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VMI iCOM – A New Alternative to Final Rubber Mixing I Learnt At RUBBERCON 2015 Chennai

The rescheduled edition of RUBBERCON 2015, held on March 1-3, 2016 at Chennai was well-organized by IRI (Indian Rubber Institute) and IRCO (International Rubber Conference Organization).

Personally, this has been one of the best attended, well-organized and amongst biggest conferences I have been to recently. And to most delegates, this has been a different experience altogether.

Kudos to the complete team of organizing committee and supporting members for their massive efforts and time invested to make this conference a success. Because of them, I think RUBBERCON 2015 Chennai would easily occupy its unique place of prominence amongst biggest international conferences.

Over 75 speakers from 19 countries presented papers.

I was fortunate to successfully attend all my shortlisted speakers.

In an earlier post on mixing, I had mentioned that Single-stage mixing is not always cheaper and two-stage mixing is not always better. So, when my good friend, Dirk G.H. Reurslag, Sales Director (Industrial Solutions) of VMI Group (innovative leaders in rubber and tyre machinery) presented a new alternative on Continuous Final Mixing, it caught my attention quickly.

If you are looking to operate the complete mixing line by a single person, then you will find this JIT (Just in Time) approach to continuous mixing and blending of final rubber compounds interesting.

Before you get excited and review it’s long list of advantages, let me brief you the basic concept.

Basic Concept:

At its heart, this “mixing approach” has a cold-feed extruder along with the gear pump and they are controlled by software. VMI calls it iCOM®.

Sound’s simple (Right?)…. Wait. There’s more to it.

VMI Continuous final mixing

VMI Continuous Final Mixing Line

Operating Principle:

If you are seeking continuous proportional blending, you will know that proper distribution-mixing should take in the screw extruder.  And for final mixing, you require the screw extruder to properly incorporate the chemicals into the compound mix. Hence, the mixing screw design from VMI is advanced and unique.

The software used is equally sophisticated to control the speeds of the screw, the pump (and input pressure) and the volumetrically operated loss-in-weight feeding system.  The mixing and proportional blending uses

  1. the volumetric operating principle of the gear pump (Read our earlier post on the concept of gear pump working) and
  2. the abilities of homogeneous plasticizing of the rubber by the screw type extruder.

The special screw extruders are the VMI SHARK® extruder gear pump combinations. Different screw types are available. VMI recommends that they select a screw for you depending on your specific application.

The chemicals to be mixed are usually polymer bound, pre-dispersed, in the form of granules and are fed to the mixing extruder by an accurate volumetrically operated loss-in-weight feeding system.

Image - VMI

Proportional Blending (L) & Continuous Final Mixing (R)

For Proportional Blending, you require another side-feeding extruder gear-pump. The function of the screw of this side feeding extruder is not to mix. Rather, it only needs to properly plasticize the rubber and feed it (free of entrapped air) to the gear pump. The gear pump, in its turn, pumps the rubber compound into main mixing extruder in a volumetrically controlled fashion.

Continuous Final Mixing:  You can adopt this volumetric controlled mixing-extrusion in combination with accurate dosing of granules (that contains vulcanizing agent and accelerators) by a loss-in-weight feeder, to do continuous mixing.

Controlled Back and Forward Blending:  This is the third type of blending you could achieve in the extruder screw and barrel combination. This ‘compensates’ for little irregularities, if they might occur, in the loss in weight feeding of your polymer bound chemicals

VMI develops new concepts and innovative uses of technology with the end-user. VMI seeks to work with clients that will become launch users and close collaborators. In this way, VMI only ever takes to market concepts that have been tested under real-world conditions and proven to deliver competitive advantage.

Emphasizes Dirk Reurslag, “iCOM® solution is the more economical alternative to mixing in an internal mixer”

VMI worked out the iCOM® final mixing process, which includes the VMI SHARK continuous mixing solution in combination with Rhein Chemie’s  Rhenogran polymer bound chemicals and Rhein Chemie’s Rhenowave in-line analytics.


