Precast Concrete x511r

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PRECAST CONCRETE ELEMENTS

SPECIAL PRINT

Pumping Concrete in a new pallet circulation plant at C.F.Structures Ltd. in Summerhill, Ireland

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PRECAST CONCRETE ELEMENTS ꔴ Construx b.v.b.a., 3600 Genk, Belgium

Pumping Concrete in a new pallet circulation plant at C.F.Structures Ltd. in Summerhill, Ireland In order to meet specific requirements such as minimal labour attendance, small existing premises, foolproof setup and guaranteed daily output, Construx b.v.b.a. installed a very compact precast production facility for filligree slabs. The customer, C.F.Structures Ltd., being a building contractor without any precast production background, insisted on a quick and above all profit-

C.F.Structures Ltd. and Construx b.v.b.a. : a strong partnership C.F.Structures Ltd. is a medium-sized construction company located in Dublin and has been erecting residential and industrial buildings for over 25 years. Their core business is on-site concrete works as a subcontractor for some of the major Irish building companies. Due to the economical boom in Ireland, there has been an enormous requirement for precast con-

crete elements in the last decade. For the last couple of years the nationwide capacity was not able to catch up with the demand. Importing precast elements from abroad was the only solution. Confronted with increasing difficulties to get precast slabs on site on time, Tim McNulty the owner of C.F.Structures Ltd. decided to start making them in his own premises. Construx b.v.b.a. a Belgian based manufacturer of shuttering and precast machinery helped him out.

Assembly of the carrousel plant in an existing building

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able concept. The Construx b.v.b.a. engineers conceived a carrousel plant with a maximum output of 590m2 slabs per shift, only requiring a staff of 4 to 5 people. The Summerhill pallet circuit system stands out because of the use of a concrete pump with placing boom (both remote controlled) and a digitally controlled hydraulic pallet lifting system with an accuracy of 0,1mm.

Extremely compact but very profitable circulation plant The complete carrousel system runs in an area of 84m x 12m which is an extremely tight setup. The size of the 20 steel pallets is 12,5m x 2,4m and they have 80mm high fixed tapered side forms on both the 12,5m long sides. On a pallet with 3 magnetic 2,4m long side shutters 2 filigree slabs with a total length of 12,3m can be poured. The pallets are transported by means of rollers and driving wheels in longitudinal direction. The transversal movement is done by pairs of cross transport wagons. The hydraulic lift is situated in between two storage racks with 9 levels each, an extra buffer position is situated underneath each rack. At a later stage the two storage racks can be equipped as curing chambers allow working in a double shift system. One position in the circulating system has vibrating wheelyokes instead of rollers. In the future another position can eventually be changed into a second vibration station because the concrete placing boom has a 10m radius. In total the circulating plant consists of no more than 9 positions, including the lift and the two storage racks. Although it still remains a very flexible system: both the lift and the vibrating station can be reached from 3 positions. Seen that demoulding, lifting the slabs, cleaning and oiling the pallets, placing the side forms, the boxouts and the steel reinforcement takes place in only 3 positions, the operator has 4 buffer positions to go to when needed. www.i-worldwide.com

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Overall view of the carrousel plant in production

Pumping concrete in the plant by means of a stationary pump and a placing boom At the moment there is no batching plant on the premises so all concrete is brought in by means of truck mixers. The initial idea of a shuttle system to bring the concrete from the ready-mix truck to a bucket spreader was quickly abandoned because of the complexity to build this type of installation in such a small area. In previous installations Construx b.v.b.a. already tried to convince some customers to go for the option of using a stationary concrete pump in combination with a placing boom to pour concrete in a quick and cost-effective way, but being the guinea pig never seemed to be an attractive idea for the clients.

Pumping concrete in a pallet circulation plant

For Tim McNulty, on the contrary, using a concrete pump almost seemed as the only way to guarantee a daily output of 20 pallets. Another very important reason for him to choose for the pump was the fact that he controlled the complete procedure: www.i-worldwide.com

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In case of any delay in the concreting while there is still concrete inside the pump or the placing boom, the end of the second leg of the boom can be connected to a tube, so the concrete can be pumped back into the hopper outside. The concrete can be pumped around in the system in order to avoid intermediate cleaning.

Digitally controlled hydraulic pallet lifting system with a 0,1mm accuracy

Remote controlled concreting with the placing boom

making precast slabs, installing those slabs on his own sites and pouring the top layer on site himself. Thus there was no real need for differences in thickness, 80mm would be perfect for all the slabs whatever the overall thickness of each individual slab finally would be. The pump used is an OLIN 1545 S-valve type which has an output of approximately 25m? per hour. As a subcontractor for Construx b.v.b.a., Reginald Maes the Managing Director of M.R.C. Betontechniek b.v.b.a. in Belgium installed the American originated pump with a sound proofing and an automatic greaser.

