Handling Guide

Violin-lr

Carbon Fiber Violin, Luis and Clark , Milton Massachusetts

Refer to PRO-SET Technical Data Sheets for specific handling characteristics, post cure schedules and physical properties for each of the resin/hardener combinations.

PRO-SET Epoxies are recommended for use by experienced fabricators. If you are new to high-strength laminating epoxies, read this guide thoroughly. We strongly recommend that you build representative panels using the proposed laminate schedule under expected shop conditions to fully understand working characteristics and suitability of PRO-SET Epoxies for your application. Read all safety information before using PRO-SET Epoxies.

For epoxy safety information, please visit our Safety page or contact us.


Handling PRO-SET Epoxies

This section is intended to provide an understanding of the general handling characteristics of PRO-SET Epoxies. Refer to the PRO-SET Resin/Hardener Technical Data Sheets for specific handling characteristics, post cure information and cured physical properties.

Combining PRO-SET Epoxy resin and hardener starts a chemical reaction that gradually changes the mixed ingredients from a liquid to a solid. Careful measuring and thorough mixing are essential for a complete reaction to occur.

Dispensing

Most problems related to curing of the epoxy can be traced to either inadequate mixing or the wrong ratio of resin and hardener. To simplify metering, we recommend using calibrated pumps to dispense resin and hardener. The PRO-SET 308 and 313 High-Capacity Positive Displacement Pumps are calibrated to dispense the proper working ratio of all PRO-SET liquid Resin/Hardener combinations.

Production quantity dispensing systems are available from several manufacturers. Contact our technical staff for recommendations.

Before you use the first mixture on a project, verify that the pumps are delivering the proper ratio. Refer to the verification procedure in the instructions that come with the pumps. Recheck the ratio periodically or any time you experience problems with curing. Production facilities should check pump ratios on a regular basis.

To measure by weight or volume, refer to the PRO-SET Resin/Hardener Technical Data sheets for the correct resin-to-hardener ratio.

Mixing

Mixing epoxy with error-free results involves three separate steps:
1. Dispense the proper proportions of PRO-SET Resin and Hardener into a clean plastic or paper mixing container. Never use glass or foam containers because of the danger of exothermic heat buildup. Begin with a small batch if you are unfamiliar with the pot life or working time of the epoxy.

2. Stir the two ingredients together thoroughly until blended to a uniform, homogeneous consistency. Scrape the sides, bottom and inside corners of the container as you mix. If you use a power mixer, thoroughly scrape the sides and corners of the container while mixing. Operate the mixer at a slow speed to prevent stirring air into the epoxy mixture.

Note: Resin and hardener may be dyed to assure thorough blending. Refer to QUALITY ASSURANCE CONSIDERATIONS for details.

3. Mix resin and hardener thoroughly in a container before transferring it to a roller pan, impregnator or part. Transfer the mixture immediately to maximize working time. If using additives, such as pigments and fillers, thoroughly stir in before transferring the mixture from the container.

CAUTION! Heat is generated by the chemical reaction that cures epoxy. A plastic mixing container full of mixed epoxy will generate enough heat to melt the container, if left to stand for its full pot life. If a pot of mixed epoxy begins an uncontrolled exotherm, quickly move it outdoors or to a safe, well-ventilated area. Avoid breathing the fumes. Do not dispose of any epoxy mixture until the reaction is complete and has cooled.

Pot Life

Selection of a resin/hardener combination may be based on the length of its pot life. Pot life is a term used to compare the relative rate of reaction or cure speed of various resin/hardener combinations. By definition, it is the amount of time a given mass of mixed resin/hardener will remain in the liquid state at a specific temperature.

For comparison, we determine the pot life of an individual resin/hardener combination based on either a 100 or 500 gram mixture in a standardized container, at a consistent temperature. Pot life is not intended to directly correlate to actual working life or assembly time, but indicates a resin/hardener combination’s potential working time relative to other resin/hardener combinations. An epoxy mixture’s mass and temperature during the manufacturing or assembly process contribute to its actual working life. See Controlling Cure Time.

