For the Purpose of Water Regulations Advisory Scheme (WRAS) material approval Laboratory testing explanation for Fusion Bonded Epoxy 250 microns Coating of Ductile Iron Pipe Fittings & Valves.
The paint material referred to in this post is suitable for contact with wholesome water for domestic purposes having met the requirements of BS6920-1:2000 and/or 2014 ‘Suitability of non-metallic products for use in contact with water intended for human consumption with regard to their effect on the quality of the water’.
The reference relates solely to its effect on the quality of the water with which it may come into contact and does not signify the approval of its mechanical or physical properties for any use.
We hereby demonstrate the process used in application of coatings, paints & linings at our factory applied Coating and Lining for Ductile Iron pipe fitting to be compatible as per WRAS equivalent section code 5030.
Steps taken are as following to achieve paint thickness of minimum 250 microns for both WRAS approved Blue Fusion Bonded Epoxy Coating complying with BSEN specification 545 as well as Red or Black Fusion Bonded Epoxy Coating Requiring for other standards such as BSEN 598.
The Ductile Iron Fitting Casting Manufacturing process flow is as under:
After the Hydrostatic Testing process, based on the method of coating required, the pre cleaning by brushing or shot blasting is to be carried out with following steps to achieve FBE (Fusion Bonded Epoxy) of 250 microns coating.
Following video gives demonstration of some of the casting process as mentioned above.
Step 1: Metal Preparation
Correct metal preparation prior to pre-treatment and coating is fundamental to all successful metal finishing operations, including coating using thermoplastic powders. Poor metal preparation can result in premature failures of the coating leading to corrosion of the coated items. Cast iron can out-gas when heated. To overcome this issue, the items can be pre-baked prior to the coating process and then left to cool down before coating. The pre-bake temperature is generally kept 30°C above the temperatures to be used in the coating process, for at least as long as the length of time to be used in the coating process.
Step 2: Mechanical Pre-treatment of Cast / Ductile Iron
For items that are going to be coated in thermoplastic powder, the most commonly used method of mechanical pre-treatment for cast iron, is grit blasting or shot blasting. The objective of blasting is to clean the surface of the metal substrate of rust, oxides or mill scale. In addition, by roughening the surface, the effective surface per unit area is increased, which results in an increased level of adhesion. If any grease or oil is present on the metal surface, grit/shot blasting alone is not sufficient as a pre-treatment process and the blast media will become contaminated. This will mean that subsequent blasting operations will leave contamination on items being processed. It is essential therefore that degreasing is carried out before blasting. However in our process there is no involvement of grease or Oil coming in contact with the Cast Metal parts hence we do not require any further chemical degreasing.
Step 3: Oven Heating
This step is required to achieve desired temperature of the uncoated fitting as readiness for subsequent step of electrostatic spray.
The oven parameters are as following:
Dimensions: 2000mm x 1500mm x 1200mm
Chamber Temperature: 350 Deg C Max.
Duration of Heating Per Fitting Size: 2 Min to 4 Min Depending on Charge weight and temperature
Make & model of Chamber: Fabricated in House by Experts.
Chamber temperature testing – We use thermocouple based temperature measurement unit with automatic temperature control
Step 4: Conveyer Pulling to Paint Chamber
Once heated Ductile Iron Fitting has achieved desired temperate, an automatic conveyer is loaded with the heated fitting to drive the product into the paint chamber. Paint Chamber is adjacent to Oven. The process takes less than one minute to ensure that temperature drop gradient is well within the tolerable range prior to application of the coating.
Step 5: Coating – using either Electrostatic Spray or Fluidised Bed
Powder application processes
The most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun, or corona gun. The gun imparts a positive electric charge on the powder, which is then sprayed towards the grounded object by mechanical or compressed air spraying and then accelerated toward the workpiece by the powerful electrostatic charge. The type of nozzle used will depend on the shape of the workpiece to be painted and the consistency of the paint. The object is then heated, and the powder melts into a uniform film, and is then cooled to form a hard coating. It is better to use an Electrostatic Spray (ES) Gun with various attachments to ensure that effective hand spray painting is performed to achieve 250 microns thickness. ES Gun compared to Fluidised bed (FB) is more effective because ES is handmade coat whereas FB is automatic and cannot be controlled as effectively as ES Gun. We use one or two guns simultaneously depending on the shape and size of the Ductile Iron Fitting Fitting undergoing the painting. This is to ensure that application of paint is complete for entire surface area prior to drop in the temperature of the metal.
Depending on the shape and size of the Ductile Iron Fitting, we use extensions for the gun to ensure that each area of the Fitting inside and outside is coated uniformly. The Flat Jet Nozzle is ideally suited to coat complicated areas and areas with deep recesses. The Conical Deflector Nozzle gives a shower-spray effect. Most suitable for coating flat surfaces. Penetrate and coat the hardest to reach areas and achieve the uniformity you have always desired. Extension muzzle are available in different sizes i.e 300mm, 500mm, 600mm, 800mm, 1000mm and 1500mm. Coat around corners and reach the toughest coating spots with this curved attachment.
Curing – If required
When a thermoset powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher molecular weight polymer in a network-like structure. This cure process, called crosslinking, requires a certain temperature for a certain length of time in order to reach full cure and establish the full film properties for which the material was designed. Normally the powders cure at 200°C (390°F) for 10 to 15 minutes. The application of energy to the product to be cured is accomplished by re-heating in the ovens.
With this process, achievable coverage is 2.1sq mtr at 300 μm coating thickness using single application of paint with our equipment. Depending on the desired coating thickness and coating finishing, step 3, 4 and 5 is repeated for different shape, size and thickness of the Ductile Iron Fitting.
We use two separate WRAS Approved paints depending on requirements. Details are as below:
FBE Paints details:
a) WRAS APPROVAL NUMBER: 1909527, RAL 5005
b) WRAS APPROVAL NUMBER: 2103521, RAL 5015, 5017
c) Red Epoxy Paint – RAL colour 3011
d) Black Epoxy paint – RAL colour 7010
FBE Equipment Details:
Model: Powder Spray Equipment – Type Manual Spray System Multi-static Series 700 Supreme Pulse Tech Technology SP especially suitable for Functional coating.
Application process photo along-with staff training as below:
Thickness Measurement
Outside coating thickness is measured using Coating Thickness Gage – INSIZE
It allows to measure thickness inside products such as Radial tee in smaller sizes also.
| Measurement Range | 0 – 1000 µm |
| Accuracy | +(2 µm + 3%) |
Step 6: Finished Product
The outcome of the above process is high quality product with at-least 250 microns of thickness. Samples photos of the product outcome is as below: