Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
1998-12-30
2001-04-17
Pyon, Harold (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S142000, C425S313000, C425S155000, C425S168000, C083S069000
Reexamination Certificate
active
06217802
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Broadly, this invention relates to a polymer pelletizing apparatus and to a system for controlling the position of pelletizing (cutting) knives or blades relative to a die in the polymer pelletizing apparatus. More particularly, this invention relates to a method and apparatus for electrically and automatically controlling the advancement of pelletizing knives relative to the die in the polymer pelletizing apparatus. In a specific embodiment, the invention relates to a system that advances (indexes) pelletizing knives a preset (predetermined) distance upon the expiration of a preset (predetermined) time period.
2. Description of Related Art
A polymer pelletizing apparatus typically includes a die for directing a molten polymer toward a series of pelletizing knives that cut the polymer into pellets. The pelletizing knives are attached to a drive shaft that rotates and can be advanced closer toward the die. The knives are designed so that when they are in proper contact with the die, they cut appropriately shaped and sized pellets. The contact between the rotating knives and the die causes the knives to be sharpened. Consequently, the knives also wear down. As the knives wear down, the distance between the die and the knives becomes larger. Although the distances involved are microscopic, they are nevertheless sufficient in magnitude to gradually cause the dimension and shape of the pellets cut by the knives to become irregular.
The present inventors have recognized that manually adjusting the knives creates problems because the knives are often moved too close to the die surface, resulting in excessive wear on the knives, and sometimes causing the knives to even break. On the other hand, the inventors have also recognized that with manual adjustment the knives may not be moved close enough to the die, i.e., resulting in excessive distance. The inventors have observed that this excessive distance causes the knives to become dulled as well as causing the production of irregular pellets. Still other times, the knives were not advanced at a proper time in that the manual adjustment was not made frequently enough, producing irregular polymer pellets, or was made too frequently, causing the knives to prematurely wear or break.
One approach is to maintain the knives in substantially constant pressure with the die. The inventors have observed that this approach does not adequately solve the problem because constant pressure causes the knives to wear too quickly, requiring a greater frequency of knife changes. Also, the necessary pressure is imprecisely determined and applied, often causing the knives to break. Furthermore, with these constant pressure devices, there is no way to predict when a knife change is needed. Thus, oftentimes, the pelletizing apparatus must be shut down to correct or adjust mechanical features or problems, and then later have to be shut down again for a knife change. In polymer pelletizing operations, these shutdowns cause great expense and inconvenience. If the need for a knife change could be accurately predicted, the pelletizing system could be shut down one time, to correct or adjust mechanical features and to change the knives. Accordingly, a need exists for not only controlling the indexing of the pelletizing blades to maximize their useful life, but also to accurately predict the exact time when such useful life is reached. In certain aspects, the present invention is directed to overcoming one or more shortcomings of previous methods and meeting needs of maximizing blade life and predicting blade changes.
SUMMARY OF INVENTION
The present invention provides a method of incrementally adjusting the position of pelletizing knives relative to a die in a polymer pelletizer to maximize the useful life of the knives while maintaining and producing consistent quality polymer pellets. The invention relates to an apparatus that incrementally advances the knives a predetermined distance at a predetermined time so as to maximize the use of the knives, maintain an acceptable knife sharpness and produce a quality pellet in shape and size. Specifically, the invention is directed to a method and apparatus for accurately and efficiently controlling the advancement (indexing) of pelletizing knives, preferably by advancing the pelletizing knives by a predetermined distance upon the expiration of a predetermined time period.
In a specific embodiment, a pelletizing apparatus of the invention includes a die with a surface having at least two apertures through it. The pelletizing apparatus also includes a drive shaft operably connected to a drive motor and at least one knife (blade) attached to the drive shaft. An advancing device is also included, which is operably connected to the drive shaft and operated to advance the drive shaft and the knives by a predetermined distance toward the die surface. The advancing device preferably acts to place the rotating knives in substantial contact with the surface of the die. The apparatus includes a programmable controller connected to the advancing device, wherein the programmable controller monitors the expiration of a predetermined time period and activates the advancing device to periodically and automatically advance the drive shaft and the knives by the predetermined distance toward the die surface after each expiration of the predetermined time period. Preferably, the predetermined time period and predetermined distance are constant. A timer (e.g., a clock) can be either included in the programmable logic controller or provided separately.
In another specific embodiment the invention is directed to a polymer pelletizing method, including the steps of: positioning rotating pelletizing knives at a first position; advancing the knives a predetermined distance in the direction of a die to a second position; stopping the advancement of the knives; maintaining the knives at the second position for a known predetermined period of time (“time interval”); advancing the knives another predetermined distance in the direction of the die to a third position; stopping the advancement of the knives and maintaining the knives at the third position. This sequence of advancing, stopping and maintaining the knives is repeated, preferably for the useful life of the knives. Preferably, all the time intervals are the same and the predetermined distances are identical. The first position of the knives is a starting position, i.e., a “zero point.” The starting position is preferably established through a calibration procedure. After calibration, the distance between the first position and the final position of the knives (total advance distance) is preferably known in advance and preferably corresponds (i.e., can be correlated) to the maximum amount of wear on the knives. Not only is the total advance distance known, but the total advance time can also be known, based on the total of all the time intervals, plus any times associated with the actual advancing of the knives, which should be negligible.
Additionally, in another specific embodiment, a method of the invention includes inputting, into a programmable controller, a predetermined time period and a predetermined advance distance for the knives to be advanced. The method also includes advancing the knives periodically and automatically by the predetermined advance distance toward the die upon or after expiration of the predetermined time period. This method may also include the steps of detecting the expiration of the predetermined time period; sending a signal indicating the expiration of the time period; advancing the knives by the predetermined distance toward the die after detecting the expiration; and repeating the detecting, sending and advancing steps until the pelletizer has been in operation for the predetermined useful life of the knives.
In yet another specific embodiment, the method of the invention preferably includes a setup sequence, an advancement cycle sequence, and a knife change sequence. In the setup sequence, the method st
Messina Gregory S.
Tofte Michael A.
Nguyen Thu Khanh T.
Pelletizer Knives, Inc.
Pyon Harold
Thomason Moser & Patterson
LandOfFree
Polymer pelletizing indexing system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymer pelletizing indexing system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer pelletizing indexing system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2531997