1 Epoxy / Urethane Users Handbook - Crosslink Technology Inc.

6 E p o x y / U r e t h a n e u s e r s h a n d b o o k C r o s s l i n k T e c h n o l o g y I n c . w w w . c r o s s l i n k t e c h . c o m Insulation Class: A B F H Temperature Rating: 0 105 C 0 130 C 0 155 C 0 180 C Practical Hardness Reference - White eraser 35-45 - Pink eraser 45-55 - Rubber stamp 55-65 - Hard eraser 65-75 - Medium rubber 75-85 25-30 Rubber shoe sole 85-95 30-40 Rubber Roller 95-100 40-50 Garden hose - 50-60 Hard book cover - 60-65 Wood desk top In some cases the recommended post cure consists of step curing at different temperatures for different periods of time. - 65-70 Moulded plastic - 70-75 Wood yard stick A manufacturing method where components are placed into containers and the containers are filled with a thermoset material. The containers remain an integral part of the assemblies in service. Diagram - 75-80 White board MODULUS MOISTURE RESISTANCE The ability of a cured material to resist absorbing moisture. POWER FACTOR RESISTIVITY SHORE HARDNESS 125 Shore D Refers to the stiffness of a material and is defined as Load/Change in shape when loaded. It is expressed in p.s.i. or MPa. A material can be loaded in tension (Tensile Modulus), flexion or bending (Flexular Modulus), compression, torsion etc. POTTING 95 90 25-30 The reduction in linear dimension that occurs in materials during the process of solidification (cross linking), expressed as a percentage of the original dimension. POST CURE 86 Shore A LINEAR SHRINKAGE POT LIFE - The period of time, after mixing or the application of heat, that the material remains useable (pourable) in the particular application. Is the reflection of the electrical losses (in the form of heat) at a specified frequency in an insulating material. The ability of an insulator to resist the flow of electric current through it. It is expressed in ohm-cm. Is the measured hardness of a cured material. Softer products are on the shore A scale, harder materials are on the shore D and Rockwell scales. Hardness Cross Reference Shore A Shore D Rockwell M 50 10 - 70 15 - 90 32 - 100 45 - - 74 - - 78 32 - 82 63 Feels like: SPECIFIC GRAVITY The mass per unit volume of a material divided by the mass of the same volume of water at a standard temperature. Expressed in 3 grams/cm . SURFACE RESISTIVITY The resistance to the flow of electric current on the surface of a specimen (between opposite edges). TENSILE STRENGTH The pulling force required to break a standard size specimen. 2 Expressed in pounds/in . TENSILE LAP SHEAR STRENGTH A measure of adhesive strength defined as the force required to break an adhesive junction in the form of a lap joint when a shear stress is applied to it. A lap joint is made by placing one substrate over another and bonding the overlapped sections together. THERMAL CONDUCTIVITY The ability of a material to conduct heat. The amount of heat that passes through a specimen of a material in a period of time until the 0 difference in temperature between the two surfaces is 1 C. THERMAL CYCLE One or more gradual changes in the temperature of the medium in which the device operates. Always involves a transition time from hot to cold.

