PDF Drive is your search engine for PDF files. As of today we have 78,, eBooks for you to download for free. No annoying ads, no download limits, enjoy . Rubber Technology. Compounding and Testing for Performance. John S. Dick. ISBNs. HANSER. Hanser Publishers. Struktol Rubber Handbook. Table of Contents. About Struktol Company of America. 6. Introduction. 7. Function of Processing Additives. 8. What are Processing.
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book covers manufacturing processes of rubber products, compounding of Modern Technology Of Rubber & Allied Industries [NI21] by NIIR Board, Rs. A catalog record for this book is available from the Library of Congress . the method has been applied to the study of rubber vulcanization (Tanaka,. Hardcover - [Free] Rubber Technologists Handbook Volume 2 Published By Smithers Rapra. Technology Hardcover [PDF] [EPUB] -. RUBBER.
Minor formulation changes are readily feasible. Minimal floor space and ceiling height is required. Disadvantages of continuous mixing 1. Supply of raw materials in free-flowing form may be costly. Clean-up from compound to compound may be very extensive. Development of the Banbury Mixer The Banbury internal mixer was introduced to the rubber industry in ; the first mixers were supplied to Goodyear for mixing tyre compounds.
For many years these mixers bore numerical designations for different sizes. These numbers approximated the quantity of 22" X 60" in mills that a specific Banbury mixer could replace. Soon after the first internal mixers were introduced, increases in speed, power and ram pressure made this relationship no longer meaningful. The earliest mixers had the same basic fundamentals of operation as those which are in service today. A ram is necessary to push raw materials into the mixing chamber, two counter rotating rotors perform the mixing action, and a door at the bottom discharges the completed batch to a secondary piece of machinery.
Improvements continued to increase the value of the design for mixing applications, despite changes in materials and in expectations. The F-series Banbury mixers were introduced during the early s. Unlike the earlier mixers, these F-series machines carried designations for each model which defined chamber volume.
The F-series Banbury mixers not only introduced many new mechanical improvements, but were designed with the user in mind. Loading and discharge features and maintenance features were designed to emphasise the mixing capabilities of the machine rather than loading, unloading and maintaining. When the F-series mixer hoppers were enlarged to accept bales and slabs of rubber more readily, the hopper door angle was steepened to assist in more rapid introduction of material to the mixing chamber.
The junction between the hopper and the mixing chamber was provided with replaceable throat wear plates. These permit maintenance in an area subject to significant wear because of the action of the ram, well ahead of wear to the chamber. In the latest models, replaceable wear plates have been extended further into the hopper to increase the stiffness of the assembly.
The end-frames have been significantly strengthened and the access to the dust seals has been enlarged to assist maintenance or replacement.
Within the mixing chamber the rotor end-plates have been converted to a one-piece design, eliminating occasional contamination associated with older, two-piece designs. This design also prevents the end-plate being dislodged from its fitting, reducing the incidence of mechanical failure.
Rotor journals are now tapered, eliminating the need for bearing sleeves. Overall manufacturing tolerances have been reduced, lowering vibration and yielding longer useful service life. The wall thickness of the sides has been increased by nearly a factor of 2 over older models, in response to the higher loads experienced with modern mixing procedures.
The dual-circuit cooling design and the size and location of the bored cooling channels provide highly improved heat transfer. The discharge area has been significantly increased to permit more rapid batch discharge, reducing the interval between batches and adding to productivity. The toggle latch locking mechanism for the drop door has been made more positive in action but with lower moving parts, requiring less maintenance.
Rotor volumes are measured by immersion displacement, chambers' volumes by measurement and calculation. It is entirely feasible to convert an older D-series Banbury to the improved F- series equivalent.
In many cases, the existing drive and hopper can be incorporated in the conversion. As shown in Figure 3, intensive mixing-the breakdown of agglomerates leading to a high level of dispersion- occurs by the action of the rotor against the side of mixing chamber.
Extensive or distributive, mixing is accomplished by the continuous moving and shearing of the batch by the rotors; it occurs mainly between the rotors and the ram, and is influenced by the geometry of both. Intensive and extensive mixing must be considered, not only in machine design, but also with regard to mixing procedures. Operating Variables The major variables in mixer operation are ram pressure, charging procedure, rotor speed, batch size and coolant temperature.
With a properly designed and well-maintained mixer, some selection of these variables will optimise the mixing of almost every rubber compound yet devised. Ram Pressure The major purpose for application of pressure to the ram is to drive the raw materials into the mixing chamber and to prevent their upward exit during mixing.
Increasing ram pressure beyond this point is often found in practice, from a folkloric belief that it will speed the mixing action or otherwise improve it. In fact, it usually has the opposite effect.
Too high a pressure can impede rotor action needed for extensive mixing. The proper seated ram position is shown in Figure 4. The most popular ram configuration, now considered standard, is the single V-bottom.
