Choosing the Right PEM Fasteners for Stainless Steel
Leading Self-Clinching Fasteners Manufacturer and Supplier in China
Choosing the right PEM fasteners for stainless steel is crucial to ensure durability, corrosion resistance, and strong mechanical performance. Whether for outdoor, medical, or industrial applications, selecting the appropriate fasteners can significantly enhance the reliability and longevity of your stainless steel components.
Table of Contents
What Are the General Characteristics of Stainless Steel?
1. Types and Properties of Stainless Steel
Stainless steel comes in various types, and the chemical composition determines its core properties such as corrosion resistance, strength, and ductility:
304 Stainless Steel
(Typical composition: 18% chromium, 8% nickel)
- Characteristics: The most commonly used austenitic stainless steel, cost-effective, with moderate corrosion resistance and good cold-workability (excellent ductility).
- Limitations: Susceptible to pitting corrosion in chloride-rich environments (e.g., marine or pool areas), and stress corrosion cracking may occur at temperatures above 60°C.
316 Stainless Steel
(Typical composition: 16% chromium, 10% nickel, 2% molybdenum)
- Enhanced Corrosion Resistance: The addition of molybdenum (Mo) significantly improves resistance to chloride corrosion (ideal for marine equipment and chemical plant pipelines).
- Cost Difference: 316 is approximately 30% more expensive than 304 but offers longer equipment lifespan.
Martensitic Stainless Steels
(e.g., 410, 420)
- High Hardness: Suitable for tools, bearings, etc., but less corrosion-resistant, requiring regular maintenance.
2. Misconceptions in Choosing Stainless Steel
Misconception: “All stainless steels have the same corrosion resistance.”
Truth: The performance of stainless steel is highly dependent on environmental conditions and application scenarios:
Environmental Factors:
- In weak acidic or alkaline environments, 304 stainless steel maintains good corrosion resistance, but in high chloride environments (e.g., coastal regions), 304 may experience pitting corrosion, whereas 316 provides better protection due to its molybdenum content.
- In strong acidic or alkaline environments (e.g., sulfuric acid, hydrochloric acid), regular stainless steel cannot withstand the corrosion, and specialized alloys like Hastelloy or duplex stainless steel are required.
Surface Treatment and Maintenance:
- If stainless steel surfaces are scratched, have deposits, or are contaminated with iron particles, their corrosion resistance will decrease. For example, if carbon steel particles are left on a 304 stainless steel surface during processing, localized rusting may occur.
- Passivation treatment (e.g., pickling or oxide film restoration) and regular cleaning can significantly extend the lifespan of stainless steel.
High-Temperature Effects:
In high-temperature environments, certain stainless steels may suffer from carbide precipitation, which reduces their corrosion resistance. For example, 304 stainless steel may experience intergranular corrosion at temperatures between 450°C and 850°C, so 321 or 310 stainless steels are recommended due to their titanium or high nickel content, which offers better high-temperature resistance.
3. Compatibility Risks with Other Materials
When stainless steel comes into direct contact with other metals, galvanic corrosion may occur. This happens when two different metals are in contact within an electrolyte (such as water or humid air), causing the more active metal to corrode more rapidly.
Corrosion Mechanism: Metals with different electrochemical potentials form an electrical circuit in an electrolyte, causing the lower-potential metal (anode) to corrode more quickly.
Stainless Steel and Aluminum Alloy:
- In humid or saline environments, stainless steel is more “inert” compared to aluminum, and aluminum will accelerate oxidation due to galvanic corrosion, leading to joint loosening or failure.
- Solution: Use insulating washers (e.g., nylon washers) or apply anti-corrosion agents (e.g., anti-corrosion grease) to reduce galvanic corrosion.
Stainless Steel and Carbon Steel:
- During manufacturing, if carbon steel tools or iron filings remain on the stainless steel surface, rust spots may form.
- Solution: Use specialized stainless steel tools for processing and perform pickling or passivation before installation.
How to Prevent Galvanic Corrosion?
- Use Insulating Materials: Plastic washers, rubber seals, etc., to isolate direct contact between metals.
- Coating Protection: Aluminum can be anodized, or anti-corrosion coatings can be applied to contact surfaces to slow the electrochemical reaction.
- Design Considerations: Choose metals with similar electrochemical properties to avoid large potential differences.
