Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
1998-01-30
2001-10-30
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S070000, C264S071000, C264S087000, C264S102000, C264S571000, C264S177110, C264S211110, C366S015000, C366S017000, C425S145000, C425S197000, C425S199000, C425S203000, C425S205000
Reexamination Certificate
active
06309570
ABSTRACT:
BACKGROUND OF INVENTION
A. Field of Invention
The present invention relates in various aspects to extruded concrete articles made from a mixture of water, aggregate and binder. According to the process, the binder hydrates in the presence of the water to form a high-strength concrete article, such as bricks. In another aspect, the invention relates to processes and apparatus for making the concrete articles.
B. Background Art
Various efforts have been made to make extruded concrete articles. But the present inventor is not aware of any successful procedures that have been implemented commercially to provide low cost building materials having properties comparable to conventional “molded” concrete. Accordingly, the present invention is believed to satisfy a long-felt need. It is contemplated that one of the problems with other processes lies in the inability to reliably make articles that meet the specifications of conventional molded concrete. Certain aspects relating to the use of vacuum to make extruded concrete articles have been published. For example, Anderson et al., U.S. Pat. No. 5,549,859, discusses a vacuum-type chamber for making concrete articles. However, these and other processes and devices have various shortcomings, and fail to disclose or suggest the present invention, which includes improved methods and apparatus for making extruded concrete articles.
SUMMARY OF INVENTION
In a specific embodiment, this invention is directed to a process of forming an extruded cement-based article, including the steps of: forming a cement-based feed mixture including water, aggregate and binder; and directing the feed mixture through a pretreatment zone with an entry section and an exit section in which the flow of the feed mixture is restricted such that the volume flow rate at the entry section is greater than the volume flow rate at the exit section. The feed mixture can then be directed to a vacuum zone, wherein sufficient vacuum is maintained in the vacuum zone to remove entrained air from the feed mixture. The feed mixture is held in the vacuum zone for a time sufficient to form a densified mixture; and the densified mixture is directed through an extruder at an elevated pressure to provide an extruded cement-based article. As used herein, the term “cement-based” is to be interpreted broadly, including, for example, materials that are called “cementitious” in U.S. Pat. No. 5,549,859.
Certain embodiments of the process are preferred. Preferably, the feed mixture is directed by a pug mill to the vacuum zone, with mixing blades that are pitched forward for advancing the feed mixture toward the vacuum zone. Where the pretreatment zone includes a barrier surface, e.g., a restrictor plate, after initially contacting the barrier surface in the pretreatment zone, at least a portion of the feed mixture should move parallel to the barrier surface and then pass through the apertures of the barrier toward the vacuum zone. Also, the step of restricting the flow of the feed mixture in the pretreatment zone preferably includes passing the feed mixture through at least two sets of apertures. The feed mixture should be shredded in a vacuum zone. Preferably, the feed mixture is shredded by passing the feed mixture through a multiple-blade rotary shredder, and the feed mixture should be shredded after the flow of the feed mixture is reduced. Preferably, the feed mixture is compressed in the pretreatment zone prior to being directed to the vacuum zone.
Preferably, the vacuum in the vacuum zone is sufficient to remove any excess water from the feed mixture; and the vacuum in the vacuum zone should be maintained at a level of from about −5 to −15 bars, such that it does not vary or fluctuate more than about 1 bar over a period of about 1 hour. The vacuum-treated mixture should have a density within the range of from about 50 to 200 lbs/ft
3
.
The process preferably includes the step of measuring the moisture level of the feed mixture after the addition of water to determine whether additional water is to be added. Preferably, the process includes measuring the moisture level indirectly. In a specific embodiment, the moisture level is measured by measuring the viscosity or thickness of the feed mixture before the feed mixture is directed to the vacuum zone. The measured viscosity or thickness can be compared to a predetermined reference viscosity or thickness which is or has been correlated with a desired moisture level, and can include the additional step of adding water based on the results of the comparison. Water can be added to lower the viscosity or thickness when the comparison shows that the measured viscosity or thickness is too high. The feed mixture should be mixed using a pug mill with a mixing shaft driven by a motor and wherein the viscosity or thickness of the feed mixture is measured by measuring the load on the motor driving the pug mill shaft. Thus, where the load on the pug mill motor is too high, such that it is above a predetermined reference level, the viscosity can be considered to be too high, and the moisture level too low, whereupon water can be added in proportion to the difference between the measured load and the reference load.
During extrusion, the elevated pressure applied to the densified, vacuum-treated mixture should be less than about 5,000 psi, and preferably is from about 300 psi to 1,500 psi. Preferably, the vacuum-treated mixture is extruded in an extruder that includes an extruder shaft driven by an extruder motor and the load on the pug mill motor is compared to the load on the extruder motor to determine whether the load on the pug mill motor is too high and whether to add water to obtain a desired moisture level. Preferably, additional water is supplied to the feed mixture through one or more valves that open in response to a control system that receives input signals reflecting indirect moisture measurements.
As used herein, unless otherwise indicated, the term “pressure” generally refers to the air pressure within the relevant part of the system, e.g., the air pressure in the pretreatment chamber or the vacuum chamber, which can also be considered the ambient pressure of that particular local environment, and “pressure” does not refer to a force being applied in a given direction by one solid body on another solid body, e.g., the forces being applied against the feed mixture by the movement of the pug mill, or the forces being applied against the feed mixture by the restrictor plate or the tapered walls of the pretreatment zone.
Preferably, at least one barrier at least partially separates the pretreatment chamber from the mixing chamber, such that the pressure of the feed mixture on the side of the barrier most proximate to the mixing chamber is greater than the pressure of the feed mixture on the side of the barrier most distant from the mixing chamber. Accordingly, in a specific embodiment, a step-wise reduction in pressure from the mixing chamber to the vacuum chamber is provided via the pretreatment zone. Alternatively, this pressure reduction in the pretreatment zone can be continuous, e.g., expressed as a smooth curve, or it can involve a series of “spikes” in pressure, e.g., where the pressure reduction is uneven and even includes upward pressure spikes. Preferably, the step of restricting the flow of the feed mixture in the pretreatment zone includes directing the feed mixture against a barrier which includes apertures through which the feed mixture is capable of passing, such that the momentum of the feed mixture is reduced when it contacts the barrier and passes through the apertures toward the vacuum zone. Preferably, the barrier has a substantially planar surface and at least a portion of the feed mixture is directed against the barrier surface at an angle of about 90 degrees to the barrier surface. Preferably, the flow area is sufficient to prevent substantial amounts of air from entering, i.e., any amount sufficient to raise the pressure of the vacuum zone about 1 bar or greater.
In another aspect, a specific embodiment o
American Equipment Systems
Fish & Richardson P.C.
Poe Michael I.
Silbaugh Jan H.
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