7 E p o x y / U r e t h a n e u s e r s h a n d b o o k C r o s s l i n k T e c h n o l o g y I n c . w w w . c r o s s l i n k t e c h . c o m THERMAL SHOCK A sudden and marked change in the temperature of the medium in which the device operates. There is no transition time, the change is directly from hot to cold. THERMOSET A product that is, once solidified, is very difficult or impossible to reliquefy. As opposed to Thermoplastic materials that may be reliquefied usually by the application of heat. THERMOPLASTIC A polymer that is solid at room temperature or at another specified temperature but may be liquefied repeatedly when heated above that temperature. Unlike Thermosets which undergo a chemical change to form a three dimensional network, thermoplastic polymer molecules generally remain linear and separate after processing. THIXOTROPIC Materials that have the ability to cling and build on surfaces. This property does not directly relate to viscosity. Examples of this are shaving cream, whipped cream etc. VISCOSITY Is the measure of a liquid materials ability to flow. It is usually expressed in centipoises. (See Centipoise above) VOLUME RESISTIVITY The resistance to the flow of electric current through a 1 cm cube of material. It is expressed as ohm-cm. YELLOW CARD A category of products that have been tested and certified by Underwriters Laboratories Inc. based on their use and intended application. UL recognized systems and components are listed yearly in the Recognized Components Directory and documented by the so-called "yellow card" Cracking (4) Excessive (5) Shrinkage Mix ratio, proper resin and hardener mix, part pre-heat, cure, gel and post cure time/temperature, uniform filler content, incorrect cure temperature, trapped air bubbles or sharp edges on part. Significantly different wall thicknesses. Fillers not dispersed properly, incorrect preheat temperature, incorrect mix ratio, not thoroughly mixed, gellation or cure temperature too high Mix ratio, lead lag problems, incorrect part temperature, sharp edges, trapped air bubbles, incorrect gel, cure and post cure temperatures, settled fillers. Significantly different wall thicknesses. Off ratio, process temperatures, filler settling, improper mix and incorrect pre-heat temperature. Notes (1) Most cure problems are mix ratio related. Accurate weighing of the resin and hardener followed by thorough mixing is very important. Dispense equipment can go off ratio through blocked lines, leaky seals and valves etc. Always hand mix a sample to confirm that the material hardens as it should. If it does, there is a dispense or handling problem that must be corrected. (2) EPOXY/URETHANE TROUBLESHOOTING TIPS Most soft spots are due to improper mixing resulting in areas of excess resin or hardener. Lead/lag problems in dispense equipment and not thorough enough hand mixing are the most common problems causing soft spots. (3) Symptom Not (1) Hardening Soft Spots Air (3) Bubbles (2) Check for (Hand Processing) Weight accuracy of resin and hardener, not thoroughly mixed. Thorough mixing (longer, scraping the container bottom and sides) Moisture in the part itself or paper container or stir stick, mixing too violent. Check for (Dispense Machine) Check weights just before mix head, not enough elements in static mix head, blocked line, leaky seal. Lead/Lag problems due to leaky valves, air in lines, leaky seals. Leaky seals, part not dry, air in feed lines, filling the part to fast, moisture in the part. Air bubbles are most commonly caused by improperly filling the mould or the container. Ideally, the material should be poured into one corner and allowed to rise slowly pushing the air ahead of it. Bubbles can also be caused by moisture in the air or in the part being potted. An air conditioned room and drying the parts will solve this problem. The application of vacuum, either to the mix or to the part being filled, may be necessary depending on part configuration and complexity. (4) Cracking is the result of internal stresses that develop in the material during the curing process. These stresses can be so great as to overcome the strength of the material. Cracking can also be caused by stressing a part in some manner before it is fully cured and had a chance to develop full strength. An example would be thermal cycling a component before the epoxy is fully cured or causing excessive shrinkage by shorter cure times at higher temperatures. Micro cracks caused by sharp edges embedded in the casting can propagate to form fully developed cracks.

