Stay Ahead: Good Basics are Key to a Winning Strategy

By Tim Young

One of the most challenging and yet fascinating concepts about composite processing is the variation in the way materials react in different situations and conditions. The great paradox? We can use the same materials, processed by the same employees to the same specifications, day in and day out, and rarely will they react the same way every time. We manage, however, to produce high quality products despite what many industry experts feel is a myriad of variables that are almost impossible to quantify. We can end up spending profits in repair departments in an effort to produce first quality products. This effort is futile because you cannot make a first quality part out of a repair.

We have all experienced the frustration of being called to the shop or receiving a report from the production floor concerning a discrepancy or condition that directly affects the quality of our products. Or worse yet, from a customer who may not understand the complex nature of our industry and therefore can’t figure out why he paid top dollar for a product that is now less than perfect.

It’s in the Basics
John Wooden, “The Wizard of Westwood,” the great UCLA round-ball coach who is considered by many to be one of the three best college basketball coaches of all time, on the first day of practice every year made all of his players sit in the middle of the court, remove their shoes, remove the laces, and re-lace them. Not because he wanted them to know how to lace their shoes, but so that they would understand the importance of practicing the basics.

In an effort to get “back to the basics,” to re-lace our composites industry’s shoes so to speak, let’s examine some common anomalies that present challenges to the bottom line of the molded polymer processing business. Remember that a humble wise man understands that he has much left to learn, and that one can’t know too much even in what one thinks they already know.

Porosity
Webster’s New Collegiate Dictionary defines porosity as a: the quality or state of being porous. b: the ratio of the volume of the interstices of a material to the volume of its mass. Interstices is defined as, a: to stand still in the middle and stare.

How many times have we all stood still in the middle, stared at porosity, and wondered what caused it? Why is it only in certain areas? Why does it usually show up in corners? Why did it happen now? Does it happen in the same way to our competitor? How can we prevent it and most importantly, now that we have it on our part, how are we going to repair it without making it worse? (The answer to that one is that unless it is confined to an isolated area, it is nearly impossible to repair. No matter how careful we are, when we feather-sand the repair, we break the surface of the surrounding gelcoat and what we end up with is a larger area of porosity.)

This has been the topic of many discussions between fabricators. Processing equipment manufactures who will tell you that it is in the material and gelcoat suppliers who will tell you it is an application issue.

We think they are both correct. Porosity is a normally occurring phenomenon in gelcoat. We know that if you look at a cross section of cured gelcoat, that behind the seemingly non-porous surface, you will find porosity. We know that when we open a new pail of gelcoat, we can see tiny bubbles in the liquid that were blended in during the manufacturing process. We know that the thixotropic agents, fillers, and pigments that we add to gelcoat, do not help in preventing porosity.

We also know that if spray equipment and air supplies are not properly maintained and calibrated, we could be causing ourselves grief by catalyzing the gelcoat at an improper ratio or contaminating it with water, oil, or solvents. If pressure regulators and fluid pumps are not functioning properly, or the tips and nozzles on gun heads are worn, they may not be atomizing the material properly.

The question that we as composite fabricators have to answer is how can we keep porosity from hanging on to the surface of our parts? The first thing we need to know is that we are fulfilling our responsibility to our employees by providing them with the proper training to do their jobs. It is foolish for us to assume that because an operator has many years of experience that he is practicing good controlled spraying techniques as established by the American Composites Manufacturers Association for instance. If the operator is not applying the gelcoat properly, the naturally occurring gas in the material cannot escape. Do your company a service and order the study guide video from ACMA, the twenty five-dollar investment is nothing compared to what an untrained operator can cost you. Operators here apply the appealing cosmetic surface that first strikes customers and first impressions are so critical.

One theory about porosity focuses on what causes it to hang onto the surface of the mold, the theory concerning static electricity. This is similar to the way a balloon charged with static hangs to the vertical surface of a wall. We know that because of the dielectric strength of composites, parts and molds do not rapidly dissipate static charges. How many times have we walked by a part and felt the hair on our arms stand up or heard the snap, and seen a bolt of lightning jump from a part being lifted from a mold? If you have noticed static electricity in your plant and have porosity on the surface of your parts, you might want to consider ways to eliminate static electricity. Static sparks are also an excellent ignition source for fire.

