Adhesive blenders

In the use of spraying blenders, the following technique can be successfully applied. All the paraformaldehyde powder hardener and 30% of the tannin adhesive spray-dried powder is removed from the liquid glue mix. The paraformaldehyde and wattle adhesive powder are then added to the wood chips just before the adhesive blender where the liquid glue mix is sprayed onto the wood particles. Core material MCs of 10 to 12% and face material MCs of 20 to 22% can then easily be achieved in spite of the high viscosity of tannin solutions. The percentage of paraformaldehyde used should be 14% based on wattle extract solids. The adhesive pH should be, in optimal cases, 6.5 to 6.7 for face material and 6.9 to 7.3 for core material. The percentage of resin solids on dry wood should be 11% for core material and 14 to 18% for face material. 

The blending operation is an important step in the production of quality part i cleboard--uneven distribution of the adhesive will result in regions of low interparticle bonding and weak particleboard. Strict monitoring of both the adhesive and particle streams delivered to the blender is required for optimum blending. 

Dry process fibreboards are made in a similar fashion to particleboards. Resin (UF, PF) and other additives may be applied to the fibres by spraying in short retention blenders, or introduced as the wet fibres from the refiner are fed into a blow line dryer. Alternatively, some fibreboard plants add the resin in the refiner. The adhesive coated fibres are then air-laid into a mat for subsequent pressing much the same as particleboard. Pressing procedures for dry process fibreboards differ somewhat from particleboards. 

Sekulic et al. reported the online monitoring of powder blend homogeneity by NIR spectroscopy in 1996 [9]. The authors commented on the error associated with insertion of a sample thief into a powder bed due to distortion of a powder bed, adhesion of certain components to the thief with subsequent displacement, and preferential flow of some components into the thief, all factors that make the NIR method attractive and which are discussed more thoroughly elsewhere. For these reasons and others, the authors developed a method of monitoring the blending process that eliminates the need for withdrawing samples from a blender. 

Chips and shavings from scrap logs or from the processing of lumber are screened to the desired size. After drying to a moisture content of about 7 %, the chips are coated with the resin adhesive, usually to about 7-9%, solids basis. The adhesive can be sprayed onto the chips as they tumble in a blender. A wax emulsion may also be applied to reduce the water absorption of the finished board. Total moisture content of the resin coated chips should be in the range of 8-12%. Too much moisture can cause blisters when the cured board is removed from the heated press. After application of the resin, the treated flakes are spread onto trays and formed into a mat which may be prepressed, and then loaded into a multiplaten heated press for curing. Cure time will depend on the thickness of the board and may be in the range of 10-20 minutes at a temperature of 125-175°C. 

A coated granule containing a solid (carbofuran) and a liquid (diazinon) insecticide is to be prepared. The solid inseeticide is ground to a fine powder the liquid inseeticide is sprayed onto an absorbent silica. A combination of two adhesives is used. Granular (0.4-0.8 mm) quartz is first sprayed with a liquid polyurethane while tumbling the quartz in a shell blender. Once the mass is wetted the inseetieide powders are added. After tumbling the mass to adhere the powders, an aqueous solution of polyvinyl alcohol is sprayed onto the surface. In order to set the adhesive the mass is transferred to a drier and heated to about 60°C. 

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