Reverse Pyramid Winder Mandrels
Reverse pyramid winder mandrels have been designed and built for up to 132,000 lbs. maximum tension. T. Sendzimir, Inc. has designed over 120 pairs of controlled collapse winder mandrels. The Sendzimir mandrel design has evolved through 3 successive stages:
- Forced Collapse design - mandrel segments shifts axially outward as the hoop stresses built up. This lateral shifting of the segments caused problems with the tracking of the strip through the mill.
- Original Controlled Collapse Design Mandrel - the segments remained fixed and the pyramid shaft moved so that the mandrel collapsed slightly as the coils wraps increased.
- Reverse Pyramid Design Mandrel - orientation of the pyramids was reversed thus enabling a vastly superior mandrel design and reduced maintenance due to stronger construction.
The Reverse Pyramid winder mandrel design was originally developed in 1968 at the request of DEW (Deutsche Edelstahlwerke) and Sudwestfallen (both German companies) in order to meet the demands of higher tension mills. The Reverse Pyramid design has been extremely successful in the years since it was introduced.
- Outboard bearing gates - T. Sendzimir, Inc. has designed for sliding sleeves which engage after the gate is fully closed. This design is superior to the tapered cone bearing design which may allow the outboard bearing gate to become partially open or move under winding tension loads which may force a bend in the mandrels. The Sliding Sleeve on the Outboard Bearing Gate is also designed to prevent engagement unless the alignment of the outboard bearing to the mandrel is correct.
- Gate alignment with respect to the mandrel is easily adjusted using the built in adjusting wedges. Our design is easier to implement in contrast to the shimmed method design.
- The rotating cylinder is designed for quick removal for service and maintenance with disturbing the mandrel. This cylinder uses a hollow shaft design, and is mounted on a stand-off which extends out from the back of the gearshaft. This design enables the cylinder to be installed and removed as a unit, without disturbing the mandrel.
- The low speed gearbox output shaft has integral splines on the ID. This direct spline connection for the gearshaft to the pyramid shaft enables an increased pyramid shaft diameter (2" to 3" greater on a 24" (610mm) diameter by 50" (1270mm) wide mandrel than competing designs) at the front bushing, giving more strength and rigidity by eliminating the spline adapter previously used. The integral spline design is especially valuable for 20" (508mm) diameter mandrels with their inherent higher internal stresses. The splines are cut directly into the low speed gear shaft.
- Coil breaks have been minimized at thin gauges and eliminated for the majority of rolling due to a re-design effort to reduce the distance between the segments. We are experiencing no coil breaks at the segment corners and minimal at the gripper slot area.
- Heat treatment of the mandrel components has been optimized for maximum strength and the mandrel components have been designed for minimal stress concentrations. This concentration on strength and reliability ensures a long service life for these mill components.
- A shear ring is provided between the nut which mounts the pyramid shaft on the rotating cylinder piston and the piston itself. This ring will break to protect the pyramid shaft against over-loading which could occur, for example, in the coil was wound on a collapsed mandrel.
- The segment retainers, which retain the segments to the gear shaft, are mounted with screws which are designed to break if an attempt is made to collapse an un-greased mandrel. Breaking of these screws thus provides a safe warning that greasing must be performed.
All the above features increase the initial cost of our mandrels, but all result in safer operation, greater ruggedness, easier maintenance, and lower overall service costs.
Typical Mandrel Specification
Two (2) - 24" (610 mm) diameter reverse pyramid design collapsible block winder sized for maximum strip width, both arranged for under-winding and each consisting of a mandrel, low speed gear shaft, rotating cylinder, and outboard gearing gate.
Expand-Collapse - of the mandrel is by a rotating hydraulic cylinder which is mounted on the back end of the output shaft and can be removed without disturbing the shaft or segments. The connection of the pyramid shaft to the rotating cylinder is provided by a threaded nut with integral shear ring.
Collapsible Mandrel Assembly - consists of four segments mounted on a four step reverse pyramid shaft. Segments are designed to minimize coil breaks at the segment joints.
Pyramid and Segments - are fabricated of forged, heat treated alloy steel with AMPCO bronze overlay weld deposited on the pyramid shaft surfaces.
Pyramid Shaft - is an integral forged steel heat-treated unit. The pyramid shaft is mounted on sleeve bearings in the gearbox output shaft. The gearbox output shaft rotates in anti-friction bearing in the gearcase. The pyramid shaft extends through the output shaft with the back end connected to the piston of the rotating cylinder and therefore becomes the draw rod for expanding and collapsing the mandrel. The pyramid shaft is spline driven for the gearbox output shaft. Screwed connection of the pyramid shaft to the rotating cylinder piston is provided in the design. This design ensures that there is no lateral movement of the segments during expand and collapse. This mandrel is designed for controlled collapse when subjected to hoop stress loading as the coil is wound onto the mandrel.
Gripper - is hydraulically operated. The gripper profile is designed to minimize coil breaks.
Outboard Bearing Gate - is designed to be easily aligned to the mandrel centerline by wedge adjustment in two planes.
Outboard Bearing - is supported by a cylindrical sleeve within the outboard bearing gate which allows the mandrel shaft to move axially while still ensuring that the outboard bearing gate remains fixed. The sleeve will not engage with the outboard bearing on the mandrel unless the gate is properly aligned.