Mechanical engineering lexicon
Technical terms simply explained
Overview
Batch-off system
Our batch-off system is an indispensable addition to rolling mills and serves to automate and simplify production. This system immerses the rubber skin coming from the rolling mill in a tank of non-stick agent, dries it and cools it down to around 5°C above room temperature. In combination with a cutting device, the rubber skin can be cut lengthwise into strips and placed in loops on pallets or in boxes using a swivel device.
The batch-off system is usually positioned so that the rubber skin or strips can be transported directly from the roller. The transfer from the rolling mill to the batch-off is usually carried out via a fold-away conveyor belt.
A width-adjustable cutting device mounted below the working roller cuts the mixture into one or more strips. These strips are manually placed on the moving conveyor belt and removed.
After passing through a non-stick bath, the compound strip is hung in loops on bars between the conveyor chain and passed through the cooling section equipped with several fans, where it is dried and cooled down to almost room temperature. The processed rubber skins can have a width of up to 1000 mm and a thickness of up to 12 mm. Strips are produced in widths from 20 to approx. 160 mm.
Modern batch-off systems can process up to 1,000 kg/h of mixture.
Please contact us if you require a special system design. As a special machine manufacturer, we are able to respond to various customer requirements.
Our batch-off systems can also be equipped with strip cutters, cross cutters, grippers, stackers, stacking and depositing devices.
Extruder
Extruders are essential machines for the production of seamless profiles, hoses or sheets of any length and constant cross-section. Plastics or rubber are extruded in a continuous process. This means that rubber, plastic granulate or powder is homogenized and pressed through a moulding die.
Structure of an extruder
An extruder consists of three main components: the drive, the processing unit and the discharge unit.
Processing unit: This comprises a hopper with feed zone, a feed roller, a screw and a cylinder. The screw is rotatably mounted in the barrel, which can be heated. The extruder head, i.e. the discharge unit, is flange-mounted to the barrel.
Homogenization: To improve the homogenization of the rubber or plastic compound, the cylinder can be fitted with pins to improve kneading. In addition, the compound can be sieved between the cylinder and the discharge part.
How an extruder works
The material is fed into the hopper and guided to the screw by the feed roller. The rotation of the screw transports the material into the barrel of the extruder. The friction between the screw and the barrel wall mixes the material, while the heated barrel facilitates extrusion. The shape of the extruder head ultimately determines the shape of the extruded product.
Extruder models
We offer a wide range of extruder models, including:
- Cold-feed rubber extruder
- Hot-feeding rubber extruder
- Vacuum extruder / extruder with degassing
- Pin extruder
- Strainer extruder
- Single-screw extruder
- Twin-screw extruder / twin-screw extruder
- Coextruder
- Laboratory extruder
- Roller head systems
- Plug extruder / Dump extruder
- Preformer / Barwell
Calender
Calender: Machines for the rubber and textile industry
Calenders are specialized machines used to produce rubber sheets and plates and to coat and duplicate fabric or steel cord. This process is known as calendering.
Structure and function of calenders
A calender consists of at least two counter-rotating, heatable rollers. There are variants with two, three or four rollers. In models with two or three rollers, these are normally arranged vertically one above the other. Four-roller calenders also have a roller in front at the top or bottom end.
Rollers
The rollers are crucial for product quality and must therefore meet high standards:
- High concentricity and dimensional accuracy at operating temperature
- High surface quality and hardness
- Flexural strength and pressure resistance to the materials to be processed
- Tightness against the temperature control medium used
Different roller types are used depending on the load and area of application:
- Chill hard cast rollers: Surface hardness from 530 to 560 HV for normal gap loads up to 600 N/mm.
- Composite cast rollers: With a ductile iron core and a chilled cast iron shell, surface hardness from 530 to 560 HV, for gap loads over 600 N/mm.
Calender stand
The stands are used to hold and support the rollers and are usually made of gray cast iron, more rarely of cast steel or welded steel plates. They are machined on all sides so that the necessary auxiliary equipment can be fitted.
Roller bearing
Slide bearings or roller bearings such as multi-row cylindrical roller bearings, spherical roller bearings or tapered roller bearings are used to support the calender rolls. Roller bearings offer numerous advantages and are now standard:
- Lower roll deflection with almost the same journal diameter
- No running-in period for new bearings or after a roller change
- Reduction in drive power by approx. 25%
- Less stress on the lubricants
Roller adjusting device / roller gap adjustment
The roll adjustment devices are designed for the roll gap forces and enable precise adjustment of the roll gap, even under load. All movement elements are manufactured with high precision to guarantee virtually backlash-free roller adjustment.
Roller set
This device compensates for the deflection of the calender rolls under load and acts on the roll gap in which the product is dimensioned. The inclination is carried out via spindles by geared motors, supported by hydraulic cylinders.
Roller counter-bending device
This device corrects the roll deflection using hydraulic cylinders that apply the bending force to the roll journals. The desired bending pressure is set via control valves.
Bearing clearance compensation
This device eliminates the existing play in the bearing and in the adjusting device and fixes the roller in the working position.
