SPI Plastic Mold Finishing Standard

The Society of the Plastics Industry (SPI), now known as the Plastics Industry Association, established a standard for mold polishing and finishing that is widely recognized in the plastics industry. GoodTech MFG uses SPI mold polish standards to categorize the surface finish quality of molds used for plastic injection molding, which directly impacts the appearance and texture of the molded parts.

SPI Mold Finish Standards

The SPI mold finish standards are typically divided into four main categories, which are further subdivided based on the level of polish or texture. These categories range from highly polished surfaces to textured finishes.

1. A Grade (Super High Polish)

A-1: Mirror finish, diamond buffed

A-2: High polish, Grade #6 diamond buff

A-3: Medium polish, Grade #15 diamond buff

Applications: The A-grade finishes are used for parts where a high-gloss, clear, or optically perfect finish is required, such as lenses or cosmetic surfaces.

2. B Grade (High Polish)

B-1: High polish, 600 grit

B-2: Medium polish, 400 grit

B-3: Low polish, 320 grit

Applications: B-grade finishes are suitable for parts requiring a high-quality finish, but not as perfect as A-grade, often used in consumer products.

3. C Grade (Standard Commercial Polish)

C-1: Low polish, 600 stone

C-2: Medium polish, 400 stone

C-3: Rough polish, 320 stone

Applications: C-grade finishes are used for parts where appearance is less critical, and a slightly matte finish is acceptable.

4. D Grade (Textured Finishes)

D-1: Grit blasted #24

D-2: Grit blasted #48

D-3: Grit blasted #80

Applications: D-grade finishes provide textured surfaces and are commonly used for parts requiring a matte or textured look, such as tool handles or surfaces designed to hide fingerprints or minor imperfections.

Usage and Importance

Impact on Final Product: The mold finish directly affects the aesthetic quality, texture, and functionality of the molded parts. A high-polish finish (A-grade) is crucial for parts that require a smooth, glossy surface, while a textured finish (D-grade) is important for grip or tactile features.

Consistency: Using these standards ensures consistency in manufacturing, allowing suppliers and clients to communicate clearly about the expected finish of a molded part.

These SPI mold finish standards are crucial for quality control in injection molding and are referenced in mold specifications, design documents, and during the manufacturing process.