What are the methods for testing the surface quality of plastic injection molded products?

Release time：2025/1/6   Click ：

1、 Visual inspection of appearance
Direct observation method: This is the most basic method, in which the testing personnel observe the surface of the product directly with the naked eye under normal lighting conditions (usually natural light or standard lighting sources, such as D65 light source, simulating natural sunlight). Check for obvious appearance defects such as burrs, burrs, sprue marks, shrinkage marks, dents, bubbles, cracks, etc. The observation distance generally depends on the size of the product, usually around 30-50 centimeters. For example, for small plastic toys, observation can be conducted at a distance of about 30 centimeters; For large plastic furniture components, it may be necessary to observe at a distance of about 50 centimeters.
Auxiliary tool observation method: Use a magnifying glass or microscope to observe small defects on the surface of the product. For products with high precision and extremely high appearance requirements, such as precision electronic equipment casings or optical instrument accessories, it may be necessary to use magnifying glasses with a magnification of 5-10 times, or even higher magnification microscopes, to inspect the surface for microscopic scratches, impurity particles, and other defects.


2、 Glossiness detection
Glossmeter measurement: Use a glossiness meter to measure the glossiness of the product surface. Glossmeter is a specialized instrument used to measure the surface gloss characteristics of an object. It determines glossiness by emitting light at a certain angle onto the surface being measured and measuring the intensity of the reflected light. The measurement angles are usually 20 °, 60 °, and 80 °, among which 60 ° is the most commonly used angle. For products with high gloss surfaces, such as car paint exteriors or high-end cosmetic packaging, a measurement angle of 20 ° is usually used to more accurately measure the glossiness of their highlights; For products with semi glossy or low glossy surfaces, such as some indoor plastic products, angles can be measured at 60 ° or 80 °. Place the probe of the glossiness meter vertically on the surface of the product, read the glossiness value displayed by the instrument, and then compare it with the glossiness range required by the standard sample or customer.


3、 Color detection
Visual colorimetric method: Place the product together with a standard color card or color sample provided by the customer, and compare visually under a standard light source. When observing, it is important to ensure that the surrounding color does not interfere with the comparison results, and that the observation angle and distance are consistent. This method is simple and easy to implement, but subjective and suitable for situations where color accuracy is not particularly high.
Colorimeter measurement: Use a colorimeter to accurately measure the difference between the product and the standard color. The colorimeter measures the reflectance of the sample at different wavelengths and compares it with data of standard colors to calculate the color difference (Δ E) value. The smaller the Δ E value, the closer the product color is to the standard color. In the European and American markets, for many products, the Δ E value is usually required to be less than 1.0. In some industries with extremely high color requirements, such as high-end fashion products or branded electronic products, the Δ E value may be required to be less than 0.5. A colorimeter can provide more objective and accurate color detection results, and can record data for quality traceability.


4、 Surface hardness testing
Pencil hardness test: This is a simple and commonly used method for evaluating the surface hardness of plastic products. Choose a series of pencils with different hardness levels (from the softest 6B to the hardest 6H), sharpen the pencil tip to expose the lead by about 3-5 millimeters, and then slide it across the product surface at a 45 ° angle with a certain pressure (usually about 750 grams). Start testing with the softest pencil and observe if there are any scratches left on the surface of the product. If there are no scratches left, use a pencil with a higher hardness level to continue testing until obvious scratches appear on the surface. Record the hardness level of the pencil at this time as a reference for the surface hardness of the product. For example, for a typical plastic toy shell, the surface pencil hardness may be required to reach 2H-3H; For products that require higher hardness, such as industrial plastic parts, it may be necessary to reach 4H-5H.
Shore hardness test (applicable to soft plastics): For some soft plastic products, such as rubber plastic accessories or soft toys, a Shore hardness tester can be used for testing. Press the indenter of the hardness tester vertically onto the surface of the product and read the hardness value displayed on the hardness tester. Different products have different Shore hardness ranges based on their usage and customer requirements. For example, the Shore hardness of some soft toys may be between 30-50A.


5、 Wear resistance testing
Falling sand wear test: By allowing a certain amount of standard sand particles to freely fall and impact the surface of the product at a certain height, and then observing the wear condition of the product surface. Parameters such as sand particle size, falling height, and impact frequency can be set according to the actual usage environment of the product and customer requirements. For example, for outdoor plastic furniture, larger sand particles may be used to conduct multiple impact tests at higher heights to simulate the wear and tear of the product caused by outdoor wind and sand.
Taber Wear Test: Using the Taber Wear Test Machine, place a certain specification of grinding wheel (such as CS-10 grinding wheel) on the surface of the product, rotate the grinding wheel at a certain pressure and speed, and let it rub against the surface of the product for a certain period of time. After the experiment, observe the degree of wear on the surface of the product, such as the size, depth, and changes in glossiness of the worn area. This method can accurately simulate the friction and wear of products during actual use, and is suitable for various plastic products such as flooring materials and electronic product casings.


6、 Touch detection
Artificial tactile evaluation: Testing personnel touch the surface of the product with their hands to evaluate its texture and tactile sensation. Mainly consider whether the surface is smooth, rough, sticky, cold, etc. For products that require a comfortable tactile sensation, such as handheld device casings or household product handles, a tactile evaluation standard is usually established, and testing personnel make subjective evaluations based on this standard. For example, for the casing of handheld devices, it is required that the surface feel is comfortable and there should be no obvious graininess or sticky feeling; For household product handles, a certain degree of softness and warm touch may be required to enhance the user experience.
Surface roughness measurement (auxiliary): For some products with strict requirements for surface roughness, a surface roughness meter can be used to measure the micro roughness of the surface. The roughness meter moves the probe on the surface of the product to measure parameters such as peak to valley height differences, thereby obtaining surface roughness values (such as Ra value). For some plastic components that require high-precision assembly, the surface Ra value may be required to be between 0.8-1.6 μ m to ensure tight and smooth assembly.