Calender drive
There are various drive solutions for calenders:
- Spur gears and coupling gears: For fixed friction ratios.
- Special gearbox with single-motor drive: Also for fixed friction ratios.
- Special gearboxes with multi-motor drive: For variable friction ratios, with peripheral speeds of up to 100 m/min.
- Individual drives: For variable friction ratios, separate drive/gearbox combination for each roller, with peripheral speeds of up to 40 m/min.
Equipment in front of and behind the calender:
- Preheating extruder
- Fabric unwinder
- Splicing equipment
- Goods storage
- Creel
- Weft breaker
- Cooling units
- Cross cutter
- Powder device
- Center rewinder
- Dock winder
Calender models
Calenders are classified according to the number and arrangement of the rollers. Here is an overview of the most important calender designs and their uses:
Two roll calender
- Calender type: Two roll calender
- Designs: I-shape, oblique shape
- Special types: IT plate calender
- Features: Simplest type; two rollers, upper roller adjustable
- Application: Pulling of simple panels,doubling ofcoated fabrics and panels, production and smoothing of sealing panels
Three-roll calender
- Calender type: Three roll calender
- Designs: I-shape, oblique shape, triangular arrangement
- Special types: Three-roll calender with lamella roll mounted above it
- Features: Universal calender; three rollers, middle fixed, lower and upper adjustable, middle roller is the drive roller. Modern calenders have separate drives for each roller and enable optimally adjustable friction.
- Application: Suitable for various applications, drawing of sheets and films from 0.3 to 2 mm thickness, single-sided covering and friction coating of fabrics, doubling of running surfaces in the flow section
Four roll calender
- Calender type: Four roll calender
- Construction forms: I-shape, F-shape, S-shape, Z-shape, L-shape
- Special types: Profile calender, five-roll calender
- Features: Four or five rollers, each roller with separate drive. Torque motors of the latest generation are particularly suitable due to the full torque at any speed and the precise control of speed and friction. Working speeds of up to 70 m/min possible.
- Application: Rolling of thin rubber films up to 0.1 mm, covering of tire cord, production of conveyor belt blanks, double-sided covering of fabrics, doubling of rubber sheets
Areas of application for calenders
Calenders are used to produce layered rubber or plastic products such as sheets, films, adhesive strips and floor coverings. Calendering is particularly useful when the specifications for the thickness of the product are within narrow limits.
Typical applications:
- Tire production
- Covering tire cord
- Production of conveyor belts
- Production of technical rubber articles
- Friction of fabrics
- Plate pulling
Webbing with simultaneous duplication
Vulcanization
Vulcanization of caoutchouc and rubber
Vulcanization makes caoutchouc and rubber dimensionally stable. The long-chain rubber molecules are cross-linked by a chemical reaction that takes place at temperatures between 120 and 160°C with the addition of sulphur.
History of vulcanization
In 1839, Charles Goodyear discovered by chance that rubber loses its solubility, stickiness and plasticity when heated with sulphur and lead oxide and takes on elastic properties. A few years later, Thomas Hancock recognized the importance of sulphur in the production of usable rubber articles. William Brockedon, a friend of Hancock's, eventually named this process "vulcanization".
Modern vulcanization
Today, vulcanization refers to all processes that convert rubber and other elastomers from a plastic to a highly elastic state. There are many methods and means for this important process, including chemical fillers and reaction materials as well as special equipment and machines.
Vulcanizing kettle
Vulcanizing kettles are used for vulcanizing injection-moulded articles, hoses, sheets, shoe parts and tires. They are available in horizontal and vertical designs. A typical vulcanizing kettle is an autoclave, which is cylindrical in shape and has a lid with a bayonet lock. The products are moved into the vessel on a trolley and vulcanized with pressure and steam or hot air, depending on the type of product.
Vulcanizing presses
Vulcanizing presses heat conveyor belts, tires, sheets and technical rubber goods. The presses must be adapted to the respective articles. There are multi-daylight presses for technical molded articles and special presses for conveyor belts and belts. The products are vulcanized in moulds, frames or sheets. Hydraulic vulcanizing presses have established themselves because they are efficient and versatile.
Compression Molding
Compression molding is a process for plastics. The blank is placed in the mold and pressed together under temperature and high pressure. This process is suitable for medium-sized series and fiber composites.
Transfer Molding
In transfer molding, the mixture is placed in a three-part mold. The compound is pressed through a sprue channel into the mold cavities. After vulcanization, the sprue is removed. This process is suitable for small and medium-sized series with a high fiber volume.
Injection molding (injection molding process)
The injection molding process is the most modern method and enables the production of complicated molded parts. A rotating screw plasticizes and heats the mixture, which is then injected into the mould at high pressure. This process is worthwhile for higher quantities.
Vulcanizing machines
The continuous automatic mat vulcanizing machine (Auma) was developed for vulcanizing rubber sheet material. This machine consists of a heating cylinder and several rollers that guide the material through various zones where it is heated and vulcanized.
