Case History #2
Silicone to the Rescue
In 2001, the trucking industry experienced some major problems when increased pollution controls raised under-hood temperatures and caused failures in big rigs, specifically in the tractortrailers' turbocharger systems. Without the extra boost from the turbochargers, these trucks had little power and were breaking down on roadsides all across the U.S. The culprit turned out to be the charged air coolers (CAGs). Much like car radiators, CAGs are used to cool the turbo units. The CAG base has soldered fins that look and function exactly like automobile radiators, and these were leaking from micro-holes that were caused by displaced solder. A means to quickly seal the CAGs was immediately needed to get the trucks back on the road. Because CAGs are constructed from a magnesium aluminum alloy with a zinc-rich surface coating, however, they presented a difficult substrate for bonding. The zinc easily flaked off and acted like a release agent, hindering any potential sealer.
Download the PDF here
Case History #8
A construction sealant firm was having low adhesion issues. A silane firm recommended that the sealant firm use more of a di-amino silane to enhance adhesion. When utilized, and upon aging, instead of the desired translucent product, a yellow colored sealant product was produced. However, better adhesion did occur. Here again, being a construction sealant firm, to keep costs down, all of the silanes including the adhesion promoter were being added at the beginning of the batch. Effectively, all of the silanes were being used to scavenge the water in the silica and the available silanol of the silica. The solution to color reduction here was to switch to a monoamino-silane adhesion promoter, add it at a lower level and at the correct point in the batch, and lastly to utilize enough crosslinker to function as a water scavenger. The mono-amino silane adhesion promoter imparts a very slight tint of yellow, when used at the correct level. It will enable an adequate level of adhesion when utilized at the end of the batch when the water and silica scavenging has already been satisfied. Crosslinkers are typically much less expensive than adhesion promoters, so by utilizing the crosslinker as a water scavenger, it reduces costs.
The lesson here: the utilization of the best adhesion promoter for the application, along with the proper order of addition and adequate crosslinker levels, all resulted in improved performance and lower unit costs. Silicone Solutions product line does not utilize high amine adhesion promoters. Through the utilization of advanced technologies, we exceed the adhesion of all competitive products without yellowing.
Case History #9
The auto industry was having a big problem with leaking oilpans and valve covers. Very thick compounds were being utilized to meet assembly test parameters of engines. These thick, heavy bodied RTV compounds were manufactured using a very high molecular weight polymer, which had a low crosslink density, very subject to reversion. In addition to causing leaks, the reversion was also causing the de-polymerization of sealants inside of the engine compartment into a jelly-like substance, which plugged inlets to oil sump pumps causing engine failure. We developed a new technique to make heavy-bodied sealants, which was less prone to reversion. However, we hedged our bets. We knew that the motor oil buffers break down upon heat exposure and the motor oil, rear axle lube and other lubricants can become acidic. In acidic and basic environments, heat accelerated reversion of cured silicone polymers can occur relatively quickly. The new product had a big edge here over the target replacement acetoxy sealant.
The new product passed all of the tests and just prior to line introduction into the Pontiac engine plant, we were invited to a meeting in Detroit by the sales and marketing group. In the GM facility, along with our contingent, GM had their plant manager and the plant engineer. The plant engineer had a reputation as a hard guy to deal with. He asked in a gruff voice, "how do I know that your product won't be worse than the current product causing all of the leaks?" The marketing staff explained that it met all of the tests. He said, "I don't care, how can you assure me I won't have a bigger problem?" The marketing staff all looked to us. There was silence. David Brassard then said "Tums." He was shocked, and then said "What?" David said "Tums," looking defiantly at him. He asked, "what about Tums?" David said, "Do you use them?" He said "yes." David then asked, "Do they work?" He said "yes." Then David said, "we have the active ingredient in Tums, calcium carbonate a buffer, in the product." David relayed that as motor oil gets old, it becomes acidic and accelerates the reversion. The buffer neutralizes the acidity and results in long gasket life. Everyone laughed, and he said, "GOOD lets go with it!"
The lesson here: when you know your technology, the confidence comes through in communications. Also, humor can disarm the gruffest of curmudgeons. Our SS-30, SS-5699 and SS-300 adhesive sealants are perfect for automotive gasketing by having excellent resistance to motor oil exposure conditions.
Tums® is a trademark of the antacid product from Glaxo Smith Kline.
Case History #10
Adhesion and modulus
A construction sealant firm wanted less cracking in the sealed joints. They were utilizing in their formulation a high level of a powerful adhesion promoter, along with low surface area untreated silica. The durometer was 50 Shore A after 30 days and the modulus was high, > 150 PSI. Also, the elongation was low ~ 200%. This firm did not test modulus at all. It only looked at durometer after 7 days when this product was at 35 Shore A. It seemed that the adhesive strength of the sealant exceeded the cohesive strength and the sealant cracked down the middle.
The lesson here: is that in a flexible joint application, a low modulus product is required to accommodate the thermal expansion and contraction encountered in building joints. Less than 100PSI is required for joint movement applications and 50 to 75PSI work well. In these applications, modulus should be measured along with durometer and monitored as a quality parameter, however, only after full cure. Our SS-301 adhesive sealant has a low, < 100PSI modulus and accommodates high joint movement applications.
Case History #31
The foaming filter sealant
We were called into an oil filter manufacturing firm that utilized a methoxy cured, adhesive RTV sealant as a hem flange sealant. The methoxy RTV is a moisture cure system that crosslinks upon exposure to moisture. After dispensing onto the flanges and flange rolling to seal prior to cure, the oil filters are then painted through a paint line and then run though ovens to dry the paint. The filters were then racked and allowed to cure for a week before testing.
Problem: the customer was seeing voids in the cured sealant. The supplier wouldn't help, saying only that their RTV product was void/gas bubble free in their package. The paint drying oven temperature was 100oC.
Solution: The oven temperature exceeded the methanol by-product boiling point temperature. The oven flash cured the outer regions of the RTV and trapped bubbles, which made a foam. This weakened rubber/foam did not pass their performance criteria. We recommended that the customer replace the RTV with an oxime system. It had a higher 83oC vs. 60oC boiling point and solved the problem.
The lesson here: customers often misuse products to suit their production line requirements. You need to insure that there is a match between their needs and your products capabilities. Our SS-30 product perfectly met the requirements of this application including a higher boiling point.
Case History #36
The cracked coating
A large multi-national firm was experiencing a fracturing problem in their coating upon exposure to a long term, high intensity UV source. They had at their disposal a large R&D center, but had no luck in solving the problem. So we were called in, in an attempt to address the problem. Methyl silicones are well known to be invisible to UV. This is due to their fully saturated bonds and high spatial free environment, which enables a high bond rotation and energy dissipation capability. Upon reviewing what they were doing, we told them that we had their solution. The senior staff laughed. At that point, we should have just left, however we told them that the problem was based on what they were using, a methyl phenyl silicone rubber product. David then filled the whiteboard with the explanation. We then called their R&D center via speakerphone. David explained some basic chemistry to the R&D center personnel associated with double bonds, energy absorption, and phenyl silicone: the unsaturation of the phenyl group, with phenyls being UV absorbers, and carbon bonds not having the energy dissipation capability of a silicone, which cracked the double bonds. With this project David had come full circle, the client being a former employer.
The lesson here: was to switch to a 100% methyl system, which is now working well. Our Silicone Solutions Gels SS-4060 thru 6139 are all methyl gels with a full range of durometers/penetrations.