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It will be helpful to have APTICOTE-ISIS running as you work through this
example.
Example 1 - A Water Pump Drive Shaft
The shaft is running in a bronze bush, with grease lubrication, and there
is a seal which prevents water from reaching the contact. Your need is
to protect the shaft from wear at all costs; it is not a component you
want ever to replace.
Entering details of the consultation
Once the APTICOTE-ISIS system is running, and you have accepted the terms
and conditions of use, you will be presented with a screen like this (click
on the thumbnail to see the full size image):
At this point, you will normally enter details of the client and the consultation
for future reference. It is important that this page is filled in accurately
because the words you use will be carried through the rest of the programme
and appear on other screens and on the final printed out consultation
report. You can use the mouse to locate the boxes before you type or you
can use the tab key.
When you have entered all you want, just press the OK button to move on
to the next step. The OK button is always used to inform APTICOTE-ISIS
that you have entered all the data and that you are ready to proceed.
Note that you must use the mouse to do this; there is no key stroke for
the OK button.
Choosing the type of contact
 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:
You have three options;
- To answer yes to contact with another engineering component.
- To answer yes to contact with a product.
- To answer yes to both.
In this case, the problem is one of a shaft in contact with a bush; there
is no abrasive, and the problem is one of metal-on-metal contact. 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 by clicking on
the cross and changing it to a tick
NOTE: If, at any time, you wish to check back at an earlier screen, just
page backwards by clicking on the BACK button
Choosing the substrate material
At this point you must specify the material from which your component
is going to be made.
For the shaft, you will be making it in a low alloy steel, typically about
0.4%C and with small alloying additions of elements like Cr or Al. It
will be a normalised condition; i.e. not hardened or tempered. Click on
this option and then press OK.
Notice how the reading on the gauge near the OK button has dropped. This
indicates that some of the possible solutions have been eliminated by
your choice of substrate. The exact figures are given in the status box
at the bottom left hand side of the screen. For instance, since your substrate
is a steel, the programme has eliminated any anodising treatments from
its list of options.
Choosing the counterface material
You are being asked to select the material against which your shaft is
running. It is a bronze bush. You have chosen this so that it is cheap
and easy to replace and you accept that, should any wear occur within
the contact, you want it to be on the bush and not the shaft.
Click on bronze then enter the name of your counterface ('Bush'). The
programme will not let you proceed without entering that name.
Now press the OK button.
Entering the contact loading conditions
This is the point at which you specify the various contact conditions
for your component. If you want more information about these, click on
the HELP button. Try it; help is always available during the APTICOTE-ISIS
consultation.
In the case of the pump shaft, the situation is one of continuous sliding
in the bronze bearing, so click on the cross next to sliding contact.
However, there may also be some cyclic loading on the shaft when it is
started up, or when the pumping load is changed. This may be a potential
source of fatigue and you must avoid any surface treatment that might
make that tendency worse. Click on bulk cyclic loading as well and press
the OK button.
Now the programme asks you if one of these conditions is more important
than the other. This is a relatively light duty pump, so you are more
concerned with the sliding than the possibility of fatigue, so click again
on sliding contact to mark it as dominant.
Entering more contact conditions
Your components are lubricated. Click on the cross next to lubricated
to change it to a tick.
Because it is lubricated, the fiction with any surface coating will be
low, so there is no need to specify low friction. This is an option you
consider in other examples when the contact is one of dry sliding.
This screen also asks about the specific loading. You can perform a simple
calculation by dividing the applied load on the shaft by the apparent
contact area in the bush. If the load on the bearing was 10Kg (100N) and
the area of the bush in contact with the shaft was 10cm2 (10-3
m2), then the specific loading would be
100/10-3 = 10-5 N/m2 = 0.1 MN/m2
(MN/m2 = MPa)
So, in relation to the value set as a definition of 'Heavy Loading',
that is 10MPa, the loading on your shaft is very low and you should not
click on it. You will see later that a specification of Heavy Loading
will eliminate many of the thinner or more brittle coating options.
Specifying the hardness
Poeton's wide selection of coatings offers a range of surface hardnesses.
These are sometimes dependent on the substrate and the software will take
this into account as it assesses the options.
You can see that the software has indicated some hardnesses for you; that
of the substrate before coating (300Hv) and that of the bronze counterface
(180Hv). 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 shaft. This is a matter
of your judgement, but since you have specified that there must be no
wear, then you must set it high. Click on the arrow and raise it to 700Hv.