In addition to discontinuous vulcanization methods, there are also continuous processes such as hot air channels, microwaves and salt baths. Here, the rubber is extruded directly into the machine in the form of profiles or seals.
Hot air ducts
Here, the extrudate (as a profile from the extruder) runs on a heat-resistant conveyor belt through a channel. A stream of hot air is passed through this channel at high air speed. The hot air transfers the heat to the profile surfaces. Heat-transferring air molecules ensure optimum heat transfer at the extrudate surface due to the high air speed. The air is heated by electricity or by natural or liquid gas burners and is usually 260-300°C. Hot air ducts are often of modular design. The modules are usually 3 m long. Depending on the application, several modules can be connected to form a long duct. The typical length is between 9 and 21 m. A special type of duct is the shock duct; there are two variants, the IR shock duct and the hot air shock duct. Here, a temperature of 500 - 600° C is achieved over a distance of 3-6 m by means of intensive IR radiation or by a more effective air flow and high air speed. These systems are used for profiles that require rapid surface cross-linking.
Microwave systems
(UHF systems) Ultra-high frequency (UHF) systems generate ultra-high frequency microwaves. The aim is to heat the material in the shortest possible time (a bipolar compound is required). The rubber absorbs the microwaves, converts them into heat and vulcanizes as a result. The UHF channel must be supplemented with subsequent hot air channels to ensure uniform heat distribution in the product and to achieve the vulcanization time.
Salt baths
In salt bath vulcanization, the rubber profile is fed from the extruder directly into the molten salt. This is a pressureless vulcanization process. Seals and profiles with smooth, dense surfaces (window seals, drive belts, wiper blades, etc.) are produced in this way. Vulcanization in a salt bath is particularly suitable for large, solid profiles (construction profiles, tunnel profiles, etc.)
Rolling mills
Rolling mills are essential for the production of rubber compounds. A basic rubber material is mixed with various additives such as fillers, plasticizers, processing aids and dyes. The two rollers of a rolling mill rotate in opposite directions, with one roller running faster than the other (friction). Shear forces act on the rubber in the gap between the rollers, causing it to be mixed.
Structure of rolling mills
A rolling mill consists of two parallel rollers that can be moved independently of each other. The speed of the rollers is set to a specific ratio. Depending on the mixture, either the front roller facing the machine operator or the rear roller rotates faster. The width of the roller gap can be adjusted to determine the thickness of the rubber layer. This can be adjusted to the respective amount of rubber during operation. As heat is generated during the mixing process, the rollers can be cooled using water cooling to achieve an optimum processing temperature.
Function of rolling mills
To begin with, the untreated rubber block is inserted into the top of the roller gap. The block is drawn into the nip and wraps around the front roller in the thickness of the nip. Additives such as fillers, plasticizers and molding aids are then added to the nip one after the other. To ensure that these are properly mixed in, the rubber is cut across the roller and wound up after the additives have been roughly distributed. The rubber roll (dummy) is then inserted lengthwise into the nip. This process is repeated until the additives have been fully incorporated into the rubber base material. The finished rubber compound is then brought into the desired shape and vulcanized.
Safety and occupational health at rolling mills
The roller gap poses a high safety risk in rolling mills and laboratory rolling mills for processing rubber. To protect employees, companies need to retrofit old rolling mills.
Application areas of rolling mills
Rolling mills are used to incorporate certain substances into very tough and resistant materials such as rubber. They are also used to crush used rubber and to refine compounds from internal mixers.
Rolling mill models
- Crushing mill
- Rubber rolling mill
- Laboratory rolling mill
- PVC rolling mill
- Refiner rolling mill
- Silicone rolling mill
Stockblender
The mixing process on a rolling mill is usually discontinuous and the quality of the finished mixture depends heavily on the care and experience of the operator. To automate this process, the stock blender was developed, a device that is known in English-speaking countries as the "stock blender" and has also become widespread in German-speaking countries.
Structure of the stick blender
The stick blender consists of two rollers that are the same width as the mixing rollers of the rolling mill, but have a significantly smaller diameter. These rollers are arranged vertically and slightly offset above the working roller. The lower roller is usually set in rotation by an infinitely variable drive, while the upper roller acts as a pressure roller. On the working side, there is a pair of material guide rollers that can be moved laterally in both directions via a separate drive system.
Function of the stick blender
After all materials have been added, a stable rubber skin forms on the work roller. The operator cuts it open and places it between the material guide rollers over the driven blender roller. The pressure roller is then pneumatically applied to the blender roller. The rubber skin is removed from the working roller and fed back into the nip of the mixing rollers via the blender roller. The laying drive of the guide rollers (also known as the wig-wag) starts, which mixes the roller skin evenly and intensively. After a predetermined mixing time or number of laying cycles, the skin is cut off by the blender and can be removed from the working roller in the form of slabs or dolls.
Advantages of the stick blender
- Fast and intensive mixing: Achieves high homogeneity of the batch.
- Effective cooling: The rubber compound cools down quickly.
- Increased capacity: Larger quantities of rubber compound can be processed on the rolling mill.
