Design Considerations: Construction Materials & Design
Structural Steel vs Formed Steel Support
Structural steel supports used in compactor
construction come in a variety of shapes including
channel, I-beam, and tube. Of these forms, the tube
is the strongest and is often used on the sides of
the compaction chamber for support in critical areas
Additionally, the closed tube shape reduces debris
deposits on the outside of the unit.
A combination of these supports are used to strengthen
the steel plate used throughout the compactor. Larger
numbers of supports as well as stronger shapes are
critical in areas such as the compaction chamber floor
and ram top which are susceptible to high impact forces
when heavy material is dropped into the compactor.
Forming a steel plate into a support shape will increase
the strength of the steel; however, the shape is not
nearly as strong as a structural shape of the same
dimensions. Structural shapes have added strength at
the bend points, formed shapes do not (in fact, forming
the steel may actually weaken it at the bend point).
When evaluating a compactor's integrity: the type, size,
and number of supports in critical areas is crucial and
more so for heavy duty applications.
The name says it all. The structure of the breaker
bar must be strong enough to withstand the forces
generated by the compactor. If the breaker bar bends
past its yield point, the compactor will become deformed
To evaluate the quality of the breaker bar, have the
compactor manufacturer give you the section modulus
of the breaker bar and what forces it can withstand. The
breaker bar should be able to withstand at least 2-1/2
times the force generated by the cylinders.
Located at the back of the compactor, the thrust beam
is used to attach the cylinder(s), and must be able
to withstand 1-1/2 times the force of the cylinder(s).
Bending this component beyond the yield point will
destroy the compactor.
Compaction Chamber Floor Plate
Steel used in construction of the compaction chamber
floor should be high quality and relatively flat. SP
Compactors use AISI grade steel A36 for commercial
units, and a harder steel AISI 1045 for all industrial ad
precrusher units. (AISI 1045 steel is considered work
hardening, which means that the steel actually gets
harder the longer it is used.)
It goes without saying that higher grades of steel are
stronger, more consistent in strength throughout, and
relatively flatter. A wavy floor will cause waste material
to build up between the ram and floor. As such, lower
grades of steel will wear and weaken more quickly,
significantly shortening the life of the floor and the
Note: the steel used on the bottom of the ram, which
rides on top of the chamber floor, should conversely
NOT be as hard as the chamber floor steel. Both plates
will last longer if the two steel plates working
Ram Guide System
A ram guide system maintains the ram from fishtailing
side-to-side, and bucking up-and-down during
Ideally, the ram should ride on the compaction chamber
floor. This uses the entire surface of the floor to support
the ram and resist waste material build-up between the
ram and the compaction chamber floor.
Engineering shows us that the ram riding on the floor
will not cause any significant loss of forward force
from the friction between the ram bottom and the
compaction chamber floor. Once the ram is moving,
the coefficient of friction is the same whether the
supporting area is one square inch or one-thousand
square inches keeping weights and materials
Top right: Structural tubing
mounted to the thrust beam
serve as a guides for the ram.
Above and inset: The 3-point
guide shoes wrap around the
tubes to limit ramp movement
and promote smooth ram
Forward force lost between a ram which rides on the floor
and one that is suspended above the floor is negligible.
The actual guide system consists of a number of
adjustable wear blocks at the back of the ram and
ram hold-down bars above the ram on each of the
compaction chamber walls. Wear blocks are made
of a special hardened plastic such as Nylatron which
will slowly wear before the steel wall or support it is in
contact with wears.
The principle is to give the guides a good surface to
work on so that the ram movement remains stable. Any
movement side-to-side or up-and-down will cause the
compactor ram and compaction chamber to wear more
quickly; shortening the life of the compactor.
A hydraulic cylinder is measured by its bore (the inside
diameter of the casing), rod (the outside diameter of
the movable rod), and stroke (the length the rod is
able to move). The force that the cylinder can exert is
determined first by the size of the bore; a larger bore
cylinder is capable of exerting greater forces. The
diameter of the rod determines whether or not the rod
can withstand the force it is generating. A larger rod
means a stronger cylinder.
Some compactors are equipped with one cylinder
(single cylinder models); others with two (dual cylinder
models). Generally, two cylinders of the same size will
have twice the force of one, and they can be spaced
to spread the force generated against the ram face
more evenly than one cylinder pushing in the middle.
Larger compactors with wider ram faces tend to have
less side-to-side ram movement when they employ two
In addition, longer cylinders must be supported to
assure against sagging or bending from the force they
generate, and their own weight and the weight of the oil
inside when they are fully extended.
Many compactor models use two hydraulic cylinders
which are crossed. The cylinders are mounted on each
side of the compactor and opposite sides of the ram.
This design helps to shorten the overall length of
the compactor and is useful in certain applications.
However, one notable shortfall is that crossed cylinders
do not generate as much force as straight push
cylinders of the same size. A crossed cylinder pushes
at an angle to the ram movement which reduces the
forward force of the ram. Cylinders with greater final
angles to the ram face will have less final forward
thrust on the ram.
The hydraulic pump moves the oil into the cylinder(s).
The rating for the pump is in GPM (gallons per minute).
The larger the number, the faster the pump can move
the oil and the faster the ram will move forward and
Two considerations should be made when the pump
is specified. First, the internal operation of the pump
is designated as vane or gear. In order to keep noise
levels during operation at a minimum, the vane pump
design operates at a lower noise or decibel level.
The pump will have an effect on how loud the machine
will operate and at what speed the ram will move. A
vane pump will operate at a lower decibel level than
a gear pump and will help to keep the equipment
operating within OSHA restrictions.
A constant displacement pump will maintain operating
speed even under load conditions; as opposed
to hi-low pump which slows the cycle time when
under pressure. If cycle times are being assessed,
consideration should be made concerning the speed of
the compaction cycle when it is actually compacting the
All components should be UL listed for compatibility
and safety. Once the control panel is complete the
entire panel can be UL certified if necessary. In this
case a UL inspector will check the panel and mark it as
The components should be NEMA rated, which are
designed for heavy duty industrial use and readily
available for repair or replacement if necessary.
An electrical panel can be designed to be controlled
with relay logic or PC logic. Relay logic uses individual
switches, timers and relays to direct the control of the
operation of the compactor. If a control fails, it can be
readily replaced with a like control.
PC logic uses an electronic control board to control
the operation of the compactor. If this board fails,
a new control board must be purchased from the
manufacturer for replacement.