Compounding of phenol-formaldehyde moulding compositions

Although there are many variants in the process used for manufacturing moulding powders, they may conveniently be classified into dry processes and wet processes. 

For the manufacture of medium-shock-resisting grades the preblend of resin, filler and other ingredients does not readily form a hide on the mill rolls. In this case the composition is preblended in an internal mixer before passing on to the mills. 

Extrusion compounders such as the Buss Ko-Kneader have been used for mixing phenolic resins. It is claimed that they produce in some respects a better product and are more economical to use than mill-mixers. 

High-shock grades cannot be processed on mills or other intensive mixers without destroying the essential fibrous structure of the filler. In these cases a wet process is used in which the resin is dissolved in a suitable solvent, such as industrial methylated spirits, and blended with the filler and other ingredients in a dough mixer. The resulting wet mix is then laid out on trays and dried in an oven. 

---