The PRESSMIXER technology was patented in Austria , the patent serving as the basis on which Mischtechnik Hoffmann & Partner in Sankt Andrä-Wördern has been conceiving and manufacturing mixing systems for 25 years. For a long time, different designs of the PRESSMIXER have been used as discontinuously working mixing units f or a wide range of viscosities, among other areas of application in the polymer-processing industry  for mixing and homogenisation jobs.

As the name suggests, the PRESSMIXER is a machine for “mixing under pressure“ , a concept which forms the basis of the original idea of the patent behind this technology.

The system comprises a horizontally arranged, cylindrical mixing chamber which is delimited by two plates: the front “ valve plate“ , which is equipped with different feed valves and a vacuum valve, and the back “ press plate“, which, like the piston of a cylinder, can be variably positioned within the mixing container and as such assumes a number of functions during the mixing process, the evacuation and the cleaning of the PRESSMIXER.

A single, centrally mounted rotor  of a maximum thickness of 100 mm is used as the mixing tool. Between the valve plate and the press plate it can be moved f rom one end position to the other at a variable rotational speed and feed rate, covering all parts of the mixing chamber without any dead space .

In addition, pasty and liquid mixing components may be added directly into the closed mixer during the mixing process via the valve plate fixtures. Via the vacuum valve in the valve plate the mixing chamber may also be ventilated or evacuated, depending on the process step in question.

In the course of the mixing process the volume of the mixing chamber is variably adapted to the batch size to be processed and the requirements of the different process steps by moving the press plate within the mixing chamber.
Thus, the PRESSMIXER allows batch sizes of between 20 and 80% of the gross volume of the mixing chamber to be processed with the same efficiency and while making optimum use of the power input.

The finished mixture can be extruded directly via a valve in the valve plate. Thus, in combination with a buffer press continuous filling is possible.
Without opening the PRESSMIXER waste-free “batch in batch”  production without the need for intermediate cleaning  is possible.

Recently, apart from the standard PRESSMIXERS, additional, more basic machines without an extrusion function with exchangeable containers have been developed on the basis of this operating principle.

Planetary mixers allow highly viscous to plastic substances to be mixed without dead space. The numerous applications range f rom simple plants to high-performance vertical kneaders. They are designed for the use of  exchangeable containers: In combination with a discharge device they may be emptied  almost without residue after the mixing process.

The use of different stirring tools provides all of the benefits that highly intensive dispersing machines have to offer for a very broad range of viscosities.
The machine is available for container sizes of 6 to 2500 litres.

The entire mixing process may be entered into a receipe control and runs fully automatically. The
process is monitored via a number of sensors (pressure, temperature, flow rate…) and stopped
automatically upon completion. In addition, built-in cleaning nozzles allow the mixer to be cleaned
efficiently once the product has been discharged.

As an additional option, filling materials can be fed in under vacuum during the mixing process via a “screw valve”  which can be closed hydraulically. Since this is done while the mixer is running and since the filling materials are immediately wetted and mixed into the liquid basis it is possible to add several times the filling material volume  in relation to the available container volume in one single step. Exposure of the product to air humidity is effectively prevented.
In this way, the shelf -life of adhesives and sealants can be increased .

We have also developed vacuum feeding, which allows powdery components to be fed into the mixing chamber under vacuum. Operators particularly benefit from the use of powders with a low bulk density, especially if large quantities of such filling materials are to be mixed in.
With this feeding system the solid can be added to the liquid basis under vacuum, i.e., at the moment of contact, direct wetting occurs under exclusion of air or gas, which leads to better wetting. In this way, the creation of gas cavities as a result of the extremely fine dispersion of the carrier gas is prevented.

As a consequence, evacuation of the finished product upon completion of the mixture is not necessary in most cases unless gaseous substances are produced during the mixing process (for example due to chemical reactions) that have to be removed.

When the mixing chamber is closed the dosing valve (screw valve) can be extended and retracted under vacuum. The rotational speed can be freely adjusted depending on the viscosity.

 By combining planetary mixers with one drive or two separate drives , together with a central or

revolving dissolver disc, this high-performance machine may also be used for processing products of

low to extremely high viscosity while at the same time assuring extremely f ine dispersion. Many

versions of these planetary dissolvers are equipped with up to three independently controllable drives.

