a. Field of Invention
This invention pertains to a shower oscillator for cleaning fabrics used in a papermaking machine and more particularly to a control motor for said shower oscillator.
b. Description of the Prior Art
Highly developed fabrics are used in the papermaking process in forming, pressing and drying. Studies have shown that a proper function of these fabrics requires that they be maintained in a clean condition. See for example the reference book entitled Pulp and Paper Manufacturer, Volume III, Second Edition, McGraw Hill Book Company, 1970, pages 376-385.
Several factors have contributed to a widespread recognition of the critical nature of the showering process in cleaning such fabrics. The increased use of recycled fiber has resulted in a high level of contamination of incoming furnish. This has resulted in an accelerated rate of fabric plugging. In addition, energy and environmental concerns have forced the substitution of dirty mill water for fresh water in many shower applications. Longer potential life of newer fabric designs has again placed great emphasis on more effective showering. Increased energy costs have produced financial pressures which emphasize the need for greater machine efficiency. Proper showering can significantly improve machine efficiency by allowing the higher operating speeds and extended fabric life achievable with cleaner machine clothing.
The accepted method of cleaning fabrics is showering. Originally, fabric cleaning showers were basically drilled pipes. They have developed, however, into sophisticated precision tools which are indispensable on the modern paper machine. Paper machine showers consist of a pipe which spans the fabric run and contains a plurality of nozzles. Cleaning showers are normally operated at relatively high pressure and are normally oscillated along the axis of the pipe in order to achieve eventual coverage of the entire fabric as it passes under the pipe.
Early oscillators, now essentially obsolete, used a crank arm or cam in order to produce an oscillating motion. Unsatisfactory variations in linear speed and a short operating life characterized these devices. Further developments included worm and pinion gearing as well as reversing the motor. This approach has been abandoned because of mechanical failure due to the high loads encountered in stroking large showers. Also, continuously reversing the conventional electrical motor can cause excessive heat rise and subsequent failure. More recently, hydraulic oscillators have been used. Hydraulic devices, however, require large quantities of fresh water, a significant amount of maintenance and do not lend themselves to the very low operating speeds now used.
However, recently it has been recognized that oscillation speeds much slower than those currently used will result in more effective cleaning. At the higher oscillation speeds commonly used, the jets produce a diamond shaped pattern in the clothing.
A recent commercial development is the diamond screw with ball followers, as described in U.S. Pat. No. 4,199,999. This method has been successful with smaller showers but not been able to handle the thrust loads encountered on the larger showers. The thrust load falls on a single ball follower and high point loads, resulting in early failure, are generated. Another undesirable feature of the diamond screw is the inability to adjust stroke length without disassembling the unit to add or exchange internal components.
Clearly, there is a need for an improved non-hydraulic paper machine shower oscillator featuring high reliability, slow speed capability and essentially instant turnaround.