The 3 Elements of Press Capacity "Torque Capacity"

On the previous page we explained pressure capacity, and now we would like to talk about the next of the 3 elements of press capacity--torque capacity.

What is Torque?

Torque is the force used to rotate objects.

One familiar example of torque is a bike, where you rotate the pedals by pushing down on them with your feet.
It may be easier to understand if you imagine the force that is being applied when you are pedaling a bike.

Let's dive in!

The press torque capacity is "the pressure capacity that can be generated at a position that is ●● mm above bottom dead center (BDC)."

The structural areas related to torque capacity--the locations or components that transmit rotational force (the clutch, crankshaft, gears, etc.)--are shown in blue in the illustration below, and 'torque capacity' refers to the maximum torque value these can withstand.

Torque Capacity and Tonnage Capacity

The following graph is called a Tonnage Curve, and it shows the relationship between the 'slide position above BDC' and the 'applied pressing force.'

This sample graph is for a 1100 kN press, and you can see that the location where 1100 kN of force can be generated is 5 mm above BDC (the blue line).
The rated tonnage point is the highest position above BDC where the pressure capacity (the nominal capacity) can be generated.
And if you look at this graph, you can see that approximately 760 kN of force can be generated at a position that is 10 mm above BDC (the red line).

This shows that the pressing force will decrease as the height above the rated tonnage point increases.
In the case of a crank press, the shaft torque will be uniform at any angle, and due to its design, the pressing force will increase as the slide gets closer to BDC, and, theoretically, an infinite load can be generated near BDC (as shown by the purple oval in the above graph).

Accordingly, presses are equipped with overload protectors to prevent damage to the press and dies by ensuring that the loads generated between the rated tonnage point and BDC will not exceed the press tonnage specification.

There is a tendency to think 'I can make the product because the required load is less than the rated capacity of our press.'
However, as shown in the example above, the reality may be that you may exceed the press capacity if the torque capacity of the press is limited at a position high above BDC.

And if you continue to use the press at a tonnage that exceeds the torque capacity, there is the very real possibility that it will cause problems, such as the clutch slipping and causing the clutch lining (surface) to heat up and wear away, broken gears, or excessive torsion being applied on the crankshaft.

And Finally...

In order to use the press safely, be sure to refer to the Tonnage Curve Drawing included in the press Instruction Manual.
Later on we will explain about torque capacity in much greater detail using real-life forming examples.