Rubber rollers play a vital role in manufacturing processes. Although rubber rollers may not always be among the most noticeable parts of a machine, they are essential elements that affect the quality of the final products on various production lines. A number of industries including printing, packaging, lamination, coating, plastic film production, textile industry, metal processing, wood surface finishing, and adhesive processing make use of industrial rubber rollers extensively to support the process. In addition to that, such rollers are used for moving, pressing, coating, dragging, and finishing the surfaces.
We are aware that many of the industrial environments, that are in use of rubber roller as their production element, face with oily substances like: inks, cleaning agents, lubricants, hydraulic fluids, and resins. This fact raises a practical question for the companies: Can these substances affect the surface layers, particularly the rubber and coating layers of a roller?
If the manufacturer's first choice would be a rubber roller that is resistant to oils when they are buying industrial NBR rollers, yet problems like roller surface swelling, less firmness, and stickiness happen, some enterprises start to ask themselves: If NBR is known as oil-resistant, why is there a breakdown from using oil over time? Is that a problem caused by inferior quality rollers?
Essentially, this issue reflects the incorrect perception in the industry concerning oil resistance. Oil resistance does not mean complete immunity to the effects of the oil. It is true that NBR rubber (Nitrile Butadiene) is significantly more resistant to oils compared to materials such as natural rubber or styrene-butadiene rubber. However, its effectiveness is limited and depends on several factors.
The performance of an industrial NBR rubber roller can be affected by factors such as the type of oil, the exposure duration, heat, pressure, environmental conditions, and rubber formulation. Taking the example of a printing equipment which uses an industrial NBR roller; it works 8-24 hours a day and constantly is exposed to an oily component of the ink and cleaning medium. If the formulation of the NBR is not compatible with the operating environment, performance degradation would have to happen in the span of a few months, despite the fact that the material is oil - resistant. Therefore, to tackle oil deterioration of industrial NBR rollers, one has to be beyond answering yes/no about oil damaging and instead focus on identifying what oils influence NBR, how great the influence is and how to correctly choose the material. How would you extend the life of your maintenance?
The article offers an elaborate explanation of oil resistance mechanisms, the effects of various oils, failure modes, and solutions, on the use of industrial NBR (Nitrile Butadiene Rubber) rollers for enterprises to make proper decisions and carry out their maintenance procedures to a high level.
Why are oil contamination problems so common for industrial NBR rollers?
The most distinct trait of industrial rubber rollers is using the elastic feature of the material for flexible contact and stable material transfer. It is very common to find in numerous manufacturing systems that although metal rollers have very high rigidity, they are only to some extent an adequate substitute for rubber rollers, which provide more cushioning, a bigger contact area, and easier way to handle the materials.
In industry, a rubber NBR roller is a very versatile item of equipment. They can, for instance, work closely with the inks at the printing factory, and then with adhesive and coating materials used in the coating industry, or lubricants in the metals processing, and even plasticizers or other oily additives in plastics processing.
Nevertheless, when oily substances come into contact with the roller they don't merely settle on its surface. As rubber is a polymeric material that allows for a certain level of openness on a molecular basis, which allows for oil molecules to permeate the inner layers over time. In fact, the interaction between those oil molecules and the basic molecular structure of the rubber can cause the physical properties of the material to deteriorate to such an extent they cannot even keep it in use anymore.
Oily penetration usually leads to effects of the following nature:
• Volumetric swelling;
• Hardness loss;
• Tensile strength decrease;
• Reduction in the ability of getting back elasticity;
• Surface stickiness or cracking.
Although these alterations usually don't affect normal rubber parts much, for industrial NBR rollers, it would be enough for the dimensional or hardness change only to disrupt the whole precision of the production process.
For example, an NBR roller which is used in precision coating gets a small absorption of oil gradually which causes the diameter to increase by 0.1 - 0.5 mm, it would mean a shifting of the pressure and a possible coating inconsistency between the two layers. Hence, besides oil resistance, industrial rubber rollers also need to demonstrate long-term dimensional stability.
What is NBR (Nitrile Butadiene Rubber)? Why is it so oil-resistant?
NBR is a man-made rubber created by copolymerizing butadiene and acrylonitrile; the level of acrylonitrile is an essential factor affecting its oil resistance.
In a nutshell, the greater the acrylonitrile content in the product, the better will NBR resist non-polar liquids like, for example, mineral oils and fuels.
According to acrylonitrile content, NBR is generally categorized as low, medium, and high acrylonitrile content types:
Low acrylonitrile: about 18%–24%;
Medium acrylonitrile: about 25%–35%;
High acrylonitrile: about 36%–50%.
