Rubber & Tyre Machinery World

Info on Equipment And Suppliers


1 Comment

A Beginner’s Guide to Rubber Refiner Mill

Are you looking for a rubber refiner mill? Great. Now you try searching this key word in google or any other search engine and explore a few sites.

How many direct search results did you get without linkages to rubber mixing mills or two-roll mills? Even more importantly, how many sites gave you clarity of information you sought for on this category of rubber machinery? Less than 2-3, on the brightest side, if I may say so.

And this is why I am prompted to write a beginner’s guide to rubber refiner mill.

First things first. You need a rubber refiner mill mainly for the refining of reclaimed rubber. The operational ease and functional performance makes this mill your preferred machinery in reclaim rubber industry for refining pure and fine rubber powder from waste.

Refiner Rubber Mill

A Rebuilt Refiner Mill From Deguma

Similar in construction to an open mixing mill, you will observe that its distinguishing feature is that both the rolls have different diameter. The front roll is smaller in diameter as compared to the back roll. And hence when you see a refiner mill identified as 21″ x 24″ x 36″, you simply need to decode it as Front Roll diameter is 21 inches, Rear Roll diameter is 24 inches and both the rolls have same face length of 36 inches.

The Rear Rolls have a higher surface speed than the Front Rolls again a similar feature of a regular rubber mixing mill. However, in your refiner mill, the differential sized rolls turning at considerably different speeds provides a high friction ratio. The ratio of speed of your Front Roll to Rear Roll could vary in the range 1:1.75 to 1:2.50 depending on your process requirement.

When the rolls are set quite tightly to each other (i.e. close nip-gap adjustment of 0.05mm), refined rubber in thin-sheet form (~ 0.10mm) is produced. This sheet that you get is usually smooth, uniform and free of grain or lumps. In this refining process, the impurities contained in reclaimed rubber are squeezed by rolls to the both sides of rubber sheet which can be removed. Therefore, the purity of your reclaimed rubber is increased in refiner mills.

In the past, this finished rubber sheet was pulled towards a wind-up attachment and layered few times to increase the thickness of the sheet (approx. 25mm), post which they are cut using a hand knife by your operator (video from YouTube). The cut sheet are then dusted and stacked. Today some reclaim rubber manufacturers rely on balers to package the rubber sheets.

These sheets are stored and sold for a wide variety of end products like new tires (especially carcass, side-wall, under-tread of passenger, light-truck and off-road tires; inner liner of tubeless passenger tires; semi-pneumatic tires), tubes, automotive floor mats, de-vulcanisation for low technology pressed or extruded rubber goods, tread rubbers, adhesives, sealing and tape compounds, belting, battery containers, molded products, and rubberized asphalt.

Summarizing, though Rubber Refiner Mill is similar in appearance, construction and features of safety and operation; as a beginner, you simply need to absorb that these are special types of two-roll mill used in reclaim rubber industry to produce smooth and homogeneous rubber sheets.

Would you like to add more thoughts?


If you liked this article, please do share with your colleagues, customers and friends. And If you would like to be informed of our articles regularly, please register with us for free updates today.


6 Comments

Why We Love Twin Screw Sheeter (And You Should, Too!)

Twin Screw Sheeter replaces the dump-mill and sheeting mill combination in a traditional rubber mixing line (an image you had seen in my earlier post – Single-Stage or Two-Stage Mixing?). This means you could visualize Twin Screw (Extruder) Sheeter, as a rubber machinery that accepts mix compound directly discharged from an internal mixer into its hopper chute and converts it into a continuous, seamless rubber sheet that is then fed into a Batch-Off Cooling Line.

For those who have been following my blog, you have already viewed a video of this equipment in action in my earlier post Rubber Mixing Room.

When you explore this equipment for purchase, you should not be surprised with different OEM’s calling it in similar sounding names. For example, you will get a Conical Twin Extruder (CTE) with Roller Head from Colmec SpATwin Screw Roller Head Extruder (TSR) from KobelcoTwin Screw Discharge Extruder (Convex™) from HF Mixing Group or simply Twin Screw Sheeter (TSS) from other rubber machinery manufacturers like Bainite Machines.

