Product Description

We offer a full range of engineered solutions; from sizing a conveyor to meet the required capacity of a simple conveyor all the way to 3-D failure analysis of the most complex press screws.. All screw components are verified using computer-aided design calculations and our standards are tighter than the industry standard.

Design Step 1 - Conveying Requirements
To properly design a conveyor to meet your needs it is important to know several parameters surrounding the application. Fortunately, to begin you only need to know a few.

These are:

• Type of material being conveyed
• Required flow (lbs per hour or cubic feet per hour)
• Distance material is going to be conveyed

Design Step 2 - Identifying Material and Material Code
The type of material being moved can have a significant affect on the size and type of conveyor. The following charts will help classify your material and will help in selecting the proper conveyor components.

For screw conveyor design purposes, conveyed materials are classified in accordance with the codes system show in Table A. This system conforms to that of the Conveyor Equipment Manufacturers Association (CEMA) which ranks each material in five categories. Table B lists the codes for many materials that can be effectively conveyed by a screw conveyor. If a material is not listed in Table B, it must be classified according to Table A, or by referring to a listed material that is similar in weight, particle size and other characteristics.

Special Materials and Applications

Design Step 3 - Determine Capacity, Size and Speed
In order to determine the size and speed of a screw conveyor, it is first necessary to establish the material code number and design capacity. In Step #2 you identified the material code number, the following will illustrate how this code number determines the cross-sectional load of the conveyor that should be used. For applications where special types of screws are required; such as short pitch screw, cut flights, cut and folded flights and ribbon flights, a design capacity must first be calculated. The design capacity is found by mulitplying the required capacity by one or more of the capacity factors that are involved. See Table C, Table D, Table E and Table F for capacity factors.

Design Capacity Calculation:
           Design Capacity = Required Capacity x Capacity Factor(s)

Speed of Conveyor (rpms)
           Speed = Design capacity / 1 rpm capacity

The "1 rpm capacity" and the "maximum recommended speed" can be obtained from Table H

Table C: Maximum Lump Size

Table D: Flight Factor

Table E: Pitch Factor

Table F: Ribbon Factor

Table H: Conveyor Size and Speed

Design Step 4 - Calculating Horsepower
The horsepower required to operate a horizontal screw conveyor is based on proper installation, uniform and regular feed rate to the conveyor and other design cirteria. The following factors determine the horsepower requirement of a screw conveyor operating under these conditions.

Dc = Design capacity in cubic feet per hour
e = Drive efficiency ( as a decimal Table G)
Fb = Hanger bearing factor ( Table K )
Fd = Conveyor diameter factor ( Table J )
Fm = Material Factor ( Table B )
Fo = Overload Factor ( Table L )
L = Total Length of Conveyor
N = Operating Speed in rpm
W = Weight of material conveyed in lbs/ft3

The horsepower requirements is the total of the horsepower to overcome the friction (HPf) of the conveyor components and the horsepower to transport the material (HPm) multiplied by the overload factor (Fo) and divided by the total drive efficiency (e), or:

L N Fd Fb                                  Dc L W Fm                                     (HPf + HPm) Fo
HPf  = -----------------                 HPm  =  -----------------------              HPtotal  =   -------------------------
           1,000,000                                   1,000,000                                                  e

It is a generally accepted practice that most power transmitting elements of a screw conveyor be sized and selected to safely handle the rated motor horsepower. If, for example, a screw conveyor requires 3.5 horsepower as determined by the above formula., a 5 horsepower motor must be used, and it is desirable that all the power transmitting elements be capable of safely handling the full 5 horsepower.

Design Step 5 - Determine Size of Components
To properly select the screw conveyor components for a particular duty, they are broken down into three component groups. These groups relate both to the material classification code and to the screw size, pipe size, type of bearings and trough thickness.

The following service tables are a guide to proper selection of the appropriate component group for the material being conveyed. Other componentsare then selected from the Components Section of this catalog to suit the physical layout of the conveyor.

The components shown in the tables below are the types most commonly used for each of the component groups shown. However, special applications and certain environments require special consideration that may not fall within the same parameters (see special materials and applications).

Light Service (Groups 1A,1B,1C)

Heavy Service (Groups 2A,2B,2C,2D)

Extra Heavy Service (Groups 3A,3B,3D)

Design Step 6 - Check torsional ratings and screw deflection

Torsional Rating
Screw conveyors are limited in overall length and size by the amount of torque that can be safely transmitted through the components selected. The shafts, bolts and pipe all need to be sized appropriately for the drive horsepower and rpm.

Table M combines the various torsional ratings of bolts, couplings and pipes so that it is easy to compare the torsional ratings of all the stressed components of a standard screw conveyor. The table conforms to the CEMC design standards (often more conservative than CEMA standards).

The lowest torsional rating figure for any given size of coupling will be the one that determines how much horsepower may be transmitted. The torque produced (TQ) from the drive of the conveyor is a function of the size of the motor (HP) and the speed of the conveyor (rpm).

63025 x HP
Torque, TQ = ----------------
rpm

Deflection
It is also important to check the screw conveyor for deflection. The amount of deflection the pipe of the screw experiences due to the weight of the screw is directly related to teh useful life of the pipe. Deflection of the conveyor screw of standard length screws is not usually a problem. However, if longer than standard sections of screw are to be used without intermediate hangers, care should be taken to prevent the screw flights from contacting the trough. Deflection should be held to a minimum to increase the useful life of the screw.

The deflection at the mid span of the screw can be calculated from the following formula:

5 W L 3 Where W=Total screw wgt in lbs

D = ----------------------- L = Screw length in inches

384 (2.9 x 107) I I=Moment of Inertia of Pipe (Table N)

As a rule of thumb, applications where the calculated deflection exceeds 0.17 inches should be refered to our Engineering Department for recommendation.

Note
When screw deflections become excessive, additional stresses are applied to component parts. These additional stresses may result in fatigue and lead to early or premature screw failure.