Materials in design

New developments in materials have been timed to coincide with a season of exhibitions to be held at the NEC in Birmingham. The autumn of 1981 sees three exhibitions of interest to the user of materials, all held within a very short space of time at the National Exhibition Centre in Birmingham. The first of these is Interplas 81, held from 15-22 September, previously staged in 1977; secondly, the annual Design Engineering Show from the 6-9 October; finally Castings 81, to be held from the 19-23 October, is a repeat of an event first staged in 1979. Interplas WOOSdesigners

Interplas 81 is one of a series of plastics exkibitions held in four major European cities (Birmingham, Paris, Dusseldorf and Milan) in strict rotation. There has been a gradual change in emphasis, away from exhibitions concentrating solely on processing, compounding and machinery, to a genuine attempt to attract materials specifiers. Many plastics suppliers believe that design engineers still do not have a high level of expertise in polymer design. This point of view has recently been supported by the National College of Agricultural Engineering, part of the CrabfMd Institute of Technology, in a report on the use of polymers in agricultural machinery. Another reason cited in the report for the low usage of of plastics in this area is the alleged widespread misconception that poly-

Fig. 2

227

Developmental Cadon moulding of a heater duct.

Fig. 1

Parts manufactured in BIP's Melmex SM, specially formulated to give a high gloss finish using the injection moulding process.

mers are insufficiently robust for agricultural environments. A series of workshops or short courses is proposed on the technical aspects of polymer usage. Many new plastics exhibited

One of the problems facing the design engineer which is not soluble by such courses is that of maintaining current awareness in the face of an ever increasing mountain of new plastic materials and grades. A few examples of new materials at Interplas includes an abuse resistant grade of acetal copolymer (Amcel), a 'semi-flexible' ABS alloy for automotive bumpers (Borg-Warner), an injection-mouldable melamine (BIP), a toughened',, and craze-resistant acrylic (ICI) and a clear styrene acrylic copolymer, stronger than acrylic, for lighting and outdoor applications (Normandy Plastics). With this proliferation of plastics resins and grades it is comforting to learn that Borg-Warner's Cycolac X-338 a general purpose ABS for food contact and pharmaceutical products, will replace up to seven existing grades of Cycolac offered for food contact applications. New polymer alloy bridges ABS/ PPO gap

One new polymer alloy which will

not be shown at Interplas, because the supplier, Monsanto, has elected not to attend, is Cadon. This is described as an impact-modified styrene/maleic anhydride terpolymer. Although it cannot match the heat resistance of PPO (Noryl) is intended to bridge the gap between PPO and ABS. Anticipated acceptance of the material in the automotive sector for external parts, may depend on its ability to withstand paint repair oven temperatures. The development of Cadon, typifies the current thinking of polymer suppliers, who are now constantly looking for alloys or blends to fill the gaps in physical property charts. These are now preferred to the development of brand new monomers and polymers for large scale use, for which the costs of research, development and capital investment are now relatively unattractive. Castings under pressure

The consumption of bulk polymers in the UK in 1980 sank by 17% of its 1979 level. Nevertheless, if this is a dire situation, it is benign in comparison to that faced in recent years by many foundrymen. The UK Steel Castings Research and Trade Association (SCRATA) has launched a promotion drive exhorting engineers to switch from fabrications

MATERIALS IN ENGINEERING, Vol. 2, SEPTEMBER 1981

a pressurised transfer system. Delivery rates, pressure and dwell times are controlled by a pre-programmed sequence for each casting. The process is reckoned by industry experts to be 20 per cent more expensive than traditional sandcasting, but to reduce dependance on skilled labour. Used for principal engine components, it is economic in the range of a few hundred to a few thousand castings per year, whilst offering dimensional consistency and soundness normally only approached by investment castings. Aluminium alloy sheet improved

Fig. 3

Developmental moulding in Cadon of headlamp surrounds.

to castings. This latest campaign, SCRATA claims, is not just an attempt to avert some of the direr consequences of the current recession in the foundry industry, but an attempt to highlight some of the advantages which castings have. To some extent, however, castings have been replacing fabrications in many areas of UK industry, a trend which has accelerated as foundries have offered lower and lower prices to gain business. This is particularly noticeable in tooling for other metal forming processes. Nevertheless, if the economic climate improves, many of these customers may stay with castings, for some of the reasons highlighted by SCRATA. New castings developments

Dynacast International has developed a special process for diecasting small parts, which removes the need for conventional high-cost multi-cavity dies. The company has its own machine for fully automatic high-speed single cavity diecasting and the technique gives very consistent dimensional uniformity. Ferrous diecasting is also on the way. Stainless steel diecasting is being used in the States for wrench sockets and valve balls. Producers claim that the process resembles aluminium diecasting, except for the temperature. Most of the demand has been from customers interested in replacing stainless investment castings, since diecasting is nearer to net shape.