How to Choose the Right PEM Fasteners for Stainless Steel?
When selecting PEM fasteners for stainless steel materials, several factors need to be considered, including material compatibility, fastener type, load capacity, surface treatment, and installation processes, to ensure durability and reliable installation.
1. Material Compatibility Principle
Same Material Matching
- Same Material Matching: Preferably choose PEM fasteners made from the same stainless steel material as the base material (e.g., if the base material is 304 stainless steel, select PEM’s SST-304 series) to avoid galvanic corrosion caused by dissimilar metal contact.
- Compatible Material Substitution: If cost is a concern, 316 stainless steel fasteners can be selected (more corrosion-resistant and compatible with 304 base materials).
Galvanic Corrosion Risk of Dissimilar Metal Contact
If the material of the PEM fastener does not match the base material, galvanic corrosion may occur due to the potential difference, accelerating metal corrosion. For example:
- Stainless Steel + Carbon Steel: Stainless steel is more noble, and carbon steel is more prone to corrosion.
- Stainless Steel + Aluminum: The potential difference is significant, causing aluminum to corrode first, leading to fastener failure.
Solutions:
- Insulating Coatings: Apply oxide film or anti-corrosion coatings (such as Teflon coating) on the fastener or stainless steel surface.
- Non-metallic Washers: Install nylon washers or insulating rings between the fastener and base material to prevent direct contact.
2. Fastener Type and Function
Select the Appropriate Type Based on Application
| Fastener Type | Application Scenario |
| Self-Clinching Nuts | Create permanent threads on stainless steel sheets |
| Self-Clinching Studs | Provide external threads for securing enclosures or equipment |
| Self-Clinching Standoffs | Used to fix PCBs or spacer components, preventing short circuits |
Selection Standards
- Sheet Thickness Requirements: Some PEM fasteners require a specific minimum sheet thickness, such as PEM CLS M3 self-clinching nuts, which are suitable for ≥1.0mm stainless steel sheets.
- Installation Strength Requirements: Fasteners like the HFH studs can withstand higher pull-out forces, making them suitable for high-load connections.
- Anti-loosening Functionality: For high-vibration environments, choose fasteners with locking features, such as Nylock insert locking nuts.
3. Load Capacity and Dimensional Precision
Load Capacity
The load types that fasteners need to withstand include static loads (e.g., securing enclosures) and dynamic loads (e.g., vibration environments).
In high-vibration environments (such as engine bays or motor equipment), it is recommended to choose locking-type fasteners:
- KEPS Nuts (with built-in anti-loosening spring washers)
- Nylock Nuts (with nylon inserts for locking)
- Secondary Locking Methods (e.g., adhesive, spot welding, etc.)
Effect of Hole Tolerance on Installation Strength
The dimensional precision of the PEM fastener installation holes directly affects the installation strength. It is recommended to strictly follow the standard hole diameter charts provided by the supplier. For example:
| Fastener Specification | Recommended Hole Diameter (mm) | Tolerance (mm) |
| M3 Self-clinching Nuts | 4.2mm | ±0.08mm |
| M4 Self-clinching Studs | 5.5mm | ±0.08mm |
| M6 Self-clinching Standoffs | 7.5mm | ±0.1mm |
4. Surface Treatment and Corrosion Resistance Enhancement
Passivation Treatment
- Purpose: Enhance the corrosion resistance of stainless steel fasteners and reduce the impact of surface contaminants.
- Application Scenarios: Suitable for industries with high cleanliness requirements, such as medical and food processing.
- Process: Nitric or citric acid cleaning to enhance the chromium oxide layer on the stainless steel surface, applicable to medical devices and food equipment.
- Prohibited Methods: Avoid zinc plating on stainless steel fasteners (which may damage the passivation layer and accelerate corrosion after plating layer peeling).
Coating Selection
- Zinc Plating: Enhances corrosion resistance but may affect the appearance of stainless steel.
- Nickel Plating: Suitable for electronic devices, prevents oxidation.
- Black Oxidation: Improves aesthetics and reduces light reflection.
Salt Spray Test Standards
The corrosion resistance of PEM fasteners is typically tested via salt spray testing (ASTM B117). For example:
- Standard Stainless Steel Fasteners: 48 hours without red rust
- Zinc-Nickel Plated Fasteners: 72-96 hours without red rust
- Black Oxidation Treated Fasteners: 120 hours without corrosion marks
5. Installation Process Considerations
Adjustment of Riveting Equipment Pressure Parameters
- Stainless steel is harder (e.g., 304 has a Rockwell hardness of HRB 70–90), requiring 20%–30% higher installation pressure than aluminum alloys.
