Reverse Tonnage - Part 1: Are You Beating Your Press to Death?

In this multipart series on Reverse Tonnage also referred to as “Snap-Through” we will examine the root cause of this issue and its adverse effects on both your press and your tooling. The effects of Reverse Tonnage can be devastating. If not addressed properly over time Reverse Tonnage will literally reduce the life of your tooling and destroy the drive train of your press. The results of ignoring Reverse Tonnage can mean a complete rebuild of your press which can be hugely expensive.  However, today Reverse Tonnage is a well understood side effect of performing “blanking” in a press and its harmful effects can be controlled.

Snap-Through

Snap Through – What is it? Somewhere during the rotation cycle of your press prior to reaching bottom dead center your tooling engages the surface of your material.  As the rotation cycle progresses over the course of microseconds an immense amount of energy accumulates in the drive train of your press and the tooling itself. This is due to the resistance of the material to being pierced by your tooling. The stored energy accumulates until it reaches a point sufficient to overcome the resistance of the material.  Here in lies the problem. In an instant all that stored energy is released as the tooling pierces or “Snaps- Through” your material. This instantaneous and uncontrolled release of energy sends a shock wave through your entire press.  Also keep in mind the greater the area to be pierced or the thicker or higher strength your material is the greater amount of energy is stored and released.

https://media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAkEAAAAJDlmN2Y1OTA1LWIxYmEtNDA5Yi05ZjllLWY5MWJmMGRiZmVhMA.jpg

Reverse Tonnage

Reverse Tonnage – What does it effect and why?  The Drive Train of your press is designed to deliver the working energy from the motor to the tooling in one direction – Forward. The Drive Train is comprised of several components: Gears, a Drive Shaft (Crank Shaft), Bushings, Tie Rod(s), and Ball Seat(s). In order to work properly all these components must have pre-engineered clearances.  This small amount of gap between the components allows the different metal surfaces of each component to slide along one another.

During “Snap Through” the clearances between the individual components will move abruptly and with great force from one side of their connection to the other.  For example the Tie Rod(s) are connected to the Crank Shaft(s) with a Bronze Bushing(s). The Bronze Bushing is perfectly round and it’s inside diameter is slightly greater than the outside diameter of the Crank Shaft.  During the downward stroke cycle when the working energy is being delivered to the tooling the bottom side of the Crank Shaft and the Bronze Bushing come into direct contact with each other.  All the clearance is driven to the top of the connection.  

https://media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAfBAAAAJDViMmFiMWYyLTg5ODAtNGI0MC1hMDkwLWM5OTZhNWI5NTY5Mw.jpg

This is the proper working cycle of the drive train. However, during “Snap-Through” the sudden release of the accumulated energy discussed earlier causes the Tie Rod(s) with the Bronze Bushing to lurch downward. When the Tie Rods lurch downward the Bronze Bushing slams into the topside of the Crank Shaft(s). The clearance in the connection point is reversed from the top of the connection to the bottom. Hence the term “Reverse Tonnage”. This same clearance reversal happens throughout the entire drive train. This sudden and uncontrolled release of energy sends a shock wave through your press and tooling. The drive train of your press must absorb the brute of this shock wave with every stroke. Over time, this uncontrolled release of energy will cause the round Bronze Bushing to become “Egg Shaped”. In addition the rest of the drive train will also have excessive wear and damage requiring in some cases a complete rebuild of the press.

In Part 2 of this series, we will examine ways to control Reverse Tonnage and its effects on your equipment.

< BACK TO SUTHERLAND NEWS

Reverse Tonnage - Part 1: Are You Beating Your Press to Death?

In this multipart series on Reverse Tonnage also referred to as “Snap-Through” we will examine the root cause of this issue and its adverse effects on both your press and your tooling. The effects of Reverse Tonnage can be devastating. If not addressed properly over time Reverse Tonnage will literally reduce the life of your tooling and destroy the drive train of your press. The results of ignoring Reverse Tonnage can mean a complete rebuild of your press which can be hugely expensive.  However, today Reverse Tonnage is a well understood side effect of performing “blanking” in a press and its harmful effects can be controlled.

Snap-Through

Snap Through – What is it? Somewhere during the rotation cycle of your press prior to reaching bottom dead center your tooling engages the surface of your material.  As the rotation cycle progresses over the course of microseconds an immense amount of energy accumulates in the drive train of your press and the tooling itself. This is due to the resistance of the material to being pierced by your tooling. The stored energy accumulates until it reaches a point sufficient to overcome the resistance of the material.  Here in lies the problem. In an instant all that stored energy is released as the tooling pierces or “Snaps- Through” your material. This instantaneous and uncontrolled release of energy sends a shock wave through your entire press.  Also keep in mind the greater the area to be pierced or the thicker or higher strength your material is the greater amount of energy is stored and released.

https://media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAkEAAAAJDlmN2Y1OTA1LWIxYmEtNDA5Yi05ZjllLWY5MWJmMGRiZmVhMA.jpg

Reverse Tonnage

Reverse Tonnage – What does it effect and why?  The Drive Train of your press is designed to deliver the working energy from the motor to the tooling in one direction – Forward. The Drive Train is comprised of several components: Gears, a Drive Shaft (Crank Shaft), Bushings, Tie Rod(s), and Ball Seat(s). In order to work properly all these components must have pre-engineered clearances.  This small amount of gap between the components allows the different metal surfaces of each component to slide along one another.

During “Snap Through” the clearances between the individual components will move abruptly and with great force from one side of their connection to the other.  For example the Tie Rod(s) are connected to the Crank Shaft(s) with a Bronze Bushing(s). The Bronze Bushing is perfectly round and it’s inside diameter is slightly greater than the outside diameter of the Crank Shaft.  During the downward stroke cycle when the working energy is being delivered to the tooling the bottom side of the Crank Shaft and the Bronze Bushing come into direct contact with each other.  All the clearance is driven to the top of the connection.  

https://media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAfBAAAAJDViMmFiMWYyLTg5ODAtNGI0MC1hMDkwLWM5OTZhNWI5NTY5Mw.jpg

This is the proper working cycle of the drive train. However, during “Snap-Through” the sudden release of the accumulated energy discussed earlier causes the Tie Rod(s) with the Bronze Bushing to lurch downward. When the Tie Rods lurch downward the Bronze Bushing slams into the topside of the Crank Shaft(s). The clearance in the connection point is reversed from the top of the connection to the bottom. Hence the term “Reverse Tonnage”. This same clearance reversal happens throughout the entire drive train. This sudden and uncontrolled release of energy sends a shock wave through your press and tooling. The drive train of your press must absorb the brute of this shock wave with every stroke. Over time, this uncontrolled release of energy will cause the round Bronze Bushing to become “Egg Shaped”. In addition the rest of the drive train will also have excessive wear and damage requiring in some cases a complete rebuild of the press.

In Part 2 of this series, we will examine ways to control Reverse Tonnage and its effects on your equipment.

back to news >

SUTHERLAND CLIENTS

REQUEST A QUOTE