Author: Dr.C.S.Sudheendranath, & Raj Kiran
Cir-q-tech Tako Technologies Pvt.Ltd

Issues and Consequences of Static caused in a Woven Sack Cir-q-tech Tako Technologies Pvt.Ltd,. One common experience many of us make when we touch a metallic surface is that as our finger nears the surface there is a tingling shock. The intensity of shock is higher during days when the relative humidity is very low (for eg: during Summer). In addition, when we try to remove the Terylene shirt we were wearing, we hear a crackling noise or see some sparks. These are all Static phenomena.

The movement of static charges from one surface to another is called Electrostatic Discharge. Electrostatic Discharges are damaging to sensitive microelectronic circuitry but are harmless to human beings. Negative static charges are nothing but free electrons. The HOLES (familiar from electronics) are positive charges. The most spectacular Electrostatic Discharge occurring in Nature is Lightning. All of us are aware how devastating Lightning is . A normal Electrostatic Discharge on the other hand is milder than Lightning since it does not deal with such high energies as in Lightning.

There are three different ways in which Static charges come into existence:

1. By friction: When two bodies rub against each other Static is generated. The process is called Tribo Charging. The extent of charge generation depends on many factors including the surface area of contact, and the frictional force.

2. By Seperation: When two bodies in intimate contact are separated from each other Static is generated. A common place example for this phenomenon is the peeling of a cellulose tape from the rest of the roll.

3. By Induction: A Static charge can be generated on a material when it is placed in a Static Field.

In the Woven Sack Industry the common Fibers in use are PolyEthylene, Nylon, Poly Propylene, Polyester etc. All these are electrically insulative materials. The basic characteristic of an Insulator is that it generates Static on Friction or on Seperation. This has serious consequences to the Industry.

1. When the shuttle containing the thread is being passed from one end to the other, the Fiber is generating Static continuously. This can result in repulsion between Fibers. Consequence is difficulty in maintaining the Denier Count. Secondly, the Shuttle may not keep its true resulting in crooked lines. The greater the speed of the Shuttle, greater is the amount of Static generated and greater is the resultant problem. The problem is more acute in mechanized weaving processes.

2. Whenever woven sacks are stacked on one another, the Sacks stick to each other due to Static. When a person tries to unstack the bundle, the sacks may not come off smoothly, forcing the individual to spend more time to take out a few Sacks from the bundle. If this happens several times during the day, considerable work time is lost.

3. Due to Static on the surface, the surface of the topmost Sack in a bundle attracts dust particles which cling to the plastic Fiber of the sack due to Electrostatic Attraction. As a consequence, several layers of a stack can carry large amounts of dust.

Two solutions suggest themselves to eliminate these sources of error which cause lowering of yield ultimate.

First solution is to use Anti Static thread so that no static is generated at all and hence nips the problem in the bud itself.

The second more general solution is to use Area Ionizers which can neutralize the static charges IN SITU . The Ionizer should be designed to cover the entire web of the Shuttle.

1. The Human Body acts like a Capacitor. It can acquire and store static charges wherever they exist. The resultant is that the accumulated charge gets discharged whenever the person comes in contact with a Conductor including a second individual. Everytime this discharge happens the individual requires some time to recover from the shock. Such delays accumulate during the entire day resulting in considerable loss in time and output. The possibility of Static Discharges rapidly increases with decrease in relative humidity. On the other hand too much humidity would result in the Fiber sticking causing reduction in the weaving velocity. If the Flooring in the work area is electrically insulative, there is no pathway for the body charges to go to ground, This causes an increase in the stored body potential. Consequently, Electrostatic Discharges become more severe and more frequent. By having a flooring which can take away the charges from a person's body through his feet (resting on the Floor) this problem can be reduced.

Whenever a person accumulates static charges and passes on these charges to the Machine, the static sensitive parts of the Machine like the Controls can get affected. A Very common observation is during machine Counting . A wrong reading may be obtained when Digital instruments are used.Whenever considerable Static charges remain on the sack, the packed material may undergo some physical modifications like Clumping etc.

A considerable Machine downtime may also occur whenever threads get snarled up or Break during operations caused by Static.

Whenever a plastic woven sack containing some material is emptied, due to Static, some of the material clings to the inside of the sack. It is extremely difficult to remove this charged Dust from the bag. Consequently, when the same bag is used to pack some other material, there is very severe contamination. The smaller the particles, the larger is the intensity of charge. The problem is severe when very fine materials are packed. The obvious solution is to subject empty bags to ionized air using Ionizers before they are repacked.

Though the above remarks appear to be very elementary by themselves, the sum of all the issues caused by Static can be very vital to the economic prosperty of the Woven Sack industry and hence have to be tackled earnestly.