1) Two-Roller Glue Spreader.
The two-roller glue spreader primarily consists of upper and lower spreading rollers and a glue pan. The lower spreading roller is partially submerged in the glue pan, and the adhesive applied to the upper spreading roller is transferred from the lower roller. As a veneer passes between the two spreading rollers, contact with the rollers causes the adhesive on their surfaces to be applied to both the upper and lower surfaces of the veneer. The amount of adhesive applied is primarily controlled by adjusting the gap between the upper and lower spreading rollers and the pressure exerted by the upper roller. Generally, the thicker and narrower the veneer, the greater the pressure exerted by the rollers on the veneer, resulting in a smaller amount of adhesive applied; conversely, a thinner and wider veneer results in a larger amount of adhesive applied. The shape and density of the grooves on the roller surfaces also influence the amount of adhesive applied. Ideally, the liquid level of the adhesive in the glue pan should reach approximately one-third of the lower spreading roller's diameter; levels that are either too high or too low will adversely affect the amount of adhesive applied.
2) Three-Roller Glue Spreader.
The three-roller glue spreader features an additional metering roller positioned adjacent to either the upper or lower spreading roller. During the spreading process, the amount of adhesive applied is determined by the gap between the spreading roller and the metering roller. When the metering roller is positioned next to the upper spreading roller, adhesive is supplied via a hose from a glue pump, utilizing the trough formed between the spreading and metering rollers to store the adhesive; when the metering roller is positioned next to the lower spreading roller, adhesive is supplied directly from the glue pan, ensuring that the amount of adhesive applied remains unaffected by fluctuations in the glue pan's liquid level. Although the three-roller glue spreader offers superior spreading quality, it allows for independent control over the adhesive amount on only one side of the veneer; consequently, it is not as widely utilized as other types of spreading equipment.
3) Four-Roller Glue Spreader.
The four-roller glue spreader incorporates an additional metering roller positioned adjacent to both the upper and lower spreading rollers, allowing for independent control over the amount of adhesive applied to the upper and lower surfaces of the veneer. The linear speed of the metering rollers is typically 15% to 20% lower than that of the spreading rollers, enabling them to function as scrapers that regulate the adhesive layer. Furthermore, the gap between the metering rollers and the spreading rollers is adjustable, ensuring that the thickness of both the upper and lower adhesive layers remains uniform and consistent. With the upper and lower spreading rollers supplying adhesive simultaneously and independently-without mutual interference-the machine is less prone to operational instability or "skipping" during the spreading process; as a result, it is a widely adopted type of glue spreading equipment.
There are two distinct configurations for the arrangement of the metering rollers in a four-roller glue spreader. 1) The upper and lower squeeze rollers are positioned on either side of the applicator roller, receiving adhesive independently from a glue pump via separate supply hoses; 2) Both the upper and lower squeeze rollers are situated on the infeed side of the applicator roller, with the upper roller supplied by a glue pump and the lower roller supplied by an underlying adhesive tank. Due to the differences in roller arrangement and adhesive supply methods, their respective functions also vary. The former ensures uniform and consistent adhesive application, thereby conserving material; the latter is better suited for scenarios requiring higher production rates.