“Thus we have the strength of the state and a huge company behind us, but we are a mid-size company with the flexibility which that brings to enable us to find solutions for our customers,” says Thomas Neuburger, general manager of the Materials Handling and Process Division.

The history of the SHW company is recorded in a museum on its substantial site and shows it still has ties with the heavy engineering and casting industries. It still produces, in a small way, artistic sculptures cast in metal, but its main involvement in heavier castings now has moved from the solid fuel stoves of the past to production of massive engine blocks used in ships or large stationary engines.

Ventilated brake discs for high speed trains, such as the German ICE, as well as for the automotive industry, are also produced by SHW.

Other specialist areas in the metal working field include the production of sinter- formed components such as gear cogs and also oil pumps for automotive engines. All these products are made at one of the company’s four locations: in Wasseralfingen; Bad- Schussenried Wilhelmshütte; Königsbronn; and Tuttlingen-Ludwigstal.

However, to the panel industry, SHW is best known for its technology in the field of materials handling and processing. The raw materials for the production of particleboard and MDF offer particular challenges due to their tendency to interlock with each other and to stick to each other – especially when wet or glued – forming bridges in silos and transport systems. The systems offered by SHW are designed to overcome these potential problems.

“The wood based panels industry accounts for a minimum of 50%, and has been up to 70%, of our turnover,” explains Günter Staiger, area sales manager for North and South America. “We also work in the pulp and paper and other industries such as cement, power, gypsum, dewatered sludges, chemical, food and pet food and environmental protection,” he says. “But free-flowing material is not our business.” Thus materials such as grain or pelletised products are not likely to require the specialist input of SHW.

The changing nature of the panel business, however, has meant an increasing demand for the company’s expertise, as Mr Staiger explains: “With the rise in continuous press lines in the last 15 years, there has been an increased need for dependable and continuous supply of bulk materials so you need reliable equipment with an even discharge rate and this is our speciality.”

It was in the mid-1960s that SHW was first asked to develop a reliable silo discharge system for wood chips and sawdust and this led to its development as a turnkey supplier of storage and conveying systems for difficult bulk goods.

The main system components offered by SHW are material relief systems, silo discharge systems and the associated handling and processing technology.

At the point of residue arrival in a panel mill, the company offers a live bottom system in the yard at ground level, in a pit, or in a storage silo. This comprises independently sliding plates, hydraulically operated, in a form resembling a ladder. The rate of discharge is controlled by level detectors in the silo. A conveyor belt system is also offered as an alternative.

To sort the raw material into fractions, SHW offers a disc screen. The discs are mounted on parallel horizontal shafts and the spacing between the discs is variable according to the size selection required. Smaller acceptable chips pass down through the screen, while larger rejects and foreign bodies are carried over it to a reject chute. This screen can handle raw material quantities up to 600m3 per hour.

To transport the acceptable chips,  chain,  belt or closed belt conveyor systems are offered, while bucket elevators and pneumatic conveying systems are also available. Intermediate storage can be in flat-, not conical- bottomed circular or rectangular silos. Rectangular silos up to 25m wide can be fitted with travelling screw augers, whose speed is adjusted to suit the raw material and to avoid either compression of it or a bending strain on the auger. It is possible to have several augers in tandem. Larger rectangular silos would employ a live bottom system with any number of plates required.

Circular silos with a diameter of more than 30m are equipped with a central rotating conical screw auger which revolves as it spins on its own axis and covers the entire cross-section of the silo. A sliding frame system is also offered, while smaller circular silos up to 7m diameter can use the SHW Rotor Discharge System.

For silos with a capacity of up to 300m3, round or rectangular, SHW offers an eccentric oscillating discharge frame which has no hydraulic components. This feeds the material to a discharge screw.

A unique feature offered by SHW in circular silos is its drag arm system. The arms are made of layers of spring steel clamped together very much like a cart spring. They are curved and one sweeps above the floor of the silo in the horizontal plane to prevent bridging of the material, while the other sweeps close to the floor, dragging the material to the discharge screw. There is a hook on the outer end of each arm, which passes close the wall of the silo to break up any ‘wall’ of chips that may form. The silo walls are also equipped with special relief wedges to prevent bridging.

The advantage of the flexibility of the arm, both in the horizontal and the vertical plane, is that it reduces the torque on its drive motor and avoids the risk of the drag arm breaking under the enormous potential strains in the bottom of a large, full silo.

MDF plant, Japan MDF plant, Japan

The drive mechanism for all SHW’s silos is located under the floor for ease of  maintenance and the drive motor/gearbox is attached by a ‘bayonet-type’ fixing so that it can be removed without emptying the silo.

“Silo rotors are also made of heavy gauge steel (8-12mm thick) because of the high abrasion of wood raw material, and especially bark, and these silos have to work continuously – they may only be emptied once a year for maintenance,” says Mr Staiger. Stainless steel can also be specified for the same reason. The whole silo is normally made of 5-6mm steel plate.

Distribution from the silo can be to several lines independently – you can specify several different augers each operating independently and feeding a separate production line, thus saving costs. You can also operate with one very large silo, since additional metering silos are not required.

For feeding dryer lines, SHW offers a metering bin to feed several drying lines if required and a fire protection bin which can be emptied rapidly in an emergency.

A silo full of fibres, such as in an MDF plant, offers special challenges and for this a special vertical conical rotor with drag arms is available, so that the silo can be completely emptied of even glued fibres. Steaming silos are available for MDF lines.

Sander dust for burning is directly metered to the furnace, again obviating the need for a metering bin, says SHW.

All systems are tailored to the specific materials and sliding frame, rotor discharge, rotating floor and pivoting wheel systems for smaller silos are all solutions which are available.

“We don’t just sell discharging systems, we decide what is best suited to the customer’s needs and his raw material – whether it is a rectangular or a circular silo, with live bottom, rotor discharge, or discharge screw,” says Mr Staiger. “The customer tells us what his raw material is and the discharge rate he requires and we do the rest. And it is not necessarily just one piece of equipment that we supply. It is often a whole system from receiving station to production line – often for a variety of raw materials, particularly in the case of biomass or the burning of recycled material.”

The company has designed, supplied and commissioned over 3,000 such systems in more than 50 countries and for a wide range of raw materials, says Jürgen Rapp, who is responsible for key accounts and dealing with the OEM’s such as Siempelkamp, Dieffenbacher and Metso who often include SHW equipment as part of their whole plant concept.

“In a particleboard plant, for example, there are separate systems for the green area and the dry area, with a surface layer, core layer and oversize silo after the dryer – some mills have as many as 12 silos,” says Mr Rapp.

While particleboard and MDF form the bulk of SHW’s involvement in the panel industry, OSB also gets a look in.

The company is currently developing, in its own test set-up at Wasseralfingen, a modified bunker for the forming head on OSB lines which will handle the strands more gently.  Strands are often broken by the conventional spike system during forming head bunker discharge and this affects the quality of the finished panel. By the time Ligna comes around next May, SHW hopes to have its improved system on show.

Of course, new-build projects are increasingly rare these days and fortunately SHW is not entirely dependent on these. It also offers upgrades to existing silos, such as converting a conical-base silo into a flat bottomed one if necessary, and changing the discharge system.

“Stable bridge building? Never!” is the slogan of SHW, referring to its silos and discharge systems. However, stability within SHW seem to be a fact – after all, the company has been in business for nearly 640 years.

Silo system for EON for use in an energy plant Silo system for EON for use in an energy plant

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