Aug 10, 2012
Liquid gaskets said to outperform traditional materialsBack
Henkel|Henkel South Africa|Loctite|Adhesives Supplier|Chemicals|Metal|Metal Surfaces|Metal-to-metal Contact|Rubber|Sealed Steel Casing|Silicone Products|Steel|Anaerobic Technology
© Reuse this
Speciality chemicals and adhesives supplier Henkel South Africa, which is also the manufacturer of the Loctite brand of sealants, maintains that liquid gaskets produce seals that create better results than traditional materials.
To ensure the integrity of a seal between two bolted flanges, it is necessary to have some form of gasket between the mating surfaces that will remain intact and leak-free in often extreme and varying conditions over a prolonged time.
In a test where a sealed steel casing was subjected to torsional stresses, a number of significant differences between various sealing methods were noted, reports Henkel.
In particular, conventional solid gaskets showed leaks after 150 000 cycles, whereas seals made with an anaerobic product con- tinued to show reliability beyond 250 000 cycles.
Further, in the conventional gasket, the tension of the bolt dropped by 25% within just a few thousand cycles.
There are three typical types of gaskets: conventional precut compression gaskets, formed-in-place (FIP) liquid gaskets and cured-in-place (CIP) gaskets.
Although a well-used and traditional method of sealing joints, these gaskets do present some significant and practical disadvantages, says Henkel.
For example, conventional gaskets require an initial compressive load to deform it into the irregularities of the mating surfaces, which, over time, is a major cause of gasket failure.
This occurs when the gasket loses its elastic properties and becomes less resilient. The load on the gasket and relative motion causes a general decrease in the gasket thickness, resulting in a bolt clamp load loss that can cause it to leak.
FIP Liquid Gaskets
Two types of sealants are available for FIP gasketing jobs: anaerobics for rigid joints, such as Loctite 510 and Loctite 518; and special silicone products for applications requiring a flexible seal, such as Loctite 5699.
Further, no retightening of the bolts is required and no allowance is needed for gasket thickness, reports Henkel.
Meanwhile, anaerobic sealants provide high shear strength that stops movement to eliminate bolt loosening and fretting and to increase the assembly’s structural strength.
Anaerobic sealants also allow relaxation of surface finish and flatness tolerances that enable scratches and scored surfaces to be sealed without rectification.
Anaerobic gasket materials only cure in the absence of air when trapped between metal surfaces. This enables it to offer extensive on-part life when exposed to the atmosphere, making multiple application methods possible and reducing the problems associated with the use of volatile or moisture-cured materials on production lines, notes Henkel.
Further, the anaerobic technology enables excess material to be wiped from exterior surfaces or flushed away from interior faces maintaining free, unblocked internal passages and channels.
An advantage of cured anaerobic gaskets is its resistance to petroleum-based fuels, lubricating oils, water-glycol mixtures and most other industrial chemicals.U
nlike precut compression gaskets that are difficult to automatically position on the parts, anaerobic gaskets can be automatically dispensed by robotic dispensers, screen printing or stencil printing systems.
Further, anaerobic gasket products reduce inventory costs, as one container of an anaerobic can be used for flanges of varying sizes and shapes. Precut gaskets can only be used on specific flanges.
They are applied as a fluid in precise beads to one of the surfaces and are cured before use, either by ultraviolet light, heat cure, two-part mix or moisture curing.
Once the bead is cured, an elastomeric material is formed that adheres to the surface. Sealing is achieved through compression of the cured gasket during assembly of the parts.
The advantages of these gaskets include automatic application, serviceability, labour savings, improved quality, reduced inventory and flexible manufacturing.
Meanwhile, Henkel states that flanges, such as pressed steel parts and thin castings with widely spaced bolts, can be considered as flexible, have inconsistent clamp pressure and may move under pressure or dynamic loading.
Sealant manufacturers offer special silicones, formulated to meet all of the requirements of a gasket for flexible joints. Such products provide high elongation to compensate for any micromovement, as well as long-term adhesion to most substrates.
It is important to consider the nature of the surfaces involved in a gasketed assembly.
For example, the original substrate used for the component may be metal – but for operational reasons the part has been painted. It is not a metal-to-metal contact that needs to be sealed but rather a metal-to-paint or paint-to-paint configuration.
In those circumstances, an anaerobic that relies on a metal surface in the absence of air to initiate the cure is inappropriate. However, a silicone – even if a rigid joint is involved – is the correct choice.
Edited by: Chanel de Bruyn© Reuse this Comment Guidelines
Other Seals, Gaskets and Sealing Mechanisms News
An environment-friendly tyre protection sealant, which improves safety for the driver, reduces fuel consumption, lowers maintenance costs and has fewer rim assembly problems, is being launched by the automotive division of South Africa-based bearings supplier Bearing...
Recent Research Reports
Automotive 2014: A review of South Africa's automotive sector (PDF Report)
The report provides insight into the business environment, the key participants in the sector, local construction demand, geographic diversification, competition within the sector, corporate activity, skills, safety, environmental considerations and the challenges...
Construction 2014: A review of South Africa's construction sector (PDF Report)
Construction data released during 2013 hints at a halt to the decline in the industry during the last few years, with some commentators averring that the industry could be poised for recovery. However, others have urged caution, noting that the prospects for a...
Electricity 2014: A Review of South Africa's Electricity Sector (PDF Report)
This report provides an overview of the state of electricity generation and transmission in South Africa and examines electricity planning, investment in generation capacity, electricity tariffs, the role of independent power producers and demand-focused initiatives,...
Defence 2013: A review of South Africa's defence industry (PDF Report)
Creamer Media’s 2013 Defence Report examines South Africa’s defence industry, with particular focus on the key players in the sector, the innovations that have come out of the defence sector, local and export demand, South Africa’s controversial...
Road and Rail 2013: A review of South Africa's road and rail infrastructure (PDF Report)
Creamer Media’s Road and Rail 2013 Report examines South Africa’s road and rail transport system, with particular focus on the size and state of the country’s road and rail network, the funding and maintenance of these respective networks, and the push to move...
Liquid Fuels 2013 (PDF Report)
Creamer Media’s 2013 Liquid Fuels report examines South Africa’s liquid fuels market, focusing on the business environment, oil and gas exploration, the country’s feedstock supplies, the development of South Africa’s biofuels industry, fuel pricing,...
This Week's Magazine
Electricity Supply Corporation of Malawi (Escom) is inviting expressions of interest from eligible firms for the supply and install automatic fire suppression systems in the cable tunnels at its Nkula B and Tedzani power stations, on the Shire river. Escom will...
Lubricant company Castrol will provide lubricants, brake and hydraulic fluids for use in the Bloodhound supersonic car (SSC). The 1 600 km/h car, which will attempt to break the land-speed record in 2015 through to 2016, is being constructed in Bristol, in the UK.
State-owned electricity producer Eskom and government are assessing ways to secure the financial resources necessary to enable the utility to resume power-saving schemes, as well as to contract with those municipalities and independent power producers (IPPs) able to...
Diversified industrial engineering group PSV’s subsidiary African Cryogenics is gearing up to increase its operating capacity through an investment into a 7 000 m2 manufacturing facility, which is under construction and expected to be completed at the end of this...
Freight and logistics service provider Grindrod has a R10-billion project pipeline planned for sub-Saharan Africa, says Grindrod CEO Alan Olivier. He says the capital expenditure for some of these projects has already been approved by the Grindrod board –...