08-02-2011, 07:53 AM,
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Christine
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How do reduce tensile strength of coating Metco 52C-NS?
Dear all,
My customer has been experiencing high tensile strength >5000psi, when the requirement is 1200-5000 psi.
The thickness of the coating is 0.006 inch minimum (per manual requirement), he has even tried to vary the thickness from 0.010 - 0.018 inch, but the result is still greater than 5000 Psi!
They use Adhesive film FM1000 from Cytec Engineered Materials Inc ( i thought they were getting false-high readings due to excessive glue penetration into the coating, but i do not think this is the case with this glue and the micro graphs of the coating are not that porous.)
They cannot spray with the OEM recommended N2/H2 parameters so they are using Ar/H2.
I suggested to increase primary gas flow rate (Argon) to decrease dwell time and therefore reduce particle heating and end coating cohesion. This is one of the 1st few suggestions that I gave to reduce tensile strength. But im kinda confused, doesn't increasing primary gas flow lead to denser coating? denser coating would mean high tensile bond strength!! If not....then, how much can he increase the value of primary gas (Argon) flow? 100 Psi? 120 Psi? Help!!! [/quote]
Below are the parameters used:
Gun Type: 3MBTD
Nozzle: GH
Electrode: 9MB63
Powder Injector 1
Spray angle (o) 90
Gun to part distance (inches) 2.5
Control Unit Type 9MC
Primary Ar gas pressure (Psi) 75
Primary Ar gas flow (scfh) 90
Secondary H2 gas pressure (Psi) 50
Secondary H2 gas flow (scfh) -
Current (Amps) 500
Start voltage (Volts) 40
Powder Feed Unit Type 3MP
Rate of deposit (inch /pass) 0.002”
Robot / Manipulator
Gun travel speed (mm/s) 4.76
Surface speed (RPM) 60
Results (Tensile Bond Strength, Psi)
Experiment 1: Avg 9467.67
Experiment 2: Avg 7379.51
Experiment 3: Avg 6018.66
NB: He is limited by the small diameter of the part and size of the gun. So, he can only set the spray distance 2,5 inches maximum.
[/font]
Christine Francis
Technical Support Engineer
mailto:Christine.Francis@sulzer.com
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08-02-2011, 09:18 AM,
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Gordon
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Hi Christine
to the Surface Engineering Forum.
That's strange, setting a maximum value on a tensile bond strength test.
If the coating is good and meets all other requirements, it really seems daft to fail it for having high bond strength, the one property most of us are trying to maximise most of the time
Is your customer using a bond coat, if not what is the substrate and surface preparation? What is the purpose or function of the coating?
I would used 0.025" thick coatings for the bond strength test. It may lower the values a bit and be a bit more comparable to OEM tests.
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08-02-2011, 09:50 AM,
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Dear Gordon,
Thanks for the warm welcome!
My customer is using Metco 52C-NS for repair (Jet engines).
But, does increasing the primary gas flow help reduce tensile strength of the coat? or will cause the coating to get denser and further increase tensile strength values?!
yes gordon, i totally agree with you when you say we are usually working the other way round
(08-02-2011, 09:18 AM)Gordon Wrote: Hi Christine
to the Surface Engineering Forum.
That's strange, setting a maximum value on a tensile bond strength test.
If the coating is good and meets all other requirements, it really seems daft to fail it for having high bond strength, the one property most of us are trying to maximise most of the time
Is your customer using a bond coat, if not what is the substrate and surface preparation? What is the purpose or function of the coating?
I would used 0.025" thick coatings for the bond strength test. It may lower the values a bit and be a bit more comparable to OEM tests.
Christine Francis
Technical Support Engineer
mailto:Christine.Francis@sulzer.com
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08-02-2011, 10:57 AM,
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Gordon
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Hi Christine
Quote:But, does increasing the primary gas flow help reduce tensile strength of the coat? or will cause the coating to get denser and further increase tensile strength values?!
First, sorry being a little pedantic - coating tensile strength is a very different property to coating tensile bond strength. I pretty sure we are talking about the latter. Just to avoid any confusion.
Any parameter change that you make that is going to significantly lower the tensile bond strength is going to significantly effect general coating quality in a negative way probably even more.