Curing

The transition period of an epoxy mixture from a liquid to a solid is called the cure time. It can be divided into three phases: working time—also called open time or wet lay-up time (liquid state), initial cure (gel state) and final cure (solid state). The speed of the reaction, the length of these phases and the total cure time vary relative to the ambient temperature.

1. Working Time

Working time is the assembly time of mixed epoxy. It is the portion of the cure time, after mixing, that the epoxy will remain in a liquid state and be workable. The end of the working time marks the last opportunity to apply clamping pressure to an assembly and obtain a dependable bond.

2. Initial Cure Phase

The working time is over when the mixture passes into an initial cure phase and has reached a gel state. It may be hard enough to be shaped with files or planes, but too soft to dry sand. Post-cure heating may begin once the mixture has reached an initial cure.

3. Final Cure Phase

In the final cure phase the epoxy mixture has cured to a solid state and, if not post-cured, will continue to cure over the next couple of weeks at room temperature. Post-curing at elevated temperatures will shorten the final cure phase of PRO-SET Epoxies, and is necessary for components requiring the best thermal properties.

Controlling Cure Time

Several factors affect cure time and can be manipulated to extend the length of the cure time and working time.

1. Type of Hardener

Each resin/hardener combination will go through the same cure phases, but at different rates. Choose the hardener that gives you adequate working time for the job you are doing at the temperature and conditions you are working under. PRO-SET Hardeners may also be blended to provide a custom blend with an intermediate cure time. Refer to the blend profile charts in the Laminating Epoxies and Infusion Epoxies sections.

2. Mixed Quantity

Mixing resin and hardener together creates an exothermic (heat producing) reaction. A larger quantity of mixed epoxy will generate more heat and yield a shorter working time and overall cure time. Smaller batches of epoxy generate less heat than larger batches and have longer cure times. Therefore, a thicker joint, thicker laminate or layer of epoxy will cure quicker than a thin layer.

3. Container Shape

Heat generated by a given quantity of epoxy can be dissipated by pouring the mixture into a container with greater surface area (a roller pan, for example), thereby extending the working time. Since the mixed epoxy will cure at a faster rate while it’s in the mixing container, the sooner the mixture is transferred or applied, the more of the mixture’s working time will be available for assembly.

4. Temperature

Heat can be applied to or removed from the epoxy to shorten or extend working and cure times. This can be especially beneficial when assembling very large or complicated components that require maximum working time and minimum final cure time. Be sure you fully understand the effects of heating and cooling on the mold before implementing these techniques. Before mixing, moderate heat can be applied to the resin and hardener to shorten the epoxy’s working time. Conversely, a cooler box can be used to
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Before mixing, moderate heat can be applied to the resin and hardener to shorten the epoxy’s working time. Conversely, a cooler box can be used to draw heat from a roller pan to extend working time (contact PRO-SET for information about building cooler boxes). For larger operations, impregnating machines with water cooled rollers are available to extend working time.

After the epoxy is applied, a fan can be used to draw heat from the process or application and extend the epoxy’s working time. The tooling itself can be designed to both extend working time and shorten cure time.

It is possible to build tooling with tubing embedded. During processing, cool water pumped through the mold draws heat from the part, extending the working time. When the process is complete, hot water or steam pumped through the mold will speed the cure of the part. Moderate heat (hot air gun or heat lamp) applied to the assembly will shorten the epoxy’s cure time. Heat can be applied as soon as the assembly is completed, but most often heat should be applied after the epoxy has reached its initial cure. Heating epoxy that has not reached its initial cure will lower its viscosity, causing the epoxy to run or sag on
vertical surfaces. In some processing procedures, heating too soon can lower the resin content of the laminate to unacceptable levels. In addition, heating parts that contain porous materials (wood or low-density core material) can cause the substrate to “out-gas.” When the air in the porous material expands and passes through the curing epoxy, it can leave bubbles or pinholes in the cured epoxy.

Regardless of what steps are taken to control the cure time, thorough planning of the application and assembly will allow you to make maximum use of the working time of the epoxy mixture.


Application Techniques

Primary Bonding/Wet Lay-Up

PRO-SET Laminating Epoxies are designed for primary bonding of composite materials like fiberglass, carbon, aramid and various core materials. Fabrics may be wet out by hand or by roller impregnating machines. Since each resin/hardener combination will have a different viscosity, test a combination for its suitability with a particular fabric and impregnating machine setup.

