Mortar mixing drum

A horizontally oriented mortar mixing drum 11 fabricated of polyethylene material having an elemental cylindrical segment opening through which mortar materials to be mixed may be deposited into or poured from. A perimeter frame having base elemental frame member 15, diametric wall frame members 16 and polyethylene grate 20 is provided for enhancing resistance to torsional stress on drum 11. Wear resistant liner 12 and side panels 13 and 14 cover the interior surface of drum 11. Paddle shaft 18 is rotatably and axially supported within drum 11 and has paddle stubs 28 attached to and extending radially therefrom. Polyethylene mixing paddles 19 are sleeved onto paddle stubs 28 to complete improved mortar mixing drum assembly 10.

BACKGROUND OF THE INVENTION 
1. Technical Field 
This invention generally relates to an improved mortar mixing drum, and in 
particular to a mortar mixing drum fabricated from polyethylene crosslink 
with a removable wear resistant plastic liner and paddles, and an 
elemental perimeter drum frame for rigidity. 
2. Background Art 
Present day mortar mixers are constructed of all steel. Typically, they 
have a cylindrically shaped drum open along the top side and a plurality 
of metal mixing paddles and wipers axially and rotatably secured within 
the drum. A rotation means, such as a gasoline engine, is provided to 
rotate a paddle axle to facilitate mixing the mortar. The ends of the 
paddles are provided with rubber wipers which contact the metal interior 
surface of the drum. This is necessary because the mortar sticks to the 
inside of the drum, as it also sticks to the paddles. It should be obvious 
that the life span of the rubber wipers is limited and they require 
frequent replacement. 
Often, due to improper maintenance and cleaning, residual mortar is allowed 
to dry within the mixing drum and other surfaces, including the paddles. 
Because dried mortar is very difficult to remove from a metal surface, 
workers often resort to breaking the mortar loose with a hammer or other 
heavy object. Consequently, mortar mixers typically spend a great deal of 
time in the shop for repairs. 
A similar problem exists in the analogous art of cement mixers. Attempts 
have been made to solve this problem, such as Bishop's U.S. Pat. Nos. 
4,435,082, 4,491,415, and 4,756,623, which all teach rotatable cement 
mixing drums manufactured of a plastic such as polyethylene. Adsit, U.S. 
Pat. No. 4,521,116, teaches a mixing apparatus having a removable and 
disposable synthetic resin drum liner. Kennedy, U.S. Pat. No. 4,711,582 
teaches a rotary mixing device which uses a bag as a disposable drum 
liner. Riederer, U.S. Pat. No. 4,569,648 teaches a self-cleaning rotating 
drum being lined with elastic webs. 
None of the above described devices are capable of mixing mortar, as they 
are designed for mixing cement. There is a significant difference between 
compositions of mortar and those of cement. Typically cement contains 
large gravel particles as compared to mortar whose largest component is 
relatively small grained lime cement and sand. There may be a substantial 
difference in weight, with standard cement gravel mixtures weighing 
approximately 150 pounds per cubic foot, whereas mortar will typically 
weigh approximately 200 pounds per cubic foot. As a result the 
polyethylene drums taught by Bishop's U.S. Patents and the rest of the 
cement mixers taught by the above-described prior art are not suitable for 
mixing mortar. 
To date the most effective apparatus for mixing mortar uses a cylindrical 
drum having a cylindrical segment opening along the longitudinal, or 
elemental, length of the drum and a plurality of paddles rotatably secured 
within the drum. The ends of the paddles are provided with rubber wipers 
which wipe the inner surface of the cylindrical drum, keeping it free of 
adhering mortar. Contrary to their cement mixing counterparts, mortar 
mixers are not easily operated by hand, primarily because of the added 
density of the material being mixed, and must use either gasoline or 
electric motor to operate the mixing paddles. 
The drum itself is rotatable from an orientation where the elemental 
segment opening is at the top to a dumping position where the opening is 
rotated downward until mortar is free to spill from the drum. Since the 
drum contains rotating paddles it presents a safety hazard, and the 
typical mortar mixer design includes protective grates covering the 
opening. Typically there are two sections to the protective grate, the 
first being fixed and the second hinged to open when mortar is being 
dumped from the drum. The grates are normally made of steel and have 
sufficient opening size to allow water and dry mortar to be easily dumped 
into the drum, yet small enough to keep operators' hands and clothing from 
being caught by the rotating mixing paddles. 
