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| Как найти нас ? |
| Моб: |
+86-15921128022 |
| Тел: |
+86-21-52303505/6/7 |
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+86-21-68453855 |
| Факс: |
+86-21-52303508 |
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+86-21-50453855 |
| Сайт: |
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| Емейл: |
info@foameps.com |
| epsmachinery@hotmail.com |
| Адрес: |
201607.NO.368 Xindan Road.Shanghai.China |
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| Aging |
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After the aging is finished, the beads are then ready for molding into blocks.Since this is a confined enviroments, the only way teh beads can expand is to fill uo any voids between them causing the soft surfaces to fuse together into a polyhedral type solid structure.
block mould machines
Simple mouldings in the form of rectangular semi- finished products are produced in so-called block moulds which are offered in various volumes.
An even distribution of the filled material is important for the production of a good block,which means that a homogenous foam density as well as an even fusion of the beads without any notable material shift within the block is required. Moreover, a consistent amount of residual moisture is required as fluctuations would cause negative effects during the further processing.
A modem block processing parts consists of the following components:
- storage for raw material
- pre- expander and fluid bed drier
- storage for pre- expanded material
- block mould
- storage for pre- expanded blocks
- cutting line
- storage for finished products
- plant for compressed air supply
- plant for steam supply
- plant for recording operational data
Plant components like pre- expanders and their fluid bed driers as well as the intermediate storage in silos were already described above. The plants for the supply of compressed air and steam and the plant for recording operational data will not be described in detail here. They are determined by the corresponding machine suppliers depending on the customers' needs and the expected throughputs.
Construction of a block mould
First, the block mould and the vacuum station will be described. The block mould itself is a steel profile welded construction with individual, integrated steam chambers. The supply leads for steaming, venting, discharge of condensate and the application of vacuum are also integrated in the welded construction by a hose system. The individual media
are fed by valves which control and limit the pressure. Homogenous and sufficiently large perforations of the mould walls bordering the mould are important. Here, wedge wires are increasingly used in order to achieve an optimal, open cross section area. A free cross section of approx. 10 to 12 % of the mould nest surface has proved to be ideal in order to achieve a low feed- in speed of the steam and a low discharge speed of the air from the interior of the mould. The perforated sheets used in the past did not at all achieve these values.
Depending on the requirements of the processing company, the block moulds are available in a horizontal or vertical version. The media connection is the same with both versions.
Demoulding
Demoulding from block moulds with a vertical construction (upright) takes places via one side wall that can be opened like a door and the block is ejected upright after having been steamed and stabilised. Ejecting takes place either by means of special ejectors or by moving the back wall towards the door opening.
Demoulding from horizontal block moulds takes place via an open door and with the help of a L- shaped combination of side wall and lid which can be slightly moved to the side so that ejectors in the back of the block mould can eject the moulding. In order to produce blocks with different dimensions, either the back wall, one of the side walls or the bottom of the block mould must be movable. There are also block moulds with two simultaneously movable walls. In the case of hori zontal moulds these are predominantly the back wall and the bottom. In order to handle the expansion forces during the moulding process, the movable elements are moved hy draulically and then they are locked hydro- mechanically. There are also special block moulds with adjustable side walls which can be used to compress the filled- in matenal when processing recycled material.
Course of Process
The block mould cycle is divided in the steps described below.
First the block mould is closed hydraulically and locked mechanically.
Filling
Today, only one method is applied to fill block moulds. The volume of the silos should approximately correspond to the volume of the block mould in order to prevent areas of different particle densities from developing in the material silo. When using the out- of- date pressure filling method, the pre- expanded beads are transported directly from a filling silo, which is located next to the block mould, into the block mould by means of a conveying blower. Here , the conveying blower is connected to the outlet of the silo at the suction side. At the pressure side, the conveying blower is connected to the lid of the block mould. This means the beads are transported through the conveyor which inevitably leads to an increase in density. Moreover, the high injection speed of the material causes a strong demixing, especially when recycled material was added.
