Plastic article or earthenware shaping or treating: apparatus – Shaping orifice and downstream work contacting gaseous...
Reexamination Certificate
1997-02-14
2001-09-25
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Shaping orifice and downstream work contacting gaseous...
C425S140000, C425S141000, C425S326100
Reexamination Certificate
active
06293778
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to blown film extrusion lines, and specifically to operations of the inlet and outlet blowers of blown file systems.
2. Description of the Prior Art
Blown film extrusion lines are used to manufacture plastic bags and plastic sheets. A molten tube of plastic is extruded from an annular die, and then stretched and expanded to a larger diameter and a reduced radial thickness by the action of overhead nip rollers and internal air pressure. Typically, air is entrained by one or more blowers to provide a cooling medium which absorbs heat from the molten material and speeds up the change in state from a molten material back to a solid material. Additionally, blowers are used to provide air pressure which is utilized to control the size and thickness of the film tube. One type of blown film extrusion line utilizes an air flow on the exterior surface of the film tube in order to absorb heat. A different, and more modern, type of blown film extrusion line utilizes both an external flow of cooling air and an internal flow of cooling air in order to cool and size the film tube.
As stated above, blowers are utilized to provide air to the interior of the film tube. Typically, a supply blower is provided in order to supply air to the interior of the film tube, and an exhaust blower is provided in order to exhaust air from the interior of the film tube. Typically, the supply blower and exhaust blower are under electrical control during production operations. However, during startup of the extrusion process, in the prior art, a great deal of human intervention is required in order to establish the bubble. Typically, a human operator will first control the supply blower until the extruded film tube is closed at its upper end by engagement with the overhead nip rollers. Then, the exhaust blowers utilized to remove air in order to prevent expansion and eventual breaking of the extruded film tube. A balance between the supply blower and the exhaust blower must be obtained in order to allow for continuous production of the extruded film tube. The startup of an extruded film is a relatively difficult operation to perform, and generally requires a relatively highly-skilled employee to oversee or perform the startup operations.
SUMMARY OF THE INVENTION
It is one objection of the present invention to provide a method and apparatus for startup of an extruded film tube which includes a supply blower, an exhaust blower, and a controller member, including executable program instructions which define at least one control routine for automatic and coordinated control of the supply blower and the exhaust blower during startup.
The control routines may comprise a startup routine which is utilized in initiating the extruded film tube, a blower optimization routine which is utilized to optimize the operating speeds of either or both of the supply blower and the exhaust blower, and a valve optimization routine wherein an operating condition is established for either or both of the supply blower and the exhaust blower in a manner which optimizes operation of a valve member which is utilized to control the application of air from the supply blower to the extruded film tube.
It is yet another objective of the present invention to utilize prior recorded operating conditions for either or both of the supply blower and exhaust blower in order to take advantage of the value of prior experience with a particular blown film line.
It is yet another objective of the present invention to provide an additional routine which can be utilized to detect bubble breaks during and after the startup operations.
These and other objectives are achieved as is now described.
A method and apparatus is provided for startup of an extruded film tube. The method and apparatus is used in a blown film extrusion apparatus in which film is extruded as a tube from an annular die and pulled along a predetermined path. A means is provided for varying a quantity of air within the extruded film tube. Preferably, the means includes a supply blower which supplies air to the extruded film tube in an amount corresponding to a supply control signal, and an exhaust blower which exhausts air from the extruded film tube in an amount corresponding to an exhaust control signal. A controller member is provided. The controller member includes executable program instructions which define at least one control routine for automatic and coordinated control of the means for varying during startup of the extruded film tube. The controller directs a series of supply control signals to the supply blower and exhaust control signals to the exhaust blower in order to set their optimum operating conditions. In the preferred embodiment, a control interface is provided for receiving operator instructions during startup of the extruded film tube. The controller further includes program instructions for receiving the operating instructions and integrating the operating instructions into the at least one control routine. In the preferred embodiment, a valve member is provided between the supply blower and the extruded film tube. The valve member is under control of the controller member, and is utilized for varying admission of air into the extruded film tube and for controlling the circumference of the extruded film tube after startup of the extruded film tube.
In the preferred embodiment, a variety of control routines may be provided. In a startup routine, the controller member initiates operation of the supply blower and the exhaust blower by first initiating operation of the supply blower in accordance with at least one predetermined operating parameter, and then initiating the exhaust blower in accordance with at least one predetermined parameter.
In a blower optimization routine, at least one of the supply control signal and the exhaust control signal is determined, at least in part, from at least one prior recorded control signal. Preferably, a table is generated in controller memory which records over time the optimum settings of the supply blower and exhaust blower. During startup, the blower optimization routine may be utilized to take advantage of the prior historical knowledge of the blown film apparatus.
In a valve optimization routine, an operating condition is established for at least one of the supply blower and the exhaust blower in a manner which optimizes operation of the valve member. In the preferred embodiment of the present invention, the objective is to allow the valve member to operate in a preferred and substantially linear range of closure conditions.
In a bubble break detection routine, a position signal (which indicates the position or size of the bubble) is utilized in combination with at least one software timer in order to detect a break in the extruded film tube. In the preferred embodiment of the present invention, one software timer is utilized to suppress operation of the bubble break detection routine until a portion of the startup routine is completed. Then, a second software timer is utilized in order to identify unacceptably long intervals of interruption in the position signal, which is interpreted to identify a break or collapse of the extruded film tube.
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Hunn Melvin A.
Leyson Joseph
Nguyen Nam
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