GB/T 12754-2019 English PDF (GB/T12754-2019)

GB/T 12754-2019: Pre-painted steel sheet and strip
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GB/T 12754-2019
NATIONAL STANDARD OF THE
PEOPLE’S 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 μm. If the
thickness of coating is less than 20 μm, 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 ΔE 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 μm. When the coating is two layers, the thickness shall not be less than
12 μm. If it is less than 12 μm, 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 ...