Each pass thickness & interpass temp. confused
06-25-2018, 02:10 PM,
#1
Each pass thickness & interpass temp. confused
Hi
Our HVOF system is MEC 2700 Hybrid gun and we are spraying with automation system, using Metco powders so far.
For mandrels (materials are 4140 - 4145), we are spraying 88-12 but still couldn' t fix our parameters because of problems. Odd thing is all advisers are advising different parameters.
Preperation: 24 grid brown aluminum oxides
Stainless brush clean, air flow for dusts.
Prespraying: 20 microns each layer
spraying: 15 microns each layer
tool temp.: max 80 degree celcius
but sometimes cracks occure under liquid penetration test.
one adviser said its reason is interpass temp. it must be around 40 degree
another said 'your cleaning is not good enough and you must reduce your layer thickness to 10 - 7 -for bond and for wc co-
one another said you must preheat tool for 100 degree and during process, 80 to 100 degree tool is okey.


so what would you say for ideal thickness and tempratures?
Reply
06-25-2018, 03:20 PM,
#2
RE: Each pass thickness & interpass temp. confused
(06-25-2018, 02:10 PM)enver Wrote: Hi
Our HVOF system is MEC 2700 Hybrid gun and we are spraying with automation system, using Metco powders so far.
For mandrels (materials are 4140 - 4145), we are spraying 88-12 but still couldn' t fix our parameters because of problems. Odd thing is all advisers are advising different parameters.
Preperation: 24 grid brown aluminum oxides
Stainless brush clean, air flow for dusts.
Prespraying: 20 microns each layer
spraying: 15 microns each layer
tool temp.: max 80 degree celcius
but sometimes cracks occure under liquid penetration test.
one adviser said its reason is interpass temp. it must be around 40 degree
another said 'your cleaning is not good enough and you must reduce your layer thickness to 10 - 7 -for bond and for wc co-
one another said you must preheat tool for 100 degree and during process, 80 to 100 degree tool is okey.


so what would you say for ideal thickness and tempratures?


If you have problems with the cracks in the layer, it means that your layer has too high tensile stresses. You can solve the problem with two independent measures, but best, do both:

1. Reduce your single layer thickness to < 10 microns (even better < 5 microns per pass) by increasing the number of revolutions of the part: triple revolution number compared to today's state.

2. Reduce the cooling and preheat the part to 150-200°C (this temperature should be kept during the whole coating process).

If you carry out both measures you will get compressive stresses in your WC88Co12 layer instead of tensile stresses like now. A layer with compressive stresses can not form vertical cracks.
Reply
06-25-2018, 04:55 PM, (This post was last modified: 06-25-2018, 05:59 PM by velocity.)
#3
RE: Each pass thickness & interpass temp. confused
Thank you for reply. I attached application photo with cracks. They re not only vertical.
On the other hand i have questions before trying you advices:
1. As you can see we are using air cooling to keep tool cool. To keep tool around 150' should i stop that?
2. If i preheat and keep tool around 150', after spraying -because of cooling shrinkage-cracks will not occure?
3. In this post you said avoid temprature for thick coatings: http://www.gordonengland.co.uk/sef/Threa...0#pid11090


Attached Files Thumbnail(s)
       
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06-25-2018, 06:58 PM, (This post was last modified: 06-25-2018, 08:16 PM by Vadim Verlotski.)
#4
RE: Each pass thickness & interpass temp. confused
(06-25-2018, 04:55 PM)enver Wrote: Thank you for reply. I attached application photo with cracks. They re not only vertical.
On the other hand i have questions before trying you advices:
1. As you can see we are using air cooling to keep tool cool. To keep tool around 150' should i stop that?
2. If i preheat and keep tool around 150', after spraying -because of cooling shrinkage-cracks will not occure?
3. In this post you said avoid temprature for thick coatings: http://www.gordonengland.co.uk/sef/Threa...0#pid11090

Hi enver,

your picture clearly shows the cracks due critical tensile stresses (crackle - crack network). With such a large component you do not need any cooling: temperature will never be too high.

