Request for solution to reduce porosity in HVOF Tungsten Carbide Coatings

[sreenuvundela]

Dear Friends,

We are having Flame Spray Technologies make HVOF Spray Gun and when we depositing WC - Co Coatings with this gun, we are achieving porosity in the range of 2 to 2.5 % which is not acceptable for most of the customers.

The porosity should be less than 1%

Kindly suggest the factors which are affecting for higher porosity levels.


Regards,

SREENIVAS

[Spraytube]

Hi ,

Assuming that you have checked your system, you could work on powder,
several factor could help you to reach the 1% :

Particle size distribution : use the narrowest distribution
Apparent density of the powder, I'm still surprising that this data is missing on several powder provider datasheet.
Primary carbide size included in your agglomerated and sintered powder

If you give more detail, it would be easier to help you.

Regards

[sreenuvundela]

Hi ,

Assuming that you have checked your system, you could work on powder,
several factor could help you to reach the 1% :

Particle size distribution : use the narrowest distribution
Apparent density of the powder, I'm still surprising that this data is missing on several powder provider datasheet.
Primary carbide size included in your agglomerated and sintered powder

If you give more detail, it would be easier to help you.

Regards

Sir,

Thank you for your reply

Kindly forward the problems in HVOF GUN also which will be cause more porosity in coatings.

Kindly do the needful


Regards,

SREENVIAS

[mmgerrie]

Hi ,

Assuming that you have checked your system, you could work on powder,
several factor could help you to reach the 1% :

Particle size distribution : use the narrowest distribution
Apparent density of the powder, I'm still surprising that this data is missing on several powder provider datasheet.
Primary carbide size included in your agglomerated and sintered powder

If you give more detail, it would be easier to help you.

Regards

Sir,

Thank you for your reply

Kindly forward the problems in HVOF GUN also which will be cause more porosity in coatings.

Kindly do the needful


Regards,

SREENVIAS

Porosity is typically caused by the flame being too cold. One thing you can try is to increase your O2 & H2 flows to achieve a hotter flame. There will be a balancing act between oxides and porosity, but when you get the parameters set right you should be able to achieve what you're looking for.

Mike

[Vig]

Hi, Sreenvias

What kind of gun do you use exactly?
What are the spray parameters?
Could you post a micrograph oа your coating?
All of these is important to understand the problem

Best regards,
Vig

[Nesher]

Dear Friends,

We are having Flame Spray Technologies make HVOF Spray Gun and when we depositing WC - Co Coatings with this gun, we are achieving porosity in the range of 2 to 2.5 % which is not acceptable for most of the customers.

The porosity should be less than 1%

Kindly suggest the factors which are affecting for higher porosity levels.


Regards,

SREENIVAS

Dear Sir
We strongly advise buyers of our equipment to pass the powder through a sieve, dry the powder before use and use a freezer to reduce moisture in the air.
90% of the quality of the coating depends on the quality of the powder.
Best Regards
A.Termika Ltd

[loriolo]

Hi Sreenivas

For me isn't clear what is your problem, is necessary to know the equipment, parameters and gun you are using, because surely there is something wrong in your equipment or parameters, With serious HVOF system and a good parameters set, you must have porosity under 1%, even with HVCW 1000 (HVOF wire), you can have porosity under 1%, so if you really need help with coatings, you must share parameters, and equipment, in order to have the correct solution to your problem, otherwise we are loosing time.

[Simon Kim]

Dear Sreenivas,

I am very late.
However I would like to share my knowledge for thermal spray.

The porosity, especially open pores are occured as some reason.
First one is size of powder, the bigger one has more porous coating layer and large open pores. Smaller powder has reduced porosity.
Second one is an absorption water molecular on surface of powder, especially agglomerated and sintered powder. It means powder drying method is not good during wet weather. Please check and compare the related moisture record for thermal sprayed work days.
And the other micro pores are related to a shadow effect by unmelted powder.

Wish your reduced porosity coating,

Simon