Crazing and Cracking
Often in an effort to decrease cycle times, parts are pulled from molds before the laminate is sufficiently cured or the part is placed under excessive loads due to improper mold release application or maintenance. Because there are no high aspect ratio reinforcements in gelcoat, it is susceptible to failure under stress from bending and flexing. Many times these conditions come back to haunt fabricators even after the surface has been repaired because the reinforcing laminate has been compromised by being taken beyond the limits of it’s flexural modulus. Whenever practical, it is best practice to gelcoat and laminate in the same day and allow the parts to cure in their molds until they have reached adequate strength. This also will help to prevent the condition known as post-cure. A part that has been pulled from the mold while still in a B-Stage or “green” can deform because it is not being held in place by the mold as it reaches C-Stage or final cure.

Blisters
This is usually caused by air entrapment in the laminate or contamination on the backside of the gelcoat prior to the laminate being placed. One common cause is catalyst leaking from the resin dispensing equipment. This can easily be determined by the smell of MEKP in the blister during the repair process. Water drops, sweat, tears, moisture and acetone contamination is identified by a milky white discoloration in the laminate and blisters may not appear until the part is exposed to heat.

Pigment Separation
How to remedy when gelcoat is too heavy or rapidly applied for its thixotropic properties to hold it to the mold surface? When the material sags, runs, or puddles, the pigments have a tendency to separate from the base resin. It is generally recommended that gelcoat be applied in an initial light coat of approximately 5-7 mills. followed by two heavier coats to achieve proper coverage and thickness. This allows the solvents to out-gas. The thixotropes will take affect and result in a less porous surface. Gelcoat should be sprayed with the gun held at 90 degrees and no closer than 18 inches from the mold surface to prevent tearing the wet film. In addition, it is recommended to use the lowest possible pump pressure and maintain a proper fan pattern. All spray equipment operators should be trained in controlled spraying techniques.

Pitting
We distinguish this from porosity by the size and random pattern of differences. Pitting on the surface of gelcoated parts is caused by contamination on the mold surface or in the material itself. Since the gelcoat surface is a direct reflection of the mold, it is imperative that the mold surface be completely clean, dry, and free of any contamination from oil or water coming from air hoses, dust, dirt and air-born particles.

Low Luster on Polished Parts
Wax buildup is a common cause of dull surfaces and imperfections. When a paste wax release system is being used, care must be taken to ensure the proper removal of all build up on the mold surface. Moisture on a mold also will cause the surface to be dull.

Since we know that the finish on the surface of molded parts is a mirror image of the mold, maintaining the condition of the mold surface is paramount in producing a class “A” product.

Sometimes, particularly on molds, that have had major modifications or extensive repairs done, it is more cost effective to polish the finished part because it is nearly impossible to maintain the finish on a gelcoat mold repair.

Blotchy, Discolored, and Yellowed Gelcoat,
If a fabricator processes Polyester polymers at a temperature below 60 degrees, the monomer will not cross-link properly and when it is exposed to the sun’s UV rays, it will discolor and turn yellow. If the first skin behind the gelcoat does not react properly, the monomer can migrate through to the surface and cause discoloration. It is more cost-effective to heat a plant than to post coat a product under warranty.

One of the common mistakes that processors make is to assume that if the material being applied is within the acceptable temperature range that they are safe. The fact is if you spray gelcoat that is at 70 degrees onto a mold that is at 50 degrees; the gelcoat is 50 degrees seconds after it hits the surface of the mold. The same holds true for the reinforcement, the exotherm from a three-ounce laminate is rapidly dissipated by a cold surface and will not allow the polymer to cure properly.

Increasing the amount of initiator and promoters such as DMA makes things worse. Never modify materials on the shop floor without authorization from your supplier unless you are willing to accept responsibility for the outcome.

Creep, Alligator
Most common causes of this condition are either beginning the lamination process before the gelcoat is sufficiently cured, or the film is too thin to keep the styrene in the laminating resin from attacking the gelcoat.

