At the Fox's Biscuits plant in Uttoxeter, Waukesha Universal 1 rotary piston Model 60, 30 and 18 pumps have proved to be successful in handling cream fat, which is a key ingredient in several of its biscuit lines. The Model18s and 30s are used on a 24/7 basis, transferring product at around 750kg/hr to dedicated production lines. The two Model 60s are run on a batch process for transferring the cream as and when needed at a volume of 2.000kg/hr. The consistency of the cream fat is similar to that of margarine and is handled at 30⁰C. The challenge of pumping this type of material is that a gear type pump would break up the structure of the material, hence the use of the Waukesha universal technology.
This pump, whilst offering many of the benefits of rotary lobe pump uses an external circumferential piston (ECP). In this design the arc-shaped rotary pistons, or rotor wings, travel in annular-shaped cylinders machined in the pump body. The resulting long sealing path reduces slippage and produces a smooth product flow without destructive pulses or pressure peaks, and without the need for valves or complex parts. Because the rotors produce a scooping action, they do not squeeze and compact the medium being pumped. This pump type combines a very gentle, pulse-free pumping action with the high suction capacity necessary for allowing thick mixes to be drawn into the pump without any separation of the ingredients.
In 2012 the Uttoxeter plant took the step of introducing Waukesha U2 pumps for handling plasticised dough fat. The difficulty with this media is that at times relatively high back pressures can be created due to the length and complexity of the production runs. Typically pressures of up to 15bar were being encountered and the existing pumps were not designed for this level of pressure.
Initially Fox's Biscuits approached pump distributor AxFlow about using the Waukesha models already in use at the plant for handling the plasticised dough. On reviewing the pressures and flow rates required, AxFlow recommended Waukesha U2 pumps fitted with mechanical seals rather than the client's preferred option of a double O ring. The units installed in a duty/standby arrangement have a duty cycle of 30% run and 70% standby during a 24 hour period and are used at the bulk ingredients stage in the early part of the production cycle. With the Waukesha U2 pump, the plant can now accommodate pressures of 20bar.
Plasticised dough fat is palm oil that has been processed by being put through a scraped surface heat exchanger at pressure and this changes its crystalline structure and causes it to become a margarine-type consistency. This ingredient is used in all the company's products. The palm oil starts in storage out at 50⁰C and then the temperature is raised and cooled in a heat exchanger before going onto a scraped surface heat exchanger at 45⁰C where it is subjected to a pressure of 10bar before exiting at 21⁰C. It is this process that changes the crystalline structure of the dough. At Uttoxeter, Fox's Biscuits produce around 1.7 tons of plasticised dough per hour, which is then held in a series of storage vessels and transferred on at an ambient temp of 29⁰C to any of the 10 production lines whenever it is needed using the Waukesha U2 pumps.
"The Waukesha pumps are kind to both the plasticised dough and cream fat as they do not crush these products, thereby keeping their desired consistency," reports Mick Walker of Fox's Biscuits Uttoxeter. "Also the compressing action helps to build pressure. However, with this type of product, should the temperature drop for any reason then the product can actually harden-off. When this happens, the pipeline has to be opened up and the solid stream of product pumped out. Pumping the product in this state increases the pressure, which is why we needed pumps that could accommodate such a situation."
The plant at Uttoxeter did use another type of pumps prior to the arrival of the Waukesha U2 pumps and since then they have never looked back. "It doesn't matter what you are pumping so long as the media is kept warm so that it can flow. If cooling occurs the material becomes sticky and the seal faces can stick together, so when the pump is started from cool there is a chance that the seals can shatter," continues Mick Walker. "We have overcome this difficulty by fitting the pumps with inverter drives on a long ramp up to maximum speed. Consequently, there is a gentle shear action which clears the seal face adhesion and enables the pressure to be increased over a longer period. The pressure is also monitored in the line so if the pressure does get too high the pump is shutdown and then restarted at a slower speed."
According to Mick Walker, compared to other processes in the food industry, biscuit manufacturing is a complex job as many commodities are brought together. "The Waukesha pump is very good and we have not encountered any problems relating to performance," he says. "If they are regularly serviced and run to specification and within tolerance, they are problem-free. We undertake maintenance according to the running cycle, but generally the pump faces are stripped down each week for cleaning and greasing. Apart from this, regular maintenance is undertaken once a month. I would recommend the Waukesha pumps and always look to utilise them."