Reverse Tonnage - Part 2: Know Your Limits

In the last issue of Press On and Forge Ahead we examined the cause and effects of Snap Through and Reverse Tonnage.  While Reverse Tonnage is a fact of life today it is well understood and it adverse effects can be controlled.  In this issue we will examine how much Reverse Tonnage is acceptable.  How Reverse Tonnage can be measured and the options available to you to address the effects of Reverse Tonnage.

Reverse Tonnage – How much is acceptable?

We all know Reverse Tonnage is a fact of life we must all deal with.  However, today's modern press designs take this in to account. Today's modern press designs can typically tolerate up to 10% of its total tonnage in Reverse Tonnage with no adverse effects.  For example if you have a 100 ton press it should be able to tolerate 10 tons of Reverse Tonnage with no ill effects on the press. This amount of Reverse Tonnage should be tolerable over the lifetime of the press.  It is when a press routinely encounters Reverse Tonnage above this 10% margin that troubles begin.

How do I measure Reverse Tonnage?

Today there are advanced control systems available which can measure Reverse Tonnage for you and display it on a screen.  These advanced systems utilize strain gauges attached to the frame of the press in various areas depending on the design of your press.  These measurements are very accurate and the control system can provide you a readout of reverse tonnage with every stroke of the press in real time.  Some of the most advanced control systems can also display the amount of working tonnage encountered by different areas on the press.  For example the display shown here is for a Straight Side Press.  The display shows Reverse Tonnage as well as the amount of tonnage exerted on the four corners of the press.  The most advanced control systems will constantly monitor the amount of Reverse Tonnage the press encounters as well as monitor the amount of working tonnage exerted on the four corners of the press.   

C:\Users\ray\Dropbox\Photos for Ray-12-16-16\I-PRESS AB PLUS CONTROLS\Screen Shots\_39-Tonnage Calibrate.PNG
Reverse Tonnage Tracking screen on the Sutherland I-PRESS system

With these highly advanced systems you can set a high and low tonnage setting for each corner of the press.  These control systems then monitor the tonnage and stop the press if the measured tonnage falls outside of your preset parameters.  For example you may have slugs building up in your tooling so you will exceed the high setting or perhaps a punch has broken off in your tooling and low you will exceed your low tonnage setting.  This type of constant and accurate monitoring can catch many problems as soon as they start.  In turn allowing you to head off any additional problems that could be caused and address the issue at hand quickly for reduced down time.    

So now we know what Reverse Tonnage is.  We know its cause and ill effects.  We know how much is acceptable and how it can be measured.  So what solutions are available to control Reverse Tonnage?

C:\Users\ray\Dropbox\Photos for Ray-12-16-16\MECHANICAL STRAIGHT SIDES\_MARK 2-121-Wintriss-Full Crop.jpg
The Sutherland Mark2

Press Size

You could consider over sizing your press based on the jobs you process.  For instance if you had a 200 ton press processing jobs typically processed on a 100 ton press your 10% margin would be 20 tons instead of 10 tons.  This is because the larger your press the more mass you have which can absorb the Reverse Tonnage.   While this is an option, it does not make a lot of economic sense and would be cost prohibitive.  There are other more economical ways to address Reverse Toonage.  

Tooling

Your first line of defense against Reverse Tonnage is your tooling.  As mentioned in our last issue, you have the instantaneous effect of Snap Through and Reverse Tonnage.  However, with proper forethought and designing of your tooling Snap Through and Reverse Tonnage can be minimized.  Consider if all the punches in your tooling are the same height.  Punches are the elements of the tooling which pass completely through your material.  When all the punches are the same height they will all Snap Through your material at the same instant.  This tooling design places the greatest amount of Reverse Tonnage on your press as is possible with the job at hand.  This is why it is always important to evaluate the design of your tooling.  As much as possible stagger the height of the punches in your tooling. 

By staggering the height of the punches they complete their tasks in succession and not all Snap Through the material at the same instant.  This minimizes Reverse Tonnage because, as one set of punches Snaps Through the material another set of punches are beginning to enter the material there by offsetting the Reverse Tonnage.  This is a simple and very effective method of addressing Reverse Tonnage.  However, it is many times over looked.  If staggering the height of the punches keeps your Reverse Tonnage under the 10% margin discussed earlier - Problem Solved.  

