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Purvis Industries

Pulley Lagging

Posted on Wednesday Nov 06, 2019 at 03:09PM in Belting & Conveyors

Article By: Billy Witherspoon

Strategic Business Manager

One of the most often overlooked/neglected components of a conveyor system is Pulley Lagging.  

Pulley lagging is a covered/coating over the surface of either a driven or non-driven pulley used as a wear surface and/or friction layer. Typical conveyor pulleys are made of a steel outer shell with end discs welded in each end to allow for mounting to a conveyor shaft, with numerous choices on mounting options. Lagging is added to the steel outer shell of the pulley, providing a replaceable wearing surface for non-drive pulleys. For driven pulleys lagging is typically made to increase the friction between the pulley and the belt being driven, with the added benefit of being a replaceable surface. Lagging comes in many rubber and non-rubber compounds, multiple surface patterns for varied applications and needs to be chosen based on the application for best results.


Increasing the friction at the drive pulley allows your conveyor to run at less overall tension, increasing belt life, as well as, bearing and component life.  Proper lagging can eliminate belt slippage in wet and frigid conditions preventing “Burn Throughs” (Pulley spinning due to loss of friction will burn through the bottom of the belt).

Pulley Lagging can be purchased already applied to a new pulley direct form the manufacturer or there are numerous aftermarket options.  We stock and can provide installation on multiple aftermarket lagging products.   High Tensile strength rubber with Diamond pattern or Flat surface can be bonded to your existing pulley either in our shop or on your conveyor.  In areas where you need more friction we can provide Rubber lagging with Ceramic inserts that provide more friction and wear resistance. Weld-on “Slide Lag” is also available.  Whatever your application requires, we have you and your pulley Covered!

Backdriving A Gearbox

Posted on Monday Oct 28, 2019 at 08:29PM in General

Where Self Locking is the inability to drive the output shaft of a gearbox, backdriving is the ability to drive the output shaft.

This essentially makes the gearbox become a speed increasing device.  This can be done intentionally or unintentionally and can occur in various ways.  Backdriving can occur when the applied load overcomes the frictional resistance or holding power of the rotating elements in the gearbox, causing the output shaft to speed up.  This is more common in lifting and inclined applications because gravity assists the force pulling the load down.

A gearbox that is backdriving may cause the motor to overspeed, which may lead to damage to the gearbox, motor or other system components. 

Intentionally using the gearbox as a speed increaser will also cause backdriving.  Not all worm gears can be backdriven because of their tendency to lock when driven in reverse rotation.  Worm gear sets generate more heat than other gear types due to the amount of sliding friction produced while rotating.  Spur and helical gears are commonly used as speed increasers.  Under a backdriving or speed increasing operation, increased noise and temperature levels may become undesirable. 

If an application has a sufficient amount of reverse momentum that may cause the load to overhaul the frictional resistance of the gear set in a reducer, a “backstopping” or “one direction” mechanical clutch should be used to prevent backdriving.  If the application requires the speed to be increased, carefully review and select a gearbox suitable for that type service. 

Screw Conveyor vs. Screw Feeder

Posted on Wednesday Jul 31, 2019 at 04:03AM in Belting & Conveyors

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Bulk Material Flow Control Gates (Part 2)

Posted on Thursday Apr 11, 2019 at 04:46PM in Belting & Conveyors

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Bulk Material Flow Control Gates (Part 1)

Posted on Thursday Apr 04, 2019 at 05:25PM in Belting & Conveyors

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Bucket Elevators

Posted on Wednesday Mar 13, 2019 at 04:19AM in Belting & Conveyors

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Posted on Friday Mar 01, 2019 at 06:01AM in General

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VFD Stopping Techniques

Posted on Tuesday Jan 29, 2019 at 06:12PM in Electrical

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Let's Start Something

Posted on Friday Jan 04, 2019 at 02:54PM in Electrical

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Posted on Tuesday Dec 04, 2018 at 03:38PM in Belting & Conveyors

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Posted on Tuesday Dec 04, 2018 at 04:13AM in Electrical

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Posted on Friday Oct 05, 2018 at 07:54PM in Fluid Power

By: Ron Polvado

To start, there are three basic types of accumulators:

1) Bladder

2) Piston

3) Diaphragm

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Posted on Thursday Jul 26, 2018 at 02:39PM in Electrical

          Many of our customers have the need for electric motor braking whether they know it or not. Most of them are unaware of the potential time and energy savings they could receive from electric motor braking.

          Once it has been determined braking is required there are several things that need to be known. The first thing that must be known is the weight and speed of the rotating load, next is how fast that load needs to be stopped and lastly how frequently this load needs to be stopped. Once these factors are known it can be determined if the VFD drive can stop the load on its own or if additional items are required. In the event the VFD drive needs additional items to stop the load you might need to add a braking resistor and or the brake chopper option to the VFD drives order code. On some occasions you will need to add an external brake module to a VFD drive that doesn’t have the option for a brake chopper. These items are used together to dissipate the excess energy that is created when stopping a rotating load.

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Posted on Thursday Jun 14, 2018 at 01:19PM in Electrical

Article Submitted By: Robert Witte

ABB PSTX Soft Starters

        When ABB first released their new PSTX Soft Starter, they were only available up to 370 amps (300 Hp @ 480v) but they have now released the full product line up to 1250 amps (1000 Hp  @ 480v). Previously, all ABB Soft Starters were a part of the ABB Low Voltage Products Group, along with products like Circuit Breakers, Across the Line Starters, Disconnect Switches, Pilot Devices, etc. Recently the Soft Starter product line has been re-aligned into the ABB Low Voltage Drives Group. 


The PSTX Soft Starters are the most feature rich Soft Starters on the market today. The detachable keypad is modeled after the current ABB Drives keypad, such as the ACS880, ACS580 and soon to be released ACS480. Navigating through the keypad to program the Soft Starter parameters has the same flow as the current ABB drives, making programming very easy, even without using the manual for assistance. This user-friendly keypad is standard on all PSTX Softs Starters.

  The PSTX Soft Starters offer a Slow Speed Jog Function, in both Forward and Reverse Directions. This feature allows for greater flexibility when operating equipment such as Conveyor Belts and Cranes. This feature provides positioning capabilities, allowing the operator to take greater control of their process.


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Posted on Monday Jun 04, 2018 at 04:25PM in Mechanical

Article by: Dan Whitehouse

Bearing failure due to lubrication is a very common occurrence. About 50% of bearing failure is related to lubrication. Below is a section of an article from that details eight failure mechanisms.  (Full article can be read here.)

When in doubt, it does not hurt to ask when lubrication comes into play.

1. Unsuitable Lubricant - First, you must choose the correct lubrication for the application. Fundamental properties, such as the viscosity, additive package and consistency (for grease), should be carefully selected based on the bearing type, speed factor and operating conditions. If these factors are not thoroughly considered and an unsuitable lubricant is applied, the lubricant may become overly stressed or be insufficient for the machine's lubrication needs. In either situation, the bearing will likely undergo premature wear and failure.

2. Lack of Lubricant - For greased bearing applications, the correct regreasing volume and frequency must be established to ensure the bearing load zones are lubricated properly. Too much time between regreasing intervals or applying too little grease will cause excessive boundary and bearing wear.

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