In construction, they all appear similar as shown below.

Kobelco Make TSR

Kobelco Make TSR with description

For reading simplicity, let me address this machinery simply as “TSS” for the rest of this article.

You will find the TSS to be ideal for conventional and diverse applications including tire manufacturing, custom compounding, hose & belt manufacturing and technical rubber goods production.

So, here’s why we love Twin Screw Extruder Sheeter (And, I feel, You Should, Too!).

  • Energy Saving: Rubber compounding is a energy-intensive process. So, any technological advancement that has the potential to reduce energy consumption receives my first preference (and I hope you will agree with me here). Let me help you with a quick back of the envelope calculation. If you are using a 270 Liter Tangential Internal Mixer, you are engaging at least two units of 26″x84″ two-roll mills in the downstream section. Each 26″x84″ two-roll mill, requires around 180 kW (minimum) motor power – totaling to 360 kW (=180 x 2) only for the mills. For a similar capacity mixer, a TSS downstream will not seek more than 300 kW power (again, there is energy-efficient models available here). So, this rough calculation, when a TSS replaces the traditional dump-mill with sheeting mill set up, straightaway gives you 16.7% savings in energy (60 kW less).
  • Labor: The second aspect is the reduction is labor cost. Unlike two-roll open mills (with or without ), where you will need two separate operators, a TSS can be set up to perform sheeting function of rubber sheet without an hands-on operator at its vicinity. Even if not fully automated, you do not need an operator once the discharge of rubber sheet from TSS is fed into a Batch-off.
  • Reduced Contamination: In open two-roll mixing mills, your rubber mixing is exposed to the environment and it is difficult to control any dirt or moisture absorption by the compound during milling process. In a TSS, this is eliminated. Your rubber and its recipe constituents are mixed and sheeted-out in a closed environment under temperature controlled conditions right from the time you feed it into your internal mixer. Hence, with reduced contamination, you get a guaranteed higher quality of your mix compound.
  • Self-Cleaning Feature: The Screw and Barrel of the TSS is at a downward inclination (15º) angle from the feed chute section to exit of the roller die head. This incline ensures that compound flow to the exit of the barrel is reinforced and no material remains inside the TSS – hence, the self-cleaning feature.
  • High Mixing Line Efficiency and Productivity: When you install a TSS , your compound batch from the internal mixer is converted into a continuous sheet and the working of TSS can be automatically synchronized with rubber mixing line speed. This in turn, improves the mixing line performance making it more efficient. The continuous sheeting without operator involvement increases your mixing line throughput and overall productivity. Original Equipment Manufacturers (OEM) can offer you customized TSS models beneath internal mixers with throughput capabilities from 500 Kg per hour to 21000 Kg per hour (….and that’s a vast range by all means).
  • Effective Temperature Control: Your rubber compound discharge temperatures from TSS is reduced while sheeting out the material because no additional work (hence no additional heat) is introduced into your compound. Additionally, there is circulation of tempered (or chilled) water inside the conical twin screws, barrel and the peripherally drilled rolls of the roller die. This flowing water facilitates an effective heat exchange to take away the heat from the rubber mix and reduces the compound temperature at the discharge sheeting section.
HF Twin Screw Extruder

HF Make Twin Screw Extruder

  • Compact Layout: Most manufacturers offer various drive options, making the design of the TSS very compact yet sturdy. This means that a TSS can be accommodated under most internal mixers starting from the lowest production range of 16-25 Liter capacities based on the OEM standards.
  • Easy Maintenance: Further, the screw tips of the energy-efficient conical twin-screws do not touch each other and hence there is minimized wear of the screws. A rapid action hydraulic cylinder arrangement for clamping and moving the roller-die calender on rails facilitates the cleaning of the screw tips and insides of the barrel tip during your scheduled maintenance. Also, the TSS does not require external pushers, as in case of single-screw dump extruders. These features make a TSS maintenance easy for you.
  • Additional Features: With increasing trend of Silica usage in rubber compounding, you need to be cautious of the metallurgy and surface treatment characteristics of any rubber compounding machinery you buy. Hence, explaining the major ingredients of your recipe to your OEM is of paramount importance. For example, in TSS you can seek rollers that has hard-surfaced rolls if you are processing silica compounds. This will minimize the compound sticking to the TSS roll and increase its life.

