Product category:
Valve positioners and actuators
News Release from: Igus UK | Subject: iglidur T500 plastic bearings
Edited by the Processingtalk Editorial
Team on 28 October 2004
Valve actuator uses plastic bearings for
life
QTRCO, a Texas-based manufacturer of a line of 1/4-turn rack-and-gear valve actuators designed to increase life cycle, has changed to plastic bearings: these provide more cycle life and less wear
High-performance polymers compete with metal, and win When choosing a bearing for any application, the three considerations are lifespan, maintenance, and cost
This article was originally published on Processingtalk on 4 Jun 2008 at 8.00am (UK)
Related stories
The ecological benefits of plastic plain bearings
A study has found that no less than half of all machine lubricants currently used seep into soil and waters, or evaporate into the atmosphere
iglidur bearings in any colour are always green
iglidur plain bearings are tribologically optimised to ensure that no lubrication is ever required: these bearings run without any oil or grease, so no contaminants escape into the environment
First, determine how long you expect the bearing to last, and what demands are going to be placed on it.
Second, consider if any maintenance is required and if so, can it be performed regularly and accurately.
And third, ask yourself how much you are willing to spend.
Further reading
Ethernet industrial applications up to 100m travel
At the last "Vision" trade show, GigE (Gigabit Ethernet) - as an alternative to FireWire, USB, and CameraLink - was referred to as the new future standard
igus to exhibit at Total 2007
igus will be exhibiting on stand 5121 at the Total show this year, promoting their latest stainless steel linear guide, designed for the food process and packaging industries
Last chance to enter bearings competition
The deadline for the Manus Plastic Plain Bearing Design Contest is the 31st August, 2006: just explain how polymer bearings have improved the technical performance of your equipment
A bearing can be one of the most inexpensive parts, yet one of the most critical.
It can fail under too high a demand or if needed maintenance isn't performed.
Bearing failure can shut down the entire machine and quite possibly halt production completely.
So, if you don't first take into consideration lifespan and maintenance, the original low cost of the bearing is irrelevant.
Most recently, designers have had to decide whether to choose bearings made from metal or polymer plastic.
Much like the automotive industry in the 1960's, when it was unheard of to think that critical components of a vehicle could be built of plastic, today every mass-produced car contains parts made of polymer-fibreglass blends.
It took the world, especially design engineers; a long time before they accepted the notion that plastic is a suitable, even more desirable material.
Similarly, plastic bearings are upping the ante, delivering more cost-effective, easy-to-maintain solutions with an increased lifespan.
Consider, then, the differences between plastic versus metal bearings: Plastic bearings are self-lubricating and maintenance-free, which ultimately leads to a lower cost over time.
Metal bearings require lubrication and regularly scheduled maintenance, which significantly increases the overall cost.
Plastic bearings are completely corrosion-free and deliver better vibration dampening than metal bearings.
Moreover, metal is highly susceptible to corrosion, and therefore the design must account for any moisture or chemical elements that the bearing may encounter.
Plastic also can handle edge loading better than metal.
For practical purpose, metal won't give, so it's either going to wear, create noise, or shock absorption and produces less noise.
Dirt can also be a virtually immobilising agent in metal bearings.
It can scratch the thin Teflon lining of a metal bearing or get caught and ruin it.
Certainly, in some circumstances like extreme speeds, massive loads, and high temperatures, metal fare better than a plastic compound.
The high-end polymer materials can sustain such conditions, but it's difficult to achieve with the more affordable plastic compounds.
Therefore, metal often holds up better under accelerated life testing in the lab where these conditions are intentionally applied.
But realistically, the machine will never be exposed to these conditions.
In the past, designers have picked metal bearings have for applications they weren't necessarily optimised for; but they did the job well enough and there really weren't any other viable options.
True, they may have performed well initially, but not over time.
Corrosion and other long-term effects eventually build up.
This is key because today's applications demand extended life and reduced maintenance costs for their machinery.
In this regard, plastic offers many long-term performance benefits beyond low initial friction.
Indeed, plastic has evolved and improved for many applications where it performs better than metal and is better designed for the application's parameters.
"The biggest hurdle for plastic today is overcoming its reputation as a weak, unstable material.
Yet plastic is a fantastic material for many machine components, such as gears and pulleys, not just bearings," said Matthew Aldridge, Director of the Bearings Division at igus UK.
"Design engineers shouldn't make the mistake of 'settling' for a metal bush, because a polymer is often able to outperform on a number of points.
igus bearings, for example, are maintenance-free, require no lubrication and have a longer, predictable life span," says Aldridge, adding that, "Once engineers use a plastic bearing, they almost never go back".
In fact, many engineers still consider plastic bearings to be a niche product, falling at each end of the spectrum and getting lost in the middle.
For example, at the low end of the spectrum are the everyday plastic bearings manufactured at a local injection moulder.
On the high end are extremely expensive, specially designed plastic materials like Torlon or Vespel.
Yet, ninety percent of engineers are working on applications that fall somewhere in between.
In the past, there wasn't a large product offering to meet the demands of this majority.
Today, there are many materials readily available and there are plenty of options for engineers whose applications are the norm, not the exception.
Consider, for example, the case of QTRCO, a Texas-based manufacturer of a unique line of 1/4-turn rack-and-gear valve actuators designed to increase life cycle.
First built using metal bearings, the application requires the bearing and sleeve assembly to rotate reciprocally around a fixed shaft.
QTRCO differentiates itself within the industry by delivering minimum internal friction and using only stainless steel components for corrosion protection.
The company employs rotating bearings to support the rack while maintaining the desired rack to gear engagement as the primary means of eliminating friction.
This is different from the conventional design, which allows the rack to slide along the cylinder wall, creating large amounts of sliding friction.
The QTRCO design dictates that all outward force be borne by the bearing, therefore it must be able to support high loads as well as extremely high speeds, rapid acceleration and deceleration, and motion reversal.
These high velocities, in turn, require the bearing to have high PV (pressure x velocity) capabilities to support.
For example, one application opens a 3-inch ball valve in 0.5 seconds, followed by closing the valve in 0.2 seconds.
This is repeated more than 120,000 times per week in excess of 7 million times per year.
In some applications, the PTFE lining of the metal bearings wears too quickly to satisfy the QTRCO engineers who strive for total perfection in their actuators.
When replaced with iglidur T500 plastic bearings from igus, the bearings incur little or no wear, despite external contaminants finding their way into the housing.
"The igus plastic bearings have demonstrated an ability to outperform PTFE lined metal bearings used in the same application, providing significantly more cycle life with minimal wear," says Ed Holtgraver, president of QTRCO "We are now working with igus to specify the optimum plastic bearing material for general and special use." Experiences like this are becoming more and more common.
Plastic has undergone extreme technical advancement in the past 20 years.
Indeed, plastic is now considered a standard bearing option, not just the last resort, unconventional choice when all else has failed. Request a free brochure from Igus UK ...
• Igus UK: contact details and other news
• Email this article to a colleague
• Register for the free Processingtalk email newsletter
• Processingtalk Home Page
Search the Pro-Talk network of sites
