PRACTICAL SHIP DESIGN

Introduction, Methods and Data
1.1 INTRODUCTION
1. I . I Design and naval architecture
There are many excellent books on naval architecture. Most of the recent ones have
been written by authors of considerable ability and handle admirably the highly
mathematical treatment that is demanded nowadays by the naval architecture of
advanced ship types.

The last chapter of most of these books is generally entitled “ship design”, butunfortunately, in the author’s opinion, these chapters rarely show the same mastery
of their subject that the other chapters of these books do, possibly because most of
the authors have an academic background and few have worked for any significant
time as designers.
There is, in fact, a surprising dearth of books which specialise in ship design.
Presumably this is partly because practitioners in this field -whether they work
for shipyards, for shipping companies or consultancies - are usually too busy
exercising their skills to find time to write and partly because they, or the firms
they work for, are reluctant to give away what they consider to be commercially
valuable secrets.
This book’s thesis is that ship design although based on the science of naval
architecture involves something more. In the author’s view naval architecture
consists of a number of quite distinct subjects which are generally taught and dealt
with in almost complete isolation from one another - structural strength, trim and
stability, and resistance and propulsion being three such subjects. Design, on the
other hand (or it may be more correct to say ‘initial design’) requires the designerto keep the essentials of all these separate subjects of naval architecture and indeedconcept which both in its main dimensions and in its general arrangement satisfies
or comes close to satisfying all these requirements.
If he can do this successfully from the start of a project, he will greatly reduce the
time and effort required to produce a design. If he fails to do so the design is likely to
require major changes as it is developed and detailed calculations can be made.
Once an initial design has been completed, each facet of it must of course be
tested using the appropriate rigorous scientific naval architectural methods, but in
the author’s view it is ponderous and time wasting to apply these methods whilst
the initial design is still being developed, although it must be admitted that the use
of computers has opened the door to the possibility of making detailed calculations
much earlier in the design process than used to be possible.
To give one example of the way in which thinking ahead can greatly reduce
design effort: the development of an outline design in which the stability is
satisfactory, or nearly so, need not necessitate detailed stability calculations at the
initial design stage (when the all-important weights are in any case likely to have a
considerable margin of error) but can instead be reasonably assured by choosing a
ratio of beaddepth which experience has shown will result in satisfactory stability.
Similar thinking can ensure that a design, almost from its inception, is such that
no really nasty surprises in strength or powering will be found when it is subjectedto the detailed scientific examination that comes at a later stage.
1.1.2 Reader’s background knowledge
This book makes no attempt to teach scientific naval architecture and it is assumed
that professional naval architects will bring a well developed background knowledge
of naval architecture to their reading and use of the book.
Ships are, however, a fascinating subject and reading this book should not be
too difficult for anyone interested in learning how they are designed. Lay readers
will want to skip those parts that invoke terms with which they are unfamiliar, but
should still find much that is intelligible to them and be able to see why ship
designers find their profession so absorbingly interesting.
1.1.3 Scope in terms of ship types
This book covers the design of a wide range of monohull displacement ship types,
but this needs to be set in the context of the even wider range of marine vehicles
shown in Fig. 1.1. These range from surface skimming vessels, through displacementships and semi-submersibles, whose main buoyancy is well under the water
surface, to wholly submerged submarines.The extremes of amphibious hovercraft and submarines have unique capabilities;
the former has an ability to travel over land or ice as well as over the sea; the latter
an ability to travel under ice flows and to remain invisible.
Many other types of marine vehicles share their market place, to a greater or less
extent, with the choice between them being determined by the required speed and
carrying capacity together with the wind and sea conditions in which they are
required to operate. The building and operational costs which these factors entail
for the alternative types of vessel determines the “winner”.
Apart from some discussion in Chapter 2 - in which the importance of setting
objectives in broad terms which admit unconventional solutions and a brief
treatment later in that chapter of planing and multi-hull vessels - this book is
devoted to monohull displacement ships. The great majority of ships sailing the
seas today are monohull displacement ships, with this solution having been shownto provide the most economical answer to the majority of design requirements.
Some challenges to this supremacy may, however, be on the way: wave-piercing
catamarans are becoming competitive for passenger ships and the excellent seakeeping
ability of the SWATH type of vessel enables a ship of this configuration to
be smaller than a competing monohull so that this type may become economically
competitive for a service in which minimum motions in a seaway are a prime need
- aircraft carriers and some research ships being distinct possibilities.
Monohull displacement ships can be divided into many categories, some of the
principal divisions by use being shown in Fig. 1.2. From a design point of view
there is, however, an alternative classification according to which design requirements
are most critical in the determination of the main dimensions of the ship (a
subject discussed in Chapter 2).1.1.4 Transfer of technology between ship types
It is perhaps obvious that a design for a particular type of ship can most readily be
prepared by a naval architect who has recently designed a successful ship of that
type. From such a background of experience, a competent design can be confidently
expected, but there must be a probability that the new design will closely follow the
trends of recent designs and is unlikely to include much innovative thought.
On the other hand, a naval architect experienced in designing a wide variety of
ships, but laclung detailed up-to-date knowledge of the particular type, will have a
harder task as he will have to start by studying magazine articles etc. about recently
built ships of the type to acquire the necessary background knowledge. Once he
has gained this background he may, however, go on to produce a more innovative
design, possibly bringing into play ideas used in other ship types which can be
adapted to the ship type on which he is working.
Unfortunately for naval architects, the tendency today is for shipyards, and to a
lesser extent shipping companies, to specialise in one (or at most a very few) ship
types, reducing the range of experience which used to be common in the versatile
shipyards of some decades ago.
1.1.5 Theauthor’s design experience
The author was lucky to have the opportunity of gaining a particularly wide range
of experience and would like to use this book to share this with his readers. The
shipyard in which he spent the first half of his career built passenger liners,
cross-channel passenger, car and train ferries, refrigerated and general cargo ships,
bulk carriers, oil tankers, many dredger types, logistic support landing ships,
frigates and destroyers, and he was deeply involved in the design of all of these
except the warships. As consultants, the firm was also involved in the design of
some of the earliest stern trawlers and fish factory ships, and of the first generation
container ships.
In the second half of his career, the author joined a major firm of consultants
which under his direction designed another wide assortment of merchant ships and
warships. The merchant ships included cargo liners, container ships, bulk carriers,
sewage-disposal ships, fishery research vessels, hydrographic and oceanographic
research ships, fishing boats.
The warships and naval auxiliary vessels included aircraft and helicopter
carriers, frigates, corvettes, mine hunters, landing ship docks, logistic support
ships, fleet auxiliary combined oil tanker and store ships.
Some of these ships feature in Chapter 16, in which the general arrangementsof
a number of ship types are examined. Other ships featuring in this chapter have
been selected as representing good recent practice.1.1.6 The general layout of the book
The next two sections of this chapter deal in a general way with design methods
and design data respectively. The section on design methods starts by discussing
the place of some of the “back of the envelope” type calculations outlined in later
chapters and then goes on to describe computer methods and how these can speed
