Prevent Thread Galling

During the assembly of precision components, have you ever encountered this situation? A carefully machined stainless steel or titanium alloy part suddenly seizes while tightening a bolt, leaving it impossible to move forward or backward, and ultimately forcing you to damage or scrap the part.

This phenomenon is known in the industry as thread galling, also referred to as cold welding. For high-value custom CNC-machined parts, this is not only a waste of material but also a significant loss in production time and project efficiency.

What Is Thread Galling?

Thread galling commonly occurs in metals with self-passivating properties, such as stainless steel, aluminum alloys, and titanium alloys. When threaded components are subjected to friction under load, the protective oxide layer on the surface can break down, exposing fresh metal atoms. Under pressure, these atoms come into direct contact and attract each other, resulting in a molecular-level “cold welding” effect.

Common factors that contribute to galling include:

• Excessive surface roughness: Microscopic irregularities on the thread surface increase friction and heat generation.
• Similar material pairing: Components made from the same material tend to have higher friction coefficients, making molecular adhesion more likely.
• Excessive installation speed: Frictional heat builds up rapidly, accelerating metal softening and galling.

Common Causes of Thread Galling

1. Excessive Surface Roughness

Microscopic peaks and valleys on the thread surface increase friction and heat generation.

2. Similar Material Pairing

Fasteners and mating components made from the same material are more prone to molecular adhesion and cold welding.

3. Excessive Installation Speed

Rapid tightening generates excessive frictional heat, increasing the likelihood of galling.

4. Misalignment or Uneven Loading

When the bolt and nut are not properly aligned on the same axis, localized stress concentrations occur. The increased contact pressure can promote localized cold welding and ultimately cause thread seizure.

5. Tight Thread Tolerance Fit

If the external thread is oversized or the internal thread is undersized, the actual clearance becomes insufficient. Increased friction during assembly can significantly raise the risk of galling.

What to Do If Thread Galling Occurs

If you notice the threads becoming stiff or beginning to seize:

Method 1: Stop Immediately

Do not continue tightening.

Applying additional force will often worsen the cold welding effect and may lead to complete seizure.

Method 2: Apply a Penetrating Lubricant

Allow the lubricant sufficient time to penetrate the threads, then attempt gentle back-and-forth rotation.

Method 3: Alternate Rotation Directions

Slowly rotate the fastener in both tightening and loosening directions. Avoid applying continuous force in a single direction.

Method 4: Heat Treatment

For large assemblies, carefully heating the nut may cause thermal expansion. Since the internal and external threads expand differently, this may help release the seized connection.

How to Prevent Thread Galling

1. Use an Anti-Seize Compound

This is one of the most effective methods for preventing thread galling.

2. Reduce Installation Speed

Avoid high-speed or forceful assembly.

3. Use Dissimilar Material Pairings

Selecting different materials can reduce the risk of metal adhesion.

Avoid:

• 304 Stainless Steel Bolt + 304 Stainless Steel Nut

Recommended:

• 304 Stainless Steel Bolt + Brass Nut

4. Apply Surface Treatments

Suitable surface treatments include:

• Zinc plating
• Nickel plating
• Dacromet coating
• PTFE (Teflon) coating
• Silver plating

5. Ensure High-Quality Thread Manufacturing

Strictly control thread finish and surface quality to minimize friction.

6. Clean the Threads Before Assembly

Thoroughly remove burrs, oil, dirt, metal chips, and other contaminants to ensure smooth thread engagement.

Why Choose Our Custom Machining Services?

At Shenzhen Pans Technology, we understand that every thread can make the difference between project success and failure.

Extensive Experience

We have years of experience machining galling-prone materials such as stainless steel, titanium alloys, and aerospace-grade aluminum.

Comprehensive Quality Assurance

From tool selection and optimized cutting parameters to final GO/NO-GO gauge inspection, we ensure every thread performs exactly as designed.

One-Stop Manufacturing Solution

In addition to CNC machining, we provide complementary surface treatment services and technical consultation, helping customers avoid thread galling issues from the design stage through final production.