NBR with low acrylonitrile has good elasticity at low temperatures but only moderate oil resistance; high acrylonitrile NBR has excellent resistance to oil, but its low-temperature characteristics and elasticity may be somewhat impaired. Hence, choosing the rubber for NBR industrial rollers isn’t as simple as picking one with the highest acrylonitrile content in the world; rather, one has to strike a balance based on actual running environment.
For example:
Typical conveyor rollers would emphasize wear and elasticity, so NBR containing medium acrylonitrile would be chosen;
Industrial NBR rollers that are coming into contact with lubricants or fuels could benefit from high-acrylonitrile content;
On the other hand, precision coating rollers made from NBR need to be tested thoroughly regarding resistance to petroleum oils, hardness, surface gloss, and elastic recovery.
A general Shore hardness scale for industrial NBR rollers runs from 30 to 90, and different levels of hardness may be required for different uses.
For example:
Shore A 30–50 is perfect for soft contacting and precision coating;
Shore A 50–70 is ideal for industrial carrying and pressing without special needs;
Shore A 70–90 is recommended for situations involving extreme pressure and severe wear.
Thus, when determining the oil resistance of a NBR roller of industrial quality, it suffices to state the base material as "NBR"- the real difference depends on the formulation design.
Can oil damage industrial NBR rollers? It's primarily a matter of the oil used.
Quite often, the operators think that an NBR roller allows oil contact of any type. This point of view is a misconception. Even though NBR has some resistance to mineral oils and fuels, the influence of one kind of oil over the rubberrubber compared with another is quite different.
I. Mineral oil generally has a negligible effect on NBR
Mineral oils such as hydraulic fluids, machine lubricants, and some process oils are among the regular fluids that industry rubber rollers (nitrile rubber) touch.
Usually, NBR rubber is stable in normal environmental temperature conditions.
You should keep in mind, however, that oil resistance decreases with increasing temperature. For the same mineral oil type:
The time for which NBR rubber remains stable at temperature range 20°C ~ 40°C is long;
The rate at which molecules penetrate through the oil increases at 80°C ~ 100°C when temperature rises, and the rubber swallows up the oil quickly.
Hence, if industrial NBR rollers are placed in such oil at high temperatures, one has to use a kind of heat-resistant NBR.
II. Aromatic solvents can cause heavy damage to NBR
To some extent at least, aromatic solvents have the ability to destroy NBR. It might, for example, involve the use of degreasing agents or solvents which contain aromatic compounds such as toluene or xylene during the production stage that have a significant effect on NBR.
Over a long exposure time the following could happen:
The rubber softens;
The rubber swells;
The surface becomes sticky;
The strength is reduced;
It is also worth mentioning here that in cases involving such industries as printing and coating it can be that an unsuitable cleaning agent would cause the degradation of performance to such an extent in the industrial NBR roller even if of high quality.
III. Vegetable oils and special fatty products should also undergo testing
Sectors such as foodprocessing and packaging are involved with contact with substances like vegetable oils and animal fats. Although none of these substances will produce such swelling at NBR as some solvents, a continued exposure at elevated temperatures can still negatively impact NBR characteristics.
Therefore, it's not enough to refer to the general category of "oil" when considering compatibility. Instead, one has to conduct tests that are based on the specific chemical properties of that oil.
What triggers accelerated oil-related degradation in industrial NBR rollers?
In fact, oil alone does not account for failure of industrial NBR rollers. Most of the time, it is not a single factor but the combined effects of oil, temperature, pressure and time, that causes material degradation.
Temperature is the first factor. At higher temperatures, oil molecules are more active, which facilitates oil penetration into the rubber. For example, NBR, which can be used for long term service at room temperature, could undergo very fast aging if the ambient temperature of the industrial environment is continuous operating above 90°C.
The second point is the duration of contact. The differences between short periods of contact and long-term contact are significant. Most industrial NBR rollers are used in dynamic, continuous mode and stay in contact with oils for several hours to the entire working day so that the effects of these oils are very long-term.
Third, mechanical pressure. Industrial rubber rollers like printing, laminating, and coating rollers have to be designed with certain pressures in mind. With pressure oil can get into the micro-structure of rubber with less effort while under fatigue mechanical stress, there is a faster wear out of the material properties.
Fourth, the presence of contamination in the production environment. In case where oil itself carries metallic particles, dust and abrasive materials, roller surface will get both mechanical damage of rubbing and a chemical damage of dissolving, which result in its quicker destruction.
