The following specification particularly describes the nature of invention and the manner in which it is to be performed.

This invention relates to the development of a novel method to coat wear resistant coating on gas turbine engine parts.

Background of the invention

In gas turbine engines there are components requiring high wear resistance and good lubrication such as gears, bearing seats, bushes etc. Some of these are made of lead bronze alloy. As the shaft rotates at higher RPM the chances for these parts to wear out and to get heated up will be very high. To avoid this there is a need of a protective coating or solid film lubricant coating which is capable of providing high wear resistance and lubrication, corrosion resistance and heat absorption capacity like graphite. But many of these coatings cannot be directly bonded on to materials like lead bronze alloys permanently and efficiently. It is required to develop a base coating which can retain the solid lubricant for a longer period of time without further treatment.

Summary of invention

A novel method comprising of following features is introduced.

Development of Indium plating solution which can be plated on materials like lead bronze alloys to act as a base material for coating the solid self lubricant film permanently on the part and thus provide lubrication and wear resistance for very long period of time without any further treatment. After solid lubricant film coating the required surface finish, required dimensions are achieved by burnishing.

Objective of invention

Main objective is to introduce a novel method for permanently binding the solid lubricant on gas turbine engine parts and thus provide lubrication and wear resistance for very long period of time without any further treatment.

To develop an indium plating solution which act as a base for the solid film lubricant.

To establish a procedure for Indium plating, spraying of electrofilm and burnishing Detailed Description of the invention

Lead bronze alloys are usually used in parts require high wear resistance as it has a very low friction factor compared to other materials. Usually these components must be provided with a protective coating which has self lubricating property, which has good wear and corrosion resistance and heat absorption capacity. But many of such coatings come up with less bonding properties and less reliability when coated directly on the material or on the required base materials. Hence a thorough study and research has been conducted on different coatings with various combinations. As a result, we found an effective coating i.e. indium plating to act as a good base for solid lubricant coating. This combination has provided us with required wear resistance and self lubricating properties along with good and longetive bonding properties and heat absorption properties with the base materials generally used for gas turbine engine parts. Indium plating possesses good infusion property on lead alloys along with good adhesiveness. So it can be used suitably as a base coating for electro film application. After the electro film which is sprayed on the indium plating gets dried, the required dimensions and geometric tolerances are achieved by a super finishing process called burnishing. Burnishing is a plastic forming operation where no metal is being removed. It is done on lathe by plunging against a special burnishing tool which is highly smooth and spherical in shape.

Procedure for indium plating

• Vapour degrease thoroughly.

• Mask as required. Vapour blast areas to be plated.

• Rinse in cold water followed by hot water, air dry.

• Suspend the part with copper wire. Immerse part in freshly prepared bright dip solution (Phosphoric acid 70%, nitric acid 30%).

• Wash thoroughly in cold water to remove bright dip solution, followed by hot water rinse, finally in cold water.

• Immediately transfer to Indium plating solution. Plate for sufficient time to give a thin but complete indium plating.

Composition of developed solution for indium plating
Solution : Indium (Metal) 20-25gm/liter
: Sulphuric acid 32gm/liter
: Anhydrous Sodium Sulphate lOgm/liter
Voltage ': 3- 4 V
Temperature : Room Temperature
Current Density : 0.4A/dm2

• Rinse in cold water thoroughly to remove plating solution. Rinse in hot water.

Air Dry.
• Procedure for electro film application
• Mix the Electro film solution.
Note:. Solution must be thoroughly mixed before and during use.

Electro film 4253 10%
Electro film 4856 10%
Dioxane • 80%

• Use Aerograph MPS spray sun No: 3 containing Aerograph needle No: 3,

Aerograph cup No: 3 and Aerograph nozzle No: 3 for the application of the electro film. The surface to be cleaned shall be clean and uniform in appearance. In the spray booth mount the part with its axis vertical in a fixture motorized to rotate the part about the axis. Rotate the component at 50RPM. Spray uniformly into the bore as per the component drawing/operation drawing. Use the suitable mandrels as per the part to check the thickness.

• Remove the masking. Bake at 190/200°C for 1 hour.

• Visually inspect for a smooth, even coating free from blisters or other imperfections.
• Perform Tape test i.e. Press a piece of Sellotape firmly on the coating and pull sharply away. The coating shall remain unaffected.

Testing and result

In the indigenously developed PTAE engine (Pilotless Target Aircraft Engine) which is manufactured by HAL, Engine Division, there are parts requiring high wear resistance and good lubrication such as gears, bearing seat, bushes etc. One of such part is a bush made of lead bronze alloy. This bush acts as a seat and support for the quill shaft of the fuel pump of the engine. As the shaft rotates at higher RPM (around 29,000 RPM) the chances of wear out of the bushes and heat generation will be very high. To avoid this, we use a proprietary solid film lubricant coating called electro film coating which is capable of providing high wear resistance and lubrication like graphite. This electro film coating cannot be directly bonded on to the lead bronze • alloy surface permanently and efficiently. As a result of the study and analysis conducted we have developed an Indium plating solution which can be coated on the lead bronze alloy which can act as a base material for coating the electro film permanently on the part and thus provide lubrication and wear resistance for very long period of time without any further treatment. The geometry and dimensions are achieved burnishing. The diameter and surface finish is inspected before using the part. These bushes are assembled on to the fuel pump and flow test and performance test was carried out and it was found satisfactory.

Claims: We Claim

1) A novel method for permanently binding the solid lubricant on gas turbine engine parts and thus provide lubrication and wear resistance for very long period of time without any further treatment.

2) Development of novel solution i.e. indium plating solution which acts as a base for the solid film lubricant.

3) Development of a novel procedure for Indium plating, spraying of electrofilm and burnishing.