Classification properties field of applications and marking of metallic coaings and chemically treated layers - SJ 42-1977 - Chinese standardNet (2024)

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Standard of the Fourth Machinery Industry Department of the People's Republic of China
Classification, characteristics, scope of application and marking of metal plating and chemical treatment layer
SJ42-77
(Replaces SJ42-64)
Classification, characteristics, scope of application and marking of metal plating and chemical treatment layer (Replaces SJ42-54)
1. Classification of metal plating and chemical treatment 2. Selection of metal plating and chemical treatment 3. Marking symbols on technical documents..
4. Characteristics, scope of application and marking of metal plating. 5. Characteristics, scope of application and marking of chemical treatment layer. 6. Characteristics, scope of application and symbols of preparation process Plating and chemical treatment of steel products
Passivation or rainbow color after galvanizing.
Passivation to military green after galvanizing
Passivation to white after galvanizing| |tt||Oxidized to black after galvanizing
Passivated to rainbow color after plating
Phosphating after pot plating
Multi-layer nickel plating·
Multi-layer semi-bright nickel plating.
Multi-layer bright nickel plating
Single-layer plating
Multi-layer chrome plating…
Multi-layer semi-bright chrome plating.
Multi-layer bright chrome plating
Multi-layer full-bright chrome plating…
Emulsion color plating
Chromium plating
Standard of the Fourth Ministry of Machinery Industry of the People's Republic of China
Classification, characteristics, application scope and marking of metal coatings and chemical treatment layers
SJ42-77
SJ42-64
This standard applies to the classification, characteristics, application scope and representation method on drawings of electroplating, chemical plating, hot-dip plating and chemical treatment of parts of wireless products. 1. Classification of metal plating and chemical treatment 1 According to different plating and treatment methods, it can be divided into: (1) Electrochemical plating of metals and non-metals: (2) Chemical treatment of metals and non-metals (including electrochemical treatment of metals) (3) Hot-dip plating of metals;
(4) Chemical plating of metals and non-metals; (5) Thermal spraying of metals and non-metals; (6) Vacuum plating of metals and non-metals (including anode spraying and vacuum coating), 2. According to different uses, it can be divided into:
(1) Protective plating or chemical treatment: used to prevent metal parts from corrosion under various conditions of use;
(2) Protective decorative plating or chemical treatment: used for parts that need to be decorated, and also to prevent metal parts from corrosion under various conditions of use; (3) Special plating or chemical treatment: used to give certain properties to the surface of parts, such as silver plating to improve the conductivity of the surface of parts, hard chrome plating to improve the hardness and wear resistance of the surface of parts, and local copper plating to prevent carburization, etc. 2. Selection of metal plating and chemical treatment 3. The reasonable selection of plating or chemical treatment methods depends on the following factors: (1) Base material: Select plating or treatment methods according to different base materials. (2) Use conditions: In order to reasonably choose plating or chemical treatment, you must be familiar with the environmental conditions of the whole machine, the location of the parts in the whole machine, and fully understand the nature of the corrosive media (industrial gases, marine salt chips, etc.) in this environment and the possibility of intrusion into the interior of the machine, as well as the changes in relative humidity during use. The classification of use conditions is shown in Table 1. Table 1 Condition classification Relative humidity ≤ 80%, no industrial, boiler and other harmful exhaust gases, such as laboratories with air conditioning devices, and inside sealed devices. Relative humidity < 95%, with a small amount of industrial, boiler and other harmful gases, such as outdoors that are not directly affected by the sun, rain, etc., sea fog and moisture-saturated atmosphere, indoors without air conditioning devices, and inside cars.
Relative humidity reaches 98% in the zone, with more industrial, boiler and other harmful gases, such as those directly affected by the sun, zero, rain, etc. and those close to the harmful gas source outdoors. Instruments and equipment directly affected by the periodic influence of seawater or working in an atmosphere saturated with sea fog. Conditions determined by various special circ*mstances. Such as situations where good conductivity is required or situations where pressure and rate are often applied.
