Hatschek process

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

Since ancient times, natural fibers have been used to reinforce brittle materials. For example, thousands of years ago, Egyptians began using straw and horsehair to reinforce and improve the properties of mud bricks. In more recent times, large-scale commercial use of asbestos fibers in a cement paste matrix began with the invention of the Hatschek process in 1898. However primarily due to health hazards associated with asbestos fibers, alternate fiber types have been investigated and introduced throughout the 1960 s and 1970 s. 

The first widely used manufactured composite in modern times was asbestos cement, which was developed in about 1900 with the invention of the Hatschek process. Now, fibres of various kinds are used to reinforce a number of different materials, such as epoxies, plastics and ceramics. Here we will concentrate on the use of fibre reinforcement in materials made with hydraulic cement binders. 

Figure 9.1 Schematic description of the Hatschek process (after Wiiliden [I]).

Hatschek process [31] see Section 9.1. Composites made using this process typically contain 7-15% fibres by volume [32],... 

Figure 10.38 Effect of PVA fibre content on the flexural stress vs. deflection curve of a cement composite produced by the Hatschek process in combination with 3% wood pulp (after Hikasa and Genba [129]).

Cellulose cement sheets cement reinforced with cellulose fibres derived by pulping processes. These composites are produced by the Hatschek process and are applied in many instances as asbestos replacement or as the processing fibre in a hybrid composite (see Chapter 11) ... 

Hatschek [1926] pubUdied a study of the throttling of the free area in a medhuu, following the depo on of sofids. The effect is most pronounced in the deposition of the first layer of particles and this early work demonstrated that the structure of subseqent deposits will be influenced by the initial throttling process. The resistance of a cloth phis a thin lay of cake is nmch greater than would be expected from the sum of the resistance of the dean cloth and the resistance of the layer. 

Among several production methods the most commonly used were the so-called Hatschek, Magnani and Manville processes. The asbestos fibre cement elements were also produced by shotcreting. More details on the production methods may be found, among other sources, in Hannant (1978) and in Bentur and Mindess (1990). 

The most common production method is the Flatschek process for sheet products, and its modification (Mazza process) for pressure pipe making. A schematic description of a Hatschek machine is presented in Figure 9.1 [1], Five stages of production can be identified ... 

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