Prepressing

Mechanical Pressing. Historically, the first large commercial production of oils from seeds and nuts was carried out using labor-intensive hydraulic presses. These were gradually replaced by more efficient mechanical and screw presses. Solvent extraction was developed for extraction of seeds having low oil content. For seeds and nuts having higher oil content, a combination of a screw press followed by solvent extraction is a common commercial practice (prepress—solvent extraction). 

Many of the tasks once performed only ia a high ead electronic pagiaation system, often called color electronic prepress systems (CEPS), are possible by usiag persoaal computers and work stations. Pages are composed on screen, and the results are output typically as PostScript files. The data are transferred over a network to the final output device. 

Networks. Image files are typically transferred among many different stages ia the prepress process. This is most oftea doae over a aetwork that connects the various computer work statioas used ia the process. Although the subject of aetworks is beyoad the scope of this article, some discussioa is useful ia understanding prepress workflow. The Hterature coataias a more complete descriptioa (16). 

The next level is the protocol that governs how the data are transmitted over the wire. Many protocols are ia use. A typical iastaHatioa may have multiple protocols mnning simultaneously on the same physical network. Vendors of network hardware and software develop protocols that are optimized for the type of appHcation for which their product is targeted. Among the protocols commonly seen ia a prepress aetwork are Apple Computer s AppleTalk and EtherTalk, and TCP/IP used by many UNIX work station vendors. The appHcation software a user employs automatically uses whatever protocol is necessary to move information over the network. 

The same concepts of a network as the local area network (LAN) ia an office can be extended over a broader area, eg, wide area network (WAN), effectively to extend the network around the world. This type of network is becoming more important as prepress operations try to work more... 

For both analogue and digital prepress processes it is frequendy necessary to check the appearance of an image and then to gain customer approval to proceed with the expensive step of image dupHcation by printing. For this purpose, proofs are made at several steps of the workflow (see Fig. 2). 

Monitors. Cathode ray tube (CRT) monitors ate a key element of electronic prepress systems, providing an electronic canvas for the operator. They may also be used to judge general adequacy of color in a process called soft proofing. 

The Printing Process. Tme integration of all facets of the printing process is limited, in most cases, to sporadic measurements of the individual elements and processes that contribute to the final product. There is only a limited effort underway as of the mid-1990s to estabUsh close links between electronic prepress and conventional processes such as proofing, plate-making, and printing. 

Digital Color Prepress, Agfa Prepress Education Resources, Mt. Prospect, lU., 1993. 

It is probably obvious at this point that the molecular weight distribution of a resole is an extremely important characteristic. It has major influence on such important performance capabilities as cure speed, viscosity, green strength development (or prepress), assembly time tolerance, required application rates. 

Assistant Manager, Composition Purchasing and Electronic Prepress... 

Cover Design Dawn Boyd Prepress Kevin Luang and Wall Cerny... 

Figure 121. Left prepressed expanded graphite forms a graphite matrix with thermal conductivity of about 25 W/m K and porosity of 90 vol.%. Right PCM-graphite matrix after infiltration of PCM with about 85 vol.%...

The editors were Lynne Lackenbach and Holly Seltzer. Cover design by Michelle Fleitz. Prepress supervisor was Miriam Gonzalez. 

ModilfetttlU- in ihe enic rvfrechmic prepress nre re Hvei uLSHjNCbitr WcnwKavftta APPROVED BY Hnni Weddc tiAtD I7.I2.2DG2... 

Typeset by Paston PrePress Ltd, Beccles, Suffolk NR34 9QG Printed by Athenaeum Press Ltd, Gateshead, Tyne and Wear, UK... 

Most powdered expls that are to be pressed are prepressed into pellets. The die of the loading tool permits closer tolerances and better finishes than are reasonable for cases that are loaded by direct pressing. Exceptions are primer mixes, PETN, and LA, although LA is pelleted in Canada on a production basis... 

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