INNOVATIVE PLASTICS BASIC CONCEPTS IN ENGINEERED BLOW MOLDING

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Juniper Wilkerson
7 years ago
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1 INNOVATIVE PLASTICS BASIC CONCEPTS IN ENGINEERED BLOW MOLDING

2 A SABIC COMPANY Innovative Plastics is a strategic business unit of SABIC. Founded in 1976, SABIC is today the first public, global multinational enterprise headquartered in the Middle East. Its products range from bulk commodity chemicals to highly engineered plastics for demanding applications. It is a leading producer of polyethylene, polypropylene, glycols, methanol and fertilizers and the fourth largest polyolefin producer. SABIC s businesses are grouped into Chemicals, Performance Chemicals, Polymers, Innovative Plastics, Fertilizers and Metals. It has significant research resources with dedicated Technology & Innovation centers in Saudi Arabia, the Netherlands, Spain, the USA, India, China and Japan. INNOVATING FOR CUSTOMER SUCCESS We believe that SABIC customers deserve the full benefit of every advantage our enterprise can offer. After all, our success is defined by our customers success. And with more than 70 years of experience pioneering advanced engineering thermoplastics, SABIC s Innovative Plastics business is positioned to help create new opportunities for growth and breakthrough applications. We offer expertise and experience to our customers in a variety of ways: Material solutions to help drive innovation and market leadership. Design, logistics and processing expertise to spark new ideas and better efficiencies. Unwavering commitment to build longterm relationships with ingenuity, trust and continuous improvement. It s what we strive for and work to deliver a mutual benefit. Excellence and nothing less. 2 INNOVATIVE PLASTICS

3 ENGINEERED BLOW MOLDING PROCESS ADVANTAGES Engineered blow molding offers a highly versatile process for fabricating parts. Effective designs for its blow molding take advantage of the inherent advantages of the process. These include: Hollow aspect of design Strength-to-weight structural integrity Suitability for large shapes PROCESS LIMITATIONS Extent to which material can be stretched Degree to which complexity/detail can be reproduced Part length limitation by material melt strength The design must also make economic sense compared to other processes and materials. FIGURE 1 THE DESIGN/PROCESSING RELATIONSHIP Engineered blow molding forms parts by blowing a hollow parison outward to conform to the shape of the mold (figure 1). Inherent to this process is stretching of the thermoplastic resin material. That stretching thins the walls. Forcing the material to stretch too much may make it impossible to control wall section thickness or even cause the parison to rupture/fracture. How much stretching occurs in the blow molding of the parison is determined by the degree of asymmetry in the basic shape and by amount of complexity and localized detail in the part. The designer can evaluate the suitability of a part for blow molding by examining the blow ratio conditions in the part. The term blow ratio describes a relationship between depth and width, and relates to the amount of material stretching that results. INNOVATIVE PLASTICS 3

4 ENGINEERED BLOW MOLDING THE CASE-BY-CASE APPROACH Each case must be considered individually. The following approach is suggested: 1. Examine the basic shape for blow ratio problems. The amount of sideways parison travel should be less than parison length. One way to address the problem is to make sure that the part is properly oriented in the tool. 2. Review complex sections and part details. Figure 2 shows the local area of complexity. Decreasing the width W or increasing the depth D will require the material to stretch more to force through opening. Filling this detail will cause gains, particularly at corners. Minimize depth, and maximize width FIGURE 2 Review the design s blow ratio to assure moldability D W MULTIPLE BLOW RATIOS A part may have dozens of blow ratio conditions if the design is a complex one. Figure 3 shows a situation where there are two separate conditions in a single area of detail. These conditions should be studied early on to determine whether various details can be reproduced in molding. Experience provides the best guide to assessing moldability and predicting local wall thickness. FIGURE 3 D1 Da Wa Wa 4 INNOVATIVE PLASTICS

5 FIGURE 4 This example of the part shown in figure 4 demonstrates what happens when three blow ratios exist First the mold closes and the parison begins to expand. After contact with the first blow ratio condition, thinning of the parison begins. Next the parison expands into the second opening More thinning occurs after the second condition is encountered. Next the parison expands into third opening. With the third condition maximum thinning takes place. INNOVATIVE PLASTICS 5

