----------+----+----+----+----+----+------+------+------+------+-----
Tensile | | | | | | | | | |
strength | | | | | | | | | |
per square|1/2″|5/8″|3/4″|7/8″| 1″ |1-1/8″|1-1/4″|1-1/2″|1-3/4″| 2″
inch of | | | | | | | | | |
section | | | | | | | | | |
allowed | | | | | | | | | |
----------+----+----+----+----+----+------+------+------+------+-----
5000 | 981|1533|2208|3006|3927| 4970 | 6136 | 8835 |12026 |15708
6000 |1178|1840|2650|3607|4712| 5964 | 7363 |10602 |14431 |18849
7000 |1374|2567|3092|4209|5497| 6958 | 8590 |12369 |16837 |21991
7500 |1472|2750|3313|4509|5890| 7455 | 9204 |13253 |18039 |23562
----------+----+----+----+----+----+------+------+------+------+-----
SHOP NAMES FOR BOILER BRACES.—1. Gusset brace (fig. 47). 2. Crowfoot
brace. 3. Jaw brace (fig. 44). 4. Head to head brace (fig. 50). These
shop terms refer to braces used in the tubular form of boiler.
A STAY AND A BRACE in a steam boiler fulfil the same office, that of
withstanding the pressure exerted outward of the expanded and elastic
steam.
SOCKET BOLTS are frequently used instead of the screw stay between the
inside and outside plates that form the centre space. Socket bolts are
driven hot the same as rivets.
The method of bracing with =T= bars is considered the best; the bars
make the flat surface rigid and unyielding even before the brace is
applied. The braces should be spaced about 8 inches apart on the =T=
bar and 7 inches from the edge of the flange =T= the bar should be 4″
× 4-1/2″ =T= iron and riveted to the head or flat surface with 11/16″
rivets spaced 4-1/2 inches apart.
HOLLOW STAY BOLTS are used in locomotive fire boxes to show when
fracture has occurred by permitting an escape of steam or water.
The flange of a boiler head 1/2″ thick will amply support 6 inches from
the edge of the flange.
A radius of 2 inches is ample for bend of flange on the head. The lower
braces should be started 6 inches above the top row of tubes. Braces
should be fitted so as to have a straight pull, _i.e._ parallel with
the boiler shell. The heads of the boiler should be perfectly straight
before the braces are fitted in place. Gusset brace plates should not
be less than 30 inches long and 14 inches wide. Braces are best made of
1 inch =O= iron of highest efficacy with tensile strength of not less
than 58,000 lbs. to the square inch.
[Illustration: Fig. 51.]
The riveted stay shown in Fig. 51, consists of a long rivet, passed
through a thimble or distance piece of wrought iron pipe placed between
plates, to be stayed together, and then riveted over in the usual
manner.
An ingenious device is in use to show when a bolt has broken. A small
hole is drilled into the head, extending a little way beyond the plate,
and as experience shows that the fracture nearly always occurs _next to
the outside plate_, that is the end taken for the bored out head: when
the bolt is broken the rush of steam through the small hole shows the
danger without causing serious disturbance.
Even where the best of iron is used for stay bolts they should never be
exposed to more than 1/10th or 1/12th their breaking strength.
The stays should be well fitted, and each one carefully tightened, and,
as far as possible each stay in a group _should have the same regular
strain upon it_—if the “pull” all should come on one the whole are
liable to give way.