As production requirements for a single type package can reach 100, 200, or even 400 million containers per year, processors are looking for the best, least complex, and the most economical machinery that can handle these extreme production rates.
Some blow molding machinery manufacturers have begun promoting tandem blow, the process of blow molding two bottles per parison that have been configured in a neck-to-neck or base-to-base arrangement in the mold. Their rationale is not necessarily that this technique produces better bottles, but that it is the only way to increase output without incurring the additional cost of multiple machines.
However, producing two identical bottles in tandem blow process is a problematic challenge, especially with free-falling parisons typically used by shuttle and reciprocating blow molding machines.
Why? Because the parison shape is never identical from the top to bottom in the mold and achieving an identical material distribution in the top and bottom containers can be next to impossible. Additional variation is added by trying to balance and set up 4, 6, 8 or more parisons to be identical. Even with wheel machines the physical variations in bottles blown in tandem process can never be totally eliminated.
Solving the Challenges
Wilmington, NC-based Wilmington Machinery, an experienced blow molding processing system manufacturer, has turned its attention to overcoming challenges in blow molding small containers at high speeds. The company has designed a new system for producing small bottles that utilize a single parison and individual cavities, instead of tandem, in order to produce the highest quality bottles with the least variation in material distribution bottle-to-bottle, and with the smallest weight variation.
The result? Processing speed, efficiency -- plus cost savings to the customer.
Wilmington Machinery's focus is on very high output applications requiring a minimum of 250,000 bottles per day or 75 million per year. Its prime objective was to eliminate the problems associated with high speed bottle handling and to make their new system extremely simple to set up, operate, and maintain.
The result is the Wilmington High Speed Small Bottle (SB) rotary blow molding wheel system. The Wilmington SB process blow molds small bottles in a single cavity mold and uses a proprietary method of guiding the containers from under the blow molder through the trimmer at extremely high speeds with maximum efficiency. The Wilmington SB system's success is made possible by miniaturization of Wilmington's proven mechanical clamping systems -- a technology originally perfected in its larger wheel machines -- combined with a proven technique for accurately positioning the clamps and molds relative to each other.
The Wilmington SB Series is designed specifically for high speed, high volume single-serve dairy, food, juice, and liquid yogurt applications for containers 200-500 ml. A smaller clamp has been added to handle bottle sizes as small as 80 ml. These machines are economical, extremely simple, and can be built with up to 60 cavities at speeds up to 30,000 bottles per hour depending upon the container. Like their larger machines, the extrusion rates and layer configuration can be designed to match any application such as white-black-white or barrier bottles.
The Results
Technical breakthroughs such as Wilmington Machinery's High Speed Small Bottle Series now give processors the ability to blow each bottle in individual molds while totally eliminating the need for high maintenance bottle knockout systems, complicated bottle takeout devices, and cut-off knives or shear steels.
Customers report easy startup and operation of Wilmington's 24-station demonstration wheel at speeds up to 240 bpm. Bottles literally fall out of the molds on their own and because Wilmington Machinery developed the technique to blow 100% of the entire parison, bottles and flash never stick together. And the process works as well for polypropylene, including multilayer, as it does for HDPE.