up and increase the accuracy of design work.
The section on data outlines the importance of data to a naval architect and the
need to store this in an easily accessible format. The sources drawn on in the
writing of this book are given together with suggestions of other sources that
designers will find useful.
Chapter 2 starts by dealing with the very important subject of setting the design
requirements. For merchant ships this task will often be carried out by the
commercial side of a shipping company; for warships by naval staff; for specialist
ships by the scientists or others involved in the specialism. The naval architect has,
however, a great deal to contribute to this task and should be fully consulted. If he
is not so consulted he should have no inhibitions about questioning the design
requirements with which he is eventually faced. The chapter then introduces the
design spirals for merchant ships and warships, compares these and goes on tosuggest how to establish which criteria are most critical in seeking a solution which
meets the requirements.
Chapters 3,4 and 5 draw quite largely on the R.I.N.A. paper “Some ship design
methods” which the author wrote in 1976 in collaboration with A.W. Gilfillan, to
whom he is indebted for permission to draw on this joint work. Most of what was
written in 1976 seems to have stood the test of time very well, but some updating
has of course been necessary and there has been some expansion of a text which
was originally limited by R.I.N.A. publication guidelines.
Chapter 3 gives the fundamental design equations for both weight and volumebased
designs. This includes data on the dimensional relationships applicable to a
variety of ship types. Data on the deadweighddisplacement ratio and the cargo
capacityhull volume ratio are given, again for a variety of ship types.
Chapter 4 deals with weight-based designs describing both approximate and
detailed methods for calculating steel-weight, outfit weight and machinery weight.
Chapter 5 deals with volume-based designs describing how to calculate the
volume required to accommodate all the space requirements of a passenger ship
and how to translate a space requirement to appropriate ship dimensions.
Chapters 6 and 7 which deal with powering, Chapter 8 which follows on to theclosely related subject of the ship lines, and Chapter 9 which deals with machinery
selection all draw on the author’s Parsons Memorial paper “Designing ships for
fuel economy” published by R.I.N.A. in 1981.The treatment of powering in Chapters 6 and 7 kept expanding under the
influence of the author’s advisers. Interestingly one of these favoured the newer
treatment of this subject as more scientific whereas the other felt that there was
much more useful data available in the earlier Froude format and believed that with
appropriate “fiddle factors” use of this data can still give satisfactory answers. The
chapters have tried to keep a balance between these two approaches.
Readers may feel with some justification that the treatment of powering falls
short of the full treatment they would like to have as the subject of propeller
efficiency has been omitted for the very good reason that the author can claim no
expertise in this science (or is it a black art?). He has instead always used the
shortcut to the quasi-propulsive efficiency which is given in Chapter 7, having
found this to be remarkably accurate.
Chapter 8 deals not only with the design of lines to minimise powering, but
looks at the qualities that the lines must have to ensure good sea-keeping, good
manoeuvrability and good stability for given dimensions.
Chapter 9, in its treatment of machinery selection, starts with a statement of the
criteria against which main engines are chosen and goes on to consider which ofthese are important for different ship types and which types of machinery best meet
them.
Chapter 10 deals with the factors influencing structural design. Although no
detailed structural calculation methods are given, the chapter gives a lot of advice
on how to design both the general arrangement and the structure itself for economy
in steel-weight and in fabrication costs, whilst avoiding many of the pitfalls of
fatigue, brittle fracture, vibration, corrosion that can be the consequence of less
then satisfactory structural design.
Chapters 11, 12 and 13 deal with the main statutory rules for merchant ships, the
need to ensure compliance with which forms a prominent part of the work
undertaken in the later design spirals.
Chapter 11 has freeboard and subdivision as its subject and gives a full
treatment of the new probabilistic rules for the subdivision and damaged stability
of cargo ships. The corresponding rules for passenger ships are not dealt with in the
same detail as it is expected that they will be brought into line with the cargo ship
rules within a relatively short time.
Chapter 12 deals with stability and trim and after dealing with the statutory rules
for these subjects for merchant ships outlines the treatment that these are given inwarship design and operation.
Chapter 13 deals with some of the remaining subjects for which there are
statutory rules for merchant ships, such as fire protection, life-saving, marine
pollution and tonnage.
Chapter 14 deals with some of the special requirements which are involved in
the design of a warship.Chapters 15 and 16 bear a considerable responsibility for this book being
written as it was the author’s view that the arrangement aspects of design were
badly neglected, both in textbooks on naval architecture and in teaching in
universities and technical colleges, that provided much of the original motivation.
Both the task of creating the general arrangement of a ship and the work
involved in drawing detailed arrangements of each part of it seem to be regarded
by many lecturers at universities and technical colleges and, to only a slightly
lesser extent, by some designers themselves as simple tasks which can be left to
draughtsmen. This attitude is compounded by the fact that draughtsmen are given
only limited instruction in much of the skills of their trade and are largely left to
learn for themselves by studying the plans of “the last ship”. Whilst studying the
plans of ships should be a “must” for all designers, this study ought to go well
beyond knowing “what” was done towards a clear understanding of “why” it was
done.
Designers should have an ability to appreciate when good reasoning about a
multitude of factors has led to a good arrangement and, even more importantly, an
ability to see the faults in other arrangements. These abilities, which can and
should be taught, deal with as fascinating a subject as anything in ship designChapter 17 goes back a long way in the author’s career to when he wrote a
standard specification for the Clydeside shipyard of Alexander Stephen & Sons.
This specification was intended both to ease the task of writing ship specifications
and to lay down standards to be followed where owner’s specifications lacked
detail.
Chapter 18 dates back to the same period of his career, but needed substantial
updating in later years to deal with the exceptionally difficult problem that faces a
consultant when his client wants an estimate of the price of a ship which may be
built, not in the adjoining shipyard (which shipyard estimators find difficult
enough) but in Japan or Korea.
Chapter 19 is, of course, closely related to Chapter 2 and might have adjoined it
in the book. The author cannot claim any specialised knowledge of this subject but
feels strongly that a book of this sort would be incomplete unless it addressed the
subject of operational economics, which is both the test of whether a good
merchant ship has been built and the starting point for the design of a new merchant
ship.
Chapter 20 deals with some solutions to the design problems that arise in major
conversion work whether this is undertaken to enable a ship to operate in a new
role or to rectify design errors.
In the hope of easing reference to the bibliography, this has been dividedinto six
sections, with each section covering a group of chapters whose subjects are related.
It has to be admitted that the bibliography is far from complete, but it is hoped
that the references given will lead to other relevant bibliographies.There are such a mass of symbols and abbreviations in use in naval architecture
and ship design that it was thought best to define these in close context to the
formulae in which they are used.
The author has tried to write this book in as plain English as possible as he has a
strong dislike of some of the modem words with which a number of today’s
technical papers seem to be inflated. In keeping with this policy, the book tries to
describe practical ship design methods and not to “elaborate the systems methodology
of the design of marine artifacts”!
One of the aims of this book is to help naval architects to co-operate closely and
harmoniously with marine engineers and other specialists whose expertise is
required in ship design and construction, which seems preferable to indulging in
“synergetic integration”.
The author has tried to follow the one acronym he really likes, “AAEFTR’ -
“all acronyms explained first time round’ and hopes that his readers will appreciate
this.
Copy rigth © by 1998-2006 NTT DATA ENGINEERING SYSTEMS CORPORATION All rights reserved.

