Frequently Asked Questions

There’s no single criterion, but there are some reliable indicators of performance and stability. Reputable suppliers list as many technical properties as possible, especially for general-purpose greases.

A general-purpose grease should have a base oil viscosity of between 100 and 200 mm²/s at 40 °C; up to 10% above that is fine. Besides base oil viscosity and corrosion protection, look at the results of the four-ball test (VKA) or the SRV test (oscillating friction and wear test). In the four-ball test, a weld load of around 320 kg or higher is a solid result.

Note: expressed in newtons, that’s around 3,140 N, which simply looks more impressive. A wear scar of 0.5 mm or less is also a good sign. If oil separation is specified as well, which is rare, you can assume you’re looking at a very good grease.

Naturally, good to excellent performance and stability come at a higher price.

If a grease has hardened, become gummy or turned brown, it has usually got too hot and some of the oil has evaporated.

Possible solutions:

1. Switch to a higher-quality grease based on lithium (complex), barium complex or polyurea.
2. The base oil viscosity may not suit the bearing geometry and speed. In that case, switch to a grease with a lower viscosity.
3. Relubricate at least four times as often and check the bearing temperature daily.
4. The grease may have no way to escape, so it builds up pressure in the bearing and heats up through fluid friction. Check whether there’s a grease outlet hole, or add one. With shielded bearings, gently bend the shield open slightly.
5. The bearing load may be very high, or external heat may be a factor. Switch to a high-performance or high-temperature grease.

Mixing two general-purpose greases usually isn’t a problem.

It’s very difficult to remove all of the wrong grease without taking the bearing out. In our experience, purging the bearing with around three times its free volume flushes out most of it. The remaining 15–20% only reduces gradually over many relubrication cycles.

Upper temperature limits leave plenty of room for interpretation. They often refer only to short-term peaks, with no defined duration. A general-purpose grease can be used safely up to 80 °C, although you should review your relubrication intervals.

In theory, you could use a general-purpose grease at 180 °C. But it ages so quickly at that temperature that you’d practically have to relubricate every minute to keep it working.

Check the data sheets for the base oil and thickener type, then compare them against a compatibility chart for base oils and thickeners.

If you don’t know exactly what’s in a grease, a simple hands-on test can help: mix equal amounts of both greases and leave them to stand for 24–48 hours. If they show any tendency to separate, they’re definitely incompatible. PFPE-based greases can generally only be mixed with other PFPE-based greases.

Look at two things: the base oil and the temperature it’s rated for in continuous operation. A PAO-based grease claiming 220 °C isn’t realistic. That figure usually only applies for a very short, unspecified period. PFPE-based greases, on the other hand, can safely be used at their stated temperatures, although there are different types to consider here as well.

That depends mainly on the temperature, as well as the grease’s thickener and base oil. Heat makes grease age very quickly. As a rule of thumb, grease life halves with every 10 °C rise above 60 °C.

At least 20 °C above your actual operating temperature. The bigger the margin, the longer your relubrication intervals.

It comes down to the raw materials. Depending on the type, PFPE-based greases can cost up to 50 times as much as a basic high-temperature grease. In return, they can last up to 1,000 times longer, which allows very long relubrication intervals.

There can be several reasons: the temperature is too high and the relubrication intervals too long, the grease simply can’t cope with the thermal load, the mechanical load is too high, or the grease has already aged thermally on its way to the lubrication point.

That depends on the temperature range. Below 210 °C, there are more affordable high-temperature greases that aren’t PFPE-based. However, you’ll need to relubricate more often and use more grease.

As long as there’s no radiation exposure, there are more affordable high-temperature greases, and some may even outperform the one you’re using.

It’s very difficult to remove all of the wrong grease without taking the bearing out. In our experience, purging the bearing with around three times its free volume flushes out most of it. The remaining 15–20% only reduces gradually over many relubrication cycles.

The grease is under severe thermal stress and needs relubricating.

Possible causes include the bearing geometry, how grease escapes from the bearing, the bearing seals, the relubrication quantity and frequency, and finally the types of grease used.

If you don’t know exactly what’s in them, mix equal amounts of both greases and leave them to stand for 24–48 hours. If they show any tendency to separate, they’re incompatible. PFPE-based greases can generally only be mixed with other PFPE-based greases.

The grease is thermally overloaded and the relubrication interval is too long.

If you use a different grease for each bearing, mix-ups are inevitable. Instead, use the high-temperature grease suited to the most heavily loaded bearing for all the others as well, and base the relubrication interval on the shortest one.

Up to 200 °C, PTFE- and PFPE-free alternatives have been available for a long time. Above that, it gets more difficult, because carrier oils burn off or evaporate at those temperatures. What’s left is a dry lubricant such as graphite or MoS₂, which needs frequent relubrication.

Apart from a rated temperature below −20 °C, look at the base oil viscosity, the base oil type and the viscosity index. Low-temperature greases have a low base oil viscosity of around 5–46 mm²/s. Viscosity changes with temperature: the colder it gets, the thicker the oil becomes.

Yes, in most cases. Both types share the same key properties, including a relatively low base oil viscosity of under 46 mm²/s.

As a guide, relubricate once a month with 25% of the bearing’s free volume, or less often depending on the load.

At least 10 °C above your actual operating temperature.

Synthetic greases outperform mineral oil-based ones. The grease should be rated for temperatures below −20 °C.

Yes, it can be. In that case, it’s most likely a grease based on linear PFPE. These have an extremely high viscosity index and therefore excellent viscosity-temperature behaviour.