What I wrote about the temperature < 120°C belongs to very thick layers (> 2 mm); with normally thick WC-Co layers (200-300 microns), the temperature of the component can be significantly higher. The thicker the coating, the lower the stresses this coating can withstand (no matter if tensile or compressive stresses). For this reason, the stresses in a very thick coatings must be close to zero.
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06-26-2018, 09:12 AM,
#5
RE: Each pass thickness & interpass temp. confused
Hi! enver,
It is look like heat cracks only due to stress. Use Diamond wheel for Pre and Final Grinding ( After Grinding do NDT & take picture for safe)

Questions??
1.Have you done leak check your console & gun hoses, if no, please verify
2. May i know your Spray rate? cross check the Actual Vs Current ? have you get the same
3. hope you will use Air for cooling purpose, if it has moisture, of course their will be a possible
I prefer, do a sample test before spray on job.

Usually mandrels required thickness below 900 Microns can be achieved by Hard chrome plating. In your case
thickness will be more than 1mm somehow. Hope you are using standard parameters. Are you using METCO DJC console? or other?
1. After Pre grinding NDT is required (during masking and blasting time do cell setup)
1. Use grit 20/24Mesh for surface preparation above 500 microns thickness ( I prefer 20 Mesh white aluminum Oxide / Blasting Pressure 40-45 Psi)
2. Clean after blasting as usual then Pre heat the part , you can add additional air jet for cooling the part
3. Apply bond coat , I recommend WOKA 1160 (Good DE%) you can go up to max 600 Microns ( 10-15 Microns per pass will be OK, do not spray continuously , part temperature should not exceed above 110 F during spray ,Max 150 F)
4. if You going to spray more than 2 mm thickness, I recommend you to do ARC Spray as bond ( Use 75 B)
You can save time and Cost but you have to do post machining after ARC Spray ( Then blasting and HVOF)
5. Try 86WC10Co4Cr as Top Coat if you are using METCO powder try WOKA 3652

Take photo graphs during each process ( Pre grinding / Masking / Blasting / Bond coat / top coat, Final Grinding, Chamfering and Super Polishing
If it is success you can make as standard procedure.

Let me know your console so that i can send you parameters.

Regards,
Krishan




Reply
06-26-2018, 04:33 PM, (This post was last modified: 06-27-2018, 08:34 AM by velocity.)
#6
RE: Each pass thickness & interpass temp. confused
(06-26-2018, 09:12 AM)demionkrishan Wrote: Hi! enver,
It is look like heat cracks only due to stress. Use Diamond wheel for Pre and Final Grinding ( After Grinding do NDT & take picture for safe)

Questions??
1.Have you done leak check your console & gun hoses, if no, please verify
2. May i know your Spray rate? cross check the Actual Vs Current ? have you get the same
3. hope you will use Air for cooling purpose, if it has moisture, of course their will be a possible
I prefer, do a sample test before spray on job.

Usually mandrels required thickness below 900 Microns can be achieved by Hard chrome plating. In your case
thickness will be more than 1mm somehow. Hope you are using standard parameters. Are you using METCO DJC console? or other?
1. After Pre grinding NDT is required (during masking and blasting time do cell setup)
1. Use grit 20/24Mesh for surface preparation above 500 microns thickness ( I prefer 20 Mesh white aluminum Oxide / Blasting Pressure 40-45 Psi)
2. Clean after blasting as usual then Pre heat the part , you can add additional air jet for cooling the part
3. Apply bond coat , I recommend WOKA 1160 (Good DE%) you can go up to max 600 Microns ( 10-15 Microns per pass will be OK, do not spray continuously , part temperature should not exceed above 110 F during spray ,Max 150 F)
4. if You going to spray more than 2 mm thickness, I recommend you to do ARC Spray as bond ( Use 75 B)
You can save time and Cost but you have to do post machining after ARC Spray ( Then blasting and HVOF)
5. Try 86WC10Co4Cr as Top Coat if you are using METCO powder try WOKA 3652

Take photo graphs during each process ( Pre grinding / Masking / Blasting / Bond coat / top coat, Final Grinding, Chamfering and Super Polishing
If it is success you can make as standard procedure.

Let me know your console so that i can send you parameters.

Regards,
Krishan
Hi
Thank you first of all.
1. Verified.
2. 25 g/min
3. I do. But Vadim said keep it hot around 150 to 200 so should i stop cooling during process?

