GMW 16317 Bloom Tests for Elastomeric Parts

Developed by General Motors Worldwide (GMW), the “GMW 16317 Bloom Tests for Elastomeric Parts” standard is a test standard used to evaluate the tendency of elastomeric materials and parts to bloom on their surfaces.

Bloom is a visible surface phenomenon in which certain components within a rubber or elastomer migrate toward the surface, forming a film, deposit, discoloration, or crystalline-looking layer. While the underlying elastomer may remain functional, excessive bloom can affect cleanliness, adhesion, friction, and the performance of mating components. Therefore, the GMW 16317 standard provides methods to determine how susceptible elastomeric parts or materials are to this phenomenon.

Elastomer formulations contain a variety of components, including:

• vulcanizing agents
• Accelerators
• Antioxidants
• plasticizers
• Processing aids
• Candles
• Fillers and other additives

Under certain environmental or aging conditions, some of these substances can penetrate the rubber matrix and accumulate on the surface. This process is known as blooming. Blooming should not be confused with ordinary contamination. It originates from the elastomer formulation itself and is affected by factors such as temperature, time, formulation, component compatibility, and environmental exposure.

The primary purpose of the GMW 16317 standard is to determine the blooming tendency of elastomeric parts/materials. The results can be used for:

• Comparing different elastomer formulations.
• To evaluate the stability of a rubber compound.
• To identify formulations that produce excessive surface deposits.
• Support materials and supplier qualification assessment.
• Investigating appearance or contamination issues on manufactured parts.
• To evaluate the suitability of elastomers for automotive applications.

This is especially true for automotive rubber components where surface appearance and interaction with adjacent materials are important.

The GMW 16317 standard is designed for elastomeric parts and materials. Previous versions have specifically defined applications such as airtight extrusion profiles, molded sections, and cooling hoses for particular test methods.

Typical automotive elastomer applications may include:

• Door and window airtight strips
• Sealing profiles
• gaskets
• hoses
• Rubber fasteners
• Washers
• Protective cases
• Molded rubber components

Precise applicability and requirements should always be determined from the relevant revision and the engineering specification of the component.

The GMW 16317 standard includes various approaches for evaluating elastomer bloom:

• Method A Environmental cycling bloom test: This method evaluates blooming after exposing elastomeric samples to a controlled environmental/temperature cycle. The aim is to accelerate conditions that can promote the migration of formulation components to the surface. After conditioning, the sample surface is examined for signs of blooming.
• Method B: This method provides another controlled approach to assess the tendency of an elastomer to bloom on its surface. Precise conditioning and evaluation requirements are included in the standard.

• Method C1 and Method C2: These methods are additional flowering assessment methods included within this standard framework. They provide alternative conditioning/evaluation approaches for assessing surface flowering behavior.

Detailed temperatures, durations, sample sizes, equipment settings, and acceptance criteria should be taken directly from the GMW 16317 standard, rather than from secondary sources.

A flowering assessment essentially follows these steps:

• Sample preparation: Representative elastomer samples or finished parts are selected and prepared according to the standard.
• Initial inspection: The initial condition and appearance of the sample are documented.
• Environmental conditioning: Samples are exposed to specified environmental or thermal conditions.
• Cyclic treatment or aging: A specified exposure sequence is performed to promote possible migration of elastomer components.
• Surface inspection: After conditioning, the surface is examined to check for signs of flowering.
• Assessment: The observed surface condition is evaluated according to applicable assessment requirements.
• Reporting: Test conditions and observations are documented for material or component suitability.

The test methods described primarily concern surface deposits resulting from the migration of components from the elastomer. Possible observations may include:

• White or gray surface deposits
• Waxy films
• Crystal-like deposits
• color change
• Loss of expected surface appearance
• Visible material migration

The formation of white or gray deposits on the surface does not necessarily mean that an elastomer has mechanically failed. Its significance depends on the application and applicable acceptance requirements.

GMW 16317 is important because elastomeric components are frequently exposed to temperature changes, humidity, chemicals, and prolonged aging in vehicles. An elastomer that appears satisfactory immediately after manufacturing may develop white or gray deposits during storage or use. This can lead to a variety of problems:

• Appearance: Visible deposits, particularly on visible air seal strips and trim-related rubber components, can cause a part to appear defective or contaminated.
• Functional performance: Surface deposits can potentially alter friction, sealing behavior, adhesion, or interaction with mating components.
• Production and assembly: Surface deposit formation can hinder bonding, coating, painting, printing, or other subsequent processes where a clean elastomer surface is required.
• Material selection: This test allows engineers to compare formulations and select elastomers that exhibit better resistance to unwanted surface migration.
• Quality control: This method can also support investigations when unexpected deposits appear in production components.

For General Motors suppliers, surface deposit testing can be part of a broader material validation program. The goal is not simply to determine if the rubber surface has changed, but to ascertain whether the material retains the required properties throughout its intended lifecycle. This makes bloom testing particularly valuable in the following situations:

• New material development
• Supplier qualification assessment
• Formulation changes
• Process changes
• Failure analysis
• Production troubleshooting
• Verification of airtight strips and seals.

In conclusion, the GMW 16317 standard is a standard developed to evaluate the tendency of elastomeric materials and components to develop undesirable surface deposits through the migration of formulation components. This standard offers various test methods, including environmental conditioning approaches, to assess efflorescence behavior.

The methods described are considered valuable for automotive manufacturers and suppliers because excessive glare can affect surface condition, assembly processes, material compatibility, and potentially component performance. Proper implementation of this standard helps engineers identify unsuitable elastomer formulations and improve the long-term quality and reliability of rubber components.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the GMW 16317 standard.