Physical properties of Stramit strawboard

STRAMIT straw conversion process

In the early 193Os, a technique was invented in Sweden for converting straw into a building board by means of heat and pressure. The technique was taken up and developed in England in the 1940s and 1950s; plants were subsequently established in some fifteen countries and have now become internationally known as the Stramit Process. At the heart of the process lies a discovery that straw, subjected to reasonably high temperature and pressure, releases its own internal resinous substances which make it possible to extrude a continuous board without the addition of resin. Since most other building boards, such as plywood, chipboard and blockboard, rely on resin to bond the material, this factor is a vital key to the great economy of the system. This is, of course, especially true since the world oil price explosion in 1973, most resins being oil based. As a matter of considerable good fortune, a wide range of straw types has proved suitable for use in the process. Principal among these are wheat, paddy rice, dry rice, barley and rye. The manufacturing technique can be followed by studying the elevation and plan of a typical machine, shown in Fig. 4, and pictures of the process, shown in Figs. 1 -3.

Straw feed section

Straw would normally be baled in the fields for ease of transportation and brought to the plant. Bales are then loaded onto the accumulative bale conveyor (Fig. 4.) (1:l) two abreast where the string or wire is cut and removed before the bales move onto the straw bale conveyor (1:2) at the end of which is bale opener (1:4). The bale opener loosens and spreads out the straw in an even mat. Provision is made for dust extraction at this point before the straw is passed at a controlled volume to a straw walker/separator unit, where it is cleaned and graded. The two straw walkers (15) consist of a series of stepped paddles, inclined upwards and moving longitudinally in a reciprocating action, thus passing the straw forward while allowing chaff, stones, grain and short straw to fall by gravity onto a waste conveyor (1:6) which discharges into a separator (1:7) for controlled separation. The straw is ejected from the straw walker system and falls onto an inclined loose straw conveyor (1:9) which carries it to the top of the straw feed hopper (1:lO) which feeds the straw to the reciprocating ram of the slab forming section (2: 1). The short but still usable straw which falls from the straw walker system (15) is separated from grain and impurities by the separator (1:7), pneumatically conveyed back to the loose straw conveyor (1:9) where it joins the main stream of longer straw moving towards the hopper (1: 10). Reject short straw is thus kept down to a minimum. Grain and small stones are fed into different reject channels in the separator, the grain being bagged for subsequent sale, while the stones are dropped into a container. Finally rejected short straw is normally ground in a separate grinding plant and sold as animal food additive.

The level of straw in the hopper is maintained by means of photo-electric cells which actuate the starters of the drive motors of the bale conveyors (1: 1) and (1:2), straw walkers (15) and the loose straw conveyor (1:9).

Slab forming process

At the bottom of the hopper, a set of mechanical fingers pull an equal amount of straw downwards for each stroke of the ram. With each stroke new straw is forced in between the top and bottom beds of the slab forming section (2:l) impacting it against the slab of straw already between the beds. When the friction between the straw and the beds, the tension of the paper liner and the weight of the slab is overcome, the slab will move forward.

The straw passes through a total of three sets of beds. In the first set, called the back cold beds, the straw is compressed into its final form. In the next set of beds, the back hot beds, which are heated by means of thermostatically controlled electrical elements, the straw is set permanently in its compressed state. From here the slab of straw enters the final set of beds, the front hot beds, heated in the same manner as the back hot beds. The paper liner is introduced between the back and front beds providing the slab with paper on both sides.

The paper liner, fed from two reels situated above and below the Stramit machine, passes through glue rollers and the pressure and heat from the bed plates bond the paper liner securely onto the straw slab. This glue requirement is minimal.

Cut-off and end sealing operation

The slab, after leaving the front hot bed, moves onto the runout table (2:2) at the end of which is an electrically driven automatic cross cut saw unit (3: 1) moving longitudinally with the slab to give a right angled cut across the slab. The saw unit is fitted with a device for automatic measuring of lengths to be cut.

Factory building requirements

Figure 5 illustrates a typical Stramit machine in elevation and plan. It also sets out a typical factory layout. No unusual demands are made on the building. Foundations need to be slightly reinforced at the slab forming section. The principal function of the factory superstructure isprotection against the elements and security required.

Utilities consumption

Table 2 sets out the utilities required for straw board production. It will be noted that there is no water requirement and that demands on electricity and compressed air are modest by manufacturing standards. There is no industrial effluent problem.

Personnel

Table 3 sets out the personnel required for a typical plant running on one, two or three eight hour shifts.

