Machinery and equipment manufacturers are feeling the pressure more than ever to reduce costs without sacrificing machine performance, a balance that can be difficult to achieve. OEMs often overlook a simple way to improve their long-term profitability and that of their customers: eliminate bearing lubricants. By getting rid of lubrication subsystems, OEMs reduce production costs while making their equipment more marketable and less expensive to operate. At the same time, the cost and hassle of properly disposing of used oil can be eliminated, and initial expenses for auxiliary processes and components such as grease lines, fittings and manifolds can be reduced. reduced or eliminated.
So what are the problems with bearing lubricants? According to a major ball bearing company, 54% of bearing failures are related to lubrication. And an MIT study estimated that approximately $240 billion is lost each year in the United States due to downtime and repairs on manufacturing equipment damaged by poor lubrication.
There is a lower cost, easier to maintain component that eliminates the total cost of bearing lubricants: high performance plastic bearings that run dry.
The hidden costs of lubrication
Proper lubrication is essential for ball bearings. Most require ongoing maintenance for relubrication, which usually requires scheduled downtime. This increases maintenance costs and leads to loss of production time.
Although some relubrication processes are automated, most are done manually using a grease gun. It takes a series of critical steps to ensure proper lubrication, including storing and handling lubricant carefully, properly cleaning the bearing, and using the correct amount of lubricant and the correct grease gun, to name a few. . In addition, it is essential to use the same grease throughout the life of the bearing.
A major oil company studied the time required to manually lubricate a single grease point. He said manual lubrication takes an average of three minutes per stitch. The average machine has 20 grease points to service, which translates to a total annual labor cost of $7,300 for one machine.
Another source claims that the average plant employs 2,196 bearings and spends $60,000 on relubrication per year; of that, $57,000 is just for labor.
Lubricated bearings can increase manufacturing complexity and expense. They often need to be fitted with grease fittings (zerks) and manifolds, oil lines, and sometimes oil reservoirs and pumps. Not only are there costs to purchase these components, but there are also manufacturing costs for machining and assembling the mating parts.
There are also parts needed to protect the bearings from contaminants. The main cause of bearing failure is lubrication contaminated with moisture and solid particles. If as little as 0.002% water is mixed into the lubricant, the probability of failure increases by 48%. And just 6% water can reduce bearing life by 83%.
Ball bearings need seals to keep oil in and water and unwanted liquids out, as well as wipers and scrapers to keep dust and debris out. Seals only last a limited time and do not perform well in dirty and dusty environments. And they also increase friction. In agricultural machinery and lawn mowers, where dust and debris are prevalent during operation, seals and scrapers often need to be replaced.
Improper lubrication or re-lubrication of bearings also accounts for up to 50% of machine failures. When a bearing fails prematurely, several steps may be necessary. Replacing bearings, shaft and even motor or other parts can be very expensive. If the machine has to be taken offline, the expenses can potentially skyrocket. In a six sigma manufacturing guide, it was estimated that the average cost of downtime is $500 per hour, and in some automotive plants and other high-volume production plants, downtime costs are considerably higher. Additionally, unplanned downtime can impact the plant’s production schedule.
Getting rid of used lubricants can add up to around 20 percent of the annual lubricant cost, Valin says. This means that if a plant spends $50,000 per year on lubricants, it will spend approximately $10,000 on disposal. Additionally, the price of oil can affect costs because lubricants are normally petroleum-based, so when the price of oil increases, the price of lubricants also increases.
Bypassed lubrication subsystems
A surefire way to eliminate lubrication costs and headaches is to use self-lubricating plastic bearings. They are made from high performance polymers and, unlike rolling element bearings, they slide instead of roll. They consist of a base polymer coated with fibrous reinforcements and solid lubricants.
Fiber reinforcements increase load capacities and wear resistance. At the same time, solid lubricants are transferred from the bearing to the shaft to form a low-friction micro-finish that reduces friction. Unlike PTFE coated bearings, the self-lubricating properties of plastic bearings are present throughout the thickness of the bearing.
They also don’t need any external oil or grease and run completely dry. Their lack of oil and fat makes them good candidates for food and medical processing, packaging, and other sanitary applications. It also means they don’t attract dirt, eliminating the risk of seizing and the need for gaskets or wiper wires.
They are ideal for laboratories and food processing machinery that require clean, oil-free operation. Plastic bearings also work well in dirty environments like agricultural workplaces because they don’t attract or hold dust and dirt.
They run on softer shafts, even those made of anodized aluminum, which has excellent corrosion resistance and is generally cheaper and easier to machine than case hardened materials and stainless steels.
Self-lubricating plastic bearings can reduce maintenance costs and unplanned downtime due to bearing failures. If a self-lubricating bearing needs to be replaced, the spare (a small, inexpensive plastic sleeve) can be purchased for a fraction of the cost of a recirculating ball bearing. And once installed, they require no maintenance, unlike traditional ball and metal backed bearings.
Plastic bearing materials resist a range of corrosive media, including water, chemicals, cleaning agents, UV rays and more. Specialty materials are also on the market that are resistant to more aggressive media, such as hydrochloric acid, steam/autoclaving and radiation. This allows them to be used in washdown applications and even underwater.
Plastic bearings are suitable for short-stroke applications, unlike linear ball bearings, which require a long stroke to be fully lubricated; short strokes can cause the ball bearings to slip instead of roll on the shaft, causing damage.
Plastic bearings weigh approximately 80% less than metal bearings. Reducing weight reduces drive requirements and can reduce operating costs, reduce fuel consumption and reduce the inertia of moving parts.
There are applications that plastic bearings cannot handle. These include those with:
- High loads with high speeds: these lead to excessive frictional heat build-up and wear.
- Severely cantilevered loads: plastic bearings slide, unlike ball bearings that roll, so linear applications with higher coefficients of friction can result in irregular movements for loads or driving forces strongly overhanging.
- Extremely precise applications: Plastic bearings have a higher running clearance than ball bearings, sometimes 0.001 to 0.002 in.
- Extreme Temperatures: Plastic bearings are not recommended for applications with long term temperatures exceeding 484°F.
From the initial purchase to the life of a bearing, plastic bearings eliminate the need for lubricants and the maintenance and protective components that come with them.
Matt Mowry is product manager for drylin linear bearings at igus Inc.