(3) Protective properties of metals: The protective properties of gold chip plating or chemical treatment are related to the ability of the metal to ionize (oxidize) in a certain medium. This metal electrochemical property can be expressed by the electrochemical potential value (volts). The more negative the electrochemical potential value of the metal in a certain medium, the greater the ionization (oxidation) ability. If in a certain dielectric, the electrochemical potential of the plated metal is negative than that of the base metal, the plated layer is the anode and will be dissolved, thus protecting the base metal from damage for a certain period of time. Its durability mainly depends on the thickness of the plated layer. Conversely, if the electrochemical potential of the plated gold chips is positive than that of the base metal, the plated layer is the cathode. When the plated layer has pores or is partially damaged, the base metal will be more susceptible to corrosion and damage than the plated layer. The greater the difference between the potential values ​​of the two, the faster and easier it is to be damaged. Therefore, the protective characteristics of the cathode coating depend on the thickness and porosity of the coating (see Appendix Table 1 for "Standard Electrochemical Potential Series of Metals".
SJ42-77
Total 58 pages Page 4
(4) Metal galvanic couple: When two different metals are combined (mechanically connected or combined) and are in a system composed of a certain dielectric (such as acid, alkali, salt or surrounding atmosphere containing moisture, industrial gas, salt spray), contact corrosion is likely to occur. When designing the structure of the whole machine and parts and selecting the plating or chemical treatment method, the contact galvanic couple between parts and between the coating metal and the base metal should be carefully considered: if the nest forms an impermissible galvanic couple and it is impossible to use other protective plating and chemical treatment, then in An insulating pad must be placed between the two connecting parts (see Appendix 2, 8, and 4 for "Allowed and Unallowed Metal Electrochemical Couples"). (5) Due to the limitations of the electroplating process, the coating on the surface of parts is often uneven: the outside is thicker than the inside, the edge is thicker than the center, the inner wall of deep holes and gaps is not easy to plate, etc. (6) For riveted, welded parts and assemblies of different gold chips, electroplating or chemical treatment is not allowed in principle, because during this process, the electrolyte penetrates into the seams and gaps and is difficult to completely remove. When stored or used, this dried solute will deliquesce into electrolyte under certain humidity conditions, which will cause corrosion of the parts. Therefore, only when necessary is it allowed to plate or chemically treat the assembly. (7) In principle, metal parts cast by sand molding or hard mold method are not allowed to be plated or chemically treated. It is allowed to use coating or chemical treatment methods for protection, because the corrosion resistance of such parts after plating or chemical treatment is unreliable.
(8) For parts with threads and three-level finishing or above, if more oxides are found locally before plating, they should be processed only after consultation and the processing quality agreed upon by the process and design personnel.
(9) Improving the surface finish of metal parts can increase the reflectivity of the part surface to light and the wear resistance of the mechanical friction part, and improve the corrosion resistance of the metal under atmospheric conditions. However, due to the particularity of chemical or electrochemical processing methods, parts that have been electroplated or chemically treated often cannot obtain the expected finish. Therefore, all finish requirements proposed in the design should be achieved by mechanical processing after electroplating and chemical treatment. ||t t||(10) Increasing the brightness of metal coating can improve the decorative performance of the product, but the brightness after electroplating or chemical treatment is related to the state of the underlying layer before processing (smoothness grade). Therefore, whenever the design requires brightness of the coating and the underlying metal needs to be polished, polished, etc., the smoothness grade of the parts before processing should be guaranteed by mechanical processing in accordance with the provisions of Article 8 of Chapter 8 of SJ1276-77 "Technical Requirements for Quality Inspection of Metal Coatings and Chemical Treatment Layers". Total 63 pages Page 5
5J42-77
(11) When partial plating is used to meet special design requirements, corrosion protection measures for the unplated parts should also be considered. It should be pointed out that partial plating is an unreliable and uneconomical processing method and can only be used when necessary. (12) The selection of plating thickness of fasteners can be carried out in accordance with the provisions of this standard. If the non-matching parts are exposed to enhance their protective properties in consideration of the use environment, it is recommended to apply protective coatings on the non-matching parts or use other corrosion-resistant materials to manufacture parts. III. Marking symbols on technical documents
4. On technical documents (design drawings and process cards, etc.), the marking symbols of metal coatings, chemical treatment layers and preparation processes shall be marked in accordance with the provisions of GB1238-76 "Methods for indicating metal coatings and chemical treatments".