Your advantages of VMI iCOM® for final mixing are

  1. Lower investment on a final mix line delivering faster ROI and time to profit.
  2. Compact, integrated solution occupying modest footprint.
  3. Lower energy consumption as compared to the use of an internal mixer based final mixing line.
  4. No electricity consumption peaks like in the case of an internal mixer. Hence, a sustainable solution that reduces energy use and improves profit potential.
  5. Decentralized final mixing: This means Just in Time production as it reduces costly transport requirements for final batches. This reduces your stock of compounds and simplifies your logistics.
  6. Just in time (decentralized) final mixing allows more ‘rapid’ vulcanizers, resulting in shorter vulcanizing time.
  7. The proportional blending capabilities gives you various kinds of possibilities – Cross Blending (Most of you in mixing would know it well. This is referred to as just blending from two stage mixing), Controlled back and forward blending or Proportional Blending (both mentioned earlier.)
  8. No ‘fading’ in the produced strip: no difference in heat treatment: With batch production the first part of the (long) strip was shorter on the mill than the last part.
  9. Consistent quality of final mix compound with no scrap or rejects.
  10. One Energy Cycle (Heat-up, Cool-down cycle) can be avoided by combining final mixing with first extrusion step.
  11. Straining in the iCOM® line is possible
  12. Degassing in the iCOM® line is possible
  13. Affordable for even smaller companies

And just in case you thought this is an entirely new concept, you are in for a surprise. A Belgian compound manufacturer has the VMI iCOM® production line installed and successfully working since 2012.

VMI Group’s leadership in Extruder-Gear Pump solutions is renowned. They specialize in designing and engineering superior customized machinery for the rubber and tyre industry.

When I visited their stall at RUBBERCON 2015, I also learnt something new in their souvenir they were gifting to their customers. Known as Klomp, (more interesting facts here – Clogs), they are a type of footwear made in part or completely from wood. Pair of these is known as Klompen.

If you had been to their stall, did you pick up Klomp or Klompen (Single or Pair)?


Summarizing, if you are looking for an innovative, automatic, decentralized, Just-In-Time, final rubber mixing line without internal mixers, this new alternative in VMI iCOM® I learnt at RUBBERCON 2015 Chennai is worth your evaluation. I am also informed, it further enables production of customized, creative and precisely targeted compounds.             

What do you think?

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Rubber Extruders And Extrusion – Special Supplement

Rubber industry only had Hot Feed Extruders until 1950’s. Then came the Cold Feed Extruders and other variations as we see them today.

Rubber extruders have a varied field of application. So, when you come across a rubber profile, strip, hose, cable, wire, cord coating, tire tread, v-belt, tube, or blank remember that they are only a few handful of products manufactured using extrusion process.

Life today is mostly spent trying to catch up with latest developments. However, in the process the basics and fundamentals are sometimes overlooked. So, in this Knowledge On-The-Go Special Supplement, we bring to you a ‘collector’s edition’ on Extruders and Extrusion incorporating the fundamentals.

(Our digital editions are available on two platforms – Youblisher or Yumpu)

Extruders_Special Supplement

Click on the Image to Flip Through The Digital Book

Download PDF Here

I hope you find this special supplement informative.

(Disclaimer: All the pictures and statements in this special supplement are sourced from web or shared by respective companies. All copyrights belong to actual owner. Rubber Machinery World does not independently verify them nor will vouch for their genuineness, hence will not be liable for any misrepresented data. The images are used here for representation purpose only.)

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If you are an equipment supplier and would like your organization to be promoted on Rubber & Tyre Machinery World, please see the opportunities on Partner Me or Contact Me at for your customized offering.


Editor’s Pick: Extruder And Extrusion Process (Part 2)

This is Part 2 of Extruder And Extrusion Process by Dr.S.N.Chakravarty.

Comparison between Hot Feed & Cold Feed Extruder

Hot Feed Extruder Cold Feed Extruder
L/D ratio varies from 4: 1 to 5: 1

In many cases the screw has increasing pitch.

L/D ratio varies from 15: 1 to 20:1.

The screw has decreasing pitch. The screw has increasing root dia with more flight depth at feed end which increase from feed to discharge.

