Author: www.foam-cut.com polyurethane foam continuous line foam cutting machine for mattress ,sofa,uphostry
What is polyurethane foam (PU FOAM) ？
(Soft or semi-rigid polyurethane foam)
(1)Polyurethane
Commonly abbreviated PU is any polymer consisting of a chain of organic units joined by urethane links. Polyurethane polymers are formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst. Polyurethane formulations cover an extremely wide range of stiffness, hardness, and densities. These materials include low density flexible foam used in upholstery and bedding, low density rigid foam used for thermal insulation, soft solid elastomers used for gel pads and print rollers, and hard solid plastics used as electronic instrument bezels and structural parts. Polyurethanes are widely used in high resiliency flexible foam seating, rigid foam insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and tires, electrical potting compounds, high performance adhesives and sealants, Spandex fibers, seals, gaskets, carpet underlay, and hard plastic parts. Polyurethane products are often called "urethanes". They should not be confused with the specific substance urethane, also known as ethyl carbamate. Polyurethanes are not produced from ethyl carbamate, nor do they contain it.
Upholstery is the work of providing furniture, especially seats, with padding, springs, webbing, and fabric or leather covers. The word "upholstery" comes from the Middle English words up and holden, meaning to hold up. The term is applied to domestic furniture and also to applications in automobiles and boats. A person who works with upholstery is called an upholsterer; an apprentice upholsterer is sometimes called an outsider or trimmer.
Polyurethane products have many uses. Over three quarters of the global consumption of polyurethane products is in the form of foams, with flexible and rigid types being roughly equal in market size. In both cases, the foam is usually behind other materials: flexible foams are behind upholstery fabrics in commercial and domestic furniture; rigid foams are inside the metal and plastic walls of most refrigerators and freezers, or behind paper, metals and other surface materials in the case of thermal insulation panels in the construction sector. Its use in garments is growing: for example, in lining the cups of brassieres. Polyurethane is also used for moldings which include door frames, columns, balusters, window headers, pediments, medallions and rosettes.
The precursors of expanding polyurethane foam are available in many forms, for use in insulation, sound deadening, flotation, industrial coatings, packing material, and even cast-in-place upholstery padding. Since they adhere to most surfaces and automatically fill voids, they have become quite popular in these applications.
Chemistry
Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, and phenolics. A urethane linkage is produced by reacting an isocyanate group, -N=C=O with a hydroxyl (alcohol) group, -OH. Polyurethanes are produced by the polyaddition reaction of a polyisocyanate with a polyalcohol (polyol) in the presence of a catalyst and other additives. In this case, a polyisocyanate is a molecule with two or more isocyanate functional groups, R-(N=C=O)n ≥ 2 and a polyol is a molecule with two or more hydroxyl functional groups, R'-(OH)n ≥ 2. The reaction product is a polymer containing the urethane linkage, -RNHCOOR'-. Isocyanates will react with any molecule that contains an active hydrogen. Importantly, isocyanates react with water to form a urea linkage and carbon dioxide gas; they also react with polyetheramines to form polyureas. Commercially, polyurethanes are produced by reacting a liquid isocyanate with a liquid blend of polyols, catalyst, and other additives. These two components are referred to as a polyurethane system, or simply a system. The isocyanate is commonly referred to in North America as the 'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as the 'B-side' or as the 'poly'. This mixture might also be called a 'resin' or 'resin blend'. In Europe the meanings for 'A-side' and 'B-side' are reversed. Resin blend additives may include chain extenders, cross linkers, surfactants, fire retardants, blowing agents, pigments, and fillers.
The first essential component of a polyurethane polymer is the isocyanate. Molecules that contain two isocyanate groups are called diisocyanates. These molecules are also referred to as monomers or monomer units, since they themselves are used to produce polymeric isocyanates that contain three or more isocyanate functional groups. Isocyanates can be classed as aromatic, such as diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI); or aliphatic, such as hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). An example of a polymeric isocyanate is polymeric diphenylmethane diisocyanate, which is a blend of molecules with two-, three-, and four- or more isocyanate groups, with an average functionality of 2.7. Isocyanates can be further modified by partially reacting them with a polyol to form a prepolymer. A quasi-prepolymer is formed when the stoichiometric ratio of isocyanate to hydroxyl groups is greater than 2:1. A true prepolymer is formed when the stoichiometric ratio is equal to 2:1. Important characteristics of isocyanates are their molecular backbone, % NCO content, functionality, and viscosity.
