Information on industry felt
Industry felt
From the mid-1980s, industry felt was used to line plastic furniture glides to protect sensitive floors and reduce noise when moving furniture. In contrast to some plastic glide facings, felt will prevent scratching or abrasive piling on sensitive floors (parquet, polished/smooth limestone, etc.) and instead accept a higher abrasive loss. However, as felt is susceptible to damage when wet, it can only be a compromise between preservation and wear.
Felt versions
Industrial felt is available in a wide range of dimensions, forms and cuts, as well as various specifications such as coloured, self-adhesive, siliconised, flame-retardant, dry cleanable, limited water-resistant, short-time water-repellent and antistatic. An essential feature is its density range, which is mostly 0.2–0.7 g/cm³. The qualities range from hardness similar to wood to softness similar to wadding. As density increases, so do the raw material costs and requirements for converting plants.
Entanglement
Wool and other animal hairs felt by friction, warmth, humidity and lye, as the fibres’ surfaces become inextricably intertwined. Anyone who has unwittingly washed a wool sock in a washing machine will be familiar with the result: the sock shrinks several sizes and becomes very hard. This household mishap can be replicated by industrial felting through machine-made bulging, knocking and pressing. This type of felting, which involves the formation of scales becoming jammed together, is a specific feature of animal hairs and wool. In contrast, other fibres are mechanically felted/entangled by nails with barbed hooks (see Manufacturing Technologies).
Felt – Definitions and Features
Felt is a layered, non-woven textile fabric made of pressed fleece, primarily consisting of fibres. It is processed from individual fibres that are tangled and partially interwoven without spinning, weaving or meshing. Raw wool and/or fibres, which have been cleaned, combed and possibly coloured, will be pressed and stabilised into a solid fabric (a textile flat material or mats with defined features according to DIN 61205) by mechanical treatment (felting and milling), which is usually supported by thermal and chemical processes. Essentially, felt is a two-dimensional, multi-layered, pressed fabric with a low three-dimensional weave. Under shear stress, felt tends to delaminate into layers.
Felt – Variants
Felt variants will be differentiated by the origin of the raw material or the manufacturing process. For example, the term ‘wool felt’ describes the origin of the fibres (essentially sheep’s wool, but also other suitable animal hairs), as opposed to ‘synthetic felt’, which is made from synthetic fibres such as nylon, polyester, polypropylene, polyacrylamide, Normex, Kevlar, glass, etc., or ‘plant fibre felt’, which is made from materials such as cotton wool, rayon staple fibre, kapok, ramie (bast fibre), jute fibre, etc. Real felts are made from fibre blankets, whereas pseudo felts are made from woven fabrics that are felted in a shaping machine. Felt can consist of one raw material or a mixture of different raw materials. The terms ‘needle felt’, ‘pressed and squeezed felt’, ‘woven felt’, ‘pressed felt’ and ‘cloth felt’ refer to the manufacturing process.
Manufacturing Technologies
Wet felting
Wet felting (according to DIN 61210 pooled under the term of pressed and squeezed felts) of unbound fleece with warm water (steam) and soap (alkaline felting support) is the traditional, craftman’s processing of wool or animal hairs. In combination with warm water and soap the top level scale layer (cuticula) forms up, the scales of hairs. Simultaneous pressing and squeezing of fibres cause a penetration of each other. The formed up scales wedge so strong in each other that they are unresolvable. The workpiece shrinks strongly and forms a solid material (textile flat). The final form can be worked out in one piece.
Pressing and squeezing felt is very expensive in time and substantially will be processed in little scale in handcraft, hobby or education. Pressed and squeezed felt has normed features according to DIN 61200 and DIN 61206 Part 2. The strength of pressed and squeezed felt is given by its densitiy. Due to animal fibres, partially in mixture with rayon staple fibres it is a biodegradable natural product.
Dry felting
In the dry felting process wool is formed with specific needles. This method is the ancestor of needle-punching with a needle girder. In the process of needle felting fibre blanket will be repeatedly penetrated by needles with a barbed hook (360 up to 720 penetrations each square centimeter), arrayed vice versa like a harpoon, so that the fibres will be pushed into the felt and the needle goes out without resistance, with the effect, that fibre clusters will be drawn to the rear side of fibre blanket and interlock to a solid flat.
Needle fleece materials are not only made of wool, but practical of all other fibres (for example sythetic fibres, look at Felt – Variants). Besides jamming will be processed with pulsed water jets or with binders. In this case fibres without scale structure are suitable (for example sythetic fibres, look at Felt – Variants). Mostly needle felts are stiffened with the support of chemicals.
Product Ranges
Wool felt and other non-woven materials are used in stamp pads, for machine damping, for noise insulation, for polishing glass, granite and some metals. Oil-moisted felt pads are used for lubrication of machines. Due to its long-term flexibility it is suitable for damper in pianos and other musical instruments. Made of wool felt are also hats, shoes and other articles of clothing. Furthermore felt is used for screens, filter and sealing purposes.
Applications
Industry felt is used for furniture glides for several years. Flat stamping felt parts are mounted in furniture glides by pressing, gluing, welding (friction or vibration welding) or injection moulding. The durability of these four methods with the same felt quality is about the same. The costs or product prices rise extremely when welding on or injection moulding. During welding on process the felt loses about 1.5 mm of its original thickness.
In case of gluing a ready pre-assembled and self-adhesive industry felt is the appropriate choice since the felt manufacturer provides for a consistently high adhesive quality during the production process. Otherwise the gluing with hot glue or other suitable adhesives requires a very special quality control.
The adhesive bonding of stamping felt parts on furniture glides made of Polyethylene or Polypropylene is only possible after a surface treatment or with special adhesives (cause of the unipolar surface of polyolefins). Usually this is disproportionately laborious and not recommended.
The durability of the felt on furniture glides depends only on the strain. The more it protrude from the furniture glide the more the felt is scraped off laminary in layers during shear stressing (cause of the marginal three-dimensional entanglement). On the other hand there is the wish to wear depth in order to extend the useful life up to the wear of the felt.
According to experience the compromise is that the felt protrude 2 – 5 mm from the furniture glide; but only on particularly sensitive floors that are dry cleaned regularly and if it can be expected that the user of the furniture handle cautiously with the furniture.
If the felt is too soft (low density) it is scraped off in layers after a short period of use or it wear out quickly. If it is too hard (high density) the contact surface (adhesive surface, welding area, moulding area) is more heafily loaded due to the lack of buffering effect during shear and impact stress. The felt starts to rub soft floors (marble, etc.) and the silencing can decline appreciably.