Macro Engineering & Technology Inc. is celebrating its 30th anniversary of providing innovative machinery to the plastic film and sheet industry.
During its 30-year history, Macro has earned a reputation as being a high technology, service driven equipment supplier. This reputation is based strongly on the combination of innovation and high quality machinery, which stem from superior components like Macro's world renowned D10 air rings, dies and winders, to its processing know-how to provide custom solutions to difficult processing requirements. Perhaps one of Macro's greatest strengths is its R&D department, in which the drive to develop new and improved technologies has always been at the forefront of what Macro is about. To date, Macro has over 40 machinery and process patents related to the plastic industry and has played an important role in pioneering new technologies.
The purpose of this newsletter is to illustrate some of the more significant developments made over Macro's 30 year history.
Through the years, Macro has seen itself go through a similar progression observed in the blown film industry - from single layer blown film lines to 9-layer blown film coextrusion lines. With this progression, Macro has developed many innovations to keep ahead of the industry's needs - one of which being die design.
Die Designs
Macro has obtained seven blown film die patents for designs ranging from the processing of multilayer films to the extrusion of degradable plastic materials with encapsulation. The most recent of Macro's die developments is the design of the 9-layer MacroPack die, which is a stackable die capable of coextruding a wide range of 9-layer structures with a variety of melt temperatures (11 layers are possible if Macro's patented encapsulation technology is also incorporated). Dozens of blown film dies varying from specialty single layer uses to complex coextrusion applications are manufactured by Macro every year.
Encapsulation
In 2000, Macro became the first in the world to successfully apply encapsulation technology in the blown film process. The immediate benefit of the patented encapsulation technology was the ability to process heat-sensitive polymers like PVdC in commercial sized dies. Additional benefits have come in the form of fast purging and greater flexibility with coextruded structures including the ability to run additional layers without changing the die. For more on Macro's encapsulation technology, pick up a copy of the Autumn 2007 MacroLetter.
Air Ring Technology
Macro is world renowned for its air ring technology. One of the industry's most versatile and reliable air rings, the D10 Dual Lip Air Ring, was initially developed by Macro in the late 1980s and later enhanced about a decade later. The popularity of the D10 is attributed to a combination of performance and operational simplicity. With easy adjustments to the air ring lips and stabilizer rings, the bubble can be quickly locked (stabilized), and highly effective cooling can be applied to the bubble. Today, the D10 Air Ring remains one of Macro's most sought after products.
Automatic Air Ring
Development of Macro’s automatic air ring began in the early 2000s to combine the versatility and ease of use of the D10 Air Ring with the ability to perform precise gauge corrections. The cooling air supplied to the primary lip of the auto air ring is segmented around its circumference by a series of air valves. Film gauge is controlled by adjusting the air flow through these valves to alter cooling at specific spots on the air ring.
Binary Air Ring System
As part of an R&D initiative back in 1984, Macro was first to patent a binary air ring cooling system designed to improve output rates along with physical and optical properties of blown films. The design was improved and patented again in 1988. The initial observations indicated output improvements of 30-100% over single air ring systems.
The binary air ring cooling system is comprised of two air rings; one air ring (the primary air ring) that sits directly above the die, and a second air ring (the secondary air ring) that is positioned above the primary air ring and below the bubble stabilizing cage.
The primary air ring pre-cools the resin, stabilizes the bubble and provides high velocity air to shield the bubble from plant fluctuations that can disrupt gauge uniformity. The secondary air ring replaces the first air stream with a new, more turbulent air stream. The highly turbulent second air stream, which can be more turbulent because the melt is cooler at this point and it's strength has increased, provides highly effective cooling, leading to significantly higher throughput rates. The effective cooling also allows the bubble to be drawn to its final shape relatively quickly, producing film that has excellent clarity and gauge.
The distance between the air rings can be adjusted to optimize the amount of cooling supplied by the primary air ring. The goal is to allow the molten polymer to cool and gain strength, yet remain in a molten state for a prolonged time to relieve the polymer of extrusion stresses after leaving the die. This results in a low stress polymer that is balanced between the machine direction (MD) and transverse direction (TD) before passing the secondary air ring for final cooling, solidification and final orientation.
To obtain maximum benefits of the secondary air ring cooling system a bubble stabilizing cage that maintains a near-complete 360° contact with the bubble, such as a curved-arm cage, should be used. Macro developed and patented its first curved arm bubble cage in 1983. The stabilizing contact provided by the cage helps to keep the bubble steady in the turbulent air stream, and also provides additional cooling. The use of internal bubble cooling and automatic gauge control dies can also improve output and gauge uniformity.
Initial outputs of 22 lbs/hr of LLDPE and 30 lbs/hr of LDPE per circumferential inch of die were achieved, along with vast improvements in the physical and optical properties of the film. In 2002, Macro's binary air ring cooling system, marketed as the D10-B Binary Dual Lip Air Ring System, was used to produce record breaking outputs of 1.9 kg/hr per mm die diameter (34 lbs/hr per circumferential inch). At a recent trial in April 2008, the D10-B Binary Dual Lip Air Ring System along with Macro's Conical IBC (see next section) was utilized on a 3-layer line running at 450 kg/hr to generate outputs of 2.25 kg/hr per mm of die diameter (40 lbs/hr per circumferential inch). Additional output was limited by extruder output. Macro is planning to upgrade the extruders and expects to exceed this output level in future trials.
