Polyurethane molding is a fabrication service offered by plastic parts manufacturers. This service encompasses a variety of processes, most notable injection mold processes. Using polyurethane materials, manufacturers create a wide range of strong, flexible, and highly useful products.
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The History of Polyurethane Molding
Molded polyurethane, also known as urethane and occasionally urethane rubber, is a polymer that has properties of both plastic and rubber, which make it one the most sought-after materials in the manufacturing industry. Primarily, molded urethane has application in manufacturing flexible, rigid memory, and structural foam; however, their application as a solid plastic is also important.
Beginning of Polyurethane Molding
The polyurethane, or urethane, molding industry began back in 1939, when Otto Bayer, a German chemist, synthesized his first batch of polyurethane. Urethane, the new synthetic polymer, had many advantages over the plastic that was manufactured by poly condensation of olefins.
Early on, urethane was used for making fibers. In addition, on a limited scale, manufacturers used urethane to coat aircrafts in the Second World War.
The large-scale manufacturing of the flexible and rigid memory foam did not start until polyisocyanates, the main ingredient of polyurethanes, were available commercially. By 1952, it was easily available, and the production of polyurethane foam stepped onto the big stage. Manufacturers brought via reaction injection molding with toluene diisocyanate and polyester polyol. The ingredients were used for making other products, such as elastomers (a polymer that has both viscosity and elasticity) and gum rubber. Gradually, manufacturers began also using other chemicals like hexamethylene diisocyanate and butanediol for making linear fibers. However, because these early 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 foamcheaper.
The availability of cheaper polyols, methylene diphenyl diisocyanate, and a new blowing agent, chlorofluoroalkanes, 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.
Introduction of Rigid Foam
The advent of polyisocyanurate changed the landscape again; where they had once only been able to make flexible foam, manufacturers were suddenly able to make thermally stable and fire resistant rigid urethane foams came on the market that were thermally stable and exhibited resistance to fire. With the introduction of rigid foam, the automobile industry realized its application in the interior of cars, and began making components, like the door panel and instrumentation panel, from thermoplastic urethane.
Urethane in molded form finally became popular after an all-plastic car, with molded urethane parts, was displayed at a show in Germany. 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.
Rise of Resin Injection Molding
The molding method reached new heights with the invention of resin injection molding, a method that uses glass mats to make products durable. The new injection mold 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.
Today, polyurethane standard and custom molding is more popular than ever. Manufacturers and customers alike have found polyurethane molded products to be more durable, reliable, versatile, affordable than the competition. To streamline the moulding process and make results more precise and repeatable, manufacturers also commonly use CNC technology. CNC machining, or the process of integrating computer technology into your system, has revolutionized many modern forming processes.
Benefits of Polyurethane Molding
Polyurethane molding is a highly advantageous process. We recommend exploring it for a number of reasons. Let’s go over them.
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.
Superior to Rubber
Polyurethane moldings have higher abrasion, cut, tear, oil, oxygen, ozone and radiation resistance than rubber parts. They also have greater load bearing ability, a broader hardness range, and better colorability.
Superior to Metal
Urethane mold parts have shown superior wear resistance to some kinds of steel products. Also, as compared to metal products in general, polyurethane parts have better noise reduction and resilience, greater abrasion, corrosion and impact resistance, and more flexibility.
Better than Regular Plastic
Molded urethane parts serve better than regular plastic parts in many applications. This is because they have higher impact resistance, temperature resistance, cold flow resistance, radiation resistance, and abrasion resistance. In addition, they have better elastic memory, noise reduction capabilities, and resiliency than plastic parts.
A Better Raw Material
Polyurethane is lightweight, easily moldable, non-conductive and non-sparking. In addition, polyurethane exhibits excellent adhesion and can easily form strong bonds with most metals and plastics. Plus, polyurethane has thick section molding and low-pressure tooling capabilities and a cast-able nature. Finally, urethane is resistant to UV exposure and chemical exposure, making it as durable as it is flexible.
Polyurethane molding has low tooling costs, especially when compared to plastic and rubber molding.
