Silicide Coating for Aerospace Parts

Problem Statement
Design, fabricate and test an apparatus that applies a uniform silicide coating (R512E) to the inside surface of a niobium based alloy (C-103) thrust chamber and rocket nozzle.

Specifications
Our first specification involves achieving the desired thickness of 120 microns. Our method for ensuring a consistent coating thickness concerns the final mass of the piece. If the our procedure can produce coated nozzles with the same final mass within a certain tolerance, it follows that these nozzles with have coatings of the same thickness, assuming the coating is even across the piece.

Our second specification involves the visual quality of the coating. In order to assess how even the coating is, the nozzles will be visually observed and compared with the desired visual qualities supplied by our sponsors. These qualities are no running, no bare spots, and no clumps; basically a visually even and smooth coating on the nozzle.

Our final specification is being able to replicate the above qualities on nozzles of various sizes, from 10-28 cm. In order to achieve this, our apparatus will be adjustable in order to accommodate nozzles of various size and geometry.

Objective
The following is our Project Objective, as given by our sponsor:

"It is desirable to have a coating system that can accommodate a range of rocket nozzle sizes and produce a uniform coating thickness on the inside nozzle surface. Potential design direction include a fill and drain method where a fixture holds and seals a nozzle partly filled with glaze, while a computer controlled stage rotates and tilts the fixture in prescribed motion before draining. Glaze thickness can be estimated from weight addition and uniformity will be assessed by visual inspection."

Manipulate nozzles from 10 to 28 cm in length Uniform inside surface coatings free of drips and runs Simple, automated operation

Electrocoating Research
Electrocoating is the process of using electrical forces to attract a coating to a surface, creating a uniform and controlled coating. Electrically charged particles are deposited out of a water suspension to coat an oppositely charged part. This process is self limiting so it will not build up layers of coating on already covered areas. This results in an even coating on all surfaces and geometries.

There are four steps to this process. Pre-treatment: clean part of all foreign material and rinse thoroughly with deionized water. E-coat Bath: 80% deionized water 20% slurry. Deionized water acts as a carrier for the slurry to be deposited on part. Rinse: remove part from bath and rinse with deionized water.

Typical voltage ranges from 25-400 volts DC for this process.

Nozzle Machining
Finished Medium Nozzle

Mass Analysis
For this Mass Analysis Sub-Project we used the Electrocoating Method we researched to coat several aluminum samples and then compare their percent mass increases.

We used the following process: Cathodic Deposition Process: Make bath consisting of 80% deionized water 20% paint Pre-treat part with deionized rinse Apply negative node to part and positive node to bath Dip the part in the bath for given period of time at given voltage Remove part from bath and rinse excess coating off with deionized water Bake part Factors that control thickness of deposited coating: Voltage (ranging from 20 to 400 volts DC) Temperature of bath

Power supply: Fluke DC high voltage power supply Voltage range 1V-3.5 kV Current: 1amp

Electrocoating Setup

Viscosity Analysis
For the Viscosity Analysis Sub-Project we used a Ford #4 Viscosity Cup to determine the viscosity of the slurry and several other paints.

Ford #4 Viscosity Cup

To perform this test, we simply filled the Ford #4 Viscosity Cup and timed the drain of the fluid.

Viscosity Test Setup

The following are the results from this test:

Viscosity Time Results

We also performed this test to try and find a surrogate coating with a viscosity similar to the slurry. To achieve this we mixed 150mL of Semi-Gloss Enamel with 100mL of water as a proof of concept for the ability to reduce the drain time. The result of this test is below:

Surrogate and Slurry Comparison

Completed Apparatus
Completed Assembly

This assembly is capable of constant on-axis nozzle rotation as well as 180 degree rotation. These motions will create the conditions needed to accurately coat the inside of the nozzles.

Stepper Motor Integration
Stepper Motor Wiring

This is the circuit used for both the Nema-32 and Nema-34 Stepper Motors and their drivers.