Valued primarily for its uses in rigid and flexible "memory" foams, polyurethane is extremely useful in solid plastic forms as well such as polyurethane rods, urethane sheets, urethane bushings and urethane wheels. Polyurethane moldings are characterized by their high performance; they combine many of the desirable qualities of plastic, rubber and metal with longer service life than plastics, higher impact resistance than rubber, elastic memory, noise reduction, heat and chemical resistance and many other properties. In addition, polyurethane molded parts require little to no secondary finishing. Urethane manufacturers fabricate diverse polyurethane moldings, including a wide variety of pneumatic seals, press tool blocks, electrical potting compounds, conveyor bushings, polyurethane belts, urethane bumpers, bowling balls and parts for a broad spectrum of industries such as construction, automotive, food processing, industrial manufacturing, engineering and athletic equipment. Polyurethane also exhibits excellent adhesion and can easily form strong bonds with most metals and plastics.
When it comes to castable urethane, the raw materials of polyurethane exist in a liquid state, which allows for easy mixing and measuring in preparation for molding, which may be one of two processes: open urethane casting or closed casting. Before the polyurethane molding process begins, both a master pattern and a silicone mold are created. Once molds are formed, the raw materials of polyurethane react with one another to form a pre-polymer, and then during the urethane molding process a curative is introduced to the pre-polymer in order to complete the polymeric transition. Accelerated by heat and/or pressure, the mixture is poured (during which it is mixed and potentially even colorized) into a mold cavity and cured to form the final polymer. During open polyurethane molding, the pre-polymer and curative are heated and mixed together, poured into an open cavity and cured without the application of pressure. During closed polyurethane molding processes such as injection molding, the pre-polymer and curative are heated and mixed together, then injected into the closed cavity through small holes. An example of a type of polyurethane molding would be polyurethane foam molding, which is commonly used by polyurethane manufacturers to make soundproof insulation. The result is a product with excellent tension and compression properties as well as flexibility and a very favorable coefficient of friction. Urethane products are also highly stable, which allows them to maintain their hardness over the entire course of their operating lives.
The polyurethane molding process is actually a subset of another molding process known as room temperature vulcanization, which is sometimes abbreviated as RTV. For this process, the three most commonly used materials are silicone, wax and polyurethanes. The benefits of this process for polyurethane molding include a high level of detail and an exceptional surface finish. In addition, this process can be used on polyurethane because of its hardness range as well as its ability to withstand high heat of up to 220º F. RTV is a rapid manufacturing and a rapid prototyping chemical process that involves converting materials, such as polyurethane, into more durable materials by means of the addition of curatives, such as sulfur. As a slow vulcanizing agent, sulfur is typically used in combination with other materials in order to increase the stability of the final molded product. In addition, as suggested by the name, the materials that undergo this vulcanization process, including polyurethane, are cured at room temperature. This method of polyurethane molding is most effectively utilized when the manufacturer desires a short run of parts that can closely match the physical appearance of previously produced parts or match the functional capabilities of previously produced parts or materials.
Although all elastomers maintain strength and versatility in many industrial applications, polyurethane elastomers possess several advantages over other elastomers and materials. Many of these advantages have been demonstrated in laboratory tests. Polyurethane has higher abrasion, cut, tear, oil, oxygen, ozone and radiation resistance, greater load bearing ability, broader hardness range and better colorability than rubber; urethane even showed better wear resistance than some kinds of steel. Polyurethane responds so well to compression loading that it can be used to make tires for trucks. Its resistance to petrochemicals is also much better than most rubber materials, and it is also highly oxidation-resistant. Polyurethane has thick section molding and low pressure tooling capabilities and a castable nature. As compared to metal, polyurethane has better noise reduction and resilience, greater abrasion, corrosion and impact resistance, more flexibility and is less costly to fabricate. Polyurethane is also lightweight, easily moldable, non-conductive and non-sparking. Molded urethane serves better than regular plastic in many applications, as it has higher impact, low temperature, cold flow, radiation and abrasion resistance, better elastic memory and noise reduction capabilities, greater resilience and provides lower cost tooling. In addition, polyurethane molding, as a process, offers the benefits of high accuracy, diverse part size capabilities, a fast turn-around and the ability to form parts with undercuts as well as parts without drafts. Also, the cost of polyurethane moulding is on par with the cost of rubber and typical polymer molding, giving urethane an economic advantage as well.
