Rusmail has designed and installed many inclined powered belt conveyors for moving unit loads between floor levels. Pic 1 shows a typical mezzanine floor conveyor installation. Although it is a frequent handling application in warehousing and storage facilities, it is essential that each conveying project is evaluated in detail to ensure the conveyor and its associated controls are correctly designed and specified to achieve safe and reliable operation.
|1. Typical Mezzanine Floor Conveyor with Power Feeder Belt at Bottom|
In developing the right conveyor design and specification it is important to consider the following:
1 - Product Characteristics – Pic 2 illustrates a mezzanine floor conveyor handling large cardboard boxes. Unit loads may be in the form of boxes or similar containers or individual components, not necessarily boxed or packaged. The characteristics of the load to be conveyed need to be considered as a fundamental part of the design process. For example, the shape and orientation will dictate the stability of the load being conveyed, which is critical on an inclined belt. If it is unstable it is unsafe and may need to be placed on a suitable base or in a suitable container. The surface of the load needs to be compatible with the belt surface to avoid sliding down the belt. Items which are more difficult to handle are boxes with smooth, shiny bases or with plastic wrapping around them and plastic crates or boxes with smooth or uneven bases. If there is any doubt how the load will be conveyed, trials are recommended before starting to manufacture the conveyor.
|2. Large Boxes on Mezzanine Conveyor: Note Power Feeder Belt and Shrouded Control Box|
2 - Belt Selection – For inclined belt unit load conveying applications it is usual to use a “grip top” belt i.e. a belt surface that will “grip” the base of the load being conveyed. There is a wide range of such materials available including rubber, various plastics and different surface patterns providing a high level of grip. Belt manufacturers have a significant range of materials and data and provide detailed technical specifications for their products. These need to be studied carefully to select the right belt for a particular application and compatibility with the site working conditions – temperature, humidity, dust etc. In addition to the different material and surface options, other means can be adopted to reduce load slippage e.g. flights/cleats or ribs can be attached to the belt, to positively support the load to be conveyed. Pic 3 shows a flighted belt on a mobile inclined conveyor. This type of belt would require the load to be placed between the flights/cleats or ribs in a controlled manner. Alternatively stop devices may be placed behind each load to reduce slippage, but they would need to be removed at the top end and returned to the bottom for reuse. This extra operating time and effort may not always be acceptable to the operator.
|3. Inclined Flighted mobile mezzanine conveyor with approx. 60 Deg Incline Angle|
3 - Incline Angle – The unit load characteristics and the belt material specification govern the choice of incline angle. The steeper the angle the smaller the foot-print of the conveyor and floor space is generally at a premium, but the angle cannot be set such that the load topples or slides down the belt. As a guide, most unit load applications operate safely with an incline angle between 25 to 30 degrees. When handling plastic tote boxes this angle may have to reduce to 20 to 23 degrees and plastic bagged items at around 18 degrees. If space is a major concern, in many cases an incline up to 30 degrees may be acceptable, but beyond that it would probably be necessary to use a flighted/cleated/ribbed belt as in Pic 3 and then angles of up to 60 degrees may be achieved depending on the size and shape of the load. The change in conveyor foot-print for changes in the incline angle is a simple design calculation. If in any doubt, trials should be carried out to verify the optimum angle for the specific application.
4 - Load Capacity/Speed – Unit loads of up to 25Kg are quite normal and inclined belt conveyors are readily available to handle this size of load and a spread load capacity of 150Kg (UDL). Pic 4 shows a typical 150 Kg (UDL) conveyor. Heavy duty unit load conveyors are available for more arduous applications involving unit loads of up to 100Kg and a spread load of up to 750Kg (UDL). Pic 5 shows a typical 750 Kg (UDL) conveyor. Generally inclined belt conveyors for unit load applications operate with a belt speed at around 18m/min and can operate as fixed speed or variable speed units.