The second essential component of a polyurethane polymer is the polyol. Molecules that contain two hydroxyl groups are called diols, those with three hydroxyl groups are called triols, et cetera. In practice, polyols are distinguished from short chain or low-molecular weight glycol chain extenders and cross linkers such as ethylene glycol (EG), 1,4-butanediol (BDO), diethylene glycol (DEG), glycerine, and trimethylol propane (TMP). Polyols are polymers in their own right. They are formed by free radical addition of propylene oxide (PO), ethylene oxide (EO) onto a hydroxyl or amine containing initiator, or by polyesterification of a di-acid, such as adipic acid, with glycols, such as ethylene glycol or dipropylene glycol (DPG). Polyols extended with PO or EO are polyether polyols. Polyols formed by polyesterification are polyester polyols. The choice of initiator, extender, and molecular weight of the polyol greatly affect its physical state, and the physical properties of the polyurethane polymer. Important characteristics of polyols are their molecular backbone, initiator, molecular weight, % primary hydroxyl groups, functionality, and viscosity.
PU reaction mechanism catalyzed by a tertiary amine 
carbon dioxide gas formed by reacting water and isocyanate 
The polymerization reaction is catalyzed by tertiary amines, such as dimethylcyclohexylamine, and organometallic salts, such as dibutyltindilaurate. Furthermore, catalysts can be chosen based on whether they favor the urethane (gel) reaction, such as diazobicyclooctane, or the urea (blow) reaction, such as bis-dimethylaminoethylether, or specifically drive the isocyanate trimerization reaction, such as potassium octoate.
One of the most desirable attributes of polyurethanes is their ability to be turned into foam. Blowing agents such as water, certain halocarbons such as HFC-245fa (1,1,1,3,3-pentafluoropropane) and HFC-134a (1,1,1,2-tetrafluoroethane), and hydrocarbons such as n-pentane, can be incorporated into the poly side or added as an auxiliary stream. Water reacts with the isocyanate to create carbon dioxide gas, which fills and expands cells created during the mixing process. The reaction is a three step process. A water molecule reacts with an isocyanate group to form a carbamic acid. Carbamic acids are unstable, and decompose forming carbon dioxide and an amine. The amine reacts with more isocyanate to give a substituted urea. Water has a very low molecular weight, so even though the weight percent of water may be small, the molar proportion of water may be high and considerable amounts of urea produced. The urea is not very soluble in the reaction mixture and tends to form separate "hard segment" phases consisting mostly of polyurea. The concentration and organization of these polyurea phases can have a significant impact on the properties of the polyurethane foam.[11] Halocarbons and hydrocarbons are chosen such that they have boiling points at or near room temperature. Since the polymerization reaction is exothermic, these blowing agents volatilize into a gas during the reaction process. They fill and expand the cellular polymer matrix, creating a foam. It is important to know that the blowing gas does not create the cells of a foam. Rather, they are formed during the mixing process as nucleating sites that the blowing gas fills and expands. In fact, high density microcellular foams can be formed without the addition of blowing agents by mechanically frothing or nucleating the poly blend prior to use.
(2) Usage of Polyurethane
1. Furniture
2. Automobile seats
3. Varnish
4. Computer mouse pads
5. Glue
6. Wheels
7. Houses, sculptures, and decorations
8. Watercraft
9. Construction sealants and fire stopping
10. Tennis grips
11. Electronic components
12. Bookbinding industry
13. Watch band wrapping
1.Furniture
Polyurethane is also used in furniture manufacture for casting soft edges around table tops and panel that are stylish, very durable and prevent injury. These are used in school tables, hospital and bank furniture as well as shop counters and displays.
Much of the foam used in chairs, couches, Comfy Sacks and mattresses is polyurethane foam. This type of foam is made by mixing polyols, diisocyanates, catalysts, blowing agents and other additives and allowing the resulting foam to rise freely. This can be done in a batch process where relatively small blocks of foam are made in an open-topped mold, or continuously where the components are poured onto an inclined moving belt. The foam is then cut to the desired shape and size for use in making furniture.
Safety concerns about the flammability of polyurethane foam, particularly in upholstered furniture, sometimes requires the addition of flame retardants to this foam.
Polyurethane is in other countries like The Netherlands used as a floor solution for houses, offices, musea.
2. Automobile seats
Flexible and semi-flexible polyurethane foams are used extensively for interior components of automobiles, in seats, headrests, armrests, roof liners and instrument panels
Polyurethane foam in the lower half of the mold in which it was made. When assembled into a car seat, this foam makes up the seat back. The forward-facing part of the seat back is the surface of the foam which face-down in the mold. The two holes in the foam at the top of the picture are for the headrest posts.
