Surface Engineering Forum

  • Alternative Forum Home PageSEF Portal
  • Old S E Message Board ArchivesOld Message Board Archives
  • Search
  • Member List
  • Calendar
  • Help

Current time: 04-23-2018, 06:36 PM Hello There, Guest! (Login — Register)


Surface Engineering Forum / Surface Engineering / Surface Engineering Threads v
1 2 3 4 5 ... 30 Next »
/ HVOF Grit Embeddment Help!




Post Reply 
Threaded Mode | Linear Mode
HVOF Grit Embeddment Help!
01-10-2018, 08:34 PM (This post was last modified: 01-10-2018 09:11 PM by Carguy1968.)
Post: #1
Carguy1968 Offline
Junior Member
**
Posts: 4
Joined: Jan 2018
Reputation: 0
HVOF Grit Embeddment Help!
Hello All!

This is my first time posting, but have read many of the forums. I am reaching out to you to engage everyone’s opinion on a defect I am currently experiencing.

First off, we are spraying cylindrical parts using HVOF. Some are sprayed with a tungsten carbide blend, others are an iron blend. Nonetheless both materials are producing the same defect.

The defect occurs after grit blasting and HVOF spraying a workpiece. The coating produced has a series of small bumps in it. After some investigation it was concluded that these bumps were actually pieces of grit being coated over. After gritblasting the work pieces undergo a blow off process with compressed air. During finishing of the coating, i.e. grinding, these pieces would fall out causing small voids. These voids were confirmed with non destructive testing.

It appears odd because one day it was fine and the next this issue appeared. Grit supplier and all parameters are the same including no changes in workpiece material. Does anyone know what may be causing this embedment or steps to correct such?

Thanks much in advance!
-C
Send this user an email Find all posts by this user
Quote this message in a reply
01-11-2018, 11:51 AM (This post was last modified: 01-11-2018 11:58 AM by Vadim Verlotski.)
Post: #2
Vadim Verlotski Offline
SuperMember
******
Posts: 113
Joined: Sep 2014
Reputation: 5
RE: HVOF Grit Embeddment Help!
(01-10-2018 08:34 PM)Carguy1968 Wrote:  Hello All!

This is my first time posting, but have read many of the forums. I am reaching out to you to engage everyone’s opinion on a defect I am currently experiencing.

First off, we are spraying cylindrical parts using HVOF. Some are sprayed with a tungsten carbide blend, others are an iron blend. Nonetheless both materials are producing the same defect.

The defect occurs after grit blasting and HVOF spraying a workpiece. The coating produced has a series of small bumps in it. After some investigation it was concluded that these bumps were actually pieces of grit being coated over. After gritblasting the work pieces undergo a blow off process with compressed air. During finishing of the coating, i.e. grinding, these pieces would fall out causing small voids. These voids were confirmed with non destructive testing.

It appears odd because one day it was fine and the next this issue appeared. Grit supplier and all parameters are the same including no changes in workpiece material. Does anyone know what may be causing this embedment or steps to correct such?

Thanks much in advance!
-C

It can have many causes. We need images of the defect and microscopy of the cross-section to this place to say more. Maybe just the filter of grit blaster was not changed too long.
Send this user an email Visit this user's website Find all posts by this user
Quote this message in a reply
01-11-2018, 04:36 PM
Post: #3
loriolo Offline
SuperMember
******
Posts: 264
Joined: Jan 2010
Reputation: 3
RE: HVOF Grit Embeddment Help!
Hi Carguy
As Vadim wrote, is necessary to tell more about your process, because the trouble could be quite infinite with indefinite notices, I don’t think that problem is on the blasting operation, there are many others as follow:
Powder sticking inside the barrel
Defective base material
Wrong parameters setting
Wrong spray system or components

Best regards
Luigi
Send this user an email Visit this user's website Find all posts by this user
Quote this message in a reply
01-16-2018, 07:57 AM
Post: #4
syam Offline
Junior Member
**
Posts: 2
Joined: Jan 2018
Reputation: 0
RE: HVOF Grit Embeddment Help!
What is the exact surface profile requirement for HVOF process. Can anyone provide the ASME standards or is it based on the Metal powder specification.
Also anything regarding this is mentioned in ASME B-46.1.