Cost of manufacturing materials

By far the largest material cost is, needless to say, straw. It is a somewhat remarkable fact that in countries where straw board is being produced, some straw producers will be spending money destroying their straw, while others will be being paid for it. Straw is generally regarded as an embarrassment to farmers in that they must get it out of the way quickly in order to get on with ploughing and sowing for the next crop. The efficiency therefore with which the straw is gathered, baled and transported to a strawboard factory is important for a successful operation to all parties. It can be very misleading to quote figures of the value of straw/ton delivered to strawboard factories around the world. Suffice it to say as a guide that the range is between 20 and 40 U.S. dollars per ton. The cost of other subsidiary materials like paper liner, resin for bonding the paper liner and utilities such as electricity represent a small proportion of manufacturing costs. And with the capacity of a typical machine being up to half a million square metres per year, the factory labour involvement of, say, twenty personnel also becomes a relatively modest proportion of the manufacturing cost.

Investment

So simple a process in theory, considerable skills surround the production of first-class board. Experience over the years has therefore led to a policy where licensees enter into a composite package which includes the licenser installing the machinery, commissioning it and running the factory for an initial period. Technical production back-up and technical marketing back-up are also built into the package. It is extremely difficult to offer a generalised figure on the level of total investment in a strawboard manufacturing business. It might just be useful, as

a guide, to say that potential new licensees are advised that total investment capital in factory, plant, raw materials stocks and working capital would probably be in the order of between one and one-and-a-half million U.S. dollars.

Physical properties of Stramit strawboard

Today Stramit strawboard is normally made to its own British Standard B.S. 4046. It is possible to vary the thickness, width, density and surface finish. Typically, the board is made

1 200 mm wide, 50 mm thick and cut in various panel lengths between two and four metres.

Optimum British Standard density is 19 kg/m2 at 50 mm thickness.

Being tightly compressed, the board offers considerable fire resistance and is used in fire

Simple houses made from straw Farmers collecting wheat straw in Nanyang, Henan province. More and more Chinese people have begun choosing products that pay heeds to the environment and health. NOVOFIBRE Panel Board Holding, China, Ltd, a wholly-owned company of Germany's Mayfair Group, said the company has a solution for the building materials industry with its latest development: panel boards made from straw. Xiong Yunbin / for China Daily

YANGLING, Shaanxi - Pierre Eloy believes straw is the ideal alternative to wood in China, a country that lacks timber resources in relation to the size of its population and has therefore been importing vast quantities as its economy has grown rapidly.

The chief executive officer of NOVOFIBRE Panel Board Holding, China, Ltd, a wholly-owned company of Germany's Mayfair Group, said he hopes his company's straw-made panel board will become a replacement for wood-based panels, helping China's interior decoration and construction industries to be more environmentally friendly.

"China has a huge market for domestic consumption, and with the increase in people's choices, they are looking to quality living more and more. Choosing products that pay heed to the environment and health has become a trend," said Eloy. "And NOVOFIBRE is this trend. China has one of the strongest agriculture industries worldwide. The wheat yield is one-fifth of the worlds, ranking it number one producer. Furthermore, the Chinese government has put emphasis on environmental protection over recent years."

At the same time as issuing policy guidance and awarding financial subsidies, the government has strengthened its appeals for environmental protection and increased public awareness of the need for it, industrial experts said.

In particular, during the Copenhagen environment conference in 2009, the Chinese delegation stressed its commitment to a "greener" future.

As a result it is easy to understand why the German group chose China to be the first and only destination to start its green initiatives after it acquired the patent from Canada's Alberta Research Council for Oriented Structural Straw Board (OSSB), a new green, healthy and low-carbon man-made panel technology using natural wheat straw.

In October 2009, the first OSSB was created at NOVOFIBRE's Yangling plant in Shaanxi province, according to the company. Using natural wheat straw as a raw material, the OSSB has zero formaldehyde emissions, unlike many of its rivals, according to Eloy.

Furthermore, OSSB enjoys better physical properties, such as high strength-weight ratio, allowing fewer deformities and easier engineering, outstanding nail-holding during further processing, great flame-resistance and is moisture-proof, which combine to make it better than man-made wood-based panels, he said.

The promising future encouraged NOVOFIBRE in 2010 to shift its focus from project construction into a business operation. In 2011, it implemented a marketing target and strategy. By August, sales had doubled those of 2010 and showed the possibility of rapid progress.