Hydraulic Shock Dampeners

When utilizing large complex tooling or sometimes due to the job at hand it may not always be possible to reduce Reverse Tonnage under the 10% margin discussed earlier.  In these situations your next line of defense are Hydraulic Shock Dampeners.  These are separate self-contained hydraulic devices which work much like the shock absorbers on your car. Hydraulic Shock Dampeners are typically retrofitable onto both new and used presses.  Hydraulic Shock Dampeners are always used in a set of 2, 4 or more depending on the size of your press.  When two are used they are placed on the right and left hand side of your press and centered front to back on the bolster.  When four are used they are set on the four corners of the bolster.  

You must always use Hydraulic Shock Dampeners in sets of two to ensure the load is centered on your press.  The dampeners height is adjustable so it can be set to come in contact with the presses slide at the same moment your tooling Snaps Through the material.  The Hydraulic Shock Dampeners are designed to provide counter balance force against the slide to absorb the Reverse Tonnage energy at the moment the tooling Snaps Through the material there by greatly reducing Reverse Tonnage to very tolerable levels.

  

http://www.w-tech.biz/img/w-tech-hp01.jpg
Hydraulic Shock Dampener

With these very desirable results why would you not always use Hydraulic Shock Dampeners?  The only potential drawback is they take up precious real estate in your bolster area.  Sometimes due to the size of your tooling there is not enough room left on your bolster to use Hydraulic Shock Dampeners.  However, some press manufacturers can offer innovative press designs where the Hydraulic Shock Dampeners are incorporated into the side frames of the press.  This innovative design permanently eliminates the need to place the Hydraulic Shock Dampeners on the bolster.  The novel design approach allows for all the benefits of the Hydraulic Shock Dampeners without giving up any precious bolster space.

In the end Reverse Tonnage is a fact of life we all have to deal with every day.  However, its ill effects on your press and tooling are well understood.  As we have seen there are different ways to manage and control Reverse Tonnage depending on your circumstances.  Which method is best is really a team effort between you, your tool maker and your press supplier.  Just be sure to always address Reverse Tonnage so You are not Beating your Press to Death.      

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Reverse Tonnage - Part 2: Know Your Limits

In the last issue of Press On and Forge Ahead we examined the cause and effects of Snap Through and Reverse Tonnage.  While Reverse Tonnage is a fact of life today it is well understood and it adverse effects can be controlled.  In this issue we will examine how much Reverse Tonnage is acceptable.  How Reverse Tonnage can be measured and the options available to you to address the effects of Reverse Tonnage.

Reverse Tonnage – How much is acceptable?

We all know Reverse Tonnage is a fact of life we must all deal with.  However, today's modern press designs take this in to account. Today's modern press designs can typically tolerate up to 10% of its total tonnage in Reverse Tonnage with no adverse effects.  For example if you have a 100 ton press it should be able to tolerate 10 tons of Reverse Tonnage with no ill effects on the press. This amount of Reverse Tonnage should be tolerable over the lifetime of the press.  It is when a press routinely encounters Reverse Tonnage above this 10% margin that troubles begin.

How do I measure Reverse Tonnage?

Today there are advanced control systems available which can measure Reverse Tonnage for you and display it on a screen.  These advanced systems utilize strain gauges attached to the frame of the press in various areas depending on the design of your press.  These measurements are very accurate and the control system can provide you a readout of reverse tonnage with every stroke of the press in real time.  Some of the most advanced control systems can also display the amount of working tonnage encountered by different areas on the press.  For example the display shown here is for a Straight Side Press.  The display shows Reverse Tonnage as well as the amount of tonnage exerted on the four corners of the press.  The most advanced control systems will constantly monitor the amount of Reverse Tonnage the press encounters as well as monitor the amount of working tonnage exerted on the four corners of the press.   

C:\Users\ray\Dropbox\Photos for Ray-12-16-16\I-PRESS AB PLUS CONTROLS\Screen Shots\_39-Tonnage Calibrate.PNG
Reverse Tonnage Tracking screen on the Sutherland I-PRESS system

With these highly advanced systems you can set a high and low tonnage setting for each corner of the press.  These control systems then monitor the tonnage and stop the press if the measured tonnage falls outside of your preset parameters.  For example you may have slugs building up in your tooling so you will exceed the high setting or perhaps a punch has broken off in your tooling and low you will exceed your low tonnage setting.  This type of constant and accurate monitoring can catch many problems as soon as they start.  In turn allowing you to head off any additional problems that could be caused and address the issue at hand quickly for reduced down time.    

