 It is of fundamental
importance for the reliability of every shaft
seal that its characteristics, as determined at the design stage, be
verifiable at any time during the manufacturing process. In ROLF's
production, a first checkup is made to
verify the product's correspondence to the design parameters. This is
done by running experimental tests on prototype shaft seals, using
testing machines capable of simulating the most demanding operating
conditions. During the
mass production stage, qualified personnel take care of performing
a series of controls at every processing stage, with
the aid of the most sophisticated labs and instruments developed
for this purpose. The finished product is then subjected
to periodical functional reliability tests.
11.1 Controls
of moulds
and
ancillary equipment
Moulds and equipment are built in the mechanical workshop with the
aid of sophisticated work-stations equipped with
numerical control
machinery. Upon start-up, and periodically during
production, they are subjected to controls capable of
monitoring the initial correspondence to the production sizes
and their proper maintenance in the course of standard production.
11.2 Product
control
During the testing stage of the equipment, dimensional controls
(height, internal and external diameters) and geometrical controls
(profile and surface) are carried out, in order
to ascertain the product's correspondence to its design, prior to
sending it to production. At the onset of every quantity
production and at predetermined time intervals, visual and
dimensional controls are carried out to verify the constancy of the
original dimensions.
11.3 Material
control
- Elastomeric materials:
One of the points of foremost importance for the reliability of
rotary shaft seals is the constancy of the rheological and chemical-physical
characteristics of the compounds. To guarantee
this constancy, every lot of elastomeric material destined
for production is subjected to a control of its fundamental parameters.
These controls are carried out by our engineers
in the ROLF technological laboratory. The parameters registered there
are available at any time from the ROLF
data bank.
- Components:
Based on special sampling plans, the following is controlled:
a) The sizes and physical-chemical characteristics of the metal
inserts
b) The sizes and physical-chemical characteristics of the Garter
springs, with particular care to their elongation loads
c) The sizes and physical-chemical characteristics of other eventual
components
d) The perfect attachment of
the rubber to the metal is also systematically checked.
11.4 Control
of the vulcanizing process
This is done by keeping all the fundamental process variables under
constant control, in particular the time intervals and
temperatures, which are registered and controlled by PLCs
connected to the moulding machines.
11.5 Statistical
process control
This control is carried out during all processing phases at a predetermined
frequency, so as to verify the dimensional and
visual characteristics.
11.6 Final
product quality control
To ensure the quality of the final product, a number of controls are
carried out as described below, by qualified personnel and using the
most modern instrumentation. These controls
ensure that the ROLF Client gets a shaft seal of a technically
advanced level as well as of a high intrinsic safety
standard. The control cycle extends over three phases:
- A dimensional control
- A 100%
visual control
- A visual control on a statistical sample.
11.6.1 -
Dimensional control
This control consists of a dimensional verification of the
main
design parameters, carried out according to DIN requirements
and of a recording of the data to monitor their
trend in time.
11.6.2 - 100 % Visual control
Each article is subjected to a visual control for an analysis
and
elimination of the defects eventually present on the seals.
This control is based on a rating system of the type and
of the critical nature of the defects, in agreement with the
international standards and in relation to the possible usage
problems associated with the defect under examination. This operating
method allows combining simple applicability
with great efficiency.
11.6.3 -
Statistical control
This control is carried out on a significant sample of shaft
seals,
as defined by a sampling program described by the UNI
ISO 2859 standard
and serves the purpose of releasing an approval of the lot produced, in
accordance with the Acceptable Quality Level (AQL).
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