This article first appeared in IMPO's September 2013 issue.
Oftentimes, a question posed to a maintenance manager about which sealant is right for a job can only be answered with another question.
- How fast does it need to cure?
- What kind of material is being sealed?
- What temperature resistance is required?
- What pressure resistance is required?
The companies who develop these formulas for the industrial environment will tell you there is a product for every job – it’s just a matter of determining which is best for each specific use. “There are sealants formulated for high speed OEM manufacturing lines that can cure in seconds, but in some cases that might be too fast for a mechanic to assemble in a maintenance application,” explains Karen Verosky, Market Manager Loctite® Products, Henkel Corporation. “That’s why there are so many different types of adhesives to choose from; there is no one solution for every application.”
According to Henkel, the three most common sealing applications relate to threadlocking (nuts and bolts), thread sealing (like pipe threads or hydraulic fittings), and gasketing applications (for sealing a flange or making a form in place gasket). And in many cases, not all materials are created equal.
The Science of Threadlocking
When people look to chemical threadlockers, they are almost always looking to secure a troublesome fastener from vibrating loose. However, a key advantage of anaerobic threadlockers often overlooked is their ability to seal the threaded joint from leaks. When dealing with nuts and bolts, what is sealed out is as important as what is being sealed in. Even if you are not looking to seal fluids from escaping a bolted joint, you will almost always want to keep water or other corrosive fluids out of the joint. “Just think of all the rusted nuts and bolts you have struggled with in your lifetime,” says Verosky. “If all the airspace in the threads had been filled with Loctite threadlocker cured to a thermoset plastic, it likely wouldn't have rusted together in the first place.”
Laurie Gibbons, Business Development Manager for the manufacturer of engineering adhesives, Permabond, concurs. “Anaerobic threadlockers require only three things to perform perfectly. Just think ‘OMG:’ Oxygen exclusion, Metal presence, and Good coverage.” According to Gibbons, good coverage is critical and the major factors in play are viscosity and placement, in order to eliminate any air spaces. “Generally, the threadlocker is applied to the threads of the fastener only,” explains Gibbons. “If the fastener is being put into a blind hole, the air in the hole will try to escape as the fastener is turned into placed. This will push the threadlocker out of the threads. To prevent this, apply sealant to both the threads in the hole, and the fastener.”
Threadlockers are available in a range of different strengths, viscosities, and cure speeds to suit various application requirements.
Thread Sealing
When it comes to sealing threaded metal pipes and fittings, Henkel recommends using an anaerobic product like a Loctite Thread Sealant versus tapes or solvent dopes.
Similar to anaerobic threadlockers, the thread sealants also cure in the absence of air and the presence of metal but, once again, there are different products for various applications. Some thread sealants, like Loctite 5452, are designed especially for hydraulic fittings while others have the addition of PTFE to help ease assembly and eliminate galling.
Much of what’s behind the use case for anaerobics is their ability to cure instead of dry – therefore they don’t shrink or crack. “Once cured to a thermoset plastic in the joint, it fills the airspace one hundred percent, forming the most reliable seal available,” says Verosky. “On the contrary, solvent-based thread dopes can leave cracks and leak paths after the solvent flashes off and it shrinks – think cracks in a mud puddle after it bakes in the sun.” Another benefit is that anaerobics will only cure in the threaded joint when deprived of oxygen, therefore any sealant that gets into the system will remain liquid and will not clog or harm the system, especially important in hydraulic systems.
It’s important to note that anaerobic sealants cannot be used on plastic. Not only will they not cure, but they can also damage the plastic components.
Gasketing
Henkel defines gasketing as a method to prevent fluid or gas leaks by forming impervious barriers that remain intact and leak-free over a prolonged period of time. In addition, a gasket must resist the fluid or gas being sealed while withstanding the operating temperatures and pressures to which it is subjected.
When it comes to industrial gasketing applications, Verosky recommends making some basic determinations before proceeding:
- Determine what gap fill is needed. For rigid/machined surfaces – generally smaller gap fill (up to 0.010”) – you would generally use an anaerobic sealant. For larger, more flexible stamped flanges – generally larger gap fill required (up to 0.250”) – you would generally use a silicone or elastomeric sealant
- What is the temperature resistance required? Most silicone sealants can be used to 500 degrees F, and some even to 700 degrees F, while anaerobic gasket sealants are generally used for applications up to 400 degrees F.
- What cure time is required? Is there a specific chemical resistance or compatibility concern? Is added oil resistance required?
- Lastly, is there a cut gasket that is needed as a shim or spacer? Not all cut gaskets can be replaced with a chemical gasket if it is required to maintain a specified clearance — for example, for the gears on a gearbox or the impeller of a pump. That said, Loctite products can be used in conjunction with most cut gaskets to improve the reliability of the gasket.
Difficult Substrates
In every industrial setting, users will be challenged to create high adhesion for difficult to seal substrates. There are several examples of these tough applications, one which relates to oily flange surfaces in a gasketing application. Henkel recommends a formula with good oil resistance – like Loctite 598 Black Gasket Maker – which is formulated to cut through oily surfaces and adhere to the flange to produce a tough, flexible rubber gasket.
In thread sealing applications, says Verosky, “hydraulic fittings pose challenges to maintenance teams, as traditional sealing methods like PTFE tape can wreak havoc if it shreds and contaminates the system.” Sticking with anaerobic products (Loctite’s hydraulic products are designed with a small particle size) means clogs and contamination can be circumvented. Stresses Verosky, “Hydraulic leaks not only come at a cost of replacing the fluid, but also the cost of hazardous waste removal and could possibly create a slip and fall hazard — the most costly expense of all.”
Additionally, Permabond notes the requirements for surface prep when it comes to weld sealing: including the need to expose the metal surface first in order to seal it properly. Cleaning off any dirt, grime, rust or paint is a must, so that there will be nothing impeding the seal. “Almost leak free is never good enough,” says Gibbons. “Remediation of water or mold damage resulting from leaky piping in sprinkler systems quickly runs into the six figures.” Permabond’s product, HL 126, has been formulated to wick into weld imperfections, pin-holes, and micro porosities to find and seal potential leaks.
And whether it’s related to the surface, application, or formula – keep asking the right questions. Many formulas get so specific you can literally find a solution for every need.