- Reference Value: An M3 self-clinching nut on a 1.5mm thick stainless steel sheet requires about 10kN of pressure (calibration required based on supplier data).
Equipment Selection
- Pneumatic Riveters are suitable for mass production, ensuring installation accuracy.
- Hydraulic Presses are more suitable for high-strength stainless steel materials, reducing substrate deformation.
Installation Quality Inspection Methods
- Visual Inspection: No cracks or deformation on the surface after installation.
- Pull-out Testing: Random checks, with tensile strength at least 90% of the PEM nominal value.
- Thread Go/No-Go Gauge Testing: Ensure thread precision after installation (e.g., M3 threads should pass the Go/No-Go gauge test).
Protecting Stainless Steel Surfaces
To avoid damage to the substrate surface during installation, it is recommended to:
- Use Dedicated Riveting Molds to reduce surface scratches.
- Cover Fasteners with Protective Film to prevent fingerprints or contaminants from remaining.
Conclusion - Choose the Right PEM Fasteners for Stainless Steel
Choosing the right stainless steel PEM fasteners requires comprehensive consideration of material compatibility, galvanic corrosion, load capacity, surface treatment, and installation processes.
- Clarify the base material type and environmental corrosion levels.
- Use locking-type fasteners in high-vibration environments.
- Strictly follow hole diameter tolerance requirements to ensure installation strength.
- Adjust riveting pressure appropriately to avoid substrate deformation or fastener damage.
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Common Applications of PEM Fasteners in Stainless Steel
1: Outdoor Communication Equipment Enclosures
Application Background
Outdoor communication equipment (such as 5G base station enclosures, wireless communication module casings) is typically exposed to harsh environments with high humidity, salt spray, and strong UV radiation. The fasteners must not only offer excellent corrosion resistance, but also ensure long-term connection strength and waterproof performance.
Customer Requirements
- Corrosion Resistance: The equipment is exposed to a humid and salt-laden environment for long periods, so fasteners must resist rust.
- Waterproof Sealing: Connection points of the enclosure must prevent water ingress, ensuring internal components remain safe.
- High Strength: The enclosure needs to withstand vibration and wind loads without compromising internal electronic components.
Solution
Recommended PEM Fasteners: 316 Stainless Steel PEM Self-clinching Studs + Passivation Treatment
Reason for Selection:
- 316 Stainless Steel: Offers superior salt spray corrosion resistance compared to 304 stainless steel, making it suitable for coastal and high-humidity areas.
- Self-clinching Studs: Provide a high-strength external thread connection that is resistant to loosening.
- Passivation Treatment: Removes free iron from the surface, enhancing corrosion resistance and extending service life.
- Sealing Washer: Adding a silicone gasket during installation improves waterproofing.
2: Medical Endoscope Housing
Application Background
Medical devices such as endoscopes, surgical robots, and ultrasound probes are usually made from precision stainless steel enclosures, requiring lightweight, high strength, corrosion resistance, and the ability to withstand high-temperature sterilization, high-pressure disinfection, and long-term usage.
Customer Requirements
- Lightweight Design: The fasteners must be compact and not affect the device’s flexibility.
- High Corrosion Resistance: They must withstand common medical cleaning agents such as alcohol, hydrogen peroxide, and glutaraldehyde.
- Surface Sterility: The surface needs to be treated to prevent bacterial retention and meet medical standards.
Solution
Recommended PEM Fasteners: Micro 304 Stainless Steel Self-clinching Nuts + Electro-polishing
Reason for Selection:
- Self-clinching Nuts: Suitable for thin-walled stainless steel enclosures, providing reliable threaded connections.
- 304 Stainless Steel: Offers good corrosion resistance while being lighter in weight.
- Electro-polishing: Removes burrs and smooths the surface, reducing bacterial attachment and enhancing cleanliness.
- Compatibility with High-temperature Sterilization: Can withstand high-temperature, high-pressure sterilization (e.g., 135°C steam sterilization).
