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MIL-L-23398 Solid Film Lubricant – Aircraft Maintenance Guide
MIL-L-23398 is a military specification for an air-cured, corrosion-inhibiting solid film lubricant used to reduce wear and help prevent seizing, corrosion and galling. The specification identifies the lubricant under NATO Code S-749 and covers two types of air-cured solid film lubricant that can be applied by dipping, brushing or spraying.
MIL-L-23398 solid film lubricants are used on aircraft and aerospace components where a dry, bonded lubricating film is preferred over conventional liquid or grease lubricants. Applications can include metal bearing surfaces, threaded components, fasteners and other areas where reducing friction, wear, galling or corrosion is important.
BAC supplies Lubri-Bond A and Lubri-Bond 220 solid film lubricants for aerospace and aircraft maintenance applications.
MIL-L-23398 at a Glance
| Specification | Lubricant Type | NATO Code | Application |
|---|---|---|---|
| MIL-L-23398 | Air-cured solid film | S-749 | Reduce wear; prevent seizing, corrosion and galling |
MIL-L-23398 remains an active specification in the Department of Defense ASSIST/Quick Search system. The current document record identifies the specification as Lubricant, Solid Film, Air-Cured, Corrosion Inhibiting, NATO Code Number S-749.
What Is MIL-L-23398 Solid Film Lubricant?
MIL-L-23398 describes a solid film lubricant that forms a bonded lubricating coating on the surface of a component. Unlike conventional oils and greases, a solid film lubricant leaves a dry lubricating layer after the carrier has evaporated and the coating has cured.
The specification is intended for applications where the lubricant must help:
- Reduce friction and wear
- Prevent galling
- Reduce the potential for metal-to-metal seizure
- Provide corrosion protection
- Provide dry lubrication on metal surfaces
The specification identifies application by dipping, brushing or spraying, allowing the coating to be applied to individual components as well as larger production or maintenance applications.
MIL-L-23398 Type I vs. Type II
MIL-L-23398 establishes two types of air-cured solid film lubricant. Both types fall under NATO Code S-749, but the specification distinguishes the materials by type and intended form/application requirements.
| Type | General Description | Typical Form | Application |
|---|---|---|---|
| Type I | Solid film lubricant for bulk applications | Bulk coating material | Dipping, brushing or spraying |
| Type II | Solid film lubricant intended for aerospace/in-field applications | Often supplied in aerosol form | Spraying and touch-up applications |
Always verify the exact specification revision and type required by the applicable aircraft maintenance documentation or engineering specification. Product form, application method and qualification status can vary by product and specification revision.
MIL-L-23398 Products Available from BAC
| Product | Specification | Type | Product Description |
|---|---|---|---|
| Lubri-Bond A | MIL-L-23398B | Type II | Air-drying solid film lubricant for aerospace applications |
| Lubri-Bond 220 | MIL-L-23398D(2) | Type II | Air-cured solid film lubricant; NATO Code S-749 |
Everlube's specification history associates Lubri-Bond A with MIL-L-23398B and associates Lubri-Bond 220 with later revisions including MIL-L-23398B Amendment 2, MIL-L-23398C and MIL-L-23398D amendments.
The current DLA Qualified Products Database identifies Lubri-Bond 220 as a qualifying product under MIL-L-23398D(2), Type II.
Lubri-Bond A vs. Lubri-Bond 220
Both products are associated with the MIL-L-23398 family of air-cured solid film lubricants, but they correspond to different specification revisions.
| Feature | Lubri-Bond A | Lubri-Bond 220 |
|---|---|---|
| MIL Specification | MIL-L-23398B | MIL-L-23398D(2) |
| Type | Type II | Type II |
| Lubricant | Solid film | Solid film |
| Cure | Air drying | Air curing |
| Primary Benefit | Dry lubrication and low friction | Dry lubrication, wear and corrosion protection |
When replacing an existing MIL-L-23398 lubricant, always confirm the required specification revision and type before selecting a replacement product. A product meeting a later revision should not automatically be substituted for an older specified product without confirming that the later revision is acceptable for the application.
Aircraft Maintenance Applications for MIL-L-23398
MIL-L-23398 solid film lubricant is particularly useful where conventional wet lubricants are undesirable or where a bonded dry lubricating film can provide better performance.
