Consolidated Tech Man - Holo-Krome

HOLO-KROME NYLOK ® HEX-SOCKET SCREWS
The Nylok Corporation is the originator of the NYLOK (R) process, by
which any threaded part can be made self-locking. The Nylok self-locking
method consists of a nylon patch, strip or pellet, permanently bonded onto
or embedded into the threads of any fastener.
Whether your application requires patch, pellet or strip, this method
provides a degree of holding power not otherwise possible. The principle
is the same for all three types. When mating threads are engaged, the
tough, resilient nylon element is compressed, and, with all of the clearances
thereby closed, a strong counterforce is established, which creates
a metal-to-metal contact, which not only locks, but also gives sealing
properties and sets up a positive resistance to vibration.
The nylon element has a strong memory, and will return to its original
shape after removal, providing an excellent degree of re-usability for the
system. It retains its high strength properties at temperatures up to 250°
F, and is virtually unaffected by alcohol, gasoline, caustic soda, and most
commercial solvents. This element can be added to standard parts, or
built into any special fasteners when needed. Holo-Krome Engineers will
be happy to recommend the proper locking method for any specific
application, based on such factors as type of material, complexity of the
parts, hardness, wall thickness, etc. Please contact the Holo-Krome
Engineering department for assistance in adapting the Nylok self-locking
fastening method to your application.
RECOMMENDATIONS FOR PROPER APPLICATION OF HOLO-
KROME NYLON INSERT SOCKET SCREWS
The Basic Function of the Holo-Krome Nylon-modified self-locking screw
is to induce greater friction between the mating external and internal
threads, thereby providing a self-locking holding action. It is, therefore,
extremely important to convey the fact that the internal mating thread has
a direct effect on the function of the induced locking torque and reusability
of the screw and, if improperly tapped, can actually cause failure of the
self-locking element. For most effective performance the following precautions
and suggestions should be observed, and recommendations as
noted herein should be followed:
1. To provide proper entry of the modified screw into the internal thread
and to prevent possible shearing of the nylon before thread engagement,
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HOW NYLON ELEMENTS LOCK
The locking element is a tough, resilient nylon coating (A) permanently
applied to a section of the thread. As the screw is inserted, the mating
threads are forced tightly together. A wedging action is created which sets
up a strong lateral counterthrust, locking the threads at (B) opposite the
coating in a strong metal-to-metal grip. Locking occurs whether the screw
is seated or not.
the leading edge of the internal thread should be countersunk approximately
90° x 1/32" in diameter larger than the thread major diameter.
2. The clearance hole (when required) for the shank of the screw should
be at least 0.015 larger than the thread major diameter to allow the
modified screw to pass through freely. (See page 51 for recommended
drill size for shank.)
3. To assure complete utilization of the tensile strength of the screw, the
self-locking area should be engaged at least two full threads beyond the
starting thread of the tapped hole.
4. The mating internal thread should be clean and smooth. Sharp thread
burrs (from improper tapping, etc.) may reduce reusability of the screw by
tearing or shearing the nylon.
5. The internal thread should be within Class 2B or 3B limits. Within these
limits, the greater the percentage of full thread, the higher the self-locking
torque attained. However, the percentage of full thread appears to have
little effect on the limits of reusability. Therefore, a variation in torque can
be attained by increasing or decreasing the tap drill size. Best results have
been attained by using a tap drill size which results in a 75% to 83% full
thread.
6. Since increased friction is the main function of the Nylon modification,
and lubrication reduces friction, the presence of a lubricant in the
assembly will tend to reduce the self-locking torque. (A short air blast is
usually sufficient to remove excessive lubrication before assembly.
7. When using Nylon modified screws in soft materials other than steel
(aluminum, brass, etc.) where the normal induced torque may cause
damage to the internal threads, it is advisable to reduce the percentage
of full thread of the internal member. If the torque still remains too high, it
is recommended that the Holo-Krome Engineering Department be consulted
relative to special pelleting dimensions to meet requirements.
8. An excessive out-of-round condition of the internal thread will cause
erratic induced torque and can lead to reduced holding power and
reusability. This condition is easily noticeable by high-low torque readings
approximately 90° apart.