Chopper for cutting fiber continuously, and method

Details Chopper for cutting fiber continuously, and method Chopper for cutting fiber continuously, and method

2001-08-22

2003-09-16

Rosenbaum, Mark (Department: 3725)

Solid material comminution or disintegration

Processes

Miscellaneous

C241S235000, C241S294000

Reexamination Certificate

active

06619573

ABSTRACT:

The present invention pertains to an improved apparatus such as a chopper for chopping strands such as mineral fiber like fiber glass, synthetic fibers like polyester or polyethylene and natural fibers like hemp and cotton, or for cutting wire, ribbon, string and like materials, and the method of using the apparatus, particularly to cut fibers continuously at high speed. In the improved chopper of the present invention, the cot or backup roll elastomer material, which is preferably polyurethane, and the blade holder can be replaced much faster and easier than was heretofore possible.
In processes of making chopped fiber of various kinds, a chopper receives continuously one or more loose, unwound strands, each made up of a plurality of fibers and chops the strand(s) into short lengths generally ranging from about ⅛th inch to 3 or more inches long. The strand(s) are often moving very fast through the chopper, typically at several thousand feet per minute, but also slower at hundreds of feet per minute. Examples of such a process are the processes of making chopped glass fiber as disclosed in U.S. Pat. Nos. 3,508,461, 3,771,701, 3,815,461, 3,869,268, 4,175,939, 4,249,441, 4,347,071, 4,373,650, 4,398,934, 4,411,180, 4,551,160, 4,576,621, and 4,840,755, which references are incorporated herein by reference.
As chopping time progresses, blade edges and the elastomeric working surface layer of a backup roll on the chopper deteriorate to the point that the chopper does not chop cleanly and “double cuts” or incomplete cuts are produced, i.e. one or more individual fibers are not cut leaving the chopped pieces linked together with one or more fibers. Incomplete cuts are unacceptable because they significantly reduce product quality by causing defects in products made from the chopped fiber. Therefore, just prior to the elapsed time where incomplete cuts can no longer be avoided or where other factors such as vibration become serious, the chopper is shut down and the old cot roll or backup roll and/or the old blade roll are removed and replaced with rebuilt or new backup and/or blade rolls. This procedure requires at least 5-8 minutes and frequently more time, especially when it is necessary to replace another part on the chopper. Also, the rolls, particularly the large backup rolls are very heavy and hard to carry or manipulate in the fiberizing rooms. In some cases, the old backup and blade rolls are shipped hundreds of miles to have a new working layer cast on the metal wheels.
While the chopper is shut down for rebuild or repair, the fiber continues to issue from the fiberizing bushings on the line serviced by the chopper and must be sent to the basement as scrap, since it is impractical to stop the bushings from fiberizing. Also, the thermal balance on the fiberizing tips of the bushings are impacted negatively when the chopper is shut down because less external air is drawn into the tip area by the slow moving fibers as compared to when the chopper is pulling the fibers at thousands of feet per minute. This condition causes the thermal equilibrium of the bushing to be disturbed, and causes the glass exiting the tips to change temperature. If a chopper is down for more than a few minutes, this will cause the strand to break out (caused by fibers breaking) numerous times for many minutes after the chopper is back on line. This condition is sometimes referred to as “false starts” and this undesirable situation results in a significant reduction in fiberizing efficiency, i.e. a percentage obtained by dividing the weight of good fiber produced in a given period of time by the weight of molten glass that exited the bushings in the same period of time.
Overheated bushings caused by chopper down times of 5 minutes or more can reduce fiber efficiency significantly for 10-20 minutes or more after the chopper is restarted and chopping fiber strands again. Also, while the bushings are “hanging”, i.e. not fiberizing at high strand speed, such as when the strands are not being pulled at a speed of at least 1000 feet/minute by the chopper, etc., the melt rate of the bushings that are “hanging” changes significantly which changes the pull rate on the melter and upsets the equilibrium of the melter reducing glass quality and fiberizing efficiency.
The chopper has to be rebuilt on a regular basis and the time between rebuilds will vary depending on the diameter of the fiber being chopped, the type of chemical sizing on the surface of the fiber (most contain lubricants and binders that complicate chopping), the condition of the chopper, the speed of chopping, and the quality of the lowest quality portion of the lowest quality blade edge or backup roll working layer. Typical life times of blade rolls/backup rolls are in the range of 6-48 hours, depending on the type of fiber being chopped as explained above. A chopper typically services about 8-15 bushings, each putting out 100 or more pounds of fiber per hour, 24 hours per day, 7 days per week and 364 or 365 days per year. A typical fiber plant will have 8-20 choppers operating. Chopper down time typically costs at least ten dollars per minute per chopper. It can be readily seen that substantially reducing the down time of the choppers during rebuilds or repair will have a substantial positive financial impact on the operation.
This problem of substantial downtime of fiberization due to rebuilds of the choppers has persisted for many years in spite of the very substantial financial incentive to reduce or eliminate the problem and still persists in the industry. Very recently an indexing chopper was developed which greatly reduces downtime required to replace a cot or backup roll and this is disclosed in U.S. Pat. No. 5,970,837. While this latter invention greatly reduces the downtime of that type of chopper, there remain many non-indexing choppers. Also, the backup and blade rolls are becoming larger in diameter and heavier in an attempt to achieve longer lives of the working parts. These large and heavy backup and blade rolls on the indexing and other prior art choppers cause a handling problem, often requiring mechanical lift assist equipment. Because lift assist devices are awkward to use in the limited space around a chopper in fiber forming rooms, there is a substantial resistance to their use. As a result, lifting injuries can result and the risk is significant in spite of good lifting policies. The time required to replace the back up and blade rolls on all choppers and the difficulty of doing so would be substantially reduced if the weight of the back up and blade rolls could be reduced substantially. But, their size and weight has been increasing in the past several years.
Chopper back up rolls currently have an elastomer working layer or band that is cast directly onto a heavy, metal hub of the backup roll and then machined to a smooth surface off line before the rebuilt backup roll is mounted onto a chopper in the fiber forming room after another backup roll with a worn elastomer working portion is removed from the chopper. The worn elastomer working portion on the heavy hub is then machined off line and outside the fiber forming room to produce a smooth surface for reuse, or is removed entirely from the heavy hub and wheel after which a new band of elastomer is cast onto the heavy hub and dressed, again outside the forming room. Often the heavy rolls are shipped to a remote location, sometimes hundreds of miles away, to have a new polyurethane working layer cast on the rim of each heavy roll. A typical back up roll with a new elastomer working portion weighs about 45-70 pounds and a back up roll having an elastomer working portion that is so worn that it needs to be replaced weighs about 40-60 pounds. Most of this weight is the heavy, metal hub as the new elastomer band typically weighs only about 15-30 pounds.
Another way of making a back up roll is to press or stretch an elastomer band of rubber or polyurethane or other suitable elastomeric material over the outer circumferential surface of a heavy wheel and then mount the heavy

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