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GB/T 12754-2019 English PDF (GBT12754-2019)

GB/T 12754-2019 English PDF (GBT12754-2019)

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GB/T 12754-2019: Prepainted steel sheet and strip

This Standard specifies terms and definitions, grade representation method, classification and code, order content, dimensions, shape, weight, technical requirements, test methods, inspection rules, packaging, marking and quality certificates of pre-painted steel sheets and strips. This Standard applies to pre-painted steel sheets and strips for building interior and exterior applications. Pre-painted steel sheets for home appliances and other purposes may also refer to this Standard.
GB/T 12754-2019
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 77.140.50
H 46
Replacing GB/T 12754-2006
Pre-painted steel sheet and strip
ISSUED ON: MARCH 25, 2019
IMPLEMENTED ON: FEBRUARY 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 4
1 Scope ... 7
2 Normative references ... 7
3 Terms and definitions ... 7
4 Grade representation method, classification and code ... 9
5 Ordering content ... 11
6 Dimensions, shape, weight ... 12
7 Technical requirements ... 12
8 Test methods ... 19
9 Inspection rules ... 20
10 Packaging, marking and quality certificate ... 20
11 Description of corrosivity of use environment of pre-painted steel sheets 21 12 Selection of pre-painted steel sheets ... 21
13 Storage, transportation and handling of pre-painted steel sheets ... 21 14 Processing of pre-painted steel sheets ... 21
15 Life to the first major maintenance and durability of pre-painted steel sheets ... 21
16 Atmospheric exposure test sites for pre-painted steel sheets ... 21
Annex A (informative) Description of corrosivity of use environment of pre- painted steel sheets ... 22
Annex B (informative) Selection of pre-painted steel sheets ... 27
Annex C (informative) Storage, transportation and handling of pre-painted steel sheets ... 31
Annex D (informative) Processing of pre-painted steel sheets ... 33
Annex E (informative) Life to the first major maintenance and durability of pre- painted steel sheets ... 36
Annex F (informative) Atmospheric exposure test sites of pre-painted steel sheets ... 37
Pre-painted steel sheet and strip
1 Scope
This Standard specifies terms and definitions, grade representation method, classification and code, order content, dimensions, shape, weight, technical requirements, test methods, inspection rules, packaging, marking and quality certificates of pre-painted steel sheets and strips.
This Standard applies to pre-painted steel sheets and strips for building interior and exterior applications (hereinafter referred to as pre-painted steel sheets). Pre-painted steel sheets for home appliances and other purposes may also refer to this Standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 247 General rule of package, mark and certification for steel plates (sheets) and strips
GB/T 1766-2008 Paints and varnishes - Rating schemes of degradation of
coats
GB/T 8170 Rules of rounding off for numerical values and expression and
judgement of limiting values
GB/T 13448 Test methods for pre-painted steel sheet
GB/T 17505 Steel and steel products - General technical delivery
requirements
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply. 3.1
pre-painted steel sheet
adsorption
Degree of firmness between the coatings or between the coating and the steel substrate.
3.10
life to the first major maintenance
Interval from the date of manufacture to the time when the performance of the original coating drops so it is necessary to overhaul it to maintain its protection against the steel substrate.
NOTE: Overhaul refers to the maintenance and repair work that must be performed on the building when the paint film becomes incomplete due to weathering or the steel substrate is perforated, including repainting, local replacement, etc.
3.11
durability
Ability of the coating to reach a specified life to the first major maintenance. 3.12
weathering
Phenomenon that the performance of the coating gradually deteriorates under the influence of the use environment.
4 Grade representation method, classification and
code
4.1 Grade representation method
The grade of pre-painted steel sheets consists of the uppercase English letter T plus the grade of steel substrate.
Example 1: TDX51D+Z
- represents the pre-painted steel sheet of which the steel substrate grade is DX51D+Z. Example 2: TDC01+ZE
- represents the pre-painted steel sheet of which the steel substrate grade is DC01+ZE. Example 3: TS300GD+AZ
Other suitable steel substrate standards may also be adopted upon agreement between the supply and demand parties.
