Reducing energy expenditures for brick production by use of vibrating cutters

Research paper conducted by the Research Alliance of the Clay Brick and Tile Industry Regd (FGZ)Project numberAiF 16074 NProject
funded byBMWi through the German ­Federation of Industrial Research Associations “Otto von Guericke” Regd (AiF)Implemented byBrick Research Institute Essen Regd (IZF)Project

managersDipl.-Ing. E. Rimpel and Dipl.-Ing. ­

S. Petereit

1 Background and problem description

Large-format, porosity-enhanced, vertically perforated clay bricks with high core-hole fractions and filigreed webs call for the use of materials with good plasticity. That, however, means that the freshly extruded brick green bodies will display diminished strength and be in danger of deforming and suffering structural damage on cutting. Moreover, their compositions are usually laced with fibrous porosity enhancers like sawdust or paper sludge that cause “smearing” of the filigreed core-hole structure due to cutting. Indeed, cutting imposes substantial loads on the highly perforated bricks – loads that can cause considerable deformation.

To a greater or lesser extent, both phenomena tend to close off the core holes. This impedes the kind of energy-conserving through-air drying that is becoming increasingly popular in modern masonry brickworks. Subsequent grinding of the fired bricks, in turn, presupposes tight dimensional tolerances in order to minimize the required amount of grinding.

For reasons of energy economy, producers try to use as little batching water as possible for extruding facing bricks. Thus, either less energy has to be expended for evaporating the water, or the freshly extruded brick green bodies can be loaded onto the kiln cars by the “direct setting method”. The force required for cutting stiff-extruded clay columns, however, imposes bottom limits on the reduction of batching water volumes.

 

2 Procedure

The mechanisms of action involved in the use of knives as cutting tools were investigated with a view to reducing the applied cutting force. The overlapping effects of vertical and horizontal motion greatly reduce the effective cutting angle (with respect to the workpiece) as compared to the actual blade angle. The flatter the effective cutting angle, the more easily the blade penetrates the workpiece.
A similar situation applies to the cutting wire. A wire pressing vertically downward through the wet green body squeezes the latter with its full, circular cross section. Superimposing horizontal motion to the wire during the cutting process effectively gives the wire the nature of an elliptical cutter plunging its narrow side into the green brick. The faster the speed in the wire‘s direction of motion, the narrower the cutting angle and, hence, the easier the wire is able to penetrate into the green body to be cut.

If the blade (wire) is not always pulled in the same direction, but made to swing back and forth, it achieves exactly that effect. The limited length of knives and saws makes this practically self-evident.

If a cutter is made to change direction very quickly, the effect is that of a longitudinally vibrating wire. The following course of events can be anticipated for a high vibration frequency: Thanks to its horizontal motional component, the wire not only penetrates more easily, it even induces local fluidization via vibrating pressure at the cutting point and therefore leaves behind a particularly smooth, integumental film on the sliced face.

 

3 Results

The implemented trials showed consistently positive results for the use of a vibrating cutting wire. Braided cutting wires, with their elevated inherent elasticity, were successfully employed as a means of preventing wire breakage (caused by operation at resonant frequency). With each increase in cutting speed, the frequency of vibration must be altered accordingly in order to maintain the positive “saw effect”. The positive results are exemplified by the cross-sectional photo of a vertically perforated clay brick in »1.

This project of the Research Alliance of the Clay Brick and Tile Industry Regd (FGZ) was funded under the project number AiF 16074 N by the BMWi through the German Federation of Industrial Research Associations “Otto von ­Guericke” Regd (AiF). and implemented by Brick Research Institute Essen Regd (IZF). The final report is 65 pages long and available for a handling fee from the Research Alliance of the Clay Brick and Tile Industry Regd in Berlin.

x

Related articles:

Issue 05/2012

Saving energy in clay brick production by use of vibrating cutting wires

In the industrial manufacture of insulative, vertically perforated clay bricks designed to help ultimate consumers save energy in their own homes, there are numerous steps of production to be...

more
Issue 6/2017

Improving the quality of cut and reducing energy expenditures for brick production by use of vibrating cutters with piezoelectric and electroosmotic drives

1 Background The vibration cutting technique employing an oscillating solenoid, as already investigated in project AiF 16074 N, enables achievement of a cleaner quality of cut coupled in most cases...

more
Issue 02/2010

Concepts for reducing the loss of exhaust air from dryers in the clay brick and tile industry

1 Initial situation and problem description More than half of the energy used in the production of clay bricks and tiles is currently used for drying green bricks and tiles. The hot air needed for...

more
Issue 08/2014

Energy-conserving method for obtaining highly porous structures in brick clay

Context and formulation of problem Vertically perforated clay bricks are highly porosity enhanced wall-building masonry units displaying low thermal conductivity. The thermal conductivity of stuffed...

more
Issue 12/2011

Theoretical and empirical studies on the shear loading capacity of clay brick masonry

1 Background Objective of the research project was the more precise description of the load-bearing behaviour of masonry built with vertically perforated clay bricks under shear load. Basis for this...

more