MIL-STD-1411B
exhausting of air and debris through the narrow neck of a cylinder is a controlling factor in a shot blasting system. Care shall also be exercised not to cut away reduced steel, thereby excessively reducing the wall thickness. Resulting surfaces are of high quality and, after removal of fine particles, are generally acceptable for charging with gas commodity without danger of contamination.
5.3.2.4.4.2 Rolling iron abrasives. For cylinders with light scale or rust or pitting and corrosive build-up, a cleaning process can be achieved by placing a quantity of iron based abrasives in the cylinder and rotating it on a mechanical rolling table. Such a system will abrade lightly and produces an excellent surface in which pit depths can be readily inspected. Cylinders coated heavily with scale and corrosive build-up respond very slowly to the rolling systems as
the oxidation residue promptly cushions the cutting action of the abrasives and the system loses efficiency.
5.3.2.4.4.3 Mandrel and chain. A mandrel and chain system utilizes a spinning shaft long enough to reach the bottom of a cylinder with a chain attached at the very end and at intervals along its useful length. The chain must be longer than the radius of the cylinder. As wear on the chain progresses, links at the ends must be replaced. The shaft shall be turned in both directions to effect an acceptable metal surface. While the cylinder bottom cannot be cleaned by this system, the internal shoulder area responds very well as the spinning chain approaches the neck of the cylinder. The oxidation and corrosive products are wiped into the pits and dents of a cylinder by the spinning chain. Pitting depths are very hard to judge at
internal inspection after a chain and mandrel process. Aqueous solution cleaning is often needed to remove losened particles.
5.3.2.4.5 Heat treatment cleaning. There are certain types of contaminants that cannot
be removed by either organic solvent cleaning or inorganic solution cleaning. The only practical method of removing these contaminants is to burn them out. Since this procedure involves heating the cylinder very close to or to the temperature at which its physical properties are modified, the procedure should be carried out by an agency completely familiar with the properties of the cylinder and in possession of the original manufacturing report for the cylinder. The cylinder is heated to a temperature dependent upon the original heat treatment of the cylinder, and held at this temperature while air is injected into it through a lance inserted nearly to the cylinder bottom. The stream of air is continued until all evidence of combustion such as flame, smoke, etc., has stopped.
5.3.2.4.5.1 Procedure. Temperatures are precise (see following guidelines).
a. Quenched and tempered cylinders -- minimum temperature: 1150 °F; maximum- tempering temperature as shown in manufacturing report.
b. Normalized cylinders -- temperatures as shown in manufacturing report.
c. If possible, the agency performing this type of cleaning should be the cylinder manufacturer.
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