How to Select and Maintain Felts for Leather Tanning Machines
One way to use felts is on machines throughout the leather making process. From wet end to finishing, the different configurations, processes, and materials mean it’s important to note the details when selecting the correct felt for your machine and maintain that felt for optimum performance and durability. When selecting the best felt, look at the machine, chemistry, process, and desired effect on the leather. Cleaning methods are then determined based on the felt selected and the process. There is no way any machine or felt manufacturer can suggest the correct felt for your machine without knowing about your process and outcome you are trying to achieve. It’s like suggesting a tire for your car. Getting the size right might get you rolling, but if you don’t consider the season, the terrain, the power of the car and how you drive, you could be limiting the performance, safety, and satisfaction of the driver. Same goes for your felts. Start with the manufacturer’s suggestion but consider your leather, your process, how you will use the machine, and what you hope to get out of it. Then clean and maintain your felt to achieve the desired results for the longest possible time.
Felts for leather manufacturing machine come in two basic types: those for wet end machines like wringing and setting out machines and those for finishing/embossing machines.
The main purpose of the felt is to provide a supporting surface for the leather with the following characteristics:
- Smooth enough not to mark or transfer a print onto the leather
- Enough grip to move the leather through the pinch point(s) of the machine
- Enough slip to avoid pleating/folding of the leather as well as allow it to spread where necessary
- Dense enough to offer a level and consistent support for the leather as it passes through the critical part of the machine
- Porous enough to allow for varying thickness of the leather and (for wet end machines only) allow for water that’s removed from the leather to drain through the felt
The features and limitations of the machine you are running will be the first thing to consider when selecting a felt. For example, a 3 roll wringing machine from 1985 will have different requirements compared to a 6 roll wringing machine manufactured in 2015. The new machine creates twice as much pressure at each pinch point (the point where 2 rollers meet to squeeze water from the leather), with twice as many pinch points (4 instead of 2) at a 50 % faster working speed. Even though the process is the same, the felt will be completely different in the type of fibers used to manufacture it and the way it’s manufactured.
Now consider how you will be running your machine. Will you run at the maximum speed? This may not be necessary if your production requirements are lower than what the machine can give you. The benefits of lowering the conveyor speed is a longer dwell time at each pinch point when wringing and more time for water to escape through the felt fibers. This is a great benefit since a buildup of water at the pinch point of a wringer can cause defects such as pleating of leather and/or leather that is too moist after wringing which could mean trouble down the line with your shaving process.
Will you run at the maximum pressure? This may dry out your leather too much as well as create unnecessary strain on the felt fibers, leather fibers, machine rollers, bearings, hydraulic circuit, etc. Once you find the balance of speed and pressure that works for your machine, providing that information to the felt manufacturer will be critical in deciding which felt type, fiber, and density will give the best result with the longest life.
Finally, keeping new felts clean by following the correct guidelines for both the benefit of the felt and the leather is important. The methods for wet end and finishing felts are quite different:
- Finishing felts
- Keeping these felts clean and smooth is important since dirt and marks on the felt can transfer onto the surface of the finished leather. Keeping the felt moist with ambient temperature water will help keep it soft and “swollen.” Then clean the felt surface with a very diluted alcohol-based cleaner. For removal of dirt, grit, leather fiber, and grease use adhesive tape. Apply the tape and strip it away, repeating until you achieve the desired effect. It’s time consuming but an important part of the process. Machines that come equipped with a cleaning brush should maintain an adjustment where the brush removes only the excess worn felt fiber and dirt.
- Wet end felts
- These types of felts require the surface to be clean but also need a deep cleaning to keep the fibers clean throughout the profile of the felts. Since water squeezed from the leather must drain through the felts, some chemicals, fats, and particulates can get left behind which can build up over time and clog the felts. These contaminants are easily removed with a regular and thorough cleaning regimen. Use a warm, low pressure water stream and a mild degreaser together with a fabric softener. The detergent will help remove the contaminants while the fabric softener keeps the natural and synthetic fibers in the felt resilient over time. A pressure wash is a common practice in the tannery but not recommended. Avoiding a pressure washer may make the cleaning process a little longer but it’s worth the extra time. Cleaning after each shift and every break is ideal. During production, a regular and steady flow of warm water applied to the upper felts will help dilute the runoff and prevent excessive buildup of contaminants within the inner felt fibers. Many machines come with a water bar over the upper felt but one can be easily fashioned by suspending a pipe with several holes across the working width of the machine.
For more information about selecting a felt with the correct properties for your machine, your production and your leather, please contact us at First Source Worldwide for a no obligation consultation. At the very least you should be able to improve the working life of your felts and by looking at every aspect of the process, you may even realize some quality and process improvements that you weren’t expecting. The same goes for maintenance and cleaning, we can review your current process, look at your areas of concern and try to find ways to improve. Click the picture below to connect with a First Source Worldwide team member.