Aircraft maintenance applications can include:
- Threaded components: Help reduce galling and seizing during assembly and disassembly.
- Fasteners: Provide dry lubrication on specified threaded or bearing surfaces.
- Metal-to-metal contact: Reduce friction and wear between compatible surfaces.
- Sliding surfaces: Provide a dry lubricating film where specified by the applicable maintenance procedure.
- Aircraft hardware: Protect specified components against corrosion and galling.
- Component overhaul: Restore or apply a specified solid film lubricant during component maintenance.
- Touch-up applications: Aerosol products can provide convenient application for appropriate maintenance and touch-up work.
FAA corrosion-control guidance identifies MIL-L-23398 as a solid-film lubricant for use on materials including aluminum alloys, copper and copper alloys, steel, stainless steel, titanium, and chromium- and nickel-bearing surfaces. Always follow the applicable aircraft manufacturer's maintenance instructions for the specific component.
Why Use a Solid Film Lubricant?
Solid film lubricants provide several advantages over conventional liquid lubricants in applications where a dry, bonded coating is preferred.
| Benefit | Why It Matters in Aircraft Maintenance |
|---|---|
| Dry lubrication | Provides lubrication without leaving a conventional wet oil or grease film. |
| Galling protection | Helps reduce metal-to-metal damage during movement or assembly. |
| Anti-seize performance | Helps prevent components from becoming difficult to disassemble. |
| Wear reduction | Provides a lubricating film between contacting surfaces. |
| Corrosion protection | Helps protect treated metal surfaces from corrosion. |
| Localized application | Can be applied to specific component surfaces by brush, dip or spray. |
MIL-L-23398 Application Methods
The MIL-L-23398 specification identifies dipping, brushing and spraying as application methods. The appropriate method depends on the product, component geometry, production or maintenance environment and the applicable process specification.
Spray Application
Spray application is particularly useful for aerosol versions and for components where an even coating can be applied without direct brush contact. It can also be convenient for field maintenance and touch-up applications when the product is supplied in an appropriate aerosol package.
Brush Application
Brush application provides controlled placement of the lubricant and can be useful for smaller components, localized areas and maintenance applications where overspray must be minimized.
Dip Application
Dip application can provide consistent coverage for suitable components and is generally more appropriate for controlled production or overhaul processes.
Application and curing requirements must always follow the product manufacturer's instructions and the applicable aircraft maintenance or engineering documentation.
MIL-L-23398 and NATO Code S-749
NATO Code S-749 identifies the solid film lubricant covered by MIL-L-23398. The DLA specification record identifies the title as Lubricant, Solid Film, Air-Cured, Corrosion Inhibiting, NATO Code Number S-749.
This means that searches for S-749 solid film lubricant may refer to the same general class of material covered by MIL-L-23398. When ordering or substituting material, however, the complete specification, revision and type should be verified rather than relying on the NATO code alone.
MIL-L-23398 vs. Other Solid Film Lubricant Specifications
Aircraft maintenance uses several different military and aerospace solid film lubricant specifications. They should not be treated as interchangeable simply because they all describe solid film lubricants.
| Specification | General Type | Cure | Key Difference |
|---|---|---|---|
| MIL-L-23398 | Solid film lubricant | Air-cured | Corrosion-inhibiting; NATO S-749 |
| MIL-PRF-46147 | Solid film lubricant | Air-cured | Different performance and qualification requirements |
| MIL-PRF-46010 | Solid film lubricant | Heat-cured | Requires elevated-temperature curing |
These specifications can have different performance requirements, application methods and cure requirements. For example, Air Force corrosion-control guidance distinguishes MIL-L-23398 and MIL-PRF-46147 as air-cured solid film lubricants from heat-cured MIL-PRF-46010.
Never substitute one solid film lubricant specification for another without confirming that the substitution is approved for the specific aircraft component or maintenance procedure.
How to Select a MIL-L-23398 Lubricant
When selecting a MIL-L-23398 lubricant for aircraft maintenance, consider:
- Required specification revision: Verify whether the documentation calls for MIL-L-23398B, C, D or another revision.
