Using reprocessed fluorocarbon elastomers for high heat and oil resistance.

Using reprocessed fluorocarbon elastomers for high heat and oil resistance

High value compounding in fluorocarbon elastomer 

Even with their high costs, ranging from $15 to $80 per pound, fluorocarbon elastomers are registering approximately 10% growth annually. The reason for this growth can definitely be attributed to their value in use.

Currently fluorocarbon rubber is considered the best, the top of the line, the most resistant of the normally processible elastomers. FKM is an H type (482|F), K class (10% max. swell in ASTM #3 oil) material.

Discussion

Today's business climate emphasizes excellence and quality, thereby encouraging the use of fluoroelastomers as seals, hoses, diaphragms and other parts where detrimental environments rapidly degrade conventional synthetic elastomers. The key to their need is that fluoroelastomers perform where other elastomers do not. In the presence of excessive heat or aggressive fluids or both, you can count on fluoroelastomers.

Excellence and high quality demand extended guarantees and warranties making it imperative that each component of the product being made uses the best materials available. With this in mind one can readily understand why the fluoroelastomer business will continue to grow.

In this article a means of maintaining the outstanding properties of this phenomenal elastomer, and at the same time reduce its cost through innovative compounding, is suggested.

Carrying out these ideas could be a vehicle for your company to enter or expand its business in this highly desirable and growing segment of the specialty elastomer market.

Technical detail

Since its inception, Cri-Tech has worked on a process directed toward the production of reprocessed fluoroelastomer that in conjunction with virgin polymer would result in HK rated compounds per ASTM D 2000 and SAE J 200. Further it was essential that this development yield compounds that offer significant cost savings with virtually no sacrifice in properties or performance.

For nearly a decade we have produced and improved the physical nature of this material and can attest to its performance, though limited acceptance. This limitation was the result of our decision to carefully identify where this material would be used so its performance could be monitored. Today we feel the concept is indeed viable and under utilized.

The product we are discussing is produced from cured flash or out of spec. parts; mis-mixes or scorched compound. It is masticated and broken down using traditional methods combined with proprietary technology, resulting in a uniform, reusable material.

Using reprocessed fluoroelastomer has definite advantages. It obviously results in lower cost compounds; helps calendering and compression molding; does not compromise heat or fluid resistance and is certainly an environmentally sound idea since we are recycling what otherwise would be scrap.

Other characteristics are that compounds made with it have shrinkages similar to the virgin material; it can be used at levels from as little as five parts for processing improvements to as much as four hundred parts for more than thirty percent cost reduction in raw materials. The properties to the left for each level of reprocessed FKM are the properties after post cure and the properties to the right are properties after heat aging for 70 hours at 482|F. Some trends are definitely noticeable. As the level of reprocessed FKM is increased, tensile strength decreases, modulus decreases and elongation increases. The tensile decrease can be overcome somewhat by the choice of polymer and filler, but in general, strengths above 1000 psi are quite acceptable for most applications.

The modulus decrease and the elongation increase are due in part to the fact that reprocessed FKM has active cure sites and is taking some of the cure from the virgin polymer. Now compare properties after aging to original properties at all levels of the reprocessed FKM; there is no appreciable change in properties after aging at all levels. Not shown here but experimentally proven is that reprocessed FKM does not affect the fluid resistant properties of FKM. The data therefore supports our claim that the addition of reprocessed FKM will result in compounds that are HK rated.

Two other phenomena of note when using reprocessed FKM are shown in figures 3 and 4. In the ODR study, we see that minimum viscosity increases and the maximum torque decreases as the level of reprocessed FKM is increased. In the compression set study, we see that compression set resistance decreases as the level of reprocessed FKM is increased. However, once we understand how the material performs we can compensate for its shortcomings through compounding.

The use of reprocessed elastomer has had its proverbial Achilles Heel, that is, inconsistency of performance. Recognizing that problem, we have concentrated our efforts on improving the quality of the process and product. The first thing we did was to establish a raw material specification which essentially catagorizes the incoming scrap (raw material). Each shipment is inspected, sorted and formulated into a test batch of: FKM 89.0; Cri-Act-45 20.0; reprocessed FKM 115.0; carbon black 35.0 and curative 0.30.

Only after passing original and heat aging tests is the incoming scrap accepted for use as a raw material. During the process significant process variables are monitored, charted and controlled. The finished product is then tested again in the test recipe.

These data represent six months of production and indicate that generally the product is in good control. Quality process improvements are continuing, consequently, we expect to achieve tighter control.

Now we would like you to turn your attention to money. We want to demonstrate how reprocessed FKM can be the source of significant savings. With SBR at 10% savings you would need a one million pound application to save $50,000. Using FKM, only a 43,000 pound application is needed to save $50,000 at 10% savings. At 20% and 30% savings, the quantities required are 21,000 and 14,000 pounds respectively. The conclusion is that comparatively little volume is needed to accomplish significant savings when using reprocessed FKM.

What percentage can you save using reprocessed FKM? The choice is yours. You can see that greater than 30% savings are possible.

We have shown you advantages and disadvantages of using reprocessed FKM in FKM formulations. Now we want to show some practical application compounds using this material in which polymer choice along with careful selection of fillers, process aids and curatives has allowed our customers to increase their market share and profitability.

The first compound is a calendered sheet compound for an aerospace application. The 15 parts of reprocessed FKM are added to this compound to rid air during calendering, resulting in a smooth nearly blister free preform off the calender. The 7% cost savings is an added bonus.

Reprocessed FKM can be used in soft compounds (app. cost savings of 24%), and hard compounds (app. cost savings of 19%). It can be used at high loadings where cost is the primary consideration such as in a sheet packing compound (app. cost savings of 30%). It can be used at low levels where flow and compression set resistance are of the utmost importance, (injection molding o-ring compound, app. cost savings of 10%). It can be used in tough applications such as valve stem seals (app. cost savings of 18%) and even in a difficult transfer molding application requiring bonding to metal (app. cost savings of 29%). In other words, by careful compounding reprocessed FKM containing recipes will perform in most rubber processes and in many demanding FKM applications.