Open Molding Test Questions and Correct Answers (All Modules), With Complete Solution 2024.

Open Molding Test Questions and Correct Answers (All Modules), With Complete Solution 2024. What are the basic process principles of open molding? Saturating a fiber reinforcement with a thermoset polymer matrix; depositing this reinforcement onto an open mold (exposed to the atmosphere, not enclosed); curing the laminate at ambient temperature. What are two advantages of composites that are used in construction applications? Material weight savings for transportation and assembly, and composites typically have excellent weathering and corrosion properties. A tool, often referred to as a mold, is used to produce parts in the open molding lamination process. Once a part has been designed, what is the first step in the tooling process? The first step is to produce a master model mode, also commonly referred to as a pattern or plug. If several molds will be required to support production it is best to construct a durable polyester or epoxy reinforced master plug from the first mold. What two things affect the durability of a master model mode? The materials and the method of construction affect the durability of a master model. During the cross-inking process, what happens to the thermoset resin? The thermoset resin shrinks. What must happen after a pattern (or mold) has been conditioned (sanded and buffed) before it is ready for production? The pattern or mold must be waxed with a release agent that has been specially formulated for open molding lamination and is compatible with the specific gel coat and resin that will be used to produce the part. The tooling gel coat should be applied in two evenly sprayed coats of what thickness? 18 + 2 wet mils for each coat. Many modern mold builders have master models in ____________ formats? Digital formats for easy reference and use with modern equipment and software packages. What is used to determine when to do a preventative maintenance program for composite tools? An evaluation of the number of parts (pulls) that a mold will allow before polystyrene begins to appear and spread over the mold surface, creating sticking. What is the purpose of the cured resin (resin matrix)? to protect the fiber reinforcement; transfer loads through the reinforcement; provide shape to the laminate What does it mean for a resin system to be pre promoted by the resin supplier? Additives, formulation and chemicals have been put into the resin at the manufacturer to provide particular properties for its intended use in production. What are the five basic components of a resin system (resin matrix)? resin polymer monomer inhibitor promoter initiator is added to begin the cure Why are polyester resins the most commonly used resin systems in open molding lamination? Polyester resins are low cost and the cured physical properties meet many of the needs in the commercial composite industry. Why would a higher cost vinyl ester resin be used in an open molding lamination? It offers superior corrosion resistance and mechanical properties. What is a polymer backbone? The polymer backbone refers to the specific type of molecule that is the basic building block of the resin system. What are the purposes of a monomer as it is used in a polyester resin? It co-reacts with the backbone polymer in a resin system when polymerization (crosslinking) takes place (reactive); It reduces the viscosity of the polymer to provide a workable liquid product, acting as a diluent. What are the two most common monomers used with polyester and vinyl ester resins? Styrene; Methyl methacrylate (MMA) What is the purpose of using an inhibitor? Raw styrene and polyester resin will self-polymerize without the addition of initiator. This polymerization cannot be stopped, but can be controlled with the addition of an inhibitor, which consumes free radicals, which naturally occur in the resin. Why is a promoter required in open molding lamination resins? Initiators do not react rapidly enough in resin to produce a workable gel time at room temperature. A promoter must be added to the resin to interact with the initiator and produce a reasonable cure time. What is the difference between a catalyst and an inhibitor? In technical terms, a catalyst causes a chemical reaction but does not enter into the reaction. An initiator initiates a reaction but becomes consumed in the process. Resin cures by a process called free radical polymerization. Explain this process. The initiator decomposes into free radical molecules, which begins the process of crosslinking the polyester molecules with the styrene molecules in the resin. Increasing the amount of initiator added to the resin will increase the rate of cure. What is the most common initiator used in open molding lamination? MEKP (methyl ethyl ketone peroxide) What are the general additives that are used to modify and enhance resin properties? Fillers; Pigments and colorants; Fire retardants; Suppressants or film formers; UV inhibitors; Conductive additives What are the active