Skill of warming mill operator and extruder operator is required to control uniform temperature and viscosity of stock. Warming mill not needed. But for preparation of strip mixing mill is needed.
Compound change requires cleaning/ changing of warming  mill and quick breakdown of new compound. No such requirement
Amount of scrap till correct extrudate comes out is dependent on operator’s skill. First few meters are scrap rough and nervy; there after uniformity attains and is less dependent  on operator’s skill.
Lower HP in extruder, but requires warming mills. Higher HP in extruder is required; but overall HP is less and no requires no warming mills.
Wearing of scroll is less. Wearing of scroll is faster.
More floor space is required. Less floor space is required.

Extruder Output Comparison

Maximum output lb./hr at equal rpm

Extruder inch

Screw Diameter mm rpm Hot feed Cold feed











8.0 200 46 4620


One of the basic characteristics of all the extrusion process is the clearance between Barrel and screw. This is generally permitted to a limit in order to :

  • control porosity
  • control extrusion temperature

Each manufacture has their own design of screw. However the basic function remain same. An adjustment can be made for volume occupied by the flight lands. Screw design has a direct bearing on out put and quality of Extrudate . Output rate depends  upon the screw design and geometry of extrudate .

Output of extruder is dependent on size of extruder i.e. the ratio of L:D. First estimate of out put is expressed as :

Output = A.(L/2).R.d

A         =          Cross sectional area of extruder

L          =          Lead Length

R         =          Revolution per minute

d          =          density of rubber

Generally these exists a liner relationship between RPM & output. Other factors also have bearing on out e.g. Pitch height , base depth, width and flight. This is expressed by following

Formula 1

Each of those parameters has an effect on extrusion characteristics and output.

However net out pat will be governed by the extension characteristics  desired by user for type of compounds. For example if temperature is a limit, this is to be optimized for each compound and shall be a crucial factor for out put.

Die Design

The die is the piece of metal which controls the final shape of extrudates. Generally die making and die design depends on experience, however a good control on compound properties gives better extrusion .

It is necessary to get a swelling factor at each point of profile for a particular compound. The same varies from centre of die to extreme ends. Die swell is defined as ratio of extrudate section & cross-section of die. Depends on Polymer, carbon – type & phr, viscosity,  Lead angle (Bevel ) of die etc.

Cold Feed Extruders

In recent year there has been an upward trend in production of cold feed extruder. In general sense an extruder which is fed with the compound at a temperature  above ambient may be said to be a hot feed extruder. On the other hand any extruder where compound is fed at ambient temperature or below may be called a cold feed extruder.  Some of the differences may be classified as under :-

  Prewarmed hot feed above room temperature No need to feed hot compound. It is fed at room temperature.
L : D Ratio Generally hot feed extruders are having 5: 1 or 4: 1 Generally vary between 12: 1 to 16 : 1
Mills A set of mill is required No mills are required
Floor space requirement More Less – Because of no mills.
Power & water consumption More Less
Temperature control Compound is homogenised on mills & is a manual job also. Compound is homogenised with better control .
Feed system Through a feed mill Must-as metal pieces may harm the pins.

Pin Type Cold Feed  Extruder

Most of the Cold Feed Extruders are now equipped with metallic pins fixed along the circumference in full length of screw. These pins help in homogenizing the compound. These number may be optimized by process & if required pins from last zone i.e. towards head may be blocked. These pins are generally 8 to 10 in circumference  in 10 rows will have 8 X 10 =  80  pins.

Dr. Chakravarty can be reached on

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Editor’s Pick: Extruder And Extrusion Process (Part 1)

Dr.S.N.Chakravarty sent me this informative piece on Extruder And Extrusion Process.

Here is Part 1 of this two-part series.


Extruders are machines, which shape rubber to a profiled strip by forcing it through a die. In the simplest form an extruder consists of four basic components viz.

  1. a device system
  2. a barrel
  3. a ram or screw for forcing the rubber through the barrel and
  4. a head holding the die which ultimately gives the desired shape.

Extruder drive system comprises of an AC or DC motor along with a reduction gear unit using V-Belt drive for power transmission or connected directly using suitable couplings. The extruder drive has to turn the extruder screw at the desired speed. It should be able to maintain a constant screw speed because fluctuation in screw speed will result in throughput fluctuation, which in turn will cause fluctuations in the dimensions of the extrudate.