3: Stainless Steel Interior Panel Fixing for Rail Transit Vehicles
Application Background
High-speed trains, subways, and other rail transit vehicles often feature brushed stainless steel interior panels, used in wall panels, seat brackets, and instrument panels. The fasteners need to provide high vibration resistance, high pull-out strength, and ensure aesthetic appearance.
Customer Requirements
- Vibration Resistance: The fasteners must stay secure despite high vibrations from the moving train.
- Avoid Thread Tapping: Thin sheet metal on the vehicle body cannot be tapped, requiring self-locking fasteners.
- Aesthetic Appearance: The fasteners must not interfere with the visual appearance of the interior.
Solution
Recommended PEM Fasteners: Stainless Steel Self-clinching Standoffs + Low Profile Screws
Reason for Selection:
- Self-clinching Standoffs: Suitable for thin sheet connections, providing spacing support.
- Stainless Steel Material: Corrosion-resistant, able to withstand continuous vibration.
- Hidden Installation: Ensures a neat appearance, ideal for high-end rail transit interior applications.
4: Stainless Steel Component Installation in Food Processing Machinery
Application Background
Food processing machinery (such as mixers, packaging equipment, and ovens) requires food-grade safety for all fasteners, which must be resistant to corrosion, easy to clean, and free from food residue that could foster bacterial growth.
Customer Requirements
- Food-grade Stainless Steel: Prevents metal contamination in food contact areas.
- Chemical Resistance: The fasteners must resist alkaline detergents, acidic disinfectants, and other cleaning agents.
- Seamless Connection: Reduces sanitary dead zones to avoid food buildup.
Solution
Recommended PEM Fasteners: 316L Stainless Steel Self-clinching Nuts + Smooth Surface Finish
Reason for Selection:
- 316L Food-grade Stainless Steel: Low carbon content, acid and alkali resistant, meeting food industry standards.
- Self-clinching Nuts: Provide reliable threaded connections that do not loosen easily.
- Mirror Polishing: Reduces particle attachment, making cleaning easier.
- Can Be Combined with Food-grade Silicone Washers: Enhances sealing, preventing liquid ingress.
5: Stainless Steel Bracket Fixing for New Energy Battery Packs
Application Background
New energy vehicle power batteries are typically fixed with stainless steel or aluminum brackets that hold modular battery packs. The fasteners need to be heat-resistant, vibration-resistant, lightweight, and should not compromise the electrical safety of the battery.
Customer Requirements
- Heat Resistance: Fasteners must maintain their integrity despite high temperatures during battery charging and discharging cycles.
- Vibration Resistance: The fasteners must stay secure during vehicle operation to prevent battery module displacement.
- Insulation: Prevent contact between metal parts to avoid short-circuiting.
Solution
Recommended PEM Fasteners: Stainless Steel Self-clinching Studs + Insulation Coating
Reason for Selection:
- High Strength Self-clinching Studs: Provide high torque strength suitable for structural fixation.
- Stainless Steel Material: Offers heat resistance, corrosion resistance, and suitability for the new energy industry.
- Insulation Coating: Prevents contact between studs and battery conductive parts, reducing the risk of short-circuits.
Summary - Common Applications of PEM Fasteners in Stainless Steel
PEM fasteners are widely used in stainless steel applications, offering advantages including:
- Corrosion Resistance (suitable for medical, food, and outdoor applications)
- Vibration Resistance (for rail transit, battery modules)
- Lightweight Design (for medical devices, precision equipment)
- High-strength Fixing (for communication equipment, rail transit)
Choosing the appropriate PEM fastener can significantly improve the stability, durability, and installation efficiency of equipment.
What Are the Recommended PEM Fastener Suppliers?
Features:
- A leading PEM fastener and rivet nut supplier in China, specializing in high-strength stainless steel fasteners.
- Offers customized solutions to meet the needs of various industries such as electronics, automotive, medical, and construction.
- Can optimize the mechanical properties of fasteners according to customer requirements to enhance strength and corrosion resistance.
Certifications:
- IATF 16949:2016 (Quality Management System for Automotive Industry)
- ISO 9001 (Quality Management System Certification)
- Provides products that meet specific industry standards, such as medical or food-grade stainless steel fasteners.
Features:
- A globally recognized PEM fastener brand, offering a variety of fastener solutions including self-locking nuts, rivet nuts, clinch studs, standoffs, and more.