Fabrics recommended for use with PRO-SET Epoxies should be classified as epoxy compatible. Avoid fabrics with styrene soluble binders or that are compatible only with styrenated resins.

Vacuum Bag Laminating

Vacuum bagging is an excellent clamping method for composite construction using PRO-SET Laminating Epoxies. Regulating the amount of vacuum pressure permits control of the resin/fiber ratio and can produce a more dense laminate, with a higher fiber volume. Generally, the higher the vacuum pressure, the lower the resin content. The optimum resin/fiber ratio for a particular component will be between 30% and 50%. A lower ratio will result in a lighter composite. A higher ratio will be heavier, yet yield higher moisture exclusion effectiveness. Various bleeder and absorber materials used in vacuum bag laminating can also influence the resin/fiber ratio. Building test panels is recommended to determine the proper vacuum bagging material schedule and vacuum pressure for a particular component.

Infusion

PRO-SET Infusion Epoxies are used for resin infusion, VARTM, RTM and other closed molding applications. Choose the resin/hardener combination that will provide proper gel time for the part and process.

Because of the many variables involved, these techniques require testing to determine the most suitable procedure and the proper resin/hardener combination for each part.

Release Fabric

In areas where you plan to do secondary bonding or additional coatings, use a release fabric (such as peel ply) over the lay-up. When peeled from the cured or partially cured surface, release fabric leaves a fine texture, free of contaminates and amine blush. After the laminate reaches initial cure and the release fabric is removed, the laminate surface is ready for bonding without further preparation. Using release fabric eliminates the need for washing and sanding in preparation for secondary bonding or coating. A laminate may be built up in several consecutive layups over period of days. Use release fabric after each day’s lay-up and remove it prior to the next lay-up. When complete, the built up layers of laminate can be post cured together.

Not all release fabrics have an epoxy compatible coating or a texture suitable for secondary bonding with epoxy. Before building a part, test for the ability to bond to a surface prepared with the intended release fabric at the proposed post-cure temperature.

Surface Preparation

The success of secondary bonding depends not only on the strength of the epoxy, but also on the ability of the epoxy to mechanically key into the surface of the material rather than chemically bond to it. If you are bonding to a surface that has not been properly prepared with release fabric, the following surface preparation steps are critical to any secondary bonding:

1. Removing Amine Blush

Amine blush is a by-product of the epoxy curing process. This wax-like film may form during the initial cure phase. The blush is water soluble and can easily be removed, but can clog sandpaper and inhibit subsequent bonding if not removed. To remove the blush, wash the surface with clean water and an abrasive pad. We recommend 3-M Scotch-brite™ 7447 General Purpose Hand Pads. Dry the surface with plain white paper towels to remove the dissolved blush before it dries on the surface. After washing with the abrasive pad, the surface should appear dull. Sand any remaining glossy areas with 80-grit sandpaper. If a release fabric is used, amine blush is removed when the release fabric is removed.

2. Cleaning

Surfaces must be free of any contaminants such as grease, oil, wax or mold release. Clean contaminated surfaces with silicone and wax remover or acetone. Wipe the surface with clean paper towels before the solvent dries. Clean surfaces before sanding to avoid sanding the contaminant into the surface. CAUTION! Provide plenty of ventilation and follow all safety precautions when working with solvents.

3. Drying

Bonding surfaces must be as dry as possible for good adhesion. If
necessary, accelerate drying by warming the bonding surface with hot air guns or heat lamps. Use fans to move the air in confined or enclosed spaces. Watch for condensation when working outdoors or whenever the temperature of the work environment changes.

4. Sanding

Sand non-porous surfaces (metal, FRP laminate, cured epoxy,
hardwoods, etc.) thoroughly to obtain an abraded surface. 80-grit
aluminum oxide paper will provide a good texture for the epoxy to key into. Be sure the surface to be bonded is solid. Remove any flaking, chalking or blistering before sanding. Wear a dust mask! Remove all dust after sanding. Laminate surfaces can be textured by using release fabric during fabrication. This may eliminate the need for additional sanding.

