Hand Lay-ups

This is the oldest and in many ways, the simplest and most versatile process for producing RP products. 

Depending on the resin preparation, the material in or around a mold can be cured with or without heat, and commonly without pressure. Curing needs include room temperature, heat sources, bag (BagM), 

The general process of hand molding can be subdivided into specific molding methods such as those that follow. The terms of some of these methods as well as others reviewed here overlap the same technology the different terms are derived from different sections of the RP industry during different periods since 1940. 

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Hamamelis [84696-19-5] Hamamelis virginiana Ham curing Hammerhead ribozyme Hammer mills Hammett equation Hamposyl 0 Hamposyl C Hamposyl C-30 Hamposyl L Hamposyl L-30 Hand factor Hand lay-up... 

The hand lay-up or spray-up process, used universally for the production of laminar composites incorporating glass fiber reinforcement, is most efficient for the manufacture of large parts, such as boats, bathtubs, tanks, architectural shapes, and recreational accessories. Resins intended for spray-up processes are usually modified with thixotropic additives, such as fumed siHca (1%), to reduce the risk of drainage when appHed over large vertical mold surfaces. Molds are also made from ERP for short-mn products usually surfaced with a tooling gel coat to provide consistent surface quaHty and appearance. 

Gel coats are pigmented polyester coatings appHed to the mold surface and are an integral part of the finished laminate. Gel coats are used widely on hand lay-up and spray-up parts to enhance surface aesthetics and coloration as weU as to provide an abrasion-resistant waterproof surface that protects the underlying glass-reinforced stmcture. 

Hand Lay-Up and Spray-Up. In hand lay-up, fiber reinforcements in mat or woven form are placed on the mold surface and then saturated with a Hquid polymer, typicaHy a polyester resin, that has been chemically activated to polymerize (cure) without the addition of heat. Multiple pHes of reinforcement and multiple cure steps aHow very heavy waH thicknesses to be achieved. 

For spas, shower stalls, bath tubs, etc, a gel coat containing no fiber reinforcement is appHed first to the mold. It forms a smooth, strong, impervious, durable chemical, weather, and wear-resistant surface. The bulk of the resin, which may be reinforced with glass fiber, is appHed by hand lay-up or by spray gun. The article is then cured at or near ambient conditions. 

Ease of cure, easy removal of parts from mold surfaces, and wide availabiHty have made polyesters the first choice for many fiber-reinforced composite molders. Sheet mol ding compound, filament winding, hand lay-up, spray up, and pultmsion are all weU adapted to the use of polyesters. Choosing the best polyester resin and processing technique is often a challenge. The polyester must be a type that is weU adapted to the processing method and must have the final mechanical properties requked by the part appHcation. Table 1 Hsts the deskable properties for a number of fiber-reinforced composite fabrication methods. 

Glass-reinforced polyester is the most widely used reinforced-resin system. A wide choice of polyester resins is available. The bisphenol resins resist strong acids as well as alkahne solutions. The size range is 2 through 12 in the temperature range is shown in Table 10-17. Diameters are not standardized. Adhesive-cemented socket joints and hand-lay-up reinforced butt joints are used. For the latter, reinforcement consists of layers of glass cloth saturated with adhesive cement. 

Slides Cars steel-pressing plant car assembly line hand lay-up of GFRP polymer moulding plant. 

The cross-linking reaction is carried out after the resin has been applied to the glass fibre. In practice the curing is carried out either at elevated temperatures of about 100°C where press mouldings are being produced, or at room temperature in the case of large hand lay-up structures. 

An interest has been developed in the use of vanadium naphthenates as accelerators. In 1956 the author found that if MEKP was added to a polyester resin containing vanadium naphthenate the resin set almost immediately, that is, while the peroxide was still being stirred in. Whereas this effect was quite reproducible with the sample of naphthenate used, subsequent workers have not always obtained the same result. It would thus appear that the curing characteristics are very dependent on the particular grade of resin and of vanadium naphthenate used. It was also observed by the author that the gelation rate did not always increase with increased temperature or accelerator concentration and in some instances there was a retardation. Subsequent workers have found that whilst the behaviour of the naphthenate varies according to such factors as the resin and catalyst used, certain vanadium systems are of value where a high productivity in hand lay-up techniques is desired. 

The major process today is the hand lay-up technique in which resin is stippled and rolled into the glass mat (or cloth) by hand. Moulds are easy to fabricate and large structures my be made at little cost. 

For mass production purposes matched metal moulding techniques are employed. Here the preform or mat is placed in a heated mould and the resin poured on. The press is closed and light pressure ( 501bf/in ) applied. Curing schedules are usually about three minutes at 120°C. It is possible to produce laminates using less resin with pressure moulding than with hand lay-up techniques and this results in better mechanical properties. 

There is one particular type of filler whose value can be in no doubt. This is the so-called thixotropic filler exemplified by certain fine silicas and silicates which appear to increase the viscosity of the resin on standing. These are useful in minimising drainage of resins from vertical and near-vertical surfaces during hand lay-up operations. 

Some typical properties of polyester-glass laminates are given in Table 25.1. From these figures it will be seen that laminates can have very high tensile strengths. On the other hand some laminates made by hand lay-up processes may have mechanical properties not very different from those of thermoplastics such as the polyacetals and unplasticised PVC. 

Property Hand lay-up mat laminate Press formed mat laminate Fine square woven cloth laminate Rod from rovings... 

The resins are also used for coating on to moulds to give a good finish that is to be used for polyester hand-lay up operations. 

The Manual processes cover methods such as hand lay-up, spray-up, pressure bag and autoclave moulding. 

Generally the lower the process pressure, the larger the product that can be produced. With most labor-intensive fabricating methods, such as RP hand lay-up with TS plastic, relatively slow process curing reaction time of the plastic can be used so that there is virtually no limit on size (Fig. 8-63). 

Class C applies to hand lay-up, vacuum bag, and other methods using molds made of RP/C material. It applies to parts that would be covered by Class B when they are not molded with a high degree of care. 

Resin Transfer Molding Spray-up Hand Lay-up Mat-Preform Compound... 

The U.S. Navy pioneered in glass-TS polyester RP (hand lay-up) large boat construction with the production of an 8.5 m... 

Basically, the hand lay-up molding process was used, with 98wt% of the structure via... 

Fig, 8-62 Example of hand lay-up using glass matt-TS polyester RP. 

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