1. Field of the Invention
This invention relates to an improved control system for maintaining a substantially constant mass flow of wire through the successive stations of a continuous cumulative wire drawing machine.
2. Description of the Prior Art
Continuous cumulative wire drawing machines can be classified as being either of the "single block" or "double block" types. In single block machines, as the term implies, at each drawing station the wire is drawn through a die by a single rotatably driven block. A segment of the wire is allowed to accumulate as multiple windings on the block before passing through a guide in the form of a pay-off eye on an overlying carrier ring which is freely rotatable about the block axis. From here, the wire continues over appropriately arranged guide sheaves either to another die at the next drawing station or to the final take-up block.
In double block machines, upper and lower blocks are arranged at each drawing station on a vertically disposed drive shaft. The lower block is keyed to the drive shaft for rotation therewith, and serves to draw the wire through the die. The upper block is freely rotatable on the drive shaft, and an independently rotatable carrier ring with a guide consisting of a transfer sheave is interposed between the two blocks. After passing through the die, wire accumulates on the lower block before passing over the transfer sheave onto the upper block where a further accumulation takes place. The wire then continues from the upper block over other appropriately positioned guide sheaves to the next station.
Under an ideal constant mass flow condition, i.e., when the mass flow rate at which wire is being wound onto the blocks equals the mass flow rate at which wire is being payed off the blocks, the carrier rings and their respective pay-off eyes or transfer sheaves will remain stationary. More often as not, however because of uneven die wear and/or other variable operating conditions, these rates will differ at one or more of the drawing stations. The carrier rings will compensate for differences between take-up and pay-off rates by rotating in either clockwise or counterclockwise directions, depending on whether the accumulations of wire on the blocks are increasing or decreasing.
There is, however, a limit to the extent to which such increases or decreases in wire accumulations can be tolerated. Thus, operating personnel must constantly monitor and adjust the wire accumulation on each block. Where the blocks are all connected via clutches to a common drive, as is usually the case, this entails frequent disengagement and reengagement of the clutches of selected blocks. This is a burdensome task, and one that requires considerable experience and a high degree of skill.
Moreover, when a clutch is disengaged to momentarily stop a selected block, the cooling time for the wire segment accumulated on that block will be extended as compared with the cooling times of the wire segments passing around those other blocks which continue to rotate. Any such localized extended cooling may produce a localized unacceptable variation in the metallurgical properties of the wire.
In the past, attempts have been made at alleviating the control responsibilities of operating personnel by providing systems designed to automatically monitor and adjust mass flow conditions. Typically, such systems employ vertically spaced pairs of photoelectric cells and light sources arranged to define the upper and lower limits of wire accumulation on the blocks. The signals generated by the photoelectric cells are used to automatically engage and disengage the clutches connecting the blocks to the common drive. While such systems can relieve operating personnel of some control responsibility, they still produce unacceptable localized variations in metallurgical properties caused by intermittent operation of the blocks. Moreover, such systems often malfunction as a result of the photoelectric cells becoming coated with the dust which usually pervades the atmosphere of a wire mill.
An object of the present invention is to provide an improved control system for maintaining a substantially constant mass flow rate of wire through the successive stations of a continuous cumulative wire drawing machine.
Another object of the present invention is to achieve the aforesaid substantially constant mass flow rate without imparting undesirable localized variations to the metallurgical properties of the wire as a result of uneven cooling.
Still another object of the present invention is the provision of a control system which can operate reliably in dust laden environments of the type often found in wire drawing mills.