Secondary Bonding

Secondary bonding operations include the bonding of structural members, blocking or additional fabric reinforcing, coating, fairing or filleting to a previously cured or existing part. Once the part has cured to a solid state, a new application of epoxy will not chemically link with it, so the surface of the component must be washed and sanded (if it was not prepared with release fabric) to provide the proper surface for mechanical secondary bonds.

PRO-SET Adhesive is a two-part, thixotropic epoxy adhesive designed for secondary bonding and assembly of composite components. It cures fully at room temperature and it can be post-cured if parts are to be assembled before they are post-cured.

PRO-SET laminating resins and hardeners can be used for tabbing and taping operations either before or after post cure. Choose the resin and hardener combination that will provide the viscosity and cure speed combination necessary for the fabrics being used and to minimize drain out.

Surface preparation for paint

Wet-sand the surface to remove any flaws and provide a texture for the paint to key into. If you are using a filling or sandable primer, use 100-grit paper. Use 220-320 grit paper if no primer is used. The thinner the paint film thickness, the finer the grit of sandpaper needed. Rinse the surface with clean water and dry thoroughly. Rinse water should sheet without beading up or fisheyeing, which could be a sign of local contamination.

Re-wash with solvent if necessary and wet-sand. Allow the surface to dry thoroughly before painting.

PRO-SET Epoxies provide an excellent base for most paint systems.
Linear polyurethane paints have proven to be the most durable protection over epoxy. Regardless of the paint system used, thorough preparation of the surface is essential for good paint adhesion and a smooth finish. For coating, follow the paint manufacturer’s instructions.

Gelcoats

We have had good results with various in-mold polyester gelcoats.
Because of their superior resistance to ultraviolet degradation, polyester gelcoats are preferred over epoxy gelcoats for exterior finish applications.

Check with your polyester gelcoat supplier for recommendations and test to determine product suitability and application technique.

Some fabricators have report good success using a 2-part linear
polyurethane paint sprayed directly onto the mold surface. This coating is allowed to cure and the epoxy laminate is applied directly to the paint An epoxy gelcoat is sometimes preferred for plugs and molds.

Contact the Gougeon Technical Staff for custom product recommendations. We recommend that each brand of gelcoat or in-mold coating and/or tie coat technique be tested for suitability in a specific application. If you have any questions about testing, call the Gougeon Technical Staff.


Post-Curing

Resin/hardener combinations reach an excellent degree of cure for
most applications with only a room temperature cure. Resin/hardener combinations with LAM-251-HT and LAM-239 Hardener require an elevated temperature post-cure to achieve optimal physical properties.

Post-curing is the controlled heating of an epoxy part—after it has reached or passed its initial cure stage—to improve the physical strength and thermal properties of the cured epoxy. Each PRO-SET Resin/Hardener combination has potential maximum cured properties that can only be achieved by post-curing the part above a minimum target temperature. For each resin/hardener combination there is a range of post-cure schedules (above the minimum) that will allow the laminate to reach 100% of its potential cured properties.

Each post-cure schedule within the range has a corresponding minimum hold time. Higher target temperatures require shorter hold times—lower target temperatures require longer hold times.
Maximum properties will not be reached if the actual post-cure schedule is below the minimum. However, even with post-cure schedule below the minimum, most resin/hardener combinations will achieve increased properties.

Determine the post-cure schedule for a resin/hardener combination by the desired physical properties of the component, or by the limits of the equipment to reach or hold temperature. Thermal shock can induce flaws in the laminate. To avoid this, increase the temperature slowly and do not exceed the maximum temperature. Refer to the specific PRO-SET Resin/Hardener Data Sheet for information on post-cure schedules and cured physical properties.

Post-Cure Schedules

During a post-cure, the temperature of the part is slowly raised to the post-cure target temperature, held for a period of time, then slowly lowered to room temperature. Post-cure schedules vary depending on the resin/hardener combination, the desired laminate physical properties, and the capability of the post-cure equipment to reach and maintain a target temperature.

