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, environment the part will be used in, and quantity of the part they need. This is how most inquiries are presented, 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 work on the ground floor with the company in order to come up with a solution.  It is often that the job can be quoted on site, but sometimes further engineering is required in order to come up with an accurate estimate.

 

Quoting

 

Quoting is the second step in the process of molding polyurethane.  Once the cast polyurethane parts manufacturer has the drawing of the part to be produced, estimating then thoroughly examines it and determines how much the part will cost.  This step is often very involved and takes into account many things such as the best material to use for the part, 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 considered, and the estimator is often collaborating with all of these departments in order to come up with accurate time estimates so that the job is properly quoted.  It is very important that all of these departments are working with incredible efficiency in order to keep manufacturing costs low by saving time, which ultimately provides the customer with a quality part with an economical price.

 

Tooling

 

Once the job has been quoted and the order has been received, the first step in the production portion of the journey is tooling.  Tooling is the process by which polyurethane molds and hobbs are made. Here, a machinist is presented with 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 that 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 to 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 it is removed from the urethane after a cure cycle, the result is a cavity that will produce the part when filled with urethane.

 

Production

 

After the mold or hobb has been made, 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

 

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 excess, leftover urethane from the molding process is shaved off, 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, where they are turned, milled, 3D’d, or grinded (depending on the type of project and tolerances).

 

Inspection

 

Once the urethane part has made it through every operation, it still has one more step in the journey before it can be shipped: inspection.  Inspection consists checking the durometer of the finished polyurethane parts, checking critical dimensions, checking color to make sure ratio was correct for every mix, checking for porosity, and checking for overall cleanliness. Here at Uniflex, we will not ship anything unless it has been thoroughly inspected.  If a part does not pass any step in the inspection process, it is thrown out and a new one is manufactured.

 

 

Shipping

 

The final step in the process of molding polyurethane is shipping. Once the polyurethane parts have been engineered, 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.

 

Conclusion:

 

As you can see, the process of molding polyurethane is very involved.  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, high impact resiliency, scraping abrasion resistance, chemical resistance, as well as a host of others.  Cast urethane also has the unique ability to molded into a seemingly infinite number of solutions because of its liquid starting state.  This 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 by adjusting formulations to alter hardness (durometer) as well as physical properties.  Different ratios of prepolymer and curing agents can be formulated 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 enhanced rebound is not needed (Quick Urethane Chemistry). This is especially useful for cost savings.  In the case of the previously mentioned example, 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 that can be formulated 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

 

 

Polyesters are typically known for their superior sliding abrasion resistance.  This makes them excellent for applications where the polyurethane surface is subjected to high levels of friction caused by abrasion, such as with chute liners and scraper blades. Typically, this is the main defining attribute when polyesters are being discussed in comparison 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.

 

 

Properties:

 

 

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

 

 

Applications:

 

 

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

 

 

 

 

 

Polyether Urethane

 

 

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.

 

 

Properties:

 

 

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

 

 

Applications:

 

 

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

 

 

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 is mixed with a curing agent and is then poured or injected into a mold.  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 can be manufactured 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.  Urethane has been consistently used in industries across the world 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) that can be tailored to specific applications.  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, which can help increase component lifespan and cut costs.

 

 

Urethane Parts Can Be Quickly Produced and Are Very Economical

 

Some other great advantages urethane parts have are fast production times combined 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?

 

Vulkollan® is one of the most powerful polyurethane elastomers to date and has become widely known for its high mechanical load bearing capacity, high tensile strength, and superior rebound capabilities.  It is generally used for 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 that is produced by reacting polyols and NDI (1,5-naphthylene di-isocyanate) to create the prepolymer, and then the polyurethane elastomer is produced by reacting the prepolymer with either glycols or water.  When the prepolymer is reacted with glycols, a solid elastomer is produced and when the prepolymer is reacted with water cellular elastomers are produced.

 

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 also be licensed in order to sell under the Vulkollan® trademark.  Of course, this can drive costs up significantly when jobs are being quoted.

 

There are many substitutes for Vulkollan® that have hit the market over the years and 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 to be pigmented (colored), 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 that have been formulated to 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 the 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 being used. What has to be realized is there are many different “grades” of urethane such as 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, but we’ll break this down a bit and try to get some clarity.

 

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 make up 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 a diisocyanate (MDI or TDI) with a polyol. A polyol is what could be referred to as the “backbone” of a polyurethane molecule and is where most of a urethane’s physical properties are derived from. For example, lets come back to a type of urethane we mentioned earlier; a PTMEG polyether.  PTMEG (polytetramethylene ether glycol) is a polyol or backbone that is used in high performance urethane systems. To produce a PTMEG polyether prepolymer, PTMEG is reacted 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 be reacted with a curing agent in order to produce a urethane elastomer (urethane elastomers are what urethane parts are made from). 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 be mixed 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 widely used 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 the 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:  https://catalogimages.wiley.com/images/db/pdf/0471958123.01.pdf

References:

  1. MDI, TDI and the Polyurethane Industry. (n.d.). Retrieved from https://catalogimages.wiley.com/images/db/pdf/0471958123.01.pdf

Polyurethane vs Rubber

A very frequently asked question is which is the better choice: polyurethane or rubber? With this debate on polyurethane vs rubber, there is often a lot of industry bias associated. 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.

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.