The function and structure of breast rollers

The breast roller is the first roller on the paper machine, which is the starting part of the net. Its function is to support the forming net. The forming net changes direction on the chest roller, and after passing through the breast roller, the non working surface of the forming net becomes the working surface. In many cases, the chest roller is also a dewatering component on the net, and the pulp fed onto the net can be partially or mostly dehydrated on the breast roller.

The breast roller is a tube roller structure that applies sufficient rigidity and minimal deflection to prevent wrinkling of the copper mesh. In order to reduce the load on the chest roller driven by the copper mesh, the weight of the chest roller should be light. Generally, the chest rollers of small and medium-sized low-speed paper machines have no medium to high height, while those of large high-speed paper machines have slightly medium to high height.

In the past, breast  rollers were mostly made of copper, but now they are generally made of thin-walled steel tubes, wrapped with 3-4mm thick copper skin or 8mm thick rubber (cloth hardness 12-17 degrees), and there are also chest rollers covered with fiberglass ladles. The chest roller needs to undergo static and dynamic balance tests.

In order to prevent fiber blocks from entering between the breast roller and the copper mesh, a plastic or wooden scraper is installed on the roller surface to clean the roller surface, and a water spray pipe is also installed between the breast roller and the lower lip plate to clean the roller surface. Usually, there is an extension plate on the back of the scraper, which guides the white water removed through the net into the first white water tray.

The breast roller also has a dewatering effect, and its dewatering amount can be controlled by the landing point of the pulp flow. If the pulp stream falls directly onto the breast roller, a large amount of water can be removed, which has a partial shaping effect. If the pulp is sprayed onto the forming plate, the dewatering effect on the breast roller is minimal, and the forming of the paper sheet is controlled by the table roller or dewatering plate.Modern high-speed paper machines that produce thin paper using free pulp use water absorbing breast rollers for strong dewatering. In this case, most of the water is removed by the chest roller. The dehydration mechanism of the breast roller is similar to that of the case roller.