The question is, without a feeder can you provide a regulated feed from a hopper full of material. My answer would be occasionally YES, but mostly NO.

In order to get a consistent flow rate controlled by aperture when you need a consistent material and that's highly unlikely unloading ships of various materials on the dockside.

So if you want a controlled rate you will need a feeder at the hopper outlet. I would suggest a single direction feeder to avoid any reversing problems under the hopper followed by a reversing conveyor to get to your two discharge points without any requirement to extract from the hopper.

Others may have different ideas. ■

Forgive the question, but are you using a true apron feeder?

For all intents an purposes it sounds like you mean a flight conveyor which uses chains and steel flights to convey material along a sealed bed floor.

An apron feeder does not have chains to move material as the mass flow is created by the motion of the steel tread used as part of the apron floor which is continually moving.

A true apron feeder has no leaks as the dozer pads interlock to provide a continuos flat surface and reduce any chance of spillage with skirting and any dust is very fine and falls off the treads when under motion as they travel under the hopper it is discharging.

The statement about pans is and backbending the chains is misleading and disturbing as a true apron feeder has a flat bed which rides on a stationary suspension with a pair of driven sprockets and a pair of passive spockets plus the carrier rollers and is tensioned with a pair of worm screws in most cases. The apron feeder is wider than the opening of the silo/ bin and skirting is used to prevent spillage out the sides of the hopper across the apron while operating.

If you are dumping this tonnage on a flight chain conveyor that in itself is a huge problem as shock loading on the chains and flights is a given.

If you used the even the simplest design of apron feeder from Pettibone or NICO and operated in one direction only you will solve this as the mass flow is regulated simply by apron speed and a single gate (in our case) and it ran for 23 years before the new screenplant was commissioned.

an apron feeder can be operated with hydraulics using Hagglunds units as an example with radila piston motors and a wide apron bed which is engineered for heavy load impacts.

An apron feeder does not allow material to become jammed or pass through as there is no space for the material to collect.

A flight conveyor will allow material to become jammed if the flight chain is not contained using shoe plates to keep the flight chain in "track" AND if the proper tension is not maintained on the flight chain which goes hand in hand with the proper maintenance of flight chain sprockets.

Even the longest narrow 24 inch wide apron feeder will allow excellent control of flow and materials no matter the type of ores in one or both directions

but the caviat is that more wear will occur and you will be required to have a drive system that will require more work and expense to create a dual direction feeding system.

You really do not need a two way directional system if you are starting from scratch and irs just another expense which is not required in my opinion ■

Originally Posted by lzaharis

but are you using a true apron feeder?

Answer YES I think.

Originally Posted by lzaharis

it sounds like you mean a flight conveyor which uses chains and steel flights to convey material along a sealed bed floor.

Answer NO I think (drag/scraper/flight machines don't have PANS).

Originally Posted by lzaharis

A true apron feeder has no leaks as the dozer pads interlock to provide a continuos flat surface and reduce any chance of spillage with skirting and any dust is very fine and falls off the treads when under motion as they travel under the hopper it is discharging.

This depends on the design of the pan, how well they were made and if they have become damaged in service.

Originally Posted by lzaharis

If you are dumping this tonnage on a flight chain conveyor that in itself is a huge problem as shock loading on the chains and flights is a given.

Beg to differ on the use of "huge problem".

Originally Posted by lzaharis

If you used the even the simplest design of apron feeder from Pettibone or NICO and operated in one direction only you will solve this as the mass flow is regulated simply by apron speed and a single gate (in our case) and it ran for 23 years before the new screenplant was commissioned.

So currently he's stuck with with an apron feeder with bi-directional operation. ■

When in doubt I always refer to my Stephens-Adamson catalogue (copyright 1941 ). Tells me lots of things, including their pans only travel in one direction.

Attachments

apronpans (PDF)

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If that is the case and he is not using an apron feeder with dozer tread aprons

Ay Caramaba!!!!!!!!

Even the smallest width apron feeder plate feeder the length of the hopper would be a night and day difference.

there are a handfull of manufacturers of apron plate feeders

MMD sizers and metso are two of them. ■

Hello

Please let me know, is it necessary to have a feeder at the hopper otlet if we don't want to control the discharge rate of materials?

