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Top 15 Skills Required For An Internal Mixer (or Kneader) Operator

Rubber Mixing is a capital and energy intensive operation. And mixing machinery are the mother equipment. This could be an Internal Mixer (Banbury or Intermix) or Rubber Dispersion Kneader depending on the size of your organization and/or products manufactured.

Hence, the cost of errors or omissions are very high when compounding a batch in a mixer. You need a skilled operator. Ever pondered on the skills that make a mixer operator successful?

Internal Mixer Operator

Here is the list of top 15 skills for an successful batch mixer (or kneader) operator. (Updated on 23rd Dec 2015: Flip through this post in our digital edition and download here)

  1. Control of Operations – Your mixer operator should be able to adjust ram pressure, control the mixing process, set parameters and ensure its completion as per SOP (temperature or time or energy as programmed/specified).
  2. Monitoring Operations – The most important skill of your operator should be to have a keen eye for watching gauges, dials, or other indicators in the control panel or HMI to make sure the mixer is working properly. He has to ensure that the mixer is kept clean, safety features are functional,  upstream and downstream equipment along with all accessories (like cooling water, hydraulic/pneumatic system, temperature control unit (TCU), lubrication system, etc) are ready
  3. Active Listening – Your operator should be a skilled listener. He should actively listen to the sounds of the mixer and its motor during a mixing cycle; pay full attention to what his supervisor (or you) or his colleagues on the mixing room safety are saying, take time to understand the points being made, and ask relevant questions.
  4. 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
  5. Reading Comprehension – An operating and maintenance manual is normally supplied together with the rubber mixer. This is a crucial document. Again your compounding process may involve specific work related instructions or SOP. Or there could be a training manual in some instances. 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.
  6. Troubleshooting, Judgment and Decision Making – Your operator is the first point of contact with your mixer in operation. Hence, he should have the experience or knowledge on mixers to determine/read the causes of any operating errors when they occur, judge the gravity of the error and also decide what to do about it – whether to reset the mixer, or escalate to supervisor or raise a service visit request of the manufacturer’s engineer.
  7. Critical Thinking – Operating a rubber mixer requires critical thinking skills because your operator should use logic and reasoning to identify alternative solutions, conclusions or approaches to problems he faces while mixer is in operation.
  8. Quality Control Analysis – Your operator should have basic skills on quality control with an outlook to meet your set mix quality parameters in every batch. This may involve need for appropriate fine tuning like helping you fix the batch weight, or sending the sample of specified compound/ batch in specified form to lab for testing.
  9. Social Perceptiveness – Emotions could run high in the rubber mixing room. Your operator should display “awareness” of others’ reactions and understanding of why they react as they do in a particular circumstance.
  10. Repairing – Your mixer operator should be able to use the required tools to both repair and assist repair of mixers when needed in the most urgent manner.
  11. Time Management – Your operator should manage his own time and display sensitivity to the time of other co-workers involved in the mixing room.
  12. Mixer Maintenance – Performing routine maintenance on mixer and determining when and what kind of maintenance is needed is an important skill that your operator should posses.
  13. Active Learning – Your operator should display active learning skills. This is because, mixers get upgraded, automation and new controls might get introduced or new methods of mixing could be introduced all of which he might have to learn or get trained in.
  14. Writing – If you could get an operator who could communicate effectively in writing to you (or his supervisor) or to other departments, then I would say you have a great asset.
  15. Complex Problem Solving – 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 reduces the downtime of your mixer.

Do you agree the above listed 15 skills, required for an Internal Mixer or Kneader Operator, are comprehensive? Let us know.


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Bale Cutter – A Rubber Machinery with a Monstrous Synonym

Bale Cutter is a common rubber machinery, also known with its monstrous synonym – Guillotine. Rubber needs to be cut into small pieces before they are fed into the batch mixer. The rubber bale cutter (aka guillotine) does this job to the satisfaction of most users.

In the past, there has been guillotine machines with a fixed knife and a table moving upwards. In its current form, hydraulic bale cutters are popular.

Rubber Bale Cutter

Image Courtesy: Bainite Machines

The standard bale cutter is designed for 33.3 kg bales. They handle all Natural Rubber (NR) and Synthetic Rubber (SR) bales in the range 25-35 kg. This is because, NR usually comes in rectangular shape with a weight 33.3 kg or 35 kg (± 5%) and dimensions 670 mm x 330 mm x 170 mm. Bulk SR such as unvulcanized elastomer is normally supplied in a dense rubber bale or slab wrapped in a thin protective plastic film. Its size is around 600 mm x 450 mm × 200 mm and weighs 24 kg.

While a bale of this size can be fed directly into batch mixers, the bale cutter is required to get the correct weight for the compound recipe being mixed in a batch. Hence, most standard bale cutters has a cutting section varying between 600-750 mm and a cutting height of 300 mm.

Each machine consist of a cutter or a precision blade, hydraulic cylinder, frame structure and hydraulic power pack unit. The hydraulic oil supplied by the hydraulic power pack unit operates the blade or cutter through hydraulic cylinder to cut the rubber bale.Most manufacturers incorporate roller conveyor or conveyor belts in their bale cutters for carrying the rubber bale to the blade and similarly discharge conveyors to transport the cut slices further away from the blade.

Advanced rubber bale cutters does not require operator attention other than during loading. They have a continuous blade cycle with conveyor advancing in a pre-determined speed. Such machines have an in-built cutting control and display unit operated by PLC controlling various guillotine functions. This includes pre-programming the required cutting information such as nominal slice thickness, total number of cuts required or dwell time between cuts. In some bale cutters, a pneumatically actuated plate keeps steady the bale during the cut operation.

