Insert Technology For Plastics, Composites And Metal Alloys

The concept of the Trisert-3 design is to provide a reliable, strong and wear resistant thread in applications, environments and materials that would be unsuitable for brass inserts.

Product Features

The design combines three cutting facets with three shallow flutes offering balanced cutting and enhanced back out performance.

The internal thread is not interrupted by cutting features and therefore will guarantee a free running internal thread without the risk of swarf jamming the screw.

The Steel variant is case hardened and is offered with a zinc nickel trivalent passivated finish to meet the requirements of RoHS and provide good corrosion resistance.

Installation may be by hand tool or Tappex FlexiArm complete with air tool and Tappex Production Driver. Additionally the installation torque can be controlled and monitored for increased reliability.

In the case of metal alloys, the use of cutting fluid is necessary to enhance the cutting action of the insert and ease installation. Alufluid supplied by Tapmatic has proven very effective.

As with the brass insert, the internal thread is used for installation. Every insert is therefore automatically checked for the presence of a good thread.

The reduced head design offers greater surface area over which application loads can be taken without increasing the receiving hole diameter.

The head diameter is designed to fit the counter bore in the receiving hole and therefore provide a flush finish.

Due to the various mechanical characteristics, a precise hole size specification is imperative.

Stainless steel threaded fasteners generally should not be assembled using very high speed equipment, as mating surfaces will be subject to galling and may cold-weld together leaving a falsely tightened joint.

It is therefore recommended that when a stainless steel screw is assembled to a stainless steel Trisert-3, a suitable lubricant containing Molybdenum Di-sulphide and PTFE is used.

However, although lubricants can assist on the assembly of a joint, they will dramatically lower the torque resistance and could cause the thread to fail if tightening torques are not adjusted.

Material Grades For Trisert-3

A key feature of this type of insert is its ability to withstand harsh environments and corrosive atmospheres whilst retaining good wear resistance and strength.

Steel
Case Hardened Zinc Nickel and Trivalent Passivate

• RoHS Compliant
• Corrosion resistance up to 720hrs to red rust
• Coating is hard and wear resistant
• Low sensitivity to temperature and temperature cycling - up to 140°C
• When passivate layer breaks down the white corrosion product is not excessive

Stainless Steel
Conventional stainless steel has at least 12% chromium to provide corrosion resistance via the formation of a thin coating of chromium oxide, known as the passivity film, which forms spontaneously upon contact with an oxidising agent. Generally the higher the chromium content, the better the corrosion resistance. Trisert-3 is available in two grades of Stainless Steel which are passivated to remove impurities from the surface left by the machining process. These impurities, if left, would interrupt the passivity film and create sites where corrosion could start.

Grade 303
This grade offers a good combination of machinability, corrosion resistance and toughness. In general, 303 has good resistance to mildly corrosive atmospheres but the sulphide inclusions act as pit initiation sites. It should not be exposed to marine or other similar environments, as these will result in rapid pitting corrosion. It is also subject to stress corrosion cracking in chloride containing environments above about 60°C.

Grade 316
This is the standard grade of austenitic stainless steel containing molybdenum. The molybdenum gives 316 better overall corrosion resistance, and its austenitic structure provides excellent toughness, even down to cryogenic temperatures. It has excellent corrosion resistance in a range of atmospheric environments and many corrosive media. It is regarded as the standard “marine grade stainless steel”, but it is not resistant to warm sea water. In many marine environments 316 does exhibit surface corrosion, usually visible by brown staining. This is particularly associated with crevices and rough surface finish.

Principal Advantages

1. Available in 316 Stainless Steel, 303 Stainless Steel and Steel Case Hardened Zinc Nickel, plated and Trivalent Passivated.
2. The reduced head provides a large bearing surface to support the load transmitted through the bolt.
3. Quicker installation when compared to similar self tapping inserts.
• Stainless Steel parts have a greater helix angle
4. Free running internal thread.
• No peripheral through holes or slots which can allow swarf into the bore of the insert.
• Cutting features designed to encourage swarf to move forward ahead of the insert.
5. Compatible with brass Trisert hole sizes where both corrosive and non-corrosive environments must be considered.
6. Reduced external diameter as cutting edges are fully supported.
7. Ease of identification for manipulative orientation.
8. Steel variant is case hardened for use into alloys and critical hard composites.
9. Steel variant offers a fully RoHS compliant corrosion resistant plated finish giving a salt spray resistance of up to 720 hrs to red rust.
• Zinc Nickel and Trivalent Passivate
10. The regular length insert will, under most circumstances, be strong enough where a free running re-usable thread is required; however a long version is available for higher load applications.
11. The insert has a self locking feature to help resist rotation where nylon patched bolts are used or where the application is subject to vibration.
12. The range includes thread sizes: M3, M4, M5, M6, M8, M10.

Installation

The Tappex FlexiArm provides a rapid and reliable method of installation for the Trisert-3 range. The FlexiArm installation machine consists of a pantograph arm with a pneumatic screwdriver attached. The screwdriver can be specified with an automatic reverse torque-clutch control at either 510 rpm or 1,100rpm, or a manual reverse torque-clutch control at 510 rpm, depending upon the size of the insert and the material into which it is being installed.
 
The FlexiArm provides a low-cost assembly solution for many different post-mould applications and its size allows it to be installed alongside the respective moulding machine, so that inserts can be fitted during the waiting time of a typical mould cycle. It is available with one, two or three arms (which can be fitted at a later date) to suit most multi-task assembly requirements.
 
With harder materials it is more critical that the insert is exactly aligned with the receiving hole. The latest Tappex FlexiArm facilitates this by being adjustable in two planes.

A range of production drivers is available to provide an accurate method of installing the inserts at various heights and positions in the moulding (see inset), and they are available separately to suit M3 to M10 threads and also equivalent Imperial sizes.
 
Hand Installation Equipment
Alternatively, the inserts can be installed by hand, using the 031 range of Tappex Hand Tools that come complete with an alignment bush to ensure correct installation.