Spray polyurethane foaming processe

Figure 8.6 Liquid (liquid), froth (center), and spray polyurethane foaming processes...

Process and Equipment. Rigid polyurethane foam processes use Ihe same high or low pressure pumping, metering, and mixing equipment for flexible foams. Subsequent handling of the mixture is determined by the end product desired. Processes include lamination, pour-in-place, molding, bun stock, box loams, and spray. 

Applications. The principal use for rigid polyurethane foams is for iasulation ia various forms utilized by a variety of iadustries. Lamiaates for resideatial sheatiag (1.2 to 2.5 cm thick with aluminum skins) and roofing board (2.5 to 10.0 cm thick with roofing paper skins) are the leading products with about 45 metric tons of Hquid spray systems also ia use. Metal doors iasulated by a pour-ia-place process coastitute another substantial use. 

Polyurethane. Polyurethanes (pu) are predominantly thermosets. The preparation processes for polyurethane foams have several steps (see Urethane polymers) and many variations that lead to products of widely differing properties. Polyurethane foams can have quite low thermal conductivity values, among the lowest of all types of thermal insulation, and have replaced polystyrene and glass fiber as insulation in refrigeration. The sprayed-on foam can be appHed to walls, roofs, tanks, and pipes, and between walls or surfacing materials directly. The slabs can be used as insulation in the usual ways. 

Foaming Process of Resol-Type Foam. The foaming processes for phenolic foam of both the resol type and benzylic-ether type are the same as those for rigid polyurethane foams. The block-foaming process (slab foaming), pouring process, continuous-laminate process, and spray process are used. See Figure 57. 

Polymers in a foamed or cellular state have many useful properties. Energy-efficient buildings have sheets (or sprayed foams) of polystyrene foam insulation in their construction, sheets made by compounding CFC-12 under pressure with liquid polymer followed by release to atmospheric pressure via extrusion. Polyurethane foams were produced using CFC-11, which was vaporized by the heat of reaction of the isocyanate with the polyol. The foaming mass was usually heat-treated to complete the process. 

Several manufacturing processes can be used to produce phenolic foams (54, 74) continuous production of free-rising foam for slabs and slab stock similar to that for polyurethane foam (65,75) foam-in-place batch process (56,76) sandwich paneling (58,77,78) and spraying (65,79). 

The Hquid monomers are suitable for bulk polymerization processes. The reaction can be conducted in a mold (casting, reaction injection mol ding), continuously on a conveyor (block and panel foam production), or in an extmder (thermoplastic polyurethane elastomers and engineering thermoplastics). Also, spraying of the monomers onto the surface of suitable substrates provides insulation barriers or cross-linked coatings. 

Polyurethanes differ from most other polymers in that polymerization frequently takes place at the same time that we are molding or forming them into a usable shape. The three most common processes of this type are reactive foaming, reactive injection molding (RIM), and reactive spray coating. 

Figures 13.4 and 13.5 show a comparison of wear properties and densities of some common shoe-soling materials the high rating of PU is clear to see. However, important as this list is, there are some disadvantages. The dominant one is cost. Polyurethanes are made from inherently expensive materials. Machinery and moulds were initially very expensive. These cost factors have improved since the early days the cost differential of more highly processed raw materials decreases as oil price increases raise the cost of basic petroleum products, and machinery costs decline as techniques are improved and as more units are required. Thus, the price of a PU foam shoe bottoming machine declined from c.a. 40 000 to 15 000 at 1973/74 prices also the cost of mould making has been halved, with the advent of metal spraying and electro-plating techniques. Nevertheless, the cost of PU soles is high, and they find their outlet in better-quality men s and children s shoes, and industrial footwear.

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