Foam after removal from the mold.
Polyurethanes are used to make automobile seats in a remarkable manner. The seat manufacturer has a mold for each seat model. The mold is a closeable "clamshell" sort of structure that will allow quick casting of the seat cushion, so-called molded flexible foam, which is then upholstered after removal from the mold.
It is possible to combine these two steps, so-called in-situ, foam-in-fabric or direct moulding. In this case, the inner surfaces of the mold have hundreds of small holes that all connect to a vacuum manifold. This creates a constant air flow from the core of the mold to the manifold. The assembly operator first places a complete, fully-assembled seat cover in the mold and adjusts it so that the vacuum in the manifold pulls the seat cover snugly against the mold surface. In some operations, this effect is improved by adding a thin pliable plastic film as a backing to the fabric to help the vacuum work more effectively. When the seat cover is in place, the operator then places the metal frame of the seat into the mold and closes the mold. At this point the mold contains what could be visualized as a "hollow seat", a seat fabric held in the correct position by the vacuum manifold and containing a hollow space with the metal frame in place.
The next step is to inject the polyurethane chemical mixture into the mold cavity. This is a two-part mixture that is metered exactly through a mixing head. Then the mold is held at a preset reaction temperature until the chemical mixture has foamed, filled the mold, and formed stable soft foam. The time required is about two to three minutes, depending on the size of the seat and the precise formulation and operating conditions. Then the mold is usually opened slightly for a minute or two for an additional cure time, before the fully upholstered seat is removed. The operator then trims any excess seat cover fabric and puts the finished seat onto a conveyor.
3 Varnish
Polyurethane materials are commonly formulated as paints and varnishes for finishing coats to protect or seal wood. This use results in a hard, abrasion-resistant, and durable coating that is popular for hardwood floors, but considered by some to be difficult or unsuitable for finishing furniture or other detailed pieces. Relative to oil or shellac varnishes, polyurethane varnish forms a harder film which tends to de-laminate if subjected to heat or shock, fracturing the film and leaving white patches. This tendency increases when it is applied over softer woods like pine. This is also in part due to polyurethane's lesser penetration into the wood. Various priming techniques are employed to overcome this problem, including the use of certain oil varnishes, specified "dewaxed" shellac, clear penetrating epoxy, or "oil-modified" polyurethane designed for the purpose. Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher "build" of film, accomplishing in two coats what may require multiple applications of oil. Polyurethane may also be applied over a straight oil finish, but because of the relatively slow curing time of oils, the presence of volatile byproducts of curing, and the need for extended exposure of the oil to oxygen, care must be taken that the oils are sufficiently cured to accept the polyurethane.
Unlike drying oils and alkyds which cure, after evaporation of the solvent, upon reaction with oxygen from the air, polyurethane coatings cure after evaporation of the solvent by a variety of reactions of chemicals within the original mix, or by reaction with moisture from the air. Certain products are "hybrids" and combine different aspects of their parent components. "Oil-modified" polyurethanes, whether water-borne or solvent-borne, are currently the most widely used wood floor finishes.
Exterior use of polyurethane varnish may be problematic due to its susceptibility to deterioration through ultra-violet light exposure. It must be noted, however, that all clear or transluscent varnishes, and indeed all film-polymer coatings (i.e.paint, stain, epoxy, synthetic plastic, etc.) are susceptible to this damage in varying degrees. Pigments in paints and stains protect against UV damage, while UV-absorbers are added to polyurethane and other varnishes (in particular "spar" varnish) to work against UV damage. Polyurethanes are typically the most resistant to water exposure, high humidity, temperature extremes, and fungus or mildew, which also adversely affect varnish and paint performance.
4.Computer mouse pads
Polyurethane is used on the bottom of some mouse pads.
5.Glue
Polyurethane is used as an adhesive, especially as a woodworking glue. Its main advantage over more traditional wood glues is its water resistance. It was introduced in the general North American market in the 1990s as Gorilla Glue and Excel, but has been used much longer in Europe.
6.Wheels
Polyurethane is also used in making solid tires. Modern roller blading and skateboarding became economical only with the introduction of tough, abrasion-resistant polyurethane parts. Other constructions have been developed for pneumatic tires, and microcellular foam variants are widely used in tires on wheelchairs, bicycles and other such uses. These latter foam types are also widely encountered in car steering wheels and other interior and exterior automotive parts, including bumpers and fenders.