6 ENGINEERED BLOW MOLDING DESIGNING FOR BASIC SHAPES Some common blow molded shapes present standard situations. Part is oriented so that the longest side is parallel to direction of parison drop (figure 5). Parison is pinched and preblown before the mold is closed. Mold closing action flattens round parison into shape. Corners tend to thin the most. FIGURE 5 L-SHAPES Part is oriented at an angle to minimize the amount of stretching (figure 6). Closing mold pushes the parison flat into shape. Thinning occurs at angles and corners. Some L-shapes cannot be molded because they require too much stretching. FIGURE 6 U-SHAPES Parts that are U-shaped are of limited moldability (figure 7). Legs must be short to avoid a material distribution problem. Center section is oriented in the direction of the parison. Locate centroid and balance amount of material in each half of the tool. FIGURE 7 S-SHAPES The moldability of S-shapes is also limited (figure 8). Orient so as to minimize the parison travel. Material thinning occurs at edges and corners. FIGURE 8 6 INNOVATIVE PLASTICS

7 FIGURE 9 FIGURE 10 Multiple tacks with several welds to reduce part wall shift Large detail is pinched out Structural ribs Corrugated for structure Structural ribs Box detail formed by compression welding slot is pinched out Hollow shapes are inherently stronger because of their structure. This existing structure can be enhanced without changing the material in three basic ways: 1. Increase the nominal wall thickness of the part. 2. Balance section modulus through ribbing a single wall (figure 9). 3. Develop compression tacking details or patterns (figure 10). Sidewalls are forced together by the closing action of the mold to form a single wall. This creates local areas with locally thick walls. It also develops localized beam sections more resistant to bending, tension and torsion. Beware of readthrough from compression; avoid tacking in appearance areas. Compressed Flange with slots pinched out SUMMARY Take maximum advantage of the inherent process strengths. Develop a basic shape that can be molded. Assess the moldability of details, and avoid blow ratio problems. Build structure into the part. Seek to make the design as simple as possible. Check economics against other process approaches. INNOVATIVE PLASTICS 7

8 CONTACT US Americas SABIC 1 Plastics Avenue Pittsfield, MA USA T F Technical Answer Center T Asia Pacific SABIC 1266 Nanjing Road (W) Floor 16, Plaza Shanghai China T F Europe SABIC Plasticslaan 1 PO Box AC Bergen op Zoom The Netherlands T F Technical Answer Center T (0) T E webinquiries@sabic-ip.com Middle East/Africa SABIC Corporate Headquarters PO Box 5101 Riyadh Saudi Arabia T +966 (0) F +966 (0) productinquiries@sabic-ip.com THE MATERIALS, PRODUCTS AND SERVICES OF SABIC INNOVATIVE PLASTICS HOLDING BV, ITS SUBSIDIARIES AND AFFILIATES ( SELLER ), ARE SOLD SUBJECT TO SELLER S STANDARD CONDITIONS OF SALE, WHICH CAN BE FOUND AT AND ARE AVAILABLE UPON REQUEST. ALTHOUGH ANY INFORMATION OR RECOMMENDATION CONTAINED HEREIN IS GIVEN IN GOOD FAITH, SELLER MAKES NO WARRANTY OR GUARANTEE, EXPRESS OR IMPLIED, (i) THAT THE RESULTS DESCRIBED HEREIN WILL BE OBTAINED UNDER END-USE CONDITIONS, OR (ii) AS TO THE EFFECTIVENESS OR SAFETY OF ANY DESIGN INCORPORATING SELLER S PRODUCTS, SERVICES OR RECOMMENDATIONS. EXCEPT AS PROVIDED IN SELLER S STANDARD CONDITIONS OF SALE, SELLER SHALL NOT BE RESPONSIBLE FOR ANY LOSS RESULTING FROM ANY USE OF ITS PRODUCTS OR SERVICES DESCRIBED HEREIN. Each user is responsible for making its own determination as to the suitability of Seller s products, services or recommendations for the user s particular use through appropriate end-use testing and analysis. Nothing in any document or oral statement shall be deemed to alter or waive any provision of Seller s Standard Conditions of Sale or this Disclaimer, unless it is specifically agreed to in a writing signed by Seller. No statement by Seller concerning a possible use of any product, service or design is intended, or should be construed, to grant any license under any patent or other intellectual property right of Seller or as a recommendation for the use of such product, service or design in a manner that infringes any patent or other intellectual property right. SABIC and brands marked with are trademarks of SABIC or affiliates Copyright by SABIC. All Rights Reserved. SABIC-PLA-6047-EN

INNOVATIVE PLASTICS HIGH & LOW SHEAR RATE RHEOLOGY

INNOVATIVE PLASTICS HIGH & LOW SHEAR RATE RHEOLOGY A SABIC COMPANY Innovative Plastics is a strategic business unit of SABIC. Founded in 1976, SABIC is today the first public, global multinational enterprise