; primer polyester, top coat high weather resistance;

 

Lining board-thickness 0.35mm; aluminum-zinc plating 100g/㎡ or galvanized 180g/㎡; primer epoxy, topcoat polyester.

 

C. Don't ask for the dryness of the sea, just ask for a meal once:

 

Roof panel-thickness 0.5mm; galvanized 180g/㎡, primer epoxy, topcoat polyester;

 

Wall panel-thickness 0.4mm; galvanized 180g/㎡, primer epoxy, topcoat polyester;

 

Inner lining board-what kind of inner lining board...

 

Don’t underestimate the last shopping mall with this package: temporary walls on the construction site, demolition and urgent construction of houses, temporary sheds, illegal establishments, etc., on the construction site, in the countryside, in the vast world of towns and towns, everywhere is lively with the cheapest PE color steel plate. The sky blue figure---add money for other colors! (The so-called sky blue can't help but complain: Is the blue sky such a "blue"? The person who named the color must be weak in color). Although the colors are so ugly, they can be seen everywhere, and there are so many annoying, but...the price is so fragrant!

 

last question:

How to ensure that the quality of the color steel plate sent by the supplier conforms to the contract?

 

There are shoddy companies! Your contract stipulates that you need to be galvanized 150g/㎡ and finish Kynar@500, but the supplier gives you 180g/㎡ and polyester finish. Can you see it after a few more glances? Give me a magnifying glass anyway, I can't see it. Don't use the rated profit to test the supplier's character.

 

One method is the verification of time: the functions of various topcoats have been introduced above, for example, PVDF will not fade for many years, while other topcoats are different. But this method will wait for you to verify it after many years. Maybe the other company is gone, change the locality, change the name to another company, and continue to pit it.

 

The second method is to try to find a company with strength and a certain history-if you want to do a lasting business, you will always cherish your reputation.

 

The third method is to send for inspection, send for inspection, and send for inspection. Find a laboratory that can do physical and chemical analysis of color steel plates, sample a color steel plate of A4 paper size, and a little fee, you can get the test results.