Agitating – Mortar mixer type – With elevating means
Reexamination Certificate
2001-10-18
2003-12-23
Soohoo, Tony G. (Department: 1723)
Agitating
Mortar mixer type
With elevating means
C366S041000, C366S050000, C366S183100, C366S150100
Reexamination Certificate
active
06666573
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to apparatus for mixing and dispensing granular materials and is particularly directed to portable apparatus for mixing, wetting and discharging pre-blended granular materials, such as cementitious-type materials, at a remote construction site.
BACKGROUND OF THE INVENTION
The products to which this invention applies can vary from concrete mixes, including bricklaying mortars and grouts. The traditional method of producing mortar or grout at a masonry job site is to count shovelfuls from a pile of sand, add mortar/cement by breaking open a 90 lb. paper bag, followed by adding water with a pail to a batch mixer. This method is still used on 80% of masonry construction jobs. Basic drawbacks of this approach are that it is labor-intensive and that the mix composition varies depending on type or condition of the sand, which when damp can increase the mixture volume by as much as 30%. Since sand is the predominant ingredient, variation in the mixture composition is inherent in the method of counting shovelfuls and cannot be precisely controlled. Mortar bond-strength, compressive strength, color and other factors of the mortar also vary. This can cause many serious problems that sometimes lead to removal of defective material, which, of course, is usually very costly.
Another method of producing mortar that addresses some of the aforementioned problems is to dry sand at a remote location and pre-blend the components, i.e., sand, mortar cement, lime and even color additives, and package the blend in bulk bags (2000 to 4000 lb.) and deliver the bags to a job site. In one approach, the bulk bags are individually placed in a silo that contains up to six bags of material. The contents of the silo is then dispensed into a batch-type mixer wherein water is added. This approach can be used to produce both grout and mortar, but requires at least two silos and two batch mixers (one for each type of material). The silo is portable only when empty to facilitate set-up delivery to a job-site. At the job site, it is set up as a fixed mixing operation remotely located from where the masonry brick laying operation is taking place. The mixing cycle is also labor intensive, requiring two workers, a forklift operator and a laborer to supply the masonry laying crew with mortar or grout.
This silo mixing operation begins with the forklift operator exchanging a full tub with an empty tub which the mixed contents are later emptied into. A laborer using a bucket pours half of the needed water into the empty batch mixer and opens a slide gate, where by gravity alone dry pre-blended mortar empties into the batch mixer below. The quantity of dry material cannot be accurately measured because opening and closing of the slide gate doesn't always cause the material to flow. The material bridges and does not flow easily. The laborer then uses a shovel to bang on the steel silo with the slide gate open which often results in the discharge of too much material. When this happens the equipment (mixer) is strained, can break down and material is wasted. This labor intensive mixing cycle continues with more water added as needed. Specifications require a minimum of five minutes mixing time. If the mix is too wet, more dry materials must be added resulting in opening and closing of the slide gate.
Another problem with this approach is in the variation in size between the various grades of sand and cement particles which promotes segregation because the material is handled and dispensed numerous times. One reason for this is that as the material flows into a silo, the material beneath the inlet of the silo piles up at the so-called “angle of response” of the material. In this case, the larger particles often roll down the peak towards the sides of the silo, leaving the finer particles in the central region. Inhomogeneity can also occur when the silo is filled and the material is drawn off through an outlet at the bottom of the silo or bulk bag. The material flows from the region directly above the opening and thus is not representative of the material in the originally packed bulk bag. To avoid this problem, the pre-blended suppliers use too fine a sand that meets only the minimum sand grading specifications as described in ASTM C144 “
Specifications for Aggregates for Masonry Mortar
”. A better product has a larger variation in sand gradation.
In addition to the problem of inconsistent mixture composition control, the silo approach also suffers from an unhealthy work environment because of the very dry sand falling on the laborer. Opening and closing of the overhead slide gate showers the laborer with very dry cementitious blended materials. The laborer ingests these sand and cement particles in the air he breathes which can cause silicosis and possibly cancer. This batch mixing operation cannot be made dust proof. The laborer's clothes are covered with dust which is brought home to possibly contaminate others. A batch mixer having a gasoline engine also endures further abuse by the intake of dust parties which can cause premature machine wear and necessitates more frequent replacement of air filters.
The mixing cycle continues and additional labor costs add up. The mixed contents are emptied into the mortar tub. The forklift operator now must stop other operations to exchange the full tub with an empty one, then carry the tub to the scaffold that may be hundreds of feet away from the mixing operation. This silo mixing operation is thus not portable, but rather is fixed in location. The 20,000 lb. weight of the forklift constantly traveling over dirt creates dust that slows the work. Another laborer at the top of the scaffold typically removes safety railings to allow the full tub to be placed on the scaffold. The forklift then moves over to pick up and lower an empty tub. The safety railings must then be reinstalled. The operation is not finished! The mortar must now be spread to the individual bricklayers by shoveling from the tub to the mortar boards so that the mortar is within easy reach of the individual bricklayers.
If the material is grout, labor costs to fill block is even a bigger factor because grout must be placed in buckets, then passed hand to hand, and poured into each individual block core by the bricklayers. This is wasteful because in addition to the time required to perform the needed operation, the bricklaying must stop in order to grout the block walls. In an attempt to address the high costs of this operation, a powered grout dispenser has been developed that must be filled at the mixing stage with all the accompanying labor intensive operations described for mixing mortar. This operation usually starts by elevating the batch mixer under the silo, charging the batch mixer with grout material, adding water and mixing for five minutes, then dumping the contents into the grout hopper. The wet mixture must then be transported to the work area where grout is dispensed from the holding hopper and directed to the block cores. The alternative to this is to fill the hopper with pre-mixed grout from a ready-mix cement truck, but this suffers from the problems of delivery truck availability and scheduling and additional costs.
Another type of mixing operation can be performed by a silo system using dry pre-blended material delivered to the job site by a bulk delivery truck that blows the material directly into the silo. The mixing can be performed by a continuous mixer installed under the silo. This approach is common in Europe and marketed as PFT, WAM. The mixed material is then typically pumped by a grout pump up to 200 ft. away where it is dispensed. The drawback in this approach is that additional equipment is required (pump and hoses), which must be cleaned and maintained. While this approach has been used in Europe for twenty years, it is not practical for masons in the United States who generally are capable of much higher levels of productivity and are less adapted for maintaining complicated machinery.
The various approaches disc
Emrich & -Dithmar
Soohoo Tony G.
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