Willie Hawkins, General Manager, Horizon Carpet
Early in 1979, we conducted a careful study of our color kitchen mixing procedures. We found that instead of making all our dyeing pastes from scratch, we could increase our production, improve consistency and minimize manpower by making a large volume of stock gum, a high viscosity gum concentrate that subsequently can be divided and diluted to the desired viscosity.
We needed a gum concentrate that had no lumps. We compared effectiveness, costs, and operating advantages of propeller style mixers, turbine agitators, and reversible homogenizers. After we considered these factors, we selected a reversible homogenizing mixer with a double stator mixing head.
The mixer, which has a 100" immersion length, was mounted in the center of a non-baffled 5,000 gallon tank (120" diameter with 96" straight wall and 6" cone bottom). Eliminating the tank baffles reduced the purchase price, made cleaning faster and easier, and improved the homogenizer's dispersing efficiency.
After several full scale experiments, we developed an optimum stock gum preparation procedure.
Approximately 2,500 gallons of water are introduced and the homogenizer is started in the downward vortex mixing mode. The gum powder is manually dumped into the tank from a slit bag. The mixer's powerful vortex pulls the gum powder almost instantly into the double stator mixing head. Clumps are crushed. Tiny gum pieces are rapidly injected into the water.
A five bladed, 6.5" diameter rotor shear the solids as the 3,600 RPM edges narrowly clear the lower stator. At the same time, the high speed impeller creates a fluid down jet that blasts the tank bottom and sweeps up the side walls. The blasting and sweeping action eliminates all dead spots.
The homogenizer continues operating in the down-mode as the operator adds - as fast as he can pick-up a bag, slit it and dump it - the rest of the 900 pounds of gum.
A press on the reversing starter switches the mixing mode to the upward umbrella flow pattern while the remaining 2,500 gallons of water are added. Now the homogenizer sucks the slurry from the tank bottom into the high shear zone, where it is sheared both mechanically and hydraulically as the double edged blades pass close to the upper stator.
The up-mode creates a high velocity flow (1,700 gallons per minute) that rises vertically along the mixer's shaft until it strikes the homogenizer's adjustable baffle plate, which is positioned just below the liquid's surface. Upon hitting the baffle plate, the stream is redirected radially to the tank wall.
The tank's contents are repeatedly pulled through the homogenizing head. By the time all the water has been added, the dispersion is complete. There are no lumps.
Next, approximately 5 gallons of hydrating acid are poured into the gum and water dispersion. Still operating in the up-mode , the homogenizer mixes the acid with the rest of the batch. In just 2 minutes, the color changes from gum yellow to an even white. The entire 5,000 gallon batch is now hydrating uniformly.
When comparing the reversible homogenizer to the commonly used turbine agitator, we found that we could add the gum powder faster, the stock gum was sure to be speck free, and we cut our mixing time in half.
We now have another reversible homogenizer in a 5,000 gallon tank. Both installations are used to make concentrated stock gum or dyeing pastes.
For making dyeing pastes, we fill the tank's cone bottom with water to prevent the heavy gum concentrate from plugging the 3" outlet. Stock gum is pumped over from the other tank, more water is pumped into the tank, and the homogenizing mixer is started in the down-mode. The large gum globs are pulled through the mixing head and rapidly dispersed. The mixer continues operating in the down-mode until all the water is added. The resultant clear paste is nearly smooth and lump free.
The homogenizer is reversed to the up-mode for the final intensive mixing step. At the same time, the dye solution (prepared in the dye boil-up tank with a smaller reversible homogenizer) is added. After 5-10 minutes of up-mode homogenization, the dye paste is uniform in color and viscosity.
Instead of 30-45 minutes to mix 5,000 gallons, we do it in less than 15 minutes.
Reprinted from the April 1981 issue of Carpet & Rug Industry