Flexo End Seals
- When installing your seals, make sure the face of the seal fits squarely against the chamber with no gaps or distortion.
- The condition of the anilox roll can also play a role in chamber leaks. If the roll lacks a dead band, ink will build up there and contribute to end seal failure. Chips on the ends of the anilox rolls can also create ink buildup and compromise the integrity of the end seals.
- Make sure to use an end seal material that is compatible with the type of ink or coating being used, the length of the run, and the press speed. Today there are a number of end seal material options for all types of inks that can offer very long life. However, these solutions are often more expensive so you need to match the material specific to your criteria.
- There a number of new end seal coatings and multiple material combinations (two part and three part) on the market today. Most of these are designed to increase end seal life. When combined with today’s longer lasting blade options they can significantly reduce the need to shut down the press just to change seals or blades.
- It is important to know that not all felts are created equal. Higher quality felts (F1, F3) will offer longer life and higher vibration absorption. Lower quality felt seals will usually have more thickness variations. It is important the felt seals are properly lubricated. The right amount of a food grade lubrication can extend the life of the seal by reducing the friction as well as, the possibility of ink build-up. Food-grade petrolatum is more effective than oils, as oil flows away (down) from the top of the seal as it is heated. Conversely, petrolatum stays cooler at the base of the seal and “wicks” toward the top of the seal as friction heat is generated.
- Foam end seals are still a very popular and cost effective solution. Some new foams, especially those with coatings, have proven to last as long as many felt seals. Longer life makes them more cost effective.
- Flexo end seal materials are available with different durometers or compression ratios. This is important as the doctor blade needs to have some upward pressure from the end seal to ensure an adequate seal is made between the shoulder of the end seal and the underside of the blade. It is important that the seal is sized properly and does not apply too much upward pressure that it causes the blade to “flare” (the end is lifted upwards beyond a degree or two from anilox parallel). Too much flare on the blade will require excessive pressure to ensure even blade pressure to the anilox and will cause uneven wear.
- Good seal design for a proper fit is critical to minimize chamber leaking from gaps. This is especially true on older presses where alterations may have been made or vendors for end seals have changed and you are working with “copies of copies”. This is the most critical in the radius of the seal. If you are considering looking at new end seal options it is important to also supply the diameter of the anilox roll to make sure that the end seal radius is correct.
- Doctor blades that are too short or too long can be another source of leaks. When changing a doctor blade, it’s important to make sure that the new blade is the right size for the chamber and installed correctly. Typically the blade should come to about halfway across the tops of the end seals when placed in the chamber. If the blade does not reach the seals, then the seals can actually prevent contact between the doctor blade and the anilox roll. If the blade extends beyond the outer edge of the end seal, it may create a small opening between the underside of the blade and the end seal which creates a path for ink to flow out of the chamber. If it’s too long, the blade may also become wavy and not lay flush with the roll, causing uneven metering and leaking.
- Many new chambers come with special molded rubber seals. These can be very effective but also very expensive. Sometimes more traditional seals can be substituted with good success.
