Adhesives

What are adhesives?

Adhesives are the glues, thread lockers, retaining compounds, and sealants used to bond, lock, seal, and secure parts in engineering, maintenance, and repair work. In machinery, vibration, shock, and temperature changes can loosen nuts and bolts, let bearings creep on shafts, and cause threaded joints and flanges to leak. Engineering adhesives solve these problems by filling the tiny gaps between parts and curing into a tough, solid material that holds components securely in place.

Many engineering adhesives are anaerobic, which means they stay liquid while exposed to air but cure once they are confined between close-fitting metal parts. This makes them ideal for threads, shafts, and flanges, and easy to apply without making a mess.

Common adhesives include:

• Thread lockers - stop nuts, bolts, studs, and screws from loosening due to vibration and shock
• Penetrating thread lockers - low viscosity grades that wick into already assembled fasteners
• Retaining compounds - secure bearings, bushes, gears, and pulleys onto shafts and into housings
• Thread sealants - seal threaded pipe joints and fittings against leaks of gases and liquids
• Gasket makers and flange sealants - form a seal between flat machined faces, replacing or supporting traditional gaskets
• Instant adhesives - also known as super glues, these bond small parts quickly in seconds

Key features:

• Prevents loosening - thread lockers keep fasteners tight under vibration and shock
• Seals against leaks - thread sealants and gasket makers seal against oils, fuels, water, and gases
• Secures cylindrical parts - retaining compounds hold bearings and bushes in place without the need for heavy press fits
• Fills gaps - fills the small gaps between parts, preventing corrosion and movement
• Range of strengths - low, medium, and high strength grades to suit parts that will be removed later or locked permanently
• Easy to apply - supplied in bottles and tubes with nozzles for clean, accurate application
• Fast curing - many products cure quickly, so equipment can return to service sooner

In simple terms, adhesives are the products that lock, seal, and bond parts so they stay secure and leak-free in service.

Why are adhesives essential?

Adhesives are essential because vibration, shock, heat, and pressure are constantly working against machinery joints. Fasteners can slowly loosen, bearings can spin in worn housings, and threaded and flanged joints can start to leak. These problems can lead to noise, damage, breakdowns, and safety risks. Engineering adhesives help prevent them, making assemblies more reliable and reducing maintenance.

Their main benefits are:

• Reliable fastening - thread lockers stop nuts and bolts from working loose
• Leak prevention - thread sealants and gasket makers create a strong, reliable seal
• Better bearing and bush fits - retaining compounds hold parts firmly, even where housings or shafts are slightly worn
• Corrosion protection - filling gaps between threads and mating parts keeps out moisture and prevents rust
• Simpler designs - can replace lock washers, split pins, and some mechanical locking methods
• Faster repairs - small parts can be bonded and joints sealed quickly, reducing downtime
• Cost savings - helps avoid repeated tightening, leaks, and premature wear of parts

Adhesives are used across a wide range of industries and applications, including:

• Engineering and maintenance - locking fasteners, retaining bearings, and sealing joints on machinery
• Pumps, gearboxes, and motors - sealing flanges and locking critical fasteners
• Hydraulic and pneumatic systems - sealing threaded fittings and ports
• Automotive and transport - locking bolts, sealing flanges, and retaining parts
• Agriculture and construction - securing fasteners on vibrating equipment
• Manufacturing and assembly - bonding and sealing components on production lines
• Workshops and DIY - general repairs and bonding small parts

The main types of adhesives

Adhesives are usually grouped by the job they do.

Thread lockers:

• Low strength thread lockers - lock small screws and adjustment screws, and can be removed easily with hand tools
• Medium strength thread lockers - the most widely used grade, locking general nuts and bolts while still allowing removal with standard tools
• High strength thread lockers - permanently lock studs, bolts, and fasteners that do not need regular removal. Removal usually requires heat
• Penetrating thread lockers - very low viscosity grades that wick into the threads of fasteners that are already assembled
• Oil tolerant thread lockers - designed to work on lightly oiled parts without the need for thorough cleaning

Retaining compounds:

• Standard retaining compounds - secure bearings, bushes, gears, and pulleys onto shafts and into housings
• High strength retaining compounds - give maximum strength for permanent assemblies
• Oil-tolerant retaining compounds - work on lightly oiled surfaces
• Gap-filling retaining compounds - help repair worn shafts and housings with slightly larger gaps