The polyurethane molding process creates little waste. This is because polyurethanes can be reprocessed again and again without the loss of structural strength. So, if a manufacturer has leftover or scrap material, he or she can simply use it again.
Polyurethane molded parts require little to no secondary finishing. This saves time, effort, and money.
Urethane products are also highly stable, which allows them to maintain their hardness over the entire course of their operating lives.
Polyurethane molding is a versatile process. For example, manufacturers can easily create foams without external energy, but if they so choose, they also can mold parts using heat. In other words, they can conduct custom mold parts to exhibit virtually any physical or chemical property.
Materials Used in Molded Urethanes
Molded urethanes are made from three classes of chemicals:
Polyester Based Urethane
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
This is another class, and its specific gravity is lower than polyester-based urethane. At low temperatures, a 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
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.
Manufacturers have a wide variety of methods at their disposal with which to create polyurethane moldings. The most common of these are extrusion, compression moulding, injection moulding, and open urethane casting or closed urethane casting.
Regardless, before the polyurethane molding process begins, manufacturers create both a master pattern and a silicone mold or a metal mold. After that, they gather the raw materials they need. When put together, the raw materials of polyurethane react with one another to form a pre-polymer, and then during the urethane molding process, manufacturers introduce a curative in order to complete the polymeric transition. Finally, they bring the raw materials into a liquid state; this allows for easy mixing and measuring in preparation for molding. Accelerated by heat and/or pressure, the mixture becomes liquid. Manufacturers then pour it into a mold cavity. Sometimes, at this point, they also simultaneously mix and/or colorize it; this is known as in-molding coating. Once they cure it, it becomes the final polymer, and they can remove it from the mold.
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 mold cavity through small holes.
Polyurethane Molding Types
- Castable Urethanes
- Elastomers that contain urethane carbamate links, are processed in liquid form, and are extremely well-suited for casting.
- Molded Urethane
- Technically referred to as molded polyurethane (or PU), is an elastic polymer, or elastomer, containing urethane carbamate links.
- Polyurethane Belts
- Formed from an elastic polymer, or elastomer, that contains urethane carbamate links.
- Polyurethane Manufacturers
- Fabricate molded urethane to produce many different products.
- Polyurethane Rods
- Bars that are straight, uniform polyurethane products that are often circular or rectangular, but may have many cross sections in different shapes.
- Reaction Injection Molding (RIM)
- RIM for short, is a mold forming process that works quite similarly to standard injection mold processes. The big difference between the two is the fact that RIM only molds thermosetting polymers, which must cure in-mold. Common RIM materials include polyurethane, polyester, polyphenols, and polyepoxides.
- In short, to make RIM work, manufacturers mix two parts of the polymer together, usually by injecting them under high pressure into an impinging mixer. Then, they inject the mixture under low pressure into a mold. Finally, they let it sit in the mold until it expands and cures.
- RIM produces parts that are strong, flexible, and easily painted. It can also be used to create large, lightweight, and thin-walled products that are hard to produce using other methods.
- Room Temperature Vulcanization (RTV)
- The polyurethane molding process is actually a subset of another molding process known as room temperature vulcanization, which is sometimes abbreviated as RTV. 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 wants a short run of parts that can closely match the surface appearance of previously produced parts or match the functional capabilities of previously produced parts or materials.
- 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.
- Rotational Molding
- During rotational molding, manufacturers take a polymer material, like polyester resin or powder, and pour it into a hollow mold. They then rotate the mold in an oven until the resin melts and coats the inside of the mold cavity. They then remove the mold from the heat, allow the part to cool, and treat it as they would any other urethane mold part.
- This urethane mold process offers parts advantages such as: consistent wall thickness, stress free outside corners, low tooling costs, fast turnaround times, and high versatility.
- Urethane Bumpers
- Urethane bumpers are protective parts that function to absorb shock or to impede contact.
- Urethane Bushings
- Urethane bushings are types of bearings used in automotive production as shock absorbers that maintain alignment and suspension components.
