The Hydraulic Press Channel is Awesome, Part 1

Finnish factory owners Lauri and Anni have a hydraulic press and use for the best possible purpose: crush things for fun.

“The first and original Hydraulic Press Channel! Wanna see stuff getting crushed by hydraulic press? This is the right channel for you.”

Pressing non-Newtonian Fluids

I encourage you to fall down the youtube rabbit hole, this is senseless destruction at its finest

Or is it?

Everything is a science demo, so let’s learn something from this.

One of the important roles of material sciences (typically a mix of chemistry, physics and engineering) is to develop new materials for specific applications. For example, when Charles Goodyear learned to vulcanize rubber, he invented an elastic, deformable, but structurally durable material that was ideal for revolutionizing the wheel. Since then, materials scientists have developed synthetic materials (usually plastics) for an incredibly wide variety of applications. Like the bronze age and, iron age are used to define the technological periods of humanity, it is no exaggeration to say the 1950’s were the advent of the age of plastic.

Materials scientists can produce thousands upon thousands of different compounds, but obviously prototyping a product with every compound and deciding which performs best would be absurd. To narrow down the usable materials, they need to characterize their compounds.

What is amusing about characterizing compounds is often tests are as simple as squishing, stretching, shearing, and otherwise playing with them like one would play with Silly Putty. The complicated part comes from determining what to measure. Typically a device will apply a force to the material, and according to Newton, the material will react. In general, it’s this reaction that’s measured – the details will vary, but this is the general principle in characterizing a material.

Not all characterization requires a complicated force measurement, though. One of my favorite devices I used when I worked for a rubber company (supplying butyl rubber for tires and shoe soles, mostly) was the extruder.

The extruder was a thin metal tube with different types of nozzles at the bottom. A material was first loaded into the tube, and then the tube was heated to a temperature specific to the given experiment. Finally, the material was pushed through the nozzle with a piston. Forces applied by the piston could be recorded, as well as the forces on the walls of the tube and on the nozzle, but just by looking at the extruded material, a trained scientist could determine some important properties of the compound. An example of one of the visual cues that tell about the material properties during an extrusion experiment is shown below. Notice how the material comes out smooth, then transitions to a rough, “shark skin”. This can mean that the temperature of the tube is too low or that the material is being pushed out too fast.

Does the extruder sounds a bit like our little hydraulic press? So this is a science demo after all! In part one we will examine the “Experimental Techniques” section of our science demo, since the way a hydraulic press achieves its massive crushing power is actually pretty cool. In part two, we will present some results provided by the Hydraulic Press Channel and discuss what they tell us about the materials.

Experimental Techniques: The Hydraulic Press

A hydraulic press was invented by Joseph Bramah and patented in 1795. While putting significant effort into developing the modern toilet, Bramah realized he could create a hydraulic equivalent to a classic lever.

A famous Greek dude from Syracuse University once said, “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world. Don’t say I won’t do it either, because I totally will.” Practical concerns like “where do I place the fulcrum?” aside, the principle is sound. When you place an object on one end of a lever and apply a force to the other side, the torque you put on the lever is transferred to the object on the other side. Since torque is the product of force and the distance the force is from the fulcrum (which is why it is easier to hold a grocery bag at your side than with your arms outstretched), a sufficiently long lever with a properly placed fulcrum should allow you to “balance the teeter-totter” with two arbitrarily-sized objects.

A Greek dude from Syracuse University

So how does this relate to the hydraulic press?

The cartoon below is a schematic of a basic hydraulic lift. A force F1 is applied to a Piston 1 with an area of A1. The force from Piston 1 creates pressure in a volume of liquid, which is sealed water-tight at the other end by Piston 2 which has an area A2. Assuming the liquid is incompressible (this is an interesting assumption unto itself, but we will not dig into it here – just know that it’s a good assumption), then the pressure caused by Piston 1 will be equal to the pressure on Piston 2.

A simple schematic of a hydraulic press in equilibrium (neither side is moving up or down). From wiki.

So how do we determine the lifting force (or crushing force, just flip the schematic upside down) of Piston 2?

Pressure is define as a Force per unit Area. That means the pressure caused by Piston 1 is F1 distributed over A1 which is written: P = F1/A1. A higher force or smaller area leads to a higher pressure. Since the pressure is transmitted from Piston 1 to Piston 2 via the fluid, P = F1/A1 = F2/A2 . So if A2 is larger than A1 and the fluid transmits equal pressure to the other piston, then F2 > F1, and we can calculate by exactly how much F2 > F1:

 

F1 = F2 (A2/A1) , so F2 is A2/A1-times larger than F1.

This may sound familiar to our lever. The similarity is that with a lever, torque is equal on both sides (if the system is stationary), while a hydraulic press has a pressure which is equal on both sides. The important part is the ratio between lengths on each end of the fulcrum and area of each piston. Note, that Torque=Force*Length and Pressure=Force/Area, so Archemedes would want a long lever on his side while Bramah would want to apply his force to the small piston.

Using this technique of focusing force into a smaller area, a hydraulic press is able to deliver an incredible amount of crushing with a reasonable amount of applied force on the small piston. For example, presses can reach in the ballpark of 9000 psi (pounds per square inch).

We can now use this device to wreak havoc on learn about the physical properties of various materials. Next week we will discuss what we can learn about materials by how they respond to crushing.

 

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