Two problems plague both the manufacturers and users of such mortar mixers, 
the first is the abrasion caused by mortar being wiped against the inside 
walls of the mixing drum which will eventually cause the drum to wear 
through. The second is that mixed mortar will adhere to grates even during 
proper operation and must be chiseled off, and on occasion, mortar will be 
allowed to dry on the inside of the drum and the paddles to which it 
readily adheres. The only effective means of removing dried mortar from 
the inside of the drum and off the grates and paddles is to break it loose 
with a hammer or other heavy object. This is a time consuming chore and 
can easily result in damaged paddles and dents in the drum which interfere 
with the contoured surface of the drum and, if severe enough, will 
interfere with the rotation of the mixing paddles causing the paddle 
assembly to jam inside the drum. In practice it has been found that when a 
mortar mixer is being used on a full-time basis, the all steel drum should 
be replaced every three to six months. This of course is time consuming 
and expensive. 
The use of plastic drums would be preferable since plastic such as 
polyethylene crosslink present a surface to which dried mortar will not 
adhere. The problems with the use of polyethylene crosslink are twofold, 
the first is wear on the inside of the drum caused by the abrasion of 
mortar being mixed, and the second is the considerable weight and high 
viscosity of mortar. The typical mortar mixer is designed to mix between 
six and eight cubic feet of mortar at a time. This can weight between 800 
to 1,600 pounds. 
The abrasiveness and high viscosity of mortar results in torque moments 
being imparted to the drum when the paddles are being rotated to mix 
mortar. These forces imparted can be considerable and can result in net 
torsional forces being imparted to the drum as a result of the means by 
which the drum is held in its upright or mixing position. These forces are 
the primary reason why steel has been the material of choice for 
fabricating mortar mixing drums. 
As a result plastic mortar mixing drums had to be fabricated of thick, and 
relatively heavy, plastic materials. 
What is needed is a plastic mortar mixing drum which has the combination of 
the non-adhering surfaces for the drum, the paddles and the grates, the 
structural strength and integrity of a steel drum, and an improved wear 
surface. The fabrication of such a drum would substantially increase its 
useful life and decrease the maintenance expenses incurred in removing 
dried mortar from the mixer parts and for periodically replacing mixing 
drums and paddles. 
DISCLOSURE OF INVENTION 
These objects are accomplished by use of an improved mortar mixing drum 
which is generally cylindrical and molded from a polyethylene material. 
The drum has an elemental cylindrical segment opening through which 
material to be mixed may be deposited into or poured from the drum. An 
elemental perimeter frame member is provided and positioned in elemental 
contact with the cylindrical drum opposite the elemental segment opening 
and serves as the base for a perimeter frame. It is attached to a pair of 
diametric end wall frame members each in diametric external contact with 
an end wall of the cylindrical drum. An elemental polyethylene grate 
opening member spans a portion of the elemental segment opening and 
completes a perimeter frame by being attached at its ends to the 
corresponding ends of the diametric end wall frame members. 
A liner of ultra high molecular weight polyethylene material is attached to 
and covers the interior surfaces of the drum. 
A paddle shaft coaxially aligned with the cylindrical axis of the mortar 
mixing drum is provided. Extending radially out from the paddle shaft are 
a plurality of paddle stubs to which are attached polyethylene paddles. 
The polyethylene paddles are integrally molded units having hollow 
rectangular sleeves which slide over and are attached to the radial 
rectangular paddle stubs by means of through hole bolts.

BEST MODE FOR CARRYING OUT INVENTION 
As shown in FIGS. 1, 2 and 5, drum assembly 10 is supported by drum shaft 
assemblies 17 for rotational motion between front frame strut 23 and rear 
frame strut 26 which extend up from mortar mixer trailer frame 24. Drum 
shaft assemblies 17 function in a dual rotational capacity in that they 
permit the rotation of the drum from an upright or mixing position wherein 
polyethylene plastic grate frame member 20 and dumping grate 21, which 
span and cover an elemental cylindrical segment opening in drum 11 are 
positioned atop the horizontally oriented drum assembly 10 to a dumping 
position where mixed mortar will spill out onto a mortar board or 
wheelbarrow, neither shown, through an opening between drum 11 and dumping 
grate 21 created when plastic dumping grate 21, which is hingedly 
connected to plastic grate frame member 20 by hinges 22, swings away from 
drum 11. 