Bale cutters can be dangerous for an operator if not securely fenced with interlocking access gates and interlocking guards to prevent access to the cutting area. So it is crucial that rubber bale cutters are comprehensively guarded for safe operations.

With user-friendly features, safety and automation incorporated, manufacturers compete to position their bale cutter as high technology rubber machinery for better quality cutting and higher productivity.


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Rubber Dispersion Kneader – The Other “Internal Mixer”

In the world of rubber mixing, when “purists” refer to “internal mixer”, they either mean a Tangential Rotor Type (aka Banbury Mixer) or a Intermeshing  Rotor Type (aka Intermix).

While “practitioners” have a third category viz. Rubber Dispersion Kneader.

When you discuss with the practitioners (mostly in Asia) it is very common to hear the terms “Kneader Banbury”, “Kneader Mixer”, “Kneader Intermix”, “Intensive Mixer Kneader”, “Internal Mixer Kneader”, “Dispersion Mixer”, “Tilt Mixer” etc being used in the same context as an “internal mixer”.

So, what is this dispersion kneader and how is this different from an internal mixer?

Dispersion Kneader

Moriyama Make Dispersion Kneader

To start with, a kneader means a machine that specializes in kneading substances, something to a dough form. I suspect it originates from Germany when Heinz List, a pioneer of modern industrial processing technology, first developed a kneader reactor to process high viscosity materials.

The respective rotor, throat, chamber and floating weight designs are different in a dispersion kneader and batch mixer (or internal mixer) . While a mixer discharges the batch through a bottom drop-door, the kneader tilts 125-140 degrees to discharge the batch. Available in more customized capacities than batch mixer, this machine can be positioned on the ground level. While a mezzanine floor is required for mixers with drop door. For similar capacities, dispersion kneaders use lower power than mixer. The mixing time is higher than an internal mixer and hence production volumes are lower in kneader.

Though developed initially for mixing thermoplastics, dispersion kneaders have a unique place in the elastomer mixing industry. Users love the ease of cleanliness on this machine especially when they have to change the colour of their compounds frequently. These machines are also easy to operate and their varied applications include

  • Oil seal, Body seal, Gasket, Belt, Hose, Tube for Automobiles
  • Rubber for Electric wires
  • Conveyor Belts & Power transmission belts
  • Rubberized Rolls
  • Rubber based products like Plug, Cap, Glove, Dental for Medical line
  • Sporting goods like rubber ball, etc

Moriyama Japan (now merged with Nihon Spindle Manufacturing Co Ltd in 2014) enjoys a leadership status in Dispersion Kneader and continues to innovate regularly. Many regional players co-exist in India, China, and Taiwan catering to different categories of customers in rubber mixing industry.

Over a period of time, these kneader manufacturers have developed designs, features and automation for high quality and optimum mixing performance to position themselves closer to the internal mixer. Hence, the confusing terminologies (that I spoke of in the beginning) needs to be viewed in this context. The only caution being when trying to articulate, discuss and solve rubber compounding issues, it is very important to know exactly which rubber machinery is being used – is it dispersion kneader or internal mixer?

Happy Mixing!


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Rubber Sheet Feeder

Internal Mixers and Mixing Mills are familiar rubber compounding machineries for short production runs. This is because of their broad range of shear capabilities and acceptance of all feed forms. Yet, rubber goods producers and tire manufacturers are familiar with their demerits viz. varying power demand, batch-to-batch quality variation and labor intensive operations.

Can you improve the experience and performance expectation? Yes, through the introduction of Sheet Feeders with Rotary Cutter.

Image Courtesy: Bainite Machines Pvt Ltd

Image Courtesy: Bainite Machines Pvt Ltd

Sheet feeders are designed for quick installation onto your existing layout. It could be either mounted to your Mixing Mill frame or put up in front of the weighing conveyor in a Mixer feed line. This means that space constraint never becomes an issue for you to extract more out of your existing mixing operations. And since only one operator can control the mill (or mixer) and sheet feeder, the operation does not increase your labor cost.

Sheet feeder’s with hugger belts replaces the conventional manual loading of rubber sheet on to the mill. This machine enhances your worker’s safety, and makes the loading operation safe. And because it facilitates continuous positive feed of the rubber sheets into the mill (or mixer), the operation feels ‘automatic’.

The rotary cutter on the sheet feeder cuts the fed rubber sheets into uniform rectangular pieces. This results in better dispersion of the rubber sheets in the mixing mill (or mixer for final batch).

The internal mixer rotors performs reactive, dispersive and distributive mixing of uniformly cut rubber sheets faster and better than a long sheet fed into the mixing chamber. The result you experience is a homogenized rubber mix, independent of the operator efficiency or any weight variations in the batch. The quicker mixing of the cut pieces shortens the mix cycle; thereby increasing the productivity of your internal mixer or mixing mill.

Summarizing, Sheet Feeders, is a simple machine which when installed to feed the mixing mill line or batch mixers, increases efficiency, reduces manual intervention and improves consistency of mix. This is also known as Mill Feeder, Rubber Feeder or Stock Loader with disc cutter.

Prodicon, Bainite Machines and few Chinese manufacturers offer them in the world market with customized specifications. Pelmar offers used-machinery of this category.

Please do let us know of your observations and notes on this allied machinery increasing efficiency into your existing rubber mixing line.


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