When To Use Anti-Seize And Other FAQs

When to use anti-seize – and other FAQs

Anti-Seize products are designed to provide controlled assembly and release of threaded fasteners and other joints: When used correctly, they protect surfaces from galling, seizure and corrosion.

Here, we look at what anti-seize does and take you through advice from our experienced technical team on how to select and apply the right product for the right application.

What is anti-seize?

Anti-seize products are designed to provide controlled assembly and release of threaded fasteners and other joints. Threaded fasteners, flange joints are considered to be ‘static’ systems, though they must withstand a small amount of relative motion and vibration without loosening. Other systems have a greater interfacial motion that must be permitted but controlled, such as splines, keyways, or couplings: These are known as ‘dynamic’ systems.

The wear that occurs under vibration in both static and dynamic systems is called fretting, and anti-seize compounds for both static and dynamic systems are designed to reduce fretting wear.

Anti-seize products are applied to bolts, fasteners, and flanges to prevent galling and seizing on assembly, and corrosion during use: This helps disassembly.

A properly chosen and applied anti-seize compound delivers a wide range of benefits to an engineering system. It can:

1. Enable more precise and consistent clamping load in fasteners
2. Prevent pick-up and galling of fasteners during assembly
3. Reduce corrosion of interfaces by preventing water ingress and chemical attack
4. Provide controlled dismantling and prevent damage to components during disassembly.

When assembling components with a tight, press or interference fit, reducing the possibility of damage during assembly is important. It improves the precision of assembly, reduces the energy required, reduces wear in service, and aids disassembly (if needed).

What are anti-seize compounds made of, and how do they work?

Anti-seize products can be pastes, greases or coatings based on a wide range of materials to suit different systems. The selection of the most effective anti-seize product for an individual system or application is crucial, and some manufacturers offer helpful product selection guides.

In greases and pastes, the oil or grease phase provides lubrication at low temperatures. At high temperatures, the oil phase will decompose and the remaining lubricating solids will provide controlled disassembly after use.

Many general-purpose anti-seize formulations contain copper. In some systems, for example, a refinery where copper can poison a catalyst bed or reaction chamber, other materials such as nickel can be used. However, many industries prefer to use formulations that are free from metal powders, where a variety of solid ingredients are used to provide optimal assembly, lubrication and corrosion performance.

Selecting the right anti-seize product for your application

Static and dynamic systems typically require different anti-seize products. Some products are specifically designed for dynamic systems: These can assist in the assembly of interference fits, reduce fretting wear of components in vibrating systems, and reduce friction and wear of mated surfaces with relative motion, such as splines and couplings.

Another key consideration in anti-seize selection is the composition and performance at the actual operating temperature of the system. The upper operating temperature of an anti-seize compound is generally defined by the melting, oxidation, or decomposition temperature of the highest temperature ingredient, for example, 1100°C for copper. However, anti-seize compounds can contain many ingredients that lose their effectiveness at different temperatures, for example, graphite at 600°C or molybdenum disulphide (MoS2) at 450°C.

Selecting anti-seize compounds based on maximum operating temperatures of 1200°C vs. 1000°C is not likely to guarantee improved performance at 200°C. For example, at 200°C, grease thickeners and base oils should still be present, both of which have a larger influence on performance than the remaining solids at 1200°C.

How to apply anti-seize compounds

For the best results when applying anti-seize, surfaces should be clean, dry, and free from oil, grease, or contamination.

Some guidance recommends completely filling the thread valleys of a bolt. However, as excess product is squeezed out under-tightening, we believe this quantity to be unsuitably large. We advise applying a thin layer, ideally with a brush, and aim to create a uniform film. Any excess product squeezed out during tightening should be wiped clean. With an aerosolized anti-seize, refer to Technical Data Sheets for the best way to achieve a thin layer with uniform coverage.

Once applied, anti-seize in static systems should last until the fastener is disassembled for servicing or an interface is parted and should only be reapplied at service intervals or on reassembly.

When selecting and applying anti-seize, it is important to consider specific system conditions. For help and advice with product selection and application, contact the ROCOL technical team.