|4. Typical 150Kg (UDL) Mezzanine Floor Conveyor: Note High Side Guides and Power Feeder Belt|
|5. Typical 750Kg (UDL) Mezzanine Floor Conveyor: Note High Side Guides and Photo sensor at Bottom|
5 - Mechanical Design Considerations – Floor-to-floor belt conveyors should normally be fitted with a level powered belt section at the bottom feed end to assist the transfer of the load on and off the incline belt. Safety side guard rails to suit the size of load and underguarding should be fitted to the conveyor. The drive for the feeder belt is achieved with the use of a chain connector and sprockets fitted between the main belt and the feeder belt. This approach is highly recommended for a 2-way reversing conveyor. If a gravity roller section is used at the bottom end, when a boxed unit load is moving downwards, the corners will catch in between the rollers and may cause a blockage. At the top end, gravity rollers or ball tables may be used or the belt conveyor may be extended to incorporate a “nose-over” or “swan neck” section. This provides a smooth, quiet transfer of products. For 2-way conveyors an under slung “centre drive” motor is strongly recommended and would normally be rated between 0.55 and 1.5kW for the unit load capacities stated above. For heavy loads a braked motor is recommended. For 1-way operation an end drive arrangement is acceptable. Belt conveyors have been designed and installed to successfully handle bulky products such as mattresses, for example, at 2m width. The usual floor-to-floor height is in the region of 2 to 3m, but a recent installation had a height of almost 6.5m. Pics.6, 7, 8 illustrate the features just described. In addition to stationary units, mobile inclined belt conveyor units are available and have been designed with an adjustable height feature to give extra operating flexibility when needed. Pic.9 shows a typical mobile, adjustable height conveyor.
6 - Electrical Design Considerations – Inclined belt conveyors are operated from a 1 phase or 3 phase electrical supply with a fixed speed or variable speed using an inverter. Generally forward/reverse/stop controls and emergency stops are fitted at bottom and top positions. For safety reasons and for two-way, one man operation, photo sensors are recommended to stop the conveyor when products reach either end. It is recommended also to incorporate an auto-restart feature which automatically restarts the conveyor when products are removed. The positioning of the controls will depend on the location of the conveyor and can be mounted on the conveyor or an adjacent wall or support post. Control switches should be shrouded to avoid damage by passing plant and equipment such as fork lift trucks etc. Pics. 2,5 and 6 show these features.
7 - Conveyor Location Considerations – It is generally more space effective to locate the conveyor along a wall. Often a mezzanine floor belt conveyor will need to go through the floor and will require an opening to be cut in the floor. In this case due allowance must be made for the height of the load on the conveyor plus a suitable clearance between the top of the load and the underside of the mezzanine floor. Guard rails would need to be fitted around the floor opening for operator safety. If a conveyor is accessible from both sides i.e. an “island” unit it may be necessary to fit controls on both sides. For safety reasons it is wise not to allow storage of anything under the conveyor and to maintain clear access around it. Support legs may need to be protected against possible damage by passing handling equipment such as fork lift trucks etc. Pics 2,10 and 11 show some of these features. If this type of conveyor should be installed outside it should be covered and protected from water or ice conditions. Galvanised steel or stainless steel construction is recommended for conveyors for outdoor locations whether covered or not, and electrical equipment should be specified to be suitable for the relevant site conditions.
|10. Conveyor Mounted Alongside Wall for Minimum Space|
|11. Mezzanine Conveyor Through Floor with Safety Guard Rails Around Opening|
We also refer to a recent article in The Chemical Engineer, issue 873, March 2014 on Slips, Trips and Falls as it is important relative to high level conveyors and overhead conveyors, both requiring extra care and attention during installation and maintenance. We suggest you visit www.tcetoday.com for more details.
8 - Health & Safety – Every conveyor installation must be designed with safe operation in mind. The basic conveyor and all associated equipment and controls must conform to relevant standards. During installation every effort should be made to ensure the installation team work in safe conditions as floor-to-floor conveyors will require high level working. On completion of installation each and every conveyor installation should display a prominent Health & Safety Notice adjacent to the conveyor for all Operatives to see. Proper training of Operatives by the conveyor Supplier is essential for each conveyor installation and is often a specific requirement by the Operator’s Insurance Provider
The use of inclined powered belt conveyors is a well-established application for the continuous movement of unit loads between floor levels and is an efficient and cost-effective solution to this handling problem. It is essential, however, to fully consider the design criteria for each project to ensure the conveyor or conveyor system is properly specified to achieve a safe and reliable installation for the user.