Increasing primary gas flow will probably lower bond strength at some point, but as you have said it is possible that strength may increase or stay the same until a point where coating quality and bond strength suffer. It's difficult to say without knowing the present coating properties relative to the parameters being used. Typically, many coatings (using OEM recommended parameters) are what I call "middle of the road" they can withstand a range of + or - parameter variance without significant change (or veering off the road). You may find just lowering the current or hydrogen secondary flow better or I should say worse for the coating
I would seriously like to know why and for what reason a maximum limit is specified. It does not seem reasonable to degrade a coating to achieve a lower bond strength, just not logical
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08-03-2011, 03:47 AM,
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Dear Gordon and Len wood,
He is using Metco 450NS as a bond coat and Metco 52C NS as a top coat. He sprayed and tested both of Metco 450NS and 52C NS separately (with different set of specimen). So far, the result of Metco 450NS is good (has met the requirement of engine manual for tensile bond strength, 5000 Psi minimum). But, Metco 52C NS is still greater than the engine requirement (1200 - 5000 Psi), i.e. still more than 5000 Psi.
He is spraying the inner diameter of compressor casing. It will meet with the rotation of rotor. The bond coat needs to be very adherent, while the top coat need to be a little abraded. (i hope this explains why he needs a "softer" top coat and why there's a tensile limit set to the abradable coat).
Christine Francis
Technical Support Engineer
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08-03-2011, 09:41 AM,
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Gordon
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Hi Christine
What other coating evaluation tests are done to check correct degree of abradability?
I can now understand having a maximum tensile strength for the coating, but not by testing for it using a tensile bond strength test.
If the coating is too hard/strong and needs to be more abradable, I would start by reducing the secondary hydrogen gas flow (reducing volts) and or current (Amps). While it may be possible to achieve this by adjusting (increasing) Ar primary flow only, (in fact increasing power levels with higher voltage) I would leave this for later tweaking if required along with possible adjustments to powder feed rates.
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08-04-2011, 03:10 AM,
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
(08-03-2011, 09:41 AM)Gordon Wrote: Hi Christine
What other coating evaluation tests are done to check correct degree of abradability?
I can now understand having a maximum tensile strength for the coating, but not by testing for it using a tensile bond strength test.
If the coating is too hard/strong and needs to be more abradable, I would start by reducing the secondary hydrogen gas flow (reducing volts) and or current (Amps). While it may be possible to achieve this by adjusting (increasing) Ar primary flow only, (in fact increasing power levels with higher voltage) I would leave this for later tweaking if required along with possible adjustments to powder feed rates.
Dear Gordon,
Thanks for your advice I am checking with him if other tests are being conducted to test abradability.
He performed the tensile test of Metco 52C-NS without bond coat for the specimen.
1. Is there any difference in results if tensile testing is performed on Metco 52C-NS with bond coat and without bond coat?
2. Does it mean, if he performs bond coat together with top coat on to a coupon, the result of tensile should follow that of the top coat requirement?
Christine Francis
Technical Support Engineer
mailto:Christine.Francis@sulzer.com
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08-04-2011, 08:16 AM,
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Gordon,
As for other tests to evaluate abradability;
Metallurgical tests were performed for the following...
=> top Coat-Bond Coat Interface Separation
=> top Coat Eutectic Phase
=> top Coat Porosity
According to the customer, majority of the results were ok though they were leaning towards the denser regions with small amounts of eutectic phases visible...
Christine Francis
Technical Support Engineer
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08-04-2011, 12:07 PM,
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Gordon
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Hi Christine
Quote:He performed the tensile test of Metco 52C-NS without bond coat for the specimen.
1. Is there any difference in results if tensile testing is performed on Metco 52C-NS with bond coat and without bond coat?
2. Does it mean, if he performs bond coat together with top coat on to a coupon, the result of tensile should follow that of the top coat requirement?
Is this the test they use?
ASTM C 633 Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings.
To answer 1 . depends on the weakest link in the chain, if that's in the top coat then differences will be little, if that's in the bond coat then yes.
2. Yes but only if top coat is weaker than bond coat. This should really be thought of as testing a coating system, not the individual parts. Point of failure will indicate weakest point in coating system.
The bond strength test is to access how well the coating will stick to the substrate. I think the coating system should be tested as a whole. Little point to testing bond strength of top coat to a substrate, when that interface does not exist on the job.
