Graphite / Metal Alloy Bearings Save $250,000/Year in High Temperature Glass Industry Application

Switching to a new graphite / metal alloy bearing material helped a major glass manufacturer save $250,000 per year in a high temperature application. Eliminating production downtime required to replace the old bearings produced most of the cost savings. Bearings used in a high temperature conveyor, 500°F failed quickly because the temperature destroyed the lubricant.

The conveyor delivered glass from the forming machine to the lehr, a special type of oven used specifically for annealing glass. The Machine Repair Supervisor for the Pennsylvania-based 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. "I started by replacing a single bearing and quickly discovered that the new GRAPHALLOY material could easily withstand the high temperatures of this application," the supervisor said. "Up to this point, we have converted conveyors for five lehrs to the new bearings and we have four more to go. We estimate the savings, once we have converted the entire plant, at just under $250,000 per year. This calculation includes the cost of downtime, the cost to greasing the old bearings, the cost of replacing 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.

The manufacturer is a leading producer of glass and value-added enhancement to the non-retail customer. The company’s products in the home décor area include candleholders, flower holders, seasonal products and tabletop items ranging from martini glasses to latte mugs. In the food preparation area, products include packaging and ovenware. Industrial products include appliance accessories such as frying pan lids and precision glass products. Finally, in the lighting area, the company makes industrial lighting products, home light fixtures, and lamp products. In today's competitive marketplace, consumers are looking for new and innovative glass products. The manufacturer has also taken the idea of decorating glass to a new level by creating a multitude of decorating options and textures. The company’s shape change program makes it possible to meet this challenge by utilizing 75% of an existing set of molds in the development of a new shape. It has reduced its up front investments and per piece price with this shape change program. The next task was to reduce its process costs.

Bearing failures hinder production

The manufacturer’s plant employs 700 people and utilizes a highly automated process in which glass moves from the forming machine, through the lehr without any manual handling seven days per week, 24 hours a day basis. Two conveyors, having flat mesh belts, are used to transport 1900-degree glass pieces. 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 itself 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 about 900 degree Fahrenheit.

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 were kept busy almost continually purging the old grease and adding 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 ranging from three weeks to three months. Each part of the production process is dependent upon the upstream and downstream operations so, when the conveyors shut down, production ground to a halt. "We tried daily lubrication of these bearings but they always seemed to fail without warning at the worst possible time," the supervisor said. "When this happened, production had to be shut down for between one to three hours in order 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 the lost production, at about $700 per hour.

Trying a new bearing material

"Over the years, we tried many different things in an effort 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 we saw that claimed to be able to work without lubrication were made of polymers so they had no chance of withstanding these temperatures." Then a local industrial distributor suggested that the supervisor look into GRAPHALLOY bearings from Graphite Metallizing, Yonkers, New York.

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 no other material. GRAPHALLOY’S self-lubricating features allow 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 impregnants 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. GRAPHALLOY wear components also improve reliability under conditions such as low speed operation, frequent starts and stops and switch-overs from standby to continuous running. GRAPHALLOY bushings are available in over 100 grades of material in any desired size or geometry, including cylindrical with or without grooves, flange or double flange, split and metal-backed.

New bearings generate substantial savings

Working with the distributor and the bearing manufacturer, a four-bolt flange unit with a GRAPHALLOY insert was selected to fit the one and a quarter inch shaft used on the conveyor with only the most minor modifications. With the new bearings, the shaft turns but not the bearings, so the manufacturer’s maintenance team simply changed the key to the opposite side of the drive, which took only about 10 minutes. "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. We saw no need to replace the bearings and that time." During this same shutdown, the manufacturer’s maintenance staff replaced machine and cross conveyor bearings on four additional lehrs.

Since the additional four conveyors were converted over to the new bearings, not a single one has failed or even exhibited substantial wear. To date, the oldest bearings have been installed for about 18 months and they are still going strong. The supervisor calculates the initial cost savings for the first set of bearings at about $4,500 for the first year. He estimates that savings will mount to $60,426 per quarter once he has installed the new bearings in every conveyor, which he plans to do during the shutdown. This represents approximately $25 savings for every $1 invested in new bearings. The vast majority of these savings come from eliminating lost production when the conveyors have to be shut down during the bearing replacement process. This figure does not include several other savings that are difficult to quantify, such as the cost of cleaning up grease that was purged from the old bearings. The new bearings have also had a favorable impact on safety in the plant since they have eliminated the need for maintenance staff to change bearings on hot conveyors and eliminated grease spills. The elimination of the need to lubricate and replace bearings also frees up the machine repair group to focus on a wide range of other tasks that they often had difficulty finding time to attend to in the past.

The manufacturer has streamlined its production with its shape change program and eliminated its process interruption problems with the use of GRAPHALLOY bearings. It is now in a better position to be more responsive and competitive in the highly competitive glass products marketplace.