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ABS NDT Rules

ABS NDT Rules
General
1 Preparation for Inspection A visual inspection is to be conducted to the satisfaction of the Surveyor. 2 Methods used for preparing and cleaning welds and nondestructive test procedures are to be to the satisfaction of the Surveyor. 3 Methods of Inspection Inspection of welded joints is to be carried out by an approved nondestructive test method, such as radiography (RT), ultrasonic (UT), magnetic particle (MT) or liquid penetrant (PT). Radiographic or ultrasonic inspection, or both, is to be used for internal (subsurface) inspection. Magnetic particle or liquid penetrant inspection or other equivalent approved detection method is generally to be used for surface inspection of welds

.4The extent and location of inspection and choice of inspection method(s) are to be in accordance with the applicable Rules, the material and welding procedures involved, the quality control procedures employed, the results of the visual inspection, and are to be to the satisfaction of the Surveyor
.5 Personnel The Surveyor is to be satisfied that personnel responsible for conducting nondestructive tests are thoroughly familiar with the equipment being used and that the technique and equipment used are suitable for the intended application. NDT personnel are to be qualified by training and experience and certified to perform the necessary calibrations and tests and to interpret and evaluate indications in accordance with the terms of the specification. Personnel certified in accordance with the International Standard ISO 9712, Training, Qualification and Certification of Non-destructive Testing Personnel, shall be classified in any one of the following three levels
.Personnel who have not attained certification may be classified as trainees
.5.1 Other Recognized National Certifying Programs The requirements of other recognized national certifying programs will be specially considered
.5.3 NDT Trainee A trainee is an individual who works under the supervision of certified personnel but who does not conduct any tests independently, does not interpret test results and does not write reports on test results
.5.4This individual may be registered as being in the process of gaining appropriate experience to establish eligibility for qualification to Level 1 or for direct access to Level 2.
. 5.5 NDT Level 1 An individual certified to NDT Level 1 may be authorized to:
. i) set up the equipment;
. ii) carry out NDT operations in accordance with written instructions under the supervision of Level 2 or Level 3 personnel;
.iii) perform the tests;
.iv) record the conditions and date of the tests;
.v) classify, with prior written approval of a Level 3, the results in accordance with documented criteria, and report the results. An individual certified to Level 1 is not to be responsible for the choice of the test method or technique to be used

