Plastic article or earthenware shaping or treating: apparatus – Press forming apparatus having opposed press members
Patent
1986-01-29
1988-02-16
Silbaugh, Jan H.
Plastic article or earthenware shaping or treating: apparatus
Press forming apparatus having opposed press members
264 72, 425410, 425429, 425432, B28B 108, B30B 704
Patent
active
047252200
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method concerning compacting newly formed concrete and the like by synchronized vibrations applied to opposite sides thereof, and to an apparatus for carrying out the method.
By conventional industrial production of concrete such as of large concrete units where the particles of the concrete are rearranged by gravitation and where it is the object of the vibration to reduce the surface forces between the particles, there is often with a view to the workability of the concrete added a large amount of cement and an amount of water that is 2-3 times larger than necessary for completely hydrating the cement.
If the cement paste content is too big and moreover filled with pores due to insufficient vibration and/or too big water content, a break in the hardened concrete unit will extend in the cement paste coating the aggregate. This is due to the fact that the weakest component in concrete is the cement paste. The strength of the aggregate is normally 3-5 times greater than that of the cement paste.
Accordingly, it is important that the leanness of the concrete defined as the ratio of aggregate to cement (a/c) is as great as possible to obtain maximum material properties.
By intensively compacting lean and comparatively very dry concrete the rate of strength development as well as final strength and the modulus of elasticity of the concrete are improved.
The rate of strength development depends on the degree of compacting so that an increase in the specific weight of the concrete by 1% results in a reduction in hardening time by approx. 25%.
There is moreover obtained increased resistance to outer physical and chemical attacks, e.g. improved waterproofing and frost safeness. Concrete with a water/cement (w/c) ratio below 0.4 is considered frost safe.
By intensive compaction the poor properties of the concrete are reduced with a view to carbonization as well as creeping and contraction.
The problem of achieving such greatly improved properties has hitherto been that by the low w/c ratios it has not been possible to rearrange the particles of the concrete to reach sufficient compactness the result being enclosed voids at a number and distribution acting as break promoters in the concrete.
During recent years producers have therefore added super-plastifiers to the concrete mixes thus reducing friction between the individual constituents of the concrete mix so that it is possible to work with a water/cement ratio of about 0.25 when simultaneously applying vibration.
These plastifiers are organic substances that are added to the concrete mix and the long-term effects thereof are not known. Moreover, the use of plastifiers has the effect that the adhesion of the concrete to the reinforcement is reduced. It is therefore desirable to be able to avoid additives of any kind so that there are only used mineral, i.e. inorganic, constituents in a concrete mix.
From German published specification DE No. 24 53 634 the technique of which is today applied by all hitherto known concrete product machines it is known to compact the enclosed mass of concrete by transmitting the vibration from an underlying vibrating table and through the concrete make a mass resting on the concrete oscillate. In this case the spring action of the piston in the cylinder is performed by having same connected with a hydraulic accumulator forming the spring unit. By adjusting the pressure in the cylinder it is possible to make the upper part oscillate when the squeeze pressure has been suitably balanced.
The arrangement is not a 2-mass system because the spring unit is not connecting the two masses. On the contrary the two masses with spring system belonging thereto each form a system with one mass and one degree of freedom where by means of a static squeeze pressure the vibration is transmitted from the part containing the vibrator to the upper piston via the concrete.
The low efficiency of this oscillation system is due to the following: amplitude of the supplied impulses from the oscillating part containing the vibrator, p
REFERENCES:
patent: 4531903 (1985-07-01), Frey et al.
Fisher Jorgen
Percinel Omer
Fischer & Nielsen
Kutach Karen D.
Silbaugh Jan H.
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