Extruders for rubber and plastic materials have been in use for many years. These extruders produce an endless flow of product having a cross-sectional configuration which is determined by the dies employed in the extruder. A primary application for this type of machinery, is in what is characterized as profile and tubing extrusion application industry. Exemplary types of products which are commonly so characterized include generally flat goods in the nature of seals or weatherstripping and tubular goods such as various types of hosing and tubing.
Depending upon the type of product in terms of cross-sectional configuration, material and other considerations, commercial extrusion operations normally consist of an extruder, suitable apparatus for curing the extruded material and apparatus for cutting the extruded material to predetermined lengths for a particular product. While both off-line and on-line cutting apparatus has been employed in the industry, off-line cutting operations are characteristically relatively expensive in terms of the equipment required and labor costs.
As a result, on-line cutoff machinery has long been used in the industry for cutting profile and tubing extrusions particularly. What is generally known as a flyknife cutter is the oldest and most widely used cutoff machine in the industry. Flyknife cutters are generally characterized by a knife blade being mounted for rotation through a cutting area with the knife blade being mounted in a plane perpendicular to the direction of travel of the extruded material through the cutoff machine. In order to provide for a clean precise severing of extruded material having relatively thick walls or of relatively large cross-sectional size, it is common for flyknife cutters to mount the knife blade on a flywheel to impart ample momentum to the knife blade for the requisite cutting action. Since the cutting cycle of a flyknife cutter must be accomplished in a single rotation of the flyknife, the use of the requisite flywheel presents technical problems which have plagued the rubber and plastic extrusion industry for many years. The basic problem has centered about the necessity for accelerating a flywheel carrying a knife blade to an angular velocity sufficient for cutting the extruded material, effecting the cutting action and stopping the flywheel, all within an angular rotation span of the knife blade through 360.degree. .
Traditionally a combination clutch/brake, an associated drive motor, belting, bearings, and suitable electric controls have been employed for accelerating and then decelerating and stopping the flywheel. Since many products can be extruded at relatively rapid linear rates and since the finished products in many instances may be short, such as on the order of an inch or even fractions of an inch, it is often necessary that an on-line cutoff machine be capable of making as many as several hundreds operating repetitions per minute. It will be readily appreciated that great demands are placed on any clutch/brake configuration when subjected to repetition rates of this order. Many of the electromagnetic clutch/brake designs essentially self-destructed in a relatively short time due to high temperatures and the complex shaft and gearing arrangements.
For many years improvements in flyknife cutters were directed primarily to efforts to design improved electro-magnetic clutch and brake configurations and materials in an effort to meet these stringent demands, while somewhat obviating the significant repair and maintenance costs which were encountered in terms of both parts and labor in operatively maintaining such flyknife cutters. Some improvements in flyknife cutter technology over the years have been significant in providing improved performance while reducing maintenance and repairs. Noteworthy in this respect was the development of electrical overexcitation of the clutch/brake assembly to achieve more rapid and positive action. More recently, vacuum clutch/brake assemblies have been adopted by much of the industry to improve repeat cycle accuracy, since power and temperature fluctuations have minimal effect on the torque of a vacuum unit, and to provide lower operating temperatures. The use of self diagnostic clutch/brake assemblies to effect early detection of malfunctions and component wear has aimed at decreasing downtime and/or operation at cutting characteristics outside accepted tolerances.
While refinements of this type have to some extent reduced maintenance and repair and out-of-tolerance production, the clutch/brake assembly of flyknife cutters has remained the weak link in cutoff machines of this type. In fact, the clutch/brake assembly of the flyknife is widely considered to be possibly the most problematical component of an entire extrusion line.