Rubber & Tyre Machinery World

Info on Equipment And Suppliers


4 Comments

Mixing Mill – A Story Of Woes to Wows

Two-Roll Mixing Mills have been in existence since the time mixing of rubber started for various applications. It is still a sacred machinery for the rubber processors. Hence, we had to think thrice or even more before we decided to write a feature on this machinery in our digital publications.

The theme ‘Mixing Mill: A Story of Woes To Wows!!’, I think, is a true reflection of what this popular rubber machinery has morphed into. Modern mixing mills are rich in features, safe and automated as compared to ancestors. (I think you will agree that our edition’s cover page sums up this contrast well!).

Please click on the below image to go to the digital edition of this special supplement.

Download PDF here

Our previous issue of a concise Knowledge On-The-Go Special Supplement to give you useful information in a concise and timely manner was a success with some exciting reviews. Thanks to each one of you – our readers and advertisers.

I hope you will find this edition too informative and interesting. Please do let me know.

(Disclaimer: The pictures and statements in our special supplements including Know Your Supplier editions are shared with us by the respective companies and/or sources are mentioned appropriately. Rubber Machinery World does not independently verify them nor will vouch for their genuineness that they share with us, hence will not be liable for any misrepresented data)


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.

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


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.