Somewhat less popular is the double, gable V-bottom which facilitates addition of powder or liquid ingredients over the ram while it is in the down or mixing position. This procedure is not recommended as it increases wear and maximises hang-up of the compound from one batch to the next. It is in exactly the same category as dumping the batch with the ram in the down position. Nevertheless, both procedures retain popularity with those more interested in saving a few seconds of mix time than in machine life or batch to batch contamination.
The flat-bottomed ram may still be found in older machines. Because of the variation in air cylinder diameters, ram pressure should not be obtained from a pressure gauge on the supply line, but measured directly on the batch. Such data can then be transferred from one mixer to another. High ram pressure is useful in charging the mixing chamber, but a lower pressure is more desirable during the actual mixing.
This has led to the development of multiple-ram pressure control systems. Two or three zones are pre-set with individual regulators to specific pressure levels. This may be automated or controlled by the mixer operator. It can include provision for relief of ram pressure if certain limits on power draw are exceeded, or even if the change in power draw indicates a likelihood that such limits may be reached.
This is particularly useful in moderating power surges with upside-down and sandwich mixes. It also provides the means for staying below certain power plateaus that, in some locations, strongly affect plant utility costs. The importance of ram pressure and position led to the development of the automatic sensing device shown in Figure 5. By means of its output graph the ram position indicator can provide a good profile of the mixing action and a guide to proper batch size.
Typical profiles are shown in Figure 6. Here, three batches of the same compound are mixed to a total elapsed time T. The desired ram action is shown in Figure 6 b. This is followed by a longer period of reduced ram action corresponding to distributive and dispersive mixing. Figure 6 a shows an oversized batch of the same compound. Almost to the end of the batch, the mixer struggles to incorporate the excess of ingredients.
Dispersion and uniform distribution will not be optimum if the ram does not reach a fully seated position in the first third of the mixing cycle. Figure 6 c depicts the same batch below optimum batch size; the ram seats almost immediately; distributive and dispersive mixing are strongly impeded.
At optimum batch size, ram displacement charts can be used to fine tune the ram pressure programme so as best to approximate Figure 6 b.
Besides this, batch to batch charts can spot equipment malfunction and aid in diagnosing improperly weighed batches. At the same time, the mixes should be capable of being processed in the factory without much difficulty and at minimum cost. Chemically speaking, a rubber "compound" is not a compound, but is merely a mixture of rubber and compounding ingredients, ready for vulcanization.
The simplest of all compounds, rubber plus vulcanizing agent, is of little use in most applications.
Since it is the basic structure for most compounds, we have to consider how it can be compounded with reinforcing agents, anti-oxidants, and plasticizers to give the best combination of properties for a particular application.
General Compounding Principles The scope of compounding consists of specifying the type and amount of various ingredients in a mix, the manner of mixing, the processing of the mixed compound, and the method and details of vulcanization.
This essentially covers the requirements of end-use and service properties, processability, and cost. The three major decisions to be made by the compounder, considering all these factors in designing a compound, are connected with the choice of rubber, the level of reinforcement, and the type of vulcanization system to be employed.
In general, these factors determine cost, mechanical and visco-elastic properties, resistance to degrading influences, processability, and special requirements such as flame resistance, low temperature flexibility and non-toxicity for application in contact with food-stuffs.
Service testing or product testing is more often than not connected with product design and manufacture. In practice, the failure of rubber articles occurs mainly by tearing, abrasion, or dynamic fatigue arising from crack propagation. Therefore, physical tests are often required for development of new materials or products or in developing new engineering uses of rubber.
However, there is generally poor correlation between laboratory tests particularly the static tests and product performance. Despite this, laboratory tests have been developed due to the advantages of low cost, quick results, and the ability to compare many compounding variables primarily for screening purposes.
For many years, physical tests on vulcanizate properties such as tensile strength, hardness, abrasion resistance resilience, tear, compression, cut, and crack growth have been standardized in the rubber industry.
We shall consider the individual tests and their significance. The tests have the following uses: 1 designing compounds to meet service conditions; 2 investigating product or process failures; 3 quality assurance of compound batches; and 4 quality control of raw material. Tensile Strength This is defined as the force on unit area of original cross-section which is required to break the test specimen, the condition being such that the stress is substantially uniform over the whole of the cross-section.
The elongation at break is the maximum value of the elongation expressed as a percentage of the original length. Hooke's law is obeyed by metals, which undergo practically only elastic changes of shape below their yield point.
However, in the deformation of rubber, we must differentiate between a an elastic deformation, b a plastic deformation and c an extension or residual deformation. In practice, this amounts to only 0.
However, the modulus of rubber is not a constant, as in the case of metals. Contrary to engineering practice, test results on rubber have no absolute meaning as they depend on the conditions of the test. Rubber specimens undergo gross changes in shape when stressed, unlike other high strength engineering materials. Rubber tensile machines can be used for various tests such as: a for the determination of tensile strength and elongation at break and b the determination of tensile stress values at given elongations.
These are the so-called "modulus" values. Physical properties can differ length-wise and cross-wise on a section of rubber compound due to anisotropy. In the direction of calendering, tensile strength is high and extensibility is low; across, the strength is relatively low and extensibility high. This phenomenon will be pronounced in the case of short-fibre reinforced rubber compounds. Tensile test specimens can be tested at room temperature with standard Schopper-type machines of 0.