 Additional benefits:

• The concurrent wall/bottom wipers support the mixing and kneading process while ensuring good heat transfer to the container wall
• Very short mixing times  for high-quality products
• Product-optimised mixing, kneading and dispersing tools
• The product temperature is directly measured via the revolving temperature probe
• Vacuum-sealed and ex-proof designs
• Easily replaceable  mixing tools

Our dissolvers are used for dispersing and homogenising liquids of low to medium viscosity. Central to the dispersion are one or more high-speed toothed discs. As a result of the circulating current that is created the material to be dispersed will hit the surface of the disc rotating at high speed. As a consequence the agglomerates will be affected by the high shear stresses and, depending on the stability of the agglomerates, broken up.

Dissolver units are not only used in the standard floor-mounted dissolver with exchangeable container, but also in a number of vertical mixers:

• Built-in Dissolvers
• Dissolvers with height-adjustable dispersion disk
• Floor-mounted or wall-mounted dissolvers
• Rotor-stator dissolvers
• Multi-shaft mixers
• Planetary mixers

Since the shape and dimeter of the toothed discs are very important factors in the process, an extensive range of different dissolver discs has been established over the decades.

They guarantee short mixing times and efficient power input.

We offer the right dissolver disc for all kinds of applications.

In many regards, these considerably less costly  machines are an alternative to planetary or multishaft mixers. Mixing times can be reduced significantly  and substantially less waste is produced since less cleaning  is required. Like the PRESSMIXER these machines are characterised by a high reproducibility. In addition to liquid and pasty products, powder mixtures can be processed.

In contrast to the horizontal PRESSMIXER the mixing tool here is arranged vertically . The mixing container can also be designed as an exchangeable container in order to be able to dose the individual components outside the mixer. The smooth valve plate tightly seals the container.

On the valve plate, different feed valves may be arranged.
In the cylindrical mixing chamber a single rotating mixing tool oscillates between the valve plate and the container bottom.

The mixing tool is a single, centrally mounted rotor of a thickness of 15 to 50 mm, which is moved between the valve plate and the container bottom at a variable rotational speed and a freely preselectable feed rate of 15 to 60 mm/sec, covering all parts of the mixing chamber without any dead space.
It is driven by a gear engine while the mixing tool is advanced by a hydraulic cylinder.

The axial distance between the mixing tool and the container bottom and the radial distance to the container casing are 5 mm. The special shape of the mixing tool in combination with the extremely small distances to the container ensures efficient agitation of the material.
A special tungsten carbide  coating, which is characterised by an excellent wear resistance and a high chemical resistance, is used to protect the shaft guide f rom wear and tear. The particularly fine machining of Ra < 0.1 μm minimises adherence of material to the coated surfaces.

 For discharging the finished mixture the valve plate is raised, and the exchangeable container can be removed from the mixer. In the case of built-in containers the finished product is pumped out.

Agitators for products of low viscosity, fluid products, wastewater treatment

Low-speed agitators

Agitators with a low circumferential speed (up to 5 m/sec) for homogenising, heating, cooling, rediluting, etc.
The agitating elements are adapted to the container’s shape and the product. The material is chosen in line with the product’s purpose.

High-speed agitators

Agitators with a high circumferential speed (up to 30 m/s) for dispersing filling materials, emulsifying, dissolving, etc. The agitating elements are adapted to the container’s shape and the product. The material is chosen in line with the product’s purpose.

Container agitators

Agitators for mobile containers and IBC containers. Driven by a gear engine and a frequency converter or with fixed rotational speed.

 

Areas of application:

•  Highly viscous products for large tonnages.
•  Pre-mixers for admixing large amounts of filling materials into liquid bases.

Twin-Screw mixer

Continuous twin screw mixer

Robust and closed mixing system with a high filling degree for high throughputs. Various process steps can be configured quickly and easily.

For this purpose, we provide many types of mixing paddles, conveyor paddles and opposed paddles, which can be slid onto the shafts.

As a rule, this mixer comes equipped with a double casing for heating or cooling. Optionally, the mixing shafts can also be heated or cooled.

We also provide feeding and evacuation devices as well as single screw extruders to discharge under pressure. For handling very abrasive products we offer special carbide linings, which guarantee extensive operating times with very low internal gaps.

