Industrial Utility Efficiency

# Plastic Extruder Optimizes Blow-Offs for Cooling

### Cooling Stations at the Cooling Boxes

At a Midwest window manufacturing plant, the cooling process for the plastic frame pieces, after leaving the extruder, was critical to process productivity and quality. Too much cooling air (or not enough cooling air) would generate scrap and rejected product.

The plants’ 17 extruders and 55 separate blow-offs in these lines had similar cooling stations at the cooling boxes. They consisted of about three hoses at each exit frame angled down to the extruded piece moving past it.  The compressed air flow was controlled by a manual control valve set by an operator. The operator used his experience to control the flow delivered and thereby control the product quality.

### Measurement of Blow-Off Air

##### Figure 4. Venturi amplifier mini nozzle at extruded frame (white) on one hose

This audit and test was performed more than two years ago. All the lines were changed to the new blow off systems. The lines are monitored as part of a very significant compressed air management system utilizing key performance indicators and the process continues on saving energy every day.

Productivity and quality improved because maintaining the critical flow in the lines with the current system was somewhat difficult due to compressed air system pressure fluctuations affecting the flow. This haD to be corrected by various plant operators with manual controls.

With the selected nozzle the estimated flow is at .13 scfm each which is almost at minimum flow. Since most of the generated air flow (2.4 to 2.5 scfm each) is from amplification, the net flow is affected almost insignificantly by system pressure fluctuation. The end result -- scrap has gone down.

### Takeaways

The most common error in using blow air for cooling is to estimate pressure or thrust needed in the air stream without evaluating the actual cooling air flow required.

Thrust is required to drive the cooling air to the point where it can absorb the heat and carry it away. The amount of heat (btu/hr) removed is a function of temperature differential and, most important, volume of working air flow (cfm).

To review the numbers in this scenario the operator-adjusted cooling air flow that worked well was 7 cfm ÷ 3 = 2.33 cfm per hose. When the air amplifier was installed the flow for all three hoses and new nozzles was .4 cfm, or .13 cfm per hose/nozzle -- .13 compressed air x 20 = 2.6 cfm per hose -- very close to the 2.33 cfm originally set by the operator. The successful production with these nozzles led to a constant, predictable flow at each work station basically unaffected by normal system pressure fluctuation and operator differences. Productivity and quality improved significantly along with a 94% reduction in compressed air use.

For more information contact Hank van Ormer, Technical Director, Air Power USA, email: hank@airpowerusainc.com or visit www.airpowerusainc.com.

To read similar Compressed Air Demand Reduction articles visit www.airbestpractices.com/system-assessments/end-uses.