Rubber & Tyre Machinery World

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An Introduction to Rotocure

A Rotocure is a shortened name of Rotary Curing Press. This machinery is designed for the continuous vulcanization of technical rubber products.

So, if you are into manufacturing of rubber belts, roof covering, rubber belts with textile inserts, sealing plates, membrane and ship textile, conveyor belts, flat belts, floor covering, etc you would have heard of this equipment (if you are not yet using one in your production line).

As a technical rubber goods producer, vulcanization is critical to your manufacturing. In an earlier post, I had introduced you to Autoclave for vulcanizing of products that you cannot achieve on a standard press-based compression molding process. You install a Rotocure to create continuous vulcanization process where the sheet is heated and vulcanized.

While every technical rubber goods manufacturing plant may not have a Rotocure, those who do have one positions their rotary curing press after the calendar.

Rotocure Line:

A typical Rotary Curing Press Line consist of following component machines – A Winding Let-off Unit, Rotocure, Cooling Unit, Equipment fo edge trimming of product and a Winding-up equipment.

Rotocure Image Collage

Rotocure Line: A Collage of Individual Images From The Web

From Winding Let-off Unit, your semi-finished calendered rubber material is led on to the lower roll and from there into pressing space between the heating drum and thrust pressing belt, where it is pressed and vulcanized.

Operating A Rotocure:

Your main vulcanizing machine is always the Rotocure in the set-up and consists of a large, steam-heated, revolving steel drum. This is partly encompassed by an endless steel band. The steel band encompasses approximately 2/3 of the circumference of the drum through the action of two conducting rollers and a tensioning pulley. The drum is heated by means of steam to a temperature of 150 – 200°C. In addition, there is a heating plate bent round approximately half of the surface of the drum and which gives some additional heat, but primarily it prevents loss of heat.

When you operate a Rotocure Equipment, you need to ensure that all the various parts work in precise alignment. It is  crucial for you to maintain all process parameters in their correct tolerance. Because a slight change in the heated roll or in the steel belt that are both in charge of the smooth vulcanization of the sheet can cause your sheet to be unevenly vulcanized. This leads to irregularities and subsequently rejection of your end-product.

Your calendered rubber material is placed between the drum and the band at the lower roller. With the aid of the tensioning pulley, the band is strained so that a pressure (say approximately 0.3 MPa) is obtained between the band and the drum.

Rotocure - Pelmar

A Fully Refurbished Rotocure From Pelmar Engineering, Israel

The linear speed of this drum can vary from a 0.04-200 m of cured material per hour, all depending on your material’s thickness and rate of vulcanization.

The drum, which is interchangeable, can have completely smooth or patterned surfaces and normally has a diameter of 700-1500 mm and a width of between 1200-2500 mm.

For a normal speed range of 5 – 50 metres/hour and a contact length against the drum of 3 minutes, you may achieve a curing time between 4 – 35 min for your specific compound.

As a user, your will quickly realize that the main advantages of a well-manufactured and correctly operated rotary curing press (or rotocure) machine are its high hourly output, long lifespan, low energy consumption and high reliability.

On the other hand, you could be challenged by the limitation of your product thickness and the pressure sought during vulcanization.

As is normal with other categories of rubber machinery, you get both New and Used Rotocure’s in the market. When you shortlist your suppliers, you could also discuss with Pelmar Engineering Ltd for Used Rotocure or Pracsol Chemicals And Machinery for New Rotocure – more of their details on this site is in our interviews section.

Summarizing, a Rotocure is an important rubber machinery if you are into manufacturing of technical rubber products. I look forward to your thoughts on this continuous vulcanizing machine.


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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?


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