The fundamental  distinction between two types of extruders is in mode of operation:

  • Continuous: Delivers rubber in a continuous manner and has a rotating member or screw; here the pressure is produced by a screw.
  • Discontinuous: Delivers rubber in an intermittent fashion and has a reciprocating  ram or screw, these type of extruders are ideally suited for batch type processes such as injection moulding.

Ram Type Extruders

Barwell Ram Type Extruder

Barwell Ram Type Extruder

In ram extruders, a quantity of warm compound is placed into the cylinder, the die is attached to cylinder and ram pushes the compound through the die to form a profiled section.


  • Extrusion can be carried out at lower temperatures.
  • Difficult compounds can be extruded.
  • Easy to clean.
  • Useful to short runs.
  • Useful for compounds which need to be strained through gauge for quality products requiring completely contamination free material .

Screw Type Extruders

A screw extruder consists of five components (a) drive system (b) a feed hopper ( c ) a screw rotating within (d) a barrel (e) a head and die. The basic principle is that the screw carries material from the feed hopper by acting as a conveyor or a hump providing pressure to extrude or force the material along the machine barrel through the head and the die.

Screw Type Extruder

Screw Type Extruder With Description

  • Feed hopper: the purpose of which is to receive material and pass it down to the flights of the screw. It is mostly supplied in the form of strip.
  • Barrel: within which the screw rotates, the usual clearance is approximately 0.40 mm. Normally, the barrel is fitted with a detachable liner in the form of a sleeve which is highly wear and corrosion resistant made of hardened steel . The barrel is made double walled for steam or water circulation so that a constant temperature is maintained in the extruder head.
  • Screw: A conventional extruder screw has three geometrically different sections.
    • Feed section (closest to the feed opening) generally has deep flights and consists of approximately 1/5th of the length of the screw. The material in this section will mostly be in solid state.
    • Metering section (closest to the die ) usually has shallow flights and consists of approximately 2/5th of the length of the screw . The material in this section will mostly be in molten state.
    • The third section, which connects the feed section and the metering section, is called as compression section. In going from feed section towards the metering section, a compression of the material in the screw channel takes place, which is essential for the proper functioning of extruders. The compression favors streamline flow and helps to eliminate air and also ensures a constant pressure in the head.

Extruders are usually designated by the diameter of the extruder barrel. The ratio of relative output of extruders varies as the square of the screw diameter . Thus the output of a 60 mm extruder will be 2.2 times that of a 40 mm machine.

An additional designation often used is the length to diameter (L/D) ratio. This is an important factor in the selection of extruders to match process requirements. The length of a rubber extruder depends on whether it is a hot feed or cold feed extruder.

Hot feed extruders are usually very short about 3D to 5D while cold feed ones range  from 12D to 20 D .

Screws are made of steel alloy forging, heat-treated to a machinable  hardness and hard-chrome plated. The flight lands are surface hardened to approximately 600 Brinnel. The screw is internally bored to facilitate water-cooling.

  • Head: the purpose of which is to equalise the pressure from the screw and barrel and to transport the compound smoothly at equal pressures and speed to the die.
  • Die: The purpose of which is to give the compound the desired shape. The extrudates shrink along their length and increase in thickness and width, the behaviour being termed “ die swell “ which depends upon (i) rheological characteristics compound  (ii) shape of head and extrudate (iii) pressure in the head (iv) the head and compound temperatures .

The  extruder is operated in such  a manner so that temperature is gradually more from feed to discharge, the die being the hottest part.

Cross Head Extruder

This is used to cover hose, wires, tyre bead wire and the extruder function here remains same as for regular extruder and cold feed type is preferred. The extruder barrel, screw and head can be heated / cooled to desired temperature. The material to be coated comes at 90° angle to the extruder screw system, and rubber thus makes a 90° turn.

In the conventional screw extruder, the rubber compound is conveyed in three states, as solid, then as a mixture of solid and melt and finally, as a melt. The movement of the material in the barrel is the resultant of four flow mechanisms. The two of these are the drag flow and transverse flow.