Sealants:

• Thread sealants - seal threaded pipes and fittings against leaks of water, oil, fuel, air, and gases, often replacing PTFE tape
• Hydraulic and pneumatic sealants - seal fine threads on hydraulic and pneumatic fittings
• Gasket makers - form a flexible seal between rigid machined flanges, such as gearbox and pump housings
• Silicone sealants - flexible sealants for gasket-forming and sealing applications with more movement or larger gaps

Instant adhesives:

• Super glues - bond metals, plastics, rubber, and many other materials in seconds, ideal for small parts and quick repairs
• Gel super glues - thicker versions that are easier to control on vertical surfaces and porous materials

Accessories:

• Activators and primers - speed up curing, or help adhesives cure on less active surfaces such as stainless steel, plated parts, and plastics
• Cleaners - degrease parts before applying adhesive for the best possible bond

How to choose the right adhesives?

Choosing the right adhesive means matching it to the job, the parts, and whether they will need to come apart again. Work through these points in order:

• Job type - choose a threadlocker to stop fasteners from loosening, a retaining compound for cylindrical parts, a thread sealant for pipe fittings, a gasket maker for flanges, or an instant adhesive for bonding small parts
• Removal - choose a low or medium strength grade if parts will need to be removed with hand tools, and a high strength grade for permanent assemblies
• Fastener size - use thinner grades for smaller threads and thicker grades for larger threads and bolts
• Already assembled parts - use a penetrating thread locker that wicks into existing threads
• Gap size - choose a product suited to the gap between the parts, as some grades are designed to fill larger gaps
• Surface condition - choose an oil-tolerant grade if parts cannot be fully cleaned, or degrease the parts first for the best result
• Materials - check that the product suits the materials. Some surfaces, such as stainless steel, plated parts, and plastics, may need an activator or primer
• Temperature - check the product’s temperature range for parts near engines, exhausts, or hot machinery
• Fluids and chemicals - check that the sealant or adhesive is resistant to the oils, fuels, water, or gases it will be exposed to
• Cure time - consider how quickly the equipment needs to return to service
• Quality and brand - choose products from reputable suppliers for reliable, consistent performance

FAQ - All you need to know about adhesives

What is a thread locker?

A thread locker is a liquid adhesive applied to the threads of nuts, bolts, studs, and screws. It cures between the threads to stop fasteners from loosening due to vibration and shock.

What is the difference between low, medium, and high strength thread lockers?

Low-strength thread lockers are for small screws that need to be removed easily. Medium strength is the most common grade, locking general fasteners while still allowing removal with hand tools. High strength is for permanent assemblies and usually needs heat to remove.

How do I remove a fastener that has been locked with high-strength threadlocker?

Apply localised heat to the fastener to soften the cured adhesive, then remove it with hand tools while it is still hot. Always take care and follow the product’s guidance.

What is a retaining compound used for?

A retaining compound secures cylindrical parts, such as bearings, bushes, gears, and pulleys, onto shafts or into housings. It fills the gap between the parts and cures to stop them from moving or spinning.

What does anaerobic mean?

Anaerobic adhesives stay liquid while exposed to air but cure when confined between close-fitting metal parts. This is why they cure in threads and joints but stay liquid in the bottle.

Can thread sealant replace PTFE tape?

In many cases, yes. Thread sealant fills the threads completely, giving a reliable seal that will not shred or unravel. Check that the sealant is suitable for the fluid, pressure, and temperature.

Can I use adhesives on oily parts?

For the best results, parts should be clean and dry. Oil-tolerant grades are available for lightly oiled parts, but heavily contaminated parts should be cleaned and degreased first.

Why won’t my adhesive cure?

Common causes include oily or dirty surfaces, gaps that are too large, low temperatures, or less active surfaces such as stainless steel, plated parts, and plastics. Cleaning the parts or using an activator or primer can help.

What is the difference between a gasket maker and a silicone sealant?

A gasket maker is designed to seal rigid, close-fitting machined flanges and cures between the metal faces. A silicone sealant is more flexible and better for flanges with more movement or larger gaps.

How should I store adhesives?

Store them in their original containers, tightly closed, in a cool, dry place away from direct sunlight and heat. Do not return unused adhesive to the bottle, as this can contaminate the remaining product.