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Technical Data Sheet - K1228


ABSTRACT

K1228 process has been designed to replace K1014. K1228 is exactly the same ion-vapor deposition process as K1014, except the aluminum is stabilized using a phosphate conversion rather than chromate. Magnetic Component Engineering offers this process for all grades of NdFeB magnets. The coating has been found to pass salt spray tests, and it is economical in large quantities; small quantities can be expensive, since the process is very involved and includes multiple set-ups. The coating is suitable for vacuum applications. The process is described below to give an idea of how this is carried out; however, it must be noted that certain pre-processing steps to enhance adhesion and retard oxidation that are carried out at MCE are considered proprietary and are not disclosed.

CLEANING

As in most metal finishing operations, preparation of the substrate is vital if good adhesion is to be achieved. To remove oil, grease, or machine lubricants, vapor degreasing with a chlorinated solvent is normally employed. From this point, operators no longer handle components without protective plastic and cotton gloves, thus avoiding contamination of the substrate.

GRIT BLASTING

To remove surface contamination, and provide a suitable "key" for adhesion of the ivadized coating, components are grit blasted with pure aluminum oxide abrasive. The substrate surface is very active at this point, and will readily absorb and retain gas or moisture. For this reason, it is important to load components into the vacuum chamber within 4 to 6 hours of grit blasting. Residues of aluminum oxide are removed with dry filtered nitrogen.

LOADING

Small components are loaded into stainless steel barrels, which rotate during the coating cycle. Larger components are jigged by hooks or wire onto a rack, which is supported and then inserted into the vacuum chamber by means of a steel frame mounted on four legs known as the "dolly."

FINAL PREPARATION & COATING

After components have been loaded into the vacuum chamber, air is evacuated by a series of pumps to a pressure of 10-5 Torr. Once this pressure is achieved, the chamber is backfilled to 10-3 Torr with Argon. The anode consists of a number of crucibles manufactured from Boron Nitride or Diboride. A dc potential is applied to the substrate in the order of 1000 to 1400 volts, with the substrate (cathode) being negatively charged. The collision between electrons and the Argon gas molecules result in ionization of the Argon, and the subsequent release of more electrons. The bombardment of the cathode produces a secondary emission of electrons, so an avalanche effect is achieved. This process will continue until a self-sustaining discharge is achieved.

Sputtering will occur at the surface of the substrate where atoms of the substrate will be dislodged through momentum transfer. During this process, surface contamination, such as grit particles, will also be removed. After a period of 15 to 20 minutes of plasma cleaning, the substrate can be coated.

COATING

Each anode crucible is fitted with a wire feed unit. When a high current is applied, the resistive heat generated melts the aluminum wire, which is subsequently vaporized in the high vacuum. Once evaporated, the aluminum atoms are ionized, then attracted to, and finally deposited on the substrate.

UNLOADING

Unloading is a simple operation using the dolly.

SHOT PEENING

This process uses a pressure blaster with a glass bead media at a pressure of 20 to 30 psi. Shot peening "densifies" the coating and reduces porosity, yielding a hard uniform coating which will readily accept an additional corrosion preventative coat of chromate, epoxy paint, etc. Special extraction equipment ensures that shattered glass particles are removed, thus avoiding damage to the aluminum coating.

INSPECTION

Micrometer and ring gauges are used to check tolerances on coated components, with magnetic permascope devices checking coating thickness. Visual inspection of all components is essential to determine presence of scratches, nodules,or inclusions/foreign bodies in the coating as well as possible damage through incorrect handling or overheating during the coating operation.

SPECIFICATION

K1014 was applied to MIL-DTL-83488 Rev D Type II Class 2. The "Type II" in the specification requires a chromate conversion. K1228 is applied to MIL-DTL-83488 Rev D Type I Class 2, followed by a non-chromate conversion. This specification states that after the IVD process, the chromate conversion is omitted. MCE's K1228 process requires a phosphate conversion. Therefore the military process differs from our process in the last step. MCE will allow the military specification on the drawing as long as the MCE specification K1228 is stated since ion-vapor deposition on NdFeB magnets MUST undergo a conversion for it to have the desired characteristics. Without the conversion, the aluminum would be susceptible to premature mechanical damage hence exposing the base material.