Regards
SG
Send this user an email Find all posts by this user
Quote this message in a reply
01-17-2018, 01:15 AM
Post: #5
Taz Offline
Member
***
Posts: 7
Joined: Jul 2017
Reputation: 0
RE: HVOF Grit Embeddment Help!
Hi Carguy,

What type of grit blasting that you use?
What are the grit blast size are you using?
Send this user an email Find all posts by this user
Quote this message in a reply
01-17-2018, 08:50 AM
Post: #6
syam Offline
Junior Member
**
Posts: 2
Joined: Jan 2018
Reputation: 0
RE: HVOF Grit Embeddment Help!
(01-17-2018 01:15 AM)Taz Wrote:  Hi Carguy,

What type of grit blasting that you use?
What are the grit blast size are you using?

we are using aluminum oxide grit
Send this user an email Find all posts by this user
Quote this message in a reply
01-18-2018, 03:09 PM
Post: #7
Artyom Offline
Junior Member
**
Posts: 4
Joined: Nov 2017
Reputation: 0
RE: HVOF Grit Embeddment Help!
Hello Carguy!

You can try to perform grit blasting using a HVOF gun as follows:
1) Pour a white alumina oxide F120 (100-125 microns) or F240 (2-45 microns) into a powder hopper. It's very convenient to use a couple of hoppers - the one for the spraying powder and the second for alumina.
2) Set up standard spraying parameters - for instance, parameters which you use for tungsten carbide coating.
3) Carry out the standard grit blasting of a part (blowing with compressed air is not required), then carry out grit blasting using a HVOF gun - 2 passes, no more isn't required.
Supersonic jet with alumina oxide particles will remove all remaining grit and will pre-heat the surface for better bonding of the coating. Temperature of the HVOF jet is not enough for melting of alumina oxide so there will be no foreign particles at the substrate-coating boundary. We are using this technique on the liquid-fueled HVOF K2 gun (GTV). Just one note: nozzle wear slightly increases, but if you have a gun with axial feeding, wear rate will be very slow.

Kind regards,
Artyom
Send this user an email Find all posts by this user
Quote this message in a reply
02-07-2018, 09:33 PM
Post: #8
demionkrishan Offline
Active Member
****
Posts: 29
Joined: Dec 2015
Reputation: 0
RE: HVOF Grit Embeddment Help!
Check your grit blasting machine first. Is there any air pressure leakage? Have you seen any difference? Check your blasting gun ID worn? How much roughness are you getting after blasting? I prefer 250-300 ra If all good.
Remove all grit from your blasting machine, empty it. Buy white alumina 20 mesh from another supplier and see the difference. I faced same issue previously.
Send this user an email Find all posts by this user
Quote this message in a reply
« Next Oldest | Next Newest »
Post Reply 




Possibly Related Threads...
Thread: Author Replies: Views: Last Post
  36 and 60 Grit AlO help! Carguy1968 7 388 04-05-2018
05:11 PM
Last Post: ThePlummer54
  Is it possible to spray powder established for gas based HVOF in Fluid HVOF system?? sreenuvundela 0 1,158 04-18-2016
07:52 AM
Last Post: sreenuvundela
  Grit Blasting Parameters DanyGans 0 1,792 05-31-2015
12:10 PM
Last Post: DanyGans
Question Brown aluminum oxide VS Chilled iron grit Bacon 2 2,055 03-27-2015
06:23 PM
Last Post: Bacon
  suction or pressure grit blast machine? stvon 2 2,469 04-17-2014
04:01 PM
Last Post: Met.Eng.
  Oxidized steel grit SriramL 3 3,295 04-28-2013
07:10 PM
Last Post: shantanu
  Grit blasting epoxy, carbon fibre and titanium in one cabinet? David Churcher 2 2,838 11-30-2012
01:42 PM
Last Post: MichiganMan
  Dimension change after grit blasting TomasCro 6 4,382 11-27-2012
09:12 AM
Last Post: TomasCro
  Surface roughness after grit blasting Leanne 8 16,033 08-15-2012
05:28 AM
Last Post: Leanne
Shy Grit size sam xu 3 3,950 03-23-2012
04:24 PM
Last Post: sam xu
  Brush instead grit blasting divanis 4 4,706 11-16-2011
05:32 PM
Last Post: divanis
  Build Up without grit blasting Met.Eng. 5 4,924 09-27-2011
03:57 AM
Last Post: kschewe
  Dirt in the grit blasting machine Aware 7 6,122 05-20-2011
05:27 PM
Last Post: Aware
  Grit Blasting Riz 5 10,427 05-10-2011
01:14 PM
Last Post: MichiganMan
  How to decide grit size ? bepsi 6 12,694 04-29-2011
05:56 AM
Last Post: wilfred1963

  • View a Printable Version
  • Send this Thread to a Friend
  • Subscribe to this thread


User(s) browsing this thread: 1 Guest(s)





Surface Engineering Forum Sponsor - Alphatek Hyperformance Coatings Ltd

    Subscribe in a reader

    Contact Us | Thermal Spray Coatings | Return to Top | Return to Content | Lite (Archive) Mode | RSS Syndication

Powered By MyBB, © 2002-2018 MyBB Group.


© Copyright Gordon England