The drag flow results due to the forward conveying action of the material towards the die, produced by the relative motion between the screw and the barrel while the transverse flow results in a circulatory flow which is important for heat transfer and mixing but is not contributing directly to the  extruder output.

In Part 2 of this article, you will read more of COMPARISON OF EXTRUDERS.

Dr. Chakravarty can be reached on

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Why You Should Spend More Time Thinking About Gearbox for Rubber Extruders?

As a rubber machinery salesman, I have sold several single screw extruders in both extrusion categories – hot feed and cold feed.  In each of my sale, the buyers had strong views and apprehensions on screw and barrel life, throughput and strained production capabilities, extrudate temperature, extrudate appearance, die head design and performance, etc (all of which I acknowledge are really important).

Strangely, the topic of gearbox usually concluded in few questions – “Which brands of gearbox do you offer and what is the SF?” or “If I select XYZ over ABC, will the delivery lead time of my extruder change?” or “Should I call you or the gearbox vendor for service during warranty period of gearbox?”

I do not recall a single discussion where the buyer asked me about gearbox technical details. Nor do I remember the buyer asking me to arrange for a separate technical discussion with extruder gearbox manufacturer to clarify their requirements.

Why do I think this aspect of joint discussion (if any) was relevant for me as a extruder supplier? Because the assembly of a rubber extruder “practically commences” only after the gearbox is ready at the extruder builder’s shop-floor. Unlike an internal mixer or a mixing mill or calender, buyers would not opt for buying the gearbox and main machinery separately. To any reputed machinery manufacturer, there is no bigger pet peeve than a customer buying different components from different vendors trying to save pennies. (But I digress here… do read Prof. Andreas Limper interview).

Extruder Gearbox

Image from Web

And yes, a gearbox is also the single-most-expensive-component on this popular rubber machinery.

I safely presume that this single argument reinforces the relevance of this post here – Why You Should Spend More Time Thinking about Gearbox for Rubber Extruders?

First things first – Why do your single screw extruders need gearboxes?

Extruder manufacturers prefer 1800/1500 RPM or 1200/1000 RPM motors (depending on your country of use) because they are economical, readily available and compact in size to mount on your extruder base. However, most rubber extruder screws during production run in the speed range of 4 rpm to 40 rpm.

Hence, the role of a gearbox or gear reducer here is to reduce the drive motor’s speed and, in turn, multiply the available torque from the motor in order to produce sufficient power to mix and push out your rubber compound.

Plain Cold Feed Extruder

A Representative Image

As an individual and independent component, the key specification that defines the capacity and durability of your extruder gearbox is the power (HP/kW) rating along with its service factor (SF). Single screw extruder gearboxes are normally rated for power (HP/kW) or torque at a specific rpm based on common calculations and standards. This uniform standard allows you to compare gearboxes from different manufacturers.

Your extruder manufacturers follow these guidelines and select a model for different service factors and applications. A key question you should ask is whether, the SF considered by your manufacturer is optimal for your extrusion application or not.

Knowledge of AGMA (American Gear Manufacturers Association) recommendation will certainly help you to discuss better with extruder manufacturers, but experienced gearbox manufacturers can guide you even better. I have witnessed buyers in Asia been taken for a ride for their ignorance and offered lower specification gearboxes on their extruders to compete on cost.

When you compare gearboxes, always evaluate on calculated power. The formula for calculated power of a gearbox is:

                        Calculated Power = Quoted Power X Service Factor.

Typically, single screw rubber extruder gearbox has service factors of 1.5 or 1.75 for optimal operating capacity. For example, a 6 inch pin type cold feed extruder gearbox with a calculated rating of 367.5 kW would have a quoted rating of 210 kW with a 1.75 service factor.

The overall rating of a gearbox is based on the ratings of all its individual components. This includes the gear teeth design, gear hardness, shaft dimensions, bearing selection and sizes, housing design (thickness & rigidity), and thermal considerations. All these considerations are to ensure that your gearbox has sufficient support and capacity to effectively transmit the motor torque to the screw without significant distortion or failure.

