Surface finish-centerless grinding of engine valves

I take it, you've dressed the two wheels and the grinding wheel is correctly selected for the material you are grinding, and also that you have your height adjusted correctly! Are the wheels old? In otherwords, loaded, unbalanced due to old absorbed coolant on one side due to storing wet? Are the head bearings clean and adjusted? Is your coolant clean?

All of comment #1, plus is the surface hardness of the valve stem uniform .?

KennyT

I notice you say it's in the same valve in 4 places, does it also repeat on other valves? if the answer is no, then I would suggest you have a problem with the valve material.

where are you located?

Is truing and dressing done at the same point as the grinding is done or at the opposite location or at 90degrees?

What is the runout of the two wheels (measured at the same point as grinding is done)?

(synchronous with multiples and nonsynchronous!)

Runout has a static and a dynamic (unbalance) component, both have often higher harmonics.

What are the speeds of the two wheels and the workpiece?

Surface generation is a complicated topic!

This is especially true if you have both parts vibrating: the difference in frequencies will be seen on the surface.

As this is nonlinear mixing there is i*frequency1+or-k*frequency2.

What you really see on the surface is often those 1 or 2 components of these very many possible frequencies that are near zero or may be that are amplified by some resonance.

In centerless grinding it is still more complicated by the two contacts!

I have done some research on this topic many years ago that is published in one of the SPIE proceedings.

RHABE

How are the supporting blocks (to support valve stem ) located. Are they loose , worn out, chipped (if made of carbide) and causing vibrations in the system. When you say the surface finish does not meet the requirements - what is the nature of the finish you are getting- Are there any vibrations, soft spots on the part? Is there a grinding temper on part of the ground stem? Is your diamond dresser for dressing the wheel in good condition. Check the form of ]dresser under the magnifying glass.

I agree with all of the other comments but 1 additional one is the cleanliness of the filters for the coolant. If they are being bypassed (because they're clogged) they will let material by that will destroy the tolerance of your finish. I would check this first but you need all of the factors mentioned in order to maintain a 1.8µ finish.

As others have already said:

1) cleanliness of your coolant

2) balance and truing of your wheels

3) condition, rigidity and placement of your guides

4) condition and adjustment of the shaft bearings for the wheels

5) condition (wear) of your wheels or soft/hard spots in the wheel

6) quality of the steel your making the valves from

these are all factors that affect the quality of your finish.

Please post some feedback on your progress!

Scooter

I would suspect that you have looked at other valves. If this problem is isolated to that particular stock of material then you have a material problem. Grind (if you can ) a longer area on the same stock and see if there is a continual problem. This will help you evaluate weather or not you have a fixturing or wheel problem. Does the problem occur on different shifts? I would put my money on the coolant filtration.

Did you ever think of using automatic Drag Finishing equipment?

These are relatively new machines which do a consistent, high

performance job and can achiever even lower Ra's.

Multifinish America Inc.

248-528-1154