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Industrial Processed Felt
Industrial processed felt is demanded beginning with the middle of eighties of 20th century for facing of plastic furniture glides due to preserve sensitive floors/ground areas and due to silencer of moved seating furnitures. In opposit to some plastic glide facings scratching or abrasive piling on sensitive floors (parquet, polished/smooth lime stone floors, etc.) will be prevented and instead of it a higher abrasive loss of felt will be accepted. For this task strongly depending on floor cleaning (dry suction cleaning - avoiding contact with water and other fluids; felt moistens and will be strongly abraded) felt can only be a compromise between preserving/silencer and wearing. Industrial processed felt is practically available in all dimensions, forms, cuts and in various specifications, like coloured, self-adhesive, siliconized, flame-retardent, dry cleanable, limited water resistant, short time water-repellent, antistatic, etc. One essential feature is its specific range of density, which mostly enfolds 0,2-0,7 g/cm³. Qualities are processible hard as wood or soft as wadding. With increasing density raw material charge and requirements to converting plants increase.
Wool and other animal hairs felted by friction, warmness, humidity and lye, as upforming scales of fibre surfaces jam with each other unresolvable. Who unawares has washed a wool sock with a washing machine knows the effect: the sock is shrinked several sizes and got very solid. What is an mishap in the household will be processed by industrial felting by machine-made bulging, knocking and pressing. This kind of felting with jammed upforming scales is a specific feature of animal hairs/wool. In contrast other fibres will be mechanical felted/entangled by nails with barbed hooks (look at Manufacturing Technologies).
Felt - Definitions and Features
Felt is a layered, textile, non-woven, pressed fleece fabric made of wool and/or fibres, which is principle a fibre composit. It will be processed from single fibres, which lay tangled one upon another and partially interleaved entangled without spinning, weaving or meshing. Cleaned, combed, maybe coloured and to fleece processed raw wool and/or fibres will be pressed/stabilized into a solid fabric (textile flat material or mats with defined features according to DIN 61205) by mechanical treatment (felting and milling), mostly with thermical and chemical support. Substantially felt is a two-dimensional pressed fabric in multi-layer array with low three-dimensional weave. On condition of shear stress felt tends to delaminate in layers.
Felt - Variants
Variants of felt will be differentiated between origin of raw material or manufaturing process. The term wool felt describes for example the origin of fibres (substantially sheep's wool but other suitable animal hairs, too), in opposit to synthetic felt (synthetic fibres of Nylon, polyester, polypropylene, polyacrylamide, Normex, Kevlar, glass, etc.) or felt made of plant fibre (cotton wool, rayon staple fibre, kapok, ramie [bast fibre], jute fibre, etc.). Real felts are made of fibre blanket, pseudo felts are made of woven flats, which are felted in a shaping machine. Felt can consist of one raw material, but also of mixtures of different raw materials. The terms needle felt, pressed and squeezed felt, woven felt, press felt or cloth felt refer to the manufacturing process.
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 pressed and squeezed felt is a biodegradable natural product.
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.
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 felt 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 (furniture glides)
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 felt is the appropriate choice since the felt manufacturer provides for a consistently high adhesive quality during the production process. Otherwise the gluing of the felt 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 the felt 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 the felt 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.