Machine direction control

Machine direction control uses MD measurement values to control the downstream quality of the paper. Advanced M D controls are based on physical process models of the papermaking process. This means, mathematical models describe the physical process and are able to predict the effect of control actions on the process and on paper quality. Such model-based controls are especially essential to achieve 

Coordinated change ot stock flow, speed and steam 

Paper C ualitv basis weight and moisuire remain constant 

Moisture controllers usually adjust a heating device, such as 

In some cases moisture at the reel is controlled by adjusting rewetting devices having a series of spray nozzles across the web. 

---

Machine-mounted blenders. By placing a volumetric or gravimetric blender directly on the feed throat of a machine, direct control is achieved over all ingredient feed rates. As with any press-mounted system, careful consideration must be given to allow access for maintenance, calibration, and cleanout. 

Equipment cells can be replaced by computer-coordinated machines - direct numerical control (DNC), flexible manufacturing systems (FMS), flexible manufacturing cells (EMC) ... 

Since fluid power is efficiently transmitted and controlled, it gives freedom in designing a machine. The need for gear, cam, and lever systems is eliminated. Fluid power systems can provide infinitely variable speed, force and direction control with simple, reliable elements. 

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. 

If machine direction thickness uniformity is a problem, it can best be remedied with the use of a gauge detector (beta gauge) that is part of a control system adjusting the speed of the take-up device, to correct for thickness nonuniformities. Small period variations are very difficult to remedy in this fashion. 

The thickness of the calendered product must be uniform in both the machine and cross-machine directions. Any variation in gap size due to roll dimensions, setting, thermal effects, and roll distortion due to high pressures developing in the gap, will result in product nonuniformity in the cross-machine direction. Eccentricity of the roll with respect to the roll shaft, as well as roll vibration and feed uniformity, must be tightly controlled to avoid nonuniformity in the machine direction. A uniform empty gap size will be distorted in operation because of hydrodynamic forces, developed in the nip, which deflect the rolls. The resulting product from such a condition will be thick in the middle and thin at the edges, as shown in Fig. 15.2. 

Abstract To appreciate the technological potential of controlled molecular-level motion one only has to consider that it lies at the heart of virtually every biological process. When we learn how to build synthetic molecular motors and machines that can interface their effects directly with other molecular-level sub-structures and the outside world it will add a new dimension to functional molecule and materials design. In this review we discuss both the influence of chirality on the design of molecular level machines and, in turn, how molecular level machines can control the expression of chirality of a physical response to an inherently achiral stimulus. 

Blown film is usually extruded vertically upward through a circular die. This forms a tube that is then blown into a bubble that thins or draws down to the required final gauge. Orientation takes place in two directions horizontally (transverse direction/TV) as the bubble is formed, and in the machine direction (MD) as controlled by adjustable-speed haul-off nip rolls. 

Orientation consists of a controlled system of stretching TP molecules in unioriented [unidirectional (UD)] or bioriented [biaxial direction (BD)]. UD orientation can be in the machine direction (MD) or transverse direction (TD).207 Orientation improves strength, stiffness, optics, electrical, and/or other properties with the usual result that improved product performance-to-cost occur. This technique is used during the processing of many different products such as films, sheets, pipes, fibers, tapes, etc. 

Different methods are used. An online ordinary common blown or cast film line uses a machine direction orienter (MDO) on the front end of biaxially oriented film heated chamber extrusion line. If only the machine direction is to be stretched, a series of precision controlled heated rolls can be used. Film is fed through a series of rolls where it is sequentially heated, drawn around rolls that increase in rotational speed providing the stretching action, annealed around larger diameter roll(s), and cooled on a final roll(s). 

Biaxial orientation leads to isotropic properties in blown film, that is, properties that are eqnal in the two primary directions the film was stretched (i.e., parallel to the flat bit ). Orientation in the machine direction of the film is controlled primarily by take-up ratio, defined above. To control orientation in the transverse direction, we measure something called the blow-up ratio, while the forming ratio provides an indication of the degree of isotropy. 

The experimental evaporator (micro two-phase jets generator) is shown on Fig. 10 -11. The heater block of the evaporator includes a hole machined directly in the centre of the copper cylinder with thick walls and is used for the installation of a nickel sintered powder evaporator. Some thermocouples are disposed inside the copper block to control the heat flow to the evaporator from the electric heater disposed on its outer surface. To minimize heat losses, the heater block was insulated. Heat input to the evaporator was calculated by conduction analysis using thermocouples that were placed at a known distance apart in the copper heater block. 

---