Non-mass flow

A different proach is used to reflect the shearing of end supports for an arch over a non-mass flow hopper outlet. In this case, the principal stress causing the arch to fail is generated by the weight of product supported over the opening. For this purpose a vertical shear-type test is conducted, see Fig. 1.5. For all such tests, the condition of the sample must reflect the loading conditions experienced by the material in the situation under consideration. Many bulk materials exhibit long-term variations of condition, and may be... 

Fig. 5.2 Non-mass flow, self-clearing hopper (funnel flow)...

In practice, flow is either mass flow, or it is not. Describing the basic flow pattern as either mass flow or non-mass flow removes all grounds for confusion. It is proposed that these should be preferred expressions in the description of pattern of flow behaviour in storage containers. 

Proven design guarantees reliable flow Flow rate is less than non-mass flow with same outlet... 

For mass flow hopper applications, these features limit the effective length of screws that vary in pitch only, to about five or six screw diameters. For non-mass flow applications, pitch changes are a useful means to reduce power and secure an improved extraction pattern, and much longer exposed sections of screws can be used. These benefits may not be essential, but offer advantages by avoiding excessive dead zones of storage. 

Progressive extraction at the screw feeder inlet is not essential for non-mass flow installations and applications where the container is totally empties before being refilled but is useful to provide at least a degree of progressive extraction on long feeder screws to reduce the drive power requirements and avoid extended length of dead material over the outlet slot. 

Mixed flow , i.e. where the non-mass flow channel expands to the container walls below the stored surface level. This can appear to be mass flow, but is not generated kick stresses on the walls at indeterminate locations. 

A further drawback of this construction is that it is not convenient to have a taper outlet slot on a container so the practice is to slope the feeder casing from the screw diameter to a parallel hopper outlet size that matches the largest diameter of the screw. All most invariably, this results in a casing wall inclination at the smaller end of the feeder that is inadequate for product slip. In combination with the gap at the side of the screw to the casing wall that fills with static product and opposes wall, the effect is to create a narrow flow channel with non-mass flow characteristics. The economics of manufacture also detract from widespread adoption of this technique as both the screw and the casing have taper components that demand extra fabrication time. 

Design for mass flow Design for mass flow or non-mass flow or non-mass flow... 

There are a number of ways to feed an air-assisted gravity conveyor. The most common feed method is simply a flood feed from a mass flow hopper. A non-mass flow hopper may cause problems with inconsistent feed which may result in blockages. That is, if too much material is fed onto the conveyor, then there will be insufficient air to fluidise the material, and if too little material, or none at all, then conveying may halt due to a maldistribution of air from the plenum chamber. While an air-assisted gravity conveyor does not work independently as a feeder, if the bulk solid is metred onto it by the use of a screw feeder or rotary valve, it will then convey this material at a constant rate. Another method of controlling the flow of material is to use a gate or baffle at either end of the conveying duct. 

The most serious is probably the separation of additive pellets during flow from side to centre in a non-mass flow hopper. 

The yellowness of the bottles varied over time, becoming very intense for short periods. It was found that the steel drum, with the vacuum loader pipe pushed down inside the pellets, behaved for periods as a non-mass flow hopper with yellow masterbatch pellets separating around the pipe entry until a point was reached where an accumulation of yellow masterbatch pellets was loaded. The answer was to vacuum load the natural pellets into a proprietary dosing/mixing device mounted on the extruder. 

The above pattern relates to a sequence of total discharge following a total fill. The behavior is more complicated when more material is fed into the container before the original load is fully discharged. In these circumstances the state of deposition is highly dependent upon the surface profile of the original material at the time that further content is added, and also to a more dramatic extent to the relative rates of fill and discharge if they occur simultaneously. In a non-mass flow container, the smface profile almost invariably adopts the form of a drained repose cone . 

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