Fiber Moisture Control for the Mill's Benefit More uniform fiber from the gin. Minimizes overheating of fiber from the cotton gin. Minimizes short fiber content from the gin. Helps minimize in-process inventory for pre-conditioning. Frequently asked questions from cotton mills.

Bales that have received intensive moisture restoration from a Steamroller system at the gin respond more rapidly to conditioning at the mill.

Fiber moisture control provides more uniform fiber from the gin. top

Mills benefit from gins that utilize cotton fiber moisture control.  One of the biggest mill benefits comes from reduction of variability in the natural cotton fiber the mill uses as raw material.

Fiber moisture control minimizes overheating of fiber from the cotton gin. top

The gin normally receives cotton that varies widely in condition due to its nature as an agriculture product coming from regional fields. By using the appropriate drying temperature for each condition (with the goal of applying only the minimum heat needed for cleaning), a gin equipped with an advanced cotton drying system can provide the mill with fiber that retains its natural wax properties. This gives the mill increased efficiency and helps provide a rich texture and hand in the finished fabric.

Learn more about advanced drying systems.

Fiber moisture control minimizes short fiber content from the gin. top

What if regional conditions are so dry that little or no drying heat is needed at the gin? These are conditions that have the potential to create big headaches for a mill. As the moisture of the seed protects the fiber properties of the lint during saw ginning, results on fiber quality by ginning in dry conditions can generate significant problems. These problems show up at the mill as increased short fiber content, short staple, loss of uniformity, and weak, brittle fiber. Humid air applied to both seed cotton at the gin stand and to lint at the bale press is a big help in overcoming these shortcomings of nature.

Learn more about seed cotton conditioning.

Fiber moisture control helps minimize in-process inventory for pre-conditioning. top

When moisture is evenly applied to fiber at the press in the gin, bales are more responsive to subsequent conditioning at the mill. The time that it takes a bale of cotton to respond to ambient temperature and humidity is called “equilibration time”. Bales that have been processed using a Steamroller have their equilibration time dramatically reduced. This helps the mill by reducing in-process inventories and increasing efficiency of dyeing and other treatments to the fiber downstream.

Learn more about the Steamroller.

The following excerpt from the Delta Farm Press (August 16, 2002) provides more insight into this aspect of fiber moisture from a mill’s perspective.

David McAlister, research leader at the Clemson, S.C., Cotton Quality Research Station, said wide variations in moisture content affects the strength and evenness of yarn spun from the cotton, as well as spinning efficiency.

In a study in cooperation with mills, he found that when cotton fiber is allowed to reach equilibrium in a controlled humidity environment, it gains additional strength, resulting in fewer yarn breaks.

“This equates to real money for the mills by avoiding expensive production shutdowns,” he said.

“There is an obvious relationship between moisture content and yarn strength; 6 percent to 6.5 percent is optimum. Higher than that, there are complications and you'd risk discounts.”

The problem, McAlister said, is that “mills don't have the luxury to open and adequately condition the cotton ahead of use. This conditioning takes at least 72 hours, whereas the mills have only about 18 hours at most.”

His conclusion: “If moisture's going to be added to cotton, the gin's the logical place to do it because mills don't have the infrastructure to provide the needed holding time.”

Questions from mills about fiber moisture control. top

I have been assured by the gins we work with that drying temperatures do not exceed our recommended maximums. Why do we continue to see high variability in the fiber we receive from our gins, almost as if drying temperatures are not always appropriate for the cotton being processed?

Many gins measure drying temperature only after the mix-point with hot air. Worse, many of these gins take the after-mix temperature reading at the bottom of a tower dryer. The mass of the tower dryer attenuates what can be large oscillations in actual drying air temperature, leading the observer to believe that heated air of a reasonable temperature is always present. This is definitely not the case, especially when handling wet cotton. We have seen oscillations in wet conditions of 250 degrees F that registered little change in the reading at the bottom of a tower! Our hot air control systems use cascaded temperature control loops to limit the air temperature ahead of the mix-point, while still responding to after-mix conditions influenced by cotton flow rates and ambient air qualities. In addition, our moisture sensors act as a feedforward element for these controls, setting drying temperatures appropriate for the incoming moisture level of the cotton being processed. Fluctuations when ginning in uniform conditions are limited to only 2-3 degrees F,  providing a more uniform fiber.

A gin we work with has bales that have a relatively hard outer layer of fiber that is quite different than the fiber inside the bale. What causes this effect?

The gin may be using a high degree of moisture restoration at the press and storing the bales in a non-humidified warehouse in an arid environment. The loss of moisture from the outer inch or so of the bale creates this effect. Humidifying the bale storage warehouse or packaging the bale in a non-permeable wrap such as polyethylene can eliminate it.

Rather than adding moisture to seed cotton at the gin stands, we ask the gins we work with to limit drying temperatures so that the moisture at the gin stands does not go below 6%. Isn’t this a more cost-effective approach than applying moisture at the stands?

No. First, if cotton passes through the gin’s pre-cleaning machinery at moisture levels higher than 5%, the cleaners cannot work efficiently. This affects both grade and turnout for the grower. Although a mill-direct contract can help compensate for grade reductions, turnout is a bigger issue that is difficult to overcome. The turnout loss occurs because trash becomes tangled with the fiber and only the lint cleaners can take it out, wasting lint in the process.

The second reason is an obvious one. If incoming cotton moisture levels are below 6% and no restoration system is present for seed cotton moisture, it doesn’t matter if you turn the drying heaters off completely, you will be ginning the cotton in a brittle state that creates short fiber problems.

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