Switching to a new graphite/metal alloy bearing material helps a major glass manufacturer save $250,000 per year in a high-temperature application. Eliminating production downtime required replacing the old bearings, resulting in the majority of the cost savings.
The manufacturer is a leading producer of glass for home decor, food preparation and industrial and home lighting. This site employs 700 people and utilizes a highly automated process in which glass moves from the forming machine through the lehr (enclosed annealing chamber), without any manual handling 24/7. Two conveyors with flat mesh belts transport glass pieces at 1,900°F.
The machine conveyor moves the hot ware from the forming machine to the cross conveyor, where the items are grouped together before being pushed into the lehr. The lehr is divided into different areas, each with its own heat source, making it possible to carefully regulate the temperature gradient to which the glass is submitted. Temperatures in the lehr average 900°F, and temperatures in the conveyors are approximately 500°F.
In the past, grease-lubricated conventional roller bearings were used on both the machine and cross conveyors. The problem was that the high temperatures of the application caused the grease to break down quickly. Maintenance personnel continually had to purge the old grease and add fresh, clean grease. Grease inevitably spilled on the floors, which created a difficult cleanup job and also represented a fire concern. In spite of these efforts, the roller bearings typically seized up over a period of operation from three weeks to three months. Each part of the production process depends upon the upstream and downstream operations, therefore, when the conveyors shut down, production grinds to a halt.
“Over the years, we tried numerous approaches to solve this problem,” the supervisor said. “We used a variety of different high-temperature lubricants but none were able to stand up to this application. We tried blowing air on the bearings to reduce their temperature, but that didn’t work either. Most of the bearings that claimed to be able to work without lubrication were made of polymers and were unable to withstand these temperatures.
“We even tried daily lubrication of these bearings but they always seemed to fail without warning,” the supervisor said. “When this happened, production had to be shut down for one to three hours to change the bearings. Sometimes we had to use a cutting torch to remove the old-style bearings from the shaft and in this case, we often had to replace the shaft as well.” The cost of the new bearings was dwarfed by the cost of lost production, at about $700 per hour.
Trying a New Bearing Material
The machine repair supervisor for the manufacturer looked for alternatives and decided to try a proprietary graphite bearing material that does not require lubrication. The self-lubricating characteristic of the material eliminates the need for grease or other lubrication and allows for improved performance under high-temperature conditions.
Graphalloy graphite/metal alloys take advantage of the special properties of graphite, the structure of which can be compared to a deck of cards with individual layers able to easily slide off the deck. This phenomenon gives the material a self-lubricating ability that is matched by few other materials. This self-lubricating feature allows for the elimination of grease or oil that would normally evaporate, congeal or solidify, causing premature failure. The graphite matrix can be filled with a variety of imbedded lubricants to enhance chemical, mechanical and tribological properties. The material provides a constant, low coefficient of friction rather than just a surface layer, helping to protect against catastrophic failure. Lubrication is maintained even during linear motion; lubricant is not drawn out and dust is not pulled in.
“I started by replacing a single bearing and quickly discovered that the new Graphalloy material could withstand the high temperatures of this application,” the supervisor said. “Up to this point, we’ve converted conveyors for five lehrs to the new bearings and have four more to go. Once the entire plant has been converted, we estimate the savings will be just under $250,000 per year. This calculation includes the cost of downtime, the cost to grease the old bearings, the cost to replace the old bearings and the fact that the new bearings are less expensive than the old ones.” This savings has been generated by an investment of less than $10,000.
New Bearings Generate Savings
“The first set of Graphalloy bushings were installed on machine and cross conveyor bearings in one of the plant’s nine lehrs in November,” said the supervisor. “They worked perfectly for just over a year and were taken out for inspection the following December. There was no need to replace the bearings at that time.” During this same shutdown, the manufacturer’s maintenance staff replaced machine and cross conveyor bearings on four additional lehrs.
To date, the oldest bearings have been installed for about 18 months without any failures. Maintenance management estimates that savings will increase to $60,426 per quarter once the new bearings are installed in every conveyor. This represents approximately $25 savings for every $1 invested in new bearings.