Filligree slabs after vibrating

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The pump sits in a shed right outside the building at a distance of only 1m from the placing boom inside the building. An electrical frequency controlled motor is mounted on the first articulation of the ACME placing boom in order to rotate the first leg of the boom. By means of two remote controls (one on the pump and the other on the electrical motor) one person can take care of the whole pouring process whilst moving by hand the end of the second leg of the placing boom. On the outside the truck driver controls the feeding of the concrete into the hopper on the pump which has a capacity of 220L.

Another critical element in the pallet circulation plant is the lift. The lack of working space in the premises resulted in a semiautomated carrousel controlled by a PLC which was programmed by the Construx b.v.b.a. engineering staff. A system with completely automated movements would simply be too dangerous to operate, so every single change of position of a pallet has to be initiated by an operator. There was a real chance on creating a bottleneck situation on the lift. To avoid such a risk Construx b.v.b.a. designed in collaboration with Vapo Hydraulics n.v. in Belgium a digitally controlled hydraulic pallet lifting system with an accuracy of 0,1mm. This system ensures a perfect positioning in height without the use of s on every single level of each storage rack. It also means that when the lift goes up, it can go straight to the exact position without the need to go a bit too high and to come back down afterwards to sit on the s. On the lift safety and accuracy go together with speed.

Placing boom connected back to the hopper www.i-worldwide.com

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Easy to clean stationary concrete pump outside the building

Digitally controlled hydraulic pallet lifting system

As already mentioned above, each storage rack has 10 positions, including the buffer position at the ground level. The height from one level to another is 550mm. By using a double chain on a pulley (as used on forklifts) all 10 positions can be reached with 3m long cylinders. The lift is moved with 4 of these cylinders. Seen that all pallets coming from the vibrating station are filled to the top of the side forms, the difference in level between all 4 cylinders should not exceed 2mm. The cylinders have a built-in magnetostrictive linear position sensor. In such a sensor a sonic strain pulse is induced in a specially designed magnetostrictive waveguide by the momentary interaction of two magnetic fields. One field comes from a movable permanent magnet which

es along the outside of the sensor tube, the other field comes from a current pulse or interrogation pulse applied along the waveguide. The interaction of the two magnetic fields produces a strain pulse, which travels at sonic speed along the waveguide until the pulse is detected at the head of the sensor. The position of the magnet is determined with high precision by measuring the elapsed time between the application of the interrogation pulse and the arrival of the resulting strain pulse. Consequently, accurate non- position is achieved with absolutely no wear to the sensing components. The accuracy of the sensors applied is 0,01mm which results in an actual accuracy on the lift of 0,1mm. 왘

Automatic positioning on 0,1mm precise without the use of s www.i-worldwide.com

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Some more difficulties had to be overcome: irregular loads on the pallets give irregular loads on the cylinders so normal hydraulic flow dividers could not be used, the stroke length of 3m results in a difference in behaviour of the hydraulic oil when the pistons are in their lowest or in their highest position. The system parameters have to be constantly adjusted in order to achieve a linear movement of the hydraulic cylinders. Therefore the use of a normal PLC was not an option, more adequate control engineering techniques had to be used. Because of its reliability, CompactRIO from National Instruments Corp. was chosen as platform to control the system. The measuring method was developed in LabVIEW (also from National Instruments Corp.). The digital sensor signals reporting the positions of the cylinders are converted by a Field Programmable Gate Array (FPGA) to figures which can be used in the LabVIEW Real-Time programme which is the controller software. These figures feed the Full State (FSF) system which controls the working pressure, the position and the speed of all four cylinders. The controller continuously evaluates the situation and can constantly adjust the flow to each cylinder. The operator interface was programmed (with LabVIEW) on a WinCC based touch module. The operator will not have to worry about any complex algorithm, he only has to indicate a position in one of the two storage racks where the pallet has to go to and the hydraulic lift will do the rest.

Conclusion: reliability and profitability To minimise any type of delay in production both the Construx b.v.b.a. engineering staff and the Vapo Hydraulics n.v. service engineers have direct online access to the PLC of the circulation plant as well as to the controller of the hydraulic pallet lifting system. This backup procedure ensures a high reliability, thus meeting the customers requirements. Proven here is that sometimes it is better to focus on the most essential bottlenecks of a carrousel plant rather than trying to automate every single detail of the process. Costly and unnecessary investments, only in order to make the production process look more sophisticated, are to be avoided under all circumstances. A producer, whether it is a precast company or a machinery manufacturer, should always be determined to get the job done in the easiest (foolproof), quickest (on time) and cheapest (cost of labour, investment) way. A satisfied customer is the best reference a company can get. 왎

Satisfied with the result (from left to right): Anthony Jannes, Managing Director Construx b.v.b.a., Tim McNulty, Owner C.F.Structures Ltd., Ward Demyttenaere, Managing Director Construx b.v.b.a.

Further information:

Construx bvba Slingerweg 1 · 3600 Genk · BELGIUM T +32 89 328855 · F +32 89 328866 [email protected] · www.construx.be

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