The following may be considered as standard instructions on how to use Epoxy and Polyurethane compounds in most applications. Since these materials are employed in a wide variety of applications, each with its own peculiarities, some of the steps presented here may not be applicable in all cases. It is best to contact the material supplier for specific instructions, especially for the more unique application of these products.
IMPORTANT
Always read the Manufacturer's Safety Data Sheets (MSDS) and observe the recommended precautions before using any material.
Single Component Epoxy
Processing Steps
Unlike two component products, the hardeners and accelerators are contained within the single formulation. In many cases, the reaction starts, although extremely slowly, as soon as the product is made. One of the by products of this reaction is heat. The heat generated is extremely small in the beginning and, since this heat will intern speed the reaction, the process will accelerate unless the material is kept cool prior to and during use. This internal heat generation also has an impact on shelf life.
Single Component Epoxy processing Steps
| Shipping | Should be shipped under cool temperatures but above freezing. Freezing could cause crystallization that can only be reversed by heat which in turn may exceed the activation temperature. During the summer, the extreme heat in transport trailers could be high enough to exceed the activation temperature and initiate cure. |
Storage |
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| Filled | Store under cool temperatures at or below 20°C. Depending on the viscosity, invert containers periodically to keep the fillers in suspension. Agitate before use. |
| Unfilled | Store under cool temperatures at or below 20°C. Depending on the chemistry, there may be some separation of liquid components and/or pigments . Best to agitate before use. |
| Shelf Life | Can be increased by cool storage. Do not freeze!!! |
| Applying | Depending on the viscosity, if possible, mix and de-air under vacuum. Apply in even thickness onto clean, dry surfaces. Remove or allow excess to drip off prior to curing. |
Dipping |
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| Best method | It is best to place the component being dipped into a vacuum tank and draw the material in from the bottom using the vacuum. This allows for both the material and the component to be de-aired. |
| Alternate method | Lower the component to be dipped into the container containing the material. Draw vacuum until there is minimal bubbling. Some products may never stop bubbling because they contain volatiles that will continue to be stripped during the vacuum process. The coarse air will be removed usually after 5 minutes of vacuuming. |
| Curing | Allow any excess material to drain off into the dipping container. This may require suspending the part at an angle over the tank to allow the material to drain from flat horizontal surfaces. Place into an oven and cure according to the supplier's instructions. |
| Cautions | Depending on the chemistry, some single component materials will develop considerable heat (exotherm) during cure and could represent a fire hazard if improperly used. Materials designed for thin film applications (such as adhesives) will usually develop greater exotherm. It is highly recommended that materials designed for thin film applications are not used for potting or in heavy sections. Attempting to heat single component materials in an oven to reduce viscosity could result in dangerously high, runaway exotherm and possibly fire. |
Two Component Epoxy
Processing Steps
Depending on the formulation, two component epoxy compounds can be heat cure, cured at room temperature or UV cured. Furthermore these products may or may not contain fillers.
Two Component Epoxy processing steps
| Casting/Potting | The casting process utilizes a mould. The part is placed into the mould and the compound is poured and cured. The mould is subsequently removed and is not part of the finished item. The potting process involves a container that remains part the finished component throughout its service life and it acts as the mould during manufacturing. |
| Preparation | The component to be encapsulated must be clean and dry. The mould surfaces must be clean and treated with the appropriate release agent for casting. For potting, the container surfaces must be clean, dry and prepared for best adhesion. The ultimate bond strength of the potting compound to the case will be as strong as the weakest link in the bonding structure. If the surfaces are contaminated, the ultimate bond strength will depend on the adhesion of the potting compound to the layer of contaminant. Each component of the encapsulating system (i.e. resin and hardener) should be mixed thoroughly, individually, to make each product homogeneous. If pre-heating is required, the components should be mixed while hot. |
| Mixing | The resin and hardener should be weighed individually and mixed together. The mixing container should be clean and dry. Containers made out of paper or cardboard are not recommended as they are often coated and, unless carefully chosen, the coating can contaminate the product being mixed. Do not use wood stir sticks as the wood may be moisture contaminated. Use stainless steel or plastic devices. Volumetrically determined proportions are not recommended as weighing the components is significantly more accurate (except in the case of automated dispense equipment). The resin and hardener should be mixed thoroughly, scraping the sides of the mixing container. The mix should be de-aired prior to use ( 29" of Hg is sufficient in most cases). |
| Pouring | Ideally, the mould should be poured under vacuum. Alternately, the mould should be de-aired after pouring. Pouring the material into the mould should be done slowly, maintaining a continuous flow, into one corner of the mould. This will allow the product to rise, finding its own level and pushing the air ahead of the rising material thereby minimizing air entrapment. Heat may be applied to reduce the viscosity but the trade-off will be a shorter pot life and faster gel time. |
| Curing | Gellation and curing should be carried out according to the manufacturers instructions. There must be enough reservoir of encapsulant provided to replenish the gelling epoxy as it shrinks. Different cure schedules and temperatures may work but can result in altered cured properties. Be careful not to inadvertently thermal cycle the potted component before it is fully cured. Inadvertent thermal cycling can occur in many ways. For example; a part may be placed on a cold surface for a period of time before it is placed into the post cure oven or to complete the curing process at room temperature. Blowing flash off with cold air will have the effect of thermal shocking the component. |
| Part Clean-up | It is easiest to remove unwanted flash right after gellation has occurred, prior to full cure. It is also best to make minor cosmetic repairs at this time simply by applying left over mixed material to the effected areas. |
| Equipment Clean-up | It is best to discard the mixing containers and stir sticks. If they are considered re-usable then they should be thoroughly cleaned, prior to material gellation, with the solvent recommended by the material manufacturer. Dispense equipment should be flushed periodically either with the recommended solvent or with fresh material well before the expiration of the pot life of the mixed material contained in the dispense line(s). |
| General | Paying attention to maintaining uniform material and mould temperatures will eliminate many problems. In addition, it is also critical to maintain the appropriate temperature gradient between the mould or container and the part inside. For best results the gellation process should commence from the part towards the mould or container while at the same time, from the mould or container toward the part. Ideally the encapsulant will gel last somewhere in the middle between the part and the mould or container. This will require some initial experimentation with temperatures. Depending on the type of compound and processing used the heat source may be the exotherm generated during the reaction or externally applied by ovens or heated moulds or both. Smaller assemblies being cast or potted will generally work without requiring any of the above experimentation, simply by following the supplier's recommendations for processing. |
Single Component Polyurethanes
Processing Steps
Two component Polyurethane compounds may be room temperature or heat cure. They may or may not contain fillers. They are generally moisture sensitive and care should be taken to prevent contamination.
