Slabstock Molding Free-Rise Foaming

Temperature control of the raw materials used in slab production is extremely important. An entire production run can be ruined if the temperature of one of the materials is allowed to change, causing a pressure change and off-ratio output. The density and other properties of slab foam are dependent upon the temperature of the foam ingredients. Foam density increases as the temperature of the foam intermediates exceeds 90°F (32 C). The temperatures of the ingredients are usually kept between 70° and 90°F (21° and 32°Q (8). 

The width of the finished foam bun is determined by the spacing of the adjustable sideboards which bank the paper through. The dimension may be up to 80 inches (203 centimeters) and, for economic reasons, it is usually a multiple of the desired width of the end product. The height of the bun (finished foam product) is a function of throughput and conveyor speed and may be up to 40 inches (102 centimeters). Interrupted slab operations may be used where it is not economically practical to produce foam on a continuous-slab basis. The resultant slabs or buns may be 60-72 inches (152-183 centimeters) wide by 80-96 inches (203-244 centimeters) long by 12-15 inches (30-38 centimeters) high. On-o f or intermittent equipment is used. While in a continuous-slab operation the first few feet of material can be sacrificed, such is not the case here (6). 

The rise time for airless sprayed urethane foam is about 30 seconds. It can be refoamed for additional thickness after this period. The foam can be walked on after 3-4 minutes and reaches its full properties in 24 hours. The airless spray gun is held about 30 inches (76 centimeters) from the surface and moved steadily over it (12). Dispens- 

Ability to lay down an expanding foam without causing its collapse or density change. 

Possibility of cross-section molding without excessive sacrifice in density. 

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