1. Please make this quest. clear for me.
1. 20 mesh brown aluminum oxides.
2. Is this cooling for keeping tool at same temp. during process like Vadim said as 150 200 degree?
3. You are disagree with Vadim so i must try both temp. limits...
4. Cant i spray over 420 arc sprayed layer with hvof? Like this for 2 mm: 50 mic 95 5 arc spray + 1.75 mm 420 arc spray + 0.2 mm wc co12 ? Is machining a must?
5. I will try.
I m attaching layer after coating and after blasting. Also a process video here:
http://sendvid.com/or7kl7jg


Attached Files Thumbnail(s)
               
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06-29-2018, 05:46 PM,
#7
RE: Each pass thickness & interpass temp. confused
Hi
We applied preheating before bond layer then we realized our wc ended. So we coated on top of bond 1 day later without additional cleaning or heating. Procrss temp is 70 degree. Attached photo belong pre grinding and seems crack free. Rpm and movement adjusted due to this forums comments. So far seems good.


Attached Files Thumbnail(s)
   
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07-03-2018, 10:25 AM,
#8
RE: Each pass thickness & interpass temp. confused
Adding to the discussion on the preheating, the 150-200 C range is good for these drive shafts and mandrel, but make sure its a soaking pre-heat, not just on the surface. make sure you do not oxidize the surface to be sprayed during the preheat. What you want to achieve is very little temperature change during the spraying process.

Probably you would not use the air cooling.

Another thing to check is what is the condition of the part before spraying, some jars, mandrels I have seen have various bad repairs by welding, and the conditions is not good even before your coating process.
Stephen James Booth
www.ipsteknokraft.com
www.teknokraft.com
Indonesia WhatsApp +6281905603262

Reply
11-14-2018, 06:23 PM,
#9
RE: Each pass thickness & interpass temp. confused
Hi,

What is ur spray parameter?

Usually 200-300 Mic WC coating dont need extra bond coat .u can apply directly

What is ur grinding per pass and total grinding thicknesses?

Is ur crack occure before grinding u have to search ur problem at cooling and traverse speed and also spray parameters

What is ur powder mesh?

how is ur preheat process? dont u preheat with gun right??

I think u can try pressure blasting with chilled iron grit 16


Reply
11-16-2018, 09:34 AM,
#10
RE: Each pass thickness & interpass temp. confused
I ll answer all in a couple days but i m thinking about blasting...
I ve high pressure blasting and a small vacuum blasting from nederman. 24 grid Al O2 sand is using.
Whats optimum ra for blasting? When i apply with high pressure, sand carves material too much and after coating these areas became my pain Smile if i know a ra or parameters for blasting i can make it automated
Reply
05-02-2019, 07:41 AM,
#11
RE: Each pass thickness & interpass temp. confused
Update:
For this mandrel type tools we solved problem with your advices. Thanks to all.
There are 3 important point for me still not very clear.
1. Sand blasting pressure and parameters like Ra and key points.
2. Spraying over 2 mm. We have arc spray but when we spray on top of wire, hvof removes with arc layer... For 2 mm thickness can you help me step by step?
3. Because of 150 degree c, sometimes shrinkage causes reduced finished diameters. Its worst thing when we were promising for a delivery to customer...
3.
Reply
05-15-2019, 10:40 AM,
#12
RE: Each pass thickness & interpass temp. confused
Thanks for the information.
Reply
02-03-2020, 11:54 AM,
#13
RE: Each pass thickness & interpass temp. confused
Dear All

Just following the thread and I need help in plasma spray coating of Cr2O3 ceramic

I make multiple pass coatings and by thread discussions I am still not sure if :

a)If i have to maintain around 150 deg C and not allow the base to cool to lets say 80 deg c during the process. In few places it also says even before applying the bond coat, preheat the blasted base metal to 150c.
b)Or do i have to bring down the temperature before starting the next cycle of coating

Which is better ? Keeping a high coating temperature or Cooling the coated surface again and again.

Can anyone brief me the correct method of coating keeping a constant temperature.
thanks in advance
Reply
02-03-2020, 03:30 PM, (This post was last modified: 02-03-2020, 03:32 PM by Vadim Verlotski.)
#14
RE: Each pass thickness & interpass temp. confused
(02-03-2020, 11:54 AM)DMan Wrote: Dear All

Just following the thread and I need help in plasma spray coating of Cr2O3 ceramic

I make multiple pass coatings and by thread discussions I am still not sure if :

a)If i have to maintain around 150 deg C and not allow the base to cool to lets say 80 deg c during the process. In few places it also says even before applying the bond coat, preheat the blasted base metal to 150c.
b)Or do i have to bring down the temperature before starting the next cycle of coating

Which is better ? Keeping a high coating temperature or Cooling the coated surface again and again.

