Grinding Sperical Surface Seat

Question

Grinding Sperical Surface Seat

Rustam1 (Materials)

(OP)

24 Apr 16 08:26

Dear all,

We design ball valves made of cermets based on titanium carbide (binder - steel and nickel alloys) for use in oil refining, energy and mining industry.

There is a problem in machining the spherical surface of the seat. Drawing the seat DN50mm (sphere diameter of 90 mm) is attached.
The deviation from sphericity must be less than 10 microns.

Burin tools (including CBN -Sandvik) are ineffective because heterogeneous material - grains of 5-20 microns titanium carbide are arranged in the structure of the cermet beetwin metal layers.

Electrochemical methods of are also not effective.

The most efficient machining - only diamond grinding wheels, at first rough diamond grains (250-400 microns), then fine grain (40-100 microns).

Question:
What machines (or lathes with a turret with protection against abrasive dust) would you suggest for grinding spheres and the rest of the surface of the seat.

I would be most grateful for the responses.

Rustam1 (Materials) · Answer 1 · 2016-04-27 06:19:56

Dear participants of the forum, please help advice on the grinding of the spherical surface of the ball valve seat - image attached.
The diameters of the spheres from 30 to 300 mm.
I would be most grateful for the responses.

Friends, please do not let me drown together with my problem.

Compositepro (Chemical) · Answer 2 · 2016-04-27 17:54:55

Your best bet to answer your question is to browse Google, YouTube, and your imagination for how to generate or make a sphere. There are a great number of ways to generate a spherical surface. The best will depend on constraints you have like wanting to use existing machines or whatever. optical lenses are made to great precision using single point diamond tooling.

Rustam1 (Materials) · Answer 3 · 2016-04-28 10:06:32

Compositepro,
Thank you very much for your answer.

The last 2-3 years I was looking for ways of treating the surface of a spherical seat. The most appropriate method is the grinding, when the workpiece rotation axis intersects the axis of the disk rotation diamond wheel - scheme attached.

On CNC lathe we treated our billet. In The chuck fastened workpiece. Diamond disc is mounted on a head drive the tool turret.
Photo attached.

We conclude - the method chosen by us, is the most preferred.
If other methods do not appear, we will work in this direction.

israelkk (Aerospace) · Answer 4 · 2016-04-28 11:04:49

How much leak is allowed?
What type of fluid?
Pressure?
To my best experience the machine lines should be fully concentric (not spiral) and not as shown. All those micro lines shown in the picture are leak paths.

Compositepro (Chemical) · Answer 5 · 2016-04-28 12:30:35

I think you want to swivel the grinding tool on an axis that is not the same as the wheel rotation axis so that you can control the sphere radius generated independently from the wheel radius.

Rustam1 (Materials) · Answer 6 · 2016-04-28 15:52:21

israelkk:
"...micro lines shown in the picture are leak paths".
Yes all true. By this method we have not gotten completely treated seat. The photo shows the seat, which is not completely processed.
Below is shown full procecced ball valve.

So far, for the treatment of the seat we use the electrochemical method of processing (electrod-tools) and grind it to a ball - see photo.

Full redy ball valve is shown below.

Compositepro:
"...the sphere radius generated independently from the wheel radius..."
That's right - we are convinced of this, and processing circuit analysis shows that this is so.
If the diamond blade have wear, the by moving along the axis Y we get the same scope 90 mm.
This treatment scheme has long been known.
In the absence of tool wear, the intersection of the axis of rotation of the details and diamond disc, of absolute rigidity of the machine, we have an ideal spherical surface.

We are at the stage of experimental work.
Manufactured ball valves DN25mm DN50 mm and put on test production (oil refining and energy) - all excellent. They work more than 3 years.
We plan to go to the industrial production stage.
Our technology is most effective for abrasion resistant articles from cermets TiC-Me having a complex configuration - a ball valve, various purpose screws, impellers of centrifugal pumps, etc.
To implement the technology requied vacuum induction furnace special construction.

If items have a simple shape and small size, there is no problem.

Obviously, machining the seat ball valve should be better and more productive.
We want to reach diameters up to 280 mm (ball valve DN150mm).
Machine tools for grinding balls are available, for example, SMG32H.
For the grinding of the outer spherical surface using the same scheme - the method of intersecting axes. Ball grinding conical grinding wheel - a form as the seat.
It turned out that grinding of seat - problem.
If there is no special equipment for grinding seat, then will be necessary to combine lathe CNC (with the protection of the moving parts of abrasive dust) + required accessories (tools, drives).

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Grinding Sperical Surface Seat