Molding Polyurethane: The Cast Urethane Process

Custom cast polyurethane products have become widely adopted throughout the manufacturing, food and beverage, mining, automotive, printing, and robotics industries.  Their relative ease of production, low tooling costs, and longevity have made cast urethane parts a staple of industry and automation. But what is the process behind manufacturing custom molded urethane parts?

The Concept

It all starts with the concept. Generally, a customer will submit a CAD file. Or, some form of drawing file along with a brief description of the uses for the part, the environment where the usage of the part will take place, and quantity of the part they need. This is how the presentation of most inquiries happens, but it is not the only way. Sometimes customers do not have a design and need in-field engineering assistance to come up with a solution.  In this case, an experienced engineer/estimator will drive or fly out to the company that is requesting the urethane product. And, works on the ground floor with the company in order to come up with a solution. Often, the quotation of the job can happen on-site. But, sometimes further engineering is a must in order to come up with an accurate estimate.


Quoting is the second step in the process of molding polyurethane. Once the cast polyurethane parts manufacturer has the drawing of the part he will produce, estimating then thoroughly examines it and determines how much the part will cost. This step often requires involvement. And, it takes into account many things such as the best material to use for the part. Also, the cost of the material, the time it will take to make the tool, the time involved in setup processes, the time the job will spend in production. And, the time the part will spend in trimming and inspection.

Every little detail is important. Also, the estimator is often collaborating with all of these departments in order to come up with accurate time estimates so that the proper quotation of the job is possible. It is very important that all of these departments are working with incredible efficiency. This is in order to keep manufacturing costs low by saving time. This is because it ultimately provides the customer with a quality part at an economical price.


Once the quotation of the job and the reception of the order happened, the first step in the production portion of the journey is tooling. Tooling is the process that results in the making of polyurethane molds and hobbs. Here, a machinist receives the drawing of the part in the form of an IGS file. The machinist is then able to take that design and come up with a CNC tool path. The tool path will make a mold for the part that when filled with urethane will form the part with extreme precision (usually within 0.005”). This can often be a very intricate process as urethane parts become more complex.

When complex polyurethane molds are made, they often have to be built in many pieces that come together in sync to form the cavity that will form the finished product.  An alternative option to a cavity-cut mold, as mentioned previously, is a hobb. A hobb is an aluminum replica of the part that has been modified for the purposes of making a urethane mold. A hobb is designed to mimic the part so that when urethane is cast around it. And then its removal from the urethane ensues after a cure cycle. The result is a cavity that will produce the part when filled with urethane.


After the production of the mold or hobb finishes, it then enters the production room. The production room is where molding polyurethane parts in mass takes place. Here, urethane is formulated using different prepolymers, curatives, and ratios to create formulations that are specific to the particular job. These specially formulated mixtures are generally processed in automated dispensers, centrifugal mixers, or hand-batched depending on the job size and requirements.  After the material is processed it is then poured or dispensed into the polyurethane molds and cured in an oven, on a hot table, or in a heated hydraulic press (for compression molded parts). Most parts cure within a few hours because they are run with a more standard polyurethane formulation, but other formulations, such as higher-end Vulkollan substitutes, can take all day.

Trimming and Secondary Machining

In fact, trimming comes after production when the newly cast polyurethane parts have fully cured. Trimming is just removing all of the “flash” from urethane parts that have just come out of production. This is essentially just a clean-up operation where shaving off excess, leftover urethane from the molding process happens, creating the finished product.

Polyurethane parts may also need secondary machining operations, depending on the final use. For this, the urethane parts are moved back into the machine shop. There, they are turned, milled, 3D’d, or grinded (depending on the type of project and tolerances). 


Once the urethane part has made it through every operation, it still has one more step in the journey before its shipment happens: inspection. Inspection consists of checking the durometer of the finished polyurethane parts. Then, checking critical dimensions, checking color to make sure the ratio was correct for every mix, checking for porosity. And, checking for overall cleanliness. Here at Uniflex, we will not ship anything unless it went through a thorough inspection. If a part does not pass any step in the inspection process, we throw it out. And, we manufacture a new one.


The final step in the process of molding polyurethane is shipping. Once the engineering of the polyurethane parts finishes, molds have been made, production has taken place, trimming is complete, and inspection is passed, the parts can finally be shipped out the door to the customer.


As you can see, the process of molding polyurethane requires involvement. There are a lot of steps along the journey from concept to finished part. So, a very professional and well-trained crew is essential for keeping things working efficiently. Without a dedicated staff and years of experience, it is very difficult to produce quality urethane products with speed, efficiency, and ultimately an economical price.