Lastly, this physically very sturdy and robust, rubber machinery is designed for intrinsically safe mixing line operation.

Summarizing, with its capabilities for conventional and diverse applications, a TSS is emerging as the standard downstream equipment in the rubber compounding process for masterbatch and final mixing lines. And that is why we love Twin Screw Sheeter.

How about you?


If you liked this article, please do share with your colleagues, customers and friends. And If you would like to be informed of our articles regularly, please register with us for free updates today.


3 Comments

9 Things About Tandem Technology Your Boss Wants To Know In Rubber Mixing

Dr Julius Peter, then Chief Technical Officer at Continental AG patented his idea of Tandem Mixing Technology in 1989. His colleague, G. Weckerle, manager at Continental Technical Rubber promoted this technology at his factory in Northeim, Germany on K2A, K4, K5 and K7 type of mixers.

Francis Shaw & Co had sole world rights for supply of the intermeshing type tandem mixers. Today, HF Mixing Group (Harburg-Freudenberger Maschinenbau GmbH) are owners of tandem mixing technology by virtue of their acquisitions in the rubber machinery world.

(Updated on 23rd Dec 2015: Flip through this post in our digital edition and download here)

Here are 9 key things about tandem technology in rubber mixing you should know to impress your boss.

  1. Tandem technology separates the two main tasks in your rubber mixing process viz. dispersion and distribution. Dispersion means breaking down of your solid materials such as the fillers. Distribution involves achieving homogeneity within your rubber mix compound with its different chemicals added. The temperature profile which is absolutely essential for inducing chemical reactions during your rubber mixing process can be better controlled when these two stages are separated.
  2. In Tandem technology you interconnect two “mixers” in series, a ram type mixer on top of aramless mixer. Each machinery is optimised to perform one rubber mixing task. Ram type mixer does dispersion well whileramless tandem mixer does the task of distribution.

    HF Tandem Mixer

    HF Tandem Mixer

  3. Your masterbatch produced in the primary ram mixer is transferred without intermediate storage to the ramless tandem mixer below. Here your batch is cooled and finals mixed. At the same time a new masterbatch is prepared in ram mixer above. The upper mixer with ram is preferably (but not necessarily) intermeshing type. As your masterbatch mixing does not involve the addition of curatives or accelerators and is essentially a heating operation, the mixing cycle may be carried out rapidly without any need to cool your mixer before the next mixing cycle.
  4. Between the two mixers is a discharge flap and chute which would be closed at all times except when the lower tandem mixer receives the masterbatch dump from above.
  5. The mixer below must be intermeshing type to enable self-feed without pressure and work without a top ram. The finals rubber mixing function is usually a shorter process than the masterbatch stage. This means that the tandem mixer has an idle time after the discharge and before receiving the next hot masterbatch. This idle period with the discharge door open allows the tandem mixer to cool.
  6. The final mix compound is then dumped into a two-roll mill or a dump extruder and processed in the normal way.
  7. When the two tasks of dispersion and distribution are separated, your compound weight is relatively smaller in the larger lower machine. Hence, you can operate this ramless mixer at a higher speed. This improves the quality of your mix because your compound is moved around the mixing chamber more number of times.
  8. Excellent cooling water circulation to the mixers is a must in tandem mixing technology.
  9. HF Mixing Group expert, Dr Harald Keuter, emphasize that a Tandem mixer improves your throughput rate by up to 25 per cent when compounding with carbon black compounds and can rise up to 100 per cent with silica compounds. Hence you can cut costs and increase output with this technology. Depending on your choice of mixing line, say for a mixing room with five tandem mixing lines and production of approx. 100,000 tonnes of rubber compound annually, he says you save up to one million euros per year. (….And that’s lot of money!!)

