Problems with Flexible Screw Conveyors: Finding the Best Setup

by Steve Simmons

So, you’re in the market for a flexible screw conveyor? Are you also wondering what the problems with flexible screw conveyors can be? Here at Spiroflow, we have been helping processors move materials for more than 45 years. The flexible screw conveyor (FSC) is the product that launched this company. It’s fair to say that we know FSCs pretty well!

We listen closely to our customers and do our best to solve any issues that come up. This article will examine the most common problems processors have with flexible screw conveyors and we’ll also talk about solutions.

Flexible Screw Conveyor Problems Caused During Install or Setup

The first item we’ll discuss involves the installation and layout of the flexible screw conveyor. If you’re not getting the results you expected, the FSC set up could be the problem.

Inspect the Conveyor Tube

Take a look at the conveyor tube. Is the tube straight? If a bend is needed, is that bend within your manufacturer’s radius restrictions? Is the bend smooth and gradual? If the radius is too tight, the spiral will be under extreme stress and will eventually break. It can also cause excessive wear. Are the inlet and outlet housings in line with one another? This minimizes the degree of the bend required to fit the layout and eliminates undesirable “S” curves, these create extreme stress on a spiral. The double curve puts the spiral in a real bind as it rotates.

Inspect the Conveyor Supports

Is the conveyor tube supported properly? Supports should be placed every 6 – 8 feet (1.8m – 2.4m) under normal conditions. If you are conveying dense materials supports should be closer together to keep the tube from sagging. As a guideline, supports should be rigid enough to support the weight of a full conveyor tube and to prevent the tube from swaying during operation. If you wonder why your spiral is breaking or tube is wearing out so quickly, the answer could be inadequate support.

Check the Drive Assembly Stability

Motor or drive assembly stability should also be examined if you’re having issues. Be sure to ask, “Is the drive assembly mounted rigidly? If the drive assembly moves too much, the spiral, tube, and steel housing components could be stressed and could lead to a system failure.

Check the Inlet Housing Setting

Another place to look if you’re encountering a flex screw failure is the Inlet housing setting. Be sure to ask if the inlet housing is adjusted properly? Communicate closely with your manufacturer. Ask about design options and possible add-ons. Also, ask how should the inlet housing be set?

Account for Spiral Stretch

Spiral stretch can lead to broken spirals or motor overload. It’s important that the spiral has room to expand under load or it could scrape the back of the inlet or restrictor cap and cause failure.

Why won’t my flex screw convey material?

A common issue flexible screw conveyor users may ask is, “Why won’t my material convey?” Here’s what to look out for.

Is the spiral turning in the right direction?

If you’re standing at the inlet end and looking toward the outlet, the spiral should turn in a counter-clockwise direction. If you’re at the discharge end and looking toward the inlet, the spiral should be turning in a clockwise direction. Correct rotational direction depends on the type of helix, left hand or right hand. Spiroflow and most manufacturers use right-hand helixes.

Is there adequate material in the hopper?

Flexible screw conveyors will not completely empty out. Even if there is some material in the hopper, it may not convey without an adequate amount of “head” of material.

Does your material rathole or bridge in the hopper?

If so, you can utilize flow aids such as an agitator, vibration, or bin aerators. Bin aerators are silicone or rubber discs inside the hopper that air is injected under from the outside. When air escaped from under the discs, they vibrate and aerate the material.

Check the Feed Restriction

Is the feed restriction opened up enough to allow adequate material into the spiral? If there isn’t adequate material being fed into the conveyor you may not attain your desired conveying rate.

Is the material fluidizing & falling back down in the tube?

Very fine materials can react like water inside a flex screw, often called a flexible auger. The solution for this problem is a full-length center core. Center cores also lighten the load when moving very dense materials. Running at slower speeds can also be effective on fluidizing materials.

Why is my Flexible Screw Conveyor locking up or failing?

Jamming, stalling, or locking up are other common issues our service technicians hear about. Several things can cause this.

The Spiral is Overloaded

Is the feed restrictor set properly? Overloading the conveyor can result in high amp draw or motor overload, motor damage, spiral damage, premature wear, etc.

Is your material ‘flexible screw friendly’?