If you have any questions about polyurethane products, molding polyurethane, or the manufacturing process, do not hesitate to give us a call at (248) 486-6000 or send us a message. We have an experienced staff that is always willing to lend support!

The Versatility of Custom Molded Urethane


Custom molded urethane has been, and still is, the most versatile solution to an ever-changing manufacturing world. It is a leader in vibration dampening, and high impact resiliency. In addition to scraping abrasion resistance, chemical resistance, as well as a host of others. Cast urethane also has the unique ability to mold into a seemingly infinite number of solutions. This is because of its liquid starting state.  his allows the polyurethane compound to fill the cavity of practically any mold; giving urethane parts the ability to take on unique shapes that other materials cannot.



Cast Urethane Parts Are Completely Customizable


Custom molded urethane parts have the unique ability to be tailored to specific applications. This can happen by adjusting formulations to alter hardness (durometer) as well as physical properties. Formulation of different ratios of prepolymer and curing agents is possible to produce varying durometers from 5A all the way up to 80D. Different prepolymers and different curing agents can also give the finished part specially formulated properties that are designed to work best for their specific applications.

For example, a TODI based prepolymer formulation might be used for a high-performance dynamic application that requires very good rebound characteristics (such as high load urethane rollers) whereas a more standard dynamic urethane such as a TDI/PTMEG polyether would work best for an application where the enhanced rebound is not needed (Quick Urethane Chemistry). This is especially useful for cost savings. In the case of the previously mentioned example, the cost for the higher performance TODI material would be approximately 5 times that of the TDI/PTMEG polyether.

There is no sense in paying more for parts if you don’t have to. As long as you know the desired physical properties you would like to obtain, chances are there is an existing urethane compound and formulation that will work for your application.


All in all, polyurethane tends to have the most versatility when compared with similar compounds such as rubber. Although rubber and other materials are essential for certain applications, polyurethane serves as the best, low-cost option when it comes to most parts. Furthermore, there is an incredible range of polyurethane compounds whose formulation can happen with general ease; allowing for standard urethane applications like polyurethane bumpers, all the way up to high-performance applications like roller coaster wheels.


Common Molded Urethane Applications:


If you have any questions about polyurethane elastomers, do not hesitate to give us a call at (248) 486-6000 or send us a message. We have an experienced staff that is always willing to lend support.

Polyether Urethane vs. Polyester Urethane



When it comes to polyurethane, there are two main types: polyether urethane and polyester urethane. Although they are both polyurethanes, each has its own unique set of physical properties that are designed for specific applications. Below is a comparison of polyether and polyester polyurethanes showing lists of properties as well as applications for each material.



Polyester Urethane



In fact, polyesters are typically famous for their superior sliding abrasion resistance. This makes them excellent for applications where abrasion subjects the polyurethane surface to high levels of friction, such as with chute liners and scraper blades. Typically, this is the main defining attribute when comparing polyesters with other materials. Polyesters are often called the “workhorse” of high abrasion applications and have gained an excellent reputation when used in highly abrasive environments.






  • Excellent Abrasion Resistance
  • Better Shock Absorption
  • Higher Tensile Strength
  • Good Chemical Resistance
  • Withstand Higher Temperatures Longer






  • Scraper blades
  • Chute liners
  • Hopper liners
  • Wear pads
  • Snowplow blades
  • Screening grids






Polyether Urethane



In fact, polyethers are the most common polyurethanes used in the cast elastomer industry. They generally have better dynamic properties than polyesters and are used in wide range of applications such as rollers, bumpers, and bushings. Polyethers tend to make up the majority of polyurethane parts because they are easy to work with and offer more desirable physical properties. Another very interesting thing about polyethers is that they can be tailored with specific additives to perform on the same level or better as polyesters for abrasion resistance. This results in a material that is essentially a hybrid polyether and performs just like a polyester in high scraping abrasion applications.






  • Excellent Dynamic Properties
  • Hydrolytic Stability
  • Low-Temperature Flexibility
  • Good High-Temperature Resistance
  • UV Resistance
  • Better Rebound






  • Rollers
  • High load casters
  • Skateboard wheels
  • Body Blocks
  • Bumpers
  • Bushings
  • Coil storage pads
  • Gears and sprockets
  • Pulleys
  • Couplings



So, if you have any questions about polyurethane elastomers, do not hesitate to give us a call at (248) 486-6000 or send us a message. We have an experienced staff that is always willing to lend support.