5.7 NDT Level 2 An individual certified to NDT Level 2 may be authorized to perform and direct nondestructive testing in accordance with established or recognized procedures
.This may include:
. i) defining the limitations of application of the test method for which the Level 2 individual is qualified; ii) translating NDT codes, standards, specifications and procedures into practical testinginstructions adapted to the actual working conditions;
. iii) setting up and verifying equipment settings;
.iv) performing and supervising tests;
.v) interpreting and evaluating results according to applicable codes, standards and specifications;
.vi) preparing NDT instructions;
.vii) carrying out or supervising all Level 1 duties;
. viii) training or guiding personnel below Level 2, and
. ix) organizing and reporting results of nondestructive tests. 5.9 NDT Level 3 5.9.1 An individual certified to NDT Level 3 may be authorized to direct any operation in the NDT method(s) for which he is certified
.This may include:
.i) assuming full responsibility for an NDT facility and staff;
.ii) establishing and validating techniques and procedures;
.iii) interpreting codes, standards, specifications and procedures;
.iv) designating the particular test methods, techniques and procedures to be used for specific NDT work;
. v) interpreting and evaluating results in terms of existing codes, standards and specifications;
.vi) managing qualification examinations, if authorized for this task by the certification body, and
.vii) carrying out or supervising all Level 1 and Level 2 duties
.5.9.2 An individual certified to Level 3 shall have:
.i) sufficient practical background in applicable materials, fabrication and product technology to select methods and establish techniques and to assist in establishing acceptance criteria where none are otherwise available;
. ii) a general familiarity with other NDT methods; and
.iii) the ability to train or guide personnel below Level 3. 7 NDT Procedures and Techniques Procedures and techniques shall be established and approved by personnel certified to NDT level 3 in the applicable inspection method. Techniques shall be prepared in accordance with the requirements stated in the applicable NDT section of this Guide. NDT inspection shall be performed by certified level 1, 2 or 3 personnel. Interpretation and evaluation of inspection results shall be performed by personnel certified to NDT level 2 or 3 in the applicable NDT inspection method
. Inspection for Delayed (Hydrogen Induced) Cracking
. 9.1 Time of Inspection Nondestructive testing of weldments in steels of 400 N/mm2 (41 kgf/mm2, 58,000 psi) yield strength or greater is to be conducted at a suitable interval after welds have been completed and cooled to ambient temperature. The interval is to be a minimum of 24 hours for steels 400 N/mm2 (41 kgf/mm2, 58,000 psi) yield strength and a minimum of 72 hours for steels greater than 400 N/mm2 (41 kgf/mm2, 58,000 psi) yield strength, unless specially approved otherwise
.9.2The Surveyor, at his discretion, may require a longer interval and/or additional random inspection at a later period. At the discretion of the Surveyor, the 72 hour interval may be reduced to 24 hours for RT or UT inspections, provided a complete visual and random MT or PT inspection to the satisfaction of the Surveyor, is conducted 72 hours after welds have been completed and cooled to ambient temperature.
. 9.3 Delayed Cracking Occurrences When delayed cracking is encountered in production, previously completed welds are to be reinspected for delayed cracking to the Surveyor’s satisfaction. The Surveyor, at his discretion, may require requalification of procedures or additional production control procedures to assure that production welds are free of delayed cracking
.11 Acceptance Standards Acceptance Standards specified herein are only applicable to inspections required by the Rules and by surveyor
.13 Documentation Adequate information as to the NDT methods, extent, location(s) and results of inspection shall be included in inspection records or reports so that conformity with the applicable NDT requirements is properly documented
.15 References International Standard ISO 9712, Training, Qualification and Certification of Non-destructive Testing personnelAmerican Bureau of Shipping
Incorporated by Act of Legislature of
the State of New York 1862
Copyright 2002

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INJECTION MOLDING

INJECTION MOLDING
Injection molding is one of the major methods for plastics molding. This method is widely used for various molded products because it is possible to produce parts of high quality at a low cost and in a short time. Molding by injecting a material into the mold.

Procedure A molding plastics is heated and mixed by the screw in the heated barrel, and will be plasticated to become molten plastics. (In this textbook, the material before heating is called a "resin" and the plasticated material is called a "molten plastics.") Inject the molten plastics from the heated barrel into the mold with high pressure. Cool to solidify the molten plastics in the mold. Push the part out with the ejection pins. Advantages Enables the molding of most thermoplastics and some thermosetting plastics. Enables the molding of high quality parts for low cost in a short time. The molding cycle can be automated. The structure of a mold can be changed freely depending on the shape or material of the parts.
Disadvantage If the setting for a certain molding material is not done in correctly, a defective molding may result.
Typical Products
Plastics products such as household goods, home appliances or automobile interiors. Now, let's learn more in detail about the movement and the role of injection molding using a screw type injection molding machine.
Closing mold, Clamping mold
When closing a mold, first close it with low pressure, and then with high pressure just before completion to close it firmly.
If a mold is closed too quickly, the mold may be deformed; therefore, clamping the mold involves two steps. Two-step mold clamping also helps to prevent foreign matter that is sometimes left behind in the mold from damaging or destroying the mold if the clamping of the mold is done by high pressure.
Injection Nozzle Seating, Injection When mold clamping is complete, the injection carriage will move forward so that the sprue bush of the mold will touch the nozzle. Then, molten plastics will be injected into the mold (the molding material in the injection carriage has already been plasticated, becoming molten plastics). Holding pressure, Cooling, Plastication Even after the molten plastics is injected into the mold, the holding pressure is maintained while the molten plastics cools in the mold. While the molten plastics is being cooled and solidified in the mold, the molten material for the next molding will be plasticated. This plastication is done by the heat generated in mixing the resin with a screw, or the band heater that is attached around the heated barrel.
Holding pressure is also called the secondary pressure. It is used to add more molten plastics by putting pressure on the filled molten plastics in the mold for mold shrinkage that is caused by cooling solidification, so that the sink mark of parts can be reduced. Injection nozzle removal, mold opening, part removal When plastication of the molding material for the next part and cooling of the current part are complete, the injection carriage is separated from the mold and the mold is opened. When the mold is completely opened, the part will be pushed out by the ejection pins. Then the whole cycle is complete. Nozzle removal may often be skipped to reduce the molding cycle ELSEVIER SCIENCE Ltd
The Boulevard, Langford Lane
Kidlington, Oxford OX5 IGB, UK
0 1998 David Watson. All rights reserved

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Diesel Engine

DIESEL BASIC
At first glance, a diesel engine looks like a heavy-duty gasoline engine, minus spark plugs and ignition wiring (Fig. 2-1). Some manufacturers build compression ignition (CI) and spark ignition (SI) versions of the same engine
Caterpillar G3500 and G3600 SI natural-gas fueled engines are built on diesel frames and use the same blocks, crankshafts, heads, liners, and connecting rods. But there are important differences between CI and SI engines that cut deeper than the mode of igniting the fuel

