With strong demand for construction products, profile extrusion plants are seeking to expand production capacity. The problem they—and possibly you—face is to simply add more single contour lines or "remove double lines." This is something you need to consider.
Although many industries have suffered losses during the coronavirus pandemic, some parts of the construction products industry have flourished. Obviously, some consumers who spend most of their time at home have discovered DIY problems and have started a "wish list" project to help create a more comfortable and enjoyable environment. One result is an increase in demand for a variety of profile extrusions, including everything from wood-plastic composite (WPC) decorative panels and window profiles to plastic wood, PVC fencing products, siding, fascia, and decorative trims.
Upstream in the supply chain, plastics and WPC processors welcomed the increased demand for these extruded construction products. But for any extrusion processor, the increased demand raises the question of how to expand production capacity cost-effectively. Recently, many extrusion processors have answered these questions by deciding to "go to dual-track", that is, converting a single-profile production line to a "dual-profile" line to capture unused extruder capacity, or by installing new and larger dual-profile Line instead of an extra single line.
Is this method suitable for your operation? Ask yourself these questions first:
1. Should I add a new row? If you are already running a production extrusion line, the easiest way to substantially expand production may be to add the same new production line. Depending on the available space in your facility, you can simply install more of the same equipment based on the exact same production model you are currently using. Therefore, there is not much risk in making it work-you don't have to push the edge of technology. More importantly, your employees already know what to do. However, this method is generally more expensive than other alternative methods.
2. Can I get more output from the products I already have? maybe. If your extruder is not running at full capacity, you can increase output by speeding up the production line. If you increase the speed of the extruder and can control the increased output without affecting the quality of the profile, you can increase the output of the production line by 10% to 20%.
Extracting more content from the existing extrusion line is certainly a cost-effective method, but it requires a willingness to risk a certain degree of process redefinition, redevelopment, and experimentation to get the additional throughput you are looking for . This is not a certain thing, because there are many variables: increasing the speed of the extruder will increase the shear, which can lead to process instability, profile stress or dimensional problems. Although existing tools may be effective, you may find that you need to lengthen or modify molds and downstream tools. You also need to adjust the speed, cooling capacity, and other settings of downstream equipment. Therefore, although you can sometimes get more benefits from the equipment you already have, the potential upside is limited to about 20%.
3. Can I convert a single line to a double hatch? Or build a new dual line from scratch? Yes. If your single-line extruder has an unused capacity of at least 50%, it may be a wise investment to convert a single-line production line to a two-line production line. If you can sell so much extra output in the foreseeable future, the return figures for conversion to dual-line downstream equipment should be beneficial. If you want to use excess extruder capacity but the facility space is limited, or if you have tried to speed up a single extruder production line but cannot stabilize the output at a higher output, dual-line conversion will become a more advantageous choice. .
Consider this example: a processor has an extruder rated at 1500 lbs/hr, but cannot stabilize the output above 1000 lbs/hr on a downstream production line. In many cases, the extrusion line can be successfully converted to dual profile production, making full use of the capacity of the extruder to drive two profiles running at approximately 75% of the original single line speed, thereby increasing the total production by 50%. Moreover, because the double extrusion runs slower than the original single extrusion, the possibility of process stability problems is much less.
Processors that require greater output should compare the benefits of adding multiple single-profile production lines and using larger-capacity dual-profile production lines. For example, with the increasing popularity of maintenance-free WPC paving, some paving manufacturers have shifted their main production from a single line running about 1500 lbs/hour (or 700 feet of 5/4 × 6 inch paving/hour) to larger The two-line operating speed is 3000 to 3300 lbs/hr-or close to 1600 feet of deck/hr.
Processors that require greater output should compare the benefits of adding multiple single-profile production lines and using larger-capacity dual-profile production lines.
Of course, packing twice as much production capacity into a limited space requires a lot of planning. Upstream, there is a need to improve material handling and preparation capabilities. If you want to extrude WPC, you also need to increase the drying and pelletizing capabilities. Due to the high moisture content of wood flour, hot air drying is usually used to dry the composite particles. And, in some applications, a second dehumidifying and drying step may be required before extrusion. Then a larger extruder is needed. Downstream, everything needs to be replicated-from tools to cooling, measuring, towing and cutting/material handling.
The commitment to the double contour represents a major commitment to skills and resources. Compared with the single production line you are accustomed to running, to make these larger, higher-capacity production lines run stably and smoothly, it does require more patience and effort, because you are working harder to break through the technological boundaries. But from a numerical point of view, two-line production may be a very wise investment (see sidebar).
The key to switching from a single profile extrusion line to a dual profile extrusion line is to work according to your known knowledge. Essentially, the idea is to create an identical second profile from the extruder and replicate as closely as possible the tool and process conditions that have proven successful on a single profile.
