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Straight Talk on Hydraulic Straightening-Press Applications

By: Tom Lavoie

Tom Lavoie is applications engineering manager, Greenerd Press & Machine Co., Inc., Nashua, NH: 603/889-4101, www.greenerd.com.

Friday, August 01, 2014
 

This fixed-head 100-ton straightening press can perform shaft work from 2- to 8-in. dia. Note the traveling carriages that allow the operator to move the shaft anywhere under the fixed head of the press.
Photo A: This fixed-head 100-ton straightening press can perform shaft work from 2- to 8-in. dia. Note the traveling carriages that allow the operator to move the shaft anywhere under the fixed head of the press.
Machining and forming processes, as well as heattreating on large shafts used in the oil, marine, aerospace and automotive industries, can cause workpieces to warp. Hydraulic straightening presses provide tight control for straightening, resulting in accurate, well-functioning parts and substantial cost savings. In some cases, straightening is the only to condition or prepare the material in order to machine the component appropriately. The same is true for straightening of plates.

Hydraulic straightening presses also often get the call for straightening large weldments and plates, as well as shafts. Large weldments can become deformed or warped from heat from the welding process; often these weldments must be straightened prior to continuing on with secondary production processes.

Shaft work, a little more complicated, can come in many sizes. Large-diameter shafts, defined as several inches in diameter or larger, are difficult to automate into a process for straightening.

The Right Press Design for the Job

Fabricators select from two types of press designs for straightening—moving-gantry or fixed-head. Plate and weldment applications typically require a moving-gantry press that moves the head over the work front-to-back or left-to-right, regardless of where it is located on the press bed. A shaft-straightening press has only one axis of travel, located on-center with the shaft.

Shown is a travelling-gantry straightening press, with x-y axis movement. The traveling carriages support the shaft and are hydraulically operated to raise and lower the shaft off of and on to the V-blocks.
Photo B: Shown is a travelling-gantry straightening press, with x-y axis movement. The traveling carriages support the shaft and are hydraulically operated to raise and lower the shaft off of and on to the V-blocks.
When straightening large drive shafts and pipes such as those used in oilfield applications, which can be difficult to manipulate, fabricators typically opt for a press that can locate over the high spot (bend in the shaft) and apply tonnage to straighten the shaft within acceptable tolerances. However, depending on the size of the shaft or pipe, a shaft can be moved under a fixed-head press via tooling on the press bed (photo A).

Photo B shows an application where a shaft is too large and heavy for an operator to load manually. This requires use of an overhead crane to lift the shaft/gear into place. The press gantry then moves over the shaft to the appropriate spot to apply the straightening force. The traveling carriages support the shaft and are hydraulically operated to raise and lower the shaft off and on to the V-blocks. After pressing the shaft, the operator hydraulically lifts the shaft and rotates it for further processing until it falls within acceptable tolerances.

Lastly, Photo C illustrates a traveling-gantry press designed to straighten large-diameter shafts. Its gantry moves only in the X axis to drive over the workpiece, and the main cylinder provides Z-axis movement downward to engage the shaft. All work remains centered under the main ram and the gantry moves over the area to be straightened. Typically, this style of press allows the gantry to move all of the to one end of the press bed in order to load the shafts from an overhead crane. The operator then drives the gantry nose tool over the high spot to perform the straightening process.

Control is the Key

The gantry of this traveling-gantry straightening press, designed for large shaft applications, moves only in the X axis to drive over the workpiece. All work remains centered under the main ram.
Photo C: The gantry of this traveling-gantry straightening press, designed for large shaft applications, moves only in the X axis to drive over the workpiece. All work remains centered under the main ram.
With the proper press selected for the application, the metalformer then turns its attention to gaining complete control over ram movement while applying tonnage to the shaft. Less control may require more hits. State-of-the-art press controls allow operator to dial-in ram depth in increments of 0.001 in.

The control depicted in Photo D, installed on a moveable-gantry press, allows the operator to view actual main-ram position and then input the desired pressing depth in increments of 0.001 in. Included control features:

1) Aux Power Unit supplies the lift and carriage assemblies. This unit finds use when performing shaft work, and can be shut off during plate or weldment work.

2) Lift Assy Up/Down selector switch moves the live centers on which the shaft is mounted.

This press control, installed on a moveable-gantry press, allows the operator to view actual main-ram position, and then input the desired pressing depth in increments of 0.001 in.
Photo D: This press control, installed on a moveable-gantry press, allows the operator to view actual main-ram position, and then input the desired pressing depth in increments of 0.001 in.
3) Carriage Up/Down selector switch lifts and lowers the carriage assemblies, to rotate the part and find its high spot.

4) Head and Gantry Lock lifts the gantry (of a traveling-gantry press) up against the bottom of the press bed to hold it in place during straightening. This prevents the gantry from tipping and moving off-center to the table surface.

5) Down Pushbutton: This button is required for anti-tiedown and anti-repeat dual-hand controls, complying with OSHA requirements to keep both of the operator’s hands engaged at the start of the cycle. He places one hand on the cycle start button and the other hand on the joystick controlling ram movement.

6) Motor On/Off button turns the motor on and off. In the off position, all pressure is removed from the system.

7) Gantry Movement Joystick Control allows the operator to jog the head of the press (cylinder assembly) front and back, while allowing the gantry to move left and right. The gantry can be positioned over a predetermined area of the press bed to allow the operator to finely control where he wants to engage the part for straightening. Some gantries only allow for X-axis movement (typically for shaft work), and others allow for X- and Y-axis movement (for plate or weldment work).

8) Main Ram Joystick Control: This joystick controls main-ram extension and retraction; the ram also is proportionally controlled for speed and pressure. MF

 

See also: Greenerd Press & Machine Co., Inc.

Related Enterprise Zones: Presses


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