When air is compressed, collisions between molecules produce heat that ignites the diesel fuel. The compression ratio (c/r) is the measure of how much the air is compressed (Fig. 2-2).
Compression ratio swept volume clearance volume swept volume Swept volume the volume of the cylinder traversed by the piston in its travel from top dead center (tdc) to bottom dead center (bdc) Clearance volume combustion chamber volume Figure 2-3 graphs the relationship between c/r’s and thermal efficiency, which reaffirms what every mechanic knows: high c/r’s are a precondition for power and fuel economy. At the very minimum, a diesel engine needs a c/r of about 16:1 for cold starting. Friction, which increases more rapidly than the power liberated by increases in compression, sets the upper limit at about 24:1.
Other inhibiting factors are the energy required for cranking and the stresses produced by high power outputs. Diesels with c/r’s of 16 or 17:1 sometimes benefit from a point or two of higher compression. Starting becomes easier and less exhaust smoke is produced. An example is the Caterpillar 3208 that has a tendency to smoke and “wet stack,” that is, to saturate its exhaust system with unburned fuel. These problems can be alleviated with longer connecting rods that raise the compression ratio from 16.5:1 to 18.2:1. It should be noted that a compressor, in the form of a turbocharger or supercharger, raises the effective c/r. Consequently, these engines have c/r’s of 16 or 17:1, which are just adequate for starting. Once the engine is running, the compressor provides additional compression. Gasoline engines have lower c/r’s—half or less—than CI engines. This is because the fuel detonates when exposed to the heat and pressure associated with higher c/r’s. Detonation is a kind of maverick combustion that occurs after normal ignition.
The unburned fraction of the charge spontaneously explodes. This sudden rise in pressure can be heard as a rattle or, depending upon the natural frequency of the connecting rods, as a series of distinct pings. Uncontrolled detonation destroys crankshaft bearings and melts piston crowns. Induction Modern SI engines mix air and fuel in the intake manifold by way of one or more low-pressure (50-psi or so) injectors. A throttle valve regulates the amount of air admitted, which is only slightly in excess of the air needed for combustion. As the throttle opens, the injectors remain open longer to increase fuel delivery. For a gasoline engine, the optimum mixture is roughly 15 parts air to 1 part fuel. The air-fuel mixture then passes into the cylinder for compression and ignition. In a CI engine, air undergoes compression before fuel is admitted. Injectors open late during the compression stroke as the piston approaches tdc. Compressing air, rather than a mix of air and fuel, improves the thermal efficiency of diesel engines.
To understand why would require a course in thermodynamics; suffice to say that air contains more latent heat than does a mixture of air and vaporized fuel. Forcing fuel into a column of highly compressed air requires high injection pressures. These pressures range from about 6000 psi for utility engines to as much as 30,000 psi for state-of-the-art examples. CI engines dispense with the throttle plate—the same amount of air enters the cylinders at all engine speeds. Typically, idle-speed air consumption averages about 100 lb of air per pound of fuel; at high speed or under heavy load, the additional fuel supplied drops the ratio to about 20:1. Without a throttle plate, diesels breathe easily at low speeds, which explains why truck drivers can idle their rigs for long periods without consuming appreciable fuel. (An SI engine requires a fuel-rich mixture at idle to generate power to overcome the throttle restriction.) Since diesel air flow remains constant, the power output depends upon the amount of fuel delivered. As power requirements increase, the injectors deliver more fuel than can be burned with available oxygen. The exhaust turns black with partially oxidized fuel.
How much smoke can be tolerated depends upon the regulatory climate, but the smoke limit always puts a ceiling on power output. To get around this restriction, many diesels incorporate an air pump in the form of an exhaust-driven turbocharger or a mechanical supercharger. Forced induction can double power outputs without violating the smoke limit. And, as far as turbochargers are concerned, the supercharge effect is free. That is, the energy that drives the turbo would otherwise be wasted out the exhaust pipe as heat and exhaust-gas velocity. The absence of an air restriction and an ignition system that operates as a function of engine architecture can wrest control of the engine from the operator. All that’s needed is for significant amounts of crankcase oil to find its way into the combustion chambers. Oil might be drawn into the chambers past worn piston rings or from a failed turbocharger seal. Some industrial engines have an air trip on the intake manifold for this contingency, but many do not. A runaway engine generally accelerates itself to perdition because few operators have the presence of mind to engage the air trip or stuff a rag into the intake. Ignition and combustion SI engines are fired by an electrical spark timed to occur just before the piston reaches the top of the compression stroke. Because the full charge of fuel and air is present, combustion proceeds rapidly in the form of a controlled explosion. The rise in cylinder pressure occurs during the span of a few crankshaft degrees. Thus, the cylinder volume above the piston undergoes little change between ignition and peak pressure. Engineers, exaggerating a bit, describe SI engines as “constant volume” engines (Fig. 2-4). Compared to SI, the onset of diesel ignition is a leisurely process
Some time is required for the fuel spray to vaporize and more time is required for the spray to reach ignition temperature. Fuel continues to be injected during the delay period. Once ignited, the accumulated fuel burns rapidly with correspondingly rapid increases in cylinder temperature and pressure. The injector continues to deliver fuel through the period of rapid combustion and into the period of controlled combustion that follows. When injection ceases, combustion enters what is known as the afterburn period. The delay between the onset of fuel delivery and ignition (A–B in Fig. 2-5) should be as brief as possible to minimize the amount of unburnt fuel accumulated in the cylinder. The greater the ignition lag, the more violent the combustion and resulting noise, vibration, and harshness (NVH). Ignition lag is always worst upon starting cold, when engine metal acts as a heat sink.
Mechanics sometimes describe the clatter, white exhaust smoke, and rough combustion that accompany cold starts as “diesel detonation,” a term that is misleading because diesels do not detonate in the manner of SI engines. Combustion should smooth out after the engine warms and ignition lag diminishes. Heating the incoming air makes cold starts easier and less intrusive. In normal operation, with ignition delay under control, cylinder pressures and temperatures rise more slowly (but to higher levels) than for SI engines. In his proposal of 1893, Rudolf Diesel went one step further and visualized constant pressure expansion: fuel input and combustion pressure would remain constant during the expansion, or power, stroke.
He was able to approach that goal in experimental engines, but only if rotational speeds were held low. His colleagues eventually abandoned the idea and controlled fuel input pragmatically, on the basis of power output. Even so, the pressure rise is relatively smooth and diesel engines are sometimes called “constant pressure” devices to distinguish them from “constant volume” SI engines McGraw-Hill eBooks Copyright © 2008, 1995, 1991, 1975 by Paul Dempsey