Polyurethane Molding - FallLine Corporation
Polyurethane Molding - FallLine Corporation
Polyurethane is a versatile polymer that can be used to manufacture a variety of products, ranging from flexible foam to hard molded urethane tires. The foams do need external energy to form, and as soon as different raw materials are mixed, it transforms into foam. On the other hand, it can be molded by applying heat. Polyurethanes as a polymer are advantageous since it can be reprocessed a number of times without the loss of structural strength.
Molded urethane products, including urethane sheets, urethane bushings, urethane wheels, and conveyor wheels, have a range of properties such as high tensile and elongation strength, high elasticity, and resistance towards grease, chemicals, and oil.
Moreover, just like thermosetting plastic, a number of methods, such as extrusion, compression molding, and injection molding, can fabricate urethane into solid components like cables and wires, sheets, tubes, hoses, and many other industrial products. Moreover, urethane can be compounded with additives for creating molded urethanes, which have application in textiles, coatings, and adhesives production.
Molded urethanes are made from three classes of chemicals:
Polyester based urethane can be blended with polyvinyl chloride and similar polar plastics. The blended form has enhanced properties, as it shows less permeability to oil and chemicals, and abrasion resistance is enhanced.
Polyether-based urethane is another class, and its specific gravity is lower than polyester-based urethane. At low temperatures, the product made with this urethane shows tear resilience and abrasion resistance while being flexible. The products also are resistant to microbial attacks and hydrolysis. This class is considered suitable for moist environments.
Polycaprolactone-based urethane combines the properties of polyester-based urethane such as toughness and abrasion resistance and high performance at low temperature. It also exhibits resistance to hydrolysis. These properties make it a suitable raw material for manufacturing pneumatic and hydraulic seals.
Evaluation of physical properties of urethane
The tensile strength of molded urethane products is evaluated by exposing a specimen to stress for a specific period. A stress-strain diagram is used to plot the deformation of the specimen under stress.
This measurement tells how resistant a molded urethane product is to penetration and indentation. It measures whether the product is soft or hard. A graph is drawn between the flexibility and hardness of a product to show the correlation.
Tear strength and compression set
As the name implies, this measurement tells tear and distortion strength of a molded urethane product. Another measurement, known as compression set, tells whether the product will be deformed permanently after the stress in the form of compression is removed.
Other than these, the physical properties of molded urethane are also evaluated regarding abrasion resistance and shrinkage.
Just like physical properties, the chemical properties of molded urethane are also evaluated. Molded urethane products are specifically vulnerable to acid and basic solution and saturated and aromatic hydrocarbons. With exposure to acid and alkaline solvents, the products swell causing the tear resistance to be reduced. To withstand the onslaught of chemicals, molded urethane products are blended to make durable products.
Molded urethane, also known as polyurethane, is a polymer that has properties of plastic and rubber, which make it one the most sought after materials in the manufacturing industry. Primarily, molded urethane has application in manufacturing flexible and rigid memory foam; however, their application as a solid plastic is also important.
The application of polyurethane has changed over years, and the best way to understand this is to trace its history.
In 1939, a German, Otto Bayer, first made polyurethane. Urethane, the new synthetic polymer, had many merits over the plastic that was manufactured by poly condensation of olefins. However, until then polyisocyanates, which is the main ingredient of polyurethanes, were not commercially available; therefore, the flexible foam could not be manufactured on a large scale. At that time, urethane was used for making fibers, and at a limited scale, aircrafts in the Second World War were coated with urethane.
The large-scale manufacturing of the flexible and rigid memory foam did not start until polyisocyanates were available commercially. In 1952, it was available easily, and the production of foam started at large scale by reacting toluene diisocyanate and polyester polyols. The ingredients were used for making other products, such as elastomers-a polymer that has both viscosity and elasticity-and gum rubber. Gradually, other chemicals like hexamethylene diisocyanate and butanediol were used for making linear fibers. However, polyester polyols were expensive and had poor water resistant properties; the industry was looking for a cheaper and durable alternative. DuPont came with the alternative in the form of polyether polyols, and soon other chemical producers started manufacturing polyether polyols, making manufacturing foam cheaper.
The availability of cheaper polyols, methylene diphenyl diisocyanate, and a new blowing agent, chlorofluoroalkane, led to the development of urethane as insulation material. The insulation material made from urethane was high-performing and had many advantages over other options, and its production soon caught up with the foam production.
