Salt spray test chamber plays an important role in product quality control. It is a device used to simulate the corrosion performance of metals and coating materials in marine environments, and can evaluate the corrosion resistance of products under harsh environmental conditions and corresponding protective measures.
1. Why do we need to measure salt spray test?
In order to verify whether the metal parts on the product will corrode when exposed to the atmosphere or other environments, the product can be placed in the use environment for a long enough time, such as a life cycle of the product. This is time-consuming and labor-intensive, and in practice It is rarely used.
This requires a convenient method to evaluate the corrosion resistance of products.
The salt spray test is an accelerated corrosion resistance evaluation method in artificial atmosphere. It atomizes salt water of a certain concentration and then sprays it in a closed thermostatic box, and observes the changes of the tested sample after being placed in the box for a period of time. It reflects the corrosion resistance of the sample being tested. It is an accelerated testing method, which means it takes a short time. It does not take several years, but only a few days or even hours.
Although the salt spray test is an effective testing method, due to many factors that affect corrosion, a single salt spray resistance cannot be used to represent the resistance to other media. Therefore, the salt spray test results cannot be used as the test material's resistance to corrosion in all environments. A direct guide to corrosion performance. At the same time, the performance of materials in tests cannot be used as a direct guide to corrosion resistance in use.
Despite this, the salt spray test method can still be used as a method to inspect the materials being tested.
2. Which products require salt spray testing?
Metals and their alloys
metal covering
organic cover
anodized film
3. Covering layer
1) Covering type
Organic coatings, such as paint, varnish, powder coating (powder), anti-rust oil, etc.
Metal coating, such as electroplating, chemical plating, ion plating, spray plating, hot dip plating, chemical vapor deposition, etc. Commonly used electroplating layers include zinc plating, copper plating, nickel plating, chromium plating, tin plating, brass plating, lead-tin alloy plating, etc.
2) The role of covering layer
Aesthetics For example: bright chrome plating
Protect base metal from corrosion
4. Classification of test methods for salt spray test
Neutral salt spray test (NSS)
Acetic acid salt spray test (AASS)
Copper Accelerated Acetic Salt Spray Test (CASS)
Commonly used standard types: ISO 9227:2006 Europe (including the United Kingdom)
ASTM B117-03 United States
DIN 50021:1988 Germany
(1) Neutral salt spray test NSS (Neutral Salt Spray)
Test standard selection
ISO 9227:2006 Europe (including UK)
ASTM B117-03 United States
DIN 50021:1988 Germany
The conditions of several test standards are the same, see the following content
Test Conditions
Sodium chloride solution concentration 50g/L± 5g/L
PH value is 6.5~7.2
The temperature inside the test chamber is 35 ±2°C
(USA 35＋1.1/-1.7 °C)
The salt spray settling rate is 1.5±0.5mL per 80cm² per hour
Sample preparation
The type, quantity, shape, and size of the specimen are determined according to the product standards. If there is no standard, it shall be negotiated by the relevant parties.
The sample must be cleaned using appropriate methods before testing, but the protective organic film intentionally coated on the sample should not be washed away.
For cut specimens, the cut area should be protected with paint, paraffin wax or tape.
Sample placement
The sample is placed in the salt spray box with the test surface facing up, and the salt spray is allowed to settle freely on the test surface. The test surface cannot be directly sprayed by salt spray.
The tested surface of the specimen should be at an angle of 20 degrees to the vertical direction.
Specimens can be placed on different levels in the chamber, but they must not come into contact with each other or the box, and droplets on the specimen must not fall on other specimens.
The sample holder is made of glass, plastic and other materials. The material for hanging the sample cannot be metal, but should be made of insulating materials such as fiber.
Test time
The test time is determined according to different product specifications. Generally speaking, it is 2/4/6/8/24 hours. If it is greater than 24 hours, it is an integer multiple of 24 hours.
For example:
Post-test sample handling
After the test, take out the sample and dry it naturally indoors for 0.5 to 1 hour, then gently rinse it with clean running water with a temperature no higher than 40 degrees Celsius to remove the remaining salt spray solution, and then blow dry immediately with a hair dryer.
5. Sample rating
Rating criteria selection
Explanation of some proper nouns
Anodic coating: refers to a coating in which the covering layer is anodic to the substrate. That is, the covering layer is more active than the base metal. If an electrochemical reaction occurs, the covering layer will corrode first. For example, galvanizing on steel, etc.
Cathodic coating: refers to a coating in which the covering layer is cathodic to the substrate. That is, the covering layer is not as active as the base metal. If an electrochemical reaction occurs, the base metal will corrode first. For example, tin plating on steel, etc.
ASTM D610-01
The assessment result generally consists of a number and a letter, such as 6-S, 4-P. The first number indicates the corrosion area, and the following letters indicate the corrosion form.The specific explanation is as follows:
The corrosion forms are as follows;
S Spot Rusting Several large pieces of corrosion
G General Rusting There are large and small corrosion sizes.
P Pinpoint Rusting Tiny pitting corrosion
H Hybrid Rusting Several forms of mixed corrosion
The diagram is as follows:
ISO 4628-3:2003
The evaluation result is Ri followed by an Arabic numeral, such as Ri6, Ri4. The number indicates the corrosion area
The corresponding relationship between numbers and corrosion area is as follows:
Rating number Corrosion area
Ri 0 0
Ri 1 0.05
Ri 2 0.5
Ri ３ 1
Ri４ 8
Ri ５ 40/50
ISO 10289:1999
The assessment results generally consist of protection rating number (Rp) and appearance rating number (RA). If only protection rating is required. Appearance ratings can be omitted.
The protection rating number (Rp) indicates the ability of the coating to protect the base metal from corrosion. It is usually represented by an Arabic number from 0 to 10. This number represents the area of the base metal where corrosion occurs.
The appearance rating number (RA) indicates the degree of damage to the covering layer. It usually consists of an Arabic numeral from 0 to 10 plus a lowercase letter and an uppercase letter. For example, 6 m A, 4 s C. In the above ratings, Arabic numerals represent the corresponding coverage damage area. Lowercase letters represent the subjective evaluation of the coverage damage degree, and capital letters represent the coverage damage type.
(Rp, Ra explained
R=Rating
p = protection
a = appearance appearance)
The corresponding relationship between numbers and corrosion area is as shown below:
Subjective evaluation of the extent of cover damage
vs = very mild
s = mild
m = Moderate
x = severe
Classification of cover damage types
A: Spots and/or color changes caused by damage to the covering layer
B: Darkening caused by coating corrosion that is difficult to see or even invisible.
C: Corrosion products of the anodic coating
D. Corrosion products of cathodic coating
E．Surface pitting corrosion
F: shatter, peel, peel off
G Bubble
H Crack
I Crack
J. Chicken-like or star-shaped defects
Rating example 1
Slight rust exceeds 1% of the surface and is less than 2.5% of the surface
Rp = 5
Minimal surface pitting causing slight darkening of the entire surface
Ra = 0 s B , vs E.
Rating example 2
Base metal corrosion occurs on 0.3% of the specimen area
Rp = 7
The corrosion products of the anodic coating cover 0.15% of the total area, and the area with slight bubbling in the top electrodeposition layer exceeds 0.75% of the total area.
Ra = 8 vs C, 6mG
Rating legend:
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If you have any questions about the environmental test chamber, please do not hesitate to contact us!
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Mr. Bob
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