Can anyone brief me the correct method of coating keeping a constant temperature.
thanks in advance


Dear DMan,

The temperature of the component while thermal spraying has a decisive influence on the stress conditions in the layer after cooling. Alone by changing the component temperature during spraying, these tensions can sometimes be varied from high tensile stresses to high compressive stresses, and this on the same material!. Your task is decisive for the correct selection of the stresses state in the coating. In most cases, mild compressive stresses in the coating are advantageous, but not always. For example, for coated parts with small radii of curvature, small tensile stresses in the layer are much better than compressive stresses (the layers with compressive stresses tend to "explode" on sharp edges).

Depending on your task, you can positively influence the quality and operating time of the coat with a suitable component temperature. In your case (anilox rollers), low compressive stresses in the layer are recommended. You get such compressive stresses if your steel roller is kept at a temperature of 150-180°C while coating with Cr2O3. On the other hand, maximum cooling of the roller must be achieved during application of the metallic bond coat (< 100°C).
No preheating should be carried out for aluminum rollers. Aluminum rolls have to be cooled as much as possible during plasma coating with Cr2O3 (also < 100°C rolls temperature).

The right temperature of the roller is achieved using an optimized robot program in combination with adjustable cooling. Of course, you also need continuous temperature monitoring of the component using a pyrometer.

Regards
Vadim
Reply
02-05-2020, 06:06 AM,
#15
RE: Each pass thickness & interpass temp. confused
Dear Vadim
Thanks once again.
Few clarifictaions needed.

1.What is the correct method of cooling such rollers during coating process.
At the moment I am just making making multiple air passes from the metco gun air silvents to get the temp of the roller down. But I am doing this lets say after every 3 passes by interupting the coating sequence which i dont know is a right method or not.

2. Lets say my coating require total 25 passes of 10 microns /pass..should all the passes be made in a single go or do i have to interupt in between (after every 4 passes ) to control the roller temperature?

3.what is the max and the minimum roller temperature permisible during coating in case of MS and ALUMINIUM?

Await your generous repsonse
Dman

Dear All

Just following the thread and I need help in plasma spray coating of Cr2O3 ceramic

I make multiple pass coatings and by thread discussions I am still not sure if :

a)If i have to maintain around 150 deg C and not allow the base to cool to lets say 80 deg c during the process. In few places it also says even before applying the bond coat, preheat the blasted base metal to 150c.
b)Or do i have to bring down the temperature before starting the next cycle of coating

Which is better ? Keeping a high coating temperature or Cooling the coated surface again and again.

Can anyone brief me the correct method of coating keeping a constant temperature.
thanks in advance
[/quote]


Dear DMan,

The temperature of the component while thermal spraying has a decisive influence on the stress conditions in the layer after cooling. Alone by changing the component temperature during spraying, these tensions can sometimes be varied from high tensile stresses to high compressive stresses, and this on the same material!. Your task is decisive for the correct selection of the stresses state in the coating. In most cases, mild compressive stresses in the coating are advantageous, but not always. For example, for coated parts with small radii of curvature, small tensile stresses in the layer are much better than compressive stresses (the layers with compressive stresses tend to "explode" on sharp edges).

Depending on your task, you can positively influence the quality and operating time of the coat with a suitable component temperature. In your case (anilox rollers), low compressive stresses in the layer are recommended. You get such compressive stresses if your steel roller is kept at a temperature of 150-180°C while coating with Cr2O3. On the other hand, maximum cooling of the roller must be achieved during application of the metallic bond coat (< 100°C).
No preheating should be carried out for aluminum rollers. Aluminum rolls have to be cooled as much as possible during plasma coating with Cr2O3 (also < 100°C rolls temperature).

The right temperature of the roller is achieved using an optimized robot program in combination with adjustable cooling. Of course, you also need continuous temperature monitoring of the component using a pyrometer.

