Pressure impregnation

In the United States creosote specification AWPA PI/89 is intended for the treatment of timber for land and fresh-water use, and the heavier grade AWPA P13/89 for the preservation of marine piling and timber. In the United Kingdom a British Standard Specification, BS. 144/90, Part 1, specifies three grades of creosote two for pressure impregnation and one for bmshing appHcation. The standards of the West European Institute for Wood Preservation (WEI) are often used in Europe. 

Procedure for vacuum pressure impregnation (with particuiar reference to HT motors)... 

Figure 9.3(a) A stator core during vacuum pressure impregnation (resin-poor insulation) (Courtesy NGEF Ltd)... 

Figure 9.3(b) Stator core after vacuum pressure impregnation (VPI)... 

Insulating materials and their properties Ageing of insulation Practices of insulation systems Procedure for vacuum pressure impregnation Maintenance of insulation Monitoring the quality of insulation of HT formed coils during manufacturing... 

Hot isostatic pressing (HIP), 16 169 cemented carbides, 4 657 ceramics processing, 5 662 Hot isostatic pressure impregnation carbonization (HIPIC), 26 767 Hot-melt adhesives, 1 530-532... 

Termites and powder post beetles cause many thousands of dollars loss of wood installations. Creosoting and vacuum-pressure impregnation of Wolman salts into pine lumber provides protection however, there exist many structures where in situ protection against termites would be of value. 

Larsson and Simonson (1994) studied the mechanical properties of acetylated Pinus sylvestris and Picea abies. The MOR and MOE decreased by about 6 % for pine, but increased by about 7 % with spruce samples after acetylation. Samples for this study were vacuum/pressure impregnated with acetic anhydride, excess anhydride was then drained off and samples were heated at 120 °C for 6 hours. The hardness of the acetylated wood samples was also found to increase, which was considered to result from the lower MC of the modified wood. Acetylated samples were also found to be less susceptible to deformation when subjected to varying RH. 

How does our research stand in rendering wood fire retardant What is the effect of fire-retardant treatments on the fire performance properties of wood and on the physical and mechanical properties of wood that are important to its utility Discussion will be limited to fire retardancy obtained by pressure impregnation, which is currently the most effective method. Fire-retardant coatings, wood-plastic combinations, and chemical modifications of wood will not be considered. 

The success of this treatment system indicated a breakthrough in the development of a commercially successful system whereby fire-retardant chemicals are pressure impregnated into the wood and fixed or converted to a leach-resistant state without serious impairment of the desirable natural wood properties. This development has stimulated research with leach-resistant type treatments. Chemicals employed usually involve organic phosphates and compounds that can react with phosphorous-containing chemicals or with the wood cellulose structure to give permanence of treatment. 

The Osmose company has been marketing a phosphate-free fire retardant (FirePro ) that contains borate and other materials. It is for the pressure impregnation of lumber and plywood and is claimed for Interior Type A high temperature (HT) applications.26 27... 

Figure 1. Scanning electron micrographs of (a) sheath of aligned matrix produced by low-pressure impregnation, and (b) transversely oriented matrix produced by high-pressure impregnation.

Although it is possible to incorporate organotin polymers in wood by vacuum or pressure impregnation with solutions of preformed polymer, it would be preferable to utilize monomer impregnation followed by in situ polymerization because the smaller molecular size, as well as the low viscosity of monomers, is conducive to efficient penetration of wood. Therefore, vinyl monomers in which the TBT group is chemically bonded, such as TBTMA, are used for in situ polymerization in wood (2). 

Compact, continuous, and uniform anatase nanotubules with diameters in the range 50-70 nm were produced inside PAO nano-templates by pressure impregnating the PAO pores with titanium isopropoxide and then oxidatively decomposing the reagent at 500 °C [230], Cleaning the surface of the template and repeating the process several times produced titania nanotubules with a wall thickness of 3 nm per impregnation. The tube exteriors appeared to be faithful replicas of the pores in which they were formed. 

Pines such as P. radiata are permeable and ean be dried quiekly (Table 8.4a). However their pits aspirate and if subsequently pressure impregnated with an aqueous preservative such as copper-chrome-arsenate using the full eell proeess they eannot be redried nearly as rapidly. If sueh resaturated, preservative treated timber were to be dried using the schedule in Table 8.4a steep moisture gradients would develop leading to severe checking. A milder schedule is required. Treated pine takes approximately twiee as long to dry. 

Creosote is the oldest modem wood preservative. It is formulated by fractionating coal tar distillate that in turn is a by-product of high temperature carbonization of coal. Creosote is a complex mixture of polycyclic aromatic hydrocarbons (PAHs), tar acids and tar bases that makes it such an effective broad-spectrum preservative. Difficult-to-treat woods can be pressure impregnated with hot creosote for lengthy periods. The wood has improved dimensional stability. However treated wood sometimes bleeds and has an oily surface, so it is not the first choice for applications where there is a high probability of human contact. Workers may dislike creosote treated wood as it soils their clothes and on contact photosensitises the skin. 

Today, just in time stock control favours a totally different approach, that of kiln-drying followed by pressure impregnation to obviate the long diffusion holding period. 

Siau, J. F. Pressure Impregnation of Refractory Woods. Wood Science, 1970, 3 (1) 1-7. 

Many polymeric systems have been adapted for applications in which they become an integral part of electrical equipment. Polymers may be used, for example, to protect components of electrical systems or to enhance the mechanical and electrical integrity of electrical apparatus. These applications are referred to as vacuum pressure impregnation, potting, encapsulation, and casting some of these are illustrated by the following examples. 

---