Page 137 - Ship Construction.DJ Eyres 6Ed

Ch13-H8070.fm Page 126 Wednesday, October 18, 2006 6:56 AM
126 Ship Construction
requirements for these and their formulation may be found in Chapter 27.
Following the priming paint stage a drying process may be provided.

PLATE HANDLING IN MACHINE SHOPS Throughout the machining
shops overhead electric cranes having capacities from 5 to 15 tonnes may
be provided to transport plates and sections to each machine process.
Individual machines may have jig cranes mounted on the frame which can
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be employed to handle the plate during the machining process.
Distribution of plates in the shop may also be by means of electric pow-
ered trolleys sometimes referred to as a ‘collacator unit’ running on rails in
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
bays between the plate working machines. Highly mechanized plant systems
are also available where conveyor systems, flame cutting tables and aligning
and clamping equipment are installed as integrated units.

Plate and Section Machining
A number of the methods in use for forming plates into the required shapes
are time honoured. This is particularly true of the methods adopted for
fitting plates to the curve of the hull, but as we have seen in the previous
ึ
chapter the information for doing this can now be derived using the CAD/
CAM systems available. Cutting flat plates to the required profiles has in
the past decade become highly automated, very sophisticated machine tools
having been introduced for this purpose. In the main, cutting is achieved by
the use of an oxy-fuel flame or plasma-arcs.

PLATE PROFILERS Where a plate is to be cut into one or more, or a
series of complicated shapes, a profiling machine is employed. Cutting is
achieved by the use of an oxy-fuel gas or plasma-arc. Where these employ
gas cutting, the machines are generally referred to as ‘flame profilers’.
Flame, or plasma-arc profilers are either –

(a) numerically controlled; or
(b) 1/1 template or drawing controlled.

(a) Numerical control implies control of the machine by means of a tape
on which is recorded the co-ordinate points of a plate profile. For a simple
plate shape having a profile consisting only of straight lines or circular arcs
the co-ordinates may be programmed manually, but for many ship plates
the contours are much more complex. Manual programming of these con-
tours would reduce considerably the efficiency of the process, and therefore
various coded data systems were initially evolved for use with a digital com-
puter programme. With the advent of CAD/CAM systems the integrated
software now developed includes, as described in Chapter 12, provision for