Air-laying process

Air-laying is the most widely used process for producing single-layer high-bulk nonwovens. The basic principle of the process is illustrated in Figure 8.3. 

In the dry laid process, the conventional staple fibers are used, which are usually 12 to 200 mm or longer. The fibrous web is prepared using the classical textile carding machine or air laying machine to separate and orient... 

Four basic methods are used to form a web, and non-wovens are usually referred to by one of these methods dry-laid, spun-laid, wet-laid and other techniques. Carding, garnetting and air-laying are examples of the dry-laid processes. The dry-laid processes provide maximum product versatility, since most textile fibers and bonding systems can be utilized and conventional textile fiber processing equipment can be readily adapted with minimum additional investment. 

Variations on this basic process are (i) vacuum bag moulding and (ii) pressure bag moulding. In the former process a flexible bag (frequently rubber) is clamped over the lay-up in the mould and a vacuum is applied between the moulding and the bag. This sucks the bag on to the moulding to consolidate the layers of reinforcement and resin. It also squeezes out trapped air and excess resin. The latter process is similar in principle except that pressure is applied above the bag instead of a vacuum below it. The techniques are illustrated in Fig. 4.67(b) and (c). 

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