US3456926A - Concrete mixing machine - Google Patents

Description

1969 s. E- HUMMELSHOJ 5,

CONCRETE MIXING MACHINE Filed May 15, 1967 ax .mx

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BY usrm/A. Hummers/v0.1 Mflmz United States Patent US. Cl. 259-478 2 Claims ABSTRACT OF THE DISCLOSURE The invention consists in aconcrete mixing machine in which the mixing process is performed by mixing shovels carried on supporting arms and operating in a pan-shaped or annular mixing tub, while steam is being injected into the mass that is being mixed, the steam injection being performed through the arms which are hollow and through exhaust openings on the back side of the shovels in such a way that the steam exhausts into the cavity created behind each shovel in the mass that is being mixed, which ensures that any risk of the steam exhaust openings getting obstructed or concrete mass flowing into the said openings is avoided. Hereby is obtained a uniform heating of the concrete mass.

It is often desirable to have freshly mixed concrete in a hated state available, such as in connection with winter building activities, in order to perform the pouring of the concrete at so high a temperature that setting and hardening may have progressed so far that damage due to frost cannot occur until the concrete has obtained a sufiicient strength, or, in the manufacture of concrete elements, to accelerate the setting and hardening so as to reduce the time of occupation of the moulds, which permits a more frequent use of the moulds.

With these objects in view, it has been attempted to add the water in a heated state, eg, up to about 90 C., but the effect of this measure is rather small. It has proved more effective to heat the aggregate, i.e. the sand, gravel, and shingle entering into the concrete, and this has so far been done by heating the said materials in the hoppers or heaps in which they are stored before being used.

The method that has so far been used to the widest extent for this purpose has been to inject steam into the hoppers or heaps containing the materials, the steam condensing on the cold materials and thereby heating them with its high latent heat. This method is more effective than heating the materials by direct flame action or by hot air, but it has severe drawbacks, particularly due to the fact that the influence of the steam on the material varies from one portion of the material to the other. This means that the heating becomes irregular, and the considerable quantities of condensate are distributed to unevenly that it becomes to diflicult to control the water in the finished concrete. Another drawback is that some portions of the materials are superheated too long, and in calciferous materials, which are the most common, this will cause the very hot steam, the temperature of which is about 106 C., to penetrate deeply into the calciferous single and make the latter swell, and this in turn involves a risk of frost breakage during building activities in the winter or of the finished structures or elements.

The invention is based on the recognition that the application of the steam to the materials should be performed in such a way that the steam jet or jets constantly impinge on new particles of the material and only 3,456,926 Patented July 22, 1969 for fractions of a second act on the same particles of the material.

On the basis of this recognition the invention consists in a concrete mixing machine, in which it is possible in a practical manner in the machine proper to apply the steam during the mixing process to the cold materials. Moreprecisely defined the invention relates to concrete mixing machines of the type which can be termed positive mixers, i.e. machines in which the mixing process is performed by means of mixing shovels carried on supporting arms and operating in a pan-shaped or annular mixing tub. The shovels may be stationary and the tub may rotate about the axis of the shovel system, or the tub maybe stationary and the shovel system with the supporting arms may rotate about the axis of the tub. The arrangement according to the invention consists in that the supporting arms of the mixing shovels are hollow and at their ends remote from the shovels are connected to a supply pipe for steam whereas at the shovels they are provided with exhaust openings for the steam. Hereby is achieved that the steam is injected into the mass that is being mixed at the points where the agitating and mixing are .most intensive, and this can be carried out without the use of separate supply pipes which would have to be forced through the mass and thereby would increase the power requirements and possibly influence the mixing process detrimentally; such supply pipes would furthermore be very diflicult to keep clean.

These drawbacks are avoided by the arrangement according to the invention, the supporting arms of the shovels being utilized as steam pipes and requiring at the most an insignificant increase in cross section as compared to what would otherwise be the case.

In an advantageous embodiment of the invention the exhaust openings are so disposed that the steam exhausts into the cavity created behind each shovel in the mass that is being mixed, which ensures that any risk of the steam exhaust openings getting obstructed or concrete mass flowing into the said openings is avoided.

The invention is illustrated in the drawing which is in section and partly diagrammatically shows an embodiment of a positive mixing machine according to the invention.

The positive mixing machine shown consists of a base frame 10 on which is mounted an electric motor 11 with a vertical shaft which by means of V-pulleys 12 and 13 drives a central shaft 14, which through a toothed reduction gear operates a head 15 located at the top of the machine, on which head a number of downwardsinclined supporting arms 4 are provided, each of which arms at its lower end carries a mixing shovel 5. The mixing shovels operate in the usual way in an annular mixing tub 6 with supply devices, not further shown, for the materials to be mixed, besides water, and discharge opening for the ready-mixed product.

The supporting arms 4 are hollow and at their upper ends connected to pipes 3 which through a stuffing box 2 are connected to a stationary steam supply pipe 1.

At their lower ends the hollow arms 4 each terminate in a slot-shaped exhaust opening 7 located behind the associated shovel 5 and rearwards-directed in relation to the direction of movement of the shovel.

During operation the shovels are in the usual manner forced around in the mixing tub 6, and as at the same time steam of a suitably slight pressure above atmospheric is supplied through the steam supply pipe 1, there will through the stuffing box 2, the connecting pipes 3, the hollow arms 4 and the exhaust openings 7 occur an exhaust of steam directly into the cavity created behind each shovel 5 in the mass that is being mixed. By this means, the steam is made to act on the materials while the latter are being violently agitated and thoroughly mixed, so that the materials are heated quickly and homogeneously by the steam without any part of the materials being subjected to a prolonged influence by the steam under stationary conditions.

The heating can be controlled carefully by adjusting the supply of steam through the steam supply pipe 1 by means of suitable control means, not shown, and the condensate formed will be distributed evenly in the mass being mixed, so that this water can be taken into account when calculating the amount of water to be added to the aggregate, and a freshly mixed concrete of the desired composition and the desired temperature can always be produced.

What is claimed is:

1. A concrete mixing machine for producing concrete at an elevated temperature comprising an annular mixing tub, a central head coaxially mounted within said tub, a plurality of hollow arms depending from said head, a mixing shovel provided on the lower end of each said arm, means to cause relative rotation between said head and said tub so that said shovels mix the concrete mixture contained in said tub, an outlet orifice adjacent the lower end of each said arm directed rearwardly with respect to said relative rotation, and a central steam supply conduit connected to the upper end of each said arm whereby steam is exhausted into the cavities formed in the mixture by the shovels during mixing.

2. A concrete mixing machine according to claim 1 in which each said orifice is located immediately behind its associated mixing shovel.

References Cited UNITED STATES PATENTS 738,148 9/ 1903 Mercer 259-24 3,081,983 3/1963 Thibodeaux. 3,273,863 9/1966 Lodige 259-9 ROBERT W. JENKINS, Primary Examiner

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