Selecting Surface Finish and Coating for Black POM Spacers

Selecting Surface Finish and Coating for Black POM Spacers

Bost’s black POM spacer made by injection molding delivers superior wear resistance and dimensional stability, ensuring precise positioning in demanding applications. This injection-molded black POM wear-resistant spacing product is designed for durability and long-lasting support in assemblies that rely on engineered plastic components. Choosing the right surface finish and coating is critical to getting the expected friction, durability, chemical resistance, and appearance from these spacers. This article explains practical selection criteria, common finishes and coatings, processing considerations, and test/inspection guidance so design and procurement teams can make informed choices for production and end-use.

Why surface finish matters for engineered plastic components

Surface finish affects multiple performance attributes of a black POM spacer: friction against mating parts, wear rate, dirt accumulation, sealing behavior, and cosmetic appearance. For engineered plastic components such as positioning spacers, small changes to surface roughness or coating chemistry can change wear life by orders of magnitude under sliding contact. POM (polyoxymethylene) inherently has low surface energy and good wear properties, but its surface is also relatively inert, which influences how well coatings adhere and how treatments modify friction.

Key performance drivers

When specifying finishes and coatings, prioritize these application-driven factors: contact load and sliding speed, environment (temperature, humidity, chemicals), dimensional tolerances, surface compatibility with mating materials, visual requirements, and cost/manufacturing throughput. Balancing these factors helps select an engineered solution that maximizes the value of the injection-molded black POM spacer.

Common as-molded finishes and when to use them for black POM spacers

Injection molding surface finish options typically mirror the mold surface treatment. Using the correct mold polish or texture can deliver the needed performance without secondary operations. Common as-molded finishes include:

• Textured (matte) finish: mask surface defects, reduce glare, and trap lubricant films. Good for visible components and where minor micro-asperities help retain lubrication.
• Gloss/polished finish: lower friction and less wear particulate generation in sliding assemblies; used when tight friction control and cleanliness are required.
• Highly polished mirror finish: for precision guides or seals where low asperity contact is essential; more expensive mold prep but can extend wear life.
• As-molded with ejector-pin marks: acceptable for non-critical spacer locations, but may require post-processing or coatings if contact stresses concentrate at marks.

For many applications, Bost’s black POM spacer performs well as-molded with a controlled gloss level. If wear or friction is critical, consider mold polishing to a specified Ra value and pair with a compatible coating or surface treatment.

Surface treatments to improve adhesion and performance on POM

POM has low surface energy, which makes coating adhesion challenging. Surface activation steps are commonly required before applying functional coatings. Typical treatments include:

• Flame treatment - rapid and effective for large batches; increases surface energy by oxidizing the top layer.
• Corona or plasma treatment - controlled, consistent surface activation; plasma provides the best performance for small parts and precision coating adhesion.
• Grit blasting - mechanically increases surface area; useful when combined with primers but can alter dimensions and generate debris.
• Chemical etching or primer layers - primers chemically bond to POM and provide a good base for paints or functional coatings.

Choose the treatment compatible with production volume, tolerance sensitivity, and the selected coating chemistry. For engineered plastic components that require high coating adhesion, plasma plus a tailored primer is often the most reliable combination.

Coating options for black POM spacers and their trade-offs

Below is a summarized comparison of commonly used coatings and functional finishes for POM spacers. The table focuses on wear behavior, friction, chemical resistance, adhesion difficulty, and typical cost level.

Match the option to the top two project priorities. If minimizing total lifecycle cost is primary, a polished as-molded spacer with design features to distribute load may be best. If maximizing run-in life in high-cycle sliding is critical, invest in PTFE or Parylene despite higher up-front cost.

Case examples: selecting finishes for typical applications

Example 1: A precision linear guide using a black POM spacer that slides against anodized aluminum. Requirement: low friction, long wear life, and consistent dimensional control. Recommendation: Polished as-molded finish plus PTFE topcoat with plasma pretreatment to ensure adhesion.