Gearbox Internals

Image from Web

Within the gearbox, the most important component (and most expensive) is it’s thrust bearing. You evaluate a thrust bearing based on its type and life (B-10 or L-10 rating).

The B-10 Life (sometimes called L-10 Life) of the thrust bearing is based on an engineering calculation that estimates the number of hours of operation at which 10% of the bearings are likely to fail. Additional rating adjustment factors are to be applied to the basic B-10 life based on application factors including how the bearing is mounted.

For example, a thrust bearing that is mounted between two radial bearings is more likely to have precise thrust bearing alignment, and will therefore have a higher rating adjustment factor.


Here are 6 other key criteria of a gearbox evaluation, which you should know

  1. Gear Design, Hardness & its Construction – Each of the individual gears that go into your gearbox assembly are rated for power or torque based on their strength and durability ratings. The calculations would be according to industry standard AGMA rating systems. Factors include the gear tooth pitch, center distance, material and hardness.
  2. Gear Shafts – The shafts must be designed to transmit the full power and torque capacity of the gears. The length and diameter of these shafts is decisive and must match the ability to transmit this torque without excessive deflection, fatigue and failure. The diameter of the input shaft must be adequate to properly support sheaves (in the case of belt driven models) or a coupling. The output shafts must be properly designed to handle the correct range of screw shanks that will be inserted. Adequate access to the drive keys is beneficial when they become worn or damaged and need to be replaced.
  3. Radial Bearings and Seals – The radial bearings support the rotational forces of the gear shafts and must be designed to handle the load forces and speeds effectively. The dynamic load capacity of these radial bearings must also be considered when evaluating the design and durability of the gearbox. Radial bearings must also be properly lubricated and sealed.
  4. Gearbox Housing Design and Construction – Cast Iron is the cost-effective material of choice for most manufacturers. Traditionally, CI gearboxes are made in two pieces, split either horizontally or vertically. Newer designs have the gearbox housing cast as one piece to reduce any potential leakages.
  5. Thrust Bearing – Thrust bearing isolates the backward forces from the screw. The larger the screw and/or the higher the back pressure, the greater the backward thrust forces. There are three basic types of thrust bearings – cylindrical, spherical and tapered.
  6. Serviceability – When you select a gearbox, you should give prime importance to the availability to affordable parts and service. It is best to select rubber extruder suppliers who purchase their gearboxes from proven and reputable manufacturers that specialize only in gearboxes for better serviceability.

Pin Type CFE

A Note of Caution:

If you plan to replace your old gearbox or comparing one, take note of below developments.

An old gearbox manufactured around through-hardened process and shaved gears technology has shafts, bearings and housings designed accordingly. Replacing new hardened gears with a higher HP capacity, does not automatically guarantee the gearbox rating to increase, if you do not replace the assembly with stronger shafts, bearings and housing.

Gear manufacturing technology today has changed and consists of carburized and ground gears. These gears are capable of delivering much more power in its smaller size. When old gear designs are constructed using the new materials and process, the power calculations yield much higher gear tooth ratings. But if the rest of the design is unchanged, and the same bearings, shafts, and housings are used, the total gearbox rating cannot simply be based on the new higher gear rating alone.

The higher torque could never be applied to the original sized input shaft without causing bending or twisting. The bearings and/or shafts would be overloaded with the higher forces, and the housing would probably not have sufficient strength to resist significant distortion. Reputed gearbox rebuilders will guide you well.

Summarizing, as an extruder buyer, you need to pay extra attention to the design and manufacture of the gearbox when evaluating and selecting a single screw extruder. 

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Skills Required For An Rubber Extruder Operator: What No One Is Talking About

To a layman and HR Department of most organizations, an extruder operator is a person who operates and maintains this rubber machinery. Period!

Is that it?


An Image From Web

Depending upon your final product, rubber extrusion could be either a very important or the most critical manufacturing aspect of your operations. Thus the skills required for your extruder operator are paramount.