A breakthrough for aluminium casting has recently been announced by Cosworth Engineering, described as combining the quality and consistency of diecasting with the flexibility of sandcasting. The new approach, which might be named 'high precision, lowpressure sandcasting', involves tackling the problem of porosity by eliminating turbulent transfer of liquid metal. Ladles are not used, but the metal is introduced into the mould cavity using

A ten-year programme has recently been completed at Alcan Plate to achieve substantially better fracture toughness in aluminium-zinc-magnesium-copper alloys. A new alloy containing zirconium, 7010, has been produced, prior to the development of which the use of the highest strength aluminium-base alloys was restricted by a susceptibility to serious cracking failures in environments of combined stress and corrosive conditions. The highest strength alloy system then available could be heat treated to improve the stress corrosion resistance, but an appreciable reduction in strength had to be accepted, thus depriving designers, mainly in the aircraft

Engineering with Ceramics You are invited to attend this meeting which is sponsored and organised by the Basic Science Section o f the British Ceramic Society. The meeting will be held at Goldsmiths College, London SE14, from 15th to 17th December, 1981. There will be three review papers: "Fabrication principles for the production o f ceramics with superior mechanical properties", R.J. Brook, University of Leeds; "Techniques for the stress analysis of ceramics", P.M. Braiden, University of Durham; and "Fracture toughness o f ceramics measurements and interpretation", R.F. Pabst, Max-Planck-Institute. iThe provisional programme contains 32 papers with a wide range o f ceramic-engineering subjects, including: static and dynamic fatigue, fracture toughness, failure probability, mechanical properties at room temperature and elevated temperatures. The materials covered include: alumina, cement, graphite, porcelain, sialons, silicon carbide, silicon nitride, tungsten carbide and zirconia. Several papers deal with engineering applications. F o r further details and registration forms please contact:

The Assistant Secretary, The British Ceramic Society, Shelton House, Stoke Road, Shelton, Stoke on Trent,

MATERIALS IN ENGINEERING, Vol. 2, SEPTEMBER 1981

ST4 2DR. Tel: (0782) 23116/7.

228

Sand mould posit,oned on casting station

Electrically-heated h01dln~ furnace allowing 'smk-or41oat' 0t impunties

Fig. 4

Casting system designed by .Cosworth for the quiescent transfer of liquid metal into moulds without the need for feeders or complex runner systems.

The structural weight includes wheels, tyres and brakes but not the engine pod structure lO0

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industry, of high strength, weightsaving potential. An additional shortcoming of the old alloy system was marked sensitivity to quench cooling rate during solution heat treatment. The result was an appreciable reduction in attainable strength levels in plates greater than 80mm thick. 7010 alloy extends the availability of tough alloys to sections up to 150ram in thickness without sacrificing strength. It is now at the commercial applications stage and has already been specified for Tornado and Airbus A300 and X A310 aircraft build programmes.

1986, 1988

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Trends in aircraft usage of structural materials, indicating urgency of developments in aluminium alloys.

Afurther into the future for aizcraft designers is a new family of aluminium alloys containing lithium, under development at British Aiuminium's Technological Centre. The objective is the production of alloys which are lighter and stiffer. These alloys have densities 10-15% lower and a modulus of elasticity 10-20% higher than conventional aluminium alloys. Three classes of alloys are under development for aerospace applications: Aluminium-lithium alloys for structures demanding highest stiffness, lowest density and medium strength for use in missiles and guided weapons; Aluminium-lithium-magnesium alloys, for structures requiring mediumhigh strength and lower density as a replacement for 2014 and 2024 alloys;

Continued on page 269

Table 1 Preliminary data for new Borg-Warner grades of ABS.

Properties

Units

Semi-Flexible Alloy for Bumpers

Electroplating ABS/Polycarbonate Alloy

(Cycolac X-340)

(Cycolac EHA)

(Cycolac X-320) (Cycolac X-337) (Cycolac X-338)

600 250

342 85

250

190

10.0

8.5

38

38

60 2.0

60 2.1

65

87

87

100

Impact Strength 23°c Izod Notched -29°C

J/M

Din Impact Notched Charpy Impact Notched Tensile Strength Tensile Modulus Flexural Yield Strength Flexural Modulus Hardness Vicat B50

kJ/m 2 kJ/M2 MN/m2 GN/m2 MN/m2 GN/m2 I.I Rockwell oC 85

229

Flame Retardant ABS

ABS for Food and Pharmaceutical Uses 330

12 50 2.4 83 2.5 111R

MATERIALS IN ENGINEERING, Vol. 2, SEPTEMBER 1981