"As OSSB can serve as both base material and surface material, and the fact that interior decoration is the key direction for the market development so far, this panel board can be applied in furniture, flooring and packaging," said Eloy.

NOVOFIBRE panels have been exported to Japan, South Korea, Australia and European countries.

"Our priority is to develop the Chinese market," said Eloy. "After market analysis, we saw our customers to be urban middle- and upper-level people who have the willingness and capacity to actively select 'green', healthy products."

There is now a distribution network for NOVOFIBRE in the 12 main cities in China.

"Having confidence in China's low-carbon and environmental protection policy and the future market, NOVOFIBRE is also optimizing the technology, process and equipment of OSSB production to try to increase product quality and production capacity as well as reduce the cost," said Eloy. "NOVOFIBRE has invested more than 600 million yuan ($95 million) so far and we will consider expanding our business based on the supply of raw materials and the market situation after this production line reaches full capacity, which will be soon."

A standard for the OSSB industry has been established, drafted in consultation with NOVOFIBRE, which says it intends to become the leader of the industry.

However, Eloy admitted that the unique features of NOVOFIBRE also brought challenges and problems in terms of raw material collection and market acceptance in the trial production phase.

"Straw collection is complex," said Eloy. "This job requires not only familiarity with the rural situation, machine operation and maintenance, but also experience of how the weather can affect production."

Supported and encouraged by local authorities, several capable straw dealers will be selected as long-term stable suppliers to act as intermediaries between farmers and the company.

The company created more than 2,000 jobs in 2010. The annual expenditure on straw collection amounted to more than 20 million yuan which was a healthy boost to farmers' incomes.

With the gradual elimination of old-fashioned farming practices by the central and local government, including the closure of small paper mills, it became necessary to find a new outlet for the straw available from farmers in order to avoid having to burn it. The OSSB project came along at the right time, said Eloy.

According to Wang Sheli, the 43-year-old owner of Limin Straw Collection Cooperative in Guozhen, Shaanxi province, the natural wheat straw, as an agricultural residue, was originally used for making paper, feeding cattle and growing mushrooms. Most of it was waste.

His cooperative, which has an annual collection capacity of 8,000 tons of straws using 85 farm machines, provided money for more than 300 local villagers in 2010.

"The price of sourcing straw for panel board production is at least 10 percent higher than that for paper-making. One farm machine can generate 50,000 yuan in revenues a month," said Wang, who earned 30,000 yuan net profit last summer.

As early as the Wenchuan earthquake in 2008, NOVOFIBRE donated houses made from environmental friendly materials to Mianzhu, Sichuan province. The houses were simple to build, cool in summer and warm in winter. In May 2010, NOVOFIBRE's panel boards were used in building the activities centre for China Charities Aid Foundation of Children in Pengzhou, Sichuan province.

Danagri-3S

Danagri-3S Ltd has been involved with the development, engineering and selling of Cormall straw processing systems since the early 1970's. Back then, most machines were made for conventional sized bales until our renowned RBS260 round bale machine was introduced in 1978. One of the major benefits of the Cormall system is the hammer mill, which both chops and lacerates the straw to open up the absorbent centre.   Over the years we have sold straw plants for:- · Bedding - for all animals - dust extracted or natural - all lengths · Bedding - mixing straw and woodflakes together · Feed - straw based diets for horses and cattle, especially mixing molasses · Manufacture of straw board and insulating products · Burning - automatic feed of straw to boilers and furnaces · Briquetting - for many uses - feed, fuel, waste · Pelleting - again for many reasons - feed, fuel, logistics etc Most plants in the UK have been sold to chop Wheat, Oat, Barley, Oil Seed Rape & Miscanthus straw or Hay, but Cormall have had experience of chopping many other crops such as Rice straw, Alfa-Alfa, cotton stalks etc. and we have plants producing over 25 tonne per hour of chopped straw! Whereas most of these plants started as agricultural sidelines, both they and the machines have now developed into semi-industrial and full commercial plant options with a full range of accessories such as bale conveyor tables, hammer mills, cyclones, mixers, buffer silos, discharge hoppers, filters, rotary valves, dust extraction units, augers etc and we have contacts with specialist companies for baling, pelletising, briquetting, palletising, reverse jet filters, spark detection, ducting etc. Each plant we sell is built to individual customer requirements, whether it be 1 tonne per hour or 25 tonne per hour, sized down to 100mm or 4mm, dust extracted or natural, mixed or un-mixed, hay or straw, round bale or square, there are many options but we offer the help and advice built up over many years’ experience dealing with these issues.

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