7.Houses, sculptures, and decorations
The walls and ceiling (not just the insulation) of the futuristic Xanadu House were built out of polyurethane foam. Domed ceilings and other odd shapes are easier to make with foam than with wood. Foam was used to build oddly-shaped buildings, statues, and decorations in the Seuss Landing section of the Islands of Adventure theme park. Speciality rigid foam manufactures sell foam that replace wood in carved sign and 3D topography industries .
8.Watercraft
Some surfboards are made with a solid polyurethane core. A rigid foam blank is molded, shaped to specification, then covered with fiberglass cloth and polyester resin.
The hull of the Boston Whaler motorboat is polyurethane foam sandwiched in a fiberglass skin. The foam provides strength, buoyancy, and sound deadening.
9.Construction sealants and fire stopping
Head-of-Wall Firestop Joint: the presence of penetrants demonstrates the need to have both operational and fire-tested compatibility between the joint sealant and mechanical/electrical through-penetrations. In other words, it is easier to insist on the use of joint firestops that can also be used for penetration seals, as otherwise penetrants may be run by mechanical and electrical subtrades that unintentionally void the fire-resistance rating of the wall, which jeopardises the entire fire safety plan in place for a building.
Head-of-Wall Firestop Joint penetrated by both electrical and mechanical services, demonstrating the need for operational and fire-tested compatibility between the joint firestop system and penetrants, be they electrical, mechanical or structural.
Polyurethane sealants are available in 1, 2 and even 3 part systems, either in cartridge, bucket or drum format. Polyurethane sealants are also sold for firestopping applications. Obviously, the sealant by itself provides no serious hindrance to fire, as its hydrocarbon bonds readily support combustion. However, when backed by inorganic insulation, such as rockwool or ceramic fibres, it can act as an effective seal to thwart smoke and hose-stream passage, particularly in inorganic joints. It is, however, advisable to avoid direct contact with metallic penetrants and through-penetrating cables, as the heat carried by the penetrants may jeopardise the sealant. This, however, requires a lot of vigilance. In concrete to concrete, or concrete to masonry joints, however, that are free of mechanical or electrical penetrants, it works well and dependably. As with all passive fire protection products and systems, the key to code compliance is demonstrable bounding.
10.Tennis Grips
Polyurethane has been used to make several Tennis Overgrips such as Yonex Supergrap, Wilson Pro Overgrip and many other grips. These grips are highly stretchable to ensure the grip wraps neatly around the racquet's handle.
11.Electronic Components
Often electronic components are protected from environmental influence and mechanical shock by enclosing them in polyurethane. Typically polyurethanes are selected for the excellent abrasion resistances, good electrical properties, excellent adhesion, impact strength,and low temperature flexibility. The disadvantage of polyurethanes is the limited upper service temperature (typically 250 °F (121 °C)). In production the electronic manufacture would purchase a two part urethane (resin and catalyst) that would be mixed and poured onto the circuit assembly (see Resin casting). In most cases, the final circuit board assembly would be unrepairable after the urethane has cured. Because of its physical properties and low cost, polyurethane encapsulation (potting) is a popular option in the automotive manufacturing sector for automotive circuits and sensors.
12.Bookbinding Industry
On the way to a new and better glue for bookbinders, a new adhesive system was introduced for the first time in 1985. The base for this system is polyether or polyester, whereas polyurethane (PUR) is used as prepolymer. Its special feature is the coagulation at room temperature and the reacting to moisture.
1st Generation (1988 at the drupa) - Low starting solidity - High viscosity - Drying time of more than 3 days
2nd Generation (1996 at the drupa) - Low starting solidity - High viscosity - Drying time of less than 3 days
3rd Generation (2000 at the drupa) - Good starting solidity - Low viscosity - Drying time between 6 and 16 hours
4th Generation (present) - Good starting solidity - Very low viscosity - Drying time is reached within few seconds due to Dual-Core-Systems
Advantages of polyurethane glue in the bookbinding industry: PUR is real wonder compared to hotmelt and cold glue. Because of the missing moisture in the glue, papers with wrong grain direction can be processed without problems. Even printed and supercalandered paper can be bound without problems. It is the most economical glue with an application thickness of theoretical 0.01 mm. But in reality it is not possible to apply less than 0.03 mm. The PUR glue is very weather-proof and stable at temperatures from -40 °C to 100 °C.
13.Watch Band Wrapping
Polyurethane is used as a black wrapping for timepiece bracelets over the main material which is generally stainless steel. It is used for comfort, style, and durability.
Article Source: http://www.articlesbase.com/cars-articles/foam-cutting-sample-photoes-1813446.html
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1. Club Goes Across the Left Palm
2. Wrap Palm Around Top of the Grip 
Overlapping Grip
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