I will stress again this test is not good for assessment of abradability. As it involves measuring tensile strength from a combination of substrate and coating, Usually an interface fails, so this test can not reliably used to assess coating tensile strength. A test failure lets say at 1200 psi, lets assume a failure at substrate/coating interface. Tells you nothing about actual coating strength does it and coating could be far too strong and not abradable enough, you just can't tell.
Hardness testing is probably simplest and best way to gauge the likely abradability of a coating.
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08-04-2011, 10:36 PM,
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Vijay Deshpande
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Hi Christine
In my opinion why you are not trying pin on disc test to determine abradability of the coating. This test will give you perfect comparison between coatings made by using various parameters.Thats what application demands.
Good luck
Vijay Deshpande
(08-04-2011, 12:07 PM)Gordon Wrote: Quote:He performed the tensile test of Metco 52C-NS without bond coat for the specimen.
1. Is there any difference in results if tensile testing is performed on Metco 52C-NS with bond coat and without bond coat?
2. Does it mean, if he performs bond coat together with top coat on to a coupon, the result of tensile should follow that of the top coat requirement?
Is this the test they use?
ASTM C 633 Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings.
To answer 1 . depends on the weakest link in the chain, if that's in the top coat then differences will be little, if that's in the bond coat then yes.
2. Yes but only if top coat is weaker than bond coat. This should really be thought of as testing a coating system, not the individual parts. Point of failure will indicate weakest point in coating system.
The bond strength test is to access how well the coating will stick to the substrate. I think the coating system should be tested as a whole. Little point to testing bond strength of top coat to a substrate, when that interface does not exist on the job.
I will stress again this test is not good for assessment of abradability. As it involves measuring tensile strength from a combination of substrate and coating, Usually an interface fails, so this test can not reliably used to assess coating tensile strength. A test failure lets say at 1200 psi, lets assume a failure at substrate/coating interface. Tells you nothing about actual coating strength does it and coating could be far too strong and not abradable enough, you just can't tell.
Hardness testing is probably simplest and best way to gauge the likely abradability of a coating.
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08-05-2011, 04:29 AM,
(This post was last modified: 08-05-2011, 04:39 AM by Christine.)
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
(08-04-2011, 12:07 PM)Gordon Wrote: Hi Christine
Quote:He performed the tensile test of Metco 52C-NS without bond coat for the specimen.
1. Is there any difference in results if tensile testing is performed on Metco 52C-NS with bond coat and without bond coat?
2. Does it mean, if he performs bond coat together with top coat on to a coupon, the result of tensile should follow that of the top coat requirement?
Is this the test they use?
ASTM C 633 Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings.
To answer 1 . depends on the weakest link in the chain, if that's in the top coat then differences will be little, if that's in the bond coat then yes.
2. Yes but only if top coat is weaker than bond coat. This should really be thought of as testing a coating system, not the individual parts. Point of failure will indicate weakest point in coating system.
The bond strength test is to access how well the coating will stick to the substrate. I think the coating system should be tested as a whole. Little point to testing bond strength of top coat to a substrate, when that interface does not exist on the job.
I will stress again this test is not good for assessment of abradability. As it involves measuring tensile strength from a combination of substrate and coating, Usually an interface fails, so this test can not reliably used to assess coating tensile strength. A test failure lets say at 1200 psi, lets assume a failure at substrate/coating interface. Tells you nothing about actual coating strength does it and coating could be far too strong and not abradable enough, you just can't tell.
Hardness testing is probably simplest and best way to gauge the likely abradability of a coating.
Dear Gordon,
Thanks so much for your detailed prompt responses, you have no idea how much it helps!
Since not many of us can believe they have set a maximum for the tensile bond strength. I managed extract the relevant portion from the manual (i cannot disclose the OEM is). Metco 52C-NS is compressor case clearance control coatings Class A in OEM spec.
Coating Tensile Bond Strength
"Tensile specimens shall be prepared for tensile bond testing & evaluated in accordance with TASK 70-71-01-700-002, Bond strength Tensile Testing of Thermal Spray Coatings. The avg tensile bond strength for CLASS A top coat (over bond coat) shall be between 1200 and 5000psi. The average tensile bond strength for CLASS B top coat (over bond coat) shall be 2500psi or greater."
Yes, he uses ASTM C 633 Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings.
He also performed the hardness test, even though according to him, it is not required by Engine Manual, the hardness he got for 52C-NS ==> 100 - 110 HRH (Metco Technical Bulletin = 90HRH).
