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Delrin® Technical Guide
Delrin® Design Guide
This Design Guide is a legacy Delrin publication and is supplied as a reference.
The most up-to-date tips, techniques and product information–including detailed information about testing
standards and grades–can be found on Delrin® Technical Data Sheets (TDS).
To access any Delrin TDS, visit the Delrin® Material Data Center at https://delrin.materialdatacenter.com
Delrin® | Technical Guide
Table of Contents
Chapter 1
Mechanical Properties...................................................................5
Stress Strain Curves....................................................................... 6
Tensile Stress Strain...................................................................... 6
Tensile Strength............................................................................. 6
Yield Strength................................................................................. 6
Compression versus Tension........................................................ 6
Shear Strength................................................................................ 6
Poisson’s Ratio............................................................................... 6
Stiffness.......................................................................................... 8
Creep and Relaxation..................................................................... 8
Thermal Aging...............................................................................12
Fatigue Resistance....................................................................... 13
Impact Resistance........................................................................14
Tensile Impact.............................................................................. 14
Izod Impact................................................................................... 14
Very Sharp Notch..........................................................................15
Repeated Impact.......................................................................... 16
Chapter 2
Thermal Properties.......................................................................17
Thermal Characteristics...............................................................18
Thermal Expansion.......................................................................18
Heat Deflection............................................................................. 18
Specific Heat.................................................................................18
Thermal Conductivity................................................................... 18
Melting Point.................................................................................18
Delrin® | Technical Guide
Table of Contents (continued)
Chapter 3
Electrical Properties and Flammability.......................................19
Electrical Characteristics............................................................. 20
Dielectric Strength....................................................................... 20
Dielectric Constant....................................................................... 20
Dissipation Factor........................................................................ 20
Volume Resistivity........................................................................ 20
Ignition Temperatures................................................................. 20
Flammability................................................................................. 20
Combustibility.............................................................................. 20
Arc Resistance............................................................................. 20
Chapter 4
Abrasion and Wear....................................................................... 23
Hardness....................................................................................... 24
Abrasion Resistance.................................................................... 24
Frictional Properties..................................................................... 24
Chapter 5
Environmental Effects..................................................................26
Weathering.................................................................................... 27
Chemical Resistance................................................................... 27
Effect of Specific Chemicals....................................................... 27
Test Data—Unstressed................................................................ 28
Test Data—Stressed.................................................................... 28
Stain Resistance........................................................................... 28
Permeability.................................................................................. 32
Exposure to Space and Radiation............................................... 32
Dimensional Considerations for Molded Parts.......................... 34
Moisture Effects........................................................................... 34
Post-Molding Shrinkage............................................................... 34
Annealing...................................................................................... 34
Tolerance...................................................................................... 36
Miscellaneous...............................................................................36
Delrin® | Technical Guide
Table of Contents (continued)
Chapter 6
Agency Approval.......................................................................... 38
UL Recognition............................................................................. 39
Regulatory Agencies—Specifications......................................... 39
Chapter 7
Applications................................................................................. 40
Painting........................................................................................ 41
Dyeing........................................................................................... 41
Chrome Plating............................................................................ 41
Hot Stamping............................................................................... 42
Silk Screening............................................................................... 43
Direct Printing.............................................................................. 43
Wipe-in Paints.............................................................................. 43
Adhesive Joining......................................................................... 43
Appendix....................................................................................44
Delrin® | Technical Guide
Chapter 1
Mechanical Properties
Contents
Stress Strain Curves
Tensile Stress Strain
Tensile Strength
Yield Strength
Compression versus Tension
Shear Strength
Poisson’s Ratio
Stiffness
Creep and Relaxation
Thermal Aging
Fatigue Resistance
Impact Resistance
Tensile Impact
Izod Impact
Delrin® | Technical Guide | Mechanical Properties
Figure 6 is a stress strain curve for Delrin acetal resin in both
compression and tension. The test was carried out at 23°C (73°F)
and at 5.1 mm/min (0.2 in/min) and 1.3 mm/min (0.05 in/min) in
tension and compression, respectively. The curve indicates that
compressive strength is greater than tensile strength.
Stress Strain Curves
Stress strain curves show the effects of resin composition, draw
rate, and environmental factors such as temperature and humidity
on the resin’s tensile properties.
Tensile Stress Strain
Shear Strength
See Figures 1–3 for Delrin® acetal resin stress strain data. Within
this range of temperature and strain rate, temperature has the
greater effect on the tensile properties of Delrin acetal resin. The
effect of strain rate becomes more pronounced at high
temperatures.
Shear stress is the resistance measured in psi or MPa of two
planes moving relative to one another in the direction of load.
Shear strength is the stress level at which fracture occurs.
Refer to Table 2 for specific shear strength values for Delrin
acetal resin.
Tensile Strength
The tensile strength values are obtained from stress strain curves
by noting the maximum stress on the curve. The maximum
tensile values are given in Table 2 and can be used in rating the
relative resin strengths.
Poisson’s Ratio
Poisson’s Ratio measures the relative ability of a material to
deform at right angles to applied stress. It permits the
mathematical determination of a material’s physical
characteristics and values in a direction perpendicular to the
direction of loading.
Figure 4 gives Delrin acetal resin tensile strength data.