The population of tandem mixers is higher in the tire industry while its economy of operations is tempting the non-tire rubber industry as well.

Do you plan to reduce the mixing stages for your rubber compound (Read on Single-Stage or Two-Stage Mixing here) using tandem technology? Let us know.


If you liked this article, please do not forget to share with your colleagues and friends. And If you would like to be informed of our articles regularly, please register with us for free updates today.


18 Comments

Rubber Mixing Room

Think rubber mixing room, and the image that conjures up in your mind is that of a “black room“!

Factories that have open two roll mill mixing have carbon black particles all over the place, lending credibility and authenticity to “black mixing rooms”. Dust collection system reduces this to a large extent.

When an internal Banbury mixer or Intermix mixers with semi/automatic carbon feeding, filler feeding, oil dosing and effective dust collection systems are deployed, they present a safer and cleaner environment. Maintenance is easier and mixing rooms need not be “black” any longer.

A representative image of a mixing room is as below.

ThyssenKrupp Mixing Room Image

ThyssenKrupp Mixing Room Image from the web

Depending on the technology and layout adopted, the set-up could vary. And if you are curious to visualize how the complete system works, here is a video of a rubber mixing line.

Automated Mixing Line From Bainite Machines

Automated Mixing Line From Bainite Machines

Newer and most state-of-the-art rubber mixing and compounding factories invest in automated rubber mixing rooms to reduce reliance on labour, increase efficiency and production.


If you liked this article, please do not forget to share with your colleagues and friends. And If you would like to be informed of our articles regularly, please register with us for free updates today.


10 Comments

Single-Stage or Two-Stage Mixing?

Have you encountered the often dilemma, “Should I do single-stage or two-stage mixing for my compound; which machinery to use?” – do not be surprised! You are not alone.

Single-stage mixing is considered for productivity reasons (and cost-effectiveness). While Two-stage mixing gives a better dispersion of the finer size blacks. And interestingly, for some compounds with high levels of blacks, even three or more mixing-passes may be necessary.

Rubber mixing as a subject would have been quite simpler, if we could answer this topic effortlessly. Unfortunately, it is not!

(Updated on 23rd Dec 2015: Flip through this post in our digital edition and download here)

Single-stage mixing in an internal mixer is a cost-effective solution but difficult for all compounds. If the compounds have high filler loadings, you may be forced to mix in two-stages due to the high amount of shear and heat generated in the mixing cycle. If you use peroxide cures or are mixing expensive FKM, then you must be even more worried of the batch temperature.

Most experts feel two-stage mixing, with short time spans for each of the mixing stages, is helpful.

One school of thought advocate an open two-roll mill for second-stage mixing because the dispersion of the batch and the mastication is higher (than an internal mixer). Open mills, though slower, are safe for short scorch compounds.

A traditional mixing line comprises of an internal mixer above a dump mill then one (or two) mill before the batch off cooling line.

Traditional Mixing Line with Two-Roll Mill Set-up

Reference Image Courtesy: Bainite Machines

Internal mixers are high-capacity rubber compounding machinery. Hence they need to be supported by open mills with advanced features to keep pace with production. The rotors of these mixers operate at high-speed to maximise dispersion of the bulk ingredients and dump the batch at high temperatures. Curatives, blowing agents, etc are added on the open mill and final homogenization happens on the last mill before batch off. Also, adding the cure system on downstream mill eliminates the batch contamination problem from “leftover’s” trapped (between the rotor end plates and ends of the rotors) in the internal mixer. These open mills are recommended to have peripherally drilled rolls to take out heat of the compound before adding heat sensitive curatives.

Open mill mixing is operator dependent and hence quality of compound varies from beginning of shift to end of shift. (Read about Stock Blender). As compared to rubber mixing in a closed environment, the probability of “fly loss” is high in open mills. Hence, an alternate school of thought propagates second-stage mixing also performed in an internal mixer. This can be at a lower speed, energy and dump-temperature configuration setting on mixer.

