Formed in Place

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To recap from the previous article, FIP (Formed-In-Place) gaskets are applied as a bead or a screen print of a liquid material, just before the two mating flanges are assembled. As the flange surfaces come together, the sealant is smeared between them and forced into surface imperfections, providing total contact and forming into a durable seal.

FIP

Unlike conventional gaskets, cured FIPGs adhere to every part of the joint and therefore don’t require extreme compresive loading to form a seal. With FIPG you can also forget about gasket relaxation and need for re-torquing. The metal to metal contact that FIPGs secure enables more accurate maintaining of tolerances while any scratches or damages to either of the surfaces can be sealed by the liquid material. Most of the FIP sealants have really good resistance to solvents and other industrial chemicals and unlike solid gaskets can be applied to vertical surfaces without any need for additional adhesive to hold them in place till assembly.

In terms of curing chemistry, there are two most frequently used types of FIP sealants:

  • Anaerobic (curing between metal surfaces in the absence of oxygen)
  • Room Temperature Vulcanising (RTV) elastomers

Anaerobic sealants are best suited for sealing of very rigid flanges such as gearbox housings, bedplates to crankcases, water pumps to engine blocks, and cam covers to cylinder heads.

They ensure minimum movement between parts, optimum stiffness between the two surfaces and transmit forces from one part to the other.

RTV elastomers cure to rubbery solids by reacting with the moisture in the environment. They are best suited for flexible flanges, like gearbox covers, timing chain covers, stamped sheet steel parts, thin walled metal castings and oil pans. Normally, they do not support the function of the component so micromovements can be tolerated.

Some of the additional benefits that RTV Elastomers offer are: high gap filling, sealing of T-joints, creating seals on non-machined flanges as well as between metal and plastic or two plastic components.

For more details, please request your copy of the Gasketing design guide.

Rigidity, positioning and surface smoothness

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Rigidity_positioning and surface smoothnessž

A flange rigidity critically influences the required minimum surface pressure at mid-point between two bolts of a flanged joint. It also very much influences the type of a gasket suitable for the said joint. Where adequate bending rigidity is maintained, soft gasket materials and non-curing liquid gaskets can be used.

When deciding which of the gasketing options is suitable for your design, apart from flange rigidity, you must also look into the required / possible bolt spacing and positioning and the resulting stress distribution. Each of these factors are inevitably influencing each other and your selection of gasket material.

With conventional gaskets, surface finish or surface texture is an additional crucial factor, since the initial compressive load required to deform the gasket into the flange surface irregularities increases with rougher surface finish. Although it’s not to be completely neglected, the surface finish becomes much less important when using a liquid gasket material. For details you can consult the Gasketing design guide which I’m happy to share on request.

When talking about liquid gasket materials, there are several types depending on application method, curing method and timing or technology.

  • FIP (Formed-In-Place) Gaskets are formed by the application of a bead or by screen printing of sealant, which is then assembled in the uncured state.
  • CIP (Cured-In-Place) Gaskets are formed by the application of a bead of elastomer to one flange that is cured before the flanges are assembled. The gasket is then compressed by the mating flange to form the seal.
  • IIP (Injected-In-Place) Gaskets are liquid gaskets that are injected, after the assembly of the joint, into a groove between the two flange faces and then cured.
  • MIP (Moulded-In-Place) Gaskets are moulded directly onto one of the mating parts, usually into a groove.

I’ll go into the details of each and their advantages and recommended application areas in the next article.

Yes, the gasket can be a liquid

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gasketing header

As unorthodox as it may sound, applying some liquid material in between two rigid metal flanges in order to keep other liquids from seeping through the gap, actually does make sense. Yet, it’s the most common procedure to use pre-cut solid gaskets for this purpose.

That, however, means that the design of the flanges needs to be suitable to use such gaskets, which normally limits the designers’ freedom. On a more operational level, it means that the manufacturer must stock a huge number of as many different gasket types as there are types of flanges they are currently producing.

Both of these issues can be mitigated by the use of liquid gaskets. To better explain it, perhaps I should first go back to what a gasket is and why it’s needed in the first place. A gasket is a material positioned between two flanges which are held together by fasteners. Gaskets prevent leaking of fluids or gases by completely filling the space between the surfaces of the flanges. It is necessary for the seal to remain intact and leak-free for a prolonged time. The gasket must be resistant to the medium being sealed and able to withstand the application temperature, pressure, and micro-movements caused by vibration as well as thermal expansion/contraction.

With all this in mind, I can perfectly understand how liquid might not seem like an obvious choice. You’ll want something firm, something to really fill that gap there! But once you look at the surface of those flanges on the microscopic level, liquid makes perfect sense.

While we see a perfectly smooth surface looking at it with a naked eye, on microscopic level it looks something like this:

surface irregularities

 

And there’s nothing like a liquid gasket to get into every one of those little valleys and perfectly seal every gap once it cures into a solid.

Same as between solid gaskets, there are certainly variations between liquid gaskets as well. Your choice will depend on general design requirements.

Regardless of the sealing material, though, there are certain considerations that have to be taken into account, such as:

  • Rigidity of sealing flanges
  • Bolt preload
  • Potentially different thermal expansion
  • Stress and strain of the joint caused by external forces
  • Compressive stress distribution

A complete and comprehensive guide to gasketing design has been published by Loctite engineers recently, tackling all of the mentioned topics and much more. I’m happy to share it on request, so please contact me if you’d like to have a complete pdf.