7.1.1.2 Unless otherwise specified, hot-dip galvanized steel substrates, hot-dip zinc-iron alloy steel substrates, hot-dip aluminum-zinc alloy steel substrates, hot-dip zinc-aluminum alloy steel substrates, hot-dip aluminum-silicon alloy steel substrates, and hot-dip zinc-aluminum-magnesium alloy steel substrates shall be subjected to flattening (or finishing) processing.
7.1.2 Performances of top-side coating
7.1.2.1 Coating types
7.1.2.1.1 The common topcoat types for pre-painted steel sheets are shown in Table 1. If other types of topcoats are required, it shall be negotiated at the time of ordering.
7.1.2.1.2 The type of primer is usually determined by the supply party. If the demand party has requirements, it shall be negotiated at the time of ordering. 7.1.2.2 Thickness of top-side coating
7.1.2.2.1 The thickness of top-side coating is the sum of the thicknesses of all coatings on the top side.
7.1.2.2.2 The thickness of top-side coating shall not be less than 20 ??m. If the thickness of coating is less than 20 ??m, it shall be negotiated at the time of ordering.
7.1.2.2.3 The thickness of top-side coating shall be the average of three specimens. The value of the individual specimen shall not be less than 90 % of the minimum specified value.
7.1.2.3 Color difference of coating
7.1.2.3.1 The color difference ???E between the coating and the standard swatch shall not be more than 1.5. The standard swatch shall be confirmed by both the supply and demand parties at the time of ordering.
7.1.2.3.2 The requirements for color difference of metallic pigment coatings shall be negotiated at the time of ordering.
7.1.2.3.3 If the demand party has special requirements for color difference, it shall be negotiated at the time of ordering.
7.1.2.4 Coating gloss
7.1.2.4.1 60?? mirror gloss is used for the coating gloss. The gloss is divided into 7.1.2.10 Self-cleaning performance
The carbon black pollution resistance color difference ??E value of self-cleaning pre-painted steel sheets shall not be greater than 1.0. The contact angle shall not be greater than 60 ??. If the supply party can guarantee, the test may be exempted.
7.1.2.11 Antibacterial performance and thermal insulation performance
If there are requirements for antibacterial performance and thermal insulation performance, it shall be negotiated at the time of ordering.
7.1.2.12 Other performances
If there are requirements for performances such as Xenon lamp accelerated weathering, heat and humidity resistance, organic solvent resistance, acid and alkali resistance, pollution resistance, boiling water resistance and dry heat resistance, it shall be negotiated at the time of ordering.
7.1.3 Performances of bottom-side coating
7.1.3.1 Thickness of bottom-side coating
7.1.3.1.1 The thickness of bottom-side coating is the sum of the thicknesses of all coating on the bottom side.
7.1.3.1.2 When the bottom-side coating is a layer, its thickness shall not be less than 5 ??m. When the coating is two layers, the thickness shall not be less than 12 ??m. If it is less than 12 ??m, it shall be negotiated at the time of ordering. 7.1.3.2 Other performances
Performances such as coating type, coating color difference, coating gloss, coating hardness, coating flexibility/adhesion, neutral salt spray resistance, UV lamp accelerated weathering performance are usually determined by the
supply party. If the demand party has requirements, it shall be negotiated at the time of ordering.
7.1.4 Surface quality
7.1.4.1 There shall be no defects such as blisters, shrinkage cavities or missing coating that may be harmful to use on the surface of steel sheets.
7.1.4.2 For steel coils, due to the lack of opportunity to cut the defective portion, the steel coil may be delivered with defects, but the defective portion shall not exceed 5 % of the total length of each coil.
7.1.4.3 Due to the natural or artificial weathering of the steel substrate, the pre- comply with the provisions of GB/T 247. In addition, the marking shall also include the contents such as plating weight of steel substrate, topcoat type and color.
11 Description of corrosivity of use environment of pre-
painted steel sheets
See Annex A for a description of corrosivity of use environment of pre-painted steel sheets.
12 Selection of pre-painted steel sheets
See Annex B for selection of pre-painted steel sheets.