Single-stage mixing in an internal mixer is possible, when you mix and drop the batch within 120⁰C. The present range of internal mixers have advanced designs to effectively control batch temperature. With many designs and rotor geometries for faster mixing, accompanied by quicker cooling features, mixers like tandem mixers allow traditional two pass to be reduced to single pass cycle. (I will cover newer mixing lines with Twin Screw Sheeter, Dump Extruder, etc in different posts). As a side note, if you opt for single-stage mixing with internal mixer; the Intermeshing Type Mixer has the best quality and efficiency.

Single-stage mixing is not always cheaper and two-stage mixing is not always better. The best way to decide is to make a cost-benefit analysis between the two processes for the different polymers that you work with. Quantify how much of your product defects are linked to poor dispersion. Analyzing them, you have your customized solution to mix effectively.

Summarizing, there is no one best way for all compounds. Your mixing process has to be designed to the polymer; depends on the viscosity of the elastomers used, the quantity of filler, mixing temperature, machinery employed, time at every stage of mixing and desired physical properties for the end use product. If you get your “desired” characteristics in a single-stage mixing, adopt it or wisely opt for two-stage mixing.


If you liked this article, please do not forget to share with your colleagues and friends. And If you would like to be informed of our articles regularly, please register with us for free updates today.


4 Comments

Should you buy a Stock Blender for your Open Mill?

The Stock Blender is an add-on accessory mounted on top of an open two-roll mill. It aids in rubber blending by pulling the mix compound from the front roll of the mill and guiding it to the nip gap between the two mill rolls.

A Mixing Mill With Stock Blender and Hydraulically Operated Mill Guides

Structurally, this machine assembly consists of a blender roll, a carriage unit with guide rolls, pressure roll and rear roll along with required automation.

The Blender Roll is a hollow roll with water passage for internal cooling. The surface of this roll is hard chrome plated, mounted on antifriction bearings at both ends and operates on a variable speed motor. The VFD allows you to tune for every compound or recipe, thus enabling the speed of the stock blender to follow mill speed. This feature is crucial to ensure that compound does not sack-in or tear-off when taken up and through the stock blender.

On the assembly frame is also a hollow pressure-roll mounted on antifriction bearings and has a swivel operating arrangement. Pneumatic cylinders actuate this movement. The Carriage with screw and guide rollers is equipped with two limit switches at either end of travel. These limit switches signal the carriage traverse motor to reverse at extreme ends during to & fro travel, while guiding flow of rubber to mill nip via blender roll.

A stock blender helps in homogeneous mixing and repeatability of the mixing operations. Many companies use them on the open mill (also known as dump mill) below the internal mixer. After masterbatch mixed in an internal mixer, curatives are added and final homogenization done on these mills. Because the mill helps incorporate undispersed curative or fillers that might have fallen off the ram or drop-door when the batch was dropped. In a different scenario, if you need to drop the mix batch at a higher dump temperature, you could use the stock blender to take some heat out of the batch and then add the curatives on the mill. Reduction in temperature is obtained by allowing the batch from the mill roll airborne to pass over the water-cooled blender roll before it returns back to the nip gap. When these mill rolls (centrally cored or peripherally drilled design) are properly cooled, the stock-blender allows you to reduce the batch’s temperature continuously for lower viscosity compounds.

Stock Blenders are also used on pre-warming mills before feeding the rubber sheet to a Calender.

A Stock blender enhances efficiency and productivity through reduced operator fatigue. Cutting down hot rubber many times, rolling the sheets and feeding them back into the nip gap of the mill rolls is a physically demanding task for the operator. Stock blenders eliminate this completely and improve your batch to batch consistency. The operator also benefits from a safe work-environment.

The operators, though need to be trained well. For an open mixing mill the stock blender can be used only when the batch has achieved a certain stage of homogeneity. When a batch from the internal mixer is dropped on an open mill with stock blender, the operator must pass the complete batch through the nip before diverting the batch to the stock blender. Else, there is a risk that only a part of the batch turns round the stock blender. A big lump,which is neither cooled nor mixed, would continue to ride and turn on top of the nip. This lump does not pass the nip until the operator evacuates the compound to second mill or batch off.