Elevated temperature cure may begin as soon as the laminate is laid up, but with precautions. Keep in mind that as the uncured epoxy warms, it becomes more fluid and may drain from vertical laminates or result in a reduced resin-to-fiber ratio in some processes. In addition, in thicker laminations, the heat of the post-cure added to the exothermic heat generated by a large mass of curing epoxy may be high enough to damage the laminate or mold. For these reasons, post-cure should begin after the epoxy reaches an initial cure at room temperature.

The post-cure schedule is usually determined by the mechanical or
thermal properties desired, but may also be determined by limitations of the post-cure equipment, or the ability of core materials or the mold
to withstand post-cure temperatures. Although minimum recommended
post-cure temperatures may be lower, 120°–180°F (60°–82°C) is the most effective range for post-curing most PRO-SET Epoxies. The post-cure schedule determines the maximum potential properties a resin/hardener combination can reach. The highest gain in properties occurs within 8 hours, with diminishing gain up to 16 hours. Use the resin/hardener technical data sheets as a guide for determining cure schedules.

The laminate thickness will determine the rate of temperature increase. A thick laminate may require a hold cycle to allow the temperature to normalize throughout the laminate. A core can insulate a portion of the laminate, causing that portion to lag behind the average temperature rise. Use thermocouples to monitor the temperature at various locations on the component during post-cure.

Increase the laminate temperature at a controlled rate so the laminate temperature does not exceed the thermal properties of the epoxy in the laminate. As the laminate is heated, the epoxy will continue to cure. The temperature ramp rate should be slow enough to allow for this additional epoxy cure, pushing the thermal properties of the epoxy up ahead of the laminate temperature. If the laminate temperature exceeds the thermal properties of the epoxy, surface distortion or laminate print through may occur.

Observe the following guidelines during the post-cure cycle:

  1. Increase the temperature from room temperature at a rate of 15°–20°F (8°–11°C) per hour.
  2. At every 40°F (22°C) increase in temperature, hold that temperature for an extra hour to allow internal laminate temperatures to equalize. Resume the temperature increase of 15°–20°F (8°–11°C) per hour.
  3. Continue this cycle until the post-cure temperature is reached.
  4. Hold the temperature as indicated on the resin/hardener data sheet. The physical and thermal properties of the component will continue to improve until 100% of the potential properties are reached. Lower target temperatures require longer post cure times to reach 100%.
  5. Decrease the temperature at a rate of 20°F (11°C) per hour.
  6. Hold at 95°F (35°C) for two hours to allow for normalization.
  7. Turn off heat and allow to cool to room temperature. This schedule is recommended when curing a lighter laminate.The temperature ramp speed should be decreased for molds, plugs and heavy laminates. We recommend building test panels of the finished laminate schedule to determine the ideal post-cure cycle. Thermocouple wires embedded in the test laminate will measure the temperature lag during the post-cure.

Heating Methods

Post-cure heating techniques vary depending on the size of the part and mold, the number of parts being built or on the resources available for space and equipment. If resources are available, a fully insulated oven with an electric or vented gas or oil heater provides the greatest control over post-cure variables.

Radiant heaters that generate long wave infrared radiation can be used to heat the part without the use of an enclosure. This post-cure technique is often used on large parts, when space is limited or when a limited production does not justify the cost of an enclosure.

Temperature

Temperature is monitored by surface mounted thermometers and the heaters are repositioned over the component as necessary to provide an overall post cure.

WARNING! It is difficult to accurately control the rate of temperature change and maintain a uniform target temperature with radiant heating. This may result in laminate that does not have uniform physical properties. This technique may also result in more print through of the laminate.

Post-Curing In Molds

Generally, parts are post-cured in the mold in which they were laminated. Molds that are subject to repeated use should be post-cured at a higher temperature than that required for the finished part. This allows the part to be post-cured in the mold at a temperature below the mold’s HDT, thereby avoiding distortion of the mold, mold surface or the part during the part post-cure.

Plugs used to build molds should be post-cured at higher temperatures than the mold to avoid distortion of the plug or plug surface while the mold is being post-cured. Check plugs for fairness after post-curing and fair as necessary before the mold is fabricated.


Quality Assurance Considerations

This section offers quality control measures that can be employed by fabricators, large and small, to assure consistent high performance of PRO-SET Epoxies.