Regards
Vadim

[/quote]

Reply
02-05-2020, 06:54 AM, (This post was last modified: 02-05-2020, 07:04 AM by Vadim Verlotski.)
#16
RE: Each pass thickness & interpass temp. confused
Dear DMan,

It is best to use two systems for cooling at the same time: stationary compressed air cooling for the entire roll length (several small nozzles every 2-3 cm) and your mobile cooling metco gun air silvents. Both systems must be adjustable (mechanical ball valves or electronic solenoid valves). By regulating the amount of compressed air in both systems together with your robot speed, you reach the required roller temperature without interrupting the spraying process. For the first time preheating, you should make a couple of burner runs without powder and without cooling.
The pyrometer for online temperature monitoring is attached to robots together with the burner.

As we said, you have to use as much cooling as possible to coat the aluminum rollers so that your roller temperature does not exceed 100-120°C (lower limit is dew point, but you cannot cool as much anyway). Upper limit: approx. 150°C.
For steel rollers and Cr2O3 layers, the optimal roller temperature is between 150 and 180°C. Lower limit: 120-130°C and the upper: 200-220°C.

Regards
Vadim
Reply
02-05-2020, 12:57 PM,
#17
RE: Each pass thickness & interpass temp. confused
Dear Vadim

Thanks once again for your informative and prompt reply. Already i see lot of improvements to be made at my end.

You just missed out the answer to my second question which is of great concern to me.

for eg..I want to coat 350 micron for both a MS roller and an AL sleeve.
Lets say i make 10 micron per pass . So i have 35 passes.

MS:
Should All 35 Passes be made one after other in one GO? Or should it be done in intervals of 10-10-10-5 with cooling passes in between?
AL:
35 passes together or in intervals ?

I feel this is important to avoid any layering effect , but what way should i go about?
Warm Regards
DMan

Dear DMan,

It is best to use two systems for cooling at the same time: stationary compressed air cooling for the entire roll length (several small nozzles every 2-3 cm) and your mobile cooling metco gun air silvents. Both systems must be adjustable (mechanical ball valves or electronic solenoid valves). By regulating the amount of compressed air in both systems together with your robot speed, you reach the required roller temperature without interrupting the spraying process. For the first time preheating, you should make a couple of burner runs without powder and without cooling.
The pyrometer for online temperature monitoring is attached to robots together with the burner.

As we said, you have to use as much cooling as possible to coat the aluminum rollers so that your roller temperature does not exceed 100-120°C (lower limit is dew point, but you cannot cool as much anyway). Upper limit: approx. 150°C.
For steel rollers and Cr2O3 layers, the optimal roller temperature is between 150 and 180°C. Lower limit: 120-130°C and the upper: 200-220°C.

Regards
Vadim
[/quote]

Reply
02-05-2020, 01:57 PM,
#18
RE: Each pass thickness & interpass temp. confused
Dear DMan,

It doesn't matter whether you coat with or without breaks, the important thing is that your roller has the necessary preheating temperature during spraying. If you take a long break and the roller cools down to room temperature, you need to preheat it before you continue coating.
Many sprayer think that the coating process must not be interrupted. It is wrong. Of course it is economically better to spray without interruptions, but even with interruptions the full coating quality can be achieved.

Regards
Vadim
Reply
02-06-2020, 06:24 AM,
#19
RE: Each pass thickness & interpass temp. confused
Dear Vadim

Thanks again.
I just missed out one point.
You suggested preheat steel roller to 150Deg before Cr2o3 coating.I will do that.
That was about Top Coat. But what about preheat before bond coat?
After AL grit blast , do we have to Preheat the roller before Bond coat and till what temp ? I use NiCrAl powder for BC.
Await to hear you.
Warm regards
Dear DMan,

It doesn't matter whether you coat with or without breaks, the important thing is that your roller has the necessary preheating temperature during spraying. If you take a long break and the roller cools down to room temperature, you need to preheat it before you continue coating.
Many sprayer think that the coating process must not be interrupted. It is wrong. Of course it is economically better to spray without interruptions, but even with interruptions the full coating quality can be achieved.

Regards
Vadim
[/quote]

Reply
02-06-2020, 06:50 AM,
#20
RE: Each pass thickness & interpass temp. confused
Dear DMan,

You don't need preheating to apply bond coat. However, all parts should be warm before thermal spraying to avoid possible water condensation (general rule). It is enough 40-50°C to remove condensation.

Regards
Vadim
Reply




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