Solid Height - Spring Manufacturers Institute

Preventive Maintenance Tips for
Your Inline Conveyor Ovens
Part I: The Heating System
By Daniel Pierre III, JN Machinery Corp.
F
undamentally, an inline conveyor oven is nothing
more than four sections: a heating system, an
insulated box, a conveyor mechanism and a control
panel. This article will focus on preventive maintenance
of the heating system. The other oven sections
will be discussed in future issues.
Each oven maker assembles the four sections in
different ways, and this is what differentiates one
oven from another. There also are differences in
the quality and quantity of parts. Some ovens have
specialized functions or added tooling. Finally, the
methods used for assembling an oven will greatly
affect the cost and ease of maintenance.
Spring manufacturers use various makes and
models of ovens in their plants for a number of
reasons: price and availability, presence of special
functions, reliability of the oven and its supplier, as
well as the ease of maintenance. These are probably
the top reasons for selecting a particular model.
However, once you have purchased and used
your inline oven for a few years, how do you know
if it is still giving you the same performance as it
did when new?
The good news is that a quality oven can last for
20 or more years if well maintained and not abused
too much. However, the very operation of an inline
oven subjects it to stress, and good old wear and tear.
It has to withstand changing from room temperature
up to 900°F and back to room temperature numerous
times. As parts go through an oven, smoke, oily
mists and other small particles become airborne,
often becoming trapped inside the heat chamber. No
matter how gentle you are with an inline oven, there
are some parts that simply will wear out over time.
Proper maintenance is by far the best way to
protect your investment in this kind of equipment.
Also, the more you understand what is going on
inside an oven, the more you will begin to see that
periodic downtime is really necessary to ensure a
long useful life of the machine. Moreover, you can
actually boost performance by following some of the
tips and suggestions offered in this article.
Heating Elements
Let me start by explaining the heating system.
First and foremost, the heat source is usually electric
heating elements. Heating elements basically do
just two things: “go on” and “go off.” Nevertheless, a
heating element has a limited useful life. The length
of time you can use an element depends on its quality,
of course; the number of times it goes on and
off; and, to a lesser extent, its operating temperature
range. (A fourth factor – the way electricity is supplied
to the element – will be discussed in the article
focusing on the control panel). In the course of one
shift, or even one production run, heating elements
will go on and off hundreds of times. Components
in the control panel will determine how often they
go on or off in order to get the chamber to a certain
temperature.
In a small furnace with three to six elements, if
one element burns out, you can usually notice an
immediate drop in performance, since 17 to 33 percent
of the heating power is suddenly gone. In large
furnaces, there can be 60, 72 or even 90 elements
inside. If one element burns out in a large furnace,
you may or may not immediately notice a change
in performance. For this reason, in large ovens, it
is imperative to check the elements individually on
a regular basis.
There are several methods for checking an element,
but the easiest is to take an ohmmeter and
test for continuity. If an element is burned out, you
will get a “nonsense” reading on the meter. (On our
meter, the numbers flash “1.000”). With a good
element, you will get a certain, steady resistance
reading. The photo below shows how each end of an
element is touched to test for continuity. Note: You
do not have to remove an element to perform this
test. However, you do have to remove any wires or
jumpers from the ends to make sure you are testing
only one element at a time.
An ohmmeter is touched to each end of a heating element to
test for continuity.
SPRINGS July 2006 21