Let’s Talk About Felt…

Felt filter materials are a staple core to the filtration industry, in fact Rosedale Products have the most encompassing offerings of felt solutions on the market with multiple permutations of felts but why is it used, where do they differ and what are they all for…

Where Are Felt Filters Used?

Felt is used in the liquid process filtration market as it offers particularly proficient level of versatility, by changing the core material, weaving the felts differently, adjusting the thickness (depth) or pairing/layering we can achieve a diverse range of performance and compatibilities to target specific requirements.

Is All Felt The Same?

So, is all felt the same? In short no, because of the fore mentioned properties it can be manipulated and manufactured in an infinite range of qualities. Much of the felt on the market today is produced cheaply in the far east on inferior quality fabric looms designed for weaving cosmetic felt for use in dry industrial applications or for clothing use. Technical felt looming is a science and Rosedale Products pride ourselves on only supplying felts sourced from technical sources in the USA and Canada. By doing this we guarantee our filter bags start off with a quality and exact specification and many of our customers notice the difference in our felt performance over that of our competitors.

Several Types Of Felt

So why are there several types of felt? Put simply one material doesn’t fit all. There are two main base materials used in the filtration industry today and by far the most popular felt in the industrial world is polypropylene felt but this has temperature limitations as well as being incompatible with some pH’s and solvents. Polyester however works to a higher temperature and is compatible with many liquids’ polypropylene is not. We at Rosedale then also offer a Nomex fibre for extreme temperature conditions.

Different Types Of Felt Used in Filter Bags

Felt filter bags are the first choice we shall explore, our filter bags are available in three plain felts, Polypropylene, Polyester and Nomex. As described above these each have their own individual properties and, in the case of our polypropylene and polyester, are provided in a range of efficiency ratings which is adjusted based on the depth of the filter felt. The thicker the filter felt the more effective (efficient) it will perform. Many standard felt filter bags in the marketplace claim to offer efficiencies of up to 70% from a single layer felt, the true efficiency is nearer 30% of the advertised micron pore size when put under test conditions, how is this allowed? Well, it is all to do with the BETA scale, which is something we will cover in another article, the BETA scale measures the performance of the filter and produces a range of efficiency, for example a 55 micron filter at 95% efficiency could be the equivalent of a 1 micron filter at 30% efficiency depending on how its constructed. Most felt filter bags on the market today do not reach a true BETA rating at all, even we do not consider a standard filter bag to be an exact enough filter to viably BETA rate it, whilst our Beta and Graded Density ranges are put through rigorous laboratory testing to obtain the BETA curve evidentially. We obtain these results by layering and pairing different specifications of felts together to create one final felt filter bag.

What Is Glaze Felt

What is and why do we glaze felt? Glazing, also known as singeing, is a process which seals the fibres of the felt filter bag to prevent migration in the liquid flow, the process is only performed on the downstream side of the bag. Glazing improves the felt efficiency by preventing movement of the fibres within the weave, the finish is generally commonplace for felt filter bags going into food or beverage production.

Woven Felts

At Rosedale Products we also use woven felts to make filter cartridges. Our unique PL range of bag sized cartridges employs a special method of construction to allow us to produce a bag capable of 416lpm at low pressure drop through a single size 2 housing. To support this flow, we support the felt weave with rigid mouldings of the same material in its construction which makes our PL bag cartridges the highest flow rating size 2 filter bag on the market today and this is working at a 99% efficiency.

What makes felt such a brilliant product for filtration is its versatility, our felt filters are found supporting clients in various industries such as:

  • Chemical engineering and manufacturing – solvents, acids, alkalis and waste
  • Food and beverage – brewing, Kombucha, edible oils, fruit juices and syrups
  • Coatings, resins and inks – China clay, pigments and particulate removal
  • Metalworking & automotive – machining fluids, parts washing and release agents
  • HVAC – rust, calcium and sediment removal and heat exchanger protection
  • Water – process water debris

Looking For Felt Filters?

We stock a wide range of felt filters for various applications needs. Visit our filter bag page now to find the right filter bag for you.