Screw Conveyor Design

The intake of a screw conveyor is generally connected to rotary valves, conveyors, screw feeders, or even additional screw conveyors.

Like screw conveyors, screw feeders or feeders are constantly flood-loaded or full in the entering section.

Factors Influencing Screw Conveyors Design

The Material Classification Code Chart lists typical characteristics of the granular particles to be transported, such as abrasiveness, corrosiveness, and flowability. To choose the best machinery for the intended purpose, it is crucial to understand and carefully examine these characteristics when designing screw conveyors.

Abrasive Particulates

When carrying abrasive grains, screw conveyor compositions may experience extreme wear and strain due to the design of the screw conveyor. As a result, various screw conveyor design types are best suited for abrasion-resistant metals.

The trough of the screw conveyor accumulates and hardens certain transporting materials. They also have the propensity to absorb moisture and pack tightly. The better the ability to prevent build-up incidents in the trough, the closer the space between the trough and the screw. Additionally, a high screw conveyor torque is required to cut through the hardened particles, which is all considered while designing the screw conveyor.

Generation of Static Electricity

Static electricity can be produced throughout the conveying process as the screw augers rotate and shake the bulk materials. Therefore, it is strongly considered when designing to ground the screw conveyor's trough. It may effectively eliminate static electricity by grounding the trough in several places. In addition, lowering the trough loading and the screw conveyor speed can also be very beneficial.

Flammability

Flammable and explosive materials will burn whenever oxygen and ignition sources are present. Screw conveyors should be made of non-sparking materials to stop the appearance of ignition sources. The tight troughs or housings of screw conveyors outfitted with shaft seals are also necessary to keep oxygen outside the machine. The design maybe is aided by filling the inside of the screw conveyor with inert gas, such as nitrogen.

The following properties of the transported bulk material directly determine the design of the conveyor size, speed, and horsepower requirements:

• Maximum particle size
• Bulk density
• Trough loading
• Material factor

Screw Conveyor Design

To design the screw feeder's size and capacity, the screw conveyor's needed capacity and the material should be known at the start; however, the screw size and properties may be unknown.

The following formula can be used to estimate the capacity of the screw conveyor, which has a standard screw flight:

Q= 60 × π⁄4 × D²×S×N×α×ρ×C

In this formula:

• Q = Screw Capacity in kg/h
• D = Screw Diameter in m
• S = Screw Pitch in m
• N = Screw speed in rpm
• α = Loading ratio
• ρ = Material loose density kg/m3
• C = Inclination correction factor

Step 1: Define the Requirement

• The requirement is defined after specifying the screw conveyor's needed capacity.
• The screw's design must have a capacity equal to or greater than this figure.

Step 2: Calculate Capacity of the Conveyor

• Assume the diameter (D)
• Define the screw pitch based on the diameter of the screw

Pitch	Pitch Length S
Standard	S = D
Short	S = 2/3 x D
Half	S = D/2
Long	S = 1.5 x D

• Estimate the screw's loading ratio based on the characteristics of the material to be conveyed.

Material	Min Loading Ratio	Max Loading Ratio
Not free-flowing	0.12	0.15
Average flowability	0.25	0.30
Free-flowing	0.4	0.45

• Values may be higher or lower than average; in extreme situations, the loading ratio may even be higher than 95%.

Step 3: Compare Calculated Capacity to Max Screw Speed

The table below lists a few examples of reference maximum screw speed to be used during the design:

Screw Diameter in m	15%	30%A	30%B	45%
0.1	69	139	69	190
0.15	66	132	66	182
0.23	62	122	62	170
0.25	60	118	60	165
0.30	58	111	58	157
0.36	56	104	56	148
0.41	53	97	53	140
0.46	50	90	50	131
0.51	47	82	47	122

The design can be maintained if the speed estimated in step 2 is less than the maximum speed allowed for the chosen screw diameter. However, suppose the calculated speed at step 2 is greater than the maximum speed for the screw diameter chosen. In that case, the design is unsuitable, and the calculation must be repeated by altering a parameter (often the diameter).

Step 4: Power Calculations

P= P_H+P_N+P_St

P_H is the power required to move the material in the conveyor horizontally.

P_N is the power required to operate the unloaded screw.

P_St is the power required for an inclined screw conveyor.

Choosing the Proper Screw Conveyor Design Company

To make sure you have the most productive outcome when selecting a screw conveyor design company, it is important to compare at least 4 companies using our screw conveyor design directory. Each screw conveyor design company has a business profile page that highlights their areas of experience and capabilities and a contact form to directly communicate with the company for more information or request a quote. Review each screw conveyor design company website using our proprietary website previewer to get an idea of what each company specializes in, and then use our simple RFQ form to contact multiple screw conveyor design companies with the same form.