Agitating – Mortar mixer type – Methods
Reexamination Certificate
2001-05-04
2003-03-04
Soohoo, Tony G. (Department: 1723)
Agitating
Mortar mixer type
Methods
C366S026000, C366S027000, C366S041000
Reexamination Certificate
active
06527428
ABSTRACT:
This invention relates to portable, batching and mixing concrete plants having a compulsory mixer. More particularly, a four trailer portable concrete plant is disclosed having a mixer trailer, silo trailer, aggregate trailer, and control trailer. The mixer trailer forms at its mounted compulsory mixer a foundation on which the trailer-transported silo is erected. An aggregate trailer mates to the assembled mixer and silo trailers to supply aggregate. These three assembled trailers when combined to a control trailer form a mobile batching and mixing plant of high capacity, which can be erected on site in a day without semi-permanent foundations, without the need of a crane and controlled in operation and powered from the control trailer.
This Continuation-In-Part relates to the elevation of a compulsory mixer during the erection of the portable plant. This elevation of the compulsory mixer enables direct discharge to underlying transporting trucks without the necessity of using an off loading conveyor for concrete from the compulsory mixer.
BACKGROUND OF THE INVENTION
In the above referenced disclosure—which at the time of the filing of this application was a pending U.S. Patent Application—we set forth the extant background and related art. The design in the former application illustrated a two trailer portable plant having a maximum capability in the range of 300 cubic yards of concrete per hour. Subsequent development and design by us has indicated that a plant of twice that size may well be required. As no such high quantity mobile concrete plants have yet been operated or disclosed, we therefore repeat the background of the invention as originally set forth in that invention.
In the discussion that follows, the prior art is set forth in terms of the need for this invention. It is to be understood that we claim invention both in the recognition of that need as well as the solution that follows.
Modem concrete paving practices impose more severe constraints on concrete quality every year. Specifically, concrete when freshly mixed is tested and measured for different desired qualities and standards pursuant to imposed and specified quality control standards. These standards include moisture content (or slump), both compressive and flexural strength after a prescribed number of days, aggregate shape, air content, and uniformity, to name a few. If the quality standards of the concrete produced vary statistically above or below the prescribed standard mean, then the concrete producer is penalized financially.
Exemplary of these standards would be concrete compressive strength where the concrete strength is to reach say 3,500 psi in 28 days. The specification might allow a variation of this standard of 5% above or below this mean or the contractor would be penalized.
It is generally agreed that higher strength concrete can be reached in a shorter period of time by better mixing action and lower water/cement (W/C) ratios. Thus the lower the concrete slump, the easier it is for the contractor to reach the specified strengths. The trend in the industry is toward lower W/C ratios. Low W/C ratio concrete mixed in conventional tilting drum mixers do not reach uniformity as quickly as the mixer used in this invention.
The cost of the concrete makes up the majority of the cost of the road or airport pavement being built. Given the large volumes of concrete processed in such paving contracts, supervisory and specifying authorities such as state and federal inspectors can only statistically sample the loads of concrete to determine the quality of the concrete delivered by the contractor. Because of the large quantity of concrete that can be produced by the contractor in a day, the contractor faces great financial risk if many days pass before he realizes the concrete he is producing is testing outside of specification mean. The above example is intended to show how important it is for the contractor to maintain quality control on the concrete he produces. It is imperative that the contractor use batching and mixing equipment capable of delivering uniformly mixed concrete of the low slump variety to precision construction specifications without increasing the mixing time required to reach uniformity. If it takes longer mixing times to reach uniformity, the number of concrete batches per hour that plant can produce decreases. This results in the contractors cost to place the concrete increasing because his fixed paving costs per hour are divided by fewer yards of concrete.
Modem concrete paving practices also call for the use of slipform pavers, which in operation consume relatively large amounts of concrete. On a typical urban size paving job, where the total cubic yards of concrete to be used on the job is relatively small, a modern paver can consume concrete in the range of 240 to 300 cubic yards per hour. On larger jobs the contractor may choose to mobilize, produce and deliver concrete to the slipform paver at a higher rate with a larger plant with higher capacity. Exemplary of such a paver is that Slipform Paver sold under the designation of model S850 built by Guntert & Zimmerman of Ripon, California. The fundamental design of this model was pioneered by the late Ronald M. Guntert, Sr. of Stockton, California as set forth in U.S. Pat. Nos. 4,493,584 and 5,135,333.
Other more recent examples of pavers consuming high volumes of concrete can be found in U.S. Pat. No. 5,590,977 entitled Four Track Paving Machine and Process of Transport by Ronald M. Guntert (herein) et al. And U.S. Pat. No. 5,615,972 entitled Paving Machine with Extended Telescoping Members by Ronald M. Guntert (herein).
As cement in the concrete starts to hydrate during transport to a paving site, portable concrete batching and mixing plants have been developed for mixing concrete adjacent the paving site. This reduces the hauling distance to where the concrete is being used and to reduce the number of concrete hauling units required. Simply stated, from a plant, which mixes concrete to the site where such mixed concrete is placed, most contract specifications set a time limit of 30 minutes for non-agitating trucks, which is about a 12 mile transport limit. This practical transport limit is reduced in high traffic areas or other situations where the average speed at which the hauling unit can travel is reduced. If the time limit is exceeded, the concrete that is hauled will start to set before the paver places it and the paver placed concrete will not meet the required contract standards.
Secondly, and given the high quality constraints placed on the paved and/or placed concrete product, so-called continuous mixing concrete plants have proven inadequate. Such plants are capable of delivering large volumes of concrete but do so on a continuous flow basis. The exacting standards of thorough mixing covered by precise constituent proportion make the continuous flow adjustment of such plants hazardous from the quality control standpoint. As a result, such continuous mixing concrete plants have not been accepted in modern paving practice, at least in the North American paving market. It is only the processing of specific “batch” quantities of cement, water and aggregates that constitute concrete that enables the relatively high quality requirements to be maintained and conventional calibration and quality assurance measures to be used.
Prior art portable modem batching and mixing concrete plants are large, require concrete foundations and are difficult to erect, often consuming three to five days in assembly. Frequently, these plants require special rigging equipment, such as cranes to accomplish erection. Specifically, it is not uncommon for such plants to occupy 7 or more (sometimes as many as 11) transporting trailers. Further, such plants utilize rotating and tilting drum mixers located high overhead so they can tilt and gravity feed the mixed concrete into the hauling units. The mixer itself is belt fed with aggregates that are gravity fed through batching/weighing hoppers to maintain precise concrete constituent propor
Campbell Lowell B.
Cape Christopher
Cape William R.
Guntert, Jr. Ronald M.
Salgarollo Roberto
Guntert & Zimmerman Const. Div. Inc.
Hynes William Michael
Soohoo Tony G.
Townsend and Townsend / and Crew LLP
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