molecules in an initiator? Oxygen What can cause a poor cross-linking reaction in open molding lamination? A poor initial cross-linking reaction can be caused by low initiator levels, improper amounts of promoter or inhibitor in the resin, and/or low shop temperature. What production procedures can be implemented to correct quality problems that are a direct result of a faulty cure? Use the proper initiator in the proper ratio; maintain shop temperatures above 60° F at all times; pay attention to details such as initiator mixture, compressed air quality; evaluate application techniques. What is the definition of viscosity as it relates to open molding lamination? Viscosity is a measure of fluid resistance to flow. This is the proper definition that should be used when discussing resins. In open molding, what flow characteristics must a resin have? A resin must be easily pumped through application equipment; it must efficiently wet-out the reinforcing fiber; it must not drain out of the laminate within the period between wet-out and gel time. Fumed silica is used to impart thixotropic properties to a resin.Explain how a thixotropic agent functions in a resin system. The chemical network is made of weak molecular attractions that are easily broken when shear stress is placed on the liquid. When at rest, the attraction between fumed silica particles is strong enough to resist flow. However, as soon as energy is applied to the system in the form of agitation, the shear stress breaks the weak bonds, and the liquid behaves as a less viscous material. In a thixotropic system, the apparent at-rest viscosity is high and becomes lower as the material is sheared, and then recovers to its at-rest state within a short time after being undisturbed. What are the important properties that are of interest when examining molding resins? Sag resistance; Shear thinning; Thixotropy; Settling; Temperature Why do glass fibers account for over 90% of the fibers used in open molding? They are inexpensive to produce and have relatively good strength to weight characteristics. What are the major categories of reinforcement used in open molding lamination? Woven reinforcement; Knitted reinforcement; Continuous strand roving; Chopped strand mat; Unidirectional reinforcement Why are core materials used extensively throughout the composites industry? They are used to fabricate stiff, lightweight composites products. The use of core materials is also called sandwich construction. What defines the hand lay-up method of open molding lamination? The hand lay-up method involves the use of roll-stock reinforcements such as chopped strand mat, woven roving, knitted fabrics, or textile fabrics. What are the two methods of distributing resin in hand lay-up open molding lamination? Manual application Mechanical application Describe the spray-up method of open molding lamination. The spray-up method uses equipment referred to as a chopper gun. The chopper gun pulls continuous strand roving (gun roving) through a chopper unit. The fiberglass roving is cut into short lengths and merged into a resin stream that is deposited on the mold. The chopper gun mixes the resin, initiator, and glass reinforcement while the operator controls the laminate application. Name three types of open molding laminating technology that are utilized for higher volume applications. Filament winding Pultrusion Continuous lamination What is gel coat? Gel coat is a specialized form of polyester or vinyl ester resin that is formulated as an on-mold coating. It is applied to the mold surface and becomes an integral part of the finished laminate. What is the primary function of a gel coat? To protect the fiberglass laminate. What is exotherm? During the cross-linking reaction, heat is generated. This heat is known as exotherm. The speed of the cross-linking reaction (gel coat cure) is affected by what three things? the formulation of the gel coat; the temperature of the gel coat; the amount of initiator that is used Gel coat is normally designed to be sprayed on a mold surface with the laminate then applied over the gel coat film. Gel coats are designed to cure in a thin film and are typically sprayed in wet film thickness of ______________? Between .016" and .024" What are the three critical components to the gel coating process? the gel coat; the spray equipment; the method of application Why should drums or containers of gel coat be rotated in storage so the oldest material is always the first to be used? All gel coats and polyester resins have a limited shelf life. Over a period of time, the properties of the material will change. Polyesters may turn solid in the container after prolonged storage or exposure to extremely high temperatures. Why is the temperature of gel coat very important to the quality of the spray application? As gel coat cools, the viscosity (thickness) increases. The colder the gel coat becomes, the more difficult it will be to achieve a good fan pattern from the spray gun. What are the ideal temperatures for the application of gel coats?