Surface Treatment Inspection and Quality Checks
Most problems with surface treated parts can be identified by a few simple checks when they are delivered to site, by carrying out these inspections at the goods-in area.
Check Coating Thickness First
Inspection of the coating thickness is the most important part of the inspection. A coated eddy-current gauge can be used to measure non-magnetic coatings on steel parts. Magnetic induction gauges are commonly used to measure most types of plated layers. The readings must be taken at a number of points on the part and compared against the relevant dimension on the drawing or against agreed limits for the relevant specification.
Look for Visual Defects Before Anything Else
Visual inspection should be carried out in good light before any processing occurs. Any parts showing signs of blistering, bare areas, burning, pitting or uneven surface(s) should be rejected as such parts are unlikely to improve with service and will indicate a processing problem with the applicator.
Confirm Adhesion on Sample Parts
Adhesion failures can be hidden until a part is under load. Testing the adhesion on sample parts from each batch can reveal problems before they cause any damage. The simplest test is to cut cross-shapes in the coating and measure how much it tries to return to its original shape. For harder coatings, such as thermal spray, a pull-off test can be used with a bonded dolly to measure the adhesion and record the result.
Ask for Documentation and Salt Spray Results
A competent applicator will supply a process certificate for the application, detailing the baths and/or process parameters used, as well as details of any salt spray tests completed to measure corrosion resistance.
A useful reference for Surface Treatments is www.poeton.co.uk/surface-treatments/.
Check Batch Traceability Records
Each batch of treated parts must have a traceable record of treatment, listing the parts treated, the process run, the operator and date of treatment.
Good inspection habits at the front end of a project are far better than costly rework or even field failures later.
