HVOF Process
Industry support for the Hard Chrome Alternatives Team
(HCAT) guidelines is increasing significantly as new
process developments and applications are established.
Initial successes, for the very highly specified aircraft
landing gear, has driven interest for applications that are
perhaps not so demanding - but have a large production
throughput.
These type of applications, such as hydraulic rams for
earth moving equipment, are much more cost sensitive.
One way to lower production costs is to use coatings fast
& efficiently. In the majority of cases, with the right equipment
this process is as accurate as the normal diamond wheel
grinding followed by a super-finishing system.
KGS Belt Solution
KGS has a range of products to enable the whole process
to be done by different belts on a suitable Tool Post
Grinder (TPG). Coarse grits from 60 with a hard backer
give a free cutting action that can accurately calibrate to
dimensions required. Further finer grits can be utilised to
give mirror finish with a very low Ra value. Because of the
speed of cut total process time is cut dramatically.
HVOF Spraying
Finishing of spray coated rolls :
As ever the key to efficient grinding and finishing resides in the quality, conformity and accurate calibration of the substrate. Then the quality of the powders and spray equipment contribute to the amount of grinding required.
The resultant sprayed surface is rough, irregular and needs grinding below a certain level to reach the homogenous layer
which can be 70 microns below the rough sprayed finish.
Roll grinding with KGS Telum CH Diamond Belts
Grinding and polishing HVOF or ceramic coated cylinders
Figure: Schematic Diagram showing
Target grinding and finishing zones
Grinding and polishing HVOF or ceramic coated cylinders
The process benefits from very precise equipment –Generally – with an accurately calibrated metal roll – They will apply say 250 micron of coating –
Depending on the quality of the sprayed powder, the type of gun and whether the application is by hand or by robot.
This coating can have an Ra of around 8 micron And an Rt of around 70 micron.
So they must remove well over 70 micron to ensure they reach below the continuous closed layer. So that the target is to remove say 100 micron to end up with accurately sized and polished roll.(in this case with a 150 micron layer)
The initial grind is normally to remove the coarse finish from spraying – Say 75 micron – is done with the red 200 or coarser if needed. (This part of the process is more often done by WHEELS today) The next 25 micron will normally be done with Yellow 400 grit down – With multiple passes –To end up with the final required diameter and a specific coating thickness & Ra. (This part of the process is often done by Diamond Film Superfinishing machines today)
Roll grinding with KGS Telum CH Diamond Belts
Tool Post Grinder Settings
Belt Grinding Machinery
HVOF grinding for large rolls has been traditionally achieved with large diamond wheel grinders followed by honing stones or Super-finishing equipment.
To take advantage of the new generation of KGS Diamond Belt finishing system - either a dedicated belt grinding machine or a retro-fitted belt attachment is required. This is the best option as the rigidity, size and quality of this type of machine enables more accurate grinding parameters.
However, in many instances, even small Tool Post Grinders can deliver excellent results with the KGS Diamond Belt System.