- Urethane Casting
- Urethane casting, technically referred to as polyurethane (or PU), is an elastic polymer, or elastomer, containing urethane carbamate links. Urethane casting is quite similar to injection molding. The main difference between the cast urethane process and the injection mold process though, is the fact that cast polyurethane materials are injected into a soft mold, not a hard mold. The urethane casting mold is usually made from a soft silicone. For the best results, manufacturers often create the master mold via CNC machining and 3D printing.
- Common urethane cast parts include: skateboard wheels, molded bearings, urethane covered rollers, and FDA approved parts. Manufacturers value the urethane casting process for the quality of parts it produces; urethane cast parts are abrasion resistant, resistant to extreme temperature changes, functional at high and low temperatures. In addition, they have excellent tear strength.
- Urethane Manufacturers
- Urethane manufacturers fabricate molded urethane to produce many different products.
- Urethane Molding
- Urethane molding, sometimes called polyurethane molding, is an elastic polymer that contains urethane carbamate links.
- Urethane Sheets
- Urethane sheets, technically referred to as polyurethane (or PU) sheets, are durable, long-lasting sheets that are constructed from an elastic polymer, or elastomer, containing urethane carbamate links.
- Urethane Wheels
- Urethane wheels are fabricated from molded urethane, technically referred to as polyurethane (or PU), which is an elastic polymer, or elastomer, containing urethane carbamate links.
Design and Customization of Polyurethane
When designing a polyurethane molded product, manufacturers think about a variety of key factors. Aside from product shape, when thinking about mold standard and custom mold products, they consider the following, as they relate to the application:
The tensile strength of a molded polyurethane product 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 the 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, manufacturers consider the physical properties of molded urethane material, like abrasion resistance and shrinkage, and the chemical properties of molded urethane parts. For example, 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 and make a more durable product, manufacturers will likely consider blending a molded polyurethane material with an additive.
Custom Urethane Parts
For specialized applications, most, if not all, manufacturers have no problem designing custom urethane parts. Find out about a manufacturer’s custom urethane molding options by visiting their site, sending them a request for a quote, or by simply calling them.
Polyurethane Molding Applications
Polyurethane molding is used to make products that exhibit characteristics of water resistance, chemical resistance, contaminant resistance, strength, and flexibility.
Because of these positive features, the polyurethane molding industry has customers from many different fields, including: medicine and health care, construction, automotive, food processing, industrial manufacturing, engineering, and sports and recreation, among others.
Products Produced Through Molding
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, urethane tires, and urethane wheels.
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 assorted parts.
Manufacturers also injection mold urethane to make cushions. Urethane cushions can be used outside, in the water, and 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 mold 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.
Things to Consider When Choosing Polyurethane Molding
If you’re interested in investing in polyurethane molding services, it’s important that you work with an experienced polyurethane mold manufacturer you can trust. While many suppliers offer polyurethane molding and similar services, not all of them are equal, and not all of them are right for you. Find the right contract manufacturer for you by discussing your application at length with multiple polyurethane mold companies. Make sure they understand your requirements and specifications, are willing and able to work within your budget and deadline, and, most importantly, that they’re dedicated to delivering you a high-quality solution. Get started by checking out the many excellent polyurethane mold manufacturers that we have listed above.
Polyurethane Molding Terms
- 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.
- Blowing Agent
- Foam producing substance (e.g. carbon dioxide).
- Breaking Strength
- The point of tension at which polyurethane will rupture in the 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.
- Cycle Time
- 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.
- Demold Time
- 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.
- A 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.
- Micro Molding
- 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.
- The urethane molding process in which a chemical reaction links together monomers to form a polymer.
- 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.
- Polyurethane Casters
- Casters are small wheels that are usually attached to an iron center and a steel bracket. Casters are used in a variety of industries and applications; from healthcare to warehouse storage to moving.
- Polyurethane Motor Mounts
- Used to attach a motor or transmission to the frame of a vehicle.
- 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.
- Urethane Molders
- Urethane molding, or polyurethane molding, is an incredibly versatile process, and it is important to look carefully for the right urethane manufacturer that will make sure your requirements and specifications are met.