So now we know what Reverse Tonnage is.  We know its cause and ill effects.  We know how much is acceptable and how it can be measured.  So what solutions are available to control Reverse Tonnage?

C:\Users\ray\Dropbox\Photos for Ray-12-16-16\MECHANICAL STRAIGHT SIDES\_MARK 2-121-Wintriss-Full Crop.jpg
The Sutherland Mark2

Press Size

You could consider over sizing your press based on the jobs you process.  For instance if you had a 200 ton press processing jobs typically processed on a 100 ton press your 10% margin would be 20 tons instead of 10 tons.  This is because the larger your press the more mass you have which can absorb the Reverse Tonnage.   While this is an option, it does not make a lot of economic sense and would be cost prohibitive.  There are other more economical ways to address Reverse Toonage.  

Tooling

Your first line of defense against Reverse Tonnage is your tooling.  As mentioned in our last issue, you have the instantaneous effect of Snap Through and Reverse Tonnage.  However, with proper forethought and designing of your tooling Snap Through and Reverse Tonnage can be minimized.  Consider if all the punches in your tooling are the same height.  Punches are the elements of the tooling which pass completely through your material.  When all the punches are the same height they will all Snap Through your material at the same instant.  This tooling design places the greatest amount of Reverse Tonnage on your press as is possible with the job at hand.  This is why it is always important to evaluate the design of your tooling.  As much as possible stagger the height of the punches in your tooling. 

By staggering the height of the punches they complete their tasks in succession and not all Snap Through the material at the same instant.  This minimizes Reverse Tonnage because, as one set of punches Snaps Through the material another set of punches are beginning to enter the material there by offsetting the Reverse Tonnage.  This is a simple and very effective method of addressing Reverse Tonnage.  However, it is many times over looked.  If staggering the height of the punches keeps your Reverse Tonnage under the 10% margin discussed earlier - Problem Solved.  

Hydraulic Shock Dampeners

When utilizing large complex tooling or sometimes due to the job at hand it may not always be possible to reduce Reverse Tonnage under the 10% margin discussed earlier.  In these situations your next line of defense are Hydraulic Shock Dampeners.  These are separate self-contained hydraulic devices which work much like the shock absorbers on your car. Hydraulic Shock Dampeners are typically retrofitable onto both new and used presses.  Hydraulic Shock Dampeners are always used in a set of 2, 4 or more depending on the size of your press.  When two are used they are placed on the right and left hand side of your press and centered front to back on the bolster.  When four are used they are set on the four corners of the bolster.  

You must always use Hydraulic Shock Dampeners in sets of two to ensure the load is centered on your press.  The dampeners height is adjustable so it can be set to come in contact with the presses slide at the same moment your tooling Snaps Through the material.  The Hydraulic Shock Dampeners are designed to provide counter balance force against the slide to absorb the Reverse Tonnage energy at the moment the tooling Snaps Through the material there by greatly reducing Reverse Tonnage to very tolerable levels.

  

http://www.w-tech.biz/img/w-tech-hp01.jpg
Hydraulic Shock Dampener

With these very desirable results why would you not always use Hydraulic Shock Dampeners?  The only potential drawback is they take up precious real estate in your bolster area.  Sometimes due to the size of your tooling there is not enough room left on your bolster to use Hydraulic Shock Dampeners.  However, some press manufacturers can offer innovative press designs where the Hydraulic Shock Dampeners are incorporated into the side frames of the press.  This innovative design permanently eliminates the need to place the Hydraulic Shock Dampeners on the bolster.  The novel design approach allows for all the benefits of the Hydraulic Shock Dampeners without giving up any precious bolster space.

In the end Reverse Tonnage is a fact of life we all have to deal with every day.  However, its ill effects on your press and tooling are well understood.  As we have seen there are different ways to manage and control Reverse Tonnage depending on your circumstances.  Which method is best is really a team effort between you, your tool maker and your press supplier.  Just be sure to always address Reverse Tonnage so You are not Beating your Press to Death.      

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