Extruded rubber products differ from those produced through moulding. In extrusion, parts are forced through a die of the required cross section under pressure of an rubber extruder. The extrusion process begins when you feed the unvulcanized rubber compound into the extruder. The rubber travels over the flutes of the revolving screw into the die, with the pressure and temperature increasing as the compound gets closer to the die. And when it reaches the die, the built up pressure forces the material through the die-opening, where it will consequently swell in various degrees based on your compound and hardness.

Most extruded products are unvulcanized before extrusion. This leaves the the rubber in a soft and pliable state post-extrusion. Hence they need to be vulcanized before they are they are rendered usable. During the vulcanization, the extruded rubber will swell or shrink in both its cross section and its length (again based on the type of rubber compound used).

Hence, the cost of errors or omissions could turn out to be very high when extruding rubber. You need a skilled operator.

Rubicon-Halle Extruder

Image of Rubicon-Halle Extruder

Here are the skills required for an rubber extruder operator.

Monitoring and Control Of Operations – The most important skill of your extruder operator should be to have a keen eye for watching gauges, dials, or other indicators in the control panel to make sure the extruder is working properly. Your extruder operator should be able to adjust screw speed, set water flow to the required rate, operate temperature control unit (TCU) or the metal detector in cold feed extruders, observe the extrusion parameters and ensure adherence to SOP (temperature or die swell). He has to ensure that the extruder, dies and its allied downstream equipment are kept clean, safety features are functional, and all accessories are ready.

Quality Control Analysis – Conducting tests and inspections of products, services, or processes to evaluate quality or performance is a desirable basic skill that your operator should have. This could be as critical as preventing wastage (from scorch of your rubber extrudate) to as trivial as sending the sample to lab for testing.

Critical Thinking, Judgement and Decision Making – Operating a rubber extruder requires critical thinking skills because your operator should use logic and reasoning to identify alternative solutions, conclusions or approaches to problems he faces while extruder is in operation. There could be many problems while extruding rubber like die-swell, melt fracture, or poor appearance amongst others. While all of them may not be extrusion related, your operator should be able to judge the gravity of the error and also decide what to do about it – whether to fine tune the extruder operating parameters, or escalate to supervisor or raise a service visit request of the manufacturer’s engineer.

Troubleshooting, Repairing & Maintenance – Your operator is the first point of contact with your extruder in operation. Hence, he should have the experience or knowledge on extruders to determine the causes of any operating errors when they occur. Performing routine maintenance and determining when and what kind of maintenance is needed is an important skill that your operator should posses. He should be able to use the required tools to both repair and assist repair of your extruders when needed in the most urgent manner.

Complex Problem Solving – As a addendum to the above skill, your operator should develop skills to identify and solve complex problems when they occur at site and support maintenance department effectively over a period of time. This will reduce the downtime of your extruder and ensure maximum availability at site.

Speaking – Your operator should be able to talk to you (or his supervisor) to convey information effectively be it to report data/problems/incidents as applicable in a timely manner.

Reading Comprehension – Extruders have an operating and maintenance manual supplied by the manufacturer. This is a crucial document that requires a reading by your operator for his safety, training as well as equipment safety. Again your extrusion process would have specific work related instructions or SOP. Your operator should be able to understand written sentences and paragraphs in these documents. Hence, reading skills is very important for a successful operator. It is not necessary (while it is preferred) that they read English, because you could translate these documents to your operator’s local language for ease of reading.

Active Learning – Your operator should display active learning skills.  This is because, the sophistication of the rubber extrusion machinery has risen over the years. Automation and new controls might get introduced or new parameters of extrusion could be introduced further too –  all of which he might have to learn or get trained in.

Summarizing, your rubber extruder operator needs high level of skills to give you maximum output. Hence, its wise that either you hire a skilled operator or train your operator to upgrade his skills. Your extruder operator must stay up-to-date on current and developing technologies and techniques. He must also have a solid understanding of safety techniques and practices.

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A Productive Rant About Fine Mesh Straining Of Rubber Compound In The Millroom

Hi. This article was sent to me by Dan McAuley*, a regular reader of Rubber Machinery World and avid follower of developments in Rubber Technology.

If you are a producer of technical rubber goods un-dispersed materials or foreign particle contamination can be a significant source of rejects especially in products demanding high show surface quality. Given increasing requirements and the risk of grit, packaging materials etc entering the production process an effective means of ensuring defect free compound for your customers is required.

