High Capacity Screw

August 17, 1995
Rev. April 1998

During the first half of 1995 Vincent made great strides in developing a low compression screw press. This is now being specified for almost all waste material dewatering applications. It is proving invaluable in the pulp and paper and plastics recycling industries.

Traditionally, Vincent presses have been used to dewater citrus peel. This requires high pressure and tight action by the press in order to break open the cells of the material.

Dewatering waste streams with fiber requires a lot less effort. It is only free water that needs to be removed from paper pulp and plastic chips. As a result the standard screw in a Vincent press over-presses these materials, resulting in jamming and reduced throughput capacity.

This problem was initially addressed a few years ago with the aid of Dr. Ashley Vincent. A change made to the compression pitch ratio greatly reduced press jams. This "Wellman" screw design became the norm used by plastics recyclers.

The new development this year involved changing the ratio between the diameters of the screw shaft, as measured at the inlet and discharge of the press. Combined with the previous pitch ratio changes, an excellent design has evolved.

With the low compression screw a wide control range is achieved. For example, in pulp and paper applications it is generally possible to "dial in" a desired solids content. This is done by adjusting the cone pressure. Typically press cake solids contents of 30% to 55%, as desired by the paper mill, can be obtained.

The new screw design permits higher press throughputs. Thus our proposals specify it as the "High Capacity" design. This is especially important in dewatering sludge from wash tanks used by plastics recyclers. Jamming is less likely to occur, abrasive wear is reduced, and at the same time a high solids content is achieved in the waste material.

April 1998 update: An even lower compression and higher throughput screw design, called the "Sterile Butterfly", is now specified for a great many applications.

Issue 30