Tenter frame

As a general rule, there is an economic break-even point at ca 0.08 mm, which coincides with the defined difference between film and sheet. Film is made mote economically by the bubble method and sheet by the tenter-frame method. The exact thickness for break-even depends on technological improvements, which can be made in both processes, in the degree of control used in regulating them and in quaUty requirements. 

Polyamides (nylons) are thermoplastic fibers that retain their form produced by heat treatment. They are usually given an alkaline scour and then heat-set. The heat-setting treatment is conducted at ca 10°C above the subsequent wet processiag steps this ensures good form retention after processiag. Woven fabrics are usually heat-set on a contact heat-setting machine and nylon tricot is generally heat-set on a tenter frame or ia steam chambers. 

In this Fig. 8-41 view (a) the feeder-roll speed to puller-roll speed ratio can be set, such as 1 4, and simultaneously the ratio of width can be set as 1 4. The machined direction ratio is usually accomplished prior to the plastic s entering the temperature controlled oven that contains the tenter frame, by having it move around heat-controlled rolls where the rotational speed of the rolls increases from one roll to the next. View (b) is a schematic of the drawdown phenomenon with swell to produce orientation in the machined (longitudinal) direction. 

Ceramic Filter. The ceramic filter collects, volatilizes, and destroys particulates and condensible organics emitted from industrial process streams, such as paint spray, lost foam casting, condensible organics, tenter frames, and cured rubber... 

Tenter frame for transverse direction orientation of sheets and fOms. (Courtesy of Marshall Williams Plastics.)... 

Tentering frame A machine used to stretch textiles and polymeric films and sheets. 

Heat-shrinkable sheets (thickness 0.040 to 0.120 inch, or 1 to 3 mm) and films (thickness 0.001 to 0.020 inch or 0. 025 to 0.5 mm) are fabricated from many of the same materials as shrinkable tubing.91 They are produced by extrusion as a tube, sheet or blown film. Irradiation is done by the equipment shown in Figure 8.10. Orientation (stretching) after irradiation can be done by several methods, namely by differentially heated and driven rolls (in the machine direction) or by a tenter frame (see Figure 8.11) in the transverse direction. If desired, biaxial stretching can be done. 

Biaxially oriented polypropylene (BOPP) films have higher stiffness than cast films and consequently can be used in much thinner gauges. Homopolvmers are used almost exclusively to provide maximum stiffness and water-vapor barrier. Oriented films are produced by the tenter frame and bubble processes. 

TABIE III. Tenter Frame Drying Ehergy Requirements as a Function of Moisture Content of filtering Fabric (Adapted from 10, 11)... 

If dyed on a tenter frame as suggested, selvages will have clip marks. (Really of little consequence as the garment industry in most cases will discard the selvages.)... 

PROCEDURE aPad, dry on a tenter frame and mild-cure on drying cans. ... 

Beard(Z.) has developed a useful mathematical model of a convection dryer for studying the use of energy in a tenter frame. The model is based on a set of simultaneous differential equations which can be solved numerically to obtain fabric temperature and macroscopic moisture contents along the length of the dryer. The model considers the fabric as a moist layer of fabric sandwiched between two dry layers of fabric. Thermal energy is convected from the dryer to the external surface of the dry layer and then from the exterior of the fabric to the interface between the wet and dry layers. At the interface, the water is evaporated and diffuses as vapor through the dry layer to the surrounding hot make-up air. Assumptions in the model include ... 

This total value is only 3% greater than the value for just thermal removal, hence we can state that thermal removal costs determine essentially the cost of drying. However, since mechanical methods are relatively cheap they should be exercised to the fullest extent. For instance if our fabric enters the tenter frame at 100% moisture content 18.9 x 10 1,dollars/m2 of fabric processed is the cost of drying. 

Beckwith, W.F., and Beard, J.N., Jr., A Scheme to Assist in the Evaluation of Tenter Frame Dryer Performance, ASME publication 78-Tex-4, Trans. ASME J. Eng, for Ind. 1978. 

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