Common Problems

The vast majority of problems encountered when working with an epoxy system can be traced to either improper mix ratio or insufficiently mixed resin and hardener. Metering the two components at the proper mix ratio and thoroughly blending them helps ensure consistent, high-quality results.

To a lesser extent, problems may also arise from not properly compensating for changes in temperature. It is important to understand how changes in temperature can effect the cure characteristics of epoxy and how to counteract those effects.

Proper Mix Ratio

PRO-SET pumps are designed to meter the correct ratio of resin and hardener for standard PRO-SET combinations. With any metering system, a frequent check of the pump ratio is recommended. You can use graduated containers to check the metered volume or a scale to check the ratio by weight. If the ratio is not within the acceptable range for the products you are using, corrective action must be taken. Re-check the ratio anytime you experience problems with curing.

Production facilities should check pump ratios on a regular basis.

Epoxy Ratio and Hardness

Each resin/hardener combination will achieve optimum working, cure and mechanical properties at a specific mix ratio. Refer to the Technical Data Sheets for the acceptable range for the resin/hardener combination you have chosen. If the actual mix ratio deviates from this ratio range, the physical properties of the resin system will decline as the ratio deviates from the acceptable range.

To check the cure of the epoxy we use the ASTM D-2240 method for Rubber Property—Durometer Hardness. This method is recommended for quality control purposes and not for establishing specifications. This test is performed using a durometer measuring the D scale. The indenter needle is pressed into the cured epoxy sample and the resistance is recorded on an indicator. Durometers are available from industrial supply companies like McMaster Carr or Grainger Supply. Any instrument meeting the ASTM D-2240 requirements can be used. Some resin manufacturers specify Barcol hardness readings. However, we feel the D scale Durometer is more sensitive than the Barcol tester and is more appropriate for epoxy testing. Unfortunately, there is no direct conversion from the D scale to Barcol scales.

It is often a good idea to prepare a special quality control sample for testing and to keep quality control samples of cured epoxy for future reference. It can be as easy as pouring a portion of the mixed epoxy you are using into a mold or suitable container. Label this sample and cure it under the same conditions as your project. It may be sufficient to check the hardness right on the part you are building, as long as there is a flat area large enough to use the durometer.

A fully cured sample of epoxy will usually show a durometer D scale hardness of 81-90. A sample that has not had sufficient time to cure will have a lower hardness. However, if the hardness does not increase after a reasonable amount of time, there are several possible causes which should be investigated. The temperature may be too low to allow the epoxy to cure properly, the epoxy may have been mixed at the wrong ratio, or it may not have been mixed thoroughly, resulting in localized areas of off-ratio material.

Thorough Mixing

When using a mechanical mixer to blend large batches of epoxy, it is crucial to scrape the sides and bottom of the container to ensure thorough mixing. Operate at low speed to reduce air entrapment.

Dyed Resins and Hardeners

We suggest using dyed resins and hardeners as a visual control of mixing thoroughness. A yellow dye in the resin and a blue dye in the hardener will yield a consistent shade of green when the proper ratio of resin/hardener is thoroughly mixed. Streaking due to insufficiently mixed resin and hardener is very apparent. PRO-SET has dye available to mix on site.

Instructions are provided to mix the dye at the proper ratio. If you are purchasing larger quantities of resin, we can premix dyes at our plant before shipment.


Compensating for Temperature Effects on Epoxy Curing

The working time and pot-life information for PRO-SET resin/hardeners combinations are shown on the Technical Data Sheets. Low temperatures can increase working time, cure time and resin viscosity. Higher resin viscosity due to low temperatures can cause pumps to meter off ratio. It may be more difficult to thoroughly mix a very thick resin and hardener batch. It may also be more difficult to wet-out the fabric with very thick epoxy. The  extended cure time can leave the epoxy vulnerable to damage if clamping pressure is removed too early. Higher temperatures will reduce working time, cure time and resin viscosity. The fabricator should carefully evaluate the working conditions, size of job and number of workers in choosing the correct resin/hardener combination. Shop temperatures should be observed and recorded during the fabrication of parts.