The Benefits of Polyurethane Parts



Polyurethane is Extremely Versatile


What makes urethane incredibly useful is its versatility. Urethane starts as a viscous liquid prepolymer resin that in mixture with a curing agent. Then, pouring it or injecting it into a mold ensues. Because urethane exists in a liquid state before it cures into a solid urethane elastomer, it can take on the shape of practically any mold cavity. There are essentially endless products that we can manufacture from urethane. The only limit is the engineer designing the product.


Polyurethane Parts Significantly Reduce Noise and Absorb Vibrations


Urethane parts are excellent for applications where noise abatement and vibration dampening are key. Industries across the world consistently use urethane to control decibel levels in the working environment as well as dampen impact related vibrations. Because of urethane’s ability to absorb vibrations and hold up against repeated extreme collision, it has become the #1 material in parts used for high impact applications where energy absorption and noise abatement are necessary.


Urethane Has Many Different Grades, Formulations, and Hardness Ranges


Urethane has many different grades and hardness ranges (durometer) whose tailoring to specific applications is possible. There are a host of different compounds such as polyesters, PPG and PTMEG polyether’s, TODI and MDI based systems, etc., that can be used to manufacture urethane parts. The parts produced from each of these compounds have their own unique set of uses, price, and physical properties. This allows the product to be designed and priced to each specific application. This can help increase component lifespan and cut costs.



Procuttion of Urethane Parts is Quick and Very Economical


Some other great advantages urethane parts have are fast production times in combination with favorable pricing. When provided with an accurate drawing, a cast urethane manufacturer can have custom molded parts out the door in a matter of days. Whether it’s single piece prototypes or high-volume production runs. Urethane parts will have the best bang for your buck along with very quick production rates.


If you have any questions about molded polyurethane parts, do not hesitate to give us a call at (248) 486-6000 or send us a message. We have an experienced staff that is always willing to lend support.

What is Vulkollan Polyurethane?


In fact, Vulkollan® is one of the most powerful polyurethane elastomers to date. Moreover, it has become widely known for its high mechanical load-bearing capacity, high tensile strength, and superior rebound capabilities. Additionally, its usage is generally common when it comes to highly demanding tasks such as in high load casters, high load conveyor rollers, valve seats, roller coaster wheels, etc. Basically, Vulkollan® is used for applications with extreme dynamic demands.


Vulkollan® is an NDI based elastomer system. Reacting polyols and NDI (1,5-naphthylene di-isocyanate) to create the prepolymer produce it. And then reacting the prepolymer with either glycols or water produces the polyurethane elastomer. When the prepolymer reacts with glycols, they produce a solid elastomer. Additionally, when the prepolymer is reacted with water cellular elastomers are produced.

It Is a Costly Material

Although Vulkollan® does hold incredible physical properties, it is an extremely costly material to work with. In order to process Vulkollan®, a manufacturer has to adhere to implemented guidelines. And, a manufacturer also has to have a licence in order to sell under the Vulkollan® trademark. Of course, this can drive costs up significantly when quoting jobs.

Substitutes for Vulkollan®

There are many substitutes for Vulkollan® that have hit the market over the years. And, they hold the same or even better physical properties. Many of these materials are much easier to work with and behave identically to Vulkollan®. Not only this, but they are much cheaper to produce and have much better UV resistance along with better stability and the ability for pigmentation (colorization), which can be very important for certain applications. See below for a comparison between Vulkollan® and some of its substitutes that we run:


High performance polyurethane table


The UHPU-A substitute (as seen above) is formulated using an aliphatic diisocyanate (PCL) based prepolymer and the UHPU-B substitute is formulated using a toluidine diisocyanate (TODI) based system. As you can see, the PCL-based substitute holds even better properties than Vulkollan® and the TODI substitute is almost neck and neck with Vulkollan®.


Now, the purpose of this post is not to bash Vulkollan® because it truly is an excellent material.  It has proven itself for many decades now and has become an industry staple. However, it is not the king of elastomers anymore as there are many materials whose formulation made them perform at the same level or better. These substitutes or replacement materials, as seen above, have also proven themselves, and many customers are switching to them because they perform just as well as Vulkollan® and are much cheaper to produce.


If you would like more information, please don’t hesitate to give us a call at 248-486-6000 or send us an email. We are always willing to share our expertise and provide helpful knowledge.

Not All Urethane Is Equal: Quick Urethane Chemistry


Urethane has gained its reputation as one of the toughest and most versatile polymers known to date.  From the mining, automotive, and oil industries all the way over to the skateboard wheel and gym equipment manufacturers; urethane has proven itself as a reliable material for many decades. What exactly is urethane, though, and are all urethanes the same?