Not all materials convey well in this type of conveyor. Cohesive materials or materials high in moisture can smear and cause the spiral to lock up. In some cases, a conveyor with a beveled spiral can convey those types of material. We always recommend having your material tested in a test lab so that you get the best type of conveyor for your application.

Check the Power Supply to the Motor

Lockout-Tagout (LOTO) the conveyor and try to turn the spiral by hand. If there is no obvious mechanical reason why the spiral will not turn, it could be an electrical issue. Check the controls to see if there has been a Variable Frequency Drive (VFD) fault or see if a thermal overload has tripped out. Refer to the VFD manual to troubleshoot the error code produced by the VFD. If the thermal overload is tripped, rest it, and try to source the cause of the overload.

Check Your Wiring

Check wiring to the controls and to the motor itself. Also, check the voltage supplied to the motor. Are you getting the proper voltage on all three phases supplied to the motor?

Do you have the right motor?

Is the motor/drive assembly sized properly? It could be that you simply don’t have enough horsepower for the conveyor to work under full load. Refer to the motor’s nameplate for its full load amperage limits and check the motor’s amp draw while under full load. If there are no physical restrictions other than the material being conveyed and the motor draws high amps, it could be undersized.

Why are my tubes & spirals wearing out so quickly?

Another issue customers may have is excessive tube and spiral wear. Most customers are aware of the abrasive nature of their material, but not all understand why their tubes and spirals fail frequently. Here are some causes of tube and spiral wear. By the way, we always recommend having a spare spiral and tube on hand to minimize any process downtime.

Abrasive Materials

Coarse sands, minerals, and sugar can be very harsh on tubes and spirals. Heavy-duty spirals are available and, in extreme cases, double wind spirals can be used. We often recommend stainless steel or rubber Rhinoveyor tubing as more wear resistant options over the standard UHMWPE tube. An undersized screw can also be placed in a conveyor to reduce tube wear. This allows more clearance between the spiral and tube allowing the material to act as a buffer between the two.

Tube Radius

The radius of the tube may be too tight. This can cause the spiral and tube in the arc area to wear out quicker than normal. As a general rule, you always want to keep the conveyor tube as straight as possible.

Heat

Heat can be a factor in tube life. A steel conveyor tube should be considered for materials hotter than 125-150˚F (51-65˚C). You should also consider the environment. Will the tube be subject to extreme ambient temperatures?

External Wear

Is the outside of the tube rubbing against anything? It is common for the flexible screw conveyor tube to move slightly during use. This constant swaying action could wear a hole from the outside if it is in contact with another object.

Spiral Fatigue

Spirals can become fatigued over time simply due to continuous use.

Welds

Improper welding techniques can also have an adverse effect on the spirals making them weaker. Welded spirals that are not assembled properly may cause the conveyor to be out of balance. This will cause excessive shaking and/or movement of the tube. It will also cause premature tube failure and put the spiral under excessive stress. Extreme cases of poorly assembled spirals can cause damage to the inlet and outlet housings too!

Problem Solved?

There’s a reason we have answers and solutions to these problems. We know a flexible screw conveyor is an important purchase that you rely on in your process. At Spiroflow we can pre-test your material in our test lab to make sure it’s suited for conveying with a flexible screw conveyor. We also have an expert staff of service technicians who work closely with our customers to make sure everything operates as promised.  If you need more help contact our service experts.

Preventing Problems

To avoid any of the issues discussed in this article you may wish to invest in installation supervision from your supplier’s service department. It’s always a good idea to have an experienced technician on hand to assist with the setup and installation process. If you are comfortable handling the installation with your in-house team, a reputable supplier should offer phone support during the installation. You may also wish to consider scheduling a startup and commissioning visit. What a good technician can see and correct during commissioning could save you thousands of dollars down the road. It also offers you in-depth onsite training.

A Flexible Screw Conveyor by any other name

Depending on where you are located and when you entered the industry you may refer to a flexible screw conveyor as a flexible auger, helix conveyor, helical conveyor, auger screw conveyor, screw auger conveyor, flex conveyor, flexible spiral conveyor, screw conveyor or spiral screw conveyor. Whatever term you use, we are here to help.

At Spiroflow, we have solved flexible screw conveying challenges for customers around the world. So if you need some help or advice contact us!