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Slatted Apron

Fiber opening equipment usually has conveyors inside them for moving fiber. These conveyors are often called aprons. Aprons can be made from many materials. One method of conveyor construction is the use of canvas conveyors with wooden slats and fabric belts. The fabric belts which may be 2 inches to 3 inches wide line up with pulleys on the head and tail shafts of the machine. A solid canvas apron is attached to the belts and wooden slats are riveted through the canvas apron to the belts. This makes a strong structure that can last for many years with good care. The apron can be made endless or it may be a laced belt that is held together by hooks and pins that connect the belts.

The slats on the apron can have various shapes and spacings depending on the need. For vertical transportation of fiber, sharp pins are inserted into the slats. This type of apron is called a spiked apron. Usually a stripping roll will knock excess fiber off the spiked apron as it travels upward. Once the spiked apron has gone over the top and is starting to travel downward, it is an easy matter for a doffing roller to knock fiber off the spiked apron and into the next piece of equipment for further processing.

Fiber Condenser and Separator

In a fiber opening system, staple fiber is often conveyed between machines through thin-walled metal pipes called ductwork. Fans produce air pressure that moves the fiber through the ducts. When the fiber gets to the end of the duct it is usually desirable to provide a means to separate the air from the fiber so the fiber can fall by gravity into the next machine in the process. The device that accomplishes the air/fiber separation is called a fiber condenser. There are two primary types of fiber condenser.

A rotary condenser, sometimes called a rotary separator, consists of a round metal screen through which a vacuum is pulled. When the fibers reach the screen they are pulled against the screen and held fast by the vacuum. Inside the screen is a baffle so that vacuum is applied to only half the screen. As the screen turns it carries the fiber around and once the fiber passes the start of the baffle, it is no longer held by vacuum to the screen and can fall off the screen in clumps Usually this is helped by a rotating scraper or belt.

An air box type condenser sometimes called a stationary separator, is nothing more that a large metal box made out of metal screen having an open bottom, , The fiber/air mixture is blown into the box and the air escapes through the screen. There are no moving parts. This type of condenser does not control the fiber a well as a rotary condenser and cannot completely separate the fiber from the air. The fiber comes out much more fluffy and continues to be blown around somewhat. For dusty fibers, the air box may be enclosed by a second solid metal box so a vacuum can be pulled to suck away dust.

Fine Opener

Fiber systems for staple fibers usually consist of balefeeds, conveyors, a storage and/or mixing bin, an opening device, and fans. The opening device is often a fine opener. There are various configurations for a fine opener, but most of them consist of a set of fluted feed rolls and a cylinder covered with short spikes or coarse card wire. The fine opener has a twofold purpose: (1) It tears up large chunks of fiber so the feed batt presented to the card has fiber chunks that are small enough to be manageable by the card. (2) Since it is located after a fiber blending bin, it presents a more intimate blend of fibers to the card.

Often the fine opener is fed from a reserve chute located above the fine opener. In this case it is called a VTO or vertical fine opener. The fine opener can just as easily be fed from a horizontal conveyor. Fiber is removed from a fine opener by means of a fiber fan. A stream of air is sucked across the cylinder with such velocity that it completely removes all fibers from the cylinder. The opening action in the fine opener takes place as the cylinder tears the fibers off the feed rolls. The feed rolls revolve slowly and the cylinder travels at quite a high speed. The speeds of the feed rolls and the cylinder are adjustable for the fiber type, denier, and length. The starting and stopping of the feed rolls is usually controlled by photo eyes sensing the fiber level in the machine downstream from the fine opener. The main cylinder runs continuously. Fine openers are usually 1 to 1.5 meters wide.

Fiber Fan

Nonwoven machines using staple fiber commonly move the fiber between the various opening machines through ductwork. The fiber can either be blown through or sucked through the ducts. One piece of equipment used to do this is a fiber fan. A fiber fan is a special type of centrifugal fan with blades made so fiber can actually pass through the fan. One would think that fiber would get tangled in the fan blades. However, the blades are made on a rotating disk and angle outward from the center of the disk. This design allows for the generation of air movement while preventing the fibers from getting entangled in the blades.
Smaller fiber fans are usually directly coupled to the motor while larger ones are belt driven from the motor. Safety is an important issues with these fans. They often have a cleanout door as they should be regularly inspected for nicks on the blades as well as buildup on the blades. The door must have a mechanical switch that requires several minutes to unscrew so that the fan will be at a complete stop and cannot start once the door is open.

Some fiber fans have motors that are controlled by inverters. This enables the fan speed to be changed while the fan is running. This is advantageous when changes are made in fiber length, type of fiber, or fiber denier.

Balefeed (2)

Several nonwoven production methods use staple fiber. Primarily, these are processes that use cards or airlaid machines to form the nonwoven web. One of the methods for introducing bales of staple fiber into the nonwoven machine is to use balefeeds. Some call these hoppers. Their purpose is to tear up the bales of fiber into small tufts about the size of plum or smaller. These balefeeds have a device to lift the bales (01) into the storage area of the balefeed. The storage area has a movable floor called an apron (02) that carries the bales to a vertical conveyer (03) that is covered with spikes. The conveyor tears off chunks of fiber and carries them upward until a spinning roll, called a stripper roll (04), knocks most of the fiber off the spiked conveyor while allowing a measured amount to continue over the spiked conveyor. A doffing roll (05) then knocks all the fiber off the spiked roll. The fiber can fall onto a collection conveyor and this is called volumetric feeding. If the fiber falls into a collection pan that is connected to a scale, it is call weigh-pan feeding. A newer method is to allow the fiber to fall onto a small conveyor attached to scales and this is a method of continuous weighing. After leaving the balefeed the fiber will be subjected to further opening and blending in various machines.