Regards,
Christine
(08-04-2011, 11:21 PM)kschewe Wrote: 52c usually has bond strength higher then 5000. i never seen a maxium for that coating from a oem spec like rolls, prat, or ge. I think a spray distance of 2" is to close for the 3mb.
to try and fix the current problem, try increasing the feed rate to high as possible.
If possible change to flame spray. metco has very small id guns for the 6pII and 14e. They are cheap and spray fast. The bond strength will be lower.
Hi!
Thanks for the advice.
Unfortunately, the OEM spec does provide limits for the Coating Tensile Bond Strength of Metco 52C-NS. I've provided a snap-shot of the spec in the post above.
Ive also asked my customer to increase the feed rate even more as per your recommendation..since he cannot meet a spray distance of at least 5" (starting parameter).
Regards,
Christine.
Christine Francis
Technical Support Engineer
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08-12-2011, 07:28 AM,
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
(08-12-2011, 04:02 AM)ServiceTech Wrote: Christine;
A former SMUS Service Engineer chiming in.......In addition to the excellent advice you have received from the panel of experts, I believe the coating parameter is too hot. The hardness is high, the tensile is high. The coating structure should present some unmelts which may not be evident without chemical etching.
Regardless, I would leave the primary gas alone and drop the amperage down to the 400 amps range and test again. Leave the powder feed rate at 45 grams/min. The voltage you submit (40 vdc) is unusual. Somethings' afoot with that. Please check this parameter again along with secondary gas flow.
Hello !!
Thanks for the great advice! I double checked, and his parameters state 40 Volts..though our start parameters state ard 75Volts!
By the way, how drastic is the effect of voltage difference on the coating? Im still learning how the different parameters (primary gas, amperage, spray distance, gun speed, powder feed rate, etc....) affect the coating
His amperage is around 450-500 Amps with secondary gas (h2) at 50psi.
Regards
Christine Francis
Technical Support Engineer
mailto:Christine.Francis@sulzer.com
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08-12-2011, 04:22 PM,
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Gordon
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Hi Christine
Quote:Coating Tensile Bond Strength
"Tensile specimens shall be prepared for tensile bond testing & evaluated in accordance with TASK 70-71-01-700-002, Bond strength Tensile Testing of Thermal Spray Coatings. The avg tensile bond strength for CLASS A top coat (over bond coat) shall be between 1200 and 5000psi. The average tensile bond strength for CLASS B top coat (over bond coat) shall be 2500psi or greater."
Yes, he uses ASTM C 633 Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings.
He also performed the hardness test, even though according to him, it is not required by Engine Manual, the hardness he got for 52C-NS ==> 100 - 110 HRH (Metco Technical Bulletin = 90HRH).
Thanks for the additional info. The 5000 psi max value now makes a lot more sense. Testing coating system as a whole you may expect bond coat/substrate interface, bond coat and bond coat/top coat interface strength to be greater than 5000 psi, so failures above 5000psi would indicate the strength of the top to be too high i.e. ideally the top coat should be the weakest link in the chain.
Where this can fall over though is when results are within specification (between 1200 and 5000psi), as you will not know for certain that this represents the top coat strength without identifying exact point of failure in coating system. So you could still have an overly strong top coat if the weakest point in the chain changes to elsewhere.
Hardness check seems to support case for too strong and hard top coat.
I would agree with ServiceTech comments:
Quote:Christine;
A former SMUS Service Engineer chiming in.......In addition to the excellent advice you have received from the panel of experts, I believe the coating parameter is too hot. The hardness is high, the tensile is high. The coating structure should present some unmelts which may not be evident without chemical etching.
Regardless, I would leave the primary gas alone and drop the amperage down to the 400 amps range and test again. Leave the powder feed rate at 45 grams/min. The voltage you submit (40 vdc) is unusual. Somethings' afoot with that. Please check this parameter again along with secondary gas flow.
The correct coating (abradable) I would expect to see higher porosity levels as well as increase levels of unmelts. I agree parameters sound "too hot"
40 V does not sound right and you will need to tell us the the plasma gas flows used, particularly secondary H2 as you only include pressure value.
Quote:Thanks for the great advice! I double checked, and his parameters state 40 Volts..though our start parameters state ard 75Volts !Exclamation
By the way, how drastic is the effect of voltage difference on the coating?
Changes to secondary H2 flow has a very significant effect on plasma voltage and to the resultant coating. Generally, increase H2 > increase voltage > increased energy/heating effect.