Below the lowest recommended temperature, the base oil solidifies and can no longer flow, and lubrication breaks down. As these figures are often based on the pour point (DIN 51597 / EN 3015:2019), the actual limit in dynamic operation can be significantly lower.

If you don’t know exactly what’s in them, mix equal amounts of both greases and leave them to stand for 24–48 hours. If they show any tendency to separate, they’re incompatible. PFPE-based greases can generally only be mixed with other PFPE-based greases.

It’s very difficult to remove all of the wrong grease without taking the bearing out. In our experience, purging the bearing with around three times its free volume flushes out most of it. The remaining 15–20% only reduces gradually over many relubrication cycles.

Observation: The 20-metre chain has elongated by 3% within three months. The oven only runs at 200 °C, and the chain looks permanently wet with oil.

Assessment: Provided the oil is ester-based with a viscosity of around 300 mm²/s at 40 °C, the chain oil can largely be ruled out as the sole cause.

Possible causes:

• The chain tensioner gauge is giving a false reading.
• The chain tension is set too high.
• Dirt is preventing the oil from penetrating the chain.
• The sprockets are worn.
• The chain material is of poor quality.
• There’s corrosion or mechanical overload.

Note: In the last two cases, corrosion and overload, the right chain oil can actually help solve the problem.

Observation: Although the chain is lubricated regularly and apparently sufficiently, it runs stiffly and its power draw has risen significantly.

Possible causes:

• The chain is worn.
• Contamination from dust or residue from the product being processed in the oven.
• Residue from the chain lubricant itself.
• Thermal overload has left sticky or hard deposits.

Solutions:

• A special chain lubricant can be used to dissolve existing residue and free up the drive.
• Depending on how dirty the chain is, cleaning may be unavoidable.
• For very large chains, such as P175, dry ice blasting or high-pressure cleaning can often clean the chain without removing it.

Bottom line: A stiff chain with high power draw is often caused by deposits or wear rather than poor lubrication. The right lubricant and cleaning method can help restore normal operation.

Observation: Chain oil consumption has risen significantly. Despite regular lubrication, far too much oil seems to be running through the system.

Possible causes:

• Dirty nozzles, outlets or brushes: The oil is no longer applied precisely to the lubrication point. It doesn’t reach the gap where it’s needed, friction increases, and the control system automatically adds lubrication cycles to bring the power draw back down.
• Incorrectly positioned nozzles: The lubrication points, such as the gaps between chain components, aren’t being hit. The nozzles need repositioning and fine-tuning during operation.
• Process changes (slower speed, higher temperature): A new product runs through the oven more slowly and needs more energy, so the oven temperature was raised considerably without anyone informing the maintenance team. The lubrication settings stayed the same.
• Wrong oil in use: A different oil with a lower viscosity is being used instead of the specified product, either by mistake or out of habit.
• Poor lubrication point: The chain is lubricated at the oven exit, so much of the oil drips off unused on the return run.

Bottom line: High oil consumption is often caused not by the oil itself, but by poor application, a lubrication setup that hasn’t kept pace with the process, or contamination nobody has noticed. A targeted review of the lubrication points, temperature profile and nozzle position is key to improving efficiency and cutting consumption.

Possible causes and solutions:

• The chain is too hot: Cold oil evaporates as soon as it hits the surface. Preheat the oil to reduce evaporation on contact.
• Too much oil is being applied: Excess oil evaporates uncontrollably. Apply less oil and dose it more precisely.
• The oil can’t handle the heat: It’s overwhelmed and evaporates too quickly. Switch to a chain oil with high temperature stability and low evaporation.

Bottom line: Smoke is usually caused by large temperature differences, overdosing or the wrong oil. Technical adjustments and the right product can keep it to a minimum.

Possible causes:

• The chain is worn and has too much play.
• The chain tension is set too high.
• The chain guide is worn, so the links engage the sprocket at an angle.
• The sprocket bearings have too much play.

Bottom line: Sprocket wear is often caused by play in the mechanics, poor chain guidance or overloaded components. Regular checks of all related parts are essential to prevent further damage.

In general, any fine-grained or powdered substance, such as sand or talc, counts as a dry or solid lubricant.

In industry, they’re only used in exceptional cases. They’re usually applied with a carrier that evaporates over time, and the real challenge is keeping the lubricant where it’s needed. Above 400 °C, however, there’s no alternative.

The most common solid lubricants in industrial use are graphite, MoS₂, boron nitride and PTFE.

Graphite, MoS₂, boron nitride or PTFE? Each has its strengths, and the best choice depends on the application. Here’s how they perform in their dry state:

• Graphite is a form of carbon, a key component of steel. It has the strongest affinity with steel surfaces and adheres best of all in its dry state. Under friction, it becomes slightly slippery. Operating temperature: up to 1,400 °C.
• MoS₂ forms a good lubricating film but doesn’t adhere quite as well as graphite. Its layered structure means it turns to dust more quickly under movement. Operating temperature: up to 400 °C.
• Boron nitride offers moderate adhesion but good wear protection. It’s used where food-grade lubrication with NSF H1 registration is required. Operating temperature: up to 900 °C.
• PTFE (also known by the brand name Teflon®) only makes sense as a dry lubricant for plastic-on-plastic or plastic-on-metal pairings. It’s also suitable for NSF H1 applications and wear-resistant, although this wear resistance drops to almost nothing as temperatures rise. Operating temperature: up to 300 °C.

Summary: Decades of experience show that graphite, the messiest of these solids, also has the most versatile, high-level properties in practice, and it’s very inexpensive. MoS₂ is well established and works well in oils and pastes. Boron nitride is popular for its good wear protection and white colour. PTFE is valued for being inert, stable under high pressure and clean.