The first challenge for successful dual-line production is to generate a dual melt flow at the exit of the extruder. This involves the development and installation of a "Y block", a tool that divides molten material into two equal streams. This output then flows through two identical die heads, providing two parallel profiles for downstream processing.
The second challenge is to steadily increase the output of the extruder. Obviously, if you want to use the excess capacity by extruding the second profile, the extruder will run faster than before. And you need to redefine and rework your process until the output of the extruder is stable and the double profile is successfully produced. Please note that the speed of the production line, not the speed of the extruder, is the key variable that affects the quality of the profile. As long as the dual profile output runs at 100% or lower than the single-line speed, the profile should be able to be processed by basically the same downstream molds and equipment, and its quality is as good as the single-line profile product.
Downstream of the extrusion die, the dual profile equipment is basically similar to the single line equipment, but replicated and arranged in parallel. (For comparison, dual-profile devices usually have the same length and the same gap as single-line devices, but about 50% wider.)
Many construction product extrudates-WPC decorative panels, WPC or PVC window profiles, PVC fences, etc.-come out of the extruder and are "dried" through a series of shaping dies on the calibration table. The molds are equipped with internal water cooling devices so that they maintain a uniform temperature relative to the hot profile, and may drip water when the profile slides to gently lubricate the profile. To help thin or complex profiles maintain their shape, some of these molds may be evacuated.
The profile then enters the dual spray cooling tank. Compared with immersion cooling, spray cooling is significantly more efficient. Although the immersed cooling water tank can form an insulating "layer" of warm water around the hot profile, the spray water tank uses more effective evaporative cooling to dissipate more heat faster. Spray cooling is necessary for WPC extrusions such as paving, because the heat index of their wood flour component is much higher than that of the typical polymer component in the composite material mixture. The water tank must also provide a higher flow of cooling water for the WPC profile-three times higher than the flow required for ordinary plastic profiles. Spray cooling is also commonly used for large or complex vinyl extrusions used in window frames and fences.
Extrusion processors considering expanding production should consider various alternatives.
The overall speed of the process is fine-tuned using a double-line splint puller, and the speed is subordinate to the main extrusion control. Although the two traction lines with splints share the same equipment housing, the speed of each traction line is independently controlled. Therefore, everyone can fine-tune or "adjust" the process speed in small increments based on the line speed and continuous feedback from the extrusion process controller. This is important because although dual extrusion lines are designed to have the same performance, small changes in the flow through the y-block and the extruder head are common, so these fine adjustments are required. (Speed adjustment greater than 10% must be handled by adjusting the extruder rpm.)
After the puller, the profile then enters the double-wire saw table. Once again, the speed of each production line—and the length of each profile—is managed by a dual independent measurement system that drives a dual saw. The profile is cut into finished lengths and then pushed onto a double dumping table, which is stacked, and then the cut lengths are unloaded into the stack for picking and packaging.
Extrusion processors considering expanding production should consider various alternatives. Although installing a new single production line with the same capacity as an existing production line is usually the most labor-saving, it is usually the most expensive in terms of capital and facility space costs. Adopting or converting to a dual-profile production line requires a lot of preliminary planning and additional start-up and process development time, but it can significantly reduce costs in terms of capital and facility space, while expanding the overall production capacity of the enterprise.
About the author: Ernie Preiato is the Vice President of Extrusion at Conair Group. Preiato joined Conair in 1988 and focuses on the development of downstream solutions for pipe, profile and tube processors. Contact: 724-584-5423; epreiato@conairgroup.com; conairgroup.com
Processors that require additional extrusion capacity are faced with difficult choices on how to best expand. The following is a "rule of thumb" and visual comparison of two common expansion scenarios.
• Example 1: Install two new single-profile production lines and a double-profile production line with the same throughput.
This example assumes that the dual line has twice the capacity and throughput of the extruder, and the dual profile is run through two sets of tools, followed by the dual line spray can, measuring system, tractor/tractor, and unloading system. Assume that the two-wire device is the same in length and gap as the single-wire device, but wider. For simplicity, each channel is assumed to be 8 feet wide.
• Example 2: Convert a single line with 50% unused extruder capacity to dual profile output.
• Example 3: Production space requirements for single-section and double-section production
The attached drawing compares the footprint requirements for installing four single co-extrusion lines (top) and two double co-extrusion lines. Lines are typical lines used to make fences and deck profiles that are topped with PVC or color-stable WPC materials. Each line includes:
• Co-extruder and die head
• Calibration table with tools
• Cooling tank
• Tractor/ Tractor
• Cutting saw
• Drop off platform
Four single lines and access channels require 9252 square feet per line, while two double lines require 5334 square feet per line to achieve twice the profile output.
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