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08-15-2011, 07:27 AM,
(This post was last modified: 08-15-2011, 08:43 AM by Christine.)
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
(08-12-2011, 04:22 PM)Gordon Wrote: Hi Christine
Quote:Coating Tensile Bond Strength
"Tensile specimens shall be prepared for tensile bond testing & evaluated in accordance with TASK 70-71-01-700-002, Bond strength Tensile Testing of Thermal Spray Coatings. The avg tensile bond strength for CLASS A top coat (over bond coat) shall be between 1200 and 5000psi. The average tensile bond strength for CLASS B top coat (over bond coat) shall be 2500psi or greater."
Yes, he uses ASTM C 633 Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings.
He also performed the hardness test, even though according to him, it is not required by Engine Manual, the hardness he got for 52C-NS ==> 100 - 110 HRH (Metco Technical Bulletin = 90HRH).
Thanks for the additional info. The 5000 psi max value now makes a lot more sense. Testing coating system as a whole you may expect bond coat/substrate interface, bond coat and bond coat/top coat interface strength to be greater than 5000 psi, so failures above 5000psi would indicate the strength of the top to be too high i.e. ideally the top coat should be the weakest link in the chain.
Where this can fall over though is when results are within specification (between 1200 and 5000psi), as you will not know for certain that this represents the top coat strength without identifying exact point of failure in coating system. So you could still have an overly strong top coat if the weakest point in the chain changes to elsewhere.
Hardness check seems to support case for too strong and hard top coat.
I would agree with ServiceTech comments:
Quote:Christine;
A former SMUS Service Engineer chiming in.......In addition to the excellent advice you have received from the panel of experts, I believe the coating parameter is too hot. The hardness is high, the tensile is high. The coating structure should present some unmelts which may not be evident without chemical etching.
Regardless, I would leave the primary gas alone and drop the amperage down to the 400 amps range and test again. Leave the powder feed rate at 45 grams/min. The voltage you submit (40 vdc) is unusual. Somethings' afoot with that. Please check this parameter again along with secondary gas flow.
The correct coating (abradable) I would expect to see higher porosity levels as well as increase levels of unmelts. I agree parameters sound "too hot"
40 V does not sound right and you will need to tell us the the plasma gas flows used, particularly secondary H2 as you only include pressure value.
Quote:Thanks for the great advice! I double checked, and his parameters state 40 Volts..though our start parameters state ard 75Volts !Exclamation
By the way, how drastic is the effect of voltage difference on the coating?
Changes to secondary H2 flow has a very significant effect on plasma voltage and to the resultant coating. Generally, increase H2 > increase voltage > increased energy/heating effect.
Dear Gordon,
Thanks for the advice
I checked and he DOESN'T use secondary gas! As for his voltage, he has yet to respond...but now that we know he doesn't use any secondary gas, is 40-45 Volts acceptable?
regards,
christine
(08-12-2011, 05:00 PM)ServiceTech Wrote: Christine;
At 40 volts, it appears he is not flowing secondary gas at all. Strange. Please verify the H2 flow, not just 50 psi of pressure. I 100% concur with Gordon regarding the effects of secondary gas flow - huge impact on the coating outcome.
Drop the amperage to 400 amps, even 375 and try again.
What is the diameter, that is, the actual, measured diameter of his test buttons????
Hello!!
yes ure absolutely correct there is no secondary gas flow...though i don't know why he included 50psi in his parameters, i'm in the process of checking with him.
The thickness and diameter of his coupons are according to ASTM C633 (tensile button) and the spray distance of the coupons is identical to that of the OEM part (to spray inner area of conical shaped part,5-7inches diameter) . Spray distance is 2.5inches maximum.
Christine Francis
Technical Support Engineer
mailto:Christine.Francis@sulzer.com
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08-15-2011, 09:22 AM,
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Christine
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RE: How do reduce tensile strength of coating Metco 52C-NS?
Hello guys!!
Thank you so much for all the suggestions and advice (especially Gordon & ST)....Guess what?!! he has managed to achieve a healthy and consistent average tensile bond strength of 2200psi!!!
How?
by simply reducing the amperage to 400amp, increasing primary gas flow and applying minimum voltage!! yay!!
Mission accomplished thanks to ya'll
Cheers,
Christine
Christine Francis
Technical Support Engineer
mailto:Christine.Francis@sulzer.com
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