Useful NOtes on Spring Maintenance
Page 39
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THE Chief Inspector of Mechanical Transport, R.A.S.C., has sent us a useful form of Christmas greeting, on one side of which are notes on the repair of road springs in order to conserve steel, and some of these may be of value to our readers.
He points but that many fractures of road springs are clue to the holdingdown bolts being allowed to work slack.
In the event of the fracture of a leaf, the complete spring must be dismantled, each leaf thoroughly cleaned and dried, and those above and below the one fractured carefully, examined for cracks. Every leaf must also be examined for wear where the tips of the one underneath may have caused
indentations. Such irregularities should be removed by grinding.
A leaf distorted by accident can be given a complete heat treatment and used again. It is particularly important
that, if it be the master leaf, the spring eyes should be brought into correct alignment, for which purpose, rods, some 2 ft. long, should be passed through the spring eyes. The ends must be within in. of truth.
When making new leaves cut from a length of metal, they should be sawn, not sheared, and the tips produced by machining rather than forging. Centre holes most be drilled, not punched, and any locating nib produced while the leaf is adequately heated, Spring leaves should never be worked cold, but the heat must be gradual and uniform, and when cooling protected from cold-air en Vents.
Spring steel is usually of the siliconmanganese type, the best results from which are obtained by heating to 950 degrees C., quenching in oil at 900 degrees C., and tempering for one hour in a furnace controlled to 500 degrees C. In an emergency and where proper facilities do not exist, the leaves must be bent to a true radius at bright-red heat and cooled off in air, but not more than two such leaves should be fitted to any one spring:
On reassembling, leaves should be thinly smeared with suitable grease mixed with 10 per cent. graphite.
When replacing shackle pins, it should be verified that they are not unduly worn. Cyanide-hardened pins can be used if the diameters be not worn more than .012 in.; with the more fully case-hardened types, the permissible reduction in diameter is .032 in. Wherever possible, the pins should be assembled so that the oil holes from the centres to the bearing surfaces point to the side where static mechanical pressure is least.
In some instances springs are net symmetrical about the centre belt. In such cases care must be taken to refit these correctly to the chassis.