SPI Standard Description Finishing method Surface roughness Ra (μm)
Posted: Sat Dec 28, 2024 9:59 am
(RA) and finishing procedure for each alphanumeric SPI surface finish standard.
Dry sanding, sandpaper, abrasive stone, and some types of diamond abrasives are used in finishing techniques. Within a range of values, RA is expressed in micrometers (µm). Injection molds that do not require one of these surface treatments may have an as-machined finish with a typical surface roughness of 3.20 RA and machining markings provided by the SPI standard.
The requirements for the different grades vary and the degree of deviation from perfection also varies. For example, a lower number allows for less deviation and a higher number for more deviation. According to the PIA (Plastics Industry Association), the four main surface finish classifications range from A1 (rough) to D3 (rough texture). The further categorization into three levels corresponds to 12 types of SPI surface finish treatments.
Brilliant Class A
Represents high-gloss polished surfaces that are preferred for objects that require a smooth or mirror-like appearance, are visually pleasing parts, and are the most expensive. They leave plastic forex datasetobjects with a glossy or clear finish; clear finishes are used for clear plastic grades, while glossy finishes are used for opaque plastic grades. For all three SPI A levels, a diamond polishing paste and a rotary tool are required for thorough polishing of the mold. They are used for optical parts such as visors, mirrors, and lenses, as well as for transparent packaging.
A-1 High gloss / optically clear Grade #3, 6000 grit diamond pad 0.012 to 0.025
A-2 Glossy / Transparent Grade #6, 3000 Grit Diamond Buff 0.025 to 0.05
A-3 Glossy / Transparent Grade #15, 1200 Grit Diamond Buff 0.05 to 0.10
Semi-gloss Class B
Brushed surfaces have fine, semi-gloss textures, making them ideal for good visual appearance and for removing tool marks on molds. These SPI finishes are intermediate-level polishes. Surface finishing involves sanding surfaces back and forth, using files of varying sizes. This sanding motion makes lines more visible compared to SPI Level A finishes. It often appears in sections of products that are not particularly important or aesthetic, such as appliance panels.
SPI Standard Description Finishing method Surface roughness Ra (μm)
B-1 Semi-gloss - Fine 600 grit paper 0.05 to 0.10
B-2 Semi-gloss - Medium 400 grit paper 0.10 to 0.15
B-3 Semi-gloss - Coarse 320 grit paper 0.28 to 0.32
Class C mat
Similar to Grade B but coarser, used for products that require a medium level of roughness to hide product defects and improve adhesion. A specific grit of sanding stone is used for each SPI Grade C finish. This is the most economical and popular surface finish. Ideal for consumer electronics, housewares and automotive interiors.
SPI Standard Description Finishing method Surface roughness Ra (μm)
C-1 Matte finish - Fine 600 grit stone 0.35 to 0.40
Dry sanding, sandpaper, abrasive stone, and some types of diamond abrasives are used in finishing techniques. Within a range of values, RA is expressed in micrometers (µm). Injection molds that do not require one of these surface treatments may have an as-machined finish with a typical surface roughness of 3.20 RA and machining markings provided by the SPI standard.
The requirements for the different grades vary and the degree of deviation from perfection also varies. For example, a lower number allows for less deviation and a higher number for more deviation. According to the PIA (Plastics Industry Association), the four main surface finish classifications range from A1 (rough) to D3 (rough texture). The further categorization into three levels corresponds to 12 types of SPI surface finish treatments.
Brilliant Class A
Represents high-gloss polished surfaces that are preferred for objects that require a smooth or mirror-like appearance, are visually pleasing parts, and are the most expensive. They leave plastic forex datasetobjects with a glossy or clear finish; clear finishes are used for clear plastic grades, while glossy finishes are used for opaque plastic grades. For all three SPI A levels, a diamond polishing paste and a rotary tool are required for thorough polishing of the mold. They are used for optical parts such as visors, mirrors, and lenses, as well as for transparent packaging.
A-1 High gloss / optically clear Grade #3, 6000 grit diamond pad 0.012 to 0.025
A-2 Glossy / Transparent Grade #6, 3000 Grit Diamond Buff 0.025 to 0.05
A-3 Glossy / Transparent Grade #15, 1200 Grit Diamond Buff 0.05 to 0.10
Semi-gloss Class B
Brushed surfaces have fine, semi-gloss textures, making them ideal for good visual appearance and for removing tool marks on molds. These SPI finishes are intermediate-level polishes. Surface finishing involves sanding surfaces back and forth, using files of varying sizes. This sanding motion makes lines more visible compared to SPI Level A finishes. It often appears in sections of products that are not particularly important or aesthetic, such as appliance panels.
SPI Standard Description Finishing method Surface roughness Ra (μm)
B-1 Semi-gloss - Fine 600 grit paper 0.05 to 0.10
B-2 Semi-gloss - Medium 400 grit paper 0.10 to 0.15
B-3 Semi-gloss - Coarse 320 grit paper 0.28 to 0.32
Class C mat
Similar to Grade B but coarser, used for products that require a medium level of roughness to hide product defects and improve adhesion. A specific grit of sanding stone is used for each SPI Grade C finish. This is the most economical and popular surface finish. Ideal for consumer electronics, housewares and automotive interiors.
SPI Standard Description Finishing method Surface roughness Ra (μm)
C-1 Matte finish - Fine 600 grit stone 0.35 to 0.40