With the suction filling method this material compression can be avoided. A side channel fan is connected to the six steam chambers and decreases the air pressure in the block mould and in the conveying lead which enables a pneumatic conveying from the silo to the block mould. Filling from the suction side enables a more careful material transport and prevents the bead bulk from demixing.
Evacuation
The next step in the cycle of modem block moulds with vacuum equipment is the pre- e-
vacuation of the chamber. The vacuum is applied by means of the condensate leads. E-
vacuation before steaming makes it easier to eject the remaining air between the beads and to replace it by saturated steam.
Short evacuation times are desired so that the cycle time does not have to be unnecessarily prolonged. Thus, a vacuum tank is installed next to the block mould. If, in special cases, the block is to be steamed from one direction after the other, it is recommended to use a divided vacuum tank. In this way, the evacuation is also sufficient for the second steaming process.
Steaming
The steaming process can be divided in three steps, namely rinsing, pressure increase and maintaining pressure.
During the rinsing, the steam flows into the pre- evacuated block mould from two or three sides. First, the remaining air escapes from the opposite side, followed by the airmixture and finally by the steam. This should take place with the lowest possible pressures
to prevent that the beads are heated too much near the steam supply and start to react while the fusion has not yet started inside the block. The quality of a block is mainly influenced by the rinsing process. Any failures during the rinsing cannot be completely remedied by subsequent process steps.
In order to prevent a shift in the loose beads or in the dust particles contained in the material bulk, low steam speeds in the bead bulk are especially important. In order to achieve low steam speeds at high steam throughputs, however, the mould walls must have a large open surface. This applies to the steam supply as well as to the air and steam discharge and can only be achieved by using wedge wires.
The second steaming step is the pressure increase. Here, the condensate valves are closed and steam continues to enter the mould. The mould wall and the beads gain the temperature required for moulding and fusion through the increasing pressure.
By supplying heat, the cell structure of the bead softens and the partial pressures of the gases inside the beads increase(predominantly air, blowing agents and steam). The bead expands due to its interior pressures. The volume between the beads is decreased in this way and their outer cell walls start to fuse.
During the third steaming step, maintaining pressure or second steaming, the maximum pressure determined by the operator is kept constant via an adjusted time and with the help of an own control device. This causes a complete fusion of the block.
Stabilising
After steaming, the pressure is decreased. Here, the steam is suddenly turned off. Then,most of the time, the foam pressure of the material rises and exceeds the steam pressure.
Now the real stabilising phase starts with the help of the vacuum described above. The purpose of the vacuum is to shorten the cycle time in a way that the condensate, which developed during steaming, evaporates again and removes the steaming heat from the beads that are not fused and from the wet mould wall by changing its physical condition
(change of face). In this way, the frame substance cools down and gains mechanic stability.
The remaining foam pressure determines the time required for the block demoulding. Generally, the block is stable enough at a remaining foam pressure of 0.15 and 0.2 bar and
will not increase further. The ideal demoulding pressure, of course, depends on the amount of the remaining blowing agents, on the intermediate storage time and on the material type.
Demoulding
When the required foam pressure has been achieved, the mould is unlocked and the door is opened. The block is de- moulded by ejectors which are installed in the wall opposite to the door. Usually, the block is weighed directly after demoulding and the weight is recorded for internal quality assurance. Moreover, the block is numbered in order to able to identify it and associate it with the used raw material or with further process data. This information is necessary in order to guarantee a complete proof of quality which is required for specific fields of application in the block processing.
Block storage
The shrinkage behaviour of EPS varies over time. Depending on the use of the produced material, it is necessary to store the blocks before processing them further. Thus, it is necessary to store the blocks in a block storage after their production for some time. Modem, western European storages with high throughputs are provided with fully automatic and computer controlled storage systems where blocks are stored according to the "first in-first out" system. Furthermore, varying storage period lengths can be guaranteed. The storage time of the block can be reduced by storing the block at increased temperatures. Here, drying chambers, as they are used in the wood industry, have proven themselves.