For those of you that would like a quick answer to this question, it is a definite no. Not all urethanes are the same, and I am not just talking about different hardness, shapes, or colors either. I am talking about on a molecular level. Urethane’s physical properties such as resiliency, tensile strength, rebound, and modulus are all subject to change based on the chemistry of the urethane that is in usage. The important thing to realize is that there are many different “grades” of urethane; polyester resins, PPG and PTMEG polyether’s, as well as MDI based systems.

Now I know this is somewhat of a foreign language to most. However, we’ll break this down a bit and try to get some clarity.

MDI’s and TDI’s

MDI’s and TDI’s are what are known as diisocyanates or the monomers of polyurethanes. MDI stands for methylene diphenyl diisocyanate and TDI stands for toluene diisocyanate. Both MDI and TDI diisocyanates combined makeup 90% of the overall diisocyanate market. And, their major use is in the manufacture of polyurethanes (1). In order to make a polyurethane prepolymer, one has to react to a diisocyanate (MDI or TDI) with a polyol. We could refer to a polyol as the “backbone” of a polyurethane molecule and it is where most of a urethane’s physical properties take root. For example, let’s come back to a type of urethane we mentioned earlier; a PTMEG polyether.  PTMEG (polytetramethylene ether glycol) is a polyol or backbone whose usage is common in high-performance urethane systems. To produce a PTMEG polyether prepolymer, PTMEG needs to react with TDI’s (see reaction below).

polyurethane reaction chemistry visual.

Now, realize that this reaction of a diisocyanate with a polyol produces what is a called a prepolymer. A prepolymer is essentially just a syrupy or waxy resin that has to react with a curing agent in order to produce a urethane elastomer (urethane elastomers produce urethane parts).

Curing Agents

There are many different types of curing agents that can used to produce urethane elastomers. These curing agents can also modify the physical properties of the urethane. Different curing agents can go into mix in different ratios with prepolymers to achieve different hardness ranges and different physical properties such as tensile strength and rebound.

A very common curing agent whose usage is wide across the polyurethane industry is 4,4’-methylene-bis(2-chloroaniline); commonly known as MOCA (you can see it reacting with a prepolymer in picture above). This compound reacts with a prepolymer such a PTMEG polyether to create a high-performance polyurethane elastomer which is excellent for dynamic applications such as rollers.


I know is this is a big gulp of chemistry. But, the important takeaway from this very brief urethane chemistry lesson is to be careful when selecting who manufactures your polyurethane parts because not all urethane is equal. Be prepared to ask questions about the materials (prepolymer and curing agents) that are being used to manufacture your parts.

Realize that polyurethanes are a family of compounds and they all have different attributes that can be favorable or not favorable when costs are being cut (some materials are designed to be cheap). Finally, if you’re uncertain just ask. If you’re unsure about anything, give us a call at 248-486-6000 or email us for any questions you may have regarding urethane elastomer systems or urethane parts in general.

I also highly recommend checking out this article if you are interested in a more in-depth lesson on MDI and TDI based systems:


  1. MDI, TDI and the Polyurethane Industry. (n.d.). Retrieved from

Polyurethane vs Rubber

A very frequently asked question is which is the better choice: polyurethane or rubber? With this debate on polyurethane vs rubber, a lot of industry bias happens. Polyurethane molding companies will say polyurethane is better whereas rubber molding companies will say rubber is better. Coming from a company that does both, the simple answer to this question is it all depends on the application.

Application is Crucial

For some applications, polyurethane is the correct choice and for others, rubber is the correct choice. For example, if you were debating on choosing a polyurethane seal vs a rubber seal for an application in an exhaust manifold that had an operating temperature of 500F; you would most definitely be choosing silicone (technically a type of rubber) over polyurethane. However, if you had a more dynamic application such as with bushings, spacers, or bumpers, then you would be much better off choosing polyurethane (depending on chemical exposure).

The key takeaway is that polyurethane and rubber have their own specific niches that they fit into. One may perform better in certain situations than the other and vice versa.  What needs to be realized is that there are many different grades of rubber and polyurethane that are designed for specific applications, and it is often best to consult with professionals to decide which material is best for your specific application.

Please reference our technical data page for more information regarding polyurethane and rubber.  If you have any questions, do not hesitate to give us a call at (248) 486-6000 or send us a message. We have an experienced staff that is always willing to lend support.