A lubricant containing asphaltic materials, which impart extra adhesiveness, that are used for open gears and steel cables.



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SKELETON TOWER

A tower, usually of steel and often used for navigation aids, constructed of open legs with various horizontal and diagonal bracing members.

SEAL

A soft synthetic rubber washer with a steel core fixed in the outer ring (in the seal groove) in contact with the inner ring to retain lubricant and keep out contamination.

BRINELL TEST

A hardness test performed by pressing a steel ball of standard hardness into a surface by a standard pressure.
a hardened steel ball of known diameter is applied to the specimen under a known loading for a period of 1 second.

The diameter of the impression resulting in the specimen is measured with a microscope. Hardness is indicated by the Brinell Number, derived by dividing the applied load in kilograms by the spherical area of the impression in square millimeters. The harder the material, the smaller the impression and consequently the higher the Brinell number. To keep the relationship between load P, diameter D and the impression produced within limits, for different materials, different P/D2 ratios are used. The following are approximate Brinell numbers, for the stated material.

Material Brinell Hardness Number
Bronze (Chill Cast) 32
Brass 60
Gunmetal 70 - 75
Mild Steel 110 - 130
Carbon Steel 150 - 200
Cast Iron 400

TRAIL-FOR-IGNITION

That period of time during which the programming flame failure controls permit the burner fuel valves to be open before the flame sensing device is required to detect the flame.

TRAIL FOR PILOT IGNITION

A timed interval when the pilot valve is held open and an attempt made to ignite and prove it. If the presence of the pilot is proved at the termination of the interval, the main valve is energized; if not the pilot and ignition are cut off followed by a safety lockout.

TEMPERING

Heat treating process that releases internal stress in hardened steel and increases toughness. Tempered steel will not crack under heavy stress or vibration or impact. Should be done as soon after hardening.

HARDENING

Accomplished by heating the steel beyond the critical temperature and following by relatively fast cooling. If heating for hardening is being accomplished in the forge fire the color should be a full red and to check on the temperature a magnet may be used, as the steel at or above the critical temperature should be non-magnetic. If the magnet is being used while the temperature is being raised from the room temperature, the correct point to stop heating is where the steel no longer responds to the pull of the magnet. If a furnace is being used to heat the steel to the hardening heat a pyrometer aids greatly in determining the critical temperature.

ANNEALING

The process of heating steel to above its critical range and then allowing it to cool slowly.

a. Process of sub critical annealing is carried out on cold worked low carbon steel to relieve internal stress and to soften the material. The steel is heated to about 50°C below lower critical temperature and then allowed to cool.

b. Full annealing is employed on steel casting and hot worked steels to obtain grain refinement and ductility. The steel is heated to about 50°C above upper critical temperature and then allowed to cool slowly in the furnace.

c. Normalising differs from full annealing in that the metal is allowed to cool in still air. Tensile strength and impact values are higher than the figures obtained by annealing.

d. Spheroidising annealing is used for softening high carbon steel to facilitate machining. The steel is heated to just below lower critical temperature. Due to surface tension effects, the cementite assumes globular form while the remainder reverts to ferrite. After shaping, the pearlite-cementite structure can be restored by heat treatment. The heat treatment ranges for plain carbon steels are shown in figure 3.

e. Case-Hardening - Where an article requires to have a hard wear-resisting surface, together with a tough core, it is necessary to employ a low carbon steel and case harden the surface to obtain this dual structure.

The carbon content at the surface is enriched by surrounding the components in materials rich in carbon, such as a mixture of charcoal and barium carbonate; the pieces to be carbonized are placed into boxes with the carbonizing materials and sealed. The boxes are then placed in a furnace and brought to a temperature around 900°C and held at that temperature for a time dependant on the depth of case required. After six to eight hours, a low carbon steel may have 0.9% carbon to a depth of about 0.040%.

A part which has been carbonized at such a temperature will have a coarse grain structure which must be refined. This is achieved by reheating the parts above the critical point and quenching in oil. This treatment results in refining the structure of the core. If it is desired, the case can be tempered at 150°C. The case is then hardened, i.e. heated to 770° then quenched in water. It can then be tempered, i.e. heated to 200°C depending on hardness required.

HATCHRAILS

Ropes supported by stanchions around an open hatch to prevent persons from falling into a hold

LUG

As applied to boiler suspension, a steel eyepiece fitted and riveted or welded to the curvature of a boiler shell or drum and connected by a steel U-bolt or sling rod to overhead steel structure; used to support the weight of a boiler.

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