Pourhead Design
While on my 4th co-op at Woodbridge Group, I worked in the R&D department that works on various testing and design projects pertaining to pourheads. Pourheads are hydraulic systems that intake high pressure foam chemicals, mix them, and then shoot the compound into a mould for the foam to cure. I had two main projects related to pourheads, one project was performing mechanical testing and the other was mechanical design focused.
Nozzle Testing
The Problem
Plants at Woodbridge facilities worldwide were reporting that many of the nozzles found inside of a pourhead were not performing as expected. The back pressure that the nozzles were generating were uncharacteristic and the jet was not straight causing cavitation and accelerated wear in the metal housings. The mixing process needs to be very precise in order to get the desired foam composition so it is clear why unpredictable nozzle performance is an issue.
See here for a video of the fixture in action!
Solution
I was tasked with designing a test fixture to validate nozzles at the point of manufacture before they get shipped out to the plants. The fixture is composed of a closed-loop system that pumps fluid through the nozzle. It contains a reservoir of plasticizer because it is of similar viscosity to the chemicals used in the plant. An inlet hose draws from the reservoir and feeds a piston pump. The pump is a 4.0GPM piston pump that can generate up to 3000psi behind the smallest nozzle which had a 1mm orifice diameter. An outlet hose connects the pump to the nozzle holder. The nozzle holder is mounted to the top of a clear enclosure where the jet can be observed. The enclosure is affixed to the top of the reservoir that the jet shoots the fluid back into, thus closing the loop. The reservoir contains a baffle that prevents air bubbles produced by the jet from entering the pump inlet.
Equipment Used
- Pump and Motor
- Flow Meter - Recorded Data for Each Tested Nozzle
- Pressure Gauge - Recorded Data for Each Tested Nozzle
- Pressure Transducer - Cuts power to system if pressure spikes
- Baffle - Prevents air from entering pump inlet
- Nozzle Holder - Common component found in pourheads
Piston Pump with Instruments and Valving
Results
The fixture was used to validate 40 nozzles while I was at Woodbridge and continued to be in use after I left. I was able to determine using this fixture what pressure and flow readings can be deemed acceptable. The test results are composed of pressure and flow readings which are linearly proportional seen below. From this data, I made the standards for the nozzle certifications including the pressure, and flow measurements as well as a picture of the jet that clearly shows its straightness.
Example of Validation for Jet Straightness
Flow Characteristics of 5 Nozzle Sizes
Takeaways
I gained very valuable mechanical design experience since I got to work with industrial equipment including high-pressure pumps, flow gauges, and machined components. I also utilized SolidWorks to build the assembly and get my parts fabricated at the machine shop. Lastly, I got to apply some knowledge from school including Bernoulli's equation to predict the pressure that the pump would be able to generate behind each nozzle size. If I had more time I would've liked to automate the pressure and flow measurements, while also implementing a more professional process for taking pictures of the jet.
Slab Mixhead Design
This project stemmed from the need of a plant to have a custom pourhead that can pour a slab of foam continuously (around an hour). Our department at Woodbridge was responsible for pourhead R&D projects, so it was our task to design and manufacture the assembly. I did a lot of work in SolidWorks to create the assembly while also researching the types seals that can be used and finding a supplier.
Components
- Drive Shaft (Purple) - Rotates mixing shaft
- Drife Shaft Enclosure (Grey)
- Mechanical Seal (Teal)
- Lubrication Housing (Yellow) - Distributes lubricant to the seal
- Mixing Chamber (Pink) - Inlet for chemicals
- Mixing Shaft (Green) - Coupled to drive shaft and stirs the chemicals inside the chemical housing
- Ball Bearings
The Seal
The most complex component of this assembly is the shaft seal because it is operating at both high RPM and high pressure which means the entire assembly will get quite hot as well. A pusher seal was selected as they are designed for high temperatures and aggressive chemicals. A pusher seal consists of a face seal that is coupled to the rotating shaft. Sealing pressure is applied from the static side of the seal that is spring-loaded to maintain contact. This kind of seal requires lubrication so there is an O-ring along the ID of the seal to make sure the lubricant doesn't leak into the foam chemicals.
Takeaways
Industrial process equipment takes a long time to design, manufacture, and implement due to the high risk and high cost of development. During my co-op we made great progress on the design and it will hopefully be in the prototype phase soon. I learned about shaft and seal design as well as different machining processes that can be used to make this equipment. I also honed my SolidWorks skills further developing my mechanical experience.