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DIE CASTING PROCESS I

Die Casting

A. Introduction
B. History
C. The Future
D. Die Casting Advantages
E. Die Casting Process
F. Die Casting vs. Other Process
G. Choosing the Proper Alloy
H. Die Construction
I. Hot Chamber Machines
J. Cold Chamber Machines
K. High Integrity Die Casting Methods
L. Automation and Quality Control
M. Die Casting Design
N. Alloy Properties
O. Comparing Materials
P. Effective Design

Introduction
Die casting is a versatile process for producing engineered metal parts by forcing molten metal under high pressure into reusable steel molds. These molds, called dies, can be designed to produce complex shapes with a high degree of accuracy and repeatability. Parts can be sharply defined, with smooth or textured surfaces, and are suitable for a wide variety of attractive and serviceable finishes.
Die castings are among the highest volume, mass-produced items manufactured by the metalworking industry, and they can be found in thousands of consumer, commercial and industrial products. Die cast parts are important components of products ranging from automobiles to toys. Parts can be as simple as a sink faucet or as complex as a connector housing.

Die cast parts are found in many places around the home. The polished, plated zinc die casting in this kitchen faucet illustrates one of the many finishes possible with die casting.


These connector housings are examples of the durable, highly accurate components that can be produced with today’s modern die casting.
History
The earliest examples of die casting by pressure injection - as opposed to casting by gravity pressure - occurred in the mid-1800s. A patent was awarded to Sturges in 1849 for the first manually operated machine for casting printing type. The process was limited to printer’s type for the next 20 years, but development of other shapes began to increase toward the end of the century. By 1892, commercial applications included parts for phonographs and cash registers, and mass production of many types of parts began in the early 1900s.
The first die casting alloys were various compositions of tin and lead, but their use declined with the introduction of zinc and aluminum alloys in 1914. Magnesium and copper alloys quickly followed, and by the 1930s, many of the modern alloys still in use today became available.
The die casting process has evolved from the original low-pressure injection method to techniques including high-pressure casting — at forces exceeding 4500 pounds per square inch — squeeze casting and semi-solid die casting. These modern processes are capable of producing high integrity, near net-shape castings with excellent surface finishes.
The Future
Refinements continue in both the alloys used in die casting and the process itself, expanding die casting applications into almost every known market. Once limited to simple lead type, today’s die casters can produce castings in a variety of sizes, shapes and wall thicknesses that are strong, durable and dimensionally precise.

A magnesium seat pan shows how complex, lightweight die cast components can improve production by replacing multiple pieces.

The Advantages of Die Casting
Die casting is an efficient, economical process offering a broader range of shapes and components than any other manufacturing technique. Parts have long service life and may be designed to complement the visual appeal of the surrounding part. Designers can gain a number of advantages and benefits by specifying die cast parts.
High-speed production - Die casting provides complex shapes within closer tolerances than many other mass production processes. Little or no machining is required and thousands of identical castings can be produced before additional tooling is required.
Dimensional accuracy and stability - Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances. They are also heat resistant.
Strength and weight - Die cast parts are stronger than plastic injection moldings having the same dimensions. Thin wall castings are stronger and lighter than those possible with other casting methods. Plus, because die castings do not consist of separate parts welded or fastened together, the strength is that of the alloy rather than the joining process.
Multiple finishing techniques - Die cast parts can be produced with smooth or textured surfaces, and they are easily plated or finished with a minimum of surface preparation.
Simplified Assembly - Die castings provide integral fastening elements, such as bosses and studs. Holes can be cored and made to tap drill sizes, or external threads can be cast.
Die Casting Process
The basic die casting process consists of injecting molten metal under high pressure into a steel mold called a die. Die casting machines are typically rated in clamping tons equal to the amount of pressure they can exert on the die. Machine sizes range from 400 tons to 4000 tons. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. The two methods are hot chamber or cold chamber. A complete die casting cycle can vary from less than one second for small components weighing less than an ounce, to two-to-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts.