However, until then only flexible foam was manufactured, but the advent of polyisocyanurate changed the landscape and urethane rigid foams came on the market that were thermally stable and exhibited resistance to fire. With the advent of rigid foam, the automobile industry realized its application in the interior of cars; components like door panel and instrumentation panel were made from thermoplastic urethane.
Urethane, however, was used in the form of foam, and molded urethane was not popular at that time. The first wide scale application of molded urethane was realized when in Germany, an all-plastic car was shown, which had parts made from molded urethane. The car exhibited how injection molding can be utilized for making different parts; additives, like mica, milled glass, mineral fibers provided necessary stiffness and made the product resistant to thermal expansion.
The molding method reached new heights with the invention of resin injection molding in which glass mats were used for making products durable. The new molding method made urethane a sought-after raw material for making a range of urethane products such as urethane sheets, urethane bushings, urethane wheels, and conveyor wheels.
Molded polyurethane is used for a variety of purposes. Molded polyurethane has a surprising mixture of strength and flexibility. It is water-resistant, and stands up well to contaminants. This is why the product is often used in the medical industry and other bacterial-conscious industries.
Another perfect application for this form of urethane is cushioning for a variety of purposes. The flexibility and cushioning power of the urethane makes it ideal for use as a cushion, and the water-resistant properties make it ideal for use in outdoor environments as well as for sports and swimming applications. Cushions can also be used in the medical industry as therapy aids, to help reduce paint, add comfort, and increase the endurance of the patients during exercise and therapy. Injection molded cushion foam is the most common form of cushioning used for high intensity purposes and exercise props today. A molded urethane cushion can support hundreds of pounds of weight and will spring back to its original dimensions every time. The urethane allows the unique properties of providing form-supporting and fitting depressions that provide comfortable support no matter the use of the cushion.
No matter what industry you are in, the beneficial properties of urethane cushions cannot be ignored. For such a versatile cushion material, urethane is surprisingly cost-effective. Urethane is also resistant to UV exposure and chemical exposure, making it as durable as it is flexible.
- Substance added to a polymer to increase the effectiveness, but not the strength, of the polymer. Examples of additives include flame-retardants, anti-static urethane casting compounds, molded urethane pigments and urethane molding lubricants.
- A discoloration of the molded urethane surface of a polyurethane product-not to be confused with dust from external sources-caused by the migration of a liquid or solid to the surface.
- Foam producing substance (e.g. carbon dioxide).
- The point of tension at which polyurethane will rupture in urethane molding process.
- A polymer made up of two monomers in which each repeating unit in the chain consists of molded urethane units of both monomers.
- The chemical linkage of polymeric chains that results in a three-dimensional network of polymers. Crosslinked polymers possess greater strength and durability than linear polymers do.
- The amount of time necessary to complete a urethane molding cycle from urethane mold preparation to demolding.
- A device placed within a urethane mold that prevents the flow of material into cavities of the mold in order to reduce, alter or eliminate a part of the cast for which the urethane mold was initially designed.
- The amount of time that passes between the dispensation of liquid components into the urethane mold and the removal of the end molded urethane product.
- Chemicals in liquid or crystalline form used in the production of polyurethane adhesives, coatings and urethane casting foam.
material capable of returning to its initial length after being stretched
at room temperature up to twice its original length.
- An ion, composed of one oxygen atom and one hydrogen atom, used in bases, acids and alcohols.
- Energy loss in the form of heat that results from the deformation of elastomeric material caused by the application of urethane molding stress.
- The forming of millimeter- or micron-sized parts through the urethane molding process. Micro molded parts, for which tolerances must be extremely tight, are increasingly in demand by biomedical, pharmaceutical, fiber-optic, electronics, telecommunications, office-automation, computer and automotive industries.
- The most basic polymeric unit, usually a liquid or a gas, consisting of molecules from the same organic substance.
- Two or more monomers bonded together in a chain through a chemical reaction.
- A chemical compound composed of two or more hydroxyl groups that, in conjunction with diisocyanate, are used in the urethane molding production of polyurethane foam.
- The comparison of the amount of energy needed to create an elastic deformation and the amount of energy needed to recover from such a deformation.
- Category of plastics that have the potential to soften and reform when heated, hardening again when cooled. During the urethane molding process, the physical makeup of the thermoplastic does not change.
- Category of plastics that cannot be reformed upon reheating. Thermosets remain permanently hard.