HOW TO

How to Increase Plant Production, 3 Types of Hoppers: Holding, Surge, & Gob Hoppers

An average 12-yard dry concrete batch plant has a typical theoretical production rate of 200 yards per hour. However, a batch plant can only produce as fast as the mixer truck will take the product. Depending on the truck, a typical mixer truck will charge at a rate of 165 to 185 yards per hour. The weigh up time for a dry batch plant is 1/3 of the overall batch time.

During the weigh up time the mixer truck will be idle under the plant until the start of the discharge of material. By incorporating discharge hoppers, the weigh batchers can be cleared sooner allowing the next batch to start while the current truck is being charged.

3 types of discharge hoppers:

Surge Hoppers are typically 3 to 4 yards in capacity and allow the aggregate on the transfer conveyor to collect if the mixer truck charge rate is exceeded. As the truck hopper begins to choke, incoming aggregate is surged into the surge hopper, and relieved into the mixer truck by gravity as the mixer pulls the material into the drum. By clearing the aggregate weight batcher faster, the next batch can be started sooner, increasing overall plant production.

Holding Hoppers are 12-yard capacity and should have separate hoppers for aggregate and cement. The individual weigh batchers weigh up and discharge into the individual holding hoppers. The holding hoppers are on separate scales which provide control of the discharge flow rate into the mixer truck. Mixer trucks are charged by the holding hoppers instead of directly from the weigh batchers. These hoppers allow the next batch to start and completely weigh up while the current batch is being discharged into the truck.

Gob Hoppers are used with central mix plants and allow the mixer to discharge the finished product into a hopper above the mixer truck. The truck is then fed the mixed material through the gob hopper versus directly from the mixer. This allows the plant to batch the next load into the mixer and begin the mixing process while the current batch is being discharged into the truck.

How to save time filling cement silo, the 2 factors

Two main factors come into play when reducing cement silo filling times, dust collection and blower CFM. Cement silos can be round or rectangular and are typically filled by a 4-inch or 5-inch fill pipe. High volume batch plants will often have two fill pipes per cement compartment.

The cement, slag, or flyash is transferred by a pneumatic blower, the blower size will determine the amount of cement that will transfer into the silo per minute. Although blower size is a key factor to speed, dust collection plays just as important of a role. If the silo is unable to expel the air being charged into the silo to move the material, the load time per minute will be drastically reduced.

Dust collection should be appropriately sized to handle the CFM of the blower being used to transfer the material. It is important to know the manufacturer’s specifications before purchasing a new dust collector or a new blower. Buying a larger blower with higher CFM than your existing dust collector can handle will not increase loading speed.

850 CFM – Typical truck mounted blower
1,250 CFM – Typical 60HP blower
1,800 CFM – Typical 75HP blower

Under sizing the silo dust collector will not only reduce loading speed, but may lead to bigger problems. Typical cement silo is capable of handling 3 PSI of pressure. If you over pressurize the silo and the emergency pop-off valve fails, the silo could get damaged or even split the silo.

4 Steps to Conveyor Belt Tracking — It doesn’t have be painful

Conveyor belt tracking can be frustrating. The key is to start with all of the conveyor components square with the conveyor frame. Ensure the tail pulley and head pulley are squared, as well as all of the return and troughing idlers. In most cases the troughing idlers center the belt on the head pulley and the return idlers center the belt on the tail pulley. The tail pulley should only be used for tension of the belt and not to track the belt.

OPERATING AND TRACKING CONVEYOR BELT

A) Before starting the belt conveyor, make sure all debris, tools and temporary bracing are clear of the belt. Caution should be exercised at all times around machinery, this is especially true when starting equipment for the first time.

B) If the belt has a tendency to run to one side or the other, it should be steered back on center in the same manner as you would steer a car.
C) While looking in the same direction as the belt travels (up the belt), all corrective action to center the belt is accomplished in the following manner:

1) If the belt tends to run to the right side, it would then require a left turn to return it to the center. Alignment should be started at the point where the turn starts. The right end of the return idlers should be pushed forward slightly or the left end should be pulled back slightly. Continue along the belt in the direction that the belt travels until the belt is centered. It is far better to move several idlers slightly than to move a few a large amount.

2) If the belt runs to the left side, the same principle is applicable, except you push the left side forward and/or pull back the right side.

3) If for some reason any of these steps cannot be completed, the alignment can be accomplished by tilting the idler slightly forward, taking note not to exceed a 2 degree tilt angle from vertical in the direction of the belt travel. This can be accomplished by placing shims under the backside idler mount bolt holes. This 2 degree limit is to avoid excessive belt wear.

4) The return idlers should be used for belt centering in spite of their flatness. Move return rolls forward and backward in the same fashion the troughing idlers were moved.

Tip: A un-squared belt splice can also throw you off, but you will easily see this problem when you start running the belt.