13 Storage, transportation and handling of pre-painted
steel sheets
See Annex C for storage, transportation and handling of pre-painted steel sheets.
14 Processing of pre-painted steel sheets
See Annex D for processing of pre-painted steel sheets.
15 Life to the first major maintenance and durability of
pre-painted steel sheets
See Annex E for life to the first major maintenance and durability of pre-painted steel sheets.
16 Atmospheric exposure test sites for pre-painted
steel sheets
See Annex F for atmospheric exposure test sites for pre-painted steel sheets. atmosphere and wet time. The more types of corrosive media, the higher the concentration, the longer the wet time, and the higher the corrosivity of the internal atmosphere.
A.4.2 When analyzing the corrosivity of the internal atmosphere, the type and concentration of the corrosive medium contained in the internal atmosphere shall be studied first.
A.4.3 The wet time depends on factors such as relative humidity, temperature, and ventilation conditions of the internal atmosphere. The formation of wet films is usually related to the following factors:
a) increase in the relative humidity of the internal atmosphere;
b) condensation occurs when the coating surface temperature reaches the dew point or below the dew point;
c) depositing of moisture absorbing substance on the coating surface;
d) the coating surface is directly wetted.
Measures such as ventilation, drying, cleaning can be taken to reduce the formation of wet film and shorten the wet time.
A.5 Other corrosion (weathering) factors
A.5.1 Illumination
Illumination (especially ultraviolet light) is one of the main causes of weathering of coatings. Pre-painted steel sheets are often affected by illumination during use. Therefore, illumination intensity and illumination time are important factors to consider when analyzing environmental corrosivity.
A.5.2 Temperature
Long-term exposure of the coating to an environment where the temperature is too high, too low, or the temperature difference is too high will accelerate the weathering of the coating.
A.5.3 Chemicals
Pre-painted steel sheets shall be avoided in direct contact with chemicals such as acids, alkalis, organic solvents, detergents, cleansers during use to avoid corrosion of the coating.
A.5.4 Sediment
The deposition of substances such as industrial dust, suspended particles on Annex B
(informative)
Selection of pre-painted steel sheets
B.1 General requirements
Reasonable material selection not only meets the requirements of use, but also minimizes costs. If the material is not properly selected, the result may be that the material performance exceeds the use requirements, resulting in
unnecessary waste, or may not meet the requirements for use, resulting in degradation or inability to use. Therefore, the demand party shall attach great importance to the importance of rational material selection and shall consult relevant experts if necessary.
B.2 Selection of pre-painted steel sheets
The selection of pre-painted steel sheets mainly refers to the selection of mechanical properties, steel substrate type and plating weight, top-side coating performance and bottom-side coating performance. Application, corrosivity of use environment, life to the first major maintenance, durability, processing method and degree of deformation are important factors to consider when selecting materials.
B.3 Selection of mechanical properties, steel substrate type and plating weight
B.3.1 Mechanical properties are selected mainly according to factors such as appliance, processing method and degree of deformation. When the strength requirements are not high and the deformation is not complicated, TDC51D and TDC52D series of pre-painted steel sheets may be used. When there is a high requirement for formability, TDC53D and TDC54D series of pre-painted steel sheets shall be selected. For components with load-bearing requirements, suitable structural steels, such as TS280GD and TS350GD series, shall be selected according to the design requirements. Cutting, bending, rolling, etc. are common processing methods for pre-painted steel sheets, which shall be selected according to the characteristics of each processing method at the time of ordering. In actual production, the mechanical properties of the pre-painted steel sheet are usually replaced by the mechanical properties of the steel substrate, and the pre-painting process may cause the mechanical properties of the steel substrate to change. In addition, mechanical properties may also vary with the increase of storage time. These will increase the possibility of a Ryders belt or crease when the pre-painted steel sheet is formed, which shall be noted.
