Concrete Product Machines

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Concrete product machines are generally designed to produce a wide range of consumer and contractor grade concrete products made from zero slump concrete as determined by the concrete slump test through a dry casting process similar to metalworking casting using permanent molds and low pressure squeezing and molding but generally using vibration to aid in the consolidation of materials. Types of concrete products produced include Concrete Masonry Units (CMUs), pavers, slabs, retaining walls, concrete brick, etc. These machines generally consist of:

• A vibration source (application and type of vibration varies widely, see below)
• A mold comprised of two main separable sections (a mold box or grid that forms the vertical surfaces of products, and a mold head that has shoes that form the top surfaces of products)
• A means of filling the forming section of the mold box (generally a box or drawer of material that passes over the mold and back)
• Beams to assist in compacting material (upper beam that moves the mold head) and stripping (de molding) products out of the mold (lower beam)
• Mechanisms to feed the production pallets the products are formed on through the machine. (Pallets are generally made from steel, composite/plastic, or wood.)

Types of Machines Differentiated by Vibration Source

Mold vibration, mechanical eccentric

These machines are manufactured primarily by Columbia Machine, Inc. using Columbia Vibration Technology commonly known as CVT, used to compact the concrete in these machines. The machines consist of the forming section of the mold mounted to die supports that are guided vertically using parallel bars and vibrated using mechanical eccentric housings that drive the mold through a set distance of .080" to .110" at speeds up to 3,000 RPM. A steel production pallet (most commonly used) is held against the bottom of the mold by a pallet table using industrial air springs, or air suspension, allowing pressure to be varied to get different levels of vibration (shock/impact) of the pallet against the mold. The Columbia Machine, Inc. system, known as CVT, is unique in that the motion of the mold is very well constrained to vertical only motion, and allows for a very robust and reactive vibration between the pallet and mold. This system is known to be very adjustable and versatile for manufacturing nearly any type of concrete product up to 12" in height. Product heights are generally accepted as the most accurate across the entire pallet for nearly all products.

Mold vibration, rotating eccentric weights on the mold

These machines are manufactured primarily by Besser Company. Their vibration of the mold is caused by using horizontal counter-weighted shafts that create a rotating imbalance , and are mounted directly to the mold while being driven independently by electric motors that rotate in opposite directions and are generally not timed by means of controls to cancel horizontal vibrations. This system is generally known to be adequate for standard CMU hollow and solid product production, products up to 8" in height. Height control is known to be less accurate than mold vibration by mechanical eccentric but better than table vibration. In North America these machines have the most widely installed customer base due to their early adoption for the production of standard CMU's. Servo control systems have been introduced to maintain the positions of the counter weighted shafts, reducing wasted energy to horizontal vibration.

Table vibration, eccentric weights on a vibration table

These machines have been manufactured by many companies worldwide such as Techmatik, Masa, Hess, Rekers, Columbia Machine, Inc.. Their vibration systems generally consist of a vibration table that generates vibration (force) using four high speed, equally weighted shafts that are either mechanically or electronically controlled, generally requiring servo controls. The forming section of the mold is mounted to resilient members and pressed against the vibration table. The vibration of the mold is reactionary to the force generated by the vibration table and is generally of significantly lower frequency than mechanical or eccentric weighted mold vibration systems. This system is generally known to be adequate for paver and patio slab production but has limitations in producing adequate quality products over 4"-6" (100mm - 150mm) in height. Height control for products above 4" (100mm) tall is generally known to be less accurate than either previously mentioned mold vibration systems.

Hydraulically vibrated mold

(cite Den Boer designs and research)

Mechanically vibrated mold and table

(cite Blockmatic equipment designs)

Types of machines differentiated by actuation type

Hand tamp, manually operated

Developed in the early 1900s, hand tamp machines use mechanically applied pressure to compress material in a mold to form concrete blocks. This type of machine is still used in many areas where inexpensive labor is plentiful or access to electric power is limited. This is generally considered a very low volume, labor intensive, production method and is generally not used in most industrialized countries.