Die Casting vs. Other Processes
Die casting vs. plastic molding - Die casting produces stronger parts with closer tolerances that have greater stability and durability. Die cast parts have greater resistance to temperature extremes and superior electrical properties.
Die casting vs. sand casting - Die casting produces parts with thinner walls, closer dimensional limits and smoother surfaces. Production is faster and labor costs per casting are lower. Finishing costs are also less.
Die casting vs. permanent mold - Die casting offers the same advantages versus permanent molding as it does compared with sand casting.
Die casting vs. forging - Die casting produces more complex shapes with closer tolerances, thinner walls and lower finishing costs. Cast coring holes are not available with forging.
Die casting vs. stamping - Die casting produces complex shapes with variations possible in section thickness. One casting may replace several stampings, resulting in reduced assembly time.
Die casting vs. screw machine products - Die casting produces shapes that are difficult or impossible from bar or tubular stock, while maintaining tolerances without tooling adjustments. Die casting requires fewer operations and reduces waste and scrap.
Choosing the Proper Alloy
Each of the metal alloys available for die casting offer particular advantages for the completed part.
Zinc - The easiest alloy to cast, it offers high ductility, high impact strength and is easily plated. Zinc is economical for small parts, has a low melting point and promotes long die life.
Aluminum - This alloy is lightweight, while possessing high dimensional stability for complex shapes and thin walls. Aluminum has good corrosion resistance and mechanical properties, high thermal and electrical conductivity, as well as strength at high temperatures.
Magnesium - The easiest alloy to machine, magnesium has an excellent strength-to-weight ratio and is the lightest alloy commonly die cast.
Copper - This alloy possesses high hardness, high corrosion resistance and the highest mechanical properties of alloys cast. It offers excellent wear resistance and dimensional stability, with strength approaching that of steel parts.
Lead and Tin - These alloys offer high density and are capable of producing parts with extremely close dimensions. They are also used for special forms of corrosion resistance.
Die Construction
Dies, or die casting tooling, are made of alloy tool steels in at least two sections, the fixed die half, or cover half, and the ejector die half, to permit removal of castings. Modern dies also may have moveable slides, cores or other sections to produce holes, threads and other desired shapes in the casting. Sprue holes in the fixed die half allow molten metal to enter the die and fill the cavity. The ejector half usually contains the runners (passageways) and gates (inlets) that route molten metal to the cavity. Dies also include locking pins to secure the two halves, ejector pins to help remove the cast part, and openings for coolant and lubricant.
When the die casting machine closes, the two die halves are locked and held together by the machine’s hydraulic pressure. The surface where the ejector and fixed halves of the die meet and lock is referred to as the "die parting line." The total projected surface area of the part being cast, measured at the die parting line, and the pressure required of the machine to inject metal into the die cavity governs the clamping force of the machine.

There are four types of dies:
1. Single cavity to produce one component

2. Multiple cavity to produce a number of identical parts

3. Unit die to produce different parts at one time

4. Combination die to produce several different parts for an assembly.
Hot Chamber Machines
Click on the image to see an animation

Hot chamber machines are used primarily for zinc, copper, magnesium, lead and other low melting point alloys that do not readily attack and erode metal pots, cylinders and plungers. The injection mechanism of a hot chamber machine is immersed in the molten metal bath of a metal holding furnace. The furnace is attached to the machine by a metal feed system called a gooseneck. As the injection cylinder plunger rises, a port in the injection cylinder opens, allowing molten metal to fill the cylinder. As the plunger moves downward it seals the port and forces molten metal through the gooseneck and nozzle into the die cavity. After the metal has solidified in the die cavity, the plunger is withdrawn, the die opens and the casting is ejected.
Cold Chamber Machines
Click on the image to see an animation

Cold chamber machines are used for alloys such as aluminum and other alloys with high melting points. The molten metal is poured into a "cold chamber," or cylindrical sleeve, manually by a hand ladle or by an automatic ladle. A hydraulically operated plunger seals the cold chamber port and forces metal into the locked die at high pressures.

High Integrity Die Casting Methods
There are several variations on the basic process that can be used to produce castings for specific applications. These include:
Squeeze casting - A method by which molten alloy is cast without turbulence and gas entrapment at high pressure to yield high quality, dense, heat treatable components.

Click on the image to see an animation
Semi-solid molding - A procedure where semi-solid metal billets are cast to provide dense, heat treatable castings with low porosity.


Automation and Quality Control
Modern die casters use a number of sophisticated methods to automate the die casting process and provide continuous quality control. Automated systems can be used to lubricate dies, ladle metal into cold chamber machines and integrate other functions, such as quenching and trimming castings. Microprocessors obtain metal velocity, shot rod position, hydraulic pressure and other data that is used to adjust the die casting machine process, assuring consistent castings shot after shot. These process control systems also collect machine performance data for statistical analysis in quality control.
Die Casting Design