IV. Characteristics, application scope and marking of metal coatings and chemical treatment layers 5.The characteristics, application scope and marking of metal coatings are shown in Table 2.6. The characteristics, application scope and marking of chemical treatment layers are shown in Table 8. :7. The characteristics, application scope and symbols of preparation processes are shown in Table 4. When the preparation process is used as an independent finishing treatment, it shall be marked according to the provisions of Table 6 in "Methods for Representing Metal Coatings and Chemical Treatments" in GB1238-76. Page 8 of 58 pages
Stationary Materials
Plating Applications
Plating Types
SJ42-77
Zinc coating belongs to the category of anodic coating. Under normal atmospheric conditions, the coating has good protective properties.
Zinc coating can withstand bending and expansion, but cannot withstand pressure. The newly electroplated coating can be welded or soldered.
Zinc coating is not wear-resistant. Its protective performance is significantly reduced when the temperature is below 70°C. When the temperature is above 250°C, the coating will be weak. Zinc coating can be dissolved in acidic or alkaline media. Its decorative properties are not high. Zinc coating is silvery white. Slightly light blue, gradually fades with time, but after passivation to rainbow color or military green, its corrosion resistance can be improved.
Galvanized parts without passivation and long-term contact with the gas emitted by certain plastics, paints and other organic substances (such as components that have been over-dried with drying oil or wrapped with varnished cloth, etc.) will also cause corrosion. In this case, it is best to apply a layer of non-oily clear on the parts.
Passivation after galvanizing
Iridescence
Passivation after galvanizing
Military green
Passivation after galvanizing
Oxidation after galvanizing
SI42-77
Overmarking
On the drawing
Use conditions
Category|| tt||Bad weather, offshore
General bad weather
Bad weather, offshore
General bad weather
DZ7·DJ
*DZ7·DJ
**DZ10.DJ
DZ7·DB
DZ15·DB
**DZ10·DB
**DZ10.YH
(micrometer) of the coating
15～20
10～12
7～10
15～20
Total 53 pages Page 7
*Fasteners with pitch <0.8mm
**Fasteners with pitch >0.8mm.
Total 53 pages Page 8
Parts materials
Type of plating
5J42--77
Application diagram
When used under normal atmospheric conditions, the pot coating belongs to the cathodic coating category. Under these conditions, the protection performance of the pot coating is not as good as that of galvanizing. When used under offshore conditions or in seawater, the coating belongs to the anodic coating category. Under these conditions, it performs better than galvanizing.
The plating is soft, elastic, lubricating and easy to weld. The color of the plating is silvery white. In order to improve the protective performance of the plating, rainbow passivation can be used. The plating with rainbow passivation can be used in humid climate conditions, especially for parts working under offshore conditions. The unpassivated plating is suitable for parts and components used in connecting parts and under current contact conditions (especially in ultra-short wave devices), and can also be used for welded parts working at low temperatures. When the atmosphere contains sulfides, the plated parts are not allowed to be used. If the plated parts are not passivated and contacted with gases emitted by organic substances such as certain plastics and paints (such as over-drying oils or components wrapped in varnished cloth) for a long time, corrosion will also occur. In this case, the components should be coated with a layer of non-oily paint.
When the plating is passivated to rainbow color as the paint base, the paint has very poor adhesion and is easy to fall off. In this case, it is not as good as phosphating after cadmium plating. Category
Plated after forging
Iridescent color
Plated after sawing
SJ42—77
Plating mark on drawing
Use conditions
Category
Coating mark
D-Ca25-DC
*D.Ca7.DC
**D.Ca1O.DC
Plating layer
(micrometer)
Total 53 pages Page 9
Continued Table 2
Cadmium plating should be strictly limited to use,
only in offshore conditions.