Cam operated, dependent axis motion

The earliest type of powered/automatic concrete block machine created by Besser Company, in the 1930's, and still widely used today, is operated using a system of mechanical cams powered from one main shaft that is driven by an electric motor to control the motion of most major machine sections (beams, feed drawer, pallet feed, etc.). This type of machine has the benefit of reduced cycle times and nearly identical motion from cycle to cycle. This type of machine motion was invented when there were only a few types of products manufactured, and machine setups did not need to vary greatly. VFD's and rotary encoders have been used on the main drive motor and camshaft to allow some changes to the speed and or dwell times for some portions of the machine cycle.

Fluid power operated, independent axis motion

First produced by Columbia Machine, Inc. starting in 1945, these machines generally use fluid power in the forms of hydraulic, and some pneumatic and electric actuators in conjunction with electrical feedback devices and PLCs to control and coordinate the motion of the major machine sections. This type of machine, when started in the mid-1900's, offered producers many ways to customize the operation of the machine to adjust to the increasing number of concrete product shapes, heights, and materials used. Most modern block machines use this method of actuation to allow the versatility required in the ever-changing market of concrete products.

Types of machines differentiated by product stripping motion

Down-strip (products move down relative to mold box)

These machines hold the position of the mold box stationary and use the upper (Compaction) and lower (Stripper) beams to strip the products made down and out of the mold. These machines generally have better mold constraint systems than up-strip systems that reduce mold wear during the vibration used in production, can allow vibration during the stripping sequence to reduce frictional forces that must be overcome during stripping, and allow for the production of products that are much taller than either their width or depth (unstable products like brick on-end and roof tiles).

Up-strip (Mold moves up relative to products)

These machines hold the position of the products stationary and use the upper and lower beams to strip the mold up while holding the products in place and to get them out of the mold. Up-strip systems generally have fewer or less robust mold constraints than Down-strip machines, limiting their use on tall and/or thin products. They tend to be more well suited to lower height products, generally 4" (100mm) or less.

Need graphic matrix showing how each manufacturers machines operate, highlights differences.

History

Production methods of concrete block started with manually operated forming machines that generally made only one CMU at a time and have progressed to machines that can manufacture up to 18 CMUs in one machine cycle.

• Manual hand operated press machine: These simple machines were first developed to produce a few units in a 10 hour day and could be purchased from companies like Sears Roebuck, Co. In the early 1900's the machine was improved by Jesse Besser of Besser Company to produce up to 200 units in the same amount of time, still a very manually operated machine.:
• Cam operated machine: The first of these machines were created in 1937 by Besser Company to create a more automated and increased level of production. These machines tend to be excellent at high production levels of standard concrete masonry units to meet ASTM specifications.
• Independent axis machine: These machines added versatility to the production cycle using timers, hydraulic controls, and features allowing not only the production of standard CMU's, but paving stones, slabs, and many other structural, landscaping, and more aesthetically pleasing units. Columbia Machine, Inc. appears to have created the first machines combining mechanical eccentric mold vibration and hydraulic actuators in 1945. Other European manufacturers followed but using table vibration for their higher demand of paving products rather than the more versatile production capability of mold vibration.

Associations

• National Concrete Masonry Association
• ICPI, Interlocking Concrete Pavement Institute

See Also

• Zero Slump Concrete Test
• Fred Neth Sr. (link needed)
• Columbia Machine, Inc.
• Jesse Besser
• Besser Company
• CVT (link needed)

Concrete Products:

• Concrete masonry unit
• Bricks

Sources

• Columbia Machine (cite history page)
• Masa (cite history page)
• Besser (cite history page)
• How Products are Made website (supply with better/more information about more current Block making technology)
• Search: "first modern concrete block machine"

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