Also, if we want to have a fix discharge rate of material what can we do?

thanks ■

A belt feeder would seem the most suitable form of equipment, with a few special features. The key to this situation is the primary need to secure reliable, controlled flow from a hopper that has to hold a range of bulk materials, with very variable flow properties. The starting point is the hopper geometry. Time consolidation or variable residence time of storage would not seem to be an issue, but a plane-flow, mass flow outlet region would have benefits in securing reliable flow through the smallest cross section of outlet, and thereby minimise feeder loads and offer best prospects for a reversible direction feeder. Some experienced judgement is required for this part of the exercise, as an assessment must be made of the largest ‘critical arching dimension’ that may be experienced from the different materials that are to be handled, and check that the orifice size so selected can accommodate the high discharge rate needed with an acceptable belt speed.

A variable width hopper outlet is not appropriate because of the reversing requirement, but a variable bed depth is quite feasible using hinged flaps at each end of the outlet and an inverted weir in the centre. ‘Rocking’ side skirts set slightly back from the side clearance, which are activated by the side pressure of the material in transit according to the direction of conveying, would complement the variable bed depth of extraction by allowing a degree of transverse bed expansion.

Impact loading should be avoided be diverting the in-feed stream to the hopper walls or fitting deflector plates to disperse the deposit of grab loads. Generous gully angle inclination with corner shedders will encourage clean emptying, or preferably plane flow construction at each level, as this would obviate any liability for ‘ratholing’.

The application appears ripe for a little imaginative design based on bulk technology fundamentals. ■

Hello,

As said earlier by respondent, you can not achieve or control finite flow by varying flow opening at hopper outlet (or in discharge chute of the hopper). So control gate (i.e. actually flow opening control gate) can not replace feeder.

Firstly, apron feeder is right type of feeder, because it is strongest compared to others. The 50 tonne grab will discharge the material at about 2.5 to 3 m height above hopper opening. Then hopper depth is likely to be at least 6 to 7 m (or more). When the hopper is empty the material will hit the feeder with velocity equal to squareroot of (2 x g x h) i.e. squareroot of (2 x 9.81 x 10) i.e. 14 mps (50 kmph). In my opinion robust apron feeder is the right equipment. Then you can have reversing belt conveyor (slow speed and full skirt board) as mentioned by you.

Aumund Germany makes belted apron feeder (as I know from their leaflet). Primarily it looks like strong slat conveyor fitted with belt on external face of steel slats. You may enquire whether their equipment can suit such abnormally high impact. If lumps are small, impact condition will get diffused and mostly create even pressure (of high value) but may be without localised denting / damaging action. A pair of cross beams in hopper, at some 2 m depth from top of hopper can retard the flow and impact velocity.

You can also contact supplier of the ship unloader for modification, in case it is possible.

Regards,

Ishwar G. Mulani

Author of Book: Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book: Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Kind.Attn jos,

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+919505175566

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Originally Posted by JvdLeer

Hello,

I like to know if somebody has experience with self unloading hoppers/continuous flow gates. At the moment we use apron feeders as discharge system for the hoppers of our shipunloaders. The hoppers have a capacity of 160tons. Ships are unloaded by grabs with a capacity of 50 tons. Grabs are discharged in a hopper.

Apron feeders has a capacity of 5000tons/hour. Because of the high maintenance costs and downtime of the apron feeders we are searching for another solution.

Most of the problems are caused by operating the apron feeders in two directions.

By pushing the upper part of the apron feeder the chains are backbent. Because the pans have only an overlap at one site the material can flow between the pans when the feeder operates in the "wrong direction".

We have two possible solutions:

The use of a apron feeder wich will operate only in one direction. This apron feeder will discharge to a conveyor belt which can operate in two directions.

The use of a conveyor belt which can operate in two directions and which is fed by a continuous flow gate (same as used in self unloading bulk carriers). The conveyor belt is placed on four loadcells. A control system will regulate the opening of the gate depending on the weight of the cargo on the belt.

The last solution is a simple system resulting in less maintenance costs but I wonder if this is the right solution. Because we discharge a wide diversity of coal and iron ore with different lumpsizes and flow properties I wonder if it is possible to control the flow rate. What about bridging, clogging etc.?

Kind regards,

Jos

Added by Moderator:

Heavy Duty Apron Feeder

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