(See the classification of use conditions)
*Fastening with a pitch of 0.8 wide meters
**Fastening with a pitch of >0.8 wide meters
Total 83 pages Page 10
Parts materials
Purpose of plating
Type of plating process
SJ42-77
Features of plating
The nickel coating belongs to the cathodic plating category. Under any use conditions, the protective performance of ferrous metal parts is reliable only when the porosity of the nickel layer is very small. The porosity of the nickel layer decreases with the increase of the plating thickness. In order to improve its protective performance, multi-layer plating can be used: steel-nickel or nickel-plated-nickel. Because the potential difference between nickel and steel is not large, single-layer plating is allowed when the thickness of the nickel coating increases. The hardness of the nickel coating is lower than that of the chromium layer, but close to the hardness of steel after tempering. When it is often bent, riveted or expanded, the coating may fall off. The wear resistance is higher than that of zinc and tin. The color of the nickel coating is silvery white with a slight yellowish color, and it can be brazed. Single-layer nickel plating is mostly used for beryllium coating of parts with magnetic requirements. Multi-layer nickel plating is used for plating of parts that do not require decorative appearance or are used under friction conditions with low mechanical load.
Multi-layer bright and semi-bright nickel plating is used for plating of decorative and protective parts that are alkali-resistant, magnetically conductive and highly stable.
Bright or semi-bright nickel plating is not suitable for use in harsh environments, such as outdoors under the direct influence of the sun, rain, zero and industrial gases. In this case, the coating will become significantly darker and lose its luster.
Multilayer semi-bright plating
Multilayer bright plating
Single layer plating
SJ42-77
Double plating mark on the drawing
Use conditions
Category
Good General
Overmarking
D.Cu10/Ni5
D.Cu15/N:10
DC30/Ni15
DLC7/Ni5bzxz.net
DLC20/N110
D.LiCu30/Ni15
DL:C.7/Ni5
DL:Cu20/Ni10
DLC 30/Ni15
Thickness of plating layer
(micron)
Total thickness 15~20
Pot 10~15
Nickel 5~10
Total thickness 30~35
Total 53 pages Page 11
Continued Table 2
If plating is carried out in the order of nickel-copper-nickel
copper 15~20, the thickness of the bottom layer nickel 10~15
total thickness 45~50
nickel 15~20 meters should be 3~5 microns
adjustment 30~35
nickel 15~20 meters,
the thickness of the middle layer
total thickness 15~20
17~10 can be reduced accordingly.
Total thickness 30~35
Hook 20~25
When the parts have a large mechanical
Inlay 10~15 load, money cannot be used
Total thickness 45~50
Copper 30~35Nickel.
Nickel 1520
Total thickness 15~20
Nickel 5~10
According to the specific situation, the thickness of the coating
Total thickness 30~35 can be appropriately increased. Copper 20~25
Nickel 10~15
Total thickness 45~50
Copper 30~35
Nickel 15~20
Nickel 35~4030/Ni15
Thickness of plating layer
(micron)
Total thickness 15~20
Pot 10~15
Nickel 5~10
Total thickness 30~35
Total 53 pages Page 11
Continued Table 2
If plating is carried out in the order of nickel-copper-nickel
copper 15~20, the thickness of the bottom layer nickel 10~15
total thickness 45~50
nickel 15~20 meters should be 3~5 microns
adjustment 30~35
nickel 15~20 meters,
the thickness of the middle layer
total thickness 15~20
17~10 can be reduced accordingly.
Total thickness 30~35
Hook 20~25
When the parts have a large mechanical
Inlay 10~15 load, money cannot be used
Total thickness 45~50
Copper 30~35Nickel.
Nickel 1520
Total thickness 15~20
Nickel 5~10
According to the specific situation, the thickness of the coating
Total thickness 30~35 can be appropriately increased. Copper 20~25
Nickel 10~15
Total thickness 45~50
Copper 30~35
Nickel 15~20
Nickel 35~40
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