Factors Affecting the Process Stability of a Heat Set Web Offset Press

In order to improve the colour control of a heat set web offset press, the effects of the process parameters on the stability of ink transfer on an eight unit press were investigated. The press was fully instrumented, experiments performed on normal production copy using orthogonal array techniques and the colour was measured using a spectrophotometer. This paper discusses in detail those parameters which affect process stability. Of these the press temperature and roll speeds were found to be most significant. They were also found to interact with the local coverage in a complex manner. A theory is postulated to explain these effects based on a heuristic analysis of the mechanical and fluid interactions in the duct region. Modelling work which is being used to validate this theory is briefly discussed.