Die casting is one of the fastest and most cost-effective methods for producing a wide range of components. However, to achieve maximum benefits from this process, it is critical that designers collaborate with the die caster at an early stage of the product design and development. Consulting with the die caster during the design phase will help resolve issues affecting tooling and production, while identifying the various trade-offs that could affect overall costs.
For instance, parts having external undercuts or projections on sidewalls often require dies with slides. Slides increase the cost of the tooling, but may result in reduced metal use, uniform casting wall thickness or other advantages. These savings may offset the cost of tooling, depending upon the production quantities, providing overall economies.
Many sources are available for information on die casting design, including textbooks, technical papers, trade journals and professional associations. While this section is not intended to provide a comprehensive review of all the factors involving die casting design, it will highlight some of the primary considerations. Additional sources of information are listed in the "Resources" section of this brochure.
Alloy Properties One of the first steps in designing a die cast component is choosing the proper alloy. Typical properties for the most commonly used alloys are shown on the linked charts.
Comparing Materials
The cost of materials is another important design consideration. Accurate comparisons require looking beyond the cost per pound or cost per cubic inch to fully analyze the advantages and disadvantages of each competing process. For instance, the relatively greater strength of metals generally allows thinner walls and sections and consequently requires fewer cubic inches of material than plastics for a given application.
Effective Design Load example illustrations to help show how design and engineering can affect final production.
Glossary and Additional Resources
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BASIC OF INJECTION MOLDING A mold is a device made of metal to produce a product faster, less expensive, and more consistently. There are various types of molds for molding different products. Here are the major types of molds. For example, a waffle maker is a kind of mold. Casting Mold Molds parts by pouring melted metal (liquid metal). (1) Assemble a mold. (2) Pour liquid metal. (3) Open the mold after cooled down. * Typical Products Engine (Cylinder block), Manifold, Wheel, Figurines Forging Forms parts by striking a material with a die. (1) Place a material. (2) Strike. (3) Strike more. (4) Complete. * Typical Products Products that require intensity such as crank shaft, conrod, or knuckle. More details The forging method of softening a material by heat before striking is called hot forging. On the other hand, the method of striking a material without heating it up is called cold forging. Cold forging is used to mold a soft material such as aluminum. Press Mold Molds by pressing a sheet against a mold (normally used for metal sheets) (1) Place a material. (2) Press a mold. (3) Complete. * Typical Products body, gate, steel wheel, or attachable steer of automobile, a pull top of a can, aluminum ash tray, mug cup More details Press type of mold includes bending (molds a shape), trimming (trims off unnecessary parts), edging (processes edge), and drawing (bends the parts that cannot be bent by a bender). Some parts are molded through several procedures, and a progressive press molding is used to perform these procedures sequentially. Die Cast Mold Molds by applying pressure to melted metal (liquid metal) and inject it into a mold. (1) Assemble a mold. (2) Inject liquid metal with pressure. (3) Open mold after cooled down. * Typical Products Aluminum products such as parts of an engine, precision products Plastics Mold A plastics mold is used to mold parts by melting a molding material such as plastics with heat and pressure into the mold. A plastics mold is used for various molding methods such as injection molding, compression molding, and extrusion. You will learn about injection molding later on. Now, let's discuss the other methods here. * Typical Products Plastics products such as household goods and home appliances, automobile interiors, or general plastics products like a plastics bottle. Compression Molding Molds by putting material in a mold first and compressing it. (1) Place a material. (2) Press, close mold and compress. (3) Open mold. More details Let's look at the detailed procedure now. Procedure Put a proper amount of molding material of thermosetting plastics powder into the mold. Close the top mold, and then heat up and pressure the mold. The material will be softened and plasticated, filling up the mold. Completely harden the material with more heat and pressure. Open the mold and remove the part using a take out pin. Advantages As a molding material is put in the mold, it will not move around and distortion of parts can be reduced. As the pressure for mold clamping is directly applied to the molding material, precise parts can be achieved. As a gate is not required, there is no limitation on the type of molding material (granule, powder, etc.). Therefore, it is used for molding of thermosetting plastics. As the structure is simple, equipment cost can be reduced. Disadvantages If heating up when the mold is not completely closed or excessively pressured, the molding material may leak out of the mold. If too much molding material is put in, it may overflow. Many flashes will be generated. Extrusion A continuous extrusion is formed by pushing material (that is fed in through a hopper) with a screw, that also mixes the material, out of the device's exit. The material will have the same cross section as the device's exit. (1) Put material in a hopper. (2) Push out while stirring with screw. (3) Complete. More details Let's look at the detailed procedure now. Procedure Put a molding material in a hopper (material feed container). Plasticate it by stirring and mixing it with a screw while heating it up. Push the molding material out by the screw through a small hole of the apex mold (a clasp used to give the material a desired shape). Finish molding by cold solidification. Advantage Performs molding continuously and effectively. Disadvantage Limited application as this method only molds parts that only have a cylindrical or tube-shaped section. Blow Molding Molds by putting a tube-shape material (parison) in the mold and blowing in air. (1) Put tube-shaped material (parison) in mold. (2) Blow in air. (3) Complete More details Let's look at the detailed procedure now. Procedure Pinch a part of a molding material that has been molded into a tube shape with a separate mold. Blow compressed air into the molding material, causing it to expand until it conforms to the shape mold to mold the part. Advantage Widely used for molding of bottle containers. Vacuum Molding A sheet material is heated and soften conform to the shape of the mold using a vacuum. Either a concave or convex mold can be used. (1) Set material sheet. (2) Vacuum air out. (3) Allow air in again and remove part. More details Let's look at the detailed procedure below. Procedure Soften a sheet of thermoplastics molding material with a heater. Suck the air out of the mold through the vent hole to form a vacuum, causing the molding material to conform to the mold and assume its shape. Allow air in again to remove the part. Advantages As molding pressure can be lowered than the atmosphere pressure (10,333kg/), plaster, wood, or thermosetting plastics can be used as a mold. Large size parts can be molded with relatively low equipment cost. Disadvantage This method is generally not used for parts with a complicated shape. RIM (Reaction Injection Molding) Molds by mixing two or more reactive materials in the mold. The reaction produces a new substance that fills the mold. More details Let's look at the detailed procedure now. Procedure Inject a molding material consisting of a mixture of a catalyst and an activator into the mold. Cause a copolymerization in the mold. Advantages As this molding requires lower pressure than regular injection molding, an aluminum or fiber mold can be used. Molding large sizes and complicated shapes is possible. Disadvantages A copolymerization generates gas, which compresses the air left in the mold and is likely to cause burns. Molding cycle is extended. FRP (Fiber Reinforced Plastics) Molding Uses the fiberglass or carbon fiber as reinforcement. There are two types of this molding - SMC (sheet molding) method and hand lay up method. More details Let's look at the detailed procedure now. SMC (Sheet Molding Compound) method, or Sheet molding method Procedure Place a sheet molding material of fiber mat wrapped by polyester in the mold. Press the material with heat and pressure. Advantages Thickness is uniform and complicated parts can be molded. Also, both sides of the parts can be finished smoothly. Hand Lay Up Method Procedure Place a fiber mat along the mold shape. Spread liquid resin over and harden at room temperature. Advantages This is used to mold relatively large FRP parts. No machine equipment is necessary. Disadvantages Manually done, it is difficult to make thickness uniform, making the molding cycle extremely long. Transfer Molding Soften the material by heating in the cavity of the mold and then push it into the mold. (1) Soften material in the heating cavity. (2) Push into mold. (3) Open the mold. More details Let's look at the detailed procedure now. Procedure Soften a molding material in the heating cavity. Push softened plastics into the mold by applying pressure. Harden the molten plastics. Open the mold and remove the part. Advantages The molding procedure is similar to injection molding; however, transfer molding involves heating of a molding material in the heating cavity to melt it into a molten plastics. Widely used for molding of thermosetting plastics. Transfer molding was developed to mold parts that are difficult to mold with compression molding, but currently is used for limited types of parts. Best used to form a complicated shape or a thick molding. Disadvantage The production cost of mold is high. The Boulevard, Langford Lane
Kidlington, Oxford OX5 IGB, UK
0 1998 David Watson. All rights reserved

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