Humidification

Nonwoven production lines run best when the relative humidity is in the 55% to 65% range. Usually this means adding humidity to the plant atmosphere and/or the fiber. This can be accomplished in three ways:

  1. Install humidification equipment as part of the general plant air conditioning system.
  2. Install humidification equipment in areas of the plant where production lines are located.
  3. Install equipment that will provide humidity to the fibers.

The first method is the best but is very expensive to install and operate. Many plants do not have air conditioning systems for the entire plant.

The second method is commonly used. Equipment used are fans that spray water into the air, rows of nozzles that used compressed air to atomize water, and pressure systems that use special nozzles to produce very fine mists or fogs.

The last method is most cost effective and usually consist of a high pressure water system connected to fogging nozzles. The nozzles are located near or inside fiber handling equipment. The nozzles are turned on and off by solenoids so that the humidification fog is applied only when fiber is being processed.

All the systems require diligent maintenance and good filtration to operate properly. Humidistats which sense the amount of humidity in the air can be used for automatic control.

Extruder

Thermoplastic polymers such as polyester and polypropylene have one component in common; they rely on extruders at some stage of the process. Carded polyester and polypropylene fabric use bales of staple fiber for the raw material. Staple fiber is produced on spinning lines that use extruders to turn thermoplastic pellets into a melt which is extruded into fibers. Spunbond and meltblown lines use extruders on the line to make a melt which is laid down as a web or blown against a drum or conveyor.

An extruder consists of a long metal tube, called a barrel, usually 4 to 8 inches in diameter which contains a metal screw. It takes quite a bit of horsepower to turn the screw. A large motor drives a reducing gearbox which in turn drives the screw up about 120 rpm. Plastic pellets are fed into the entrance throat of the screw. The barrel is heated with electric heaters. Heat is also produced as the screw compresses the pellets, with the resulting heat and pressure causing the pellets to melt. All the parameters of temperature, pressure, screw speed, and feeding rate are very closely controlled to produce a consistent melt from the extruder.

Extruders often have a filter at the exit of the screw to prevent contamination from going into the spinnerets. Usually this filter works automatically to constantly remove contaminants. An extruder can be started and stopped when hot, but there is an extensive heating process that can take several hours when starting an extruder from a cold state.

Relative Humidity

The manufacturing of nonwovens is greatly affected by the conditions of the manufacturing environment. Primary in those conditions is relative humidity. The raw materials, equipment, and manufacturing employees are all greatly affected by relative humidity.

Relative humidity is defined as the amount of water vapor a given quantity of air is holding divided by the maximum amount of water vapor that could be held at the existing temperature. The relative humidity is expressed as a percentage. We often hear the weatherman on television in the summertime say the humidity is 80%. We know such conditions cause us to sweat. In the winter the humidity may drop to 30% or less. Hot air has the ability to hold more moisture than cold air.

For raw materials and process machinery, problems occur when the humidity is low. Low humidity causes fiber to cling together and to cling to plastic surfaces. This usually causes difficulty in opening and transporting fibers. It can even show itself as static electricity and cause operators to receive shocks. Equipment and opened fibers tend to process better in the summer when the humidity is high.

For equipment operators the problem is the opposite. We enjoy a working environment with lower temperatures and lower humidity.

Relative humidity is measured with an instrument called a hygrometer. They can be simple de-vices that hang on the wall to complex and highly accurate ones with data logging. The ones with data logging record the humidity every few minutes in computer memory. The memory can be downloaded and graphed to see how the humidity varies over time and to measure the effectiveness of plant controls.

Spinneret

There are three primary nonwoven processes that uses spinnerets: spunbond, meltblown, and spunlace. A spinneret is a metal plate having hundreds to thousands of holes in it. The purpose of the holes is to precisely direct small diameter streams of liquid. The first two processes use hot thermoplastic resins like polypropylene, polyester, and nylon to produce filaments that are combined to form a web and then a fabric. A spunbond spinneret creates streams with laminar flow to produce continuous filaments of fiber. A meltblown spinneret directs the liquid to a point of intersection with streams of air. The resulting fibers are discontinuous and vary in diameter. The spunlace method uses spinnerets to direct streams of water through a dry laid web to interlace the fibers and bond them together. A spunlace spinneret converges high pressure water into tiny jets that blast fibers against a moving screen to intertwine the fibers.

Meltblown

One of several methods of producing a web of fibers from a thermoplastic resin such as poly-propylene is meltblown. This particular method derives its name from the fact that fibers are blown from the spinnerets by a jet of air that is adjacent to or surrounds the spinneret. The melt supplied to the spinnerets is produced by an extruder that heats and melts thermoplastic pellets to a viscosity that will allow them to flow through the spinnerets. The picture shows the fibers being blown out of the spinnerets and collected on a rotating drum. The drum is porous and has a vacuum inside that causes the fibers to cling to the surface of the drum. As the drum revolves, the vacuum is removed and the unbonded web proceeds to a bonding station which is usually a calender, though other methods can be used. The resultant fabric is rolled up on a winder.

One of the prime characteristics of the meltblown process is that it produces fibers of very low denier. These fibers are called micro denier. Also since the blowing process is somewhat un-controlled at the end of the spinneret, the resultant fibers have many deviations in denier. Meltblown fabric is usually soft because of the fine denier fibers and it also is not as strong as other nonwovens. Meltblown fabric is often sandwiched with spunbond fabric to combine the best properties of both. The most common resin used to make meltblowns is polypropylene.