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Quality inspection of phenolic moulding compounds (made from phenolic resin matrix with added fillers, curing agents, lubricants, etc., primarily used for compression molding) must cover core dimensions including appearance, processing performance, physical and mechanical properties, thermal properties, and chemical resistance to ensure compliance with molding requirements and product performance. Specific inspection items and considerations are as follows:

Basic Appearance and Visual Quality Inspection

Appearance serves as an intuitive indicator for preliminary quality assessment, directly reflecting the uniformity of raw material mixing and pelletization (or powder preparation) during production. Specific inspection items include:

Color and Uniformity

Requirement: Products within the same batch must exhibit consistent color with no noticeable color difference (verifiable through visual comparison against standard color charts or quantitative measurement using a color difference meter).

Significance: Color variation may stem from resin batch differences, uneven filler dispersion, or processing temperature fluctuations, impacting the final product’s visual consistency.

Granule/Powder Condition

Granules: Inspect for rounded shape, absence of agglomeration or breakage (breakage rate must be ≤ specified value, typically ≤3%), and uniform particle size distribution (verifiable via standard sieve analysis; e.g., 20-60 mesh percentage must meet corporate standards).

Powder: Free of lumps and foreign matter (e.g., metallic impurities, fiber clumps). Test using a 100-mesh screen; residue must be ≤0.5%.

Impurities and Defects

Inspect visually or with a magnifying glass. Impurities such as metal shavings, stones, or undispersed resin lumps are not permitted. Granule/powder surfaces must be free of oil stains or mold spots (to prevent bubbles or delamination during molding).

Processing Performance Testing

The processing performance of phenolic moulding compounds directly determines the ease of compression molding and product yield rate. Core testing items include:

1. Flowability (Melt Flow Characteristics)

Test Method: Typically the Spiral Flow Length Method (per GB/T 14049-2008 “Phenolic Moulding Compounds”). Inject the molding compound into a spiral mold at specified temperature (e.g., 160-180°C) and pressure (e.g., 5-10 MPa), then measure the length of the spiral formed by the flowing melt.

Judgment Criteria: Flow length deviation within the same batch must be ≤±10%. Specific values should match the product structure (complex thin-walled products require high flowability, while thick-walled products require medium flowability to prevent overflow).

Significance: Excessively low flowability may cause incomplete filling or corner voids in products; excessively high flowability may lead to flash or overflow, increasing post-processing costs.

2. Curing Speed (Gel Time and Cure Time)

Gel Time: Measures the time from heating to loss of flowability (gel state) at a specified temperature (e.g., 175°C) (per GB/T 14049). Typically required: 50-150 seconds (adjusted based on part thickness; thicker parts require slightly longer gel time to prevent internal uncuring).

Curing Time: Measures the time required for complete curing at specified temperature and pressure (determined by hardness changes in molded test specimens; e.g., a Barcol hardness of 80 or above indicates full cure). Typically 3-5 times the gel time.

Significance: Excessively fast curing may cause internal stress and cracking in products; excessively slow curing prolongs production cycles and reduces efficiency.

3. Shrinkage Rate (Post-Forming Dimensional Stability)

Test Method: Mold a standard specimen (e.g., 120mm × 120mm × 3mm). After cooling to room temperature, measure the specimen’s actual dimensions. Compare these to the mold dimensions to calculate the shrinkage rate (Shrinkage Rate = (Mold Dimensions – Specimen Dimensions) / Mold Dimensions × 100%).

Judgment Criteria: Phenolic moulding compound shrinkage typically ranges from 0.4% to 1.2% (lower with inorganic fillers, slightly higher with organic fillers). Batch shrinkage deviation must be ≤±0.2% to prevent dimensional deviations in finished products.