There is no point is specifying a higher value; 700Hv will guarantee no
wear when in contact with a bronze bush. Because the software will eliminate
coatings softer than your specified value, putting a higher value will
unnecessarily restrict your options.
You may also specify a maximum value if you wish; some very hard rough
surfaces might cause excessive wear on your counterface (the bronze bush).
If you skip the question, it will default to 10,000Hv.
Finally, if you are not used to working in Vickers Hardness values, use
the HELP screen for a conversion table.
Specifying the required surface finish
The surface roughness of a component is important not only for aesthetic
reasons, but also because it affects the mechanical performance. In general,
no coating will provide a smoother finish than that of the substrate without
finishing after coating. Thus, you are asked the initial roughness before
coating and the maximum you will accept after coating. You can also specify
whether or not you are prepared to accept another finishing operation
(e.g. grinding) to achieve your desired finish.
All values should be entered in micrometers Ra. A table of surface roughnesses
obtained from various manufacturing processes is available by clicking
on the HELP button if you aren't sure what to use.
You shaft has a ground finish, so enter 0.2µ in the upper box. You want
the same good finish after coating so enter 0.2µ again in the next box.
Click on the post finishing to change it to a tick, since you are prepared
to grind it after coating. Then enter 0.5µ for the finish of the bronze
bush; a typical turned surface. (Note that, if you skip these questions,
the programme will enter some default values and ask for your agreement).
When you click on the OK button the computer asks you if you will allow
the substrate to be roughened prior to coating. This is necessary for
many sprayed coatings and you should answer yes, since you are going to
finish the coating afterwards.
Selecting partial coating options
There are three options in relation to coverage of your component.
- The whole of the component must be coated. This is usual for corrosive
situations and there can be sometime be a problem in holding the component
in the processing equipment. It might need to be treated in two stages.
- Defined areas must be coated. This is the simplest situation where
you specify that a certain part of the component must be coated - in
the case of the shaft, the part that is contact with the bush. If the
rest gets coated as well, or if there are remote holding points that
don't get coated, you declare this to be of no consequence.
- Defined areas must be uncoated. Here you are specifying that certain
areas of the component must not be coated, so there will be a need for
selective coating or masking to protect those areas. It may be that
there are tight tolerances elsewhere on your component or that there
are parts of it with more specialised properties that you wish to retain.
For your shaft, click on Option 2, the simplest.
Entering the operating temperature
You may specify both the continuous likely operating temperature and
a short term temperature of your component. You may leave either or both
blank, then the computer will assume a default value of 20oC. The definition
of short term is vague; you must be the judge of whether any temperature
fluctuations will last long enough to warrant inclusion.
In the case of the pump. it runs smoothly at a temperature no higher than
50oC; click on the arrows to put this value in both upper boxes.
The processing temperature is important because some coatings require
heat in their application. It may temper or distort your component, or
cause loss of mechanical properties. For your shaft, the material is normalised
low alloy steel and you are going to finish grind if necessary, so you
can allow any processing temperature without fear of the consequences.
Click on Don't Care and press OK
Specifying chemical contamination
A full list of all possible chemical contaminants would be impractical,
so only the common ones are listed. You should select as many as are likely
to be present in the environment of your component. Click on them; they
will move to the right hand box. To deselect them, click on them again;
they will move back. If you skip the screen, the programme will assume
there are no contaminants.
Important points to note are:-
- If the relative humidity exceeds 70%, you should click on water as
a chemical likely to be present.
- Although it is possible to select chemicals in combination, the programme
cannot predict the combined effects of any such groups, it can only
consider them individually.
In the case of the shaft, we have specified an effective seal, so the
only fluid presents will be the lubricant. Click on it and press OK
Requirements for mould release or food approval
This is not a food application or a mould of any sort. You can leave
these as crosses and click on OK.
This is a screen which will be used in later examples.
Describing the component's geometry
There are several types of geometrical feature which can make coating
more difficult (and therefore more expensive). In general, these features
fall into four categories:-
- Holes. Line-of-sight processes, such as those involving spraying,
can be unable to coat the bores of long, narrow holes.
- Sharp edges. Although a component with sharp edges can be coated without
difficulty, some processes may result in blunting of the edge because
of preferential coating. This is particularly apparent for coatings
which involve electric fields.
