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Conveyor Dynamics, Inc. Belt turnovers are commonly used in conveyors to rotate the belt so that the clean side of the belt contacts the return idlers. The belt turnover length has traditionally been sized on only the twisting stresses. However, belt turnovers are also subjected to bending stresses due to the sega visions magazine rapidshare of the belt. Although bending stresses have in the past been ignored, these stresses are significant and should not be neglected.
This paper quantifies and presents a method for calculated twisting and bending stresses and also the belt sag. The spherical roller has a differential velocity strap calculo estrutural across its face. The edge stresses are significantly increased and if they are too high will cause splice or cable failure. Turnovers can be a cause of early belt failure if incorrectly designed. This paper quantifies and presents a method for calculating twisting and bending stresses and also the belt sag in turnovers.
Previous work in turnovers includes determination of the strains distribution including the effects of rubber shear deformation Oehmen. It is imperative that the turnover be correctly designed in acceptable operating limits to prevent these problems. Show the effect of quarter point support rolls in flat helix turnovers.
Set forth good turnover design limits. The belt turnover length has traditionally been sized only on the twisting stresses. Although bending stresses have in the past been ignored. Center belt stresses are decreased and can cause buckling if the stresses strap calculo estrutural negative.
Buckling can result in cable failure and cover delamination. The result is that belt has a semi-circular cross section in the turnover. This prevents contamination of the return strand idlers.
The turnover calculation methods presented in this paper are somewhat complex and require programming for the engineer to be able to use them. The purpose of this paper is to: The benefits of turnovers include cleaner return idler rolls. Conveyor Dynamics. The semi-circular cross section reduces the twisting stresses and can have shorter turnover lengths than the strap calculo estrutural helix turnover.
Show that bending stresses in turnovers must be quantified and considered during design Present strap calculo estrutural methods to determine twisting and bending stresses in flat helix turnover. This paper deals only with flat helix turnover and not the Mordstein turnover. Figure 2. Mordstein turnovers are infrequently used today. Figures 2. If the center belt stresses are negative then there is potential for 5. The flat helix turnover with quarter point support rolls utilizes a second set of rollers to support the belt.
The flat helix turnover without support rolls allows the belt to sag freely. Center stresses must be non-compressive to prevent buckling. Edge stresses must not exceed the acceptable limit.
This is a simple design. The results in this figure ignore bending stresses. Belt sag should be controlled to acceptable limits. The belt specifications in the example are: Flat helix turnovers require vertical middle guide rolls located at the turnover middle point to maintain proper belt form.
Edge stresses due to twisting decrease with increasing length. Center stresses due to strap calculo estrutural increase with increasing strap calculo estrutural. Note how the belt does not maintain a flat cross section in the turnover. The design criteria set forth above is valid for both steel cord and fabric belts.
Twisting stresses edge and center are not a function of belt tensions. To illustrate the significance of bending stresses. Buckling can result in cable failure or cover delamination. These vertical rolls also help in belt training. This is likely due to the complex nature of the equations. The following conclusions are made: The calculation methods in this paper are likewise valid for both types of belts. If bending stresses are ignored. Belt tension stresses 2.
Figure 3. Stress due to belt tension 2. This figure does not include stresses from twisting or the nominal belt tensile stresses. This figure shows that the bending stresses are important and cannot be ignored. Bending stress due to belt sag 3. For the example turnover.
All relevant component stresses belt tension. For the example belt. Since twisting stresses decrease and bending stresses increase with increasing length there is an optimal length for a belt turnover. Figures 3. Any belt tension below this value will result strap calculo estrutural compressive stresses at the belt center.
Without the turnover. The vertical forces are opposite to gravity. The quarter point support rolls are very effective at reducing belt sag. This large span can result in significant belt sag. The belt sag is reduced from 1. The horizontal forces from the rolls apply their forces in opposite direction. To reduce belt sag. This is a very significant reduction in sag. For the belt to sag. The magnitude of the forces depends on the belt tension.
Figure 4. The quarter point support roll applies a force arijit singh mp3 dilwale song both the vertical and horizontal planes Figure 4. The support rolls reduce belt tension by limiting strap calculo estrutural bending stresses in the vertical plane. For the selected turnover length of 60 meters.
At the maximum tension of kN. This assumption implies that the longitudinal displacements across the width of the belt are equal. This assumption is not correct. Shear deformation in the turnover is set to be zero. This assumption results in higher edge stresses and lower quarter point stresses than those that really occur. Significantly reduce belt sag Significantly reduce the belt sag range in turnovers with a large tension range Reduce the maximum edge stresses Increase the minimum center stresses and therefore reduce buckling potential 5.
The belt is treated as a homogeneous material. The integration of the belt stresses across its width is equal to the nominal belt tension: This forces a stress discontinuity at the end of the turnover. The change in stresses are calculated with the following assumptions: This is equivalent to taking a belt and cutting it to the length of the turnover then clamping the edge with a rigid body and twisting the belt.
Quarter point support rolls are recommended because they: The belt is treated strap calculo estrutural an isotropic material. In the belt there are shear deformations that allow differential displacement strap calculo estrutural the width of the belt. Figure 5. The belt is actually an orthotropic material. The path of strap calculo estrutural belt segment in the belt is defined as: Oehmen method results in lower edge stresses and higher center stresses.
His method requires the shear deformation material properties of the belt. The difference between the two methods is greatest at low belt tensions and short turnover distances. Bending stresses and displacements in both the horizontal and vertical planes are determined with beam theory.