Causes for short life of a Felt
Why do felts deteriorate to quickly?
Causes for Felts Short Life
As the felt around the roll is the weakest component of the whole laundry process it’s obvious that when something goes wrong in the washing process or if the ironer is not well tuned, the padding will, first, show a defect and as consequence have an abnormally short life as consequence.
1. Mechanical Reasons
Symptoms: the felt is broken over the width or the felt is so laminated that it starts to lose its top fibres (chest side)
1.1 Temperature of the chest
For some reason, the temperature from the boiler is lower than normal, forcing the chest to narrow its diameter, which will laminate or break the felt or you can “see” the springs trough two turns of felt.
1.2 Washing products
Too much deposit (precipitation) of washing products in the chest because of poor bleaching and neutralizing, poor rinsing (to save water), poor quality water (hard water) or poor recycled water.
1.3. Additional Strain
After a few hours of working with a new padding, the third turn overlap should be cut off to avoid additional strain of the felt and so avoid a damp strip on the linen.
1.4 Steam Traps
Steam traps have to work properly, otherwise there will be cold spots in the chest because of condensation. It will cause a potential deformation and rapid destruction of the felt as well as a bad finish of the linen.
1.5 Bake the felt
When mounting a new Needled felt, it should be screwed on both edges of the roll and attached every 20 cm with a thin wire to the holes of the cylinder to avoid potential deformation of the felt if one side slipped on the roll!: a typical launderers complaint is that the felt shrunk so that the springs are visible. In fact, the felt did not shrink; it has deformed and has a diamond shape, instead of rectangular one. The only option is to put on a new felt and observe the basic mounting requirements and it is always recommended to”bake the felt” at full steam pressure for one hour before starting work.
1.6 Spring Condition
Always check the springs, as with many years of work, they might break and create mechanical damage to the felt.
1.7 Objects in between roll and chest
Mechanical damage of the felt and springs can be caused by a foreign hard object (like scissors) or
by linen which has jammed.
2. Chemical Reasons
Symptoms: the felt loose strength progressively and is finally reduce to dust
2.1. Hydrolysis:
the typical phenomenon which reduces the life of the felts is the molecular destruction of polyester fibres, because of the combined factor of three elements: steam, temperature and time - this is called the hydrolysis effect. The higher the humidity content in the linen and/or in the felt, the higher the temperature, the faster the felt will be reduce to dust! To check this, push a thin screwdriver through the felt. If it goes easily through, the felt is hydrolysed and should be changed rapidly. If it goes through the felt with difficulty or does not go through, the felt is still good. This hydrolytic attack shows itself very strongly on the polyester, as its fibres start to be attacked at only 95ºC. It is obvious that if there is a modern feeding machine which feeds the ironer at high speed, the quantity of evaporated steam going through the felt is much higher than before and consequently the working life of the Needled felt will be reduce. As a field example, the life of a 4000 gr/m² polyester Needled felt was 3030 hours at the speed of 18m/min, but in the same type of ironer with the same type of felt, the life was only 1486 hours at 40m/min approximately half of the working life!.
To reduce the hydrolysis and increases the working of the polyester felt, you have to:
- Check the humidity content of the linen before ironing (moisture retention).
- Especially when using polyester felt, use a top felt with special polyester fibre with higher resistance to the hydrolysis destruction. The air permeability of the top felt should be superior to 660 litres/dm²/min. under 20 mm water in order to run dry and increase the output of the ironer.
2.2 Chemical Hydrolysis:
Hydrolytic attack could be greatly accelerated if the residual ph of the linen is going away from the neutral point. If it is on the acid side, it will shorten the working life of the aramid Needled felt; if it is on the alkaline side, it will shorten the working life of the polyester felt. Residual Ph of the linen should be as closed as possible to the neutral point (7), and checked often.
2.3 Thermolisis:
Hydrolytic attack can be teamed with thermolisis attack, which is the destruction of the polyester fibre exposed to too much heat, especially on the last roll of a multi-roll ironer. The special polyester fibre should not be submitted to steam pressure heating temperature superior to 10/11 bars. Above this temperature, a meta aramid felt should be used.
Note: If the case is a mix of Mechanical Reasons and Chemical Reasons, the needled felt might only last a few weeks.