The lower grip of such a machine moves at constant speed, while the upper grip is connected with a pendulum type dynamometer. The specimen is strained by a uniform movement of the lower grip, to which one end of the specimen is attached. The other end of the specimen is held by its upper grip. The pendulum is displaced from its normal position by a pull on the specimen and the amount of displacement indicate the force. The pendulum is lightly ratcheted to a notched sector so that after the specimen breaks, the pendulum and the pointer which is geared to it will remain stationary at the maximum load.
The pendulum moves with varying usually increasing angular velocity, i. The pendulum-type machine is widely used by reason of its simplicity and lower cost, but it is subject to error mainly due to the pendulum inertia and the unavoidable friction in the pendulum bearings. Some machines have a constant rate of traverse of the lower grip usually 50 5 cm per minute , while others have a gear box to provide a range of speed. Movement of the upper grip occurs during deflection of the pendulum.
This may cause variation in the straining rate of the specimen.
Other machines have a heating chamber in which tests can be carried out at temperatures from approximately C to C. The specimens used take the form of dumb-bells cut out from products. This design of a satisfactory test specimen takes into account two main problems in tensile testing.
First, the difficulty of holding the rubber securely without any slipping, and second, the avoidance of high local stresses in the test piece which would cause premature rupture at the grips. The broader portions at the end of the dumb-bell are held in self-tightening grips which automatically tighten as the thickness diminishes during stretching. The broader portions are joined to the narrower central portion, i.
The true length of the test specimen cannot be measured by recording the distance between the grips; this is done by marking the central portion of the piece with two parallel crosslines, the volume of rubber between the marks is regarded as being stretched uniformly. The dumb-bell pieces are punched from press moulded sheet, taking care to ensure that the cut be as clean as possible. For a complete determination of the force-extension curve, a record of the total course of the extension up to the point of break, taken with the help of an autographic recorder is required.
Electrical-force measuring machines have been developed to overcome the inertia of the pendulum-type testing machine. In these devices, the load on the upper grip results in the deformation of a light but perfectly elastic metal ring. The extent of this deformation is then measured by electrical means. These instruments have a greater range, and force-extension graph or read out devices. There is negligible movement of the upper grip, and inertia effects are avoided. Most of them also have facilities for reverse motion to enable a retraction curve to be drawn, or for cycling tests.
They also have cycling, automatic zeroing of load and extension outputs, and fast cross-head return, making them particularly suitable for repetitive quality control-type testing. Tensile tests are almost invariably used either to indicate the quality of rubber vulcanizate or for purpose of quality control in production, but are seldom if ever, used in component design. Tensile strength in itself bears little relation to product service, as rubber is not normally used at such high elongations that there is a danger of failure due to tensile rupture even after moderate ageing.
As a service test, tensile strength tests are valueless but for many purposes of comparison, they are extremely useful. High tensile strengths coupled with a reasonable elongation at break can only be obtained with high quality rubber mixes and for this reason tensile strength is very often included in specifications, e.
They are also useful for determining the curing characteristics of compounds-the cure condition giving the highest tensile strength being widely adopted as optimum cure. Deterioration of rubber on ageing can be followed by the drop in tensile strength. Effect of many compounding ingredients as well as that of pigment dispersion can be decided by tensile strength tests. Finally, as a control test, it is invaluable since any mistake in mixing or processing giving inferior product is indicated by a drop in tensile strength.
Unlike most other engineering materials, rubber can be compounded to give a wide range of elastic modulus values. This enables a product of fixed dimensions to be made in a variety of stiffnesses. In most applications, the modulus of rubber is more important in compression, shear and torsion, than in tension. In compression, the shape factor plays a significant part. Empirical curves have been compiled to illustrate this feature.
Modulus measurements show less variations than values taken at rupture and thus, more reliable. Modulus is a useful property to measure as the compounder and designer generally have a reasonable idea of what level of modulus is most likely to suit the applications, e. Comprehensive Injection Moulding Hb. Rs 1, Analog And Digital Electronics. Handbook Of Rubber Technology, Vol. In stock Book Code: Recently Viewed. Book Description Book Information Reviews Details This volume dealing with basic concepts of rubber technology, natural and synthetic rubbers, elastomers, latex and rubber related polymers, chemistry and technology of vulcanisation and materials for compounding and reinforcement is the first volume of Handbook of Rubber Technology.
This useful handbook endeavours to present a comprehensive, accurate and the most recent account of rubber technology. In the modern industrial world, rubber is a familiar and indispensable raw material, remarkable for its unique qualities of elasticity and toughness.
Rubber is increasingly finding more uses for itself in our fast developing technical world. Recognizing the great importance of rubber, this reference text book is intended for the practising rubber and polymer technologists, chemical and mechanical engineers, industrial chemists and research students. This book also provides an up-to-date information for the users of rubber products in other industries.