Calendering machine

Rubber sheets are the most important materials for the construction and fabrication of much chemical plant equipment such as storage tanks, reactor vessels, pipelines, seals, hoses and rubber lined mild steel equipment of different sizes and shapes, inflatables, etc., and almost all equipment subjected to different corrosive environments. The rubber sheets can be either plain or fabrics coated with rubber. The fabrics used for coating are nylon, rayon, cotton or various other synthetics. Rubberized fabric cords are also used as reinforcing members in various products. 

In the production of fine rubber sheets or coated rubber sheets, the main equipment used is a calendering machine. Though rubber extruding machines which are later developments are used for manufacturing some sheet profiles, the calendering machines are the ones used widely in the rubber industry for the manufacture of rubber and coated rubber sheets. Calenders are conveniently used for the continuous production of rubber sheets from different types of rubbers. 

In the rubber industry, apart from the mixing mill, the two major processing machines are calender and extruder. These machines 

There is little work of a fundamental nature done that helps towards a better understanding or control of calendering of rubber. Most theoretical studies were concerned with the pressure developed when a stock of thick viscous rubber sheet material is reduced to a thinner sheet by passage between rolls. Calenders with 3, 4 or more rolls might be assembled to quite different configurations. Calenders in L shaped, F shaped, I shaped or Z shaped configurations with roll diameters of 168 mm, 250 mm and 350 mm are available on the market. 

The calendering machine of three, four or more hollow rolls has arrangements for heating by steam or hot water or cooling by refrigerated water. The widths of the calender rolls may be only six inches for a laboratory size calendering machine or up to hundred inches when heavy work and a large volume production are required. 

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Taking the example of a three-roll calendering machine, the successful calendering operation is ensured by the following basic features. 

Suitable provision for heating and cooling by means of steam and cold water lines are provided in the calendering machine. 

The three samples (Ci, C2, and C3) taken from the calendering machine have been studied by coulometric titration and dehydrochlorination. Taking into account the calcium stearate and the zinc stearate and... 

A calender machine used to add materials when preparing rubber has 18 in. diameterrolls. The rolls rotate at 60 rev/min. 

To manufacture EPDM sheeting/membrane, pre-warmed, plasticised EPDM compound at a temperature of 80-100 °C is used for calendering in a 3 roll in-line T configuration rubber calender machine or in a 4 bowl Z configuration rubber calender machine. 

Chapter 16C Compression, Transfer and Injection Molding of Specialty Elastomers by Dr. Robert W. Keller will give the rubber compounder an excellent view of the considerations necessary in the molding operation in the factory. This is only one aspect of rubber processing, but similar approaches are needed for other processes such as extrusion, calendering, machine, and hand building of hose, belts, rolls, tank, and pipe linings, and so on. 

Calendering can achieve surprising accuracy on the thickness of a sheet. Typically the tolerance is 0.005 mm but to achieve this it is essential to have very close control over roll temperatures, speeds and proximity. In addition, the dimensions of the rolls must be very precise. The production of the rolls is akin to the manufacture of an injection moulding tool in the sense that very high machining skills are required. The particular features of a calender roll are a uniform specified surface finish, minimal eccentricity and a special barrel profile ( crown ) to compensate for roll deflection under the very high presurres developed between the rolls. 

The calendering configuration of rolls may consist of two to at least seven rolls. The number of rolls and their arrangement characterizes them. Examples of the layout of the rolls are the true L , conventional inverted L , reverse fed inverted L , I , Z , and so on. The most popular are the four-roll inverted L and Z rolls. The Z calenders have the advantage of lower heat loss in the film or sheet because of the melts shorter travel and the machines simpler construction. They are simpler to construct because they need less compensation for roll bending. This compensation occurs because there are no more than two rolls in any vertical direction as opposed to three rolls in a four roll inverted L calender and so on. 

A machine for masticating rubber, mixing rubber compounds and for warming up rubber compounds prior to calendering, extrusion, etc. See Open Mill. 

A diagram showing how rubber sheet, fabric, linings, etc., are let off through tensioning devices into calenders, spreading machines, etc., and finally taken up on box rollers. Direction of travel and position of rubber nips are usually included in such diagrams. 

Hose constmcted by wrapping the reinforcing fabric and the calendered cover on to the inner tube which has been fitted over a mandrel of the desired diameter. The application of the fabric, the cover and of the wrapper may be done either by hand or by machine. 

An alternative method to that of using a spreading machine or a calender for the initial preparation of fabrics for application of rubber (for composite product assembly) can be by the use of dip coaters. Application of rubber compound by this method ensures a better penetration of the fabric interstices than can be achieved by conventional frictioning techniques using calenders. More delicate fabrics which would not be strong enough for calender application can also be treated with rubber by this technique. 

Control of product gauge is of considerable importance for the majority of products produced from calenders and various means have been used to achieve this from the early days of the machine. Inaccuracies in gauge on calendered products can not only mean out of specification goods being produced, but also one can be giving away free of charge considerable quantities of expensive compounds (unless the product is sold by weight, of course). 

Early thickness control systems relied on the calender operator setting up the machine correctly by the use of hand-held thickness gauges, with the consequent slowness of response time during set-up and running before any desired modification to gauge could be achieved. It was usual to run the calender at a low speed to set-up the required dimensions for the product and then to speed up the... 

Calenders are very expensive and specific machines that are used only for high-output production. 

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