Backstops to Prevent Reversal of Inclined
16Pages

Backstops to Prevent Reversal of Inclined Conveyors and Vertical Bucket Elevators Forwarded from Clutch Clutch An Altra Industrial Motion Company

Marland Products The Need For Adequate Backstops Since 1931, Marland has been producing backstops, clutches and clutch couplings. Marland products are based on a one-way clutch design, utilizing the principle of cylindrical rollers on inclined cam planes. The Marland principle of rollers on inclined cam planes has proven its dependability for over 60 years in worldwide installations ranging from food processing plants to equipment used in steel mills and heavy mining industries. Proving the inherently longlife Marland design, the first two Marland clutch units installed in February, 1931,...

Operating Details During freewheeling, (normal operation), the cam and roller assembly rotate with the headshaft as shown by the arrows in Illustration 2. The outer race is secured to stationary coverplates and "I" Beam Torque arm. An oil film wedges and separates the rollers from the outer race. This moves the rollers a few thousandths of an inch imparting relative angular motion between the roller cage and cam. This slight movement of the rollers into the deeper cam zones, with a clean lubricant film wedged between rollers and outer race, permits freewheeling without metal to metal...

Design Features Design Features Marland backstops are completely mechanical, automatic operating units, incorporating a time proven basic operating principle, to provide greater safety and longer life with minimum maintenance requirements. Seventeen standard sizes are available up to 1,200,000 pound-feet of torque. Superior performance is assured by the following design features: SIMPLE INITIAL INSTALLATION. Backstop is symmetrical and can be mounted for desired free shaft rotation. Arrows on cam faces or inner labyrinth show the direction of free rotation. The torque arm is a single "I"...

Advantages of Marland Cylindrical Rollers on Flat Inclined Cam Surfaces Free Rotation Accurate Dimensions Lower Stress The cylindrical rollers used in all Marland clutch products are free to rotate in their individual pockets during freewheeling permitting the load to be engaged and re-engaged on any part of the roller circumference and cylinder surface as indicated by the arrows in Illustration 5. Cylindrical rollers are easy to produce and reproduce to precision dimension limits which are readily checked with micrometers, go-no-go gauges, or if necessary, with the extreme closeness of...

Locate Backstops Where Reverse Torque Loads Originate Where Reverse Torque Loads Originate The ideal time to prevent reversal of a loaded inclined conveyor or elevator is at the very instant when forward rotation of the headshaft ceases. Even a small time lag before arresting the backward travel results in a greater effort needed to bring the inclined conveyor to rest and to hold the load. It is obvious that a reversed torque load, further reinforced by any accumulated backlash in the drive system, could result in the failure of any one of these connecting drive components when the reverse...

Recommended Backstop Locations for Typical Conveyor Arrangments Single Drive Pulley For head pulley driven inclined conveyors or elevators, the backstop should be located on the head pulley drive shaft. With the drive at one end of the head pulley shaft, the backstop should be located at the opposite end, away from the speed reducer and coupling. (See Illustration 7) For a single drive pulley other than the head pulley, the backstop should be located on the drive pulley shaft, rather than on the head pulley shaft. The head pulley may not have sufficient belt wrap to keep the loaded belt...

Principles of Backstop Size Selection for Low Speed Shafts In the past, the usual basis for determining the size of a backstop included only consideration of calculated lift and frictional loads. In some cases selection was made based on subtraction of all of the frictional load from the lift load to arrive at the net backstop capacity required. Backstops so selected could prove to be of inadequate capacity and could result in very serious and costly damage. More conservative selection was based on subtracting only one-half the frictional load from the lift load. Lift loads were also...

How to Select a Marland Backstop General Step 2 — Service factor to be used Ordering Information Backstop selection is based on stalled torque rating of the driving motor to provide for the conditions when overloaded motor "cut-out" may occur and the "stretched rubber band" effect of the stalled belt would react on the pulley to rotate it in reverse against the nonreversing backstop. Multiply the value obtained in Step 1 by the proper factor for the driving motor shown in Table B (factors are based on the maximum stalled torque percent of the normal motor rating). The result will be the...

Marland Backstops Type BC MA 3-18 1 Ball Bearing Outer Race Roller Assembly Clearance for axial positioning Grease pressure fittings See note N page 10 F Breather Filter Oil Fill Fitting Grease pressure fittings See note N page 10 Oil Level Indicator Grease Relief Fittings G Min. clearance to permit backstop to center itself when freewheeling Stirrup for end of torque arm by customer. Make brackets above and below torque arm sufficient for "L" loads. STIEBER GmbH Hatschekstraße 36 | 69126 Heidelberg | Fon +49 (0) 62 21.30 47-0 | Fax +49 (0) 62 21.30 47-31 | sales@stieber.de | www.stieber.de

Dimensions and Data The torque arm end must not be rigidly attached to steel framework. The bracket or stirrup for the end of the torque arm must provide clearance to permit the backstop to center itself in axial and angular positions to prevent pinching of bearings and damage or failure of unit, and must be sufficient for "L" loads above and below torque arm for backstop size selected. The preferred position is horizontal to reduce bearing loading for longer bearing life. Refer to certified drawings and instruction bulletins furnished with each order. Note: M - Backstop is symmetrical and...