For your babies

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4moms blog

I bet you’re thinking that’s a funny headline for an article in an engineering blog! But there is a connection, just as there is one between pineapples and shipping containers :-).

A regular Joe rarely stops to think how many of the everyday things we use are products of engineers and engineering. As a bumper sticker that ended up on an engineer’s office door says: God made the world, and engineers made everything else :-).

All jokes aside, there are very few things in life that come even close in importance to the safety and wellbeing of our children. And engineers who design baby carriers, buggies, cots, beds and baby accessories in general, know that very well. The first thing new parents are interested in is safety and reliability of any of those items. Which is why the design engineers submit them to rigorous testing and often rely on adhesives to make sure every assembly put together stays together, regardless how many hours of rocking or how many kilometres of rolling over roughly paved park paths they have to serve. Loctite threadlockers ensure that they always open, close and function reliably, while instant adhesives are used to keep together parts made of difficult to bond plastic materials. Company “4moms” is an example of such a manufacturer and you can see more about their use of adhesives here.

Generally, people are often surprised to learn how many things we take for granted would look and function much differently if there were no adhesives used in their making.

Making the right choice made easier

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Product selector visual

I’ve talked and talked and talked about how to choose the right adhesive for your application and emphasised time and again how important it is to get expert help in making this decision. I’m coming back to this topic because Loctite now has a tool that can make this process considerably shorter for you. You will still need to contact an expert and likely test the product at the end, but instead of reading through pages and pages of technical data in search for the answers, you can “tell” what you need to a simple digital selection tool by answering some simple, but specific questions: which substrate you want to bond to which other substrate, what kind of strength is required from the assembled parts, do they need to withstand high temperatures, are they subjected to static loads or is there movement, how quickly do you need the adhesive to cure or what kind of a gap needs to be filed. It takes only a few minutes, and apart from English, it’s available in several other languages you can choose from.

Wishing you a happy search!

The Hybrids

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Hybrids_design

Apart from the fact that they can pull trains, carry trucks and tractors, perhaps it’s time I said a few more words about what hybrid adhesives really are and what makes them special.

Like many other human inventions, hybrid adhesives came to be as a reaction to the need or, if you will, a problem that needed to be solved. Generally, in the world of bonding there are two main sides of what adhesives can do. On one side there are instant adhesives, based on cyanoacrylate technology, which are easy to use, bond really fast and are therefore known also in consumer, household use and by do it yourself-ers as the so called super-glue. They have their rightful place also in engineering, due to their safe and simple use, quick curing and high performance on plastics which are nowadays one of the most common materials in industrial use. However, they lack in flexibility and gap filling properties.

On the other end of the scale, are so called structural bonders. In terms of chemistry, they can be epoxy, acrylic, polyurethane, silicone or SMP (silane modified polymer) based. Their strongest traits are, apart from excellent structural performance that gives the range the name, high gap filling properties, excellent performance on metals and environmental durability.

From everything said, it’s fairly obvious that the two ranges of adhesives will be used in practically opposite situations. But naturally, the engineering reality doesn’t always fall into one of these two extremes. There are certainly cases when you might need to fill a small gap, while you still need the adhesive to cure fairly quickly. Plastic does not always get bonded to other plastics, sometimes you need to bond it to a metal or a composite material, and you’ll need your part to be durable and resistant to environmental influences.

This reality is what the chemists in Loctite research & development had in mind when they created the first hybrid adhesive. Not only did they succeed in creating an adhesive that has structural and environmental durability, universal adhesion to multitude of substrates and cures fast through high gap, but they also managed in making it one of the safest adhesives to handle in terms of minimised health hazards.

You can choose from several Loctite grades, depending on whether you’re designing something new or repairing existing parts.

Hybrids_repair

 

LED in function of curing adhesives

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LED upgrades blog

When it comes to equipment involved into application of adhesives, we divide it into two main groups:

Curing equipment works on different principles, depending on the type of adhesive you’re looking to cure. One of the most common cases are light curing adhesives which cure under the impact of either UV or visible light. Clearly, one could just leave the parts to the sun to take care of it, but that would take much longer than acceptable in any production process.

The most innovative of curing systems are LED based and satisfy both needs in one. They provide a specific spectral wavelength of i.e. 365, 375 or 405 nm. They consume a very low amount of electric energy. Well established light bulb systems, on the other hand, provide a broader emission spectrum i.e. 220-550 nm. This can be helpful if you need to cure a thick layer of adhesive where longer wavelength (VIS) need to go deeper into the layer. Radiation with a shorter wavelength (UV) will be absorbed at the top layer. Due to this principle you do not get a sun-burn behind a closed window. UV radiation is absorbed and you just feel warm because of the longer infrared wavelength.

The systems vary in terms of area coverage from hand held, spot, line array, to flood systems covering large areas where less precision and more coverage is needed. Nowadays, they come with improved power levels, portability, service life and are optimised for curing an extensive line of adhesives in continuous use (see more in the two example product description sheets.

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PDS_CL30_LED_Flood_365_380_405_en_2017-10

There are various options of setting up the curing equipment and related accessories to best fit specific needs of a given application, so it’s best to always consult an expert before making any decisions.