Single Component Polyurethanes processing steps
| Preparation | The component to be encapsulated must be clean and dry. The mould surfaces must be clean and treated with the appropriate release agent for casting. For potting, the container surfaces must be clean, dry and prepared for best adhesion. The ultimate bond strength of the potting compound to the case will be as strong as the weakest link in the bonding structure. If the surfaces are contaminated, the ultimate bond strength will depend on the adhesion of the potting compound to the layer of contaminant. Each component of the encapsulating system (i.e. resin and hardener) should be mixed thoroughly, individually, to make each product homogeneous. If pre-heating is required, the components should be mixed while hot. |
| Mixing | The resin and hardener should be weighed individually and mixed together. The mixing container should be clean and dry. Containers made out of paper or cardboard are not recommended as they are often coated and, unless carefully chosen, the coating can contaminate the product being mixed. Do not use wood stir sticks as the wood may be moisture contaminated. Use stainless steel or plastic devices. Volumetrically determined proportions are not recommended as weighing the components is significantly more accurate (except in the case of automated dispense equipment). The resin and hardener should be mixed thoroughly, scraping the sides of the mixing container. Avoid moisture contamination during mixing. The mix should be de-aired prior to use ( 29" of Hg is sufficient in most cases). |
| Pouring | Ideally, the mould should be poured under vacuum. Alternately, the mould should be de-aired after pouring. Pouring the material into the mould should be done slowly, maintaining a continuous flow, into one corner of the mould. This will allow the product to rise, finding its own level and pushing the air ahead of the rising material thereby minimizing air entrapment. Heat may be applied to reduce the viscosity but the trade-off will be shorter pot life and faster gellation. |
| Curing | Gellation and curing should be carried out according to the manufacturers instructions. There must be enough reservoir of encapsulant provided to replenish the gelling urethane as it shrinks. Different cure schedules and temperatures may work but can result in altered cured properties. Be careful not to inadvertently thermal cycle the potted component before it is fully cured. Inadvertent thermal cycling can occur in many ways. For example; a part may be placed on a cold surface for a period of time before it is placed into the post cure oven or to complete the curing process at room temperature. Blowing flash off with cold air will have the effect of thermal shocking the component. |
| Part Clean-up | It is easiest to remove unwanted flash right after gellation has occurred, prior to full cure. It is also best to make minor cosmetic repairs at this time simply by applying left over mixed material to the affected areas. |
| Equipment Clean-up | It is best to discard the mixing containers and stir sticks. If they are considered re-usable then they should be thoroughly cleaned, prior to material gellation, with the solvent recommended by the material manufacturer. Dispense equipment should be flushed periodically either with the recommended solvent or with fresh material well before the expiration of the pot life of the mixed material contained in the dispense line(s). |
| General | Paying attention to maintaining uniform material and mould temperatures will eliminate many problems. In addition, it is also critical to maintain the appropriate temperature gradient between the mould or container and the part inside. For best results the gellation process should commence from the part towards the mould or container while at the same time, from the mould or container toward the part. Ideally the encapsulant will gel last somewhere in the middle between the part and the mould or container. This will require some initial experimentation with temperatures. Depending on the type of compound and processing used the heat source may be the exotherm generated during the reaction or externally applied by ovens or heated moulds or both. Smaller assemblies being cast or potted will generally work without requiring any of the above experimentation, simply by following the supplier's recommendations for processing. |
| Critical Items | Moisture contamination is most often the cause of problems. Polyurethanes are moisture sensitive by nature. All containers and storage tanks should be purged with Nitrogen and should be sealed at all times. It is not possible to reverse moisture contamination. Moisture will have a major impact on gel time and will effect cured properties. Extremely contaminated urethanes will look like a foam when cured. |
