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This site shows my DIY work mainly at imaginative level.

Water jet cutter


Water jet cutter

This is the perfect DIY of make believe (fancy DIY). Nothing is made in fact.
This is an extract from the past record which considered its original work of the pump for water jets.
Water jet (= Water cutter = Ablation jet processing) is the cutting machine that is cut by narrow water jet with some sand.
The water jet speed is mainly about 500〜800m/s but some of them are mach 3.
To make the speed, the water compress about 300MPa and flow out from the hole of 0.1mm〜1mm diameter.

Began consideration from the water pressure of water service

I began consideration from the place which carries out increase pressure of the water pressure of the water of water service.
Suppose that the pressure of tap water is increased 1000 times temporarily.
If the diameter of primary plunger is 100mm, the secondary plunger should be less than 100/31.6=3mm.
400MPa is 4000kg/cm2 then 283kg if φ3mm=0.07cm2, it must be compression buckling.
Since a cylindrical secondary section moment is Ix=(1/4) *pi*r^4, it is Ix=3.796 as diameter =3mm.
A buckling load is 808.376[kN] (x0.10197 =82.4kg),
when it is temporarily referred to as length =100mm and Young's modulus of steel is set to 20E+10[Pa] =20E+4 [MPa].
Then compression buckling is carried out, if it is 283 kg.
Conversely, 10 mm in diameter brings the result that it wants,
as the round trip of 50 mm, and cylinder length of 100 mm noting that SUS will be used,
if it calculates from which is required in order not to carry out compression buckling.
Then, a primary cylinder diameter is set to 316 mm. This is too large for DIY.

It will think from another direction. Which grade is a required flow?
In order to consider it as 4 L/min by the secondary plunger, and if it is 1000 times, it is 4000 L/min necessity for primary plunger.
This is not a not much realistic quantity.

And from another direction. The speed of plunger.
Since it is cylinder volume =3900mm3=3.9cm3 in order to make 4 L/min by 10 mm in diameter and 50 mm lap,
1025*50/60=854 mm/s is needed by 4000/3.9=1025 round trip / min.
It is too fast for DIY.

If 30 mm in diameter and 100 mm lap, since it is 4000/70.7=56.6 lap/min, it is 56.6*100/60 = 94 mm/s.
It is rather a little too fast, but the primary plunger become too large if the speed set to slower.
A length of compression buckling limit will be about 200 mm at this condition.

Anyway it is not realistic by using the water pressure of water service.

How about to use a motor

Then consider about to use a motor for the next.
In order to push by 30 mm in diameter by the pressure of 4000 kg/cm2, 4000/28.3=141kgf (1380N) is needed.
It is 2.8 Nm if it is 141kgf (with 2.5 kgf*m), since seemingly the axial tension of M10 screw is about 1250 kgf.
Since about 5 Nm of continuation can use it at 0.5 kW servo motor, then a quite small motor can be used.
Since withstand load is about 1000 kgf also in the thrust bearing of about 24 mm of outside diameters,
it is not mechanical so big a value which is called 141 kg.
If it is 10 mm in diameter in a ball screw, it is not less than 3 mm of leads, and it is about basic dynamic load rating 3000N.
It is the calculation which should just have 0.1 mm or more of leads (pitch) of a ball screw
in obtaining the speed of 100 mm/s as 1000RPM temporarily since a servo motor is 1000...2000RPM.
Since a general lead is 1 mm or more, it is not necessary to take minimum restrictions of a lead into consideration.
Lead should be less than 5000 N-mm/1380N=3.6mm to obtaining 1380N by 5 Nm servo motor.
That is, when it is 10 mm in ball screw diameter at a 0.5 kW motor, lead is set to from 3 mm to 3.6 mm, and is narrow.
It will rather be said that a motor is powerless.
A motor is likely to be 0.75...1 kW and 4...5 mm of leads seem to be appropriate.

Well, the solution which is made somehow came out.
It will become as the following if this is made.

DIY plan

Target performance : 400MPa, and 4 L/min
Servo motor: 0.75...1kW
Ball screw: 10...15 mm in diameter. 4...5 mm of pitches -- 2 shafts for press the plunger at the middle of them
Plunger (piston): made from SUS, 30 mm in diameter, 100 mm in length of a plunger part, 50 mm lap.
The both ends of shaft of 40...50 mm in diameter and 250...300 mm in length
are cut in 30 mm in diameter, and length of 100 mm for plunger.
40 mm length of tips of a plunger are further cut in diameter of 20 mm for packings.
Packing: A PTFE pipe, 30 mm in outside diameter, 20 mm in inside diameter, 40 mm in length
or some of PTFE pipes, 30mm in outside diameter, 20 mm in inside diameter, 5 mm in length with some spacer of a between
Cylinder: Make a hole 30 mm in diameter in the pillar made from SUS 100 mm in length, and 70...100 mm in diameter.
Or make a hole 30 mm in diameter in the square pillar made from SUS which is 70...100 mm in one side.
The accuracy and the smoothness of this hole will be a key point. Honing processing will be indispensable.
The method of inserting a beautiful inside thin pipe in a hole is also considered.
It is almost processing of an engine.

Probably, I have to get a contractor to make a cylinder and a plunger at least.
Processing in an individual seems to be difficult.
However, talking about total cost, it does not seem to be unable for DIY.

   


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