How to Turn Gearbox Contamination Control into a Competitive Advantage

by | Articles, Contamination Control, Current Issue, Gearboxes, Recommended

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At any given point, the overall contamination in a gearbox is BIG!

Remember that contamination ingression is the overall amount of contaminant in the oil with:

B – Built-in contamination from the unit’s manufacture.

I – Ingested is the “sucked in” contamination during operation, whether as the unit cools or other activity such as top-ups and oil changes.

G – Generated during operation, or in other words, wear and fatigue creating debris, whether from the lubricant, ingested contamination, or other root causes.

Simply put:

Ingression = Built-in Contaminants + Ingested Contaminants + Generated Debris

 Generated debris (or wear) is the result of several root causes, namely;

  1. Tightness – fasteners torqued correctly to eliminate vibration from movement
  2. Rotating set-up – alignment and balance set-up to avoid overload on the bearings and teeth
  3. Lubricant quality means the right specification and the right oil used during lubrication tasks
  4. Lubricant contamination levels
  5. Other root causes

Based on the Pareto Principle or the 80:20 Rule, the other root causes are the 80% causing 20% of the problems, while the first four listed are the 20% of the root causes creating 80% of the problems.

The Pareto Principle

Because tightness, rotating set-up, and lubricant quality are in control, contamination levels or ingested contaminant levels are left. 

Sadly, contamination control is overlooked on gearboxes, so the ingested levels are usually high, resulting in day-to-day damage. 

Identifying the Sources of Contamination – Built-in and Ingested

Having made sure that the right lubricant is in use on the gearbox to meet the demand of the application and that any overloading or operational abuse has been dealt with, the final stage in a proactive gearbox focus should be to deal with the ingression points of the contamination. 

But, first, it is essential to identify contamination as it can be in one of many forms.  

Contamination is any matter or body that enters the system and causes physical or chemical harm to either the lubricant or the machine, which reduces the effectiveness and life of the lubricant or the asset and potentially impacts the effectiveness of the operation.

Such examples include:

  • hard particles from external sources or generated within (wear),
  • water, or moisture, from rain or wash-down sprays,
  • high temperature from overloading or poor heat transfer,
  • aeration from incorrect levels of oil or poor specification in terms of the defoamant,
  • UV radiation
  • or process matter (chemical or physical) from the environment.

There are several easily identifiable ingression points on a gearbox, namely:

  • the seals,
  • damaged gaskets,
  • the breathers,
  • contaminated new oil
  • other maintenance activity, such as top-ups from contaminated handling units, or complete drain and refill of the unit not following best practices.

These all allow the introduction of contaminants. Bear in mind that the rate at which these enter the unit will depend to some extent on ambient conditions and, depending on the contaminant type, will be subject to such issues as whether the equipment is located inside or outside, whether it is raining, or whether it is windy. 

For example, in wet conditions, the likelihood of moisture ingress significantly increases; however, the ingress of hard dust particulates from the environment is reduced accordingly. 

On the other hand, given a hot, dry, and windy day, while the risk of moisture ingress is minimized, the risk of ingesting hard atmospheric silica-based particulates is greatly increased.  Of course, depending on the nature of the organization, some contaminants may be unique, such as coal dust or iron ore dust. 

Process chemicals in a nylon spinning or paper mill environment.  Another aspect of increased risks of contamination is nearby activity, for example, the risk of cement dust when construction work is taking place, and again, the risk will be greater in windy or dry conditions.

Of course, the above is a controllable situation on-site and can be dealt with accordingly.  What must be dealt with is the manufacturing debris in the gearbox during commissioning. 

This requires that either the OEM or the installer take the appropriate actions to ensure a clean unit before start-up; otherwise, this debris will immediately impact the system’s reliability.

Dealing With the Contamination

 Rectifying the situation involves upgrading existing fittings and implementing some new components to bring the necessary improvements. 

 However, as a gearbox manufacturer customer, you have two choices.  How you move forward will depend on your Original Equipment Manufacturer’s (OEM) cooperation in these matters.

Unfortunately, owing to certain design criteria, as an end-user, it is difficult to walk away from an uncooperative OEM since they may be the sole source of gearboxes to meet the design constraints of the machine train. 

