Polyurethane (PU) is an elastomer mix (urethane) material that can be formed into in a wide variety of shapes, sizes, and hardnesses. Its uses range from insulation and cushioning to adhesives and car parts and more. PU’s unique ability to withstand tension and compression while maintaining its shape and flexibility makes it a great lining for mass finishing equipment.
The ability to specify the size, shape, and hardness of PU allows equipment manufacturers like Rosler Metal Finishing to build machinery with custom inserts and linings to protect components and enable precise surface finishing as well as relining existing equipment with upgraded lining.
Our expert engineers create a custom blend of shore hardness, PU type, and forming method to produce durable and resilient materials that can withstand the harsh demands and stresses found within mass finishing operations.
Measuring Material Hardness
The shore hardness of PU is measured by the material’s resistance to localized deformation. This hardness or durometer is identified with a durometer tester, which forces a conical shaped indicator into the surface of the material and then measures the depth of the indentation. The scale ranges from 0-100 durometer with many different properties in between.
Understanding how a PU will react to and rebound from stress, compression, and tension allows engineers to use the most appropriate material in a situation where repeated stress and wear is expected.
Selecting the Right Type of Material
PU hardness is typically measured using the shore A or shore D scale. Shore A is often used for rubbers, elastomers, and softer plastics such as mouse pads, food-grade silicone products, and belts. Harder materials, such as solid truck tires, hard hats, and cast urethane plastics are measured using shore D.
Shore A PU is a softer material that possesses great rebound and tensile strengths along with good tear strength. Shore D material is extremely hard with relatively no flexibility.
Rosler Metal Finishing mainly uses shore A materials but has used shore D on special occasions. Shore A materials provide the strength and durability needed to protect internal parts while absorbing and standing up to the motion of workpieces and media within mass finishing equipment.
Methods of Applying PU Material
Whether brand new or as expected maintenance and upkeep of an existing machine, PU can be used to protect mass finishing bowls, tubs, and barrels. Highly wear-resistant, mercury-free PU linings can be applied using hot-pour, cold-pour, spray, and casting techniques.
Hot pour PU lining is our most popular method of relining. This technique is typically used for 90-95 durometer materials including heavy parts and for use with ceramic and plastic media. Hot pour produces a considerably longer service life than traditional liners and is very resistant to chemicals. If machining is required after lining, for instance with tubs and spinners, hot pour is the best method to use.
Cold pour occurs at room temperature and is typically used for 80-90 durometer materials. This is the most common material used for general applications. It provides good rebound, tensile, and tear characteristics. Cold pour is also a good material to use when rolling steel media or heavy sharp parts such as diecasting and stamped or sintered metals.
Spray lining eliminates the need for expensive molds. Instead customized, wear-resistant linings are applied to special shapes and sizes, tumbling barrels, vibratory hoppers and screening machines, wear plates, and when using a mold is not practical. This method reduces the cost of lining and provides the fastest turnaround time while providing the same durability.
PU casts can create small, custom parts such as car wash rollers or blower housings as well as replacement urethane parts for all makes and models of shot blasting and mass finishing machines. Custom PU masking for existing shot blasting and mass finishing operations is also available.
No matter what method is used, the surface which the PU is to be applied to is carefully prepared. Once all usable parts are removed, the unit is placed in an EPA-approved burn-out oven. Extremely high temperatures are applied for 24 hours to remove any remnants of prior coatings.
After repair and coatings, the unit returns to the oven to be cured at 180 degrees Fahrenheit for 16 hours. This step brings the PU to its full potential for performance and long-term durability.
The Rosler Way
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Post written by
Doug Van Dyke
Rosler Metal Finishing, USA
Chief Aftermarket Technical Officer
Email Doug or call him at 269-441-3616