Rolling mill laying head

Abstract

Aspects of the present invention relate to a rolling mill laying head. The rolling mill laying head comprises a quill rotatable about a central axis, said quill being equipped with a guide pathway configured and arranged to form a longitudinally moving product into a continuous series of rings; a stationary support structure; and axially spaced radial bearings supporting said quill for rotation about said axis, one of said bearings comprising a hydrostatic oil film bearing having an internal diameter of at least about 500 mm, and having a L / D ratio less than 0.25.

Description

BACKGROUND[0001]1. Field[0002]Embodiments of the present invention relate to laying heads of the type employed in rolling mills to form hot rolled products into helical formations of rings.[0003]2. Description of Related Art[0004]In a conventional laying head, a stationary support structure contains a hollow quill rotatably supported between axially spaced bearings. The quill is equipped with a guide pathway, which may typically comprise a curved guide pipe having an entry end aligned with the rotational axis of the quill, and a curved intermediate section projecting in a cantilever fashion from the quill to an exit end spaced radially from the quill axis. The quill is rotatably driven by known means, with the guide pipe being configured to receive a product at its entry end and to form the product into a helical formation of rings emerging from its exit end.[0005]Roller bearings are typically employed to rotatably support the quill. Under high speed operating conditions, e.g., when...

AI Technical Summary

Benefits of technology

The present invention provides a laying head with a quill that is rotatably supported by multiple bearings, with at least one bearing being a hydrostatic oil film bearing. This design reduces vibration and enables the quill to align with the bushing during operation without the need for a high starting torque. The hydrostatic bearing design allows for centering of the rotating mass regardless of the applied load or speed, making it more stable than hydrodynamic bearings, particularly during a wobble cycle.

Problems solved by technology

Under high speed operating conditions, e.g., when handling products traveling at speeds exceeding 100 m / sec, experience has shown that the roller bearings are prone to producing vibrations that disturb operation of the laying head.

Although such design modifications have been proven to be beneficial, they have not adequately addressed the vibration problems which continue to plague the laying heads as they are operated at the ever increasing speeds of modern day rolling mills.

A number of potential problems are encountered when operating hydrodynamic oil film bearings at high speeds under lightly loaded conditions.

For example:The bearings are known to suffer from an instability effect called “whirl” where the rotating member orbits inside the bushing in a highly undesirably mode.A laying head application is unusual in that, depending on the operating conditions, there can be an additional transient load at nearly any angle as the hot rolled product heads-in to the laying pipe.

Application of a hydrodynamic oil film bearing to a laying head has all of the above problems.

However, given the speeds of operation, whirl is a particularly critical problem, as high rotational speeds and low loads will ensure that the bearing will be running in an unstable condition at all times.

When implementing the wobble function at the lower operating speeds that are commonly used when processing the larger product sizes, the overall system stability of a hydrodynamic bearing is severely compromised as the load zone is continually shifted from one side to the other of the bearing in response to alternating acceleration and deceleration.

The rapid acceleration during tail end speed up is similarly detrimental to bearing stability.

Hydrodynamic oil film bearings have been introduced for use in rolling mill laying heads but have not been widely accepted, likely because of the above described problems.

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