Capacity range: 100 to 2000 kg/h
Operating temperatures of up to 250°C

 

Structure

The screw presses of the type SP consist of a robust closed housing made of stainless steel with covers, which are optionally arranged on the top or on the sides. The advantage of covers arranged on the top is that opening them does not lead to contamination of the working environment. Inside the machine there is the screen basket and the rotating screw shaft, which is driven by a NORD offset geared motor. On the screw flanks, the sealing lips are fixed with fastening screws as a seal between the screw shaft and the screen basket. To allow easy access to the screw shaft for changing the sealing lips, the screen basket is divided in the longitudinal and transverse directions.

Washing System

The screw press is equipped with a washing system for cleaning the screen basket during and after the dewatering process. The washing device comprises a washing ring with exchangeable nozzles, which, from size SP 500, is pulled along the entire longitudinal axis of the screen basket by a washing carriage with chain drive (at freely adjustable speed). The travel of the washing carriage is limited by the two built-in limit switches. In the smaller screw presses, the movement of the washing ring is effected by pneumatic cylinders.

Functional description:

The screw press was developed for dewatering municipal and industrial sludge. In order to achieve the best possible dewatering results and flocculation of the sludge, we design sludge dewatering plants with screw presses together with mixing tanks. The polymer is prepared in the polymer plant. The polymer metering pump conveys the polymer towards the mixing tank. Before entering the mixing tank, it is mixed with the thin sludge coming from the thin sludge feeding pump and together they flow into the mixing tank. There, an agitator designed as an agitator shaft with an agitator paddle ensures mixing and flocculation. Subsequently, the flocculated sludge at the top passes through the sludge inlet of the screw press into the front section of the screw shaft.

In the screen basket, the solids are separated from the filtrate as the filtrate trickles out of the screen basket’s screen holes and is collected in the filtrate trough, from where it then flows out of the machine via the filtrate drain. The solids that are larger than the screen holes remain inside the screen basket and are advanced by the rotating screw shaft.

At the end of the screw shaft, the dewatered sludge is continuously ejected. At the discharge, a press cone is mounted, which presses against the sludge to be ejected by means of an air pressure cylinder via a pressure control valve.

The discharge of the screw press is designed as a discharge chute as standard and, depending on the design, leads either directly into a container installed on site under the machine or into a discharge conveyor.

Advantages:

• Safe and automatic operation
• Low wear due to low rotational speed
• Easy access for maintenance
• Long service life
• Low drive power
• Low operating noise
• Robust housing made of stainless steel
• Years of experience in the field of sludge dewatering
• Countless references at home and abroad

Container discharge station

Special presses and discharge devices allow differently shaped exchangeable containers to be emptied at discharge pressures of up to 100 bar. Depending on the specification of products to be discharged, the press can be equipped with one or more hydraulic cylinders. A vacuum cover allows the container to be evacuated prior to being emptied. Thus, the product at the downstream filling station will be air-free. Depending on the requirements, the lifting frame can be designed to be hydraulically adjustable to the required filling height.

Buffer press

In order to ensure an efficient and continuous production process of sealants and in order to avoid bottlenecks at the filling stage, a buffer press is used to intermediately store the readily mixed product before the filling stage.

The presses can be used both for batch and continuous processes.

Various sizes are available depending on the requirements:

VPP 30 bis VPP 2000
Discharge pressures of 6 to 30 bar

Process stages

Filling and buffering

The buffer container is arranged vertically and delimited by the fixed lower base plate and the movable upper press plate in the cylindrical container casing. The press plate is sealed towards the carbidecoated inner wall of the container in a product-tight and vacuum-tight manner.

Before filling the buffer container it is evacuated via a vacuum valve after the press plate has been lowered. Then, the product is fed in via a ball valve in the base plate. The press plate is pressed up by the incoming product.

Depending on the product requirements, the buffer press can be designed with a heating or a cooling unit in order to appropriately condition the product – also over longer periods of time.

Discharging and cleaning

The product can be removed directly from the closed buffer container via ball valves in the container bottom. In order to do so, the press plate is lowered hydraulically and the product is discharged at pressures of up to 30 bar. In the same process step, the container wall is cleaned by a wiper on the press plate. Product residues between base plate and press plate only have to be removed in case of a product change. If that is the case, the container casing is disengaged f rom the base plate and lifted hydraulically. Subsequently, the press plate is lifted up so that both the press plate and the base plate can be easily accessed and cleaned. If the product does not change, the buffer press can be operated for months without having to be cleaned.