Example 2 - A Vane Pump Extracting Fuel Vapours

This is a small pump with a mild steel stator and an eccentric rotor with four siding graphite vanes to maintain a seal against the I/D of the stator. You wish to coat the internal diameter of the stator with a surface which will provide low ear (there is no lubrication) and low friction against the vane tips. 

Entering details of the consultation

Do this as in the first example. Remember that your description must be accurate, since the words are carried through the consultation.
Call the component a 'Pump Stator'. 

Choosing the type of contact

Again, the first consultation screen is very important. You are asked to describe the type of contact and, based on your choice, the programme will tailor its subsequent questions.
You will see a screen like this:

In this case, the problem is one of a vane in contact with the bore of the stator; there is no abrasive, and the problem is one of metal-on-graphite metal contact. As in the first example, this situation is refereed to as adhesive wear and the programme will assess it as such by following the sequence of questions on the top line of the flow diagram on the facing page.  Answer yes to contact with another engineering component 

Choosing the substrate material

Click on mild steel. 

Choosing the counterface material

Click on carbon/graphite. You will need to scroll down the list to find it. Call it a 'Vane'. 

Entering the contact loading conditions

This is pure sliding. Click on it and move on. There are no impact loads or cyclic loads. 

Entering more contact conditions

Your components are not lubricated, so leave the cross in place. But you do specify low friction, so click on that to change it to a tick.
This is a lightly loaded situation; you can assume that there is no Heavy Loading. 

Specifying the hardness

Again, you can see that the software as indicated some hardnesses for you; that of the substrate before coating and that of the counterface. You can adjust these (use the mouse to click on the arrows) if you wish to represent the exact values for your materials if you know them. Most important is the hardness you want for the stator. This is again a matter of your judgement, but since you have specified that there must be no wear, then you must again set it relatively high. Click on the arrow and raise it to 500Hv. There is no point is specifying a higher value; 500Hv will guarantee no wear when in contact with a graphite vane. Because the software will eliminate coatings softer than your specified value, putting a higher value will unnecessarily restrict your options. 

Specifying the required surface finish

You want a good finish; one that will not cause excessive wear on the relatively softer graphite vanes. Enter 0.2µ for the finish before and after coating.  This is not a component you want to finish afterwards. Ideally, the I/D will be plated to its final dimensions and finish. Say No to post-finishing. The counterface roughness is somewhat indeterminate. It's graphite, so it's not likely to be smooth. Enter 1.0µ for the finish, press OK and then say No to surface roughening before coating. You don't want to detract from your final finish. 

Selecting partial coating options

Press Defined Areas Must Be Coated. You want the I/D to be coated, but if the O/D gets coated as well, it's of no consequence. There is no point in specifying unnecessary masking. 

Entering the operating temperature

In service, it is unlikely to operate at above 40oC. Enter that value in the operating temperature boxes.
This is a robust component made in mild steel. You 'Don't Care' how hot it gets when being coated. 

Specifying chemical contamination

Ideally, you would specify 'Fuel' at this point. But, in this version of APTICOTE-ISIS, fuel and its effect on coatings is not available in the data-base. In fact, that effect will be minimal, so leave this screen without specifying any contaminant. The programme will proceed on the assumption that there are no detrimental effects. 

Requirements for mould release or food approval

These are not an issue in this example. Leave the screen by pressing OK.   

Describing the component's geometry

This is a wide bore, not a tight hole; it should be relatively easy to coat. Leave the screen with negative answers, but remember that any 'line-of-sight' spray processes might need some careful jigging.
 
 

Entering the component dimensions

The part is 100mm diameter and 50mm long. Enter these values.
 

Examining the results

The programme recommends a number of composite coatings based on low friction polymers and either precision chrome plating or electroless nickel plating. For the latter, it is assumed that the nickel is heat treated to increase the hardness above the specified level of 500Hv.
On of the lowest friction coatings, APTICOTE 450F, does not appear on the list of acceptable coatings. Find it amongst the rejections and click on it. It has been rejected because of its hardness. Click on that, return to the hardness screen and reduce your specification from 500Hv to 300Hv. Press OK and you will see that the list of solutions now includes the 450F. But, although it will provide the low friction, it is questionable as to whether it will provide sufficient wear resistance. In fact, experience show that it doesn't, and that the first specification of 500Hv was entirely appropriate.

Poeton Industries Ltd. Head Office, Eastern Avenue, Gloucester GL4 3DN, England, UK   Tel: 01452 300500  Fax: 01452 500400
Production facilities in Cardif & Gloucester and in Wisconsin. USA.