 It is necessary to discuss your contamination control program with your OEM and have them implement your requirements at the build phase. It is also necessary to ensure compliance through a regular supplier audit. Remember, it is always much cheaper in the long term to pay more upfront at the supply stage than to retrofit the better-quality hardware later.

 A further aspect is to ensure the supplier follows best practices for storing the new or rebuilt units before shipping to the site.

 Whether you choose to implement yourself or set up an ongoing improvement program, you will need to consider the following:

 Seals

 Standard lip seals are a low-cost item but require frequent replacement, and their performance at sealing against oil leakage and contaminant ingress is poor compared to labyrinth seals. 

 Although labyrinth seals are at a greater cost initially, their superior performance will ensure minimal risk from water or dirt ingress and minimize lubricant loss and potential process/environmental problems. 

 In addition, many of the gearboxes I see fitted with labyrinth seals also have a greasing point, as fresh grease should regularly be applied to aid the sealing action yet are often overlooked. 

 Of course, training the maintenance staff to avoid using high-pressure wash-down sprays directly on the seals is a must, although, in food and beverage-related environments, this cannot always be avoided.  In this instance, a seal guard can prove beneficial.

Seals: Elastomer vs. Labyrinth

 Breathers

 In many cases, older units still have an open tube for breathing, although newer units now incorporate a vent plug into the fill plug.  When stopping large bodies from falling into the gearbox, these serve their purpose but are ineffective at stopping a destructive smaller than 20µm particle. 

 Essentially, upgrading the breather should minimize or eradicate the ingestion of hard particulates and moisture.  There are several ways to achieve this.  The first would be to fit a good quality breather, such as a 1µm rated unit that will remove as much airborne particulate as possible. 

A standard ß10>200 spin-on filter will perform up to ten times more effectively in air than oil, making these possible in a dusty but dry location. 

 If in a moist environment, then the use of desiccating breathers is advisable.  Please beware of the desiccant in some industries; ensure that the appropriate handling guidelines are adhered to and that they comply with food and other related industries. 

 Also, remember to set them up to minimize damage, so provide a protective housing such as in the photo example of a desiccant breather used on a crusher gearbox where rocks may fall over the side.  Consider mounting the breather away from the unit in a wet environment to avoid wash-down sprays or process water falling on it directly.

Breather

However, on splash-lubricated gearboxes, there is little actual need for breathers. Generally, they are there to allow for changes in volume because of top-ups, leakages, and temperature-related volume changes. 

For applications with minimal volume changes, the ideal form of breather is a bladder type.  This effectively seals the internal of the gearbox from the atmosphere, but a small bladder allows for expansion and contraction of the air within because of temperature changes. 

These are especially ideal where high levels of particulate or moisture occur in the environment. In addition, creating a vacuum as levels fall may also reduce leakages.

Bladder Type Breather

Breathers/Fillers/Samplers

 It is helpful to combine the functions where regular sampling or using a filter cart occurs, particularly where cost and space constraints dictate. 

 When filling or topping up, it is imperative to ensure that the oil is delivered clean to the gearbox.  This may mean dispensing through a filter cart or using the sealable oil canisters that have become the norm in the industry.

Apart from the supply of clean, new oil, the fill port must be clean before use, so any type of protection that can be added to the fill area is beneficial, mainly where process debris could fall into the fill port when in use. 

Using quick connectors is ideal as, like sampling ports, they minimize the risk of ingested contamination. My preference is to use the sealable type containers with a hand or battery-operated pump piped direct to a quick or snap-on connector on the gearbox to ensure clean delivery of the oil and to minimize any risk of spillage, while also minimizing any longer-term injury resulting from lifting and pouring from heavy containers.

Breather with Connector

Portable Off-line Filtration

 While some gear units may incorporate a small pump and perhaps even a filter, many gearboxes are not equipped with a pump for circulating the oil, nor are they filtered. This can be easily overcome, and a filter cart can make significant gains quickly. 

 Sometimes, it is impossible to make the necessary upgrades or modifications without a major shut-down, so as mentioned, always specify these upgrades as part of the new order or during the gearbox rebuild. However, filter carts can be applied by quickly changing the fill and drain plugs.

