We are Team Shark, a group of Product Design Engineering students and as part of our uni course we've been given the challenge to design and build a water pump. The task is to design and manufacture a pump that could lift 5 litres of water up a height of 600mm in a time of 5 minutes or less. We've decided to make an Archimedes Screw and here's how we're getting on.
Step 1: Materials/ Tools Needed
Wooden dowel (27mm Diameter)
1mm thick sheet steel
1.5m steel rod (19mm Outer Diameter)
1.25m plastic downpipe (65mm Inner Diameter)
Bracket for downpipe
Gearbox (We used one out of a cheap drill)
Step 2: Calculations
Our results gave us 40 blades with a pitch of 30mm and we kept our angle flexible at this stage.
Step 3: Making Templates
In order to make the screw more efficient, we wanted all of the blades to be of equal size and pitch. To make the blades of equal size we simply cut a template out of wood by turning a cylinder of wood on a wood lathe, slicing it into discs then drilling through the centre.
For the pitch we created a template using a CNC machine. We know that a lot of people don't have access to a CNC machine so the discs can also just be bent into shape during the welding process using a hammer.
Step 4: Making the Discs
Each disk is cut out of a sheet of steel using a plasma cutter. The template [made in Step 3] is clamped to the sheet of steel then the plasma cutter is run round the template cutting the disk.
The edges of the discs are then ground to the right size using a bench grinder [our discs were 64mm diameter]. This also removes the burr left by the plasma cutter. The surface of the discs are also ground down using an angle grinder to remove any burr from the surface and improve the aesthetic.
Each disc is then clamped in the CNC template [made in Step 3] in the bench vice to bend it to the correct pitch.
Step 5: Welding & Refining the Screw
The welding caused the central pole to warp slightly so we had to manually bend the pole back so that it was as straight as possible. This took some time! We made supports for the screw to sit in so that it was held at one level and span it using a drill to see where the warping was, we then had to bend it by hand.
Also at this stage when we tried fitting the screw in the downpipe it was too tight a fit so we had to grind down some of the blades using an angle grinder. To find out which blades needed grinding we forced the screw in the pipe and ran it off the drill, this made the screw cut the inside of the pipe and when we pulled the screw out, the blades that had lots of plastic on them, and therefore had been cutting into the pipe most, were the ones that needed ground down.
Step 6: Sealing the Screw
The screw fits tightly into the pipe anyway but in order to make it sealed we first had to run silicon sealant [any bathroom sealant should work, we used multipurpose silicone sealant from the pound shop] round the central pole so that there were no gaps between it and the blades. We then put a generous line of sealant round the outsides of the blades and then forced the screw into the pipe and left it to dry over the weekend [we recommend leaving it for at least 24 hours]. This sealed the screw to the pipe and this way hopefully no water will run back down the pipe like it would in a traditional Archimedes Screw.
Step 7: Testing, Testing, 1 2 3...
Step 8: Making the Frame
Two 'legs' come down from the back end of the square frame and this had two sets of hooks on it in which another dowel with another bracket sits in and this can alter the angle further. The screw is held in place on the frame by a simple collar that sits over the bottom with a plate on the end that the end of the screw rests against and there is also another collar that sits before the first bracket and stops the pipe from slipping down any further holding it in place.
Step 9: Gearing the Motor
We decided the best way to do it was to buy a cheap drill and salvage the gearbox from it. We then attached it to the motor and we estimated this increased the torque to about 20Nm. However once we'd done this we realised that by increasing the torque so much, we'd decreased the speed by too much and the screw was now going too slowly to pull up any water so we had to introduce another gear box, this time gearing it back up slightly.
We also greased up the gearbox from the drill to make it run more smoothly.
Step 10: Housing the Motor
We had to find a way of holding the motor safely above the screw and it also had to be held in such a way that it couldn't rotate. To house the motor we used the casing from the cheap drill as it was already the correct size so fitted perfectly over the motor and chuck. We cut the drill handle off and sanded down the rough edges to get the right shape.
We decided, as we are Team Shark, as a bit of fun, to make the motor housing look like a shark so we first spray painted the casing white and then shaded a blue grey colour over the top. We added an MDF fin and voila - shark. As I said, this is just a bit of fun and it passed the time while we were waiting to get things done in the workshop.
The motor is stopped from rotating as it is screwed to the back plate of the holder and the holder will be securely attached to the frame.
Step 11: Funnel
When we did the test runs of the screw, we found that when the water was exiting the pipe a lot of it was running back down the outside of the pipe and because it was still spinning when it exited it tended to splash everywhere. So we decided to create a funnel to channel the water into the exit bucket.
Firstly we vaccuum formed over a hemisphere to create a bowl type shape. Then we drilled and filed out a hole that fit tightly over the end of the pipe. Finally we heated up the plastic again using a heat gun and bent it into the shape of a spout.