Hand Roller Application

Wall waterborne adhesives are frequently applied with hand rollers (wool or foam cover), as shown in Fig. 3. 

It is always necessary to apply two coats crosswise at 90° angle to obtain an even coat. Adhesive coating may vary from 80 to 200 g/m in one pass by pressing more or less the roller on the substrate. Primers which are always fluid, may be applied conveniently and fast on large surfaces with hand rollers. 

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This process also called just bag molding. It is the conventional hand lay-up or spray-up that is allowed to cure without the use of external pressure. For many applications this is sufficient, but maximum consolidation may not be reached. There can be some porosity fibers may not fit closely into internal corners with sharp radii but tend to spring back. Resin-rich and/or resin-starved areas may occur because of draining, even with thixotropic agents. With moderate pressure (hand rollers, etc.) these defects or limitations can be overcome with significant improvement in mechanical properties. 

In the bulk container, the paint should be of sufficiently low viscosity so that it can be readily utilized in the applicator. For application by a brush or a hand roller, the paint should readily penetrate the spaces between the bristles of a brush or the porous surface of the roller. The paint is then held by capillary/surface tension forces during the transfer to the surface to be painted. Control of brush loading is crucial in any paint application. If the brush loading is too high, the total weight of the paint becomes sufficient to overcome the capillary forces, leading to paint drip or run-off the brush, clearly an undesirable result. In contrast, if the brush load is too low, this results in a thin paint film, or a nonuniform film with thicker film over a smaller surface area [30]. To achieve the optimum film thickness one should control the flow-out properties as will be discussed below. 

The next process that must be considered in paint application is film formation. The loading eind transfer of the pednt by a brush or a roller from the bulk container to the surface to be painted is followed by regular movement of the brush or roller over the surface to transfer the load of paint from the brush to the surface and spread it out in an even layer. During this process, hand pressure on the brush causes shearing and compression of the brush bristles or fibers of the rubber foeim or fibrous mat typically covering the surface of a hand roller. The flow processes involved are very complex and very difficult to analyze. However, some attempts have been made to calculate... 

Solvent cements are usually supplied at concentrations of 10-25% solids, with viscosities in the range of 1,000-30,000 cPs. They may be applied by brush, spray, doctor blade, reverse-roll coater, hand roller, trowel, and many other application methods. The proper coating of the adhesive is obtained by establishing the correct viscosity for the particular application method. After application, the solvent is removed by ambient drying or by forced drying in heated ovens or tunnels. 

Bench coaters are roughly 20 to 35 percent faster than hand-brushing and cut waste by up to 20 to 35 percent. They start to be useful at rates of 200 pieces per day and can reach 12,000 pieces per day. Roller sizes range from 4 to 26 in, and they come with various surfaces from smooth for thin applications to increasingly coarse for heavier adhesive layers. 

Another version of finish apphcation with transfer rolls is the loop transfer system, Fig. 2.5.A loop of fabric is immersed in finish liquid and then squeezed with the fabric to be treated between squeeze rollers. The finish is transferred to the fabric at a much lower wet pickup than possible by direct immersion. These roll transfer techniques are especially useful for the backside application of finishes, for example hand builders and flame retardants, to pile fabrics (without crushing the pile). 

The main application technique in the decorative area is still by hand (brush). Hence, future trends continue to reflect attention on worker exposure and environmental issues. This is already seen in the move to low aromatic content white spirits and isoparaffin solvents in conventional systems. High solids and waterborne technologies are being developed and both possess certain advantages and disadvantages, mainly relating to appearance and ease of use. Water-based systems bring, in principle, increased potential for water pollution, as consumers continue to rinse their brushes and paint rollers under the tap and transfer the water-soluble components such as amines and biocides to the aqueous environment. The consequence of diffuse water emissions of this type is still under debate. 

Several different processes can be used to produce a laminate. In what is called the hand application process, for example, glass-fiber mats are impregnated with unsaturated polyester resins. The impregnated mats are then removed from the mold by hand and pressed between rollers. The final molding is effected by cold pressing. The method is suitable for small numbers of objects with large surface areas (e.g., boat hulls). 

The growth of TPE usage in nonautomotive applications has also been rapid. Specific parts are as diverse as dishwasher sump boots, architectural window glazing, flashlight housings, hand-tool gaskets, typewriter and printer rollers, and household plumbing seals. 

Hand Lay-uplSpray up Spray up and open contact molding (hand lay-up) in one-sided molds is one of the cheapest and most common process for making fiber composite products. Typical products are boat hulls and decks, truck cabs and fenders. In a typical open mold application, the mold is first waxed and sprayed with gel coat and cured in a heated oven at about 49°C. In the spray up process, after the gel coat is cured, catalyzed resin (usually polyester or vinyl ester at 500-1,000 cP viscosity) is sprayed into the mold, along with chopped fiber. A secondary spray up layer imbeds the core between the laminates (sandwich construction). Then it is cured, cooled, and removed from the reusable mold. In hand layup processing, continuous fiber strand mat and other fabrics such as woven roving are manually placed in the mold. Each ply is sprayed with catalyzed resin (1,000-1,500 cP) and the resin is worked into the fiber with brush rollers to wet-out and compact the laminate. 

A medium viscosity epoxy which is ideal for vertical drapping applications where minimum drain-off is desired. Works well with roller-type impregnation, although its higher viscosity makes hand wet-out slower. Recommended for use with Pro-Set hardeners, 226 (medium speed), 229 (slow) and 237 (very slow). Can be blended with Pro-Set 125. 

In the power transmission field, standard roller chain applications range from fractional horsepower drives to those requiring in excess of 1000 hp. The V4-in. pitch chains, weighing less than 2 oz./ft., have been applied to such intricate machines as microfilm projectors. On the other hand, large-pitch multiple-strand chains, weighing over 50 Ib./ft., meet the requirements of such heavy-duty service as oil field equipment (Figure 2-9). 

Flooring adhesives are used for attaching floor coverings to a variety of substrates. The adhesives must develop a strong and durable bond between the floor covering and the substrate. They should not adversely affect coverings, supports and substrates, and after application, should remain odorless and have low emissions. Usually flooring adhesives are applied to the substrate by hand with trowels or sometimes rollers. 

Contact adhesives are used where immediate and high bond strength is required. The adhesive is applied to both surfaces to be joined, and allowed to dry completely. Then the substrates are bonded, generally with hand pressure for consumer applications and nip rollers and presses for industrial bonding operations. Open time can vary from several minutes to several hours. 

Hand lay-up manual laying of fiber reinforced material and application of resin to mold to build up the thickness. Hand or roller pressure removes any trapped air. 

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