China Inspection and Quarantine Inspection, Factory Inspection, Certification and Testing [Inspector Encyclopedia] Plastic Parts Testing and Inspection Knowledge

1. Basic knowledge and inspection points of six common plastics

During the inspection and quality management process, being familiar with the material properties and common defects of commonly used plastics is the basis for ensuring product quality. The following is basic knowledge about six common plastics and their key points during factory inspection and testing:

1. PE (Polyethylene)
   Polyethylene is soft, waxy, lightweight, somewhat transparent, and burns with a blue flame. It is commonly used in daily necessities such as plastic wrap, vest bags, food bags, baby bottles, and buckets.
   Inspection focus : During the inspection process, you need to pay attention to whether there are impurities, bubbles, deformation, etc. on the surface; the PE material used for packaging food must meet food grade standards, and the source of raw materials and qualification certificates should be verified during the factory inspection.

2. PP (polypropylene)
   Polypropylene is non-toxic and odorless, resistant to high temperatures (no deformation at 100°C), and resistant to acids and alkalis. It is widely used in medical devices, auto parts, food packaging and other fields.
   Inspection focus : During inspection, it is necessary to confirm that the product has no burrs, shrinkage, white top, etc.; in high-temperature applications, its thermal stability must be verified to avoid performance degradation due to oxidation.

3. PS (polystyrene)
   It is colorless and transparent, and is commonly used in optical instruments, daily necessities such as tea trays, soap boxes, etc. It can also be used as food packaging film.
   Inspection focus : The transparent area should be checked for appearance defects such as silver threads, bubbles, and spots; it is relatively brittle, so when inspecting the goods, pay attention to whether there are any cracks or hard scratches.

4. PVC (polyvinyl chloride)
   It is divided into soft and hard types and is commonly found in raincoats, cable sheaths, artificial leather, etc. It cannot be used for food packaging.
   Inspection focus : When inspecting the factory, you need to pay attention to whether the raw materials contain harmful substances; when inspecting, pay attention to whether the smell and color are uniform, and whether there are process defects such as deformation and weld marks.

5. ABS (Acrylonitrile Butadiene Styrene)
   Engineering plastics have high strength and good heat resistance and are commonly used in electronics, automobiles, and mechanical parts.
   Inspection focus : When inspecting, check whether the surface coating is uniform, whether there is white top, welding marks, color difference, etc.; impact strength and weather resistance are key performance indicators and require sampling testing.

6. PA (nylon)
   Wear-resistant and corrosion-resistant, used in civil and industrial fields such as mechanical parts, industrial fabrics, and fishing nets.
   Inspection focus : During factory inspection, attention should be paid to the drying process to avoid silver streaks and bubbles; during inspection, emphasis should be placed on testing its wear resistance and dimensional stability.

2. Common materials and inspection requirements for transparent plastic products

Common materials for transparent plastic products include ABS, PET, PS, etc. During the inspection process, special attention should be paid to the appearance quality and optical properties:

1. ABS plastic
   ABS is typically opaque, but some grades of transparency exist. Inspection should focus on light transmittance, surface smoothness, and the presence of defects such as bubbles, specks, and silver streaks. Factory inspections should also confirm whether recycled materials have been added to the raw materials to avoid affecting transparency and strength.

2. PET plastic <br>has good transparency and wear resistance, and is widely used in beverage bottles, electronic components, etc.
   Inspection focus : During inspection, check whether the preforms are free of bubbles, black stripes, and deformation; electronic components need to verify their insulation performance and dimensional accuracy.

3. PS plastic <br>High light transmittance, second only to acrylic, but has a brittle texture.
   Inspection focus : During the inspection, attention should be paid to stress cracks, fine scratches, weld marks and other problems, and the use of benzene solvents for cleaning should be avoided.

III. Definition of defects and inspection criteria

During the inspection process, it is necessary to clarify the criteria for determining various defects. Common defects include:

1. Spots/impurities : Point defects, measured by the maximum diameter, are usually acceptable if they are not visible to the naked eye at a distance of 30 cm from the product.

2. Burrs : Linear protrusions at the parting line or joint line are considered poor molding. During inspection, it is necessary to determine whether it is allowed according to customer standards.

3. Silver streaks : Often caused by insufficient drying of the resin. The drying process records should be reviewed during factory inspection.

4. Whitening and deformation : Whitening and deformation caused by the ejector pin. When inspecting the product, pay attention to whether the demoulding structure is reasonable.

5. Weld marks and flow marks : The confluence of molten plastic or the flow marks affect the appearance and strength, and need to be judged based on the location and degree of obviousness.

6. Color difference and color separation : Use a colorimeter to compare with standard samples, and reject if it exceeds the ΔE range.

7. Hard scratches and bumps : These involve surface treatment and packaging processes. The operating environment and packaging methods should be evaluated during factory inspection.

4. Plastic Product Inspection Standards and Key Points for Factory Inspection

When formulating inspection specifications and factory audits, the following contents must be included:

1. Appearance inspection : Check for spots, burrs, shrinkage, bubbles, scratches, etc. under standard light source, and make judgments based on AQL sampling standards.

2. Dimension measurement : Use tools such as calipers and projectors to check whether key dimensions are within the drawing tolerances.

3. Performance testing : Conduct corresponding tests based on product usage, such as heat resistance (oven test), impact strength (drop hammer test), melt index test (MFI), etc.

4. Raw material control : During factory inspection, it is necessary to review the raw material inspection report and traceability system to determine whether compliant new materials or controllable recycled materials are used.

5. Process review : Injection molding parameters (temperature, pressure, cycle), mold maintenance records, drying process, etc. are the focus of the factory inspection.

6. Packaging and labeling : Check whether the packaging is damaged or scratched, and whether the label content is correct and meets environmental protection requirements.

Summary: Plastic product inspection needs to combine material properties, process defects and functional requirements, and establish a comprehensive quality control system from factory inspection to final inspection to ensure that products meet appearance, performance and safety standards.