Generally, the best practice is to tack test the gelcoat for sufficient cure on an area off the part. Always use a wet mil gauge to assure proper gelcoat thickness. If this anomaly occurs in small areas, it may indicate that there was an intermittent pause in the catalyst delivery system when the operator was triggering the gun. Because styrene is heavier than air, it has a tendency to settle in low spots. This can inhibit the cure of gelcoat in these areas. All spray equipment operators should be trained in controlled spraying techniques.

Laminate Print Through on Surface
This is one of those surface anomalies that can be caused by many different variables or a combination of variables. Usually it’s caused by excessive exotherm from over catalyzation, or a resin-rich laminate or too much material applied at one time. It is a common occurrence in “chopper gun shops” where the operators have not been properly trained. Ridges left in overlaps of roll stock reinforcements cause another common condition that is easily remedied. When laminators do not feather the edges of chopped strand mat, it leaves a ridge that causes a resin rich transition that transfers to the surface during the cure process.

Print through can also be caused by improper placement of reinforcements, bulkheads, and secondarily bonded back-up materials. It is a generally accepted practice to use filled resin paste as a potting compound to fair the edges of items placed in or on a laminate. Care must be exercised to assure that the items being placed are not in direct contact with the laminate because when the paste or subsequent laminate shrinks during the curing process, it will cause the point of contact to transfer onto the surface of the part.

Pre-Release
Pre-release is a term used to describe a condition where the gelcoat or laminate separates from the mold surface before the reinforcement has reached a cure of sufficient strength to hold it in the shape of the mold.

There are probably more causes of pre-release than we will ever know, but it is generally accepted that the primary causes are shrink and improper application of mold release.

We know that a larger mass of material creates a higher exotherm and greater shrinkage. We also know that when material is sprayed into an inside corner that there is a tendency for the material to be trapped in the corner and accumulate into a larger mass than when applied in a flat area, say next to the inside radius. When the larger mass in the corner shrinks, it has a tendency to close as inside corners do and pull the material on the flat surface away from the mold.

It is a common practice to use bee’s wax fillet to form a radius and transition at flanges and inserts, and to fill imperfections in patterns and molds. The melt temperature of bee’s wax is lower than the peak exotherm of gelcoat, therefore it is important to make sure that there is no residue from the wax left on the mold surface. Any residue left on the mold surface can melt and allow the gelcoat to pre-release.

Another method of temporary mold repair and forming radius is the use of plastic-based clay. This technique has been standard practice in the cast polymer industry forever and they have it perfected to a science. There is a slick little machine available from Gruber Systems that will extrude a pre-formed clay radius. This is the proper method of application and will save mold set-up and repair time and deliver a higher quality product.

Whenever possible, gelcoat should be reinforced while the mold is in the same position in which it was gelcoated. If it is necessary to move the mold after it is gelcoated, it should be moved before the gelcoat becomes set, being careful to avoid shock or vibration that may cause it to sag. If molds are moved after the gelcoat takes a set, care must be exercised not to let them bump or flex because this could cause pre-release.

There are many excellent mold release agents available to the composites industry today, which, if used according to the manufacturers specifications, work well.
We know that these are but a few of the anomalies that present challenges to all of us. We wish that we could say that we have all of the answers, but every time we think we have it all figured out, it changes and something presents us with a new opportunity to learn, hopefully not the hard way. Alvin Graves, the proprietor of White Star Boats once said that the hardest thing about growing old was learning everything over again.

At his first team meeting with the Green Bay Packers in 1959, Coach Vince Lombardi said, as quoted by Bart Starr, “Gentlemen, we are going to relentlessly chase perfection. Perfection is not attainable. But by relentlessly chasing it, we will catch excellence. I am not remotely interested in being just good.”

These are the principles that we must strive for. The men who are the pioneers of our industry that came before us passed them down. It is our responsibility to pass along the knowledge that was so freely given to us, to the next generation of composite professionals.

Tim Young is a plant manager for Plastics Unlimited in Preston, Iowa: 563.689.4752.