Examples of cast grates whose construction was based on previously used "old" patterns of the technological equipment for heat treatment furnaces (TEq) are presented. Manufacturers of this type of castings have at their disposal numerous earlier designs of the applied TEq. Their adaptation for the needs of a new order, i.e. the creation of a new design or modification of the already existing one, significantly reduces both cost and time of the implementation. It also allows making new grate constructions of various shapes and sizes, reducing in this way the number of patterns stored by the manufacturer of castings. The examples of cast grates shown and discussed in this study document the variety of ways that can be used when making them from the already existing patterns or castings. The presented grates were made using master patterns, entire castings or their fragments, and modular segments.
The paper presents the results of studies on the development of manufacturing technologies to cast hearth plates operating in chamber
furnaces for heat treatment. Castings made from the heat-resistant G-X40CrNiSi27-4 steel were poured in hand-made green sand molds.
The following operations were performed: computer simulation to predict the distribution of internal defects in castings produced by the
above mentioned technology with risers bare and coated with exothermic and insulating sleeves, analysis of each variant of the technology,
and manufacture of experimental castings. As a result of the conducted studies and analysis it was found that the use of risers with
exothermic sleeves does not affect to a significant degree the quality of the produced castings of hearth plates, but it significantly improves
the metal yield.
The main aim of this study was to examine the compression-induced state of stress arising in castings of the guide grates during operation
in pusher-type furnaces for heat treatment. The effect of grate compression is caused by its forced movement in the furnace. The
introduction of flexible segments to the grate structure changes in a significant way the stress distribution, mainly by decreasing its value,
and consequently considerably extends the lifetime of the grates. The stress distribution was examined in the grates with flexible segments
arranged crosswise (normal to the direction of the grate compression) and lengthwise (following the direction of force). A regression
equation was derived to describe the relationship between the stress level in a row of ribs in the grate and the number of flexible segments
of a lengthwise orientation placed in this row. It was found that, regardless of the distribution of the flexible segments in a row, the stress
values were similar in all the ribs included in this row, and in a given row of the ribs/flexible segments a similar state of stress prevailed,
irrespective of the position of this row in the whole structure of the grate and of the number of the ribs/flexible segments introduced
therein. Parts of the grate responsible for the stress transfer were indicated and also parts which play the role of an element bonding the
structure.
Various examples of the design of cast elements of the equipment used in furnaces for the heat treatment of machine parts are given.
Shortcomings in their performance are indicated. Reasons for required stability of equipment are briefly discussed. Elements of equipment
illustrate the possibilities of using a charge-carrying pallet with dimensions of 900×600×45 mm as a basis for multi-component
technological equipment. Introducing additional elements, such as metal baskets, intermediate pallets or crossbars to the main pallet, it
becomes possible to create different configurations of this equipment. The technological equipment presented and discussed here is offered
to different plants which heat-treat a wide variety of produced parts. It was found that the reliability and durability of new designed
equipment can be checked only during practical use. For large plants dealing with the heat treatment of bulk quantities of parts
homogeneous or similar in shape is recommended to use the dedicated tooling.
The lifetime of guide grates in pusher furnaces for heat treatment could be increased by raising the flexibility of their structure through, for
example, the replacement of straight ribs, parallel to the direction of grate movement, with more flexible segments. The deformability of
grates with flexible segments arranged in two orientations, i.e. crosswise (perpendicular to the direction of compression) and lengthwise
(parallel to the direction of compression), was examined. The compression process was simulated using SolidWorks Simulation program.
Relevant regression equations were also derived describing the dependence of force inducing the grate deformation by 0.25 mm ‒ modulus
of grate elasticity ‒ on the number of flexible segments in established orientations. These calculations were made in Statistica and Scilab
programs. It has been demonstrated that, with the same number of segments, the crosswise orientation of flexible segments increases the
grate structure flexibility in a more efficient way than the lengthwise orientation. It has also been proved that a crucial effect on the grate
flexibility has only the quantity and orientation of segments (crosswise / lengthwise), while the exact position of segments changes the
grate flexibility by less than 1%.