Fill and Drain Plugs

Portable Off-line Filtration

 While some gear units may incorporate a small pump and perhaps even a filter, many gearboxes are not equipped with a pump for circulating the oil, nor are they filtered. This can be easily overcome, and a filter cart can make significant gains quickly. 

 Sometimes, it is impossible to make the necessary upgrades or modifications without a major shut-down, so as mentioned, always specify these upgrades as part of the new order or during the gearbox rebuild. However, filter carts can be applied by quickly changing the fill and drain plugs.

Quick Connects

Permanent Off-line Filtration

 A permanent off-line circuit could be employed on larger units, particularly where large volumes of oil and high cleanliness levels must be maintained. The benefit of the permanent mount is that it can continue to operate while the gearbox is not in use. However, the optimum filtering time is during the higher operating temperatures. 

 If high running temperatures are an issue, a cooling circuit could be designed with the offline circuit to reduce the oil temperature and increase the oil life and performance.

 In addition, with a permanent offline filtration loop on a gearbox, the circuit can be started separately before starting the gearbox, particularly for vertical shaft gearboxes; this can be beneficial in ensuring a “wet start” with oil flowing to the components before start-up.

 The choice between a portable unit and a permanent mount unit will come down to criticality of production (i.e., the need for reliability), safety, severity/penalty of failure, and if none of the above are important, then the need to achieve a reasonable life extension within a limited budget on contamination improvement.

Absolute cleanliness levels should not be quoted as individual units within the same site may have differing needs, imposing higher or slacker cleanliness limits.  However, in the majority of cases, there are areas for significant improvement from the typical ISO 4406 25/23/20 often seen. 

It is also safe to say that the stringent cleanliness levels required by complex hydraulics are not necessary with gearboxes unless circumstances are exceptional. However, aiming at a cleanliness target of ISO 4406 18/16/13 or better is not unreasonable.  With improvements to that level, life extensions over 3 times are realistic.

Built-in Filtration

As dealt with earlier, the cleanliness of units at the commissioning stage is crucial to ensuring successful infant reliability and increased unit life.  It is common to find manufacturing debris (casting sand, machining swarf, etc) present in a new gearbox. 

At least one OEM told me this is normal and that it will be an extra cost if the client wishes to remove it! This is unacceptable, and as a client, vote with your order book.  Unfortunately, reality sometimes means staying with the supplier, but at least ensure that the best quality breather and seals are fitted as standard when specifying new units. 

Storage

In terms of the gearboxes in storage, ensure that any openings in the castings, etc, are plugged, the shafts and gears are covered with a protective film of grease or oil, and this is thoroughly removed before use. 

Use the portable filter cart to flush the gearbox through before it is turned during installation.  The best way is to use a low-viscosity oil of the specified gear oil that can splash through the box, ensuring that all the dead zones are cleaned and that any debris is dislodged and trapped by the filter cart. 

If you request the OEM to do this before delivery, ensure they flush according to the appropriate standards and show certification or proof of achieving your required levels. 

While all these additional specifications add to the initial purchase cost, the savings incurred in the increased reliability and life of the unit far outweigh the penalty.

Other Opportunities?

 Where several identical gearboxes are in close proximity, a possible upgrade that assists with contamination control is to put in a circulating “dry sump” setup as in the diagram below. Having the tank as central to the lubrication minimizes effort because of:

  • The oil is maintained in the ideal state, so it will last much longer and reduce the need for individual oil changes on each gearbox.
  • The oil is always being filtered and cooled again, adding to the oil life and reducing the gearbox wear.
  • The circuit can be started before the start-up of the gearboxes so “dry starts” are avoided.
  • A single oil analysis sample is all that is required on the common return to monitor for oil health, contamination, and wear debris, albeit if wear debris levels change, trouble-shooting samples will need to be taken on each gearbox drain.

Circulating Dry Sump

Author

  • Martin Williamson is the founder and managing director of KEW Engineering Ltd., a company specializing in lubrication and reliability engineering services. With over 30 years of experience in the field, Martin is recognized for his expertise in oil analysis, lubricant management, and condition monitoring. He has authored numerous technical articles and presented at conferences worldwide, further solidifying his reputation as a thought leader in the lubrication industry. Martin is a certified Machine Lubricant Analyst (MLA) and Machinery Lubrication Engineer (MLE)®.

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