- Products are widely used in aerospace, electronics, automotive, medical, and defense industries.
- Strong research and development capabilities, continuously introducing high-performance PEM fastening technologies such as SpotFast® and microPEM®.
Certifications:
- ISO 13485 (Medical Device Quality Management System)
- FDA Certification (Food-grade fasteners available)
- RoHS / REACH (Environmental Standards Compliance)
Features:
- Headquartered in Germany, specializing in high-precision fastener technology, with widespread applications in automotive, aerospace, and electronics industries.
- Offers high-strength stainless steel PEM fasteners suitable for corrosion-resistant and vibration-resistant applications.
- Provides customer-specific engineering support to optimize design solutions and improve fastener installation efficiency.
Certifications:
- IATF 16949 (Automotive Industry Quality Management System)
- ISO 9001 (General Quality Management)
- Complies with EU RoHS / REACH standards
Features:
- An internationally renowned supplier of construction and industrial equipment, offering shock-resistant, high-strength PEM fasteners suitable for construction and mechanical assemblies.
- Fasteners are known for their corrosion resistance, impact resistance, and fatigue fracture resistance, making them ideal for high-stress environments.
- Provides a complete set of fastening installation tools to ensure efficient and stable construction processes.
Certifications:
- ISO 9001 (Quality System Certification)
- ASTM B117 (Salt Spray Testing Standard)
- Complies with construction industry corrosion resistance standards
Features:
- Provides comprehensive PEM fastening solutions covering industries such as electronics, aerospace, home appliances, and automotive.
- Products feature high corrosion resistance, high strength, and lightweight properties, suitable for high-end manufacturing.
- Supported by a global supply chain, ensuring stable supply for large-scale production needs.
Certifications:
- ISO 13485 (Medical Device Standards)
- IATF 16949 (Automotive Industry Certification)
- Complies with RoHS / REACH standards
Supply Chain Selection Recommendations
Certification Requirements:
- Food-grade applications: Choose suppliers certified by FDA to ensure fasteners meet food contact standards.
- Electronics industry: Choose fasteners that comply with RoHS / REACH environmental standards to reduce harmful substances.
- Medical devices: Opt for suppliers certified by ISO 13485 to ensure compliance with medical industry regulations.
Supply Chain Strategy:
- Choose suppliers that offer stainless steel PEM fastener technical support to ensure fastener strength, corrosion resistance, and reliable installation.
- Ensure suppliers have stable inventory management and global distribution capabilities to avoid supply chain disruptions affecting production.
- Prioritize suppliers that offer customized services, such as surface treatments or additional corrosion coatings, to meet specific application requirements.
FAQs - Choosing the Right PEM Fasteners for Stainless Steel
Q1: Can carbon steel PEM fasteners be used on stainless steel?
Carbon steel and stainless steel have a risk of galvanic corrosion. It is recommended to use stainless steel PEM fasteners. If carbon steel fasteners must be used, an insulating coating (such as nickel plating or epoxy coating) should be applied, or they should only be used in dry environments for short periods, as otherwise, significant corrosion may occur.
Q2: How do you test the tensile strength after installation?
Refer to the technical manual provided by PEM. Use a dynamic torque tester or pull-out testing machine for verification. Ensure the test meets industry standards (such as ISO 898 or ASTM F606) and check whether the fasteners meet the load strength requirements based on actual application needs.
Q3: What is the difference between 316 and 304 stainless steel when choosing PEM fasteners?
316 stainless steel contains molybdenum (Mo), which provides greater corrosion resistance, especially in high humidity, salt mist, or chemical environments (e.g., marine equipment, chemical plants). 304 stainless steel is suitable for general industrial and indoor applications and offers a more cost-effective solution.
Q4: Do stainless steel PEM fasteners require special tools for installation?
Due to the higher hardness of stainless steel, it is recommended to use high-strength riveting equipment and ensure that the pressure parameters are aligned with the fastener specifications. Avoid excessive pressure, which may lead to deformation, and also ensure sufficient pressure to secure a firm rivet.
Q5: Do stainless steel PEM fasteners require additional surface treatments?
It depends on the application environment. For high-corrosion environments, passivation treatment (to remove the surface oxide layer and enhance corrosion resistance) or electropolishing (to improve surface smoothness and reduce dirt buildup) can be chosen. In environments with electromagnetic interference, tin or nickel plating may also be used.
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