Roll speed

P,n and the roll compaction time control compact density. Generally speaking, as compaction time decreases (e.g., by increasing roll speed), the minimum necessary pressure for quahty compacts increases. There may be an upper limit of pressure as well for friable materials or elastic materials prone to delamination. 

The major advantage of film blowing is the ease with which biaxial orientation can be introduced into the film. The pressure of the air in the bubble determines the blow-up and this controls the circumferential orientation. In addition, axial orientation may be introduced by increasing the nip roll speed relative to the linear velocity of the bubble. This is referred to as draw-down. 

A calender having rolls of diameter 0.3 m produces plastic sheet 1 m wide at the rate of 2(XX) kg/hour. If the roll speed is 5 rev/minute and the nip between the rolls is 4.5 mm, estimate... 

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. 

The film thickness varies with the rolling speed as shown in Fig. 4 in which Curve (a) is from the measured data and Curve (b) is the measured value of thickness minus the static film thickness, that is, the thickness of fluid film. The data of Curve (c) are calculated from the Hamrock-Dowson formula [44]. In the higher speed region (above 5 mm/s) of Fig. 4, the film becomes thinner as speed decreases and the speed index 4> is about 0.69 (Fig. 4, Curve b), which is very close to that in Eq (1). When the film thickness is less than 15 nm, the speed... 

Fig. 11 —Isometric views and associated contour line plots of film shape for k=2.9 and rolling speed of 0.021 and 0.042 ms" (Ref. [56]).

The relationship between film thickness of hexadecane with the addition of cholesteryl LCs and rolling speed under different pressures is shown in Fig. 25 [50], where the straight line is the theoretic film thickness calculated from the Hamrock-Dowson formula based on the bulk viscosity under the pressure of 0.174 GPa. It can be seen that for all lubricants, when speed is high, it is in the EHL regime and a speed index 4> about 0.67 is produced. When the rolling speed decreases and the film thickness falls to about 30 nm, the static adsorption film and ordered fluid film cannot be negligible, and the gradient reduces to less than 0.67 and the transition from EHL to TFL occurs. For pure hexadecane, due to the weak interaction between hexadecane molecules and metal surfaces, the static and ordered films are very thin. EHL... 

Fig. 27—Influence of dc voltage on thickness [50]. Load 0.174 GPa, Rolling speed 68 mm s . ...

The cases under the pressure of 297 MPa as shown in Fig. 37(b) are similar to that under 174 MPa, except that the films are a little thinner than that under the latter pressure. Furthermore, when speed is less than 1 mm/s, the film thickness of pure PE under a higher pressure decreases by a larger slope with the rolling speed, and there is little difference in the film thickness of UDP-containing PEs under different loads. 

Fig. 37—Film thickness for different rolling speed [60], Base oil PE Temperature 20°C, Pressure (a) 174 MPa, and (b) 297 MPa.

The unit of Pf here is MPa is the kinetic viscosity of lubricant in mm /s u is the velocity in mm/s, for the oil without polar additives, k is 23.5 X 10". If the tribo-pairs need to be lubricated with the fluid film in the TFL and EHL regime, the lubricant and the rolling speed should be chosen according to the pressure applied as Eq (9) so as to make that the liquid factor L is larger than the failure fluid factor L. Otherwise, the liquid film caimot be maintained under the pressure added. 

The present author has performed computer simulations to examine the transition of pressure distributions and shear response from a hydrodynamic to boundary lubrication. Figure 4(a) shows an example of a smooth elastic sphere in contact with a rigid plane, the EHL pressure calculated at a very low rolling speed coincides perfectly with the... 

Fig. 5—Film thickness measured by Luo et al. using the interferometer versus the rolling speed.

Similar results were reported by other investigators, [19,20], but attention was paid to investigating the effect of lubricant additives on the boundary film thickness. It is speculated that there should be no adsorbed layers formed on rubbing surfaces if purified and nonpolar lubricants are applied. The interferometer measurements show that in the case of using base oils, the relation between the film thickness and rolling speed follows the EHL power law pretty well down to 1 nm (Fig. 6(a)), or sometimes the film thickness may deviate from the Hamrock and Dowson s line and turn down quickly (Fig. 6(b)). If there is a small percentage of additives in the lubricant, on the other hand, the deviation from the power law occurs in a different way that the h-V... 

Figure 35.34 shows a slight dependency of the pressure buildup on the calender hne speed, which equals the circumferential roll speed. The general shape of the pressure curve can be understood as follows. A converging drag flow yields a pressure buildup until a barrier has been passed. The material left (=upstream) from the pressure maximum will take part in the roUing bank flow. The material between the pressure maximum and the clearance of the calender flows by means of the drag flow and pressure flow. Each material volume element wfll pass the clearance. At the position where the pressure vanishes the sheet will be taken apart from one of the rolls. 

The flow behaviour of rubber on a mill is dependent on the material, nip width, roll speed and temperature, and certain combinations can give flow instabilities, the worst case from the mixing point of view being bagging , i.e., loss of adhesion of the rubber compound to the mill rolls. A decrease in nip width, an increase in speed or temperature, can overcome this problem. 

Process parameters of primary importance include roll speed, differential roll speed, roll gap, metal flow rate, metal stream velocity, and melt superheat. The mass median diameter of particles diminishes exponentially as the roll speed increases. It is possible to obtain a smaller mass median diameter when one of the rolls is kept stationary rather than rotating the two rolls at the same speed. Metal flow rate seems to have a negligible effect on the mass median diameter. However, the mass median diameter increases with increasing metal stream velocity, suggesting that the relative velocity of the metal stream to the periphery of the rolls may be a fundamental variable controlling the mass median diameter. The size distribution is approximately constant for the conditions studied. 

Roll crusher Typical roll speed = 50- 100 rpm Typical capacity —10-25 ton/hr (6 mm particles) [31]... 

Note Compactor parameters roll pressure = 62-65 bar, roll speed = 8rpm, horizontal screw feed = 52 rpm, de-aeration = —0.2 bar, sized by double rotary granulators 4 mm and 1.2 mm screens. 

Trial no. Vacuum deaeration (15 in. Hg) Roll pressure (kN) Roll speed (rpm) Screw speed (rpm) Compact density (g/cm ) Compact rate (g/min) Fines not compacted (%)... 

The TF-Mini and TF-156 compactors (Vector Corporation, Marion, Iowa, U.S.A.) were equipped with concavo-convex rolls and single flight screws. The roll speed of the TF-156 was scaled to achieve the same linear velocity 74.2 in./min as the TF-Mini model. This setting maintained a comparable dwell time for material in the compaction zone. The TF-156 roll force was scaled to 5.6 ton, which equaled a force per linear-inch approximately equal to the TF-Mini 3.1 ton/in. roll width. The authors established a feed screw speed to roll speed ratio of 1.3 1 for the trials. Table 7 gives the compactor equipment settings. 

Roll speed and vacuum deaeration were kept constant at 8 rpm and 0.2 atmospheres, respectively. Roller compactor was equipped with 5 mm primary screen. Final sizing was conducted using an oscillator equipped with 20 mesh screen. 

---