The Blow Molding Process

THEORETICAL BACKGROUND Blow molding is a fabrication process to convert the raw materials (resin) into finished hollow containers (products). It is a manufacturing process by which hollow plastic parts are formed. Principle of the Most Basic Type of Blow Molding 1. Resin is melted by heaters and plasticized by an extruder. 2. Then it is extruded so that it forms a tube-shaped parison matching the size of the product as it passes through the die. 3. Air is then forced into the parison and press it against the inner walls of the mold. After the parison cools and become solid in the mold, the air is released. 4. Finally, the mold will open and the product is deflashed and ejected or taken out the machine. Higher Institute for Plastics Fabrication WORKBOOK for Extrusion Blow Molding Practical Course Prepared by Extrusion Blow Molding Department 1st Edition 2009

Safety factor

A safety factor (SF) or factor of safety (FS) (also called factor of ignorance) is used with plastics or other materials (metals, aluminum, etc.) to provide for the uncertainties associated with any design, particularly when a new product is involved with no direct historical performance record. There are no hard and fast rules to follow in setting a SF. The most basic consideration is the consequences of failure. In addition to the basic uncertainties of graphic design, a designer may also have to consider additional conditions such as: (1) variations in material property data (data in a table is the average and does not represent the minimum required in a design); (2) variation in material performance; (3) effect of size in stating material strength properties; (4) type of loading (static, dynamic, etc.); (5) effect of process (stress concentrations, residual stress, etc.); and (6) overall concern of human safety.

The SF usually used based on experience is 1.5 to 2.5, as is commonly used with metals. Improper use of a SF usually results in a needless waste of material or even product failure. Designers unfamiliar with plastic products can use the suggested preliminary safety factor guidelines in Table 7.3 that provide for extreme safety; intended for preliminary dcsign analysis only. Low range values represent applications where failure is not critical. The higher values apply where failure is critical. Any product designed with these guidelines in mind should conduct tests on the products themselves to relate the guidelines to actual performance. With more experience, more-appropriate values will be developed targeting to use 1.5 to 2.5. After field service of the preliminary designed products has been obtained, action should be taken to consider reducing your SF in order to reduce costs.

Plastics

Engineered

Product

Design

Dominick Rosato and

Donald Rosato

ELSEVIER

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Mold Setup & Parison Processing

Performance Objective Setup to generate good container welds with even, easy flash removal at target flash to container interface temperature. Mold Setup •Setup molds with carbon paper to identify even mold compression •Setup mold temperature control of 80F to 110F (25C-40C) at pinch areas to achieve container deflash interface temperature of 180F to 200F (80C to 95C) Processing Techniques •Use mold cracking timer to enable larger containers to vent upon mold opening •Use blow pin lift timer to allow container to release from mold •Insure that container releases easily from the mold –Observe for scrapes on container –Observe for flash retensionto container or mold during mold open and container extraction •Avoid heavy pinch terminations –Program parisonto light weight pinch area –Capture parisonin inflated region –Locate pinch terminations up on base to sidewall radiaway from base footprint –Option: Locate pinch terminations within the base pushup –Option: Locate one end of pinch termination within the base pushup and the other end on the container sidewall Processing Techniques •Pinch weld termination location 1.Locate pinch terminations up on base to sidewall radii away from base footprint 2.Locate pinch terminations within the base pushup 3.Locate one end of pinch termination within the base pushup and the other end on the container sidewall EASTMAN Extrusion Blow Molding Presentation.

SCALE RATIOS

Engineering and architectural drawing scales The recommended scales for use in engineering drawing practice and in architectural and building drawings are specified in Table 5.1.

NOTE: If, for special applications, there is need for a larger enlargement scale or a smaller reduction scale than those shown in the table, the recommended range of scales may be extended in either direction, provided that the required scale is derived from a recommended scale by multiplying by integral powers of 10. In exceptional cases where for functional reasons the recommended scales cannot be applied, intermediate scales may be chosen.

Australian Standard

Technical drawing

Part 101: General principles

For history before 1992, see Preface.

Second edition AS 1100.101—1992.

PUBLISHED BY STANDARDS AUSTRALIA

(STANDARDS ASSOCIATION OF AUSTRALIA)

1 THE CRESCENT, HOMEBUSH, NSW 2140

ISBN 0 7262 7806 8

Accessed by WOODSIDE ENERGY LTD on 21 Nov 2001

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