What is the physical evidence of the damaging effects of oil in the industrial nitrile rubber roller?
Factories can determine quite easily if the industrial nitrile rubber roller has suffered an oil damage by examining the various indicators.
The first indicator is a change of dimensions. The roller can become larger as the NBR takes in the oil which could affect pressure and accuracy of the equipment.
The second sign is a change of hardness. A stable hardness is required for the industrial nitrile rubber roller when running to be able to handle a variety of pressures in processing. In case oil softens NBR, the roller's load capacity of the surface gets reduced.
A third signal is that of the change in external appearance. Typical features that can appear are :
A shiny or smooth surface;
An extremely sticky or tacky one;
Cracks;
Flakes coming off.
Last, a processing performance decline. Such as, for example,
Uneven thickness coatings;
Sliding of goods along the material;
Loss of laminating capacity;
Surface imperfection on the product.
Such problems signify that the industrial nitrile rubber roller has had a significant impact from its surrounding environment and hence should be taken for immediate examination.
How can oil resistance of nitrile rubber rollers be improved for industrial use?
The best strategy to improve industrial nitrile rubber roller oil resistance is through material, manufacturing, and operation level optimizations.
First, the appropriate NBR formulation must be decided based on the application environment. For example, a medium oil-resistant formula is enough for the standard oil environment. But a different case is high temperature and highly oil contact conditions in which a high acrylonitrile or specially-modified NBR is required.
The second stage is to optimize the vulcanization system of the rubber. Appropriate cross-linking structure not only enhances resistance to oil-induced swelling but also retains the required elasticity.
Inefficient cross-linking results not only in a decrease of oil resistance but also of mechanical performance. On the contrary, overcrosslinking can lead hardness in the rubber and a loss in elasticity.
The third point is about controlling the operating temperature. Limiting high-temperature operation is one of the most important ways to increase the service life of industrial nitrile rubber rollers. In some cases, a temperature reduction of 10 to 15°C would significantly delay the material degradation.
Fifth, setting up a routine inspection plan helps. Businesses may periodically check:
Roller surface hardness;
Increase or decrease in diameter;
Appearance of surface cracks;
The roller's ability to bounce back after compression.
Early identification of the above mentioned problems will help in reducing the downtime caused by a complete equipment breakdown.
Industrial NBR/Nitrile rubber rollers are better than other types of rubber rollers in which ways?
Many types of rubbers are used in industry as rubber roller materials like natural rubber, silicone rubber, polyurethane, and SBR (styrene-butadiene rubber).
For instance, compared to natural rubber rollers, the most important thing in favor of NBR is better resistance to oil. While rubber in general is a good material for high elasticity, upon contact with mineral oil or oily stuff it tends to swell very much.
NBR as a material offers in general greater durability and mechanical performance than the ones of silicon rollers so they are often the choice of material for high-speed production processes.
On other hand the standard polyurethane material tends to lose its properties sooner in the presence of the said oils, where NBR is more consistent.
As a result, industrial NBR rollers are still an essential choice in case a combination of oil resistance, wear resistance, elasticity, and cost-controllability is required.
FAQ: Common questions regarding the oil resistance of industrial NBR rollers
1. Will oil inevitably damage industrial NBR rollers?
Not necessarily. Industrial NBR rollers possess good oil resistance and are particularly well-suited for mineral oil environments. However, performance degradation can still occur if they come into contact with incompatible oils or solvents, or are exposed to high temperatures for extended periods.
2. Why do oil-resistant NBR rollers still swell?
The primary reason is often that the type of oil exceeds the material's compatibility range, or the operating temperature is too high. "Oil-resistant" implies resistance, not total immunity to oil absorption.
3. Which oils are industrial NBR rollers suitable for?
They are generally suitable for contact with mineral lubricating oils, hydraulic fluids, certain fuels, and machining oils. However, specific applications should be verified based on the oil's composition.
4. What causes industrial NBR rollers to become sticky?
Common causes include swelling due to oil, the influence of solvents, rubber aging, or surface contamination. The cause should be determined based on the specific production environment.
5. How can the service life of industrial NBR rollers be extended?
Selecting the appropriate NBR formulation, controlling operating temperatures, avoiding contact with incompatible chemicals, and establishing a regular inspection schedule can effectively extend the service life of industrial NBR rollers.
6. Can industrial NBR rollers completely replace other types of rubber rollers?
No. Different rubber materials offer distinct advantages. While industrial NBR rollers are better suited for oil-resistant applications, other materials may be required for scenarios involving extremely high temperatures, harsh chemical environments, or specific elasticity requirements.