Further processing of blocks
Most of the blocks produced world wide are sold only after being further processed by the block producer. There are industries in some regions which process the blocks with the help of contour cutting machines to form products like mouldings. These contour cutters are adjustable in up to 5 axes and can cut manifold contours and forms from a block. In
most cases a block section is used to produce this mouldings.
Function principle of hot wire cutting
EPS cutting plants work with a thermal hot wire separation process. Thermal cutting is the ideal processing method for the thermoplastic material of EPS.The cutting medium is the heat energy of a current- carrying conductor. The wire heats due to its electric resistance. Cutting wires on nickel- chromium basis show a high specific ohmic value which remains constant in wide temperature ranges. Depending on their use, their diameters vary from O. 3 to 0.6 mm, and up to 1.6 mm in certain cases.When the wires are fixed and immobile, operating temperatures of 150 to 250~C are rec-
onnnended.
The cutting temperature has a great influence on the cutting quality to be achieved and on the surface structure of the cut products. In general: the higher the intensity of the current, the higher the wire temperatures is and the cutting power will be lower. The cutting quality improves with a smaller wire diameter and this also reduces the cutting waste, or the amount of melted foam.
Assuming the wire diameter kept the same, the cutting quality improves with lower wire temperatures and with a higher feeding power. When the conditions are the same, the cutting quality reduces with increasing non- homogeneity of the material (grinding stock, water, raw density etc. ). In the case of material with a constant density, the target cutting speed rises when the feeding power is equal and the wire temperature increases. According to physical laws, an equal feeding power and electrical power accompanied by a decreasing wire diameter result in an increase in the wire temperature.
The residual moisture impairs the maximum cutting speed to be achieved because it causes the wires to cool down. Thus, in daily operation it can be chosen between two extremes: a high cutting speed which puts high mechanic and thermal strain on the wire, or a low cutting speed which puts lower strain on the wire but causes the wire to be idle for longer periods of time.
The basic element of a cutting plant is a chain conveyor equipped with various processing stations. Modem, fully- automatic cutting plants are constructed according to the following principle:
- fully automatic block feeding
- automatic centering of the block
- sheet cutting
- upper trim removal
- lateral block trimming
- lower trim remov
- acceleration station to move the block into
the cross cutting
- cutting plant station where the
- single sheets are cut to their final dimensions
- waste disposal
Below the trimming station there is a conveyor belt which transports the block waste to a central pre- breaker at the end of the cutting line. From there, the pre- broken material is transported to a central breaker and the contained recycled material is returned to the
block moulding process.
So far we reported only about pure thermal cut- ting. However, it turned out that oscillating cutting wires increase the cutting speed and improve the surface structure of the cut prod ucts. The efficiency of the mechanic energy depends on the amplitude and frequency of the oscillation. Even after a long intermediate storage time of the blocks, the differences in residual moisture have not completely balanced. While the outer surface area is dry up to a depth of approx. 50 mm, there is still condensate inside the block. When the wire oscillates with a short stroke while cut ting, its temperature decreases in regions with an in creased humidity and it rises in regions of dry foam. The result is that the foam melts relatively fast in dry outer regions while regions in the centre of the block show a better cutting quality. To avoid a "picture- frame" effect, the stroke of the wire is increased to approx. 60 mm. In this way, the two separation processes "melting" and "cutting" are connected. As already mentioned above, the cutting speed is Improved with this and the picture- frame" effect can be avoided. Function of a router Besides cutting, there are further mechanic processing methods, like milling, sawing, cutting with knives or cutting with a rotating cold wire. These mechanic processing methods, however, are only used in special cases, like model making or in special applications in the construction industry.
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