The stock blender designs vary among manufacturers. Hence, not paying attention to the design features can result in owner’s or operator’s nightmare. For example designs with ledges behind the rolls can cause compound to accumulate and these must be cleared out regularly to prevent contamination. Similarly, a ball screw with tube casing for carriage movement is superior to a conventional screw design and eliminates contamination from lubrication of the screw. Compact designs and increased level of automation with programmable carriage traverse movements make the stock blenders a joy to work with a high level of safety.

Summarizing, buying a good robust stock blender increases the mixing capacity of an open mill, improves the batch cooling, reduce mixing time and improves dispersion. With a trained operator, you can extract the best returns out of your investment in this rubber mixing machinery accessory.

 


If you liked this article, please do not forget to share with your colleagues and friends. And If you would like to be informed of our articles regularly, please register with us for free updates today.


11 Comments

Peripherally Drilled Rolls or Centrally Cored Rolls?

Do you use centrally cored rolls or peripherally drilled rolls in your two-roll mixing mills? Or a combination of both?

Roll selection for a mixing mill is of decisive importance for the quality of many high-tech products manufactured by the rubber industry. Open two-roll mills in rubber processing are recommended when quick cooling for the batch being mixed is sought, say for example in final mix compounds.

Generally, these rolls are made of Chilled Cast Iron (CI) through a process of vertical casting. Chilled CI has greater resistance to deflection and uniform heat transfer characteristics. Depending on the presence or absence of alloy, the hardness of the outer working (chill) zone could be in the range of 460-650 HV with a thickness 12-20 mm.

Basis the application, manufacturers take extreme care on the properties of the rolls that include breaking strength from journals and core material, thermal conductivity, surface quality and wear resistance of the roll, overall machining and surface quality.

As these rolls operate at high speeds, precise concentricity with proper balancing of rolls is a prerequisite for efficient utilization of material and energy. The surface quality of the rolls is crucial for the products to be produced. The smoother and more precise the rolls, better the product.

Viscous deformation of the rubber compounds occurs between the rolls of mills during mixing and mastication. This generates heat that needs to be removed through effective cooling. Hence, water circulation passages for cooling are an essential feature of the roll design in rubber mills. These passages allow a pre-defined circulation of the cooling agent (mainly water) and ensure that the temperature can be kept within a prescribed tolerance over the entire face length of the rolls.

Two designs are normally available – centrally cored rolls and peripherally drilled rolls. Peripherally drilled rolls are possible for diameter greater than 150mm (or 6 inches). The cross-section of a centrally cored roll is easy to visualize. But, ever wondered how the insides of a peripherally drilled roll looks like?

Well here is with a sectional view with water flow.

Peripherally Drilled Roll

The water entering into the roll is cooler (blue colour) and as the heat transfer occurs, the water temperature rises gradually (red colour at exit).

The efficiency of heat transfer is relatively higher in the case of peripherally drilled rolls than in centrally cored rolls due to close proximity of the water channels to the roll surface. In peripherally drilled rolls, the passages for heat exchange are provided approximately 25mm under the roll surface and can vary nominally between manufacturers. Reputed roll manufacturers like Walzen Irle, Leonhard Breitenbach and Karl Buch, in their decades of existence, have built their own standards. Roll manufacturers are also available in China, Taiwan and India for various sizes.

The manufacturing processes and costs involved in producing a peripherally drilled rolls is relatively high, hence they are priced higher than cored rolls. Your choice of peripherally drilled or cored rolls depends on the quality of rubber processing required in mixing mills and the marketability of your rubber products for a price that profitably covers your investment.

Any state-of-the-art Calender in rubber processing also use peripherally drilled rolls for its stated advantages.


If you liked this article, please do not forget to share with your colleagues and friends. And If you would like to be informed of our articles regularly, please register with us for free updates today.