Other Masking Systems For Diffusion Coating Processes

In addition to the Dry Powder Materials listed: M-1, M-5, M-7, M-8, M-10, and M-17, APV has developed a new Dry Powder Material. A description of which is below:

M-13A

An overcoating powder which when combined with APV Binders provides a top coating to the M-1. The M-13A forms a tight envelope over the M-1. The M-13A as different from the M-7 does not require Aluminum to create a tight envelope after thermal treatment. It is especially effective in pure CVD coating processes which do not introduce the coating gases until the part to be coated reaches the coating temperatures. Necessarily, a tight envelope or sheath is required to be formed before the coating gases are introduced. Other applications where M-13A is effective are in those cases where internal coatings are applied using powdered coating materials, and no coating is permitted on the external surfaces of the part. Usage of the M-13A will prevent coating in these areas. After processing, the envelope (sheath) is hard and retains both the M-1 and itself intact, thereby avoiding contamination of the coating pack or coating source material. The easily removable, soft (powdery) M-1 is readily evident under the M-13A.

M-1 Masking Tape

A highly flexible tape containing our standard M-1 material. It is supplied in 0.050 in. thick in 25 foot rolls in widths from 3/8 inch to 8 inches. Further, it can be supplied as a stamped preform. As a preform the tape has been used as a "gasket" on the bottom of turbine blades being coated internally with aluminides. Use of the tape prevents coating leakage onto "no-coat" areas of the turbine blade. It has also been used as an adjunct to slurry and/or dry masking processes in difficult-to-mask areas; especially near blade platforms. Other applications include turbine blade squealer pockets with no-coat areas, and other "spot" no coat area requirements. Metallographic examinations have shown maximum alloy depletion zones of less than 0.0004 inches.

The M-1 Tape can be supplied with adhesive backing on one or both sides and as different from other commercially available masking tapes does not require a parting layer of inert material necessary to prevent sintering of the masking material onto the area to be masked. No ash or other deposits are present after the coating runs, and all that is necessary is to brush off the surface lightly or blast with air.

M-1 Masking Putty

A moldable "putty" containing our M-10 material. Note: M-10 is chemically exactly the same masking material as M-1. M-10 is manufactured by taking M-1 and reducing its mesh size by ~ 50%. It is supplied in pieces ranging in size from 4 in x 4 in to 8 in x 8 in. Custom sizes can also be made, with no "practical" limit to size. The putty has been used as an adjunct to masking with Nickel foil and/or dry and slurry maskants. It too, has shown maximum alloy depletion of 0.0004 inches. No parting layer of inert material is required to prevent sintering of the masking material onto the area to be masked. No ash or other deposits are present after the coating runs, and all that is necessary is to brush off the surface lightly or blast with air.

P-1 Coating Tape

A highly flexible aluminizing coating tape. The tape produces an outward diffusion coating from 0.001-.0025 inches, depending on exposure temperature. The tape can be used under dry M-1 maskant to coat specific areas requiring coating. Prior to the use of tape, these areas were coated after the dry maskant was removed. Areas to be coated were then painted with an aluminum slurry and then diffusion treated in a separate operation. This multi-step process was labor intensive and the additional processing time consuming. The tape can also be used to coat locally repaired, e.g. turbine blade tips, by just placing the tape in areas where the original coating was removed to allow for weld buildup and/or crack repair.

The availability of coating tapes and putties provide a product which allows for simple, inexpensive, low-labor application of an outward diffusion coating. It also opens up enormous possibilities in both the OEM and Overhaul & Repair disciplines.

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