- Thin webs or small features. Processes involving elevated temperatures
may cause preferential heating of small features, or distortion of thin
sections. Special jigging (at extra cost) can usually overcome these
problems,
- Complex shapes. This is a catch-all category to take into account
designs which may not exhibit the features listed above, but may nevertheless
be difficult to process. Typical complex shapes include those where
one part of the surface is occluded by another, preventing line-of-sight
coating application, or parts which require special jigging to support
them.
None of these apply to the pump shaft, so click on the OK button.
Entering the component dimensions
Components that are particularly large may require special arrangements
to coat them,. particularly when using processes involving immersion in
a liquid or vacuum chamber. This can usually be managed, but only at extra
cost.
In general, if your component is less than 0.5m (18 inches) in each direction,
there will be no problem with any process. Your pump shaft is 900mm long
and has a diameter of 100mm. Enter these and click on OK. You don't need
to enter three values.
Examining the results
The results of your consultation are displayed in three groups:-
Good Solutions
The first group is those coatings which are likely to be effective
solutions for your application. By clicking on one of the buttons below
the list, you can rank these in order of cost, wear resistance, corrosion
resistance or ecological impact. If you click on one of the solutions,
you will be presented with any application notes which have been generated
during the consultation.
Probable Solutions
The second group (which is often not entered) includes those coatings
which will probably work, but for which there may be some uncertainty.
You should consult your Poeton Sales Engineer about these. Clicking
on any of these candidates will give you an explanation of why it has
been eliminated.
Unacceptable Treatments or Coatings
The final group is list of those processes which have been eliminated
because they do not meet your requirements. Clicking on any one of them
will tell you why it has been rejected.
For the example we are following, you will see that it tells you that
any of 28 processes would be acceptable to solve your problem.
To get more information about the coatings, select Contents form the HELP
menu, then look at the APTICOTE range.
Printing the results
Just click on the PRINT button on the toolbar, select the options you
wish to print, and you'll get a hard copy.
Examining and changing the entered data.
You can look at the data you have entered and change it very easily.
Just click on the DATA button on the toolbar. You'll see this:
The data screen presents a summary of all the requirements you have entered
for the system to satisfy. From here, you may speedily edit requirements
to make them more or less restrictive. To do so, just click on the particular
piece of information.
If you wish to know which of your requirements have caused the most solutions
to be eliminated, select Elimination form the View menu.
Try some experiments with this example:-
- Go to the DATA screen, find 'Allow Machining?' At the moment, it says
'Yes'. Click on it; when the relevant screen comes up, change that condition
to 'No'. Now press OK and you will see that the number of solutions
has dropped from 28 to 22. That is because the thermal sprayed coatings
have been eliminated; they will be too rough as-sprayed if you don't
allow post-finishing.
- Now return again to the DATA screen and look for 'Chemical Environment'.
Click on it and you will return to the Chemicals screen. Let's suppose
that the seal in the water pump may allow some leakage, so that water
may ingress into the contact area. Click on 'Water' and move it to the
right-hand side. Click on OK and you will now see that the solutions
have fallen to 19. For instance, the programme now rejects Carburising
and Nitriding because of the risk that those surfaces would be corroded
in the contact by the water.
- Finally, return again to the DATA screen and select 'Max Process Temperature.'
Click on it and return to the Temperature screen. Imagine that you are
determined not to distort the shaft in any way, so that you wish not
to heat it above 200oC. At present, the screen says 'Don't Care'; change
it to 200oC and press OK. Now there are only 9 solutions because the
electroless nickel options (where the heat treatment is above 200oC)
have been eliminated.
Try some more experiments of your own.
More ways to change the data
If, on your, screen showing the list of results, you wish to explore
the possibility of using one of the solutions that has been rejected,
just click on it and the box will tell you why it has been rejected. If
you then click again on that rejection statement (or one of them if it
has been eliminated for more than one reason), the programme will take
you back to the specific data screen and provide an opportunity for you
to change it. For instance, if the solution was rejected because
it didn't meet your hardness requirements, you can try reducing them.
Pressing OK will then take you directly to a new results screen which
reflects the effect of the change you have just made.
Try some experiments with this example.
The Elimination Browser
The Elimination Browser appears in a smaller window. It presents a list
of the coating selection criteria and the number of possible solutions
eliminated by each one. From this, you can see which of the requirements
you have specified are the most harsh, and perhaps relax them to permit
more solutions. Just click on the one you wish to change.
The final screen
Press OK at the Results screen and you will see information on the location
of your Poeton coating service centres around the UK.
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