8 E p o x y / U r e t h a n e u s e r s h a n d b o o k C r o s s l i n k T e c h n o l o g y I n c . w w w . c r o s s l i n k t e c h . c o m 4. (5) Too much shrinkage is most commonly caused by incorrect preheat temperatures in heat cure systems and too much localized exotherm in room temperature cure products. In every case, the epoxy or urethane will start to cure around the component at the highest temperature. Curing will progress from the hottest to the coolest area. Since shrinkage occurs during cure, the compound will “replenish” itself by drawing material from the cooler areas of the casting where gellation has not yet started. Built in stresses are higher if the material cures from the inside out or from the outside in. Ideally, the mass should start curing at the same time from the inside out and the outside in to yield the least amount of built in stresses and the least amount of shrinkage. . Epoxy compounds are used to cast various shapes and sizes of components. Although epoxies are relatively simple to use, there are some basic steps that must be followed to establish a trouble free casting operation. Epoxy casting compounds must be carefully selected to suit the application at hand. The following are the basic considerations for selecting an appropriate epoxy compound: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Processing limitations Tool (mould) design Viscosity Reactivity Exotherm Vapour pressure Shrinkage Expansion characteristics Thermal shock capabilities Thermal stability characteristics Processing limitations Consideration must be given to the availability of appropriate processing equipment. Epoxy systems are available to suit hand casting, automated casting, heat curing and higher temperature (oven) curing. Epoxy compounds may contain fillers or may be unfilled liquids. Tool (mould) design The following are the basic considerations for tool design in casting with epoxy compounds: 1. The pour hole should be located for the shortest path into the cavity being filled. 2. Provide vent openings to allow air to escape as the epoxy fills the cavity. Air vents should be provided for all areas where air might be trapped such as flat surfaces and around intricate inserts. 3. A reservoir of material should be available to draw from as the epoxy shrinks during the gellation process. Most often the reservoir will be located over the pour hole which is usually the largest opening into the mould. 5. Avoid sharp corners and undercuts wherever possible as these are areas conducive to air entrapment. Provide uniform wall thickness (mass) throughout the tool to allow for uniform heating and to prevent large temperature variations due to different rates of cooling. Viscosity The lower the mixed viscosity the easier it is to process the epoxy. The mixed viscosity of two component epoxy compounds can be reduced significantly by separately heating the resin and hardener prior to mixing together or warming the mixture itself. Storing materials containing fillers under heat will require constant agitation to prevent filler settling and the possibility of an off ratio mix. Heating will normally result in shorter pot life. Reactivity o "For every 10 C rise in temperature the reaction rate doubles" This means that for every o 10 C rise in temperature, the pot life (the time during which the mixture remains pourable) is reduced by (half) 50%. For example; if an epoxy system is formulated to gel (become firm) in o o o o 30 minutes at 25 C (77 F), then if warmed to 35 C (95 F) it will gel in approximately 15 minutes. Exotherm Exotherm is the heat generated by the compound, above the cure temperature, during the reaction. The amount of heat (exotherm) generated depends on the epoxy formulation and the (mass) amount of product being reacted at one time. The exotherm generated by resins and/or hardeners heated to reduce the viscosity will be greater than without the application of heat. As a general rule, fast reacting epoxy systems generate higher exotherm during the reaction. Vapour pressure If a curing epoxy system becomes too hot, it will generate gas bubbles which, if the bubbles form just before gellation (hardening), can become trapped in the structure. Vapour pressure is also a key consideration for the use of vacuum to remove air from the epoxy mixture. Certain key ingredients such as accelerators or portions of the curing agent itself can be stripped out of the mixture under vacuum. Shrinkage Shrinkage is the reduction in volume during cure. Excessive shrinkage will cause internal stresses and serious degradation in the performance of the solidified epoxy. Epoxy systems containing fillers shrink less than unfilled epoxies. As a rule, the higher the filler content the lower the shrinkage. Providing a reservoir of product to replenish the shrinking epoxy improves the end result.

