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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Specification leaflet for H&H steel brake drums, detailing their construction, material, and performance tests.

Identifier  ExFiles\Box 120\1\  scan0134
Date  24th November 1934 guessed
  
H&H

SPECIFICATION, etc.

The rim is made from rolled section of special analysis steel (4/.45% carbon), normal strength 40/50 tons, which can be heat treated to 55/60 tons per sq. in. tensile.

This material is bent into a circle and electrically welded, thus forming a rim of hard wearing material which may be of any desired section. Into this rim is spigoted a disc of high quality mild steel, preferably flat, but this may be of any desired dish form. Dowels are screwed into the rim flange and disc, rivetted over and electrically welded, thus the welding of the disc to rim is not continuous. This latter feature and the fact that the rim and disc are of different steels, provide the anti-vibration effect which explains the entire absence of "ring" or "squeak." If the drum is struck with a hammer only a dull thud is heard.

All these operations are achieved with an accuracy that makes exceedingly small final machining allowances possible, ensures perfect concentricity and evenness of rim thickness.

In drums supplied finished machined, the braking surface is ground, and this polished condition remains (in fact, improves), even under hard braking conditions. This better and smoother braking is obtained with less lining and drum wear, consequently fewer brake adjustments are necessary.

In this construction, a wearing surface can be used without interposing a joint through which all heat must flow, as in the case of cast drums with liners or pressed drums with outer stiffeners.

The grain of the metal runs in the direction of travel, thus giving equal expansion, and retention of concentricity when heated, also eliminating tendency to distortion when cooling with brakes left on.

The material has strength and reliability not possessed by cast iron or other cast alloys, consequently the drum is lighter than cast iron for an equivalent section and approximately equal to the weight of a pressed drum fitted with outer stiffener. The latter is liable to defects from unequal expansion and also to suffer from restricted heat flow.

Compared with a pressed steel drum there is an advantage in compactness and rigidity. This last feature is due both to the compact layout and to the fact that the rim can be ribbed and can also be thicker than a pressing. The pressed steel drum must be wide for a given shoe width to allow for the radii where the rim joins the disc and the outer edges where the rim is turned outwards to form a lip.

The advantage of being able to place the brake shoe close to the disc cannot be over estimated, as the tilting and distorting forces are thus reduced enormously. This is particularly important with Servo shoe mechanisms.

The appearance of a narrow rimmed drum is considered by most observers to be an enhancement, and these drums, having a rib on the rim which becomes adjacent to the road-wheel, give the effect of a larger drum.

Coupled with the advantage of a lessened need for brake adjustment, due to less lining and drum wear, is the fact that resistance to distortion means less pedal movement for a given braking effect.

Manufactured by HOLDEN & HUNT,
OLD HILL, STAFFS.
Phone: CRADLEY 6015.

Representatives: PRATT & MANLEY,
Guildhall Buildings, Navigation Street, BIRMINGHAM.
Phone: MIDLAND 4130.

"SUNBEAM."
"LAGONDA."
"M.G."
"ASTON MARTIN."

All the merits claimed for the H.{Arthur M. Hanbury - Head Complaints} & H.{Arthur M. Hanbury - Head Complaints} Steel Brake Drum have been proved over very extensive road tests. Tests have also been made on apparatus specially designed for such purpose. In the latter tests, the drum proved to be a very capable performer, coming through very severe tests in excellent style—even with temperature raised to 600 degrees F.{Mr Friese} on 25 occasions :—

The closest examination failed to detect the welded joint.
Rigidity was not affected even with 500 lbs. shoe tip pressure at a temperature of 750 degrees F.{Mr Friese}
In these tests a brake force at the drum radius of 1,150 lbs. was used, this force being applied 2,000 times at a rate of 132 applications per hour.
The drum remained true, and torque readings remarkably steady.
After a certain amount of rubbing the surface probably became work hardened, in which condition it would resist any tendency to abrasion.
(The above tests were carried out by courtesy of Messrs. Ferodo Ltd.)

Certain rim sections have been standardised, and in these the inside depth of the drum exceeds the shoe width by 1/8in. These sections can be used with any form of straight or dished disc, also any special desired section can be rolled to suit customers' requirements.

Drums are supplied in the rough or finished condition, those supplied in the rough being partly machined. They are being manufactured on a full production basis and being supplied in large quantities.

Technical Expert examination reveals this fact :—

"Comparison has been made between the "H.{Arthur M. Hanbury - Head Complaints} & H.{Arthur M. Hanbury - Head Complaints}" drum and drums of alloy cast iron, and in the latter there is a considerable falling off from the normal co-efficient of friction when heated, whereas there is no falling off with "H.{Arthur M. Hanbury - Head Complaints} & H.{Arthur M. Hanbury - Head Complaints}" drums, consequently high tensile steel drums give more consistent braking under severe conditions."
  
  


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