Commonly used primers are epoxy, polyester and polyurethane. There are
some differences in the adhesion, flexibility and corrosion resistance of different primers. Epoxy has good adhesion to the steel substrate and high corrosion resistance, but not as flexible as other primers. Polyester has good adhesion to the steel substrate and excellent flexibility, but the corrosion resistance is not as good as epoxy. Polyurethane is a primer with relatively good overall performance. Detailed performance indicators for various primers can be found in the relevant materials or consulted with experts. The primer is usually selected by the supply party based on the production process, application, corrosivity of use environment, and the matching relationship with the topcoat. B.4.3 Coating thickness
Coating thickness is closely related to the corrosion resistance of pre-painted steel sheets. The corrosion resistance generally increases with the increase of the coating thickness. The coating thickness shall be determined according to factors such as corrosivity of use environment, life to the first major maintenance and durability.
B.4.4 Color difference of coating
Pre-painted steel sheets may have color difference during production and use. Because color difference is affected by various factors such as production organization, color depth, use time, use environment, and application, it is usually negotiated between the supply and demand parties.
B.4.5 Coating gloss
Coating gloss is selected mainly according to the application and use habits. For example, pre-painted steel sheets for buildings usually have medium and low gloss, and pre-painted steel sheets for home appliances usually have high gloss.
B.4.6 Coating hardness
Coating hardness is the ability of the coating to resist the mechanical effects such as scratches, friction, impact, pressing. It is closely related to the scratch resistance, abrasion resistance and indentation resistance of pre-painted steel sheets. It is selected mainly according to factors such as appliance, processing method, storage and transportation conditions.
B.4.7 Coating flexibility/adhesion
Coating flexibility/adhesion is closely related to the processability of pre-painted steel sheets, and is selected mainly according to the processing method, degree of deformation, etc. When the deformation speed is fast and the degree Annex C
(informative)
Storage, transportation and handling of pre-painted steel sheets
C.1 Storage, transportation and handling are important factors that affects the quality of pre-painted steel sheets. If improperly operated, various defects such as scratches, embossing and corrosion may occur during storage,
transportation and handling. In order to minimize and avoid the occurrence of various types of defects, the following is a brief description of some of the precautions in the operation. Specific provisions regarding storage,
transportation and handling may refer to the relevant information or consult an expert.
C.2 The precautions for storage of pre-painted steel sheets are as follows: a) Pre-painted steel sheets shall be stored in a clean and tidy indoor
environment to avoid the erosion of various corrosive media.
b) The ground of the storage site shall be flat, free of hard objects and have sufficient load-bearing capacity.
c) Horizontal steel coils shall be placed on devices such as rubber mats, skids, brackets; the lock of straps shall be upwards; they shall not be placed directly on the ground or on transport tools.
d) In order to avoid crushing, steel coils are usually not stacked. When steel sheets are stacked, the number of stacking layers shall be strictly limited, and the sheet package with large weight and size shall be placed below. e) The products shall be stored in a dry and ventilated indoor environment, avoiding open storage and storage in areas prone to condensation and
large temperature differences.
f) The storage site shall have sufficient space for the lifting equipment to be used.
g) The storage locations of steel sheets and steel coils shall be reasonably arranged for easy access and minimize unnecessary movement.
h) It shall be noted that the mechanical properties and coating performance of pre-painted steel sheets may vary with the increase of storage time. C.3 The precautions for transportation and handling of pre-painted steel sheets are as follows:
Annex D
(informative)
Processing of pre-painted steel sheets
D.1 Processing is an important part that affects the quality of pre-painted steel sheets. In order to ensure product quality, some precautions during processing are briefly introduced below. For specific specifications on processing, it may refer to the relevant information or consult an expert.
D.2 Pre-painted steel sheets are coated on the surface, so there are many differences in the processing from common cold-rolled sheets and plated sheets. The most important difference is that it shall be processed under the premise of ensuring the coating is intact. The precautions for processing are as follows:
a) Mechanical properties (such as yield strength, tensile strength, elongation) are important indicators for measuring formability, are important
parameters for determining and adjusting the processing technology, and are one of the main factors considered during processing.
b) Coating performance (such as pencil hardness, T-bend value, impact
energy) is closely related to the processability and is another major factor considered during processing.
c) Part of the mechanical properties (such as yield strength, elongation) and part of coating performances (such as pencil hardness, T-b...

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