_MACHINERY OF APPLICATION._
The term application has been selected as a proper one to
distinguish machines that expend and apply power, from those
that are employed in generating or transmitting power. Machines
of application employed in manufacturing, and which expend their
action on material, are directed to certain operations which are
usually spoken of as processes, such as cutting, compressing,
grinding, separating, and disintegrating.
By classifying these processes, it will be seen that there is in
all but a few functions to be performed by machines, and that they
all act upon a few general principles. Engineering tools employed
in fitting are, for example, all directed to the process of
cutting. Planing machines, lathes, drilling machines, and shaping
machines are all cutting machines, acting upon the same general
plan--that of a cleaving wedge propelled in straight or curved
lines.
Cutting, as a process in converting material, includes the force
to propel cutting edges, means to guide and control their action,
and mechanism to sustain and adjust the material acted upon. In
cutting with hand tools, the operator performs the two functions
of propelling and guiding the tools with his hands; but in what
is called power operations, machines are made to perform these
functions. In nearly all processes machines have supplanted hand
labour, and it may be noticed in the history and development of
machine tools that much has been lost in too closely imitating hand
operations when machines were first applied. To be profitable,
machines must either employ more force, guide tools with more
accuracy, or move them at greater speed, than is attainable by
hand. Increased speed may, although more seldom, be an object in
the employment of machinery, as well as the guidance of implements
or increased force in propelling them. The hands of workmen are not
only limited as to the power that may be exerted, and unable to
guide tools with accuracy, but are also limited to a slow rate of
movement, so that machines can be employed with great advantage in
many operations where neither the force nor guidance of tools are
wanting.
There is nothing more interesting, or at the same time more useful,
in the study of mechanics, than to analyse the action of cutting
machines or other machinery of application, and to ascertain in
examples that come under notice whether the main object of a
machine is increased force, more accurate guidance, or greater
speed than is attainable by hand operations. Cutting machines as
explained may be directed to either of these objects singly, or to
all of them together, or these objects may vary in their relative
importance in different operations; but in all cases where machines
are profitably employed, their action can be traced to one or more
of the functions named.
To follow this matter further. It will be found in such machines as
are directed mainly to augmenting force or increasing the amount of
power that may be applied in any operation, such as sawing wood or
stone, the effect produced when compared to hand labour is nearly
as the difference in the amount of power applied; and the saving
that such machines effect is generally in the same proportion. A
machine that can expend ten horse-power in performing a certain
kind of work, will save ten times as much as a machine directed
to the same purpose expending but one horse-power; this of course
applies to machines for the performance of the coarser kinds of
work, and employed to supplant mere physical effort. In other
machines of application, such as are directed mainly to guidance,
or speed of action, such as sewing machines, dove-tailing machines,
gear-cutting machines, and so on, there is no relation whatever
between the increased effect that may be produced and the amount of
power expended.
The difference between hand and machine operations, and the
labour-saving effect of machines, will be farther spoken of in
another place; the subject is alluded to here, only to enable the
reader to more fully distinguish between machinery of transmission
and machinery of application. Machinery of application, directed to
what has been termed compression processes, such as steam hammers,
drops, presses, rolling mills, and so on, act upon material that is
naturally soft and ductile, or when it is softened by heat, as in
the case of forging.
In compression processes no material is cut away as in cutting
or grinding, the mass being forced into shape by dies or forms
that give the required configuration. The action of compressing
machines may be either intermittent, as in the case of rolling
mills; percussive, as in steam hammers, where a great force acts
throughout a limited distance; or gradual and sustained, as in
press forging. Machines of application, for abrading or grinding,
are constantly coming more into use; their main purpose being to
cut or shape material too hard to be acted upon by compression or
by cutting processes. It follows that the necessity for machines
of this kind is in proportion to the amount of hard material which
enters into manufactures; in metal work the employment of hardened
steel and iron is rapidly increasing, and as a result, grinding
machines have now a place among the standard machine tools of a
fitting shop.
Grinding, no doubt, if traced to the principles that lie at the
bottom, is nothing more than a cutting process, in which the
edges employed are harder than any material that can be made into
cutters, the edges firmly supported by being imbedded into a mass
as the particles of sand are in grindstones, or the particles of
emery in emery wheels.
Separating machines, such as bolts and screens, which may be
called a class, require no explanation. The employment of magnetic
machines to separate iron and brass filings or shop waste, may be
noted as a recent improvement of some importance.
Disintegrating machines, such as are employed for pulverising
various substances, grinding grain or pulp, separating fibrous
material, and so on, are, with some exceptions, simple enough
to be readily understood. One of these exceptions is the rotary
"disintegrators," recently introduced, about the action of which
some diversity of opinion exists. The effect produced is certainly
abrasive wear, the result of the pieces or particles striking one
against another, or against the revolving beaters and casing. The
novelty of the process is in the augmented effect produced by a
high velocity, or, in other words, the rapidity of the blows.
(1.) Name five machines as types of those employed in the general
processes of converting material.--(2.) Name some machines, the
object of which is to augment force--One to attain speed--One
directed to the guidance of tools.--(3.) What is the difference
between the hot and cold treatment of iron as to processes--As to
dimensions?--(4.)