Example 2: An exterior automotive trim spacer exposed to road salts and cleaning chemicals. Requirement: chemical resistance and stable appearance. Recommendation: Parylene coating for barrier protection, with design allowances for coating thickness and a high-durability mold texture for appearance.

How Bost’s black POM spacer supports your engineered plastic components strategy

Bost’s black POM spacer made by injection molding combines the dimensional stability of POM with process controls to deliver consistent part geometry. The product is engineered for wear resistance and precise positioning, making it an excellent base part for additional surface treatments. Bost partners with coating specialists and uses validated surface activation methods so customers receive spacers that meet both mechanical and coating adhesion requirements. Benefits include:

• Repeatable molded geometry that minimizes post-process adjustments
• Compatibility with common treatments (plasma, flame) and coatings (PTFE, dry-film lubricants, Parylene)
• Quality control plans that include coating adhesion and tribology testing
• Production scalability for prototype to high-volume programs

Inspection, traceability, and supplier qualification

For critical assemblies, require traceability for batch, molding parameters, and coating lot numbers. Include inspection checkpoints for coating thickness, adhesion, and dimensional compliance. When qualifying suppliers of engineered plastic components, request process capability (Cp/Cpk) data for critical dimensions and documented coating process windows. This reduces risk of field failures and supports continuous improvement.

Implementation checklist before production run

Use this checklist to ensure readiness:

• Define performance targets: friction coefficient, allowable wear volume, environmental resistance
• Select finish/coating and document surface prep method
• Prototype and run tribo/adhesion/chemical tests to validate choice
• Update CAD tolerances to account for coating thickness
• Agree inspection and acceptance criteria with suppliers
• Plan for pilot run and monitor first-article inspection

Frequently Asked Questions (FAQ)

Q: Do coatings always improve wear life for black POM spacers?

A: Not always. Coatings can reduce friction and wear but must be compatible with POM and the mating material. Poor adhesion or inappropriate coating thickness can cause flaking or increased wear. Validate through tribological testing and adhesion checks.

Q: What surface treatment provides the best adhesion on POM?

A: Plasma treatment combined with an appropriate primer typically gives the most consistent adhesion for subsequent coatings on POM. Flame treatment is effective at scale, while grit blasting is mechanical and may alter tolerances.

Q: How much coating thickness should I expect and how does it affect tolerances?

A: Coating thickness varies by process: dry-film lubricants and PTFE can range from 1 to 10 microns, Parylene from 1 to 25 microns, and paints from 20 to 100 microns. Always specify tolerances relative to the post-coating dimension or plan for selective masking and post-coating machining if needed.

Q: Can I plate metal onto a POM spacer?

A: Direct metal plating on POM is difficult due to low surface energy. It usually requires aggressive pretreatments or conductive interlayers. Consider metallization only when absolutely required and after technical feasibility studies.

Q: Which is more cost-effective: polishing the mold or applying a coating?

A: Polishing the mold gives permanent as-molded finish with minimal per-part cost but higher mold preparation cost. Coatings add per-part processing cost but can provide functional properties not achievable by polishing alone. Choose based on required function and volume.

Q: How should I test adhesion and wear during qualification?

A: Use industry-standard adhesion tests (cross-hatch/tape, peel tests) and application-specific tribology tests (pin-on-disk, reciprocating wear) under representative loads and speeds. Include environmental conditioning before testing.

Contact Bost / See product

If you need assistance selecting the right surface finish or coating for your black POM spacer or want a sample run for validation, contact Bost’s technical sales team. Request a datasheet, sample parts, or testing protocol to accelerate your design validation and supplier qualification.

Authoritative references and further reading

• Polyoxymethylene (POM) - Wikipedia: https://en.wikipedia.org/wiki/Polyoxymethylene
• Injection molding - Wikipedia: https://en.wikipedia.org/wiki/Injection_molding
• Delrin by DuPont (POM product info): https://www.dupont.com/brands/delrin.
• Coatings for plastics overview - AZoM: https://www.azom.com/article.aspx?ArticleID=11957
• About plastics - PlasticsEurope: https://www.plasticseurope.org/en/about-plastics/what-are-plastics/major-plastics