9 E p o x y / U r e t h a n e u s e r s h a n d b o o k C r o s s l i n k T e c h n o l o g y I n c . w w w . c r o s s l i n k t e c h . c o m Thermal expansion characteristics This must be considered especially if the casting contains embedded component such as inserts within the cured epoxy. Large differences between the expansion characteristics of the epoxy and the embedded inserts can be the cause of cracking and reduced thermal cycling abilities. In general, the more flexible the cured epoxy the more it will expand and the higher the filler content the lower the rate of expansion. Symptom Thermal shock capabilities The higher the elongation capabilities of the cured epoxy the better the thermal shock capabilities. Unfortunately, highly flexibilized systems exhibit rather poor thermal stability. The epoxy system must be formulated to achieve a suitable compromise between cured hardness, tensile strength and elongation to achieve the desired characteristics for the application. Thermal stability The thermal stability of a cured epoxy system is its ability to operate at elevated temperature while maintaining a specified set of minimum properties. A common test method to determine thermal stability is % weight loss in a period of time at a given temperature. Since every manufacturing process is somewhat unique and the parts manufactured must meet different performance requirements, it is not possible to provide hard and fast rules that could apply to all processes and materials. The following is a general set of trade-offs caused by specific changes in the handling of epoxy compounds: Result Action Mixed Viscosity Pot Life Gel Exotherm Shrinkage Time De-mould Time Heating the mix Lower Shorter Shorter Higher More Shorter Cooling the mix Higher Longer Longer Lower Less Longer Heating the mould Lower NE More Sorter Cooling the mould Higher NE Recommended actions based on symptoms experienced Shorter Higher Longer Lower Less Longer Prob. of Cracking Higher Less Recommended corrective actions Excessive shrinkage during gellation Reduce mould temperature, reduce mix temperature, increase reservoir size. Bubbles in casting. Mix the resin and hardener together more gently avoiding turbulence, de-air the mix before use, pour slowly into one area, make sure inserts are dry and free of any volatile substances, avoid high humidity. Skinned over cavities in Reduce mould temperature, reduce insert temperature, increase the casting. reservoir size. Surface blemishes. Clean tool surfaces, reduce the amount of mould release applied to the tool, slightly reduce the mould temperature. Part sticking in tool. Clean tool surfaces from baked on deposits, apply a thin even layer of mould release. Cracking Reduce mould temperature, Reduce the difference between the insert temperature and the mould temperature. Soft spots in part Probably an improper or off ratio mix. Mix resin and hardener more thoroughly scraping the sides of the mixing container. Excessive yellowing of part after post cure. Some products will experience surface oxidization in post cure. For best results cure immersed in an inert oil. Automated dispense equipment for Epoxy and Urethane compounds Higher Lower Epoxy and urethane compounds are best processed through automated dispense equipment, especially in high volume production situations. From time to time, problems are encountered due to various causes, resulting in the improper cure of the epoxy or urethane mix. Check List o Check that the correct amount of resin and hardener is dispensed just prior to the mix head. This is best accomplished by removing the mix head and placing individual cups under each opening, dispensing the material and weighing the contents of each cup. Depending on the location of the ratio check valves, a simple

10 E p o x y / U r e t h a n e u s e r s h a n d b o o k C r o s s l i n k T e c h n o l o g y I n c . w w w . c r o s s l i n k t e c h . c o m ratio check does not always reveal the problem because these valves are often located before lengthy feed lines and checks at this point will not reveal off ratio situations caused by back pressure. o Check that the mix head is clean and clear of obstructions. If the equipment has been functioning properly for some time and this problem has not been encountered before, it may be assumed that the mix head is doing its job. If the materials being dispensed are different from before or the system frequently encountered this problem all along, it may be worthwhile to consult the supplier of the mix head. Some products are harder to mix together than others. The number of elements, the diameter and/or the length may have to be increased. In the case of dynamic mix heads, the orifices or rpm may have to be adjusted. o Check that the solvent flush valve is functioning properly. Leaky solvent flush valves can allow cleaning solvent to enter the mix and interfere with the reaction, cause bubbles and soft spots. On the other hand, valves that don't fully open will not allow the lines and/or mix head to be flushed clean, leaving residual amounts of mixed material to gel or cure causing partial blockages. o Check the dispense lines for obstructions. Reduced dispense line diameter, due to settled fillers or gummed up material, could not only cause increased back pressure but also cause insufficient supply of the effected component, especially in the presence of the increased back pressure. o o o Check the timing and synchronization of check valves. Some shut off valves are mechanically linked to each other while others are operated individually but in sync by electronics. If they are not exactly in sync, there will be extra resin or hardener in the line and the next shot will be off ratio. Some equipment manufacturers use solenoid valves for this purpose. Particles preventing the valve from s

Product Viscosity in Centipoise Water 1 cps Milk 3 cps SAE 10 Motor Oil 85 - 140 cps Castor Oil 1,000 cps Karo Syrup 5,000 cps Honey 10,000 cps Chocolate Syrup 25,000 cps 275 Ketchup 50,000 cps Sour Cream 100,000 cps Shortening 1,200,000 cps . Epoxy and Urethane compounds can be heated to reduce viscosity however there are other .