A second rotational function served by drum shaft assembly 17 is to 
support, for rotation, paddle shaft 18 which in turn supports a plurality 
of paddle assemblies 19 which are sleeved onto paddle stubs 28 which 
extend radially out from paddle end 18 as shown in FIGS. 5 and 6. Paddle 
assemblies 19, as shown in FIG. 6, are attached to paddle stubs 28 by 
means of through lock bolts 29 inserted through aligned paddle stub bolt 
holes 30 and paddle assembly bolt holes 31. Since mortar mixers are used 
at remote construction sites, the entire assembly is mounted on trailer 
frame 24, and is provided with a gasoline engine 33, inside cowling 
assembly 25. Engine 33 is used to rotate paddle shaft 18. Rotation of drum 
assembly 10 from the mixing position to the dumping position is 
accomplished manually by an operator grasping drum handle 27 and pulling 
the same downward to rotate drum assembly 10. 
In the preferred embodiment, as shown in FIGS. 2, 3 and 5, drum 11 is 
fabricated of polyethylene crosslink material or other suitable plastic 
composition capable of holding between six cubic feet to eight cubic feet 
of mortar. Mortar is substantially heavier than cement aggregate 
compositions, and as a result the total weight of mortar mixed at any one 
time will weigh between 800 to 1,600 pounds. In practice it has been found 
that a polyethylene crosslink drum can be easily fabricated to withstand 
such weight in and of itself. 
But, in addition to the weight of the mortar itself, there are two 
additional forces which must be considered. The first is the torque 
moments about the axis of the drum induced by the rotating paddle 
assemblies being rotated through the highly viscose mortar mixture which, 
if unchecked, would also cause or induce rotation of the drum in the same 
direction as the paddle shaft assembly. This type of rotation is prevented 
by means of a cam stop 32 as shown in FIGS. 1, 2 and 5, which engages 
front frame strut 23 to prevent this rotation. This is the point at which 
all of the countering forces which counter this induced torque moment are 
applied to the drum assembly 10, and results in a torsional stressing of 
drum 11 between rear frame strut 26 and front frame strut 23. Even if 
additional cam stops were provided for rear frame strut 26, there would 
still significant torsional stresses imparted to drum 11. 
As a result it has been found that the construction of an elemental 
perimeter frame around the cylindrical drum 11 provides adequate 
reinforcement for the polyethylene crosslink drum 11 to the extent that 
thickness of drum 11 can be reduced and drum distortion resulting from the 
torque moment and resulting torsional stresses are eliminated. The 
perimeter frame is comprised of a metal elemental perimeter frame member 
15 which runs the length from one end of drum 11 to the other and is 
positioned opposite the elemental cylindrical segment opening in drum 11. 
Elemental frame member 15 provides a base for supporting drum 11 and its 
contents which may weigh between 800 and 1,600 pounds. 
Metal diametric frame members 16 are attached to each of the end walls of 
drum 11 and extend upward from elemental frame member 15 through the 
central axis of the drum assembly and serve as a convenient attachment 
point for drum shaft assemblies 17. 
In the preferred embodiment the perimeter frame assembly is completed by 
the addition of polyethylene crosslink grate frame member 20 which also 
connects to diametric frame members 16 to complete the perimeter frame. 
Grates 20 and 21 are necessary to prevent operators from inserting their 
hands, shovels or other tools into drum 11 when paddle shaft 18 and its 
attached paddles 19 are being rotated. Without grate frame member 20 and 
dumping grate 21, there would be a substantial risk of harm to the 
operator and the mortar mixer. 
It should be apparent that mortar is an abrasive substance and would wear 
the surfaces of drum 11. As a result a wear resistant plastic liner 12 is 
provided to line the inner cylindrical surface of drum 11. In the 
preferred embodiment the wear resistant plastic is fabricated of ultra 
high molecular density polyethylene which is a material that cannot be 
rotomolded but instead can only be made in extruded sheets. As a result a 
generally rectangular, but flexible, panel 12 is then inserted into the 
interior cylindrical section of drum assembly 10. In practice it has been 
found that it can be bolted (not shown) or glued to drum 11 so as to 
facilitate removal and replacement as necessary. FIG. 4 shows two side 
panels 13 and 14, also extruded of ultra high molecular density 
polyethylene, a pair of which are bolted to each of the end walls of drum 
11 to complete a wear resistant surface inside of drum 11. 
While there is shown and described the present preferred embodiment of the 
invention, it is to be distinctly understood that this invention is not 
limited thereto but may be variously embodied to practice within the scope 
of the following claims.