Extrusion processes have relied on the use of screen packs to provide some measure of protection from such defects and develop back pressure to stabilize output. This stated the extruder screw to barrel interface generates shear heat as it conveys rubber compound to the die in turn reducing its viscosity to promote flow. The use of finer mesh screens will result in greater material resonance time and higher back pressures increasing heat input which can create pre-cure and reduce run duration. Molding processes via injection, compression or transfer are at greater risk as screen use is not possible.

Enter the rubber gear pump or straining device.

Gear pumps are not new technology as they have been used for a multitude of applications ranging from automotive oil pumps to plastic melt pumps and with consideration for its unique and temperature sensitive characteristics are an ideal means of “filtering” your rubber compound.

Unlike extruders, gear pumps offer positive displacement and use two counter rotating gears in place of a screw as a means of conveying material. Shear heat (minimal) in a gear pump is introduced as material enters and is conveyed between the gears and the surrounding housing, both of which are typically temperature controlled.  Similar to an extruder the material then passes through the screen pack and supporting breaker plate en-route to the die. As flow is directional and the shear area is much smaller than an extruder the gear pump is capable of gently processing temperature sensitive materials at pressures in excess of 500 bar with screen packs finer than 100 mesh.


Representative Image From Web

Although extruders are self feeding devices, gear pumps rely on being fed with a consistent supply of compound and this may be accomplished in several ways. Selecting the appropriate design depends on your install application however supply via strip fed extruder or two roll cram feeders are typical methods employed.

Regardless of feed design choice, the gear pump entrance is typically pressurized to less than 50 bar and is maintained by varying the feed device speed relative to gear pump speed.

Gear pumps used for rubber straining are unique in the sense that conventional bearing support of the gear shafts and lubrication with oil or grease can present a contamination risk given the high working pressures. Designs vary, however a common solution permits rubber leakage flow between the rotor  shaft and the housing effectively making the compound the lubricant highlighting the need to ensure consistent gear fill. The tailings generated due to the rubber leakage may in many cases be recycled back into your process to minimize waste.

Gear pump technology in the mill room – in line

Straining technology has advanced to the point where machines capable of outputs in excess of 10000 kg /hr are possible. The use of a gear pump at the source of compound production can reduce capital and operating cost at end use processes, permit the use of lesser grade raw materials and produce continuous and consistent strip feed for your extrusion or downstream mixing operations.

Mill room operation can also benefit as the straining process generates a steady/stable output which establishes a process ”heartbeat” or pull to which other systems must be optimized.

Key considerations in the selection of an appropriate machine include the design of the pump feeding method, touched on earlier. Options such as a mill fed continuous strip to an extruder or a two roll feed mechanism are available as is a conical twin screw feed which presents an alternative to the roller die at mixer discharge.

Taking advantage of the warm feed output from the mixing process to the strainer permits inline fine mesh straining of a wide variety of compound types and viscosity. To accommodate throughput rates, machines make use of large breaker plate -screen pack configurations and may be equipped with dual heads etc to facilitate quick screen change.

Given the nature of the device, the low impact on material temperature vs working pressure and the ability to achieve extremely fine filtration the technology is suited to both master batch and final compound production.

Your peers in the industry are taking advantage of inline straining to provide end users with clean compound improving their operations by reducing defects at the source.  This coupled with added flexibility in raw material selection and the continuous flow output to your mill room’s downstream operations can offer a significant improvement in operating efficiency. A win-win result.

Image of UTH Strainer Extruder

Image of UTH Strainer Extruder

*Dan McAuley is a Mechanical Engineering Technologist with extensive rubber industry experience primarily as a project engineer. He has participated in equipment installations in green field start-up ventures in Brazil and Mexico as well as implementing new processes and supporting programs within existing production facilities. He has worked as project engineer, plant engineer, project engineering manager having worked in the UK, USA, Brazil, Mexico and Canada for various extended assignments. He can be reached at

Contact me if you seek more details. Or if  you are looking for New or Used Rubber Machinery?

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