- Required type: Confirm whether Type I or Type II is specified.
- Application method: Select a product suitable for the required spray, brush or dip application.
- Component material: Confirm compatibility with the substrate being treated.
- Operating conditions: Consider load, movement, temperature and environmental exposure.
- Aircraft documentation: Follow the applicable AMM, CMM, SRM, overhaul manual or engineering specification.
- Qualification requirements: When a qualified product is required, verify the product's qualification status against the applicable QPL.
Frequently Asked Questions About MIL-L-23398
What is MIL-L-23398?
MIL-L-23398 is a military specification for an air-cured, corrosion-inhibiting solid film lubricant. It is intended to reduce wear and help prevent seizing, corrosion and galling. The specification identifies the lubricant under NATO Code S-749.
Is MIL-L-23398 still active?
Yes. The Department of Defense ASSIST/Quick Search record currently lists MIL-L-23398 as an Active Document, with the current record dated July 22, 2019.
What is NATO Code S-749?
S-749 is the NATO code associated with the solid film lubricant specified by MIL-L-23398. The DLA specification title identifies it as NATO Code Number S-749.
What is MIL-L-23398 Type II?
Type II is one of the two lubricant types covered by MIL-L-23398. Type II products are commonly encountered in aerospace applications and may be supplied in aerosol form. Always verify the required type and specification revision against the applicable maintenance documentation.
Does Lubri-Bond 220 meet MIL-L-23398?
Yes. The current DLA Qualified Products Database lists Lubri-Bond 220 as a qualifying product under MIL-L-23398D(2), Type II.
Does Lubri-Bond A meet MIL-L-23398?
Lubri-Bond A is associated with MIL-L-23398B. Everlube's specification guide identifies Lubri-Bond A with MIL-L-23398B and Lubri-Bond 220 with later revisions of the specification.
What is the difference between Lubri-Bond A and Lubri-Bond 220?
The primary distinction for specification purposes is the revision of MIL-L-23398 to which each product is associated. Lubri-Bond A is associated with MIL-L-23398B, while Lubri-Bond 220 is associated with later revisions including MIL-L-23398D(2). Verify the required specification revision before selecting a product.
Can MIL-L-23398 be used on aircraft components?
Yes. MIL-L-23398 is intended for aerospace and military applications and FAA corrosion-control guidance identifies MIL-L-23398 for use on materials including aluminum alloys, copper and copper alloys, steel, stainless steel, titanium, and chromium- and nickel-bearing surfaces. The applicable aircraft maintenance documentation should always determine whether the lubricant is approved for a specific component.
How is MIL-L-23398 applied?
The specification identifies dipping, brushing and spraying as application methods. The actual application procedure, surface preparation, coating thickness and cure requirements should follow the product manufacturer's instructions and the applicable aircraft maintenance documentation.
Is MIL-L-23398 the same as MIL-PRF-46147?
No. Both are air-cured solid film lubricant specifications, but they have different requirements and should not automatically be treated as interchangeable. Always verify the exact specification required by the aircraft manufacturer or maintenance procedure.
MIL-L-23398 Products from BAC
BAC stocks solid film lubricants for aircraft maintenance and aerospace applications, including products associated with the MIL-L-23398 specification.
| Product | MIL Specification | Type | View Product |
|---|---|---|---|
| Lubri-Bond A | MIL-L-23398B | Type II | Lubri-Bond A |
| Lubri-Bond 220 | MIL-L-23398D(2) | Type II | Lubri-Bond 220 |
Summary
MIL-L-23398 is an active military specification for air-cured, corrosion-inhibiting solid film lubricant. The specification is designed to reduce wear and help prevent seizing, corrosion and galling on aircraft and aerospace components.
For aircraft maintenance, the most important considerations are the required specification revision, Type I or Type II designation, application method and specific aircraft maintenance requirements.
BAC supplies Lubri-Bond A, associated with MIL-L-23398B, and Lubri-Bond 220, which is currently qualified under MIL-L-23398D(2), Type II. Always verify the required specification and revision before selecting or substituting a solid film lubricant.
Need help selecting the right solid film lubricant for an aircraft maintenance application? Contact BAC for assistance identifying the appropriate product and specification.