Yield Strength
Poisson’s Ratio is defined as the ratio of the transverse strain
to the longitudinal strain of a material. For plastics, the ratio is
affected by time, temperature, stress, sample size, etc.
The yield strength, also taken from the stress strain curve, is the
point at which the material continues to elongate (strain) with no
increase in stress. The yield strength normally has a lower value
than the tensile strength. When fracture occurs before yielding,
the maximum stress value is recorded as tensile strength, and
there is no yield value.
Poisson’s Ratio for Delrin® 500 at 23°C (73°F) is
0.35. The value is not expected to change significantly for other
Delrin acetal resins.
In the design of plastic parts, yield strength is the most common
reference, as it is uncommon for a part to be stressed beyond the
yield point. Unless one is designing gaskets and washers, which
are often stressed beyond the yield point, it is good practice to
design within the proportional limit, which is substantially below
the yield point. Selection of proper design stress is covered in the
Design Principles Module.
Tensile yield strength data for some Delrin acetal resins is shown
in Figure 5. For data on resins not shown, consult your Delrin
representative.
Compression versus Tension
In some design work, it is important to know the stress strain
relationship in compression as well as tension. At high stress
levels, the strain in compression is less than in tension. For all
practical purposes, however, the tensile and compressive stress
strain curves are identical at normal working stress levels, and
the compressive modulus is equal to the tensile modulus.
Delrin® | Technical Guide | Mechanical Properties
Delrin® | Technical Guide | Mechanical Properties
Stiffness
Flexural modulus is a measure of the stiffness of a plastic. It is
expressed as the ratio of stress to strain before permanent or
severe deformation occurs. Although the elastic modulus can be
determined in tension and compression, it is commonly shown in
flexure because of the greater likelihood of bending stress in use.
The effect of temperature and rate of loading on Delrin® acetal
resin is shown in Figures 7 and 8.
For design purposes, assume that the effect of chemical
substances on the flexural modulus of Delrin acetal resin is
proportional to the effect on the tensile modulus of Delrin acetal
resin as shown in Section 8—Chemical Resistance.
The fact that flexural modulus values are lower than tensile and
compressive modulus values can be explained, in part, by noting
that the fiber strain rate in the flexural modulus test is a small
fraction (1/20) of the tensile test machine crosshead speed,
whereas in the tensile and compression tests the fiber strain rate
is equal to the crosshead speed.
Creep and Relaxation
Creep
When stressed within the proportional limit, a plastic material
shows an initial strain proportional to the modulus of
elasticity, followed by a slow but steady increase in strain with
time. This phenomenon is called creep. Creep is the combination
of plastic flow and elastic deformation expressed as the sum of
the initial strain plus the incremental strain that occurs with time
at constant stress. Creep rates will vary with composition,
ambient temperature, stress level, and moisture content.
Consequently, designs must incorporate the estimated creep
behavior of a particular resin under the load and environmental
conditions expected.
Delrin® | Technical Guide | Mechanical Properties
Relaxation
Stress relaxation is defined as the decrease over a given time
period of the stress required to maintain constant strain over the
same period of time. Like creep, it can occur in tension,
compression, flexure, or shear.
Figures 9 and 10 show the effect of creep and stress relaxation
plotted on stress strain diagrams, and is the method commonly
used for calculating creep and relaxation modulus, sometimes
referred to as “apparent modulus.”
• Creep in Air
The results of experiments in flexural creep at various air
temperatures and stress levels have been plotted in Figures
11–14. Data from these figures may be used to predict creep
in Delrin® acetal resin parts in tensile, compressive, or flexural
loadings. This prediction is made by substitution of the
stress-temperature-time dependent (creep) modulus in the
appropriate engineering formulae.
• Stress Relaxation
Figure 15 shows the tensile relaxation properties of Delrin
acetal resin at various stress levels.
Delrin® | Technical Guide | Mechanical Properties
Delrin® | Technical Guide | Mechanical Properties
Delrin® | Technical Guide | Mechanical Properties
• Recovery from Dynamic Loading
Few plastic materials exhibit good recovery characteristics
when subjected to repeated loading at relatively high
stress levels.
Thermal Aging
– Short-Term Dynamic Loading
Figure 16 shows stress strain curves for Delrin® acetal resin
stressed and relaxed five times at three successively
higher stress levels. At a stress level of 35 MPa (5,000 psi),
well above normal working stress levels, recovery is
complete. Even at very high stress levels, hysteresis is
surprisingly low.
Unstressed in Air
Test bars molded in Delrin® 500 NC010 more than 20 years ago
were stored in the absence of light at room temperature. The bars
retained their elongation, tensile strength, original luster, impact
strength, and molecular weight.
This section describes the behavior of Delrin acetal resin under
conditions of no load, in the presence of both air and water over a
temperature range.
At elevated storage temperatures, the unstressed bars retained at
least 78% of their original tensile strength as shown in Figure 19.
Delrin® 100 has 10 to 20% better retention of properties at higher
temperatures than Delrin® 500 or 900.
– Long-Term Dynamic Loading
Figures 17 and 18 typify